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

Abstract

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 (≈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 >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.