Saturday, 15 July 2006

Nitrogen Transfer between Clover and Wheat in an Intercropping Experiment.

Agathi-Valentini Pappa1, Robert M. Rees1, and Christine A. Watson2. (1) The Univ of Edinburgh - Scottish Agricultural College, Soils Building, Bush Estate, Penicuik, Midlothian,Scotland, Edinburgh, EH26 0PH, United Kingdom, (2) Scottish Agricultural College, Crop and Soil Group, SAC, Craibstone Estate, Aberdeen, AB21 9YA, United Kingdom

There is currently widespread concern that intensive systems of agriculture production may result in unacceptable environmental impacts. Alternative methods of supplying nutrient inputs to arable farming systems are widely recognisable, as providing a range of environmental benefits. A novel approach to the problem of nitrogen supply is to use intercropping of cereals with a legume to provide transfer within a cropping season and/or to following crops. Previous investigations have found that intercropping winter wheat with clover resulted in yield decreases of 10-25% compared with wheat sole crop, although grain N concentrations were increased. The aims of this study were i) to examine the different intercropping techniques and the relative contributions of shoots and roots to N transfer and ii) to quantify the nitrogen transfer from clover to wheat and the nitrogen fixation. The effects of intercropping were studied using mixtures of winter wheat (Triticum aestivum var.Claire), with white clover (w.c.) (Trifolium repens var. Barblanca) and red clover (r.c.) (Trifolium pratense var. Britta). Four different treatments were prepared ((1) Cutting (2) Cutting and soil disturbance (3) No cutting, (4) Controls). Transplanted clover plants were grown to glued PVC columns filled with light sandy soil in a "split-root" design, to allow roots to grow on both sides of the columns without any connection. One month after planting, 15Nlabelled ammonium nitrate solution was applied to one side at rate of 15 g N m-2 in treatments one two and three. After another month, wheat seeds were sown into the column without nitrogen and harvested one month later. The cutting treatment produced the highest yield of wheat (r.c: 270 kg ha-1; w.c: 252.5 kg ha-1). It seems that this treatment provided the ideal environment for N mineralisation, and it is possible that the lower yield in the non-cutting treatment was due to greater immobilisation. The concentrations of available N (NH4+and NO3-) were often lower in the soils where the wheat plants had been growing. Higher concentrations of NO3: N (13 μg N kg-1) were observed in the soil disturbance treatment. The non-cutting treatment always had lower concentrations of NO3: N. These results have potential practical applications in low input systems. It is possible that drilling cereals into a cut clover crop or cutting strips of clover grown between strips of cereals may enhance crop nutrition and cereal growth and increase yield. Additionally the intercropped system is likely to produce healthy soil with better structure and aeration and more organic matter. Keywords: Intercropping; Winter wheat; Red clover; White clover; N fixation; 15N-labelling.

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