Sorghum Stature and Mixing Ratio Effects on Sorghum-Legume Intercropping Productivity.

The Ogallala Aquifer has converted the Southern Great Plains from a Dust Bowl to one of the productive agriculture region in the country. This irrigated agriculture has supported large dairy and beef industry. However, declining aquifer has increased the importance of producing high quality forage with less water to sustain the large animal population. Intercropping forage sorghum (that produces more forage but quality is lower) with lablab (a legume that produces higher quality forage) can improve resource use efficiency early in the season, which can lead to improved forage productivity and quality. However, the taller growing conventional forage sorghum cultivars seems to over compete with legume to produce biomass. Therefore, recently developed Brachytic Dwarf (BMR cv. 26837) or lower lignin containing tall BMR (cv. Dairy Master) were intercropped with lablab (cv. Rongai) at six different mixing ratios to assess effect on resource use and productivity. A two year field study was conducted at the Agricultural Science Center at Clovis, NM. Leaf area index of two sorghum cultivars or six intercropping mixtures did not show any significant differences among treatments, which was reflected in radiation interception. Seasonal pattern of forage production showed that Brachytic dwarf produced either more or equal forage compared to tall BMR during most of the growing season. Forage production was not benefited from intercropping. Increasing legume population in the mixture increased legume biomass, but it was always lower than sorghum biomass and was not proportional to its population. For example, sorghum with 25% or 50% population had almost double the forage production compared to 75% or 50% population of legume.  Thus, both dwarf and standard height BMR sorghums limited biomass contribution by legume.