Differential response of wheat to retained crop stubbles. II. Other factors influencing allelopathic potential; intraspecific variation, soil type and stubble quantity

Abstract

The allelopathic potential of the unweathered stubble of field-grown sorghum and sunflower was examined under controlled conditions in a series of glasshouse experiments. Wheat emergence was significantly inhibited in the presence of stubble from the eleven sorghum, and ten of the twelve sunflower cultivars tested. Inhibition of wheat emergence in the presence of sorghum stubbles ranged from 10 to 31%, and in the presence of sunflower stubbles from 4 to 33%, demonstrating a high degree of intraspecific variation in allelopathic potential. Many of the wheat seedlings emerging in stubble treatments exhibited an abnormal geotropic response. A threefold increase in stubble quantity, from 0.5 to 1.5% w/w soil, resulted in an approximate doubling of phytotoxicity. Wheat emergence was significantly reduced when stubble was incorporated into all three soils tested, with greater inhibition recorded in chocolate soil and a 50: 50 chocolate soi1:sand mixture than in sand. The choice of crop cultivar and the management of stubble quantity, especially in harvester trails, have important implications for the minimization of negative allelopathic effects in stubble retention systems.