Quantitative estimates of the budgets of nitrogen applied as fertilizer, urine and feces in a soil-grass system
1991
Kimura, T. (National Grassland Research Inst., Nishinasuno, Tochigi (Japan)) | Kurashima, K.
Efficiency and budget of fertilizer and animal nitrogen (N) in a soil-grass system were subjected to analyses with a 15N-tracer method. The utilization efficiency of fertilizer N by orchardgrass was high in spring, while it was low in autumn, depending on seasonal variation in the ability of N uptake by grass and the behavior of soil inorganic N. Annual recovery of labeled N in the orchardgrass sward receiving 250 kg N.ha(-1).yr(-1) was 78-90%, although it was lower in the older sward than in the newly established one. The recovery rates varied among the herbage, the other parts of the plants and soils: i.e. 37-50% in the herbage, 14-18% in the stubbles, litters and roots, and 23-24% in the soil layer up to 50 cm depth. Unrecovered N was 10-22%. The experiment using 15N fertilizer showed that more than half of the N absorbed by grass was derived from soil N. This indicates the importance of N supplying capacity of soil for maintaining grassland productivity. Immobilized fertilizer N in soil contributes to soil fertility through remineralization. The N budget during the 5-year period showed that 76 kg.ha(-1) of non-labeled N accumulated in the surface soil layer up to 20 cm depth, and 480 kg.ha(-1) of non-labeled N was removed by cut herbage. This indicates that 556 kg.ha(-1) of non-labeled N was supplied from outside of the system including the soil below 20 cm. Urine N was readily available, but 40-59% of N was lost from the patches receiving 81-88 N.m(-2) of urine. Fecal N was less available, and 48-57% of N was incorporated into soil in unavailable forms. Losses of urine N and accumulation of feces N in soil may reduce the efficiency of N returned to pasture through excretion by ruminants
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