Effects of Nitrogen Fertilizer on Growth and Yield of Spring Wheat

Abstract

Nine amounts of nitrogen fertilizer, ranging from 0 to 200 kg N ha−1, were applied to spring wheat cv. Kleiber in the 3 years 1972-1974. In 1972 grain dry weight with 125 kg N ha−1 or more was 100 g m−2 (23 per cent) greater than without nitrogen. Grain yield was unaffected by nitrogen in the other years. Leaf area at and after anthesis was increased throughout the range of nitrogen tested, most in 1972 and least in 1973. Consequently, the addition of 200 kg N ha−1 decreased the amount of grain produced per unit of leaf area by approximately 25 per cent in all years. The dry weight of leaves and stems at anthesis and maturity was increased by nitrogen in all years, similarly to leaf area. However, the change in stem dry weight between anthesis and maturity was not affected by nitrogen; stems increased in dry weight for about 20 days after anthesis and then decreased to values similar to those at anthesis. The uptake of CO2 per unit area of flag leaf or second leaf (leaf below the flag leaf) was slightly decreased by nitrogen when the increase in leaf area caused by nitrogen appreciably decreased the light intensity at the surface of these leaves. In spite of such decreases the CO2 absorbed by flag and second leaves per unit area of land was always increased by nitrogen, and relatively more than was grain yield. It is suggested that increases in respiratory loss of CO2 with increasing nitrogen fertilizer may explain why nitrogen increased vegetative growth and leaf area relatively more than grain yield.