The influences of preceding crops on the nitrogen topdressing effects to winter wheat variety “Sato-no-sora”

Abstract

Using wheat (Triticum aestivum L.) variety "Sato-no-sora", the effects of nitrogen topdressing were examined in southern part of Ibaraki prefecture. The experiments were conducted in 2016/2017, 2017/2018, 2018/2019, 2019/2020. After cultivation of different crops (paddy rice (Oryza sativa L.), soybean (Glycine max Merr.) etc.), wheat was sowed at late November. Four topdressing treatments, which were 1) control, 2) standard, 3) improvement 1, and 4) improvement 2, were conducted. In 1) control plots, nitrogen was not applied as topdressing. In 2) standard plots, 4 g/m² nitrogen was applied at late February. In 3) improvement 1 plots, 4 g/m² nitrogen was applied at late January and late February. In 4) improvement 2 plots, 4 g/m² nitrogen was applied at late February and late March. As topdressing, ammonium sulfate was applied. By topdressing, grain yield and grain protein percentage increased, and nitrogen uptake by grain, which is estimated by yield and protein percentage, increased. However, in the same topdressing treatment, nitrogen uptake by grain varied with preceding crops. Nitrogen uptake by grain increased in wheat after soybean in comparison with wheat after paddy rice. Probably wheat absorbs approximately 50 % of nitrogen from fertilizer, and it absorbs rest from soil. Therefore, it is suggested that the variation of nitrogen uptake by grain was influenced by the nitrogen uptake from soil. In this result, much of nitrogen uptake from soil probably consists of the nitrogen mineralized from organic matter (organic nitrogen).