Effects of long-term crop rotations, fertilizer, farm manure and straw on soil productivity. II. Mineral composition of plants, nutrient balances and effects on soil.

摘要

Mineral composition of crop species, nitrogen and mineral balances and the effects on soil conditions for a 12-year period in a crop rotation-fertilizer experiment on clay loam at As Norway are reported. Four six-course rotations were used: spring grain only (1); 3 years of grain crops and 3 years of row crops (II); 4 years of grain and 2 years of clover-timothy ley (III); 2 years of grain and 4 years of ley (IV). The crop rotations were in a split block design with 4-8 fertilizer rates including farm manure every sixth year and also in arable rotations with yearly ploughed-in straw. The nitrogen concentration in grain was higher after ley than in the all-grain rotations, and in relation to obtained yields. Nitrogen balances were negative in all four rotations when only moderate amounts of mineral fertilizers were applied. Total-N in topsoil in 1990 was 0.9 and 1.1 t/ha higher in ley rotation IV than in rotations I and II which was explained by differences in soil nitrogen mineralization and leaching losses. In 37 years the increased N-uptake in crops was 25-30% of the N added to FYM, and 60-75% for additional doses of N in calcium nitrate, which increased after a higher proportion of ley in the rotation (I vs. IV). The amount of N left in the soil since 1954 was _ 20% for farm manure, almost the same for fertilizer N in all arable rotations, and somewhat less in the ley rotation. Unaccounted-for losses of N were large for FYM and for ploughed-in cereal straw. Only one-third of the surplus additional P was found as readily soluble P in soil. Exchangeable K in soil increased from 1972 to 1990 despite large negative balances. By using calcium nitrate, pH was maintained without liming in the period 1978-90. The lime status of soil could be assessed by excess bases/N in the crop removals.