The Role of Soil Organic Matter and Manures in Sustainable Nutrient Cycling - Sustainable Management of Soil Organic Matter - page 276

Table 4.7.3. Average concentrations (p.p.m.) and amounts (kg N ha − 1 ) of nitrate N collected at
depths > 75 cm under three experimental treatments at three sites in the mid-hills of Nepal in 1998.
Values in parentheses represent a standard error of the mean.

Pakhribas Dordor Tar Dordor Gaun

Treatment p.p.m. kg N ha − 1 p.p.m. kg N ha − 1 p.p.m. kg N ha − 1

Zero input 1.18 (0.176) 8.9 2.61 (0.280) 19.6 0.14 (0.021) 1.1

Fertilizer 3.28 (1.011) 24.6 2.25 (0.185) 16.9 0.15 (0.021) 1.1

Manure 1.11 (0.179) 8.3 1.87 (0.219) 14.0 0.14 (0.023) 1.1

in the concentration of nitrate in the soil solution in the three treatments, at
least at Dordor Tar and Dordor Gaun. The apparently greater value for the
fertilized treatment at Pakhribas is not significantly different from the other
two treatments. It may however reflect the impact of top-dressing N to
maize which gave initially high nitrate concentrations in the soil solution
that subsequently declined to values similar to the other treatments, thus
giving a larger mean and error than found for other treatments. The
absence of any treatment differences indicates a constant rate of mineraliza-
tion of soil N irrespective of nutrient inputs to the surface. Applications
of 15 N-labelled fertilizer show that much of the applied N fertilizer is
immobilized rapidly in the soil (C.J. Pilbeam, unpublished data). Assuming
a drainage loss of 750 mm, which is approximately half of the annual
rainfall, then losses of nitrate N by leaching vary considerably between sites,
but in 1998 were always < 25 kg N ha −1 , often considerably so. These data
broadly support the range of values used in Fig. 4.7.1.

Conclusions

N budgets have two purposes. The first is to identify gaps in knowledge
which are amenable to measurement. The second is to facilitate the
efficient management of N inputs, and thereby control outputs of N from
the system, particularly losses to the environment. N inputs to and outputs
from a hypothetical household in the mid-hills of Nepal appear to be
roughly in balance, and so, at the level of the household, productivity is
sustainable. However, this requires the importation of N into the house-
hold, perhaps as fertilizer, but more commonly from the forest areas in tree
fodder and grass, with the attendant degradation of the forest resource
base in the mid-hills of Nepal. In other developing countries, particularly
in Africa, similar degradation occurs where fodder is removed from
communal areas, especially forests, and carried to the homestead. Deduced