Archived at http://orgprints.org/7907 

Title of paper: Use of green manure, catch crops, and deep rooted crops for nutrient management in an organic vegetable crop rotation

Authors: Kristian Thorup-Kristensen

Green manure crops are important in organic rotations to improve soil quality and to deliver nutrients for the cash crops. Many of the effects of green manure contribute to long term improvement of soil quality. This is also true for their effect on nitrogen supply, but they typically have a large effect in the first year, followed by quite small effects in the succeeding years (Thorup-Kristensen et al, 2003). New strategies for including green manure and cover crop in the rotations may be needed, to avoid excessive nitrogen release from green manure compared to cash crop demand, and to secure good nitrogen supply not only for one crop following a full year green manure, but for more of the crops in a rotation. 

Results from a crop rotation experiment (Thorup-Kristensen, 1999) have shown the potential of strategies with more frequent use of short term green manure crops and catch crops. Green manures grown only in the autumn after cash crop harvest can release much nitrogen for the succeeding crops, and reduce nitrogen leaching losses. In any crop rotation, and especially in vegetable rotations, some nitrogen will inevitably be lost by leaching. In order to reduce these losses, deep rooted catch crops or cash crops can be used strategically in the crop rotation, to retain nitrogen in the soil, or to take up nitrogen which has already leached to larger soil depths (Thorup-Kristensen, 2001; 2002). Results from the rotation, show that some crops or cover crops with deep root systems are able to assimilate nitrogen from more than 2 meters soil depth, and that this can be a powerful tool in reducing nitrogen losses from the crop rotation.

References (maximum of 4 references)
Thorup-Kristensen, K., Magid, J. and Jensen, L.S. 2003 Catch crops and green manures as biological tools in nitrogen management in temperate zones. Advances in Agronomy, 79: 227-301
Thorup-Kristensen, K. (2002) Utilising differences in rooting depth to design vegetable crop rotations with high nitrogen use efficiency (NUE). Acta Horticulturae 571: 249-254
Thorup-Kristensen, K. (2001) Are differences in root growth of nitrogen catch crops important for their ability to reduce soil nitrate-N content, and how can this be measured? Plant and Soil, 230: 185-195
Thorup-Kristensen, K. (1999) An organic vegetable crop rotation aimed at self-sufficiency in nitrogen. In: Olesen, J.E., Eltun, R., Gooding, M.J., Jensen, E.S. & Köpke, U. (Eds) Designing and testing crop rotations for organic farming. DARCOF Report no. 1. p 133-140