Directory UMM :Data Elmu:jurnal:S:Soil & Tillage Research:Vol56.Issue1-2.Jul2000:
Soil & Tillage Research 56 (2000) 105±116
Management of cracked soils for water saving during
land preparation for rice cultivation
Romeo J. Cabangon, T.P. Tuong*
Soil and Water Sciences Division, The International Rice Research Institute, MC P.O. Box 3127, Makati City 1271, Philippines
Abstract
High water loss during land preparation of soils for rice (Oryza sativa L.) production results from bypass ¯ow through cracks.
It was hypothesized that the losses can be reduced by measures that minimize crack development during the soil drying period
or impede the ¯ow of water through these cracks. The effect of straw mulching and shallow surface tillage on crack formation
during the fallow period, and on water ¯ow components during land preparation was investigated in ®eld experiments on an
Epiaqualf and a Pellustert in the Philippines. Cracks did not completely close upon rewetting, resulting in high loss (152±
235 mm of water) during land preparation of the control (i.e. no soil management treatment) plots. Straw mulching helped
conserve moisture in the soil pro®le, and reduced the mean crack width by 32% of the control. Mulching did not signi®cantly
reduce mean crack depth and the amount of water used in land preparation. Shallow tillage formed small soil aggregates which
made the crack water ¯ow discontinuous and impeded groundwater recharge from the water ¯ow through cracks, reduced total
water input for land preparation by 31±34%, equivalent to about 120 mm of water. The average surface irrigation water ¯ow
advanced faster and less time was needed for land preparation in the shallow tillage plots compared to the control. Shallow
tillage offers a practical means for improving water-use ef®ciency of irrigation systems. In rainfed areas, it may facilitate early
crop establishment and, thus, reduce the risk of late-season drought. # 2000 Elsevier Science B.V. All rights reserved.
Keywords: Bypass ¯ow; Irrigation; Shallow tillage; Mulching; Water-use ef®ciency
1. Introduction
Over the next 30 years, rice production must
increase by 70% from the present production to avoid
rice shortage (IRRI, 1995). Rice is known to be less
water ef®cient than many other crops, and water for
irrigation is becoming increasingly scarce because of
escalating demand for non-agricultural uses. Improving water-use ef®ciency of rice culture is a pre-requisite for food security in Asia.
*
Corresponding author. Tel.: 63-2-8450563;
fax: 63-2-8911292.
E-mail address: t.tuong@cgiar.org (T.P. Tuong).
The ®rst step in lowland rice production is land
preparation. Water is applied to rice ®elds until the
topsoil is saturated and a ponding water layer of 10±
50 mm depth is maintained (land soaking) for 2 days
or more on the ®eld. Land soaking is followed by
plowing and harrowing several times under saturated
condition to puddle the topsoil to a depth of 10±20 cm.
After transplanting or direct seeding, the ®eld is kept
¯ooded to a depth of about 50 mm throughout the
growing season. To facilitate harvesting, irrigation is
often stopped 2 weeks before the crop reaches maturity (De Datta, 1981). Fields often are left fallow and
allowed to dry before the next crop.
Drying of a puddled soil usually results in soil
shrinkage and cracking. Cracks are especially promi-
0167-1987/00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved.
PII: S 0 1 6 7 - 1 9 8 7 ( 0 0 ) 0 0 1 2 5 - 2
106
R.J. Cabangon, T.P. Tuong / Soil & Tillage Research 56 (2000) 105±116
nent if expanding clay minerals are present, but they
may also be clearly noticeable in kaolinitic soils and
can reach depths of 20±65 cm (Moorman and van
Breemen, 1978; Ishiguro, 1992; Wopereis et al.,
1994; Ringrose-Voase and Sanidad, 1996; Tuong
et al., 1996). Irrigation for land preparation of the
next rice crop, thus, involves water application to
cracked soils and results in bypass ¯ow losses (water
that ¯ows through cracks to the subsoil). Tuong et al.
(1996) reported that bypass ¯ow accounted for 41±
57% (equivalent to about 100 mm of water) of the total
water applied in the ®eld during land soaking. Water
loss throughout the period of land preparation may be
much greater than this, because cracks may not close
after rewetting (Moorman and van Breemen, 1978;
Ishiguro, 1992; Wopereis et al., 1994; Tuong et al.,
1996), and bypass ¯ow may continue until soil is
repuddled. This might explain the very high percolation losses during land preparation, accounting for up
to 40% of the total water supplied for growing a rice
crop (Wickham and Sen, 1978). Reducing these losses
will contribute greatly to improving water-use ef®ciency of rice.
Tuong et al. (1996) quanti®ed the ¯ow process
when ¯ood irrigation is applied to cracked soils.
Irrigation water moves rapidly in the crack networks,
ahead of the surface water front. Part of this crack
water in®ltrates into the subsoil, bypassing the topsoil,
thus, recharging the groundwater. When the subsoil is
permeable, about 70% of this bypass ¯ow may be lost
to the surroundings through lateral drainage. Since the
¯ow processes are dominated by water ¯ow in cracks,
measures that in¯uence crack geometry or the water
¯ow in the cracks may affect the amount of water loss.
Straw mulching, by reducing evaporation from the soil
surface (Hundal and Tomar, 1985) can minimize soil
shrinkage, lessen crack development during the fallow
period before land soaking and, therefore, may reduce
bypass ¯ow losses. Shallow tillage can also reduce
evaporation loss. It may also form soil aggregates
which block the cracks and impede water ¯ow into
them. Wopereis et al. (1994) showed that shallow
tillage reduced the crack bypass ¯ow in undisturbed
cores by 45±60%. Tillage effectiveness in reducing
water loss in the ®eld conditions has not been tested.
This study was carried out to assess straw mulching
and shallow tillage, as possible measures to reduce
water loss during land preparation of dry, cracked rice
soils. The processes by which these measures affects
crack development during the fallow period and water
balance components during the land preparation were
quanti®ed in ®eld experiments.
2. Methodology
2.1. Experimental sites
The study was conducted in rice ®elds (i) at the
International Rice Research Institute (IRRI), Los
Banos, Laguna (148300 N, 1218150 E) during the
1993 and 1994 dry seasons; (ii) in the Angat River
Irrigation System, Bulacan (148470 N, 1208550 E) during the 1993 wet season and (iii) in Munoz, Nueva
Ecija (158400 N, 1208500 E), during the 1995 dry season. All sites have two distinct seasons, i.e. wet from
June to November and dry from December to May.
According to soil taxonomy (Soil Survey Staff, 1992),
the soil at IRRI was classi®ed as an Aquandic Epiaqualf, at Bulacan Typic Epiaqualf (Tuong et al., 1996)
and at Nueva Ecija Entic Pellustert (Raymundo et al.,
1989). Some major soil characteristics of the sites are
presented in Tables 1 and 2. At the time of land
soaking, water table depths were 0.85 m (1993) and
1.1 m (1994) at the IRRI ®elds, 0.5 m at the Bulacan
site, and 1.1 m at Nueva Ecija.
2.2. Treatments
2.2.1. At IRRI
The experiments were conducted in 6 m11 m
plots surrounded by bunds (30 cm width and 25 cm
height). The plots were hydraulically isolated by
polyethylene sheets installed to 0.7 m depth along
the center of the bunds. At the start of the experiment
(18±20 April 1993 and 23±25 January 1994), all plots
were ¯ooded, plowed, puddled to depth of 10 cm and
leveled to attain similar conditions before the treatments were applied. Surface water was drained 1 day
after land leveling. All ®elds were allowed to dry
under the sun during the fallow period until irrigation
for land soaking for the next rice crop was carried out
on 31 May 1993 and 17 May 1994.
During the fallow period, three soil management
treatments were imposed in a randomized complete
block design with four replications:
107
R.J. Cabangon, T.P. Tuong / Soil & Tillage Research 56 (2000) 105±116
Table 1
Texture and vertical saturated hydraulic conductivity of the experimental ®elds at IRRI, Bulacan and Nueva Ecijaa
Depth (m)
Clay (g kgÿ1)
Silt (g kgÿ1)
Sand (g kgÿ1)
Saturated conductivity
(m per day)
IRRIb
0±0.2
0.2±0.5
420
490
440
370
140
140
±
0.5
Farmers' fields, Bulacanb
0±0.2
0.2±0.3
0.3±0.5
290 (3, 9)
400 (3, 9)
400 (3, 9)
560 (3, 2)
440 (3, 2)
420 (3, 3)
150 (3, 7)
150 (3, 2)
170 (3, 5)
±
±
0.1 (3, 004)
Farmers' fields, Nueva Ecija
0±0.2
0.2±0.4
0.4±0.6
530 (10, 36)
560 (10, 39)
550 (10, 38)
340 (10, 44)
300 (10, 48)
310 (10, 57)
130 (10, 41)
140 (10, 44)
140 (10, 40)
±
±
0.007 (6, 0004)
a
b
Number of observations and standard deviations are indicated in parentheses.
Source: Tuong et al. (1996).
Straw mulching. Dry rice straw (5 Mg haÿ1) was
broadcast over the plot 1 day after drainage (DAD)
and remained on the soil surface during the fallow
period.
Shallow surface tillage. Plots were rototilled to 5±
10 cm depth by two passes of a IRRI-manufactured
rototiller at 18 DAD in 1993 and 14 DAD in 1994. The
schedule of rototilling was decided by the operator
based on the adequacy of soil bearing capacity to
support the implement. Shallow tillage produced topsoil aggregates of about 1±5 cm diameter.
Control. No treatment was applied during the fallow
period.
In the 1994 experiment, the straw mulching treatment was not included.
2.2.2. In Bulacan
The amount of water used in six farmers' ®elds
(measured 80±90 m120±165 m) were monitored
from 17 June until land preparation activities were
completed. After harvest of the previous rice crop on
second week of March 1993, three ®elds were left
Table 2
Bulk density and soil water content at saturation and at different dates in farmers' ®elds; Bulacan and Nueva Ecijaa
Depth (m) Bulk density (mg mÿ3)
Control
Shallow tillage
Soil moisture content (mÿ3 mÿ3)
Saturated
Control
Shallow
tillage
Start of monitoringb
Start of land soakingc
Control
Control
Shallow
tillage
Shallow
tillage
Farmers' fields, Bulacan
0±0.2
0.99 (4, 0.05) 0.90 (4, 0.04)
0.2±0.3
1.06 (9, 0.04) 1.06 (9, 0.04)
0.3±0.5
1.04 (9, 0.04) 1.04 (9, 0.04)
0.63 (4, 0.03) 0.65 (4, 0.03) 0.42 (9, 0.02) 0.40 (9, 0.01) 0.52 (9, 0.02) 0.48 (9, 0.03)
0.61 (9, 0.01) 0.61 (9, 0.03) 0.49 (9, 0.01) 0.51 (9, 0.01) 0.57 (9, 0.02) 0.59 (9, 0.01)
0.61 (9, 0.02) 0.61 (9, 0.05) 0.50 (9, 0.01) 0.51 (9, 0.01) 0.56 (9, 0.02) 0.57 (9, 0.01)
Farmers' fields, Nueva Ecija
0±0.2
1.24 (4, 0.01) 1.17 (4, 0.02)
0.2±0.4
1.32 (4, 0.04) 1.32 (4, 0.04)
0.4±0.6
1.35 (4, 0.05) 1.35 (4, 0.05)
0.52 (4, 0.02) 0.55 (4, 0.12)
0.50 (4, 0.01) 0.50 (4, 0.01)
0.48 (4, 0.01) 0.48 (4, 0.01)
a
0.26 (4, 0.05) 0.28 (4, 0.02)
0.41 (4, 0.03) 0.43 (4, 0.04)
0.46 (4, 0.02) 0.46 (4, 0.01)
Number of observations and standard deviations are indicated in parentheses.
17 June 1993 in Bulacan.
c
20±26 December 1994 in Nueva Ecija; 10±11 July (control treatment) and 28 June±10 July (shallow tillage treatment) in Bulacan.
b
108
R.J. Cabangon, T.P. Tuong / Soil & Tillage Research 56 (2000) 105±116
fallow until land soaking was carried out on 10±11
July. Land was prepared and ®nal land leveling completed on 15±20 July. In the other three ®elds, farmers
used tractor-powered rototillers to rototill the land to a
depth of about 10 cm at the onset of the rainy season
(12, 20, and 29 May 1993). In these ®elds, land
soaking was carried out on 28 June, 6 and 10 July
and land leveling accomplished on 4±17 July.
2.2.3. In Nueva Ecija
An experiment was conducted in eight farmers'
®elds (measured 16±27 m220±610 m) from December 1994 to 15 January 1995. The previous rice crop
was harvested on the second week of November 1994.
Two tillage treatments were imposed during the land
preparation period in a randomized complete block
design with four replications. In each replication, the
dimensions of the ®elds were almost similar. The
treatments were:
Control. Fields were kept fallow until land soaking
on 20±26 December 1994, plowed on 21±28 December and harrowed using comb-tooth harrow on 24±29
December. Final leveling was completed on 3±12
January 1995.
Shallow surface tillage. Fields were dry rototilled to
a depth of 10 cm on 15±16 December 1994, using
four-wheel tractor drawn rototillers. Land soaking was
carried out from 21±26 December 1994. The ®elds
were harrowed using comb-tooth harrows and ®nal
leveling was completed on 4±13 January 1995.
2.3. Measurements of soil water content and physical
properties
All measurements in the IRRI plots were taken from
walk-boards installed in each plot to minimize the
disturbance to the soil and crack formation. Samples,
collected using 100 cm3 cylinders, for bulk density
and volumetric moisture content of the puddled and/or
the tilled layer (approximately 0.1 m thick), and layers
at depths 0.1±0.2, 0.2±0.3 and 0.3±0.5 m were taken at
2±3 days intervals during the fallow and land soaking
periods. Similar samples were used to determine the
saturated water content (Tuong et al., 1996). Vertical
saturated conductivity of the 0.3±0.5 m layer at the
sites were determined using constant head method and
encased soil columns 0.25 high and 0.20 m in diameter
(Wopereis et al., 1994).
In Bulacan and Nueva Ecija soil moisture contents
were monitored by the same method as at IRRI, at the
start of the monitoring program before and after land
soaking at four stations along the center transect of
each ®eld. Sampling depths varied depending on the
soil pro®le of each site: 0±0.1 m (tilled layer), 0.1±0.2,
0.2±0.3, and at 0.3±0.5 m in Bulacan and 0±0.1 m
(tilled layer), 0.1±0.2, 0.2±0.4, and 0.4±0.6 m in
Nueva Ecija.
For simplicity and for the presentation purpose, the
above depths (and else where in this paper) refer to
distances from the original soil surface. The puddled
or tilled layer, however, might change its thickness due
to shrinking and swelling during the fallow and land
soaking periods. To ensure that the same layers were
sampled at various times, all subsoil samplings used
the bottom of the tilled layer (0.1 m from the original
soil surface) as the datum. For example, for the layer
at depth 0.2±0.3 m, the sample was taken from
0.1±0.2 m below the bottom of the tilled layer.
2.4. Measurement of crack dimensions
At the IRRI ®elds, crack depth and width were
monitored at 1±2 days intervals during the fallow
period in a 1 m1 m subplot in each of the control
and mulched plots. In the mulched plots, straw was
removed before and replaced after each measurement.
Crack dimensions of the shallow tillage plots before
the shallow tillage were assumed to be the same as
those in the control plot. In the farmers' ®elds, crack
dimensions were monitored in two 1 m1 m subplots
per ®eld 2±3 days before land soaking. Methods of
measuring and computing crack depth, width, volume
and the surface area of soil islands (soil masses
distinctively separated by cracks) are presented in
Tuong et al. (1996).
2.5. Water application and monitoring
Irrigation was applied from one end of each ®eld,
through pipes (7.5±10 cm diameter) at IRRI and
Nueva Ecija; and from irrigation channels via
15 cm culverts in Bulacan. Application rates were
measured using 908V-notch weirs (at IRRI) and trapezoidal weirs (in farmers' ®elds). Discharge per unit
®eld width was 0.14±0.26 l sÿ1 mÿ1 at IRRI, 0.06±
0.12 l sÿ1 mÿ1 in Bulacan and 0.28±0.60 l sÿ1 mÿ1 in
R.J. Cabangon, T.P. Tuong / Soil & Tillage Research 56 (2000) 105±116
Nueva Ecija. The applied water was spread uniformly
across the width of the ®eld by a distribution channel
as described by Tuong et al. (1996).
In Nueva Ecija, the distance traveled by the advancing surface irrigation water front along the center
longitudinal transect of the plots during the land
soaking process was monitored at approximately
1 h interval. Groundwater table tubes were installed
at 10 m apart along the same transects. The water table
at each location was monitored from the start of land
soaking until the water table reached the soil surface,
following the procedures in Tuong et al. (1996).
2.6. Computation of water ¯ow components during
land preparation
Water balance calculation was carried out during
land soaking at the IRRI ®elds. In Bulacan and Nueva
Ecija, water balance during land preparation was
divided into two phases, namely, land soaking phase
(from ®rst water application to ®rst harrowing) and
harrowing phase (from ®rst harrowing to ®nal leveling). In Bulacan, water balance prior to land soaking
(from start of the monitoring, 17 June 1993 to land
soaking irrigation) was also carried out to take into
account the rainfall at the beginning of the wet season.
For each period, the water balance for the topsoil (0±
0.2 m depth), expressed in mm of water over each
®eld, can be quanti®ed with the following equation
(Tuong et al., 1996):
I R Ss Sc A E L
(1)
where I is the irrigation water, R the rainfall, Ss the
surface water storage, Sc the crack storage, i.e. the
amount of water that ®lls the cracks in the ®eld, A the
water absorbed in the soil layer under consideration, E
the evaporation from the ®eld, L the losses, i.e. the
amount of water that goes beyond the topsoil, recharging the groundwater.
Irrigation water was calculated from the total
volume of water applied (integral of ¯ow discharge
over time) divided by the ®eld area and Ss was the
change in depth of surface water. R was monitored
with rain gauges installed at the experimental sites.
The Sc was the volume of cracks under the surface
expressed in mm of water depth. The A was computed
from the difference in soil moisture contents at the
beginning and end of the study period. After land
109
soaking, soil became saturated, there was no more
increase in crack storage and absorbed water. The E
from the start of the monitoring period to land soaking,
when the topsoil water content in the ®elds changed
from dry to saturated, were estimated by multiplying
open water evaporation (measured by Class A pan) by
0.5 (Tuong et al., 1996). Evaporation after land soaking was estimated by open water evaporation. The
losses were derived from the difference between the
sum of inputs (IR) and the sum of soil surface
storage, crack storage, soil absorption, and evaporation losses Ss Sc A E:
The water balance was computed separately for
the tilled layer (approximately 0.1 m thick) and for
the 0.1 m layer immediately below the bottom of the
tilled layer, before being summed up for the topsoil
under consideration (0±0.2 m depth of the original
soil).
3. Results and discussions
3.1. Soil moisture content
Soil moisture contents at different depths at IRRI
are presented in Fig. 1. Fluctuations in soil moisture
content from 10 DAD (1993) and from 44 DAD (1994)
were due to intermittent rains. In the 1993 experiment,
soil moisture content of the mulched plots was consistently higher than the control and the shallow tilled
plots for depths 0±0.1 and 0.1±0.2 m; and for depth
0.2±0.3 m until about 18 DAD. The difference among
treatments at the later stage, being affected by intermittent rains, was not signi®cant. Moisture content at
0.3±0.5 m depth did not differ among treatments (data
not shown). The results con®rmed previous ®ndings
that straw mulch was effective in reducing soil surface
evaporation (Hundal and Tomar, 1985).
Water content of the 0.1 m top layer of the tilled
plots did not differ signi®cantly from that of the
control. At deeper layers, the tilled plots had signi®cantly higher soil moisture content than the control
plots (Fig. 1b and c). Shallow tillage formed a soil
mulch that reduced water losses from deeper layers. At
the start of land soaking, soil moisture content of the
topsoil in Bulacan was higher than in Nueva Ecija due
to intermittent rains before land soaking (Table 2). Soil
moisture content of the tilled plots in 0.2±0.3 m
110
R.J. Cabangon, T.P. Tuong / Soil & Tillage Research 56 (2000) 105±116
Fig. 1. Soil moisture contents in different treatments after ®eld drainage at the IRRI ®elds, 1993 and 1994 dry seasons, (a) soil moisture at 0±
0.1 m depth; (b) at 0.1±0.2 m depth, and (c) at 0.2±0.3 m depth. Error bars are standard error (n3); (c) also includes daily rain (vertical bars).
R.J. Cabangon, T.P. Tuong / Soil & Tillage Research 56 (2000) 105±116
(Bulacan) and 0.2±0.4 m (Nueva Ecija) depths were
slightly higher than that of the control.
3.2. Crack dimensions
Mean crack width and depth of the control and the
mulched plots at IRRI are presented in Fig. 2. Initial
increase in crack depth and width on the ®rst 8±10
DAD corresponded to the rapid loss of moisture from
the surface layer (Fig. 1). Both crack width and depth
increased more rapidly in the control plots than in the
mulched plots. This corresponded to the slower rate of
soil drying in the mulched plots (Fig. 1) and resulted to
a lower crack volume in the mulched compared to the
control. In the control treatment, a slower rate of
increase in crack depth and width in the 1994 experiment compared to the 1993 experiment conformed
with a slower rate of decrease in moisture content in
Fig. 2. Mean crack (a) widths and (b) depths in different treatments
after ®eld drainage at the IRRI ®elds, 1993 dry season. Error bars
are standard error (n55±161); (b) also includes daily rain (vertical
bars).
111
soil layers in 1994. Ringrose-Voase and Sanidad
(1996) reported similar rates of crack development
in fallow rice ®elds.
In the 1993 experiment, the mean crack depth in the
control treatment reached maximum value of about
115 mm and width about 40 mm at 19 DAD. Both
mean crack width and depth did not change signi®cantly afterwards. At the end of the fallow period, the
crack width of the mulch treatment was signi®cantly
lower than that in the control treatment (Fig. 2). This
corresponds to wide differences in the ®nal moisture
content of the soil surface layer (Fig. 1) in the two
treatments. The ®nal mean crack depth in the mulch
treatment was also less, but not signi®cantly than that
in the control treatment (Fig. 2). The formation of
cracks at lower depths was in¯uenced by the soil
moisture in the subsoil. The non-signi®cant differences in soil moisture at deeper soil layers from 20
DAD between two treatments might have resulted in
only slightly different crack depth. It was likely that at
the day of shallow tillage (at 18 DAD), crack depth of
the shallow tillage plots are similar to those of the
control plots. In the 1993 experiment, this depth was
about 110 mm (Fig. 2), i.e. about the same as the ®nal
crack depth of the mulched plots (106 mm).
Crack width in the control plot in the 1993 and 1994
experiments were of about the same size (Fig. 2). The
zero shrinkage portion of the shrinkage characteristic
curve of the same puddled soil began at a soil moisture
content of 0.25 m3 mÿ3 (Wopereis, 1993). This
implies that upon further drying, no more shrinkage
will take place. Soil moisture of the topsoil layer in
both years, was below 0.25 m3 mÿ3, implying maximum shrinkage had taken place in this layer. Crack
depth was, however, greater in the 1994 experiment,
reaching a mean value of about 130 mm (Fig. 2b). This
corresponded to a lower soil moisture at the deeper
soil layers in the 1994 experiment.
The crack dimensions prior to land soaking at
IRRI, Bulacan and Nueva Ecija are shown in
Table 3. The average widths and depths of cracks
were similar to results of Ishiguro (1992), Wopereis
et al. (1994), and Tuong et al. (1996). The wider and
deeper crack at the Nueva Ecija site was probably
due to the higher clay content in the Nueva Ecija
®elds. Intermittent rains during the fallow period at
IRRI and in Bulacan probably caused some swelling
and closure of cracks.
112
R.J. Cabangon, T.P. Tuong / Soil & Tillage Research 56 (2000) 105±116
Table 3
Dimensions of crack and soil islands (soil masses distinctively separated by cracks) prior to land soaking in IRRI, Bulacan and Nueva Ecija
Location and treatment
Crack
Soil island
Width
(mm)a
Depth
(mm)a
Volume
(m3 mÿ2)b
Surface area
(m2 mÿ2)b,c
Peripheral surface
area (m2 mÿ2)b
IRRI 1993
Mulched
Control
2719
4016
10531
11029
0.009
0.013
0.840.04
0.760.03
1.5
1.9
IRRI 1994
Control
2815
11338
0.020
0.680.01
1.8
Bulacan
Control
3415
14253
0.010
0.800.03
3.8
Nueva Ecija
Control
3620
17856
0.025
0.710.03
3.4
a
MeanS.D. of 120±139 observations at IRRI, 148 in Bulacan, and 352 in Nueva Ecija.
Per unit ®eld surface area.
c
MeanS.D. of six sampling subplots in IRRI, six in Bulacan, and 12 in Nueva Ecija.
b
3.3. Overland and subsurface ¯ow
During land soaking of the control treatment in
Nueva Ecija, water moved in the crack networks
and on the soil surface. Water ¯ow in the cracks
advanced faster than overland ¯ow of irrigation
water. As a result, the water table rose close to the
soil surface at a distance of about 10 m ahead of
the advancing surface water front. No signi®cant
rise of the water table was observed ahead of the
surface water front in the shallow tillage treatment (Fig. 3). The surface water front advanced
faster in the shallow tillage than in the control plots
(Fig. 4).
Fig. 3. Groundwater pro®les with distance from surface water front in the control and shallow tillage plots during ¯ood irrigation for land
soaking at Nueva Ecija. Bars indicate standard deviation for 25 (in the control) and 23 (shallow tillage) measurements.
113
R.J. Cabangon, T.P. Tuong / Soil & Tillage Research 56 (2000) 105±116
surface water front (Bassett et al., 1983) in the shallow
tillage plots. Shallow tillage can, thus, help reduce
time for land soaking. In Muda Irrigation scheme,
Malaysia, it is credited with the bene®ts of timely crop
establishment (Ho et al., 1993).
3.4. Water ¯ow components during land preparation
Fig. 4. Distance travelled by the advancing surface water front in
the control and shallow tillage plots, Nueva Ecija, 1995 dry season.
Observations in the control plot con®rmed ®ndings
by Tuong et al. (1996) and indicated that part of water
that moved in the cracks bypassed the topsoil, in®ltrated into the subsoil, and recharged the groundwater.
Small soil aggregates in the shallow tillage treatment
blocked the cracks, making them discontinuous and
impeded water ¯ow in the cracks and reduced recharge
to the groundwater. This conformed with Wopereis
et al. (1994) who reported that small soil aggregates
reduced 45±60% of the bypass loss through cracks in
large undisturbed soil columns. Less loss to the subsoil
meant more water was available for the surface water
¯ow, and resulted in a faster rate of advance of the
Table 4 shows the water balance components for
different treatments during the 1993 and 1994 experiments at the IRRI ®elds. The amount of irrigation
water needed for land soaking ranged from 93 to
272 mm. The increase in water needed for land soaking in the control plots in 1994 compared to 1993 was
caused mainly by increased water loss. This corresponded to deeper cracks and deeper water table in
1994.
In the 1993 experiment, compared to the control
plots, straw mulching did not reduce signi®cantly the
amount of irrigation water for land soaking at IRRI
®elds (Table 4). By reducing the evaporation loss
during the fallow period, mulching reduced the
amount of absorbed water needed to saturate the
surface soil layer (27 mm compared to 53±56 mm
in other treatments). This reduction was a very small
portion of the water input and did not result in total
water savings.
In both years at the IRRI ®elds, the shallow tilled
plots used signi®cantly less water for land soaking
Table 4
Water balance components during land soaking as affected by surface soil management treatments at the IRRI ®elds in 1993 and 1994
Componenta
Year
Treatment (mm)
Mulch
Shallow tillage
Control
109 abb
93 b
172 b
130 a
272 a
Irrigation water
1993
1994
Surface storage
1993
1994
20
20
25
20
21
Crack storage
1993
1994
9
0
0
13
20
Water absorbed in the 0±0.2 m layer
1993
1994
27
53
48
56
26
Losses
1993
1994
53 a
20 b
99 b
a
b
There was no rain and evaporation was neglected during land soaking.
In the same row, means followed by a common letter are not signi®cantly different at 5% level by DMRT.
41 a
205 a
114
R.J. Cabangon, T.P. Tuong / Soil & Tillage Research 56 (2000) 105±116
Table 5
Water balance components during land preparation as affected by tillage treatments in farmers' ®elds, Bulacan, 1993
Component
Total water input
Irrigation water
Rainfall
Evaporation
Surface storage
Crack storage
Absorbed in 0±0.2 m layer
Losses
Duration (day)
Loss rate (mm per day)
Prior to land soaking
Land soaking stage
Harrowing stage
Total
Control
With shallow
tillage
Control
With shallow
tillage
Control
With shallow
tillage
Control
With shallow
tillage
170
0
170
43
0
0
28
99
23.7
139
0
139
32
0
0
19
88
17.7
150 a*
89
61
11
1
10
11
117 a
4.6
25 a
69 b
57
12
8
20
0
11
30 b
2.3
13 b
26 a
17
9
12
ÿ5
0
0
19 a
2.7
7a
30 a
0
30
9
ÿ1
0
0
22 a
3.3
7a
346 a
106
240
66
ÿ4
10
39
235 a
31
8
238 b
57
181
49
19
0
30
140 b
23.3
6
*
All water components are expressed in mm of water over the area of the ®eld. Total water inputs are sum of irrigation water and rainfall.
In the same row and land preparation stage, treatment means followed by a common letter are not signi®cantly different at 5% level by DMRT.
than the control plots. Losses from the shallow tilled
plots (20 mm in 1993 and 99 mm in 1994) were about
50% of those from the control plots (41 mm in 1993
and 205 mm in 1994). In 1993, the amounts of
irrigation water for land soaking and water loss in
shallow tilled plots were signi®cantly less than those
in the mulched plots, though cracks in shallow tilled
were at least as deep as those in the mulched treatment
plots. This highlighted the role of small soil aggregates
in blocking and impeding water ¯ow through the
cracks.
In farmers' ®elds, shallow tillage reduced the total
water input for land soaking by 54±58% of the amount
needed in the control plots (69 mm compared to
150 mm in Bulacan, Table 5; and 95 mm to
227 mm in Nueva Ecija, Table 6). Most of the savings
in the water input for land soaking came from the
reduced losses in the shallow tillage plots compared to
the control. Findings in farmers' ®elds, thus, con®rmed those at IRRI.
Shallow surface tillage reduced the total water input
for land preparation by 31% in Bulacan (238 mm
Table 6
Water balance components during land preparation as affected by tillage treatments in farmers' ®elds, Nueva Ecija, 1995
Component
Total water input
Irrigation water
Rainfall
Evaporation
Change in storage
Crack storage
Water absorbed in 0±0.2 m layer
Losses
Duration (day)
Loss rate (mm per day)
*
Land soaking Stage
Harrowing stage
Total
Control
With shallow
tillage
Control
With shallow
tillage
Control
With shallow
tillage
(227) a*
224
3
26
43
25
46
87 a
6.0
14.5
(95) b
91
3
4
30
0
41
19 b
1.9
10.0
(122) a
121
1
58
ÿ1
±
±
65 a
10.6
6.1
(137) a
136
1
57
20
±
±
60 a
13.1
4.6
(349) a
345
4
84
42
25
46
152 a
16.5
9.2
(232) b
228
4
60
50
0
41
79 b
14.9
5.3
All water components are expressed in mm of water over the area of the ®eld. Total water inputs (values in brackets) are sum of irrigation
water and rainfall. In the same row and land preparation stage, treatment means followed by a common letter are not signi®cantly different at
5% level by DMRT.
R.J. Cabangon, T.P. Tuong / Soil & Tillage Research 56 (2000) 105±116
versus 346 mm, Table 5); and by 34% in Nueva Ecija
(232 mm versus 349 mm, Table 6) of the amount
needed for the control plots. Much of the differences
in the amount of water-use between the two treatments
occurred during the land soaking phase. High loss rate
sustained in the control plots during this phase indicated that water loss through cracks continued until
the ®rst harrowing was carried out. Harrowing reduced
the loss rate of the control plots considerably and made
them equivalent to those of the shallow tillage plots.
The ®ndings supported the observation that cracks did
not completely close upon rewetting (Moorman and
van Breemen, 1978; Ishiguro, 1992; Wopereis et al.,
1994; Tuong et al., 1996). Harrowing broke soils in the
control plots into aggregates, which sealed the cracks
and produced the puddling effects which reduced soil
permeability (De Datta, 1981). Where dry shallow
tillage can not be carried out, shortening the duration
between land soaking and the ®rst harrowing may be
an important measure to reduce water loss during land
preparation.
In the above computations, it was assumed that the
same soil was taken into consideration before and after
land soaking. Since the whole puddled layer (control
treatment) and the tilled layer (shallow tillage treatment) were included in the water balance, changes in
their thickness during land soaking did not cause any
error in the computation. Soaking decreased the bulk
density of the 0.1 m stratum below the tilled layer by
about 10% (e.g. from 1.15 to 1.04 at IRRI, data not
shown). Assuming an isometric swelling in the stratum, the corresponding change in thickness of the
stratum would be about 3%. Thus, error due to
neglecting the effect of soil swelling in the computation was negligible.
4. Conclusion
Straw mulching helped conserve moisture in the
soil pro®le, reduced crack development during the
fallow period but did not reduce the bypass loss during
land preparation. Shallow tillage formed small soil
aggregates, which blocked and impeded water ¯ow in
the cracks and reduced the amount of water that
recharged the groundwater via the bottom of the
cracks and crack faces. Water was, therefore, retained
better in the topsoil. Shallow surface tillage could
115
reduce about 31±34% of the water input for land
preparation, equivalent to a saving of 108±117 mm
of water depth and shortened time required for land
preparation. Water savings during land preparation
may increase the service area of an irrigation system.
In rainfed areas, shallow surface tillage may also lead
to earlier crop establishment and, thus, reduce the risk
of late-season drought. This kind of tillage does not
necessarily require high-powered tractors. Further
more, tractors/rototillers are becoming more accessible to small farmers for custom hiring, offering better
opportunities for incorporating shallow surface tillage
practice in the rice production system.
References
Bassett, D.L., Fangmeier, D.D., Stelkoff, T., 1983. Hydraulics of
surface irrigation. In: Jensen, M.E. (Ed.), Design and Operation
of Farm Irrigation Systems. Am. Soc. Agric. Eng., St. Joseph,
MI, pp. 447±498.
De Datta, S.K., 1981. Principles and Practices of Rice Production.
Wiley, New York, 618 pp.
Ho, N.K., Chang, C.M., Murat, M., Ismail, M.Z., 1993. MADA's
experiences in direct seeding. In: Paper Presented at the
Workshop on Water and Direct Seeding for Rice. Muda
Agricultural Development Authority, Ampang Jajar, Alor Setar,
Malaysia, 14±16 June 1993.
Hundal, S.S., Tomar, V.S., 1985. Soil-water management in rainfed
rice-based cropping systems. In: Soil Physics and Rice.
International Rice Research Institute, Los Banos, Laguna,
Philippines, pp. 337±349.
IRRI, 1995. Water: A Looming Crisis. International Rice Research
Institute, Los Banos, Philippines, 90 pp.
Ishiguro, M., 1992. Effects of shrinkage and swelling of soils on
water management in paddy ®elds. In: Murty, V.V.N., Koga, K.
(Eds.), Soil and Water Engineering for Paddy Field Management. Irrigation Engineering and Management Program, Asian
Institute of Technology, Bangkok, Thailand, pp. 258±267.
Moorman F.R., van Breemen, N., 1978. Rice, Soil, Water and Land.
International Rice Research Institute, Los Banos, Laguna,
Philippines.
Raymundo, M.E., Mamaril, C.P., De Datta, S.K., 1989. Environment, Classi®cation and Agronomic Potentials of some Wetland Soils in the Philippines. Philippine Council for
Agriculture, Forestry and Natural Resources Research and
Development and International Rice Research Institute, Los
Banos, Laguna, Philippines, Book Series No. 85/1989, 174 pp.
Ringrose-Voase, A.J., Sanidad, W.B., 1996. A method for measuring
the development of surface cracks in soils: application to crack
development after lowland rice. Geoderma 71, 245±261.
Soil Survey Staff, 1992. Keys to soil taxonomy. Soil Manage.
Support Serv. Technol. Monogr., 5th Edition, Vol. 19.
Pocahontas Press, Blacksburg, VA.
116
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Tuong, T.P., Cabangon, R.J., Wopereis, M.C.S., 1996. Quantifying
¯ow processes during land soaking of cracked rice soils. Soil
Sci. Soc. Am. J. 60, 872±879.
Wickham, T., Sen, L.N., 1978. Water Management for lowland
rice: water requirements and yield response. In: Soils and Rice.
International Rice Research Institute, Los Banos, Laguna,
Philippines, pp. 649±669.
Wopereis, M.C.S., 1993. Quantifying the impact of soil and climate
variability on rainfed rice production. Ph.D. Thesis, Wageningen University, ISBN 90-5485-147-3.
Wopereis, M.C.S., Bouma, J., Kropff, M.J., Sanidad, W.B., 1994.
Reducing bypass ¯ow through a dry, cracked and previously
puddled rice soil. Soil Till. Res. 29, 1±11.
Management of cracked soils for water saving during
land preparation for rice cultivation
Romeo J. Cabangon, T.P. Tuong*
Soil and Water Sciences Division, The International Rice Research Institute, MC P.O. Box 3127, Makati City 1271, Philippines
Abstract
High water loss during land preparation of soils for rice (Oryza sativa L.) production results from bypass ¯ow through cracks.
It was hypothesized that the losses can be reduced by measures that minimize crack development during the soil drying period
or impede the ¯ow of water through these cracks. The effect of straw mulching and shallow surface tillage on crack formation
during the fallow period, and on water ¯ow components during land preparation was investigated in ®eld experiments on an
Epiaqualf and a Pellustert in the Philippines. Cracks did not completely close upon rewetting, resulting in high loss (152±
235 mm of water) during land preparation of the control (i.e. no soil management treatment) plots. Straw mulching helped
conserve moisture in the soil pro®le, and reduced the mean crack width by 32% of the control. Mulching did not signi®cantly
reduce mean crack depth and the amount of water used in land preparation. Shallow tillage formed small soil aggregates which
made the crack water ¯ow discontinuous and impeded groundwater recharge from the water ¯ow through cracks, reduced total
water input for land preparation by 31±34%, equivalent to about 120 mm of water. The average surface irrigation water ¯ow
advanced faster and less time was needed for land preparation in the shallow tillage plots compared to the control. Shallow
tillage offers a practical means for improving water-use ef®ciency of irrigation systems. In rainfed areas, it may facilitate early
crop establishment and, thus, reduce the risk of late-season drought. # 2000 Elsevier Science B.V. All rights reserved.
Keywords: Bypass ¯ow; Irrigation; Shallow tillage; Mulching; Water-use ef®ciency
1. Introduction
Over the next 30 years, rice production must
increase by 70% from the present production to avoid
rice shortage (IRRI, 1995). Rice is known to be less
water ef®cient than many other crops, and water for
irrigation is becoming increasingly scarce because of
escalating demand for non-agricultural uses. Improving water-use ef®ciency of rice culture is a pre-requisite for food security in Asia.
*
Corresponding author. Tel.: 63-2-8450563;
fax: 63-2-8911292.
E-mail address: t.tuong@cgiar.org (T.P. Tuong).
The ®rst step in lowland rice production is land
preparation. Water is applied to rice ®elds until the
topsoil is saturated and a ponding water layer of 10±
50 mm depth is maintained (land soaking) for 2 days
or more on the ®eld. Land soaking is followed by
plowing and harrowing several times under saturated
condition to puddle the topsoil to a depth of 10±20 cm.
After transplanting or direct seeding, the ®eld is kept
¯ooded to a depth of about 50 mm throughout the
growing season. To facilitate harvesting, irrigation is
often stopped 2 weeks before the crop reaches maturity (De Datta, 1981). Fields often are left fallow and
allowed to dry before the next crop.
Drying of a puddled soil usually results in soil
shrinkage and cracking. Cracks are especially promi-
0167-1987/00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved.
PII: S 0 1 6 7 - 1 9 8 7 ( 0 0 ) 0 0 1 2 5 - 2
106
R.J. Cabangon, T.P. Tuong / Soil & Tillage Research 56 (2000) 105±116
nent if expanding clay minerals are present, but they
may also be clearly noticeable in kaolinitic soils and
can reach depths of 20±65 cm (Moorman and van
Breemen, 1978; Ishiguro, 1992; Wopereis et al.,
1994; Ringrose-Voase and Sanidad, 1996; Tuong
et al., 1996). Irrigation for land preparation of the
next rice crop, thus, involves water application to
cracked soils and results in bypass ¯ow losses (water
that ¯ows through cracks to the subsoil). Tuong et al.
(1996) reported that bypass ¯ow accounted for 41±
57% (equivalent to about 100 mm of water) of the total
water applied in the ®eld during land soaking. Water
loss throughout the period of land preparation may be
much greater than this, because cracks may not close
after rewetting (Moorman and van Breemen, 1978;
Ishiguro, 1992; Wopereis et al., 1994; Tuong et al.,
1996), and bypass ¯ow may continue until soil is
repuddled. This might explain the very high percolation losses during land preparation, accounting for up
to 40% of the total water supplied for growing a rice
crop (Wickham and Sen, 1978). Reducing these losses
will contribute greatly to improving water-use ef®ciency of rice.
Tuong et al. (1996) quanti®ed the ¯ow process
when ¯ood irrigation is applied to cracked soils.
Irrigation water moves rapidly in the crack networks,
ahead of the surface water front. Part of this crack
water in®ltrates into the subsoil, bypassing the topsoil,
thus, recharging the groundwater. When the subsoil is
permeable, about 70% of this bypass ¯ow may be lost
to the surroundings through lateral drainage. Since the
¯ow processes are dominated by water ¯ow in cracks,
measures that in¯uence crack geometry or the water
¯ow in the cracks may affect the amount of water loss.
Straw mulching, by reducing evaporation from the soil
surface (Hundal and Tomar, 1985) can minimize soil
shrinkage, lessen crack development during the fallow
period before land soaking and, therefore, may reduce
bypass ¯ow losses. Shallow tillage can also reduce
evaporation loss. It may also form soil aggregates
which block the cracks and impede water ¯ow into
them. Wopereis et al. (1994) showed that shallow
tillage reduced the crack bypass ¯ow in undisturbed
cores by 45±60%. Tillage effectiveness in reducing
water loss in the ®eld conditions has not been tested.
This study was carried out to assess straw mulching
and shallow tillage, as possible measures to reduce
water loss during land preparation of dry, cracked rice
soils. The processes by which these measures affects
crack development during the fallow period and water
balance components during the land preparation were
quanti®ed in ®eld experiments.
2. Methodology
2.1. Experimental sites
The study was conducted in rice ®elds (i) at the
International Rice Research Institute (IRRI), Los
Banos, Laguna (148300 N, 1218150 E) during the
1993 and 1994 dry seasons; (ii) in the Angat River
Irrigation System, Bulacan (148470 N, 1208550 E) during the 1993 wet season and (iii) in Munoz, Nueva
Ecija (158400 N, 1208500 E), during the 1995 dry season. All sites have two distinct seasons, i.e. wet from
June to November and dry from December to May.
According to soil taxonomy (Soil Survey Staff, 1992),
the soil at IRRI was classi®ed as an Aquandic Epiaqualf, at Bulacan Typic Epiaqualf (Tuong et al., 1996)
and at Nueva Ecija Entic Pellustert (Raymundo et al.,
1989). Some major soil characteristics of the sites are
presented in Tables 1 and 2. At the time of land
soaking, water table depths were 0.85 m (1993) and
1.1 m (1994) at the IRRI ®elds, 0.5 m at the Bulacan
site, and 1.1 m at Nueva Ecija.
2.2. Treatments
2.2.1. At IRRI
The experiments were conducted in 6 m11 m
plots surrounded by bunds (30 cm width and 25 cm
height). The plots were hydraulically isolated by
polyethylene sheets installed to 0.7 m depth along
the center of the bunds. At the start of the experiment
(18±20 April 1993 and 23±25 January 1994), all plots
were ¯ooded, plowed, puddled to depth of 10 cm and
leveled to attain similar conditions before the treatments were applied. Surface water was drained 1 day
after land leveling. All ®elds were allowed to dry
under the sun during the fallow period until irrigation
for land soaking for the next rice crop was carried out
on 31 May 1993 and 17 May 1994.
During the fallow period, three soil management
treatments were imposed in a randomized complete
block design with four replications:
107
R.J. Cabangon, T.P. Tuong / Soil & Tillage Research 56 (2000) 105±116
Table 1
Texture and vertical saturated hydraulic conductivity of the experimental ®elds at IRRI, Bulacan and Nueva Ecijaa
Depth (m)
Clay (g kgÿ1)
Silt (g kgÿ1)
Sand (g kgÿ1)
Saturated conductivity
(m per day)
IRRIb
0±0.2
0.2±0.5
420
490
440
370
140
140
±
0.5
Farmers' fields, Bulacanb
0±0.2
0.2±0.3
0.3±0.5
290 (3, 9)
400 (3, 9)
400 (3, 9)
560 (3, 2)
440 (3, 2)
420 (3, 3)
150 (3, 7)
150 (3, 2)
170 (3, 5)
±
±
0.1 (3, 004)
Farmers' fields, Nueva Ecija
0±0.2
0.2±0.4
0.4±0.6
530 (10, 36)
560 (10, 39)
550 (10, 38)
340 (10, 44)
300 (10, 48)
310 (10, 57)
130 (10, 41)
140 (10, 44)
140 (10, 40)
±
±
0.007 (6, 0004)
a
b
Number of observations and standard deviations are indicated in parentheses.
Source: Tuong et al. (1996).
Straw mulching. Dry rice straw (5 Mg haÿ1) was
broadcast over the plot 1 day after drainage (DAD)
and remained on the soil surface during the fallow
period.
Shallow surface tillage. Plots were rototilled to 5±
10 cm depth by two passes of a IRRI-manufactured
rototiller at 18 DAD in 1993 and 14 DAD in 1994. The
schedule of rototilling was decided by the operator
based on the adequacy of soil bearing capacity to
support the implement. Shallow tillage produced topsoil aggregates of about 1±5 cm diameter.
Control. No treatment was applied during the fallow
period.
In the 1994 experiment, the straw mulching treatment was not included.
2.2.2. In Bulacan
The amount of water used in six farmers' ®elds
(measured 80±90 m120±165 m) were monitored
from 17 June until land preparation activities were
completed. After harvest of the previous rice crop on
second week of March 1993, three ®elds were left
Table 2
Bulk density and soil water content at saturation and at different dates in farmers' ®elds; Bulacan and Nueva Ecijaa
Depth (m) Bulk density (mg mÿ3)
Control
Shallow tillage
Soil moisture content (mÿ3 mÿ3)
Saturated
Control
Shallow
tillage
Start of monitoringb
Start of land soakingc
Control
Control
Shallow
tillage
Shallow
tillage
Farmers' fields, Bulacan
0±0.2
0.99 (4, 0.05) 0.90 (4, 0.04)
0.2±0.3
1.06 (9, 0.04) 1.06 (9, 0.04)
0.3±0.5
1.04 (9, 0.04) 1.04 (9, 0.04)
0.63 (4, 0.03) 0.65 (4, 0.03) 0.42 (9, 0.02) 0.40 (9, 0.01) 0.52 (9, 0.02) 0.48 (9, 0.03)
0.61 (9, 0.01) 0.61 (9, 0.03) 0.49 (9, 0.01) 0.51 (9, 0.01) 0.57 (9, 0.02) 0.59 (9, 0.01)
0.61 (9, 0.02) 0.61 (9, 0.05) 0.50 (9, 0.01) 0.51 (9, 0.01) 0.56 (9, 0.02) 0.57 (9, 0.01)
Farmers' fields, Nueva Ecija
0±0.2
1.24 (4, 0.01) 1.17 (4, 0.02)
0.2±0.4
1.32 (4, 0.04) 1.32 (4, 0.04)
0.4±0.6
1.35 (4, 0.05) 1.35 (4, 0.05)
0.52 (4, 0.02) 0.55 (4, 0.12)
0.50 (4, 0.01) 0.50 (4, 0.01)
0.48 (4, 0.01) 0.48 (4, 0.01)
a
0.26 (4, 0.05) 0.28 (4, 0.02)
0.41 (4, 0.03) 0.43 (4, 0.04)
0.46 (4, 0.02) 0.46 (4, 0.01)
Number of observations and standard deviations are indicated in parentheses.
17 June 1993 in Bulacan.
c
20±26 December 1994 in Nueva Ecija; 10±11 July (control treatment) and 28 June±10 July (shallow tillage treatment) in Bulacan.
b
108
R.J. Cabangon, T.P. Tuong / Soil & Tillage Research 56 (2000) 105±116
fallow until land soaking was carried out on 10±11
July. Land was prepared and ®nal land leveling completed on 15±20 July. In the other three ®elds, farmers
used tractor-powered rototillers to rototill the land to a
depth of about 10 cm at the onset of the rainy season
(12, 20, and 29 May 1993). In these ®elds, land
soaking was carried out on 28 June, 6 and 10 July
and land leveling accomplished on 4±17 July.
2.2.3. In Nueva Ecija
An experiment was conducted in eight farmers'
®elds (measured 16±27 m220±610 m) from December 1994 to 15 January 1995. The previous rice crop
was harvested on the second week of November 1994.
Two tillage treatments were imposed during the land
preparation period in a randomized complete block
design with four replications. In each replication, the
dimensions of the ®elds were almost similar. The
treatments were:
Control. Fields were kept fallow until land soaking
on 20±26 December 1994, plowed on 21±28 December and harrowed using comb-tooth harrow on 24±29
December. Final leveling was completed on 3±12
January 1995.
Shallow surface tillage. Fields were dry rototilled to
a depth of 10 cm on 15±16 December 1994, using
four-wheel tractor drawn rototillers. Land soaking was
carried out from 21±26 December 1994. The ®elds
were harrowed using comb-tooth harrows and ®nal
leveling was completed on 4±13 January 1995.
2.3. Measurements of soil water content and physical
properties
All measurements in the IRRI plots were taken from
walk-boards installed in each plot to minimize the
disturbance to the soil and crack formation. Samples,
collected using 100 cm3 cylinders, for bulk density
and volumetric moisture content of the puddled and/or
the tilled layer (approximately 0.1 m thick), and layers
at depths 0.1±0.2, 0.2±0.3 and 0.3±0.5 m were taken at
2±3 days intervals during the fallow and land soaking
periods. Similar samples were used to determine the
saturated water content (Tuong et al., 1996). Vertical
saturated conductivity of the 0.3±0.5 m layer at the
sites were determined using constant head method and
encased soil columns 0.25 high and 0.20 m in diameter
(Wopereis et al., 1994).
In Bulacan and Nueva Ecija soil moisture contents
were monitored by the same method as at IRRI, at the
start of the monitoring program before and after land
soaking at four stations along the center transect of
each ®eld. Sampling depths varied depending on the
soil pro®le of each site: 0±0.1 m (tilled layer), 0.1±0.2,
0.2±0.3, and at 0.3±0.5 m in Bulacan and 0±0.1 m
(tilled layer), 0.1±0.2, 0.2±0.4, and 0.4±0.6 m in
Nueva Ecija.
For simplicity and for the presentation purpose, the
above depths (and else where in this paper) refer to
distances from the original soil surface. The puddled
or tilled layer, however, might change its thickness due
to shrinking and swelling during the fallow and land
soaking periods. To ensure that the same layers were
sampled at various times, all subsoil samplings used
the bottom of the tilled layer (0.1 m from the original
soil surface) as the datum. For example, for the layer
at depth 0.2±0.3 m, the sample was taken from
0.1±0.2 m below the bottom of the tilled layer.
2.4. Measurement of crack dimensions
At the IRRI ®elds, crack depth and width were
monitored at 1±2 days intervals during the fallow
period in a 1 m1 m subplot in each of the control
and mulched plots. In the mulched plots, straw was
removed before and replaced after each measurement.
Crack dimensions of the shallow tillage plots before
the shallow tillage were assumed to be the same as
those in the control plot. In the farmers' ®elds, crack
dimensions were monitored in two 1 m1 m subplots
per ®eld 2±3 days before land soaking. Methods of
measuring and computing crack depth, width, volume
and the surface area of soil islands (soil masses
distinctively separated by cracks) are presented in
Tuong et al. (1996).
2.5. Water application and monitoring
Irrigation was applied from one end of each ®eld,
through pipes (7.5±10 cm diameter) at IRRI and
Nueva Ecija; and from irrigation channels via
15 cm culverts in Bulacan. Application rates were
measured using 908V-notch weirs (at IRRI) and trapezoidal weirs (in farmers' ®elds). Discharge per unit
®eld width was 0.14±0.26 l sÿ1 mÿ1 at IRRI, 0.06±
0.12 l sÿ1 mÿ1 in Bulacan and 0.28±0.60 l sÿ1 mÿ1 in
R.J. Cabangon, T.P. Tuong / Soil & Tillage Research 56 (2000) 105±116
Nueva Ecija. The applied water was spread uniformly
across the width of the ®eld by a distribution channel
as described by Tuong et al. (1996).
In Nueva Ecija, the distance traveled by the advancing surface irrigation water front along the center
longitudinal transect of the plots during the land
soaking process was monitored at approximately
1 h interval. Groundwater table tubes were installed
at 10 m apart along the same transects. The water table
at each location was monitored from the start of land
soaking until the water table reached the soil surface,
following the procedures in Tuong et al. (1996).
2.6. Computation of water ¯ow components during
land preparation
Water balance calculation was carried out during
land soaking at the IRRI ®elds. In Bulacan and Nueva
Ecija, water balance during land preparation was
divided into two phases, namely, land soaking phase
(from ®rst water application to ®rst harrowing) and
harrowing phase (from ®rst harrowing to ®nal leveling). In Bulacan, water balance prior to land soaking
(from start of the monitoring, 17 June 1993 to land
soaking irrigation) was also carried out to take into
account the rainfall at the beginning of the wet season.
For each period, the water balance for the topsoil (0±
0.2 m depth), expressed in mm of water over each
®eld, can be quanti®ed with the following equation
(Tuong et al., 1996):
I R Ss Sc A E L
(1)
where I is the irrigation water, R the rainfall, Ss the
surface water storage, Sc the crack storage, i.e. the
amount of water that ®lls the cracks in the ®eld, A the
water absorbed in the soil layer under consideration, E
the evaporation from the ®eld, L the losses, i.e. the
amount of water that goes beyond the topsoil, recharging the groundwater.
Irrigation water was calculated from the total
volume of water applied (integral of ¯ow discharge
over time) divided by the ®eld area and Ss was the
change in depth of surface water. R was monitored
with rain gauges installed at the experimental sites.
The Sc was the volume of cracks under the surface
expressed in mm of water depth. The A was computed
from the difference in soil moisture contents at the
beginning and end of the study period. After land
109
soaking, soil became saturated, there was no more
increase in crack storage and absorbed water. The E
from the start of the monitoring period to land soaking,
when the topsoil water content in the ®elds changed
from dry to saturated, were estimated by multiplying
open water evaporation (measured by Class A pan) by
0.5 (Tuong et al., 1996). Evaporation after land soaking was estimated by open water evaporation. The
losses were derived from the difference between the
sum of inputs (IR) and the sum of soil surface
storage, crack storage, soil absorption, and evaporation losses Ss Sc A E:
The water balance was computed separately for
the tilled layer (approximately 0.1 m thick) and for
the 0.1 m layer immediately below the bottom of the
tilled layer, before being summed up for the topsoil
under consideration (0±0.2 m depth of the original
soil).
3. Results and discussions
3.1. Soil moisture content
Soil moisture contents at different depths at IRRI
are presented in Fig. 1. Fluctuations in soil moisture
content from 10 DAD (1993) and from 44 DAD (1994)
were due to intermittent rains. In the 1993 experiment,
soil moisture content of the mulched plots was consistently higher than the control and the shallow tilled
plots for depths 0±0.1 and 0.1±0.2 m; and for depth
0.2±0.3 m until about 18 DAD. The difference among
treatments at the later stage, being affected by intermittent rains, was not signi®cant. Moisture content at
0.3±0.5 m depth did not differ among treatments (data
not shown). The results con®rmed previous ®ndings
that straw mulch was effective in reducing soil surface
evaporation (Hundal and Tomar, 1985).
Water content of the 0.1 m top layer of the tilled
plots did not differ signi®cantly from that of the
control. At deeper layers, the tilled plots had signi®cantly higher soil moisture content than the control
plots (Fig. 1b and c). Shallow tillage formed a soil
mulch that reduced water losses from deeper layers. At
the start of land soaking, soil moisture content of the
topsoil in Bulacan was higher than in Nueva Ecija due
to intermittent rains before land soaking (Table 2). Soil
moisture content of the tilled plots in 0.2±0.3 m
110
R.J. Cabangon, T.P. Tuong / Soil & Tillage Research 56 (2000) 105±116
Fig. 1. Soil moisture contents in different treatments after ®eld drainage at the IRRI ®elds, 1993 and 1994 dry seasons, (a) soil moisture at 0±
0.1 m depth; (b) at 0.1±0.2 m depth, and (c) at 0.2±0.3 m depth. Error bars are standard error (n3); (c) also includes daily rain (vertical bars).
R.J. Cabangon, T.P. Tuong / Soil & Tillage Research 56 (2000) 105±116
(Bulacan) and 0.2±0.4 m (Nueva Ecija) depths were
slightly higher than that of the control.
3.2. Crack dimensions
Mean crack width and depth of the control and the
mulched plots at IRRI are presented in Fig. 2. Initial
increase in crack depth and width on the ®rst 8±10
DAD corresponded to the rapid loss of moisture from
the surface layer (Fig. 1). Both crack width and depth
increased more rapidly in the control plots than in the
mulched plots. This corresponded to the slower rate of
soil drying in the mulched plots (Fig. 1) and resulted to
a lower crack volume in the mulched compared to the
control. In the control treatment, a slower rate of
increase in crack depth and width in the 1994 experiment compared to the 1993 experiment conformed
with a slower rate of decrease in moisture content in
Fig. 2. Mean crack (a) widths and (b) depths in different treatments
after ®eld drainage at the IRRI ®elds, 1993 dry season. Error bars
are standard error (n55±161); (b) also includes daily rain (vertical
bars).
111
soil layers in 1994. Ringrose-Voase and Sanidad
(1996) reported similar rates of crack development
in fallow rice ®elds.
In the 1993 experiment, the mean crack depth in the
control treatment reached maximum value of about
115 mm and width about 40 mm at 19 DAD. Both
mean crack width and depth did not change signi®cantly afterwards. At the end of the fallow period, the
crack width of the mulch treatment was signi®cantly
lower than that in the control treatment (Fig. 2). This
corresponds to wide differences in the ®nal moisture
content of the soil surface layer (Fig. 1) in the two
treatments. The ®nal mean crack depth in the mulch
treatment was also less, but not signi®cantly than that
in the control treatment (Fig. 2). The formation of
cracks at lower depths was in¯uenced by the soil
moisture in the subsoil. The non-signi®cant differences in soil moisture at deeper soil layers from 20
DAD between two treatments might have resulted in
only slightly different crack depth. It was likely that at
the day of shallow tillage (at 18 DAD), crack depth of
the shallow tillage plots are similar to those of the
control plots. In the 1993 experiment, this depth was
about 110 mm (Fig. 2), i.e. about the same as the ®nal
crack depth of the mulched plots (106 mm).
Crack width in the control plot in the 1993 and 1994
experiments were of about the same size (Fig. 2). The
zero shrinkage portion of the shrinkage characteristic
curve of the same puddled soil began at a soil moisture
content of 0.25 m3 mÿ3 (Wopereis, 1993). This
implies that upon further drying, no more shrinkage
will take place. Soil moisture of the topsoil layer in
both years, was below 0.25 m3 mÿ3, implying maximum shrinkage had taken place in this layer. Crack
depth was, however, greater in the 1994 experiment,
reaching a mean value of about 130 mm (Fig. 2b). This
corresponded to a lower soil moisture at the deeper
soil layers in the 1994 experiment.
The crack dimensions prior to land soaking at
IRRI, Bulacan and Nueva Ecija are shown in
Table 3. The average widths and depths of cracks
were similar to results of Ishiguro (1992), Wopereis
et al. (1994), and Tuong et al. (1996). The wider and
deeper crack at the Nueva Ecija site was probably
due to the higher clay content in the Nueva Ecija
®elds. Intermittent rains during the fallow period at
IRRI and in Bulacan probably caused some swelling
and closure of cracks.
112
R.J. Cabangon, T.P. Tuong / Soil & Tillage Research 56 (2000) 105±116
Table 3
Dimensions of crack and soil islands (soil masses distinctively separated by cracks) prior to land soaking in IRRI, Bulacan and Nueva Ecija
Location and treatment
Crack
Soil island
Width
(mm)a
Depth
(mm)a
Volume
(m3 mÿ2)b
Surface area
(m2 mÿ2)b,c
Peripheral surface
area (m2 mÿ2)b
IRRI 1993
Mulched
Control
2719
4016
10531
11029
0.009
0.013
0.840.04
0.760.03
1.5
1.9
IRRI 1994
Control
2815
11338
0.020
0.680.01
1.8
Bulacan
Control
3415
14253
0.010
0.800.03
3.8
Nueva Ecija
Control
3620
17856
0.025
0.710.03
3.4
a
MeanS.D. of 120±139 observations at IRRI, 148 in Bulacan, and 352 in Nueva Ecija.
Per unit ®eld surface area.
c
MeanS.D. of six sampling subplots in IRRI, six in Bulacan, and 12 in Nueva Ecija.
b
3.3. Overland and subsurface ¯ow
During land soaking of the control treatment in
Nueva Ecija, water moved in the crack networks
and on the soil surface. Water ¯ow in the cracks
advanced faster than overland ¯ow of irrigation
water. As a result, the water table rose close to the
soil surface at a distance of about 10 m ahead of
the advancing surface water front. No signi®cant
rise of the water table was observed ahead of the
surface water front in the shallow tillage treatment (Fig. 3). The surface water front advanced
faster in the shallow tillage than in the control plots
(Fig. 4).
Fig. 3. Groundwater pro®les with distance from surface water front in the control and shallow tillage plots during ¯ood irrigation for land
soaking at Nueva Ecija. Bars indicate standard deviation for 25 (in the control) and 23 (shallow tillage) measurements.
113
R.J. Cabangon, T.P. Tuong / Soil & Tillage Research 56 (2000) 105±116
surface water front (Bassett et al., 1983) in the shallow
tillage plots. Shallow tillage can, thus, help reduce
time for land soaking. In Muda Irrigation scheme,
Malaysia, it is credited with the bene®ts of timely crop
establishment (Ho et al., 1993).
3.4. Water ¯ow components during land preparation
Fig. 4. Distance travelled by the advancing surface water front in
the control and shallow tillage plots, Nueva Ecija, 1995 dry season.
Observations in the control plot con®rmed ®ndings
by Tuong et al. (1996) and indicated that part of water
that moved in the cracks bypassed the topsoil, in®ltrated into the subsoil, and recharged the groundwater.
Small soil aggregates in the shallow tillage treatment
blocked the cracks, making them discontinuous and
impeded water ¯ow in the cracks and reduced recharge
to the groundwater. This conformed with Wopereis
et al. (1994) who reported that small soil aggregates
reduced 45±60% of the bypass loss through cracks in
large undisturbed soil columns. Less loss to the subsoil
meant more water was available for the surface water
¯ow, and resulted in a faster rate of advance of the
Table 4 shows the water balance components for
different treatments during the 1993 and 1994 experiments at the IRRI ®elds. The amount of irrigation
water needed for land soaking ranged from 93 to
272 mm. The increase in water needed for land soaking in the control plots in 1994 compared to 1993 was
caused mainly by increased water loss. This corresponded to deeper cracks and deeper water table in
1994.
In the 1993 experiment, compared to the control
plots, straw mulching did not reduce signi®cantly the
amount of irrigation water for land soaking at IRRI
®elds (Table 4). By reducing the evaporation loss
during the fallow period, mulching reduced the
amount of absorbed water needed to saturate the
surface soil layer (27 mm compared to 53±56 mm
in other treatments). This reduction was a very small
portion of the water input and did not result in total
water savings.
In both years at the IRRI ®elds, the shallow tilled
plots used signi®cantly less water for land soaking
Table 4
Water balance components during land soaking as affected by surface soil management treatments at the IRRI ®elds in 1993 and 1994
Componenta
Year
Treatment (mm)
Mulch
Shallow tillage
Control
109 abb
93 b
172 b
130 a
272 a
Irrigation water
1993
1994
Surface storage
1993
1994
20
20
25
20
21
Crack storage
1993
1994
9
0
0
13
20
Water absorbed in the 0±0.2 m layer
1993
1994
27
53
48
56
26
Losses
1993
1994
53 a
20 b
99 b
a
b
There was no rain and evaporation was neglected during land soaking.
In the same row, means followed by a common letter are not signi®cantly different at 5% level by DMRT.
41 a
205 a
114
R.J. Cabangon, T.P. Tuong / Soil & Tillage Research 56 (2000) 105±116
Table 5
Water balance components during land preparation as affected by tillage treatments in farmers' ®elds, Bulacan, 1993
Component
Total water input
Irrigation water
Rainfall
Evaporation
Surface storage
Crack storage
Absorbed in 0±0.2 m layer
Losses
Duration (day)
Loss rate (mm per day)
Prior to land soaking
Land soaking stage
Harrowing stage
Total
Control
With shallow
tillage
Control
With shallow
tillage
Control
With shallow
tillage
Control
With shallow
tillage
170
0
170
43
0
0
28
99
23.7
139
0
139
32
0
0
19
88
17.7
150 a*
89
61
11
1
10
11
117 a
4.6
25 a
69 b
57
12
8
20
0
11
30 b
2.3
13 b
26 a
17
9
12
ÿ5
0
0
19 a
2.7
7a
30 a
0
30
9
ÿ1
0
0
22 a
3.3
7a
346 a
106
240
66
ÿ4
10
39
235 a
31
8
238 b
57
181
49
19
0
30
140 b
23.3
6
*
All water components are expressed in mm of water over the area of the ®eld. Total water inputs are sum of irrigation water and rainfall.
In the same row and land preparation stage, treatment means followed by a common letter are not signi®cantly different at 5% level by DMRT.
than the control plots. Losses from the shallow tilled
plots (20 mm in 1993 and 99 mm in 1994) were about
50% of those from the control plots (41 mm in 1993
and 205 mm in 1994). In 1993, the amounts of
irrigation water for land soaking and water loss in
shallow tilled plots were signi®cantly less than those
in the mulched plots, though cracks in shallow tilled
were at least as deep as those in the mulched treatment
plots. This highlighted the role of small soil aggregates
in blocking and impeding water ¯ow through the
cracks.
In farmers' ®elds, shallow tillage reduced the total
water input for land soaking by 54±58% of the amount
needed in the control plots (69 mm compared to
150 mm in Bulacan, Table 5; and 95 mm to
227 mm in Nueva Ecija, Table 6). Most of the savings
in the water input for land soaking came from the
reduced losses in the shallow tillage plots compared to
the control. Findings in farmers' ®elds, thus, con®rmed those at IRRI.
Shallow surface tillage reduced the total water input
for land preparation by 31% in Bulacan (238 mm
Table 6
Water balance components during land preparation as affected by tillage treatments in farmers' ®elds, Nueva Ecija, 1995
Component
Total water input
Irrigation water
Rainfall
Evaporation
Change in storage
Crack storage
Water absorbed in 0±0.2 m layer
Losses
Duration (day)
Loss rate (mm per day)
*
Land soaking Stage
Harrowing stage
Total
Control
With shallow
tillage
Control
With shallow
tillage
Control
With shallow
tillage
(227) a*
224
3
26
43
25
46
87 a
6.0
14.5
(95) b
91
3
4
30
0
41
19 b
1.9
10.0
(122) a
121
1
58
ÿ1
±
±
65 a
10.6
6.1
(137) a
136
1
57
20
±
±
60 a
13.1
4.6
(349) a
345
4
84
42
25
46
152 a
16.5
9.2
(232) b
228
4
60
50
0
41
79 b
14.9
5.3
All water components are expressed in mm of water over the area of the ®eld. Total water inputs (values in brackets) are sum of irrigation
water and rainfall. In the same row and land preparation stage, treatment means followed by a common letter are not signi®cantly different at
5% level by DMRT.
R.J. Cabangon, T.P. Tuong / Soil & Tillage Research 56 (2000) 105±116
versus 346 mm, Table 5); and by 34% in Nueva Ecija
(232 mm versus 349 mm, Table 6) of the amount
needed for the control plots. Much of the differences
in the amount of water-use between the two treatments
occurred during the land soaking phase. High loss rate
sustained in the control plots during this phase indicated that water loss through cracks continued until
the ®rst harrowing was carried out. Harrowing reduced
the loss rate of the control plots considerably and made
them equivalent to those of the shallow tillage plots.
The ®ndings supported the observation that cracks did
not completely close upon rewetting (Moorman and
van Breemen, 1978; Ishiguro, 1992; Wopereis et al.,
1994; Tuong et al., 1996). Harrowing broke soils in the
control plots into aggregates, which sealed the cracks
and produced the puddling effects which reduced soil
permeability (De Datta, 1981). Where dry shallow
tillage can not be carried out, shortening the duration
between land soaking and the ®rst harrowing may be
an important measure to reduce water loss during land
preparation.
In the above computations, it was assumed that the
same soil was taken into consideration before and after
land soaking. Since the whole puddled layer (control
treatment) and the tilled layer (shallow tillage treatment) were included in the water balance, changes in
their thickness during land soaking did not cause any
error in the computation. Soaking decreased the bulk
density of the 0.1 m stratum below the tilled layer by
about 10% (e.g. from 1.15 to 1.04 at IRRI, data not
shown). Assuming an isometric swelling in the stratum, the corresponding change in thickness of the
stratum would be about 3%. Thus, error due to
neglecting the effect of soil swelling in the computation was negligible.
4. Conclusion
Straw mulching helped conserve moisture in the
soil pro®le, reduced crack development during the
fallow period but did not reduce the bypass loss during
land preparation. Shallow tillage formed small soil
aggregates, which blocked and impeded water ¯ow in
the cracks and reduced the amount of water that
recharged the groundwater via the bottom of the
cracks and crack faces. Water was, therefore, retained
better in the topsoil. Shallow surface tillage could
115
reduce about 31±34% of the water input for land
preparation, equivalent to a saving of 108±117 mm
of water depth and shortened time required for land
preparation. Water savings during land preparation
may increase the service area of an irrigation system.
In rainfed areas, shallow surface tillage may also lead
to earlier crop establishment and, thus, reduce the risk
of late-season drought. This kind of tillage does not
necessarily require high-powered tractors. Further
more, tractors/rototillers are becoming more accessible to small farmers for custom hiring, offering better
opportunities for incorporating shallow surface tillage
practice in the rice production system.
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