64 C.J. Pilbeam et al. Agriculture, Ecosystems and Environment 79 2000 61–72
Table 1 A summary of characteristics selected from the available literature
to define a hypothetical household in the mid-hills of Nepal and subsequently used for calculating the N budget
Characteristic Attributed values
Total land area ha 1.0
Pieces of land 4
Bari : khet
a
2 : 1 Trees
50–80 No. of Animals
Buffalo 2
Bullock Ox 2
Cows 1
Goat 3
Chicken 6
Crops kg ha
− 1
Average grain yield
b
Maize Zea mays L. 2000 3000
Finger millet Eleusine coracana 1160 1740
Rice Oryza sativa L. 2000 3000
Wheat Triticum aestivum L. 2500 3750
a
Bari land is rainfed, while khet land is irrigated.
b
Average straw yield kg ha
− 1
in parenthesis assuming an harvest index of 0.4.
3. Estimating a nitrogen balance
3.1. N produced in faecal material According to Rasali et al. 1996 annual rates of
production of manure per animal are 4.7 Mg for cows, 5.5 Mg for buffalo, 0.3 Mg for goat and sheep, and
0.2 Mg for pigs. Annual amounts of manure produced per household vary and are especially dependent on the
numbers of large ruminants kept. Nevertheless, using the above rates of manure production and the number
of animals designated for a hypothetical household, then a hypothetical household might produce 26 Mg
FYM per year. This falls within the range of 1–31 Mg FYM per household per year measured by Vaidya
Table 2 Amount of N produced in manure per day per livestock type in a hypothetical household in Nepal
Livestock Manure
a
kg per day of N
a
Amount N kg per day No. of animals
Amount N kg per household per day Buffalo
12 0.33
0.04 2
0.08 Cattle
10 0.25
0.025 3
0.075 Goat
0.51 0.83
0.004 3
0.012 Pig
2.8 0.44
0.012 –
–
a
Source: Khadka and Chand 1987.
1988, but is greater than the estimate of 20 Mg FYM per household per year derived from the figures of
Khadka and Chand 1987. While it is likely that both Rasali et al. 1996; Khadka and Chand 1987 doc-
ument fresh weights rather than dry weights, a possi- ble explanation for the greater values of Rasali et al.
1996 may be that they report values for manure fae- cal material plus bedding while Khadka and Chand
1987 report values for faecal output only. Khadka and Chand 1987 measured the daily faecal output kg
fresh weight for different livestock species in Nepal Table 2, and assumed a N concentration on a wet
basis Table 2. The total N output in manure for a household depends on the numbers of each species
kept by a particular household. Using representative values for numbers of animals per household Table 1
and the quantity and quality values for faecal output of Khadka and Chand 1987, the daily output of N in
manure from a hypothetical household is 0.2 kg N, or 61 kg N per year Table 2.
3.2. N inputs through fertilizer and manure to cropping system
Rates of application of manure FYM may vary by an order of magnitude between farmers in different
locations; 3–30 Mg FYM ha
− 1
according to Kiff et al. 1995 and 5–55 Mg FYM ha
− 1
according to Sharma 1996b. Tuladhar 1995 reported application rates
of 20–50 Mg FYM ha
− 1
to bari land. However, the estimates by Gurung and Neupane 1991 of 18 Mg
FYM ha
− 1
for bari and 11 Mg FYM ha
− 1
for khet land more closely match not only the recommended appli-
cation rates of 10 Mg FYM ha
− 1
for wheat and maize LARC, 1997, but also the average annual applica-
tion rates of 2.5–10 Mg FYM ha
− 1
per year Vaidya, 1988 based on average data, and assuming 20 ropani
equal 1 ha and a doko a basket contains 20 kg manure
C.J. Pilbeam et al. Agriculture, Ecosystems and Environment 79 2000 61–72 65
Table 3 Calculation of the total manure N application for a hypothetical household. See text and Table 1 for details
Crop Area
Amount FYM Mg ha
− 1
Amount FYM Mg area
− 1
of N Amount N kg N area
− 1
Maize 0.66
10 6.6
1 66
Wheat 0.33
10 3.3
1 33
Rice 0.33
10 3.3
1 33
when full. In the hypothetical household it is assumed that maize, rice and wheat crops each receive FYM
at a rate of 10 Mg ha
− 1
. According to Pandey 1996, FYM has an average N concentration on a dry weight
basis of 1 ±0.5, a value confirmed in some stud- ies by Subedi et al. 1996, so between 25 and 100 kg
N are applied as manure per ha per year. In a hypo- thetical household, crops occupy 1 ha, and so it is
possible for the annual household production of ma- nure to match the crop requirements. For example, if
66 of a 1 ha farm is bari land sown to maize and the remainder is khet growing wheat, the total application
of N is 99 kg N ha
− 1
a
− 1
, which is within the limits of manure application calculated above Table 3. How-
ever, it should be noted that manure is also increas- ingly applied to rice, perhaps at the expense of maize,
and this may alter the N requirement of the household.
Recommended application rates of N fertilizer for improved varieties of rice and maize are 100
and 120 kg N ha
− 1
respectively, and 80 kg N ha
− 1
for wheat LARC, 1997. Finger millet is grown on residual soil fertility. On average hill-farmers apply
less; 12.8 kg N ha
− 1
NAPP, 1995, depending espe- cially on location, farmer perception of soil fertility,
economic status of the farmer and land type. On av- erage, between 10 and 25 kg N ha
− 1
are applied to maize grown on bari land, while 10–15 kg N ha
− 1
are
Table 4 Grain and straw yields kg ha
− 1
and amounts of N kg N ha
− 1
in grain and straw of crops commonly grown in the mid-hills of Nepal, and found in a hypothetical household defined in Table 1
Crop Grain yield kg
Straw yield
a
kg of N
Amount of N kg per household
b
Ha household
b
Ha Household
b
Grain Straw
Grain Straw
Total Maize
2000 1320
3000 1980
1 0.5
13.2 9.9
23.1 Millet
1160 766
1740 1148
1 0.5
7.66 5.74
13.4 Rice
2000 660
3000 990
1 0.5
6.6 4.95
11.6 Wheat
2500 825
3750 1238
1 0.5
8.25 6.19
14.4
a
Assuming a constant harvest index of 0.4.
b
Assuming a 2 : 1 ratio bari : khet land.
applied to both rice and wheat grown on khet land Sherchan, pers. commun., 1998. For a hypotheti-
cal household therefore, a total of 26 kg N ha
− 1
are applied to land in a year.
3.3. N offtake in crops The proportion of N in the grain and straw of a
cereal crop at harvest is generally consistent between years and locations. Grain has approximately 1–1.5
N, while straw has 0.5–1.0 N. This consistency en- ables the calculation of the approximate amount of N
removed in the crop. For example, the total amount of N removed in a single year from a maize-finger millet
rotation on 0.66 ha of bari land is approximately 37 kg N 21 kg N in grain and 16 kg N in straw; Table 4. If
the remaining 0.33 ha of land owned by the household is sown to a rice-wheat rotation, then the annual total
N removed from khet land is calculated to be 26 kg N 15 kg N removed in grain and 11 kg N removed in
straw; Table 4.
3.4. N input to livestock The amount of feed eaten by livestock depends
on the season and the associated availability of feed sources, and on the animal species.
66 C.J. Pilbeam et al. Agriculture, Ecosystems and Environment 79 2000 61–72
Neopane et al. 1990 estimate that 25 kg fresh ma- terial is fed to a buffalo per day, although Delobel
1986 estimated between 8–36 kg fresh weight per day depending on season and lactation. In a survey of
farmers in eastern Nepal, Thorne unpublished data, 1997 estimated that buffalo, cow, ox and goat were
fed 30, 21, 12.5 and 3 kg fresh material per day, re- spectively, during the monsoon period assumed to be
155 days, and about less than half of this amount per day during the dry post-monsoon period assumed to
be 210 days, assuming a liveweight of 450 kg for buf- falo, 225 kg for cows and oxen and 25 kg for goats.
Crop residues dry and green, grass and tree fodder account for more than 90 of the large ruminant feed,
and approximately 70 of goat feed, with broadleaved weeds accounting for much of the rest Thorne, un-
published data, 1997. The relative importance of these three feed types varies with animal species. Tree fod-
der accounts for 10–15 of large ruminant feed, but 30 of goat feed, while crop residues dry and green
account for 35–45 of large ruminant feed but 10
Table 5 Average amounts of dry matter kg a
− 1
and N fed per annum kg N a
− 1
from different feed-stuffs to different numbers of livestock from different livestock classes used to calculate the total annual N requirement kg N a
− 1
from different animal feeds for a hypothetical household in the mid-hills of Nepal
Feed type Livestock class
DM fed
a
N intake No. of
Total N required animal per year
animal per year livestock
household per year Dry crop
buffalo 800
3.6 2
7.2 Residue
cattle 600
6.1 1
6.1 ox
442 4.6
2 9.2
goat 10
0.1 3
0.3 total: 22.8
Tree fodder buffalo
362 6.5
2 13
cattle 229
5.2 1
5.2 ox
84 1.8
2 3.6
goat 78
1.7 3
5.1 total: 26.9
Grass buffalo
1135 10
2 20
cattle 829
12.6 1
12.6 ox
463 7.2
2 14.4
goat 96
1.6 3
4.8 total: 51.8
Green Crop buffalo
271 16.5
2 33.2
Residue cattle
184 3.1
1 3.1
ox 144
2.5 2
5 goat
6 0.1
3 0.3
total: 41.6
a
Assuming 155 days for monsoon period and 210 days for dry period.
goat feed. Grass accounts for 30–45 of feed require- ments irrespective of livestock class.
The percentage crude protein content of tree fodder was found to be 9–14 Subba and Tamang, 1990
or 18 Shrestha and Tiwari, 1992, or approximately 1.5–3.0 N assuming a N to crude protein conversion
factor of 6.25. Consequently, each buffalo, cow, ox and goat is annually fed approximately 6.5, 5, 1.8 and
1.7 kg N, respectively, in tree fodder Table 5; Thorne, unpublished data, 1997. Annual values of N fed as
grass to the same livestock classes are 10, 12.6, 7.2 and 1.6 kg N, respectively. Totals of 27 and 52 kg N
are required as tree fodder and grass, respectively, per household per year. Table 5. Little N is fed as dry
crop residue, approximately 3.6, 6, 4.6 and 0.1 kg N per year for each buffalo, cow, ox and goat. Accord-
ing to Table 5 the total amount of N fed in dry crop residues is 23 kg N per household per year. This com-
pares well with the 27 kg N ha
− 1
removed in straw per household Table 4. Green crop residues provide ap-
proximately 16.6 kg N for each buffalo per year i.e.,
C.J. Pilbeam et al. Agriculture, Ecosystems and Environment 79 2000 61–72 67
ca. 40 of N intake by buffalo but their significance as a source of N for cows, oxen and goats is less ca.
10–15 of N intake. The total annual N requirement for animal fodder
is approximately 167 kg N per household. 143 kg N is provided in dry and green crop residues, grass
and tree fodder. Broadleaved weeds, N-rich vegetable matter and concentrates provide the remainder. Ap-
proximately 10 of food offered to large ruminants buffalo, ox and cow is refused, whereas 30 is
refused by goats Thorne, unpublished data, 1997. Slightly more is refused in the dry season than in the
monsoon Thorne, unpublished data, 1997. Conse- quently, 23 kg N per household of the total annual N
requirement is refused, and perhaps enters the com- post heap directly without passing through the animal.
3.5. N inputs to soil Nitrate concentration in rain is generally 0.5
mg l
− 1
Collins and Jenkins, 1996 and has changed little over time; measurements in snow and ice from
glaciers give similar concentrations Nijampurkar et al., 1993. Ammonium concentrations in rainfall
are low, on average 0.5 mg
− l
Collins and Jenk- ins, 1996. Assuming an annual rainfall of 1500 mm,
15 kg N ha
− 1
will be deposited in rain, half as ni- trate and half as ammonium. A similar amount may
be added through wet and dry deposition, although it has not been measured in Nepal.
Mineralization of organic N is dependent particu- larly on the N and C contents of the soil, and soil
temperature and moisture content. These latter envi- ronmental factors change markedly between the mon-
soon and dry seasons. Net mineralization of soil N may be estimated from the yield of unfertilized crops
Subedi, 1993, 1994; Sherchan et al., 1999, assum- ing a harvest index 0.4 and a N content similar to
that described above 3.2 and Table 3 and subtract- ing a value ca. 25 kg N ha
− 1
for N deposited in rain and dust above gives a value for mineralization of
50–75 kg N ha
− 1
a
− 1
. Nitrogen may also be added to soils on khet land
through irrigation water. Analyses of stream water for four catchments in the Likhu khola watershed show
skewed distributions of both nitrate and ammonium concentrations Collins and Jenkins, 1996. Although
extreme values of ammonium and nitrate were 1.25 and 2.0 mg l
− 1
, respectively, the mean values were approximately 0.1 mg l
− 1
for both nutrients. Unfortu- nately, the volume of water used to irrigate khet land
has not been measured in Nepal. Organic N may also be found in irrigation water, but its concentration is
not known.
3.6. N losses from soil High rainfall 1000 mm within a few months
in the mid-hills of Nepal probably results in N be- ing leached especially from bari land. Nitrate may
also be leached when khet soils are flooded prior to rice transplantation if nitrate accumulates in the
soil profile after the harvest of the preceding wheat crop. Buresh et al. 1989 estimated that 95 of
nitrate accumulated during a dry season crop was lost upon flooding of the soil. Nitrate may also be
leached during rice cultivation where puddling prior to transplantation does not create a completely im-
permeable layer. Singh et al. 1991 reported that ca. 13 of urea fertilizer was lost due to leaching in
coarse textured soils. Actual amounts of N leached have not been quantified, although model predictions
for 4 catchments in the Likhu Khola watershed sug- gest losses of 5.8–18.5 kg N ha
− 1
a
− 1
Jenkins et al., 1995, approximately equal to that added in rainfall.
Runoff occurs on bari land and was estimated to be between 5 and 10 of total rainfall for cultivated
erosion plots on bari land in the Likhu Khola in 1993 Gardner et al., 1995, although exceptionally it
may be between 20 and 30. Assuming a rainfall of 1500 mm and a concentration of 0.1 mg l
− 1
for both ammonium and nitrate in the runoff, then the loss of
N in solution will be 0.5 kg N ha
− 1
, which accords with the runoff data from Gaskin pers. commun.
1997, although Collins and Jenkins 1996 state that concentrations of N in stream water increases during
the monsoon due to runoff from highly fertilized bari land.
Gaseous losses of N by denitrification or volatiliza- tion from khet and bari land have not been measured
in Nepal, although preliminary data on losses of
15
N-labelled fertilizer from bari land Pilbeam, 1997 and 1998; unpublished suggest that they may be
significant. Gardner et al. 1995 reviewed the literature on
soil erosion from cultivated land in the middle hills
68 C.J. Pilbeam et al. Agriculture, Ecosystems and Environment 79 2000 61–72
and concluded that annual losses broadly fell into two groups, those 5 and those 15 Mg ha
− 1
a
− 1
, although different methodologies make comparisons
difficult. Larger losses are particularly common on the red soils of central and eastern Nepal. Losses are af-
fected by rainfall intensity, ground cover, cultivation and previous rainfall, and so vary considerably during
the monsoon season. Analyses for the percentage total N in 340 soil samples from bari land in the western
development region of Nepal averaged 0.27 Tur- ton et al., 1995 so that 13.5 kg N ha
− 1
will be lost when 5 Mg soil ha
− 1
are eroded. This equates to 9 kg N ha
− 1
a
− 1
from the bari land of a hypothetical house- hold. The N concentration of agricultural soils in the
Jhikhu Khola watershed 0.12; Schreier et al., 1994 was lower than that mentioned above, and so losses in
eroded material would be commensurately lower.
3.7. Constructing the balance A N balance for a hypotheical household in the
mid-hills of Nepal is shown in Fig. 1. There is remark- ably good agreement between the data from diverse
sources. Total losses of N in eroded material from bari
Fig. 1. A flow diagram of N for a hypothetical household in the mid-hills of Nepal, showing the amounts of N flowing through different pathways. Unknown quantities are represented by? See text for details.
land 9 kg N ha
− 1
, and runoff 0.5 kg N ha
− 1
and leaching 12 kg N ha
− 1
from both bari and khet land are quantitatively similar ca. 21 kg N ha
− 1
either to inputs in rainfall plus deposition 25 kg N ha
− 1
, or to inputs of fertilizer N 26 kg N ha
− 1
. These losses of N are both small amounts relative to the amount of N re-
moved in grain and straw 63 kg N ha
− 1
. The amount of N removed in grain 36 kg N ha
− 1
is greater than that added as fertilizer, but less than the amount of
N mineralized from soil organic matter 50–75 kg N ha
− 1
. The N off-take in straw 27 kg N ha
− 1
is comparable to the amount of N fed to livestock as
dry crop residue 23 kg N ha
− 1
. Amounts of N fed to livestock are inevitably greater than those produced
as manure because some is retained as animal prod- ucts, and not all is excreted. Further discrepancies are
introduced by the loss of ammonia from the rumen, or from the urine and faeces prior to measurements.
4. Impact of perturbations to the system
