SORGHUM AND SOYBEAN CULTIVAR BY PLANT DENSITY INTERACTIONS IN ONE INTERCROPPING PATTERN; INTERCROP SYSTEM GRAIN PRODUCTION AND INTERCROP EXPERIMENT ANALYSIS CONSIDERATIONS

Two soybean/sorghum intercrop experiments were conducted at two locations. Tall (N4692) and short (Martin) sorghum cultivars at four plant densities were combined with tall (Will) and short (Elf) soybean cultivars at a constant plant density (Experiment I). Soybean cultivars at four plant densities were combined with sorghum cultivars at a constant plant density (Experiment II). In Experiment I, total grain production (TGP) was not significantly affected by soybean cultivar or sorghum plant density, but was affected by the interaction of sorghum cultivar and locations. Sorghum grain yield of both cultivars increased as sorghum plant density increased, while soybean grain yield decreased. In Experiment II, soybean cultivar or density had no significant effect on intercrop TGP. All intercrop systems in Experiment II had significantly higher grain production than the most productive soybean monoculture. The soybean:sorghum plant population ratio used in a \u27Replacement Series\u27 to equate the competitive abilities of the two species was examined. The ratio varied between locations, sorghum cultivars, and sorghum plant densities. A comparison of \u27Replacement Series\u27 which used a constant soybean:sorghum ratio and \u27Triangulation Method\u27 which adjusted for soybean\u27s differential competitive abilities showed that the latter was preferable because the ratio of the two species changed between and within a range of total \u27plant unit\u27 populations. The \u27Triangulation Method\u27 was suggested as a way to calculate equality between inter-specific and intra-specific competition in intercropping experiments