Farm Table says:
What is the problem?
Wheat grown after brassica crops normally yields more than wheat grown after wheat. Previously, 33 experiments reviewed and concluded that wheat after canola yielded about 19% more than wheat after wheat that the gross margin of a canola-wheat sequence was 27% greater than a wheat-wheat sequence. This is an even more extensive review of brassica crops.
What did the research involve?
This review involved comparing yields of experiments of wheat after wheat with wheat after canola or juncea canola. Some were long-term rotation experiments but most were biennial crop sequence experiments. Of the 180 canola experiments, 53 were in Australia, 100 in Sweden and the rest in other parts of Europe and North America. Most of the 42 experiments with juncea canola and the 36 experiments with both canola and juncea canola were in Australia. Another evaluation of break crops came from a survey of 52 whole-paddock wheat yields conducted by the Harden-Murrumburrah Landcare Group in 1995. This survey obtained data from farmers about sowing date, soil nutrient status, fertiliser application, pH, lime, rainfall and previous crop.
What were the key findings?
Data collated from 180 canola experiments and 42 experiments with juncea canola where the grain yields of wheat grown after a Brassica were compared to yields of wheat following a previous wheat crop. Yields of wheat grown after brassicas were generally greater than wheat grown after wheat .
Yields of wheat following canola were greater than yields of wheat following wheat in 156 of 180 experiments and yields of wheat following juncea canola were greater than wheat following wheat in 31 of 42 experiments . There was no significant difference between the regressions for canola sequences in Australia and other countries and not enough data from outside Australia for an equivalent comparison for juncea canola.