Effect of growth retardant soil residues on succeeding agricultural crops

Abstract

Abstract The growth retardants paclobutrazol, flurprimidol, and chlormequat chloride may be used to increase perennial ryegrass seed yield. However, the former two retardants are soil-active and residues may affect succeeding crops. A trial at Palmerston North examined possible soil residual effects of all three retardants on succeeding crops of wheat, rape, turnip, Italian ryegrass, and field bean, sown 200 days after retardant application to the previous crop. Chlormequat chloride exhibited no soil residual activity. Paclobutrazol and flurprimidol reduced the stem length or plant height of all five species tested. Retardation of plant growth increased as the original retardant application rate increased. Paclobutrazol residues reduced total dry matter (DM) in field bean only. Reductions in stem length of wheat and Italian ryegrass were compensated by increased tillering and for turnip and rape by increased stem width. Flurprimidol residues, particularly at an original application rate of 2.0 kg a.i./ha,...