Effects of wheat seed rate and fertiliser nitrogen application practices on populations, grain yield components and grain yields of wheat (Triticum aestivum)

Wheat (Triticum aestivum) plant and crop responses to seeding rates and fertiliser nitrogen (N) application practices were measured in 19 field experiments undertaken in three successive cropping years. Increasing the number of wheat seeds sown produced more dense wheat populations, reduced both plant grain yield components and plant grain yield, boosted some crop grain yield components but generally failed to improve crop grain yield. Mostly, wheat population was not significantly affected by fertiliser N which enhanced all plant grain yield components (except mean grain weight), plant grain yield, crop grain yield components, and crop grain yield. The high rate of fertiliser N (either 120 or 140 ka N ha(-1)) had greater effects (including reduction of mean grain weight) than the low rate (either 60 or 70 kg N ha-1). However, the additional positive effects caused by the extra fertiliser N supplied in the high rate were much smaller than those produced by the initial increment. Fertiliser N effects on wheat crop grain yield did not vary significantly with wheat population. Variation of either fertiliser N application time or fertiliser N application mode had little effect on wheat crop grain yield. The negative responses by plant grain yield components and plant grain yield to increases in wheat seed rate and wheat population, and by mean grain weight to applied fertiliser N were the result of self-thinning. It was concluded a low rate of wheat seed (165 seeds m(-2)) and a single application of a moderate rate of fertiliser N (not exceeding 90-100 kg N ha(-1)) are sufficient for the successful cultivation of autumn-sown wheat in Canterbury, New Zealand.