Biological Indices and Nutrient Concentration in Sorghum–Cowpea Intercropping Under Foliar and Soil Application of Molybdenum in a Semiarid Environment

The objective of this study was to evaluate the effect of foliar and soil application of molybdenum (Mo) fertilizer on the biological efficiency, competitive ability, and nutrient uptake of the sorghum–cowpea intercropping system. The experimental design was a randomized complete block design with four replications and nine cropping systems: sorghum–cowpea intercropping with foliar Mo application; sorghum–cowpea intercropping with soil Mo application; sorghum–cowpea intercropping without Mo application; sole sorghum with foliar Mo application; sole sorghum with soil Mo application; sole sorghum without Mo application; sole cowpea with foliar Mo application; sole cowpea with soil Mo application; and sole cowpea without Mo application. Overall, molybdenum (Mo) application did not affect most indices of biological efficiency and competitive ability of the intercropping system, with effects observed only on the current loss or gain in sorghum yield, the partial land equivalent ratio of sorghum, and the area-time equivalent ratio. Regarding Na+ and K+ concentrations, the treatments affected these nutrients only during the second cropping cycle. On the other hand, no effect of the treatments was observed on Cl− concentration in the sorghum shoot. Therefore, molybdenum fertilization did not alter the overall biological efficiency or competitive ability of the intercropping system. The changes in Na+ and K+ concentrations were localized and dependent on the cropping cycle, without causing changes in Cl− accumulation in the sorghum shoot.