Four Swedish long-term experiments with N, P and K, 3: After-effects of N-fertilization
1988
Mattsson, L. (Sveriges Lantbruksuniv., Uppsala (Sweden). Inst. foer Markvetenskap)
After-effects of previous N applications on soil N mineralization were investigated. Impacts of annual N rates ranging from 0 to 160 kg ha-1 during 12 to 27 years without animal manure and between 35 and 245 kg ha-1 at the two sites where manure was applied regularly were investigated. Rates of manure corresponded to 35 kg ha-1 year-1, N. In order to determine the after-effects barley was grown in 6 l Mitscherlich pots without N fertilization and all above-ground parts were harvested approximately one week before ear emergence. To allow for differences in easily decomposable fresh organic matter and impacts from residual inorganic N, barley was grown and harvested twice. Reported data concern the second harvest. Yields of dry matter and Kjeldahl N were determined in each pot. There were statistically significant positive after-effects on dry matter yields at three sites, whe1595re the yield increases were of the order of 42-92% for the highest previous N rates compared with the lowest ones. The N yields were also positively related to previous N rates at three sites, two of which identical with those where positive dry matter effects were obtained. Estimations of the N mineralization capacity gave values in the interval 0.66 to 1.57 mg 100-1 g soil at zero or low previous N applications and 0.77 to 2.37 mg 100-1 g soil at high previous N applications. The N mineralization differences between high and low previous N applications were considered to be a measure of the size of the active-N pool. Its size was estimated to 1-41% of total N mineralized. There were significant correlations of mineralized N, on previous N application and soil C content. The interaction effect between soil C content and previous N application on N mineralization was negligi
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