EFFECTS OF MORPHOLOGICAL TRAITS AND CULTURAL PRACTICES OF INTERCROPPED SOYBEANS AND CEREALS

Research on intercropping systems has become of importance because of the serious concern over increasing world population and the concurrent demand for more food. Intercropping and other types of multiple cropping are viewed as possible methods of increasing food production. In experiments reported here, soybeans (Glycine max (L.) Merrill) were intercropped with either sorghum (Sorghum bicolor (L.) Moench) or maize (Zea mays L.) to study (1) the effects of sorghum plant height, maize leaf angle, delayed planting of sorghum and maize, and row width on interrow-intercropped soybeans, and (2) the effect of nodulating and nonnodulating near-isolines of soybeans on intercropped sorghum. Three experiments were conducted to consider each of the general objectives.;Experiment 7802, in the second series of experiments was planted near Experiment 7801 in Puerto Rico. A short sorghum cultivar was planted with the soybean 'Hardee' (nod) and its nonnodulating (nonnod) near isoline in 40 and 80 cm rows with either 0 or 100 kg N/ha. Experiment 7901 was similar except that it was planted at Brownstown IL and that 'Clark' and its nonnod near-isoline L73-1054 were used. Experiment 8001 was also planted at Brownstown, but soybeans were either planted 20 or 38 cm from sorghum rows which were 76 cm apart. Soybean cultivars were the same as in Experiment 7901, but N was increased to 0 and 175 kg/ha. Intercropped sorghum yields were similar with nod and nonnod cultivars in all experiments. Sorghum N-yield (%N-seed x grain yield), %N-seed, and %N-stalk were often greater with nod than with nonnod, but these increases could not be attributed solely to N-transfer from nod soybeans. Closer row spacings in these three experiments failed to increase any sorghum N-trait.;Experiment 7701, in the first series of experiments, compared the effects of short (1 m) and tall (1.5 m) sorghum cultivars on 'Amsoy' soybeans; the sorghum was either planted simultaneously with the soybeans or at one week intervals after soybean planting for a total of four sorghum planting dates at Urbana IL. Experiment 7702, also at Urbana, compared the effects of normal-leaved and liguleless counterparts of two maize genotypes on Amsoy soybeans. The maize cultivars were planted simultaneously with the soybeans and at one week intervals after soybean planting for a total of three plantings. The second planting was excluded from the analysis because of poor emergence. Experiment 7801 compared two short sorghum cultivars and two tall cultivars intercropped with four soybean cultivars in 40 and 80 cm rows, at Isabela, Puerto Rico. Soybean yields with tall sorghum were 46 and 18% less than those with short sorghum in Experiments 7701 and 7801, respectively. These decreases were due to fewer pods/plant and seed/pod. In Experiment 7801 tall sorghum cultivars yielded 46% more than did the short cultivars. Soybean yield in 40 cm rows was 43% greater than that in 80 cm rows due to increased seed/pod and seed weight. Sorghum yields were greatest in 40 cm rows, but short sorghum yields were greatest in 80 cm rows. Delayed planting of either sorghum or maize into soybean stands resulted in less sorghum and maize yield, but in greater soybean yield due to increased pods/plant. Soybean yields were decreased 31% and sorghum yields were decreased 55% by intercropping in Experiment 7801. Price ratio analysis of Experiment 7801 data indicates, that with sorghum/soybean price ratios greater than 0.36 tall sorghum intercropped with soybeans would result in the largest gross returns, that 40 cm rows would produce larger gross returns than 80 cm rows, and that intercropping would produce larger gross returns than monoculture of either species if the price ratio was between 0.51 and 0.95.