Author(s)

Clark B. Neely¹, Francis M. Rouquette Jr.^2*, Cristine L. S. Morgan³, Frank M. Hons⁴, William L. Rooney⁴, Gerald R. Smith²

¹Department of Soil and Crop Science, Washington State University, Pullman, WA, USA.
²Texas A&M AgriLife Research, Overton, TX, USA.
³Soil Health Institute, Morrisville, NC, USA.
⁴Department of Soil and Crop Science, Texas A&M University, College Station, TX, USA.

Before the advent of cheap, synthetic fertilizers, legumes were commonly used as green manure crops for their ability to fix atmospheric nitrogen (N). A three-year study at Overton, TX examined legume integration into high-biomass sorghum (Sorghum bicolor L.) production systems on a Lilbert loamy fine sand recently cultivated after a fertilized bermudagrass [Cynodon dactylon (L.) Pers.] pasture. In this split-split plot design, ‘Dixie’ crimson clover (Trifolium incarnatum L.) and ‘Iron and Clay’ cowpea (Vigna unguiculata L.) were integrated into a high-biomass sorghum production system to evaluate impacts on N concentration, C concentration, and yield of high-biomass sorghum and their impacts on soil total N and soil organic carbon (SOC). Main plots were split into crimson clover green manure (CLGM) and winter fallow (FALL) followed by three sub-plots split into warm-season crop rotations: cowpea green manure (CPGM), cowpea-sorghum intercrop (CPSR), and sorghum monocrop (SORG). Three N fertilizer treatments (0, 45, 90 kg N∙ha⁻¹) were randomized and applied as sub-sub plots. The CLGM increased (P < 0.01) sorghum biomass yield (16.5 t DM∙ha⁻¹) 28% in year three but had no effect in the first two years. The CPSR treatment reduced sorghum yield up to 62% compared to SORG; whereas CPGM increased sorghum yield 56% and 18% the two years following cowpea incorporation. Rate of N fertilizer had no effect on sorghum biomass yield. Decrease in SOC and soil N over time indicated mineralization of organic N and may explain why no N fertilizer response was observed in sorghum biomass yield. Cowpea showed strong potential as a green manure crop but proved to be too competitive for successful intercropping in high-biomass sorghum production systems.

High-Biomass Sorghum, Legumes, Green Manure, Intercrop, Cowpea, Crimson Clover, Soil Organic Carbon, Soil Nitrogen

Neely, C. , Rouquette Jr., F. , Morgan, C. , Hons, F. , Rooney, W. and Smith, G. (2024) Legume Green Manure and Intercropping for High Biomass Sorghum Production. Agricultural Sciences, 15, 605-621. doi: 10.4236/as.2024.156034.