Response of winter wheat to N-fertiliser: Quantitative relations for components of growth

Abstract

Measurements were made of yield of dry matter, plant-N content, and the distribution of mineral-N down the soil profile in 10 fertiliser-N experiments. In one of them detailed measurements were made throughout growth. Rate of N-uptake by the crop was unaffected by the amount of mineral-N in the upper 90 cm of soil when it was above about 30 kg N ha⁻¹. The %N in plants that received ample N-fertiliser declined with increase in plant mass according to a previously derived equation. During senescence there was an apparent loss of N from the crop.

N-nutrition in the different experiments had little effect on the partition of assimilate between grain and straw. At harvest grain and straw weights were well related by a linear model which had the same gradient but different intercepts for each experiment. Grain %N was about four times greater than straw %N. Regression analysis supported the view that high evaporative conditions or temperatures during the growing period induced earlier harvest dates, less grain relative to straw, and a higher %N in the plant when ample N-fertiliser was applied but not when N-fertiliser was withheld.

Other analyses indicated that cereal roots were generally unable to extract mineral nitrogen from the soil when the concentration was less than about 0.18 kg N ha⁻¹ cm⁻¹, that at low levels of N-nutrition the recovery of available inorganic-N from soil by the grain and straw was about 80%, and that the average mineralisation rates from early spring to shortly after harvest date varied between 0.22 and 0.88 kg N ha⁻¹ d⁻¹ from site to site.