NITROGEN FERTILITY MANAGEMENT IN CORN -- A CASE STUDY ON A MIXED CROP-LIVESTOCK FARM IN PENNSYLVANIA (ORGANIC FARMING, ROTATIONS)

Nitrogen (N) fertility management for corn (Zea mays L.) production was investigated in 1978, 1979, and 1980 on the Benjamin and John Brubaker farm, near Kutztown, Berks County, Pennsylvania. A preliminary study of the N-supplying capability and yield potential of corn fields was done n 1978. In 1979, eight replicated field trials were conducted with five N rates and two N sources on selected fields. In 1980, three replicated field trials were conducted each with five N rates, two N sources, and three plant population levels.;In general, supplemental N applications resulted in luxury consumption rather than increased yields. Soil N-supplying capabilities ranged from 111 to 249 kg N/ha and averaged 166, 165, and 148 kg N/ha for first, second, and third year corn after alfalfa, respectively.;Soil analyses were not accurate enough to detect significant differences due to treatments except for No(,3)('-)-N. Soil N availability indexes were poor predictors of N availability as measured by crop uptake.;Overall corn productivity of this farm was high and with refinement of the management system could be increased. Nitrogen requirements for corn production could be supplied almost entirely by on-farm sources without imports. The avoidance of synthetic fertilizers, herbicides, and insecticides on this farm appeared to be incidental to high productivity; however, no benefit could be seen to altering this practice.;Generally, there were no yield responses to rates of supplemental N as either NH(,4)NO(,3) or leather dust in seven field experiments in 1979. In 1980, a severe drought depressed yields throughout the region. There were no grain yield responses to supplemental N either as NH(,4)NO(,3) or poultry manure. However, total dry matter production did exhibit a significant response to supplemental N. Responses to different N sources were not different. Crop uptake of N increased with increasing N rate similarly for both sources of N in both 1979 and 1980. Increasing plant populations significantly increased grain yields and dry matter production in 1980.