EFFECTS OF INCORPORATING OR BURNING STRAW, AND OF DIFFERENT CULTIVATION SYSTEMS, ON WINTER-WHEAT GROWN ON 2 SOIL TYPES, 1985-91

Disposal methods for straw from continuous winter wheat were tested on two soil types, a flinty silty clay loam and a sandy loam, over 7 yea rs (1985-91). The methods tested were burnt or chopped straw in full f actorial combination with four cultivation methods (tined to 10 cm, ti ned to 10 cm then to 20 cm; ploughed to 20 cm; tined to 10 cm then plo ughed to 20 cm). Measurements were taken to determine the effects on c rop establishment and growth, pest and disease incidence, and the cons equent effects on yield. Another experiment (1985-91) on the flinty si lty clay loam site, investigated the interactions between straw treatm ents (burnt, baled or chopped in plots that were all shallow cultivate d to 10 cm) and five other factors; namely, time of cultivation, insec ticides, molluscicides, fungicides and autumn nitrogen. All the straw x cultivation systems allowed satisfactory crops to be established but repeated incorporation of straw using shallow, non-inversion cultivat ions resulted in very severe grass-weed problems. Early crop growth, a s measured by aboveground dry matter production, was frequently decrea sed by straw residues, but the effect rarely persisted beyond anthesis . Pests were not a problem and their numbers were not greatly affected either by straw or cultivation treatments, apart from yellow cereal f ly which, especially on the heavier soil, was decreased by treatments which left much straw debris on the soil surface. Incorporating straw also caused no serious increases in the incidence of diseases. Indeed, averaged over all sites and years, eyespot and sharp eyespot were bot h slightly but significantly less severe where straw was incorporated than where it was burnt. Eyespot, and even more consistently sharp eye spot, were often more severe after ploughing than after shallow, non-i nversion cultivations. Effects on take-all were complex but straw resi dues had much smaller effects than cultivations. Initially the disease increased most rapidly in the shallow cultivated plots but these also tended to go into the decline phase more quickly so that in the fourt h year (fifth cereal crop) take-all was greater in the ploughed than i n the shallow cultivated plots. On average, yields did not differ grea tly with straw or cultivation systems, although there were clear effec ts of take-all in those years when the disease was most severe. In the last 2 years, yields were limited by the presence of grass weeds in t h plots testing chopped straw incorporated by tining to 10 cm.