| 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. |
