Accumulation of fertilizer nitrogen applied at different times into grain and uptake of soil nitrogen by winter wheat in Hokkaido

摘要

The percentage uptake of N fertilizer by winter wheat (Triticum aestivum cv. Chihokukomugi) and the distribution of absorbed N into the grain were investigated using 15N in field experiments. Ammonium sulfate (12 g N m-2) was applied in 3 split applications. The time course of uptake of soil N by winter wheat was compared with the estimated progress of N mineralization by kinetic analysis. The recovery rates of fertilizer N were 29-40% from application at sowing time, 43% in mid-April, when the regrowth of wheat plants starts after snow melt, and 58-64% at the heading stage. At harvest, the proportion of labelled N absorbed in the grain was 52-63% of application at sowing time, 59-66% at mid-April and 73-81% at the heading stage. At 10-13 days before harvest, 33-45% of absorbed fertilizer N applied at the heading stage was still found in the leaf and stem, and a part of it translocated to the grain during the ripening process. The amount of N absorbed from soil N was 46-60% of the total N in thegrain. That indicated the necessity of estimating the progress of uptake of soil N by wheat plants to control the yield and quality of grain. The amount of N mineralized in the soil from sowing time to harvest was estimated at less than 40% of the amountof soil N absorbed by winter wheat. The residual inorganic N in soil, especially in the sub-soil at sowing time, contributed considerably to N uptake by winter wheat.