Canopy Development of Annual Legumes and Forage Sorghum Intercrops and Its Relation to Dry Matter Accumulation

CORE IDEAS: Canopy and light interception characteristics of forage sorghum and sorghum‐legume systems were evaluated.Intercropping with sorghum increased canopy coverage and light interception early in the growing season.Intercropping legumes with forage sorghum increased LAI compared with sole forage sorghum.LAI was an accurate growth predictor of light interception in sole sorghum and all sorghum‐legume systems. Livestock production is an important agro‐industry in many semiarid regions of the world including the southern High Plains, USA. Therefore, objectives of this study were to understand how canopy development and light interception patterns impact biomass yield of several legume species when intercropped with forage sorghum [Sorghum bicolor (L.) Moench] grown under irrigation. Field studies were conducted at Tucumcari and Clovis, NM in 2008 and 2009, respectively. Five annual legumes [cowpea (Vigna unguiculata L.), pigeon pea (Cajanus cajan L.), lima bean (Phaseolus lunatus L.), lablab (Lablab purpureus L.), and pole bean (P. vulgaris L.)] were intercropped between two rows of sorghum spaced at 0.75 m and compared with sole sorghum under irrigation. Intercropping legumes with sorghum increased leaf area index (LAI) compared with sorghum alone, at both locations. Intercropping legumes with sorghum resulted in faster canopy coverage and greater light interception early in the growing season compared with sorghum alone. Lablab, cowpea, lima bean, and pole bean were promising legumes to improve light interception when intercropping with sorghum. The LAI was an accurate growth predictor of light interception in all intercropping systems and sorghum alone (R² > 0.94). Overall, optimum LAI (90% light interception) was lower in all intercropping systems compared with sorghum alone. Dry matter accumulation had strong correlations with LAI and light interception at both locations before canopy closure (58 d after planting). Overall, intercropping legumes in forage sorghum benefits producers by providing protein to livestock and reduces the need to purchase dietary supplements in their traditional livestock production systems.