Nitrogen Fertilizer Use Efficiency of Furrow‐Irrigated Onion and Corn

Abstract

Furrow‐irrigated onion (Allium cepa L.) production, with high N fertilization rates, may be contributing NO3–N to ground water in southeastern Colorado. This study determined the growth and N uptake patterns of onion grown on a silty clay soil, N fertilizer use efficiency (NFUE) of onion, and recovery of residual N fertilizer by corn (Zea mays L.) following onion in rotation. Onion was sampled biweekly from 18 May to 15 Sept. 1998 from plots receiving 0 and 224 kg N ha−1. Nonlabeled N and labeled 15N fertilizer were band‐applied near the onion row in split applications of 112 kg N ha−1 each on 18 May and 25 June. Onion dry matter accumulation was slow from planting to about late May, followed by a rapid increase in biomass production and N uptake. Because residual soil NO3–N was high, N fertilization resulted in only a small increase in bulb yield. Greatest demand for N by onion occurred during bulb development. Fertilizer N recovery by onion was 11 and 19% for May and June N applications (average 15%), respectively. Much of the fertilizer N remained in the upper 60‐cm soil profile at harvest and had moved toward the onion bed center. Fertilizer 15N detected at 180‐cm soil depth indicated leaching losses from the root zone. The unfertilized 1999 corn crop recovered 24% of fertilizer N applied to onion for a total fertilizer N uptake by the two crops of 39%. Delaying N fertilizer application until onion bulbing begins may improve NFUE. Planting corn directly on the previous onion bed may result in greater N fertilizer recovery by corn.