Growing-season rainfall, ear number and the water-limited potential yield of wheat in south-western Australia

Knowledge of the contribution of ear number per unit area, grains per ear, and kernel weight to grain yield is important in understanding the limits to the water-limited potential yield of wheat in rain-fed agricultural regions. This paper analyses the relationships between grain yield, yield components and growing-season rainfall using data from the low-, medium-, and high-rainfall zones of the cropping region of south-western Australia. The aim of the paper is to quantify the contribution of ear number, grains per ear and kernel weight to grain yield and define the yield components of wheat required to achieve its water-limited yield. The grain yield of wheat was closely related to the number of grains per unit area (r(2) = 0.90) and ears/m(2) (r(2) = 0.75), but poorly correlated with kernel weight (r(2) = 0.30) and grains/ear (r(2) = 0.09). The number of grains per unit area was highly related (r(2) = 0.75) to the number of ears per unit area across the rainfall zones of the cropping region, and strongly correlated (r(2) = 0.88-0.94) to the spike dry weight at anthesis. The highest yields achieved in the field were close to the water-limited potential estimated using the French and Schultz method. To achieve this water-limited potential, wheat requires 1 ear per m(2) for every mm of growing-season rainfall (r(2) = 0.92). We conclude that the number of ears per unit area is the most important factor required in order to achieve high yields of up to a yield of 6 t/ha in wheat in rain-fed south-western Australia.