Corn-stalk lodging and borer damage as influenced by varying corn densities and planting geometry with soybean (Glycine max. L. Merrill)

Cultural practices which increase the amount of insect pressure can also increase the amount of lodging that occurs in the corn crop. Studies were therefore carried out, in the late crop- ping seasons of 2002 and 2003, on the effect of corn planting densi- ties and geometry with soybean on corn lodging and infestations by stem borers. Treatments comprised three corn population densities of 40 000, 60 000 and 80 000 plants ha -1 and three geometrical arrangements of corn-soybean mixtures of 1:1, 1:2 and 1:3, in all possible combinations. There were also three sole crop populations of corn and one of soybean. This resulted in 13 treatments which were laid out in field plots in a Randomized Complete Block Design (RCBD) with three replications. Results of the studies showed that increasing corn population significantly (P<0.05) increased corn-stalk lodging and plant height, but significantly reduced the stalk diameter, shoot dry weight and infestations and damage by borers on corn, as well as the grain yields of corn and soybean. This is such that plants at 80 000 stands ha -1 recorded the highest amount of lodged stalks and the tallest plants, but the least stalk girth, shoot dry weight, infestation and damage by corn borers. The lowest grain yield was also obtained at this density. Differences in geometrical arrangements of corn-soybean and its interaction effects with planting density among these parameters did not attain any level of statistical significance. Similarly, the effect of intercropping corn with soybean did not produce any significant result on corn with respect to these parameters. These results are discussed in the light of corn planting densities and geometric arrangements with soybean, on corn production.