First and second year nitrogen effects of autumn and spring-incorporated green-manure crops in field vegetable production

This field experiment was aimed at assessing possibilities for controlling N mineralisation and uptake in a vegetable crop rotation with green-manure crops. The influence of spring- and autumn-incorporated preen-manure crops, i.e. Persian clover (Trifolium resupinatum L.), white clover (Trifolium re pens L.) and yellow-sweet clover (Melilotus officinalis Lam.), as a N sourc e was studied in iceberg lettuce (Lactuca sativa crispa L.) and in leek (Al lium porrum L.). The second year N effects of green-manure crops were studi ed in red-beets (Beta vulgaris L.). Oats (Avena sativa L.) was used as a co ntrol. The N and total FW yields of iceberg lettuce, leek and red-beets var ied independently of green-manure species and time of incorporation of the green-manure crops. However, the N and FW yields were higher in treatments with green-manure species as preceding crops compared with the treatment wi th oats as preceding crop. Leek as a preceding crop gave a higher FW yield of red-belts compared with iceberg lettuce as preceding crop.