Managing yield reductions from wide row spacing in wheat

Experiments were conducted to investigate row spacing effects on wheat yield and grain quality and the interactions between row spacing and cultivars, plant population density, nitrogen application rate, time of sowing, fertiliser placement and row spread from 2000 to 2002 in the south coast region of Western Australia. In the experiments that were conducted following pasture or lupins, wider row spacings of 240 and 360 mm consistently reduced wheat yield and increased grain protein and small grain screenings compared with a narrow row spacing of 180 mm. Average plant numbers were reduced in the wider rows in all experiments. This result, possibly related to increased competition for water as the seeds were placed closer together in the wide rows, may also have been related to reductions in wheat grain yield. The yield decline in wider rows was lowest for the long season cultivar Camm with a May sowing in 1 experiment and at the higher N rate in another experiment. The response of Camm at wider row spacings can be partially explained by its higher dry matter production as measured in 2000 and may also help to explain the observed advantage of Camm in suppressing weed growth at all row spacings. In 2002, the row spread ( seed width within the row) was varied from normal 25 mm widths to 50 and 75 mm widths. Yield was increased at the widest row spacing ( 360 mm) by using the wider row spreads of 50 or 75 mm. Fertiliser placement methods significantly affected plant establishment but not grain yield. Grain quality ( protein percentage, small grain screenings and hectolitre weight) was reduced in wider rows in some cases or unaffected in others. This research has demonstrated that yield reductions due to wide row spacing can be minimised by using a long season cultivar when sown in May, by using adequate N fertiliser and by increasing the spread of seed across the row.