Effects of Compost and Nitrogen Fertilizer on Wheat Nitrogen Use in Japanese Soils

Received for publication March 1, 2006. Wheat (Triticum aestivum L.) grain yield (GY) and grain protein concentration (GPr) are influenced by N availability and supply. This study aimed to investigate wheat (cv. Ayahikari) response to compost and N fertilizer. A 3 -yr field experiment was conducted on four Japanese soils varying in N mineralization potential with or without annual compost application ((almost equal)220 kg N ha^–1 yr^–1). Four N fertilizer treatments including a zero-N control were established each year, and equal amounts of N were applied at preplanting and stem elongation. A significant quadratic relationship of increasing GY with greater N uptake, and increasing GPr with greater N factor (aboveground N uptake, Nup, per unit of GY) occurred for the pooled data. From these relationships, the optimum Nup for appropriate GPr (105 g kg^–1) for Japanese ‘Udon’ noodle was estimated to be 139 kg ha^–1 and GY could be (greater than)5000 kg ha^–1. Fertilizer N rate for optimum N uptake in each soil–compost regime was estimated from a significant linear or quadratic relationship between N uptake and fertilizer N rate (Nf). The agronomic efficiency (yield increase per unit of fertilizer N) and apparent fertilizer N recovery at a given rate of fertilizer N tended to be lower in soils with annual compost than without. However, the fertilizer N requirement for an equivalent yield decreased, thus the fertilizer N surplus (Nf – Nup) at optimum N uptake was lower in soils with compost application than without.