Comparing cover crops in organic farming for weed suppression and soil fertility.

The study compared several plant species, and their mixes, as autumn sown cover crops in an organic farming system. Cover crops were assessed for their suitability in crop rotation including effects on the following crop. Their weed suppression effects were also examined. Some cover crops tested showed between 72% and 90% reductions in total weed dry weight in the spring. The best weed suppression was observed in plots of ryecorn, oat and peas and oat and tares. The results identified several cover crops which can be sown as late as May in Canterbury. Forage brassica, oats and, oat and peas were especially successful. Growth and vigour of the succeeding wheat was correlated with soil nitrogen (N) content after cover crops e.g. higher leaf chlorophyll content and greater biomass of wheat after oat and peas correlated well with higher soil N following this mixture. In contrast, oat plots had the lowest soil N and poor growth of following wheat. Potential benefits of cover crops in terms of soil fertility are analysed.