THE EFFECT OF WHEAT STRAW MULCH ON WEED CONTROL AND CORN GROWTH

Research was conducted to determine the effect of wheat (Triticum aestivum L.) straw mulch level on weed control and corn growth in a winter wheat-ecofallow corn (Zea mays L.)-fallow rotation at Wilber, North Platte, and Sidney, Nebraska from 1981 to 1983. Wheat straw mulch was established at levels of 0, 1.68, 3.36, 5.04, and 6.72 t/ha in stubble fields after harvest (fall-adjusted) or the following spring (spring-adjusted). Atrazine {2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine} concentration remained higher in unmulched soil than in soil with high levels of mulch for more than 9 months following application after wheat harvest due to interception of atrazine by the mulch. Metolachlor {2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide} concentration remained higher in unmulched soil than in soil with high levels of mulch for more than 4 months after application at corn planting due to interception by the mulch. Even though the amount of atrazine and metolachlor in the soil was reduced by mulch in fall-adjusted experiments and the amount of metolachlor was reduced in spring-adjusted experiments, weed control was not reduced and usually increased with increasing mulch level. Thus increasing atrazine and metolachlor rate was not necessary to maintain adequate weed control in no-till wheat stubble since the mulch itself had an adverse effect on weed growth. The response of corn to mulch level varied with environment. Overall, early corn growth was retarded by increasing amounts of mulch, but, after tasseling, corn grew taller as the mulch level increased. Soil water content, silking date, kernel moisture at harvest, stover dry matter, total dry matter, ears per plant, and kernel weight increased with increasing mulch level. Kernel number reached a maximum at a mulch level of 4.4 t/ha while grain yield reached a maximum at a mulch level of 5.1 t/ha. Grain yield was better correlated with kernel number than with kernel weight. Unmulched corn usually had the lowest kernel number and lowest grain yield