INVESTIGATIONS ON THE NITROGEN DYNAMIC AS A BASIS FOR THE N FERTILIZER RECOMMENDATIONS IN VEGETABLE PRODUCTION

Authors:	H. Scharpf, U. Weier
Keywords:	N_min target value, N fertilizer recommendations, N immobilization, N calculation, N mineralization
Abstract: Results of many investigations of the last 10 – 15 years on the nitrogen dynamic have made N fertilizer recommendations in vegetable production more reliable. Four important aspects have to be taken into account: Measuring the N content of the soil on very plane sites at planting time or before top dressing means a good precision for determining the amount of fertilizer. If the mineralization rises strongly because of adding new organic substance, this has to be included to correct the target value. The same holds true in the case of extreme summer rainfall with leaching losses of nitrate. Approaching mathematical estimates to establish the target values for nitrogen fertilization, it proves useful to consider N_min content of the soil, N release from humus and from fresh organic substance on the supply side and N uptake of the plants, necessary mineral N content of the soil, and N immobilization on the demand side. When these aspects are considered it is likewise possible to plan N fertilization for those crops where no long-term experiments exist and to improve N fertilization on the basis of N_min soil analyses.
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