Long-term effects of organic manure application on the productivity of winter wheat grown in a crop rotation with maize in Japan

Abstract

Achieving high productivity using organic manure as a source of N offers new soil management possibilities in intensive agriculture. Our objective was to study the growth response of winter wheat ( Triticum aestivum) to different fertilization regimes in long-term experiments in Japan. Semi-dwarf wheat varieties were grown in crop rotation with maize ( Zea mays) with a high rate of organic manure (OM; 80 t ha −1 yr −1 for >10 years, estimated N application rate is 739 kg N ha −1 yr −1), and standard (SF; 204–252 kg N ha −1 yr −1) or low (LF; 102–126 kg N ha −1 yr −1) rates of inorganic fertilizer for 3 years. We observed greater biomass production in OM than in SF or LF, which was attributable to a higher leaf area index, leaf N status, and stomatal conductance in OM. Grain yield in OM (6.6–8.9 t ha −1) was significantly higher than that in LF (3.5–6.6 t ha −1) for both cultivars, and comparable to that in SF (6.6–8.5 t ha −1). However, the dry matter partitioning during the grain-filling period suggested an imbalance in the sink–source relationship in OM: the number of grains was too large for the assimilation rate. Varietal differences in grain weight in OM resulted from differences in dry matter production during grain filling and, to a lesser extent, differences in grain density. The growth pattern of wheat under intensive manure application should be modified to favor biomass production during the post-anthesis stages. Based on our results, we discuss possible strategies for wheat improvement under high soil fertility in Japan.