A simple model for nitrogen balance calculations of temporary grassland-ruminant systems
1988
Kirchmann, H. (Sveriges Lantbruksuniv., Uppsala (Sweden). Inst. foer Markvetenskap) | Torssell, B. | Roslon, E.
A low resolution nitrogen model was developed to complement an existing grassland production model. Basic knowledge of agronomy and animal husbandry was integrated to calculate nitrogen balances of ley-ruminant systems. Net changes of the N flow within the whole system were expressed as yearly changes of nitrogen in grassland soil. Simulated soil N changes in grassland were expressed as functions of fertilizer N input, clover percentage and harvesti2048ng date. Combination of climatic conditions (examples are valid for Uppsala, average climatic conditions during 20 years) and management resulted in the following main conclusions concerning changes of soil N in grassland. In pure grassland, 210 N kg ha-1 had to be applied to keep the amount of soil N constant if no manure was returned. Unfertilized pure clover showed a negative soil N balance since the fixed N content in roots was lower than the uptake of soil N. Application of 120 kg fertilizer N needed 60% clover to keep the soil N at a constant level if no manure was returned. If 50% of the manure produced was returned to grassland, high fertilizer N input (240 N kg ha-1) to pure grass and a surplus of N in purchased fodder (0-90 N kg ha-1) had relatively little effect on the soil N balance, varying between 50 and 65 N kg ha-1. Total nitrogen losses from the system (soil N, fertilizer N and manure N) were compensated by biologically fixed nitrogen when clover percentages were 50% or lar
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