Manageable agronomic practices in organic production of cowpea (Vigna unguidulata [L. Walp] in a mixed culture with sorghum
A three year (2002, 2003 and 2004) field experiment was conducted with the main objective of achieving optimum cowpea grain yield without starter mineral nitrogen and inorganic pesticides. Three spatial arrangements were tested against three weeding frequency. The experiment was a factorial design with a Completely Randomized Block layout. The treatments were replicated three times. The effects of these cultural interventions were observed on cowpea srtiga count nodulation, net assimilation rate (NAR) and grain yield. Data collected were subjected to ANOVA and means were separated using LSD (P ≤ 0.05). NAR were enhanced (P≤0.05) by the interaction of weeding frequency and spatial arrangement. Weeding × spatial arrangements reduced (P ≤ 0.05) striga incidence on cowpea during 2003 and 2004. Weeding thrice × sowing 1:2 and weeding twice × sowing on the same hill gave a statistically similar result. Nodulation was enhanced by the interaction of weeding frequency and spatial arrangement. Weeding frequency × planting arrangement significantly increased (P ≤ 0.05) cowpeas grain yield during 2004. The highest grain yields (1344 and1347 Kg/ha) were recorded from weeding twice × sowing 1:2 and weeding thrice × sowing on the same hill. Based on these field data the frequency of weeding enhanced physical removal of weeds, minimized competetion for growth resources, improved soil conditioning for optimum aeration, increased soil air-water ratio for optimum mycorraler and other beneficial soil microbial activities; While intercropping possibly provided canopy coverage for moisture conservation and pest control.