Effects of undersown legume crops on the production of a succeeding lettuce crop
2001
Sorensen, J.N. | Thorup-Kristensen, K. (Danish Institute of Agricultural Sciences, Aarslev (Denmark). Department of Horticulture)
In organic farming, the nitrogen supply can be provided by nitrogen cover crops or nitrogen fixing legume crops. However, legume crops used as green manure need to be established rather early to ensure a sufficient nitrogen accumulation before winter. Establishment of legume crops after harvesting cereals is often too late. By undersowing in cereal crops it is possible to overcome this problem. The objective of this experiment was to investigate the potential of several species of undersown legume crops in their ability to deplete soil nitrate and to accumulate nitrogen. A further objective was to measure the effects of the legume crops as a green manure for a suceeding lettuce crop. In two years, different undersown legume crops were compared to a control treatment where no crop was undersown. At the end of the growing season, the legume crops reduced the content of mineral nitrogen in the top 100 cm soil profile to one third of what was available when no crop was undersown. The total uptake of nitrogen in the entire legume plant was in the range of 100-160 kg N ha sub(-1). In May the succeeding year, the content of soil mineral nitrogen was increased due to a positive net mineralization. This was also the case in the control treatment, although, the increase was less significant. The main increase was seen in the top 25 cm profile of soils, which had been grown with legume crops. The yield of lettuce was increased when legume crops were used as green manure. On average of the two years, the most promising species were red clover, white clover, and black medick. Compared to the control treatment, these species increased the yield of lettuce by 20-50 per cent. This yield was comparable to that obtained in conventional farming
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