INTEGRATION OF NITRATE COVER CROPS INTO SUGAR-BEET (BETA-VULGARIS) ROTATIONS - II - EFFECT OF COVER CROPS ON GROWTH, YIELD AND N REQUIREMENT OF SUGAR-BEET

Between 1989 and 1993, 17 experiments tested the effects of autumn-sow n coves crops on the yield, processing quality and N nutrition of subs equent sugarbeet crops. Cover crops had no effect on sugarbeet plant p opulation density or pesticide requirement. In nitrogen response exper iments, the mean beet yield at the economic optimum was 83 t/ha. The m ean N fertilizer requirement was 96 kg N/ha and the N uptake at maximu m yield averaged 180 kg N/ha. Cover crops had no effect on yield, fert ilizer requirement or N uptake. In addition, cover crops generally had no effect on the efficiency of N fertilizer use, the mineralization o f N from the soil organic matter nor the amount of soil mineral nitrog en at sowing or at harvest of the beet crop. Processing quality was al so not affected by cover crops. The cost of growing a cover crop range d from 0 to 50 pound/ha. Since these costs cannot be offset against in creases in yields or reduced fertilizer application rates, cover crops need to be low cost, i.e. cheap seed and minimal cultivation Cover cr ops using volunteer cereals and weeds or farm-saved grain that are est ablished with a single stubble-cultivation should fulfil these criteri a.