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
Having developed a N balance for a hypothetical household in the mid-hills of Nepal, it is possible to
C.J. Pilbeam et al. Agriculture, Ecosystems and Environment 79 2000 61–72 69
examine the effect of changes to the system. Possible scenarios are as follows:
1. The number of large ruminants kept by a household is declining Kiff et al., 1995 as a specific conse-
quence of a reduction in grazing areas and labour shortages. This means not only that less manure
will be produced, but also that less forage will be required. For example, if in the hypothetical house-
hold either the cow or both oxen were removed, then annual manure production would fall by either
3.7 or 7.3 Mg per year, respectively. These reduc- tions are equivalent to a reduction in N of 9 and
18 kg N per household per year, 9 or 18 of the annual requirement of N from manure. The impact
on total feed requirement is much less. The total N requirement of feed is reduced from 167 kg N per
household to 138 or 133 kg N if the cow or both of the oxen are removed, respectively.
2. An increase in the application of fertilizer is predicted NAPP, 1995. Evidence Pilbeam, un-
published suggests that applications of fertilizer increase the amount of nitrate-N leached from
beneath the rooting zone of crops grown on bari land. This leached N is not the recently applied
fertilizer, but N derived from the re-mineralization of organic N, which is not taken up by the crop.
Clearly, the timing and size of each application is critical if N losses are to be minimized and the
efficiency of N use is to be maximized. There is some indication in rice-systems that top-dressed
N is used more efficiently than basally-applied N Subedi et al., 1995. A more efficient use of
fertilizer N may mean either that less manure is required or that the storage of nutrients increases.
3. Erosion control mechanisms may be introduced. Since losses of N through soil erosion are small,
these control mechanisms would appear to have little impact on the N budget.
4. According to the few studies that have measured it, the loss of N from FYM may be significant. Im-
provements in the management of manure, either during storage, or in its application and incorpora-
tion Subedi et al., 1996 may increase the N con- centration of the manure. If the N in manure in the
hypothetical household were increased from 0.3 N for buffalo, cow and ox to 0.5 N, then annual
production of N in manure would increase from 61 to 103 kg N. Labour shortages may prevent the re-
Table 6 Normalized contribution of men, women and children to tasks
relating to the management of soil fertility in 13 villages in the mid-hills of Nepal
a
Task Men
Women Children
Collection and carrying of 0.2
0.57 0.23
fodder and grasses Collection of bedding
0.15 0.48
0.37 Cleaning animal shed
0.35 0.48
0.17 Turning manure pile
0.57 0.38
0.05 Carrying FYM to field
0.16 0.59
0.25 Spreading FYM
0.27 0.53
0.2 Buying and carrying fertilizer
0.55 0.35
0.1 from depot
Applying chemical fertilizer 0.65
0.35
a
Source: Turton et al., 1995.
alization of these large potential benefits. Such in- creases in manure application may mean that less
fertilizer is required or that soil fertility increases. 5. Traditionally children have played a significant role
in supporting the women in the collection of animal feed and leaf litter for bedding, and in the carry-
ing of manure to the field Table 6. As more chil- dren attend school, the burden of these tasks will
increase for the women. This has a number of im- plications not only for the health of the women and
their quality of life, but also for the soil fertility of land, especially that furthest from the household,
which is likely to decline if less labour is avail- able for the transportation of manure. If less labour
is available for collecting forage and bedding this may ensure that vegetation resources are depleted
less rapidly, it may also mean that less bedding is used. Consequently, it is possible that less of the
N excreted will be trapped by the bedding mate- rial and incorporated into the manure heap. Thus,
more N may be lost gaseously or through leaching beneath the animal stalls.
6. Poorer families have a larger proportion of bari-land, while wealthy families possess relatively
more khet-land. If it is assumed that the N inputs in fertilizer and manure and N yields in grain and
straw change in proportion to the area of each land type according to the values identified for es-
tablishing the initial N balance, then changing the proportion of bari-land owned relative to khet-land
from 2 : 1 to 9 : 1 makes very little difference to the N flows. Total amounts of N fertilizer required
70 C.J. Pilbeam et al. Agriculture, Ecosystems and Environment 79 2000 61–72
decrease from 26 to 24.6 kg N, while N inputs in manure decrease from 132 to 110 kg N, which is
a saving of approximately 2 Mg manure per year, assuming a N concentration in manure of 1 on
a dry weight basis. The balance of N recovery is obviously dominated by maize and finger millet
as the proportion of bari-land increases from 2 : 1 to 9 : 1, but the overall recovery of N in crops de-
creases by 5 kg N, from 62.5 to 57.7 kg N. The overall recovery of N in grain for the household
decreases from 35.7 to 32.9 kg N, and the recovery of N in straw decreases from 26.8 to 24.8 kg N.
5. Conclusions
