Simulation of nitrate leaching before and after conversion to ecological farming
1999
Ulen, B.
A nine year nitrogen (N) simulation (SOIL/SOILN) from a clay soil in central Sweden, carried out while the field was being converted to ecological farming, showed a good relationship (r = 0.91) between measured and simulated mineral N in the soil. Simulated nitrate leaching output of the model was as a mean 67% of measured leaching. Simulated as well as measured nitrate leaching showed the critical point to be early ploughing in of a ley followed by sowing of winter wheat. Much less leaching (4.8 kg ha(-1)) was simulated with late ploughing. During the two years following early ploughing, nitrate leaching was found to be twice the amount of that leached during the remaining seven years together. During three years of conventional farming--and a similar period after conversion--the system was characterized by a reasonable balance between N input and output with only a minor net input of nitrogen (26 and 14 kg ha(-1), respectively). However, during the latter period larger changes in the soil organic N pool took place.
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