4. Nitrogen cycling in high-input versus reduced-input arable farming.
Netherlands J. of Agric. Sc., 38, 1990, pp. 265-282
In this paper, N1-balance calculations covering the growing season will be discussed as well as changes in soil N mineralization rate, in N uptake by the crop, and in N losses due to changes in management. A conventional farming system was compared with two integrated systems, each system with the same rotation of winter wheat, sugar beet, spring barley and potatoes on a silt loam soil. Soil physical conditions and meteorological data necessary to account for some of the differences in overall N budget are discussed.
Field work was carried out at an experimental farm on a calcareous silt loam soil.
A previous experiment at the experimental site, in which three different input regimes of organic matter were compared, was taken as a starting point.
Agroecosystems are inherently more 'leaky' than undisturbed natural ecosystems where vegetation is continuously present. Increased inputs of nitrogen into agriculture have greatly increased crop (N) outputs, but they have also increased N losses to the environment.
Integrated management might give lower crop yields than conventional management, but because of lower costs, the profitability to the farmer could be similar.
Nitrogen balance sheets for the growing seasons of 1986-1988 showed N deficits of 0-170 kg ha-1, suggesting substantial N losses to the environment.
The uncertainty about actual N losses mainly depended on the uncertainty of estimated net N mineralization. Periods with much rainfall in 1987 and 1988, inappropriate use of animal manure and soil compaction may partly account for the heavy N losses in all farming systems. Potential rates of N-cycle processes were studied over the years to observe effects of changes in management.
The following conclusions can be drawn from these studies:
- The uncertainty about actual N losses mainly depended on the uncertainty in the calculated net N mineralization for field conditions. Especially uncertain was the contribution of the layer 40-100 cm, with a rather high organic matter content, to N supply of the crops.
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Review, symposium, rice farming, green manure, cropping systems
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