An analysis of the effects of nitrogen deficiency on the growth and yield of a Western Australian wheat crop

Abstract

A wheat crop was grown on a nitrogen-deficient sandy soil. Urea was supplied at rates of 0 (N₀), 56 (N₁), and 336 (N₂) kg nitrogen/ha.

In general, the relative growth rate (R) decreased with time. During the first half of the growing season R for N₂ > N₁ >> N₀, but in August deficient plants recovered rapidly. The recovery was associated with the emergence of the second tiller, an increase in net assimilation rate and nitrogen uptake, and a decrease in nitrogen stress. There was no evidence that the recovery was due to an increase in mineralization of soil nitrogen.

Nitrogen stress in treatment N₀ decreased from 48% in July to 14% in September. By contrast, stress in treatment N₁ increased rapidly from 6 to 23% during July and fell to 5% by September.

Flower initiation in N₀ plants was delayed 14 days and ear emergence was delayed 8 days compared with N₁ plants.

The grain yields of N₀ and N₁ plants were 30 and 60% respectively of those of N₂ plants. The decrease was due mainly to differences in the number of heads per sq metre, although nitrogen deficiency also reduced the number of grains per head and the weight per grain. The duration of photosynthetic activity after anthesis was not affected by nitrogen treatments. Harvest index was highest on N₀ treatment and similar on N₁ and N₂ treatments.