ALBERT

Description: SUMMARYDisposal methods for straw from continuous winter wheat were tested on two soil types, a flinty silty clay loam and a sandy loam, over 7 years (1985–91). The methods tested were burnt or chopped straw in full factorial combination with four cultivation methods (tined to 10 cm, tined to 10 cm then to 20 cm; ploughed to 20 cm; tined to 10 cm then ploughed to 20 cm). Measurements were taken to determine the effects on crop establishment and growth, pest and disease incidence, and the consequent effects on yield. Another experiment (1985–91) on the flinty silty clay loam site, investigated the interactions between straw treatments (burnt, baled or chopped in plots that were all shallow cultivated to 10 cm) and five other factors; namely, time of cultivation, insecticides, 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 cultivations resulted in very severe grass-weed problems. Early crop growth, as measured by above-ground dry matter production, was frequently decreased 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 fly 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 both slightly but significantly less severe where straw was incorporated than where it was burnt. Eyespot, and even more consistently sharp eyespot, were often more severe after ploughing than after shallow, non-inversion cultivations. Effects on take-all were complex but straw residues 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 fourth year (fifth cereal crop) take-all was greater in the ploughed than in the shallow cultivated plots. On average, yields did not differ greatly with straw or cultivation systems, although there were clear effects 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 the plots testing chopped straw incorporated by tining to 10 cm.

Description: A series of three experiments on loam to sandy loam soil at Woburn, all following winter or spring wheat, tested the effects of six different 1-year set-aside treatments and crops of winter wheat in 1989, 1990 and 1991 on two following winter wheat test crops. Effects of the treatments on overwinter changes in soil mineral nitrogen (SMN) and plant N in the set-aside years and in the first test crops were measured, as were the grain yields of both the first and second test crops.Differences in net overwinter changes in SMN plus plant N between set-aside treatments were variable and dependent on rainfall. During a wet winter, SMN plus plant N losses were large under fallow and natural regeneration, intermediate under winter wheat and small under Italian ryegrass (Lolium multiflorum). Ryegrass restricted the growth of the following wheat but yields were unaffected where fertilizer N was applied. Ryegrass proved difficult to control in the subsequent wheat test crops. Forage rape (Brassica napus) took up large amounts of N but after topping did not compete well with weeds.Yields of the first wheat test crops after winter wheat were smaller than after the set-aside treatments, take-all was probably the cause of this yield depression. No consistent yield differences were recorded in the second wheat test crops.

Description: Three experiments on winter wheat, each lasting 5 years and on different soil types, were used to test the effects of incorporating different amounts of straw, mainly to determine the importance of achieving uniform distribution to avoid adverse effects on grain yield. Decreases in crop growth and/or grain yield as a consequence of incorporating straw were detected in the first year. The decreases were much larger in one experiment where straw was imported and applied to soil that had been fallowed for 12 months before sowing the wheat than in the other two where the straw was incorporated following the harvest of a winter wheat crop. In the subsequent 4 years, incorporating up to 20 t straw/ha had no significant effects on grain yield but there were some significant effects on concentrations and uptakes of N, P and K, especially on the heavier textured soils. The effects on crop growth and yield that were detected in the first year on each site are tentatively attributed to decreases in available N representing that which was required to support the decomposition of the incorporated straw. The relative lack of significant effects in subsequent years seems to imply that a significant proportion of this N was remineralized relatively quickly, and thus available to support the decomposition of the straw that was incorporated in the second year and, after further recycling, in the years after that. Eyespot, caused by the fungus Pseudocercosporella herpotrichoides, was decreased by incorporating straw but there were few significant effects on other diseases. The results provide a generally reassuring message for farmers in suggesting that on most, if not all, soils there is little cause for concern about the consequences of incorporating even large amounts of wheat straw before sowing a further crop of winter wheat.

Description: Six management regimes for 1-year set-aside were compared with continuous winter wheat for their effects on weed control in two following test crops of winter wheat. The experiment was repeated in each of three years (1989–91) on predominantly sandy loam soils in eastern England. The weed flora was dominated by Poa spp., Stellaria media, Matricaria spp., Chenopodium album and volunteer crops, predominantly wheat.Managing set-aside by allowing natural regeneration and cutting it 2–4 times during the growing season resulted in fewest weeds in the following wheat crop. It was also a low cost option. Winter wheat, despite the application of herbicides, was not as effective in minimizing weeds in the winter wheat test crops as the best set-aside options.An Italian ryegrass cover crop set seed despite being cut 2–4 times per year. The only serious weed infestation arising in following wheat crops was from volunteer ryegrass in the second wheat following set-aside. The effects of management in the set-aside year were generally greater in the second of the following wheats than in the first.