Combinations of green manure crops ensure a higher yield in the next year, shows a study by Wageningen soil ecologists.
After harvesting, many arable farmers and vegetable growers nowadays sow green manure crops such as grasses, rye, yellow mustard and phacelia. These crops leave a legacy behind in the soil in the form of nutrients and soil organisms which are good for the growth of the next generation of crops.
PhD candidate Janna Barel conducted a field trial in which she alternated two main crops, oats and endive, with winter manure crops. She then assessed which combination of crops did the most for the productivity of the latest crop.
The use of green manure crops leads to higher yields the next year than leaving the field fallow over the winter, states Barel in the Journal of Applied Ecology. And the rule that you should avoid growing a succession of closely related crops in the same field turns out to be good advice. The successive combination of oats-English ryegrass-oats led to a lower oat harvest second time round than the combination of oats and less closely related manure crops. Mixes of manure crops were the most productive, and helped suppress diseases and pests, says Barel. This is because these diseases and pests are less able to spread in mixed fields than in monocultures.
Some combinations of green manure crops seem to lead to higher crop yields than others. Barel found that oat and endive production was higher with a combination of radish and vetch than with a mix of English ryegrass and white clover.
With their results, the Wageningen researchers endorse the recommendations of the world food organization FAO and of the Dutch government.