The effects of green manures on soil fertility and crop production in organic and conventional field vegetable systems

摘要

Replicated farm trials were set up on two conventional, one organic and one in conversion site in the UK. The five treatments (in comparison with a bare ground control) comprised different mixtures of ryegrass, cocksfoot, red clover, white clover, crimson clover, sweet clover and yellow trefoil that were grown for either 9 months or 16 months. The mixture containing perennial ryegrass produced more dry matter than the cocksfoot containing mixture and covered the ground quicker. At the time of incorporation (in December), at least 130 kg ha"1 of N was incorporated from green manure swards. They were followed by a crop of onions at one of the sites and potatoes at the other three. At the organic site, all the green manure treatments significantly increased the tuber yield. At the other sites, additional nitrogen was applied either as a mineral fertiliser or manure and this reduced the effects of the green manure. This highlights the need to reduce fertiliser applications accordingly after growing a green manure, in order to take advantage of their full benefit.