Organic production of horticultural crops with green manure, composted farmyard manure and organic fertiliser

A three-year organic crop rotation was set up in a field with sandy loam soil, with a cover crop of rye and vetch grown over the three autumn/winter seasons for green manure, followed by potato and lettuce (1st year), Swiss chard and turnip (2nd year), and Portuguese cabbage and carrot (3rd year). Nitrogen (N) mineralisation was determined by field incubation in response to green manure (GM), GM with 20 and 40 t ha(-1) farmyard manure (FYM) compost (C20 and C40) and GM with 1 and 2 t ha(-1) of commercial organic fertiliser (CF1 and CF2). The second season crops (lettuce, turnip and carrot) yields were higher for the treatment C40 compared to all other treatments because most of the commercial fertiliser was mineralised during the previous crop. Swiss chard, grown in a short season (54 days), produced higher yield for CF2 compared with C40. However, this was not true for potato (1st year), probably because of increased compost mineralised N recovery during the longer growing season for the potatoes (124 days), nor for the cabbage (3rd year), which had a short growing season (56 days), because of increased N availability with continuous compost and green manure application. This study highlighted that field incubation can be used to assess mineralisation rates and that the fast N release of commercial fertilisers increased the yield of the first crop of the year, whereas the slowly released N of FYM compost increased yield of both crops of the year, with lower risk of N loss.