N Behavior Under No-Till vs. Conventional Corn Culture. I. First-Year Results Using Unlabeled N Fertilizer

This study comparing corn yields from different rates of applied N under no-tillage and conventional culture was prompted by numerous field observations in Maryland that no-till corn, with low to moderate rates of N, often showed more pronounced N deficiency symptoms than did conventionally tilled corn. Little is known regarding the relative N requirements of untilled corn grown in cover-crop residues as compared to conventional tillage. The purpose of this study was therefore, to determine whether tillage method affected optimal crop requirements for fertilizer N. First-year effects of tillage method and fertilizer N applications (0, 45, 90, 135, and 180 kg/ha) on corn (Zea mays L.) yields, N uptake by the crop, mineral N accumulation in the soil, and total and potentially mineralizable soil N are reported. With suboptimal N rates, N deficiency symptoms were more severe throughout the season on untilled than on cultivated plots. However, the optimal level of applied N for grain and dry matter yields did not differ with tillage method. After grain harvest, the amount and distribution of residual mineral N in the root zone for a given rate of applied N were similar in tilled and untilled plots at two locations (Poplar Hill and Plant Research Farm). At the third site (Wye Institute), however, residual mineral soil N was higher with conventional than with no tillage. These differences were attributed to variation among sites in amounts of precipitation between planting and harvest, as it affected relative water infiltration in tilled and untilled plots. Total residual mineral N in the root zone tended to increase with N application rate. Between harvest (1973) and planting (1974), however, most of the residual mineral fertilizer N was removed by the cover crop or lost. Total soil organic N to a depth of 30 cm was unaffected by N rate or tillage method during one cropping season. At one rate, however, potentially mineralizable N was higher in untilled than in tilled plots. Studies are continuing on two of the sites, with ˡ⁵N-lepleted fertilizer, to determine relative changes with time in soil N status as influenced by tillage method.