Cowpea as a Multifunctional Legume in a Texas Double Cropping System

Cropping systems involving legumes are increasing due to the costs and environmental concerns attributed to N fertilizer. A green manure cover crop in a cropping system can benefit the soil by improving fertility and disrupting disease, insect or weed cycles. Two studies were conducted during two years at the Texas A&M AgriLife Research and Extension Center at Overton, TX. Cowpea (Vigna unguiculata [L.] Walp) was evaluated as a multifunctional legume in a double cropping system with forage rye (Secale cereale L.), and 37 cowpea plant introduction (CPI) lines were evaluated for seed and biomass production. These studies measured cowpea biomass production, seed yield, carbon and nitrogen plant concentrations, and soil N contributions. Primary objectives were to 1) maximize rye biomass production through the incorporation of cowpea biomass in combination with different nitrogen rates concurrently; and 2) evaluate new CPI lines for traits needed in the cropping system and for potential seed production. The green manure cover crop of cowpea showed no impact (P ≥ 0.34) compared to fallow plots when comparing rye biomass in 2015 and in 2016 (P ≥ 0.26). Nitrogen rates had a positive linear relationship with rye biomass for 2015 (r^2=0.79) and 2016 (r^2=0.97). The lack of response of soil N from the summer green manure cover crop may be likely due to the soil type. Darco loamy fine sand (loamy, siliceous, semiactive, thermic Grossarenic Paleudult), is an excessively drained soil and has very little nutrient holding capacity. The CPI lines were evaluated based on biomass production and seed yield by late September to incorporate into a cropping system with forage rye, and nematode resistance. Cowpea biomass production peaked at 3021 kg ha^-1 in 2015 and at 6009 kg ha^-1 in 2016. Cowpea seed yield ranged from 0 to 2322 kg ha^-1 in 2016 and 9 to 351 kg ha^-1 in 2015. One CPI line was identified with root-knot nematode resistance. Separately the CPI lines exhibited valuable traits such as biomass production, seed yield, and nematode resistance and will be further evaluated for additional breeding programs