NITROGEN ACCUMULATION AND NITROGEN RESIDU ES OF FIELD BEANS (VICIA-FABA L) .2. DEVELOPMENT OF THE N-MIN-CONTENT OF THE SOIL AFTER FIELD BEANS

The objective of the investigations was the development of the N-min-c ontent of the soil after field beans, returning between 70 and 170 kg N/ha by vegetative residues. Field experiments were conducted in 1990 at one location (Ihinger Hof) and in 1991 at two locations (Ihinger Ho f, Oberer Lindenhof). Factorial variation included with/without residu es and with/without soil preparation after harvest. Commencing at the harvest date at 6 to 8 dates until April/May soil samples (0 to 90 cm) were taken to analyze the N-min-content. Additionally after harvest s mall lysimeters containing the 0 to 30 cm soil layer were put in espec ially choosen plots of the Ihinger Hof - 1991 experiment. Continuously the percolated water amounts were collected to analyze the NO3-N-cont ent. Furthermore groups of soil columns (empty set 5 cm) of the 0 to 3 0 cm soil layer were taken and incubated for 16 weeks at 20 degrees C and 35 degrees C, respectively. At five consecutive dates during this period the NO3-N-content was analyzed. During autumn in all field expe riments N-min-contents (0 to 90 cm) increased. Interactions between ye ars and soil preparation after field bean harvest determined the furth er development of the N-min-content. In contrary to results of the per iod investigated in 1990/91, soil preparation seemed to decrease N-min -levels of field plots and especially of incubated soil columns in 199 1/92. Nevertheless N-min-levels between 30 and 60 kg N/ha and the resu lts of the lysimeters indicated available NO3-N-amounts and NO3-N-tran slocation during the investigated period.