Evaluation of Grain and Graze Traits in Cowpea Genotypes

Low availability and inadequate nutritional contents in pasture/fodder are constraints for livestock production in northern Australia. Alternative feed sources are required to mitigate feed gaps, especially in the dry season. Dual-purpose cowpea can offer suitable legume option for mixed farming systems where fodder/grazing an immature crop can meet the feed gaps for livestock and produce grain for food market. The research was conducted in Central Queensland University (CQU), Australia to examine the dual-purpose traits (response to regrowth) after cutting (removal of 50% and 75% plant height) at anthesis for four cowpea genotypes across three seasons (summer, autumn and winter). 

Biomass cutting occurred at anthesis between 36-41 days after sowing (DAS) in summer, 34-36 DAS in autumn and was delayed in winter (68-79 DAS) with no significant difference between genotypes. The crop maturity, however, was delayed in winter (123-140 vs 68-103 DAS in summer and 60-90 DAS in autumn) and by cutting treatments across all seasons. Biomass harvest was higher in summer (241 g/m2), followed by autumn (215 g/m2) and lowest in winter (149 g/m2). Likewise, the biomass yield increased significantly with higher cut regime at 75% (2.41 g/m2) particularly in the summer season compared to low cut regime at 50%. Additionally in the summer, AVTCP#1, and AVTCP#4 outyielded other genotypes under the 75% and 50% cut treatments respectively, whereas in the winter, no significant difference observed between the genotypes. 

Results showed variations in seed and total biomass yield due to treatments, genotypes, and seasons. In summer, moderate biomass removal (50%) stimulated seed yield (343.9 vs 264 g/m2) and no penalty for 75% biomass removal compared to control (274 vs 264 g/m2), particularly for the AgriVentis cowpea genotypes. In autumn, however, 50% biomass removal resulted into no penalty on seed yield (258 vs 276 g/m2) compared to control whereas 75% biomass removal reduced the seed yield significantly. In winter, however, seed yield decreased significantly with biomass removal for all genotypes, but more severely so in Red Caloona. 

Regarding the forage quality analysis, the effect of biomass cut treatments was less prominent in proximate compositions and bioactive compounds. Overall, the Red Caloona recorded higher Total phenolic contents (TPC) and antioxidant capacity in forage, while AgriVentis genotypes had high digestibility and dry matter (DM) contents. The gross energy (GE) contents of the forage ranged 17.1-18.6 MJ/kg and did not differ significantly for variety, cutting treatments and seasons. However, the crude protein (CP), decreased significantly in summer (22.9%), compared to autumn (28.1%) and winter (29.1%). The high intensity cutting (75%) reduced CP (22.3 vs 23.5%) compared to low cutting intensity (50%) in summer but no significant effects of cutting treatments on autumn and winter. Higher CP was recorded by AVTCP#1 for summer and winter and by Red Caloona for autumn. 

Regarding the seed quality analysis, the CP ranged 22.2-25.5% with significant genotypes x treatments effect for summer and winter crop and no effects of genotypes and treatments in autumn. The bioactive compounds varied significantly between genotypes such that Red Caloona recorded highest TPC, Ferric reducing antioxidant power (FRAP), and Cupric reducing antioxidant power (CUPRAC) compared to AgriVentis genotypes. Genotypic effect on seed physical quality was also observed where AgriVentis genotypes recorded the highest test weight and seed diameter, whereas Red Caloona recorded higher seed density. However, no significant effect of cutting treatment was recorded for test weight, seed diameter, seed density, bioactive compounds (TPC, FRAP, CUPRAC) and fiber analysis, both acid detergent fiber (ADF) and neutral detergent fiber (NDF). 

The overall results demonstrated the scope for developing cowpea as a dual-purpose crop as shown by the total first cut biomass yield up to 6.05 t/ha and seed yield up to 10.5 t/ha over three seasons within a year. The first cut biomass resulted into good quality fodder (high DM, CP, and moderate GE) for livestock and end of season harvest of grain for human consumption. Current assessment for seasonal adaptations and biochemical properties associated with cowpea traits conferring grain and graze uses present large variation between genotypes and cutting treatments. These results underpin strong genetic and crop physiological basis conferring traits for dual-purpose cowpea and suggest further exploring cowpea as dual-purpose crop for Northern Australia for different farming systems. In addition, the study also provided valuable insights into the potential dual-purpose traits of cowpea genotypes under cutting (biomass removal) pressure, which can support future breeding and management strategies for dual-purpose cowpea production in tropics.