ily in the efficiency of the use of nutrients, above all nitrogen Schepers and Fox, 1989. A study on
different kinds of breeding farms in Piemonte Grignani, 1996 showed a general imbalance be-
tween farm global inputs and outputs, with a nitrogen surplus of 300 kg ha
− 1
year
− 1
, on aver- age. The nitrogen inputs were mainly concentrates
and fertilizers, but only 30 of the total input was found in farm outgoing products meat, milk and
grain. Consequently, most of the nitrogen input was leached with drainage water, lost in volatile
compounds or accumulated in the farm system, such as in soil organic pools. These and similar
results obtained in other countries Jarvis, 1993; Simon et al., 1994; Weissbach and Ernst, 1994;
Cuttle, 1997 have often led policy makers to ascribe high nitrate leaching losses to intensive
livestock farming systems.
Although several studies of nitrogen leaching have been undertaken over many decades in vari-
ous environments Juergens-Gschwind, 1989, the general understanding of the effects of agricul-
tural practices on N leaching remains fragmen- tary. Assessment of N leaching is in particular
greatly influenced by the method used to measure leachable mineral N such as soil-core extractions,
ceramic cups, lysimeters, tile drainage, plot or farm balance, as well as by the scale at which N
leaching quantification is undertaken such as soil profile, experimental plot, farm or catchment;
Armstrong and Burt, 1993.
Most studies have been conducted at the point measurement scale, focusing on the soil mineral N
concentration Cavazza et al., 1986; Patruno, 1987; Verte´s and Decau, 1992; Benoit, 1994; Par-
dini et al., 1995; Grignani et al., 1996. At this scale, a theoretical deterministic description of the
vertical water and solutes movement is available, obtained from several decades of laboratory ex-
periments Jury and Flu¨hler, 1992. Two-dimen- sional field studies have been conducted, mainly
using tile drains Decau and Le Corre, 1992; Scholefield et al., 1993; Lewan, 1994; Drury et al.,
1996; Borin, 1997, while three-dimensional stud- ies on catchments and model applications coupled
to GIS systems are becoming extremely popular Shaffer et al., 1996; David et al., 1997; Richter et
al., 1998 among others. A further difficulty encountered in N leaching
research is that of the representativeness of exper- imental treatments in comparison to the agricul-
tural practices
adopted by
farmers. Crop
management is often conditioned to a great extent by farm organization systems, in particular in
forage systems oriented to livestock production, where both the forage yield in terms of fodder
quality, rather than DM production and the organic fertilizer supply are connected to animal
husbandry. Hence, choices on the crop, rotational system, time, amount and type of fertilizer appli-
cations, tillage, irrigation, etc., are not indepen- dent, and an evaluation of the real effects of the
cultivation system can be carried out through an analysis of real situations, in real farms. Some
authors have therefore tried to work in situations where agricultural practices were a variable rather
than a factor Benoit et al., 1995; Vereijken, 1997, although this may imply a higher degree of
uncertainty, as not all variables can be measured with the same precision as in experimental plots.
The objective of this study was to assess the response of the mineral nitrogen concentration of
the soil solution to various aspects of forage system management crop and crop rotation, kind
of fertilizer supplied, time and amount of supply in real conditions, after monitoring the effectively
adopted agricultural practices. The analysis was conducted in four private farms, two dairy cow-
breeding farms and two pig breeding farms, com- paring two fields cultivated with different crops.
2. Materials and methods
2
.
1
. Experimental design Two typical breeding systems of the western Po
plain were considered in four private farms in Piemonte NW Italy: two were intensive dairy
cow breeding farms C and two intensive pig breeding for fattening farms P. As reported in
Table 1, two farms of each kind lay on shallow and stony soils CS and PS and two on deep soils
CD and PD. The analysis was carried out in two fields, or cultivation systems, in each farm, a and
b Fig. 1:
C .
Grignani ,
L .
Za 6
attaro Europ
. J
. Agronomy
12 2000
251 –
268
253 Table 1
Soil type, maximum soil depth and main characteristics of the eight fields averaged over 0–50 cm
a
Site Bulk density g cm
− 3
Soil type USDA, 1997 OM N
Max soil depth cm Field Fine earth fraction
Stone content vol Silt Clay
Sand 8.0
1–5 1.50
2.66 42.9
0.154 CS
49.1 a
1
50 Dystric
Eutrochrept 41.0
3.9 15–35
1.37 4.34
0.256 B
55.2 8.9
B 1
1.47 1.60
0.106 43.1
CD 48.0
a
1
\ 200
Aeric 14.8
B 1
1.46 1.40
0.094 Epiaquept
b 42.0
43.3 12.1
5–15 1.58
1.75 52.1
0.112 35.8
a
2
60 Typic
PS 65.0
29.4 5.6
15–35 1.44
2.00 0.133
Haplustalf b
9.7 1–5
1.50 1.92
0.129 43.5
46.8 PD
Aquic ustochrept a
2
and b 100
a
CS, cattle breeding and shallow soil; CD, cattle breeding and deep soil; PS, pigbreeding and shallow soil; PD, pig breeding and deep soil.
1. field a was a permanent meadow in the dairy cow breeding farms a
1
, and a double crop- ping with barley or Italian ryegrass as a winter
crop, and maize marrow plant in one in- stance as a summer crop in the pig breeding
farms a
2
; 2. field b was cultivated with grain maize or
silage maize as a single crop at all four sites. Maize as a single crop was chosen as an exam-
ple of a crop that leaves the soil bare during winter. Because it is very frequent in the Po plain
it was used as a common treatment for all the farms. The other crops in field a were chosen from
those that provide an active growing potential during winter, and differed according to the farm
organization. However, the permanent meadow a
1
represented a less intensive cultivation system compared to maize as a single crop, while the
double cropping a
2
was more intensive. In this work the crop systems are analyzed as the whole
combination of crops on a year basis, without referring to single components.
All the measurements were carried out in two 6 × 8 m plots, drawn within a large field and
considered as replicates. The distance between the two plots ranged approximately from 30 to 60 m,
depending on the field size, but the plots were far enough from the field edges to avoid border ef-
fects. The experiment was carried out for 2 years, between autumn 1994 and autumn 1996.
2
.
2
. Soil characteristics and climate Three soils were Inceptisols sites CS, CD and
PD and one was an Alfisol site PS, as reported in Table 1. The soils at sites CS and PS were
particularly shallow because the stone content exceeded the fine earth fraction below 40 – 60 cm.
The texture in these soils was coarser than at the CD and PD sites. The soil at site CD, evolved on
loess depositions, was deep and less stratified than the other three, which evolved on river deposi-
tions. At site PD, a water table lay in a gravel layer below the 1-m deep topsoil, the depth of
which oscillated between 90 and 120 cm Zavat- taro, 1998. The total N and OM contents of the
soil were particularly high at CS, compared to the other locations, which were more representative
of normal soil conditions in the area. Further details on the soil characteristics are reported in
Zavattaro 1998. Synthetical weather information is reported in Table 2.
2
.
3
. Agricultural practices The experimental activity did not interfere with
the farmers’ choices on agricultural practices. No external machinery was used. Neither the time nor
the amount of fertilizer supply was influenced, except in the zero-nitrogen plots, as indicated
below. The time and kind of nitrogen supply for each crop are reported in Fig. 1.
2
.
4
. Nitrogen supply The amount of effectively spread organic fertil-
izer was measured at each application. Cow ma- nure spread on two 2 × 2 m-plastic sheets laid side
by side was weighed at each plot. The amount of
Fig. 1. Crop sequence in the eight examined fields. The sowing and harvesting dates, and the time of nitrogen fertilizer appli-
cations are also indicated. CS, cattle breeding and shallow soil; CD, cattle breeding and deep soil; PS, pig breeding and
shallow soil; PD, pig breeding and deep soil; a
1
, permanent medow, a
2
, double cropping; b, maize.
C .
Grignani ,
L .
Za 6
attaro Europ
. J
. Agronomy
12 2000
251 –
268
255
Table 2 Three-month averaged maximum and minimum temperatures, rain and potential evapotranspiration ET
o
calculated with the Penman–Monteith formula Sites PS and PD
Site CD Data
Site CS T
max
°C Rain mm
ET
o
mm T
min
T
max
Rain mm T
min
°C ET
o
mm T
min
°C ET
o
mm Rain mm
T
max
°C −
1.8 −
1.4 7.9
58 94
0.7 8.1
23 109
9.2 40
95 Dec 94–Feb 95
17.5 231
310 6.7
15.9 284
4.5 323
6.0 Mar 95–May 95
340 455
17.5 14.6
15.8 27.2
178 459
15.9 25.5
191 468
26.7 174
520 Jun 95–Aug 95
5.9 7.0
16.7 304
171 8.1
16.0 194
197 17.4
255 205
Sep 95–Nov 95 4.6
232 59
0.0 5.3
122 −
1.3 75
246 80
Dec 95–Feb 96 −
1.0 6.5
5.4 6.7
16.2 199
280 7.0
15.1 272
306 16.7
205 340
Mar 96–May 96 27.2
164 460
15.6 25.1
134 Jun 96–Aug 96
460 16.1
26.5 210
503 13.9
16.3 254
173 7.8
14.9 361
6.9 185
16.7 Sep 96–Nov 96
7.4 189
312 5.7
6.7 16.1
1004 1021
7.4 15.2
922 1096
16.6 1152
1161 Avgerage year
Table 3 Average dry matter, pH and total nitrogen content and their variability coefficient of variation of the organic fertilizers used in
this trial C.V.
Mean values pH
N g kg
− 1
of fresh matter Dry matter
Dry matter pH
N 8.3
6.5 Cattle manure
46.1 25.0
1.5 28.0
8.0 2.5
44.8 5.9
81.9 Cattle slurry
21.0 8.2
6.0 11.7
89.4 14.3
Pig slurry 5.9
cattle and pig slurry was measured in 15 circular basins 40 cm in diameter and 6 cm in height
placed in each plot at a rectangular grid of 6 × 4 m. A chemical analysis was performed on a sam-
ple of organic fertilizer, at each application. Only the results concerning the total N content are here
discussed. Some relevant average characteristics are reported in Table 3.
The mineral fertilizer supply was not directly measured. The total amount spread over the field
was simply divided by the field area.
2
.
5
. Crop production and uptake Crop and grass yields were measured just be-
fore harvesting on sampling areas randomly placed at each plot. Sampling areas were 18 m
2
for maize, 4 m
2
for barley, and 0.5 m
2
for ryegrass and meadows. Total above-ground biomass and
grain yield were weighed over the whole sampling area. A sub-sample of about 2 kg was dried at
70°C for 48 h for determination of DM produc- tion. DM tissues was subsampled and ground for
subsequent total N analysis.
Two additional zero-nitrogen plots were drawn in each field, to test the fertilizer efficiency. No
N-fertilizer was spread over these plots over the two years. Yield and N uptake were the only
measurements carried out in the 0-N plots.
Four indexes for N fertilizer efficiency were considered: calculated surplus fertilizer minus re-
moval; removal-fertilizer ratio; apparent recov- ery, obtained as N uptake in the fertilized plots
minus N uptake in the 0-N plots N supplied through fertilization; N use efficiency, obtained as
DM production in the fertilized plots minus DM production in the 0-N plots N supplied through
fertilization Guillard et al., 1995.
2
.
6
. Monitoring the soil solution concentration The nitrate and ammonium concentration of
the soil solution was monitored every 2 weeks, although samples could not be collected when the
soil was too dry. The soil solution was extracted by creating a suction of approximately 0.7 bar in
a set of three porous cups placed about 1 m apart in each plot. After 24 h, the contents of the three
cups were extracted and mixed, and a sample was refrigerated and analyzed using a colorimetric
technique Verte´s and Decau, 1992. Three cups were used to average the small-scale spatial vari-
ability and also to assure a sufficient amount of solution for the analysis.
Porous cups are widely used to assess solute leaching through unsaturated soil. Although sev-
eral authors pointed out that results may be af- fected by the fact that they sample water from a
limited size of pores, expecially from macropores Grossman and Udluft, 1991; Webster et al.,
1993, there are evidences that they are reliable and accurate for monitoring nitrate leaching on
fairly homogeneous soils, particularly where the amount of clay is not too high, as in the situations
examined here Poss et al., 1995. Another advan- tage of ceramic cups is the fact that, as they can
be left in place, changes over time are not con- founded with changes due to sampling from dif-
fering locations as is the case with successive soil sampling Poss et al., 1995.
Porous cups were placed at a depth of 50 cm at all sites. This depth was chosen as a reference to
compare the different soils and treatments. This corresponded approximately to the maximum ex-
plorable depth in the two shallow soils CS and PS, because underneath the stone content pre-
vailed over the fine earth fraction Table 1. In all soils and fields the number of roots remark-
ably decreased below 40 – 60 cm, hence the depth of 50 cm can be considered as the bottom
boundary of the active root system in all the explored situations. Additional cups were placed
in the two deep soils and used for modelling nitrate leaching Zavattaro, 1998, but field re-
sults are not discussed here. In the permanent meadows, the cups were completely buried and
collecting tubes were gathered in a pit, in order not to hinder mechanical operations. In the
arable fields, the cups were removed before tillage and installed again afterwards, 2 – 4 times
a year, depending on the crop rotation. In maize, they were placed along the crop rows.
The ceramic cups used were 3 cm in diameter and 7.4 cm long, with a nominal conductivity of
8 × 10
− 7
cm s
− 1
and an air entry value of 100 kPa.
2
.
7
. Statistical treatment of the nitrate concentration data of the soil solution
In order to test whether the nitrate concentra- tion of the soil solution was different in the two
fields in each site, due to the effect of the culti- vation system field a versus b or the season
summer versus winter, where winter is the bare soil period in field b, an analysis of variance for
repeated measures, corresponding to a split-split- plot design Diggle et al., 1994, was performed
on the time series of NO
3
-N concentration. Time was regarded as a factor on n-levels, in a hierar-
chical design, with time units as sub-sub-plots. The data represented time successions and
were tested for autocorrelation. This analysis was made shifting each series by multiples of the
time lag, corresponding to the sampling interval. The serial correlation coefficient Camussi et al.,
1995 was calculated for each pair. The signifi- cance a = 0.05 of the serial correlation coeffi-
cient was tested according to Vianelli 1959.
The variables affecting the average nitrate concentration in the soil solution were searched
for with a simple correlation and a multiple re- gression approach. The input variables tested
were:
the physical characteristics of the soil: percent- ages of sand and clay, volumetric stone con-
tent, saturated hydraulic conductivity at the soil surface K
s
, bulk density, soil depth. All these variables except K
s
were measured at a depth of 50 cm;
the chemical characteristics of the soil: organic carbon, humus carbon extracted in sodium
pyrophosphate according to IPLA, 1984, total nitrogen, potentially mineralizable N Stanford
and Smith, 1978, CN ratio, pH and cation exchange capacity;
crop variables averaged over 2 years: N up- take and removal, days of bare soil between
subsequent crops;
management variables averaged over 2 years: N fertilizer supply, fertilizer supplied before
ploughing or harrowing that is, excluding sur- face applications, total N supply fertilizer and
crop residues;
N fertilizer efficiency indexes: calculated sur- plus, removal-fertilizer ratio, apparent recov-
ery, as previously defined. The concentration of the soil solution depen-
dent variable was averaged over the 2 years after weighting over time, while the two plots were
considered separately, therefore the total number of cases was 16. The selection of variables was
stepwise, with the entry criterion a = 0.05 and the removal criterion a = 0.10. The input variables
were tested for correlation, to ensure that the choice of variables entering the model was not for
numerical reasons.
2
.
8
. Assessing nitrate leaching using the LEACHM model
The amount of nitrogen leached below the maximum root depth was evaluated using the
LEACHM model. The water section of the model was parameterized on the measured hy-
drological properties of the soil, while the nitro- gen section parameters were partly derived from
literature values and partly calibrated on the ni- trate
concentrations of
the soil
Zavattaro, 1998.
3. Results and discussion
