ABSTRACT

Three field experiments were conducted in 2016 and 2017 cropping seasons at Umudike to study the effects of intercropping and intra-row spacing, examine the most suitable time to introduce sweet potato, and determine the effects of intercropping and integrated nutrient management on sweet potato and mungbean growth, yield and productivity in south eastern Nigeria. The experiments on intra-row spacing and integrated   nutrient management on sweet potato / mungbean were laid out as factorial fitted in a randomized complete block design (RCBD), while the experiment on time of introducing sweet potato on sweet potato / mungbean mixture was a randomized complete block design (RCBD) with three replicates. Treatments on intra- row spacing, consisted of all combinations of two cropping systems (sole and intercrop), four intra-row spacings of sweet potato (15, 30, 45 and 60cm) and four intra-row spacing of mungbean (5, 10, 15 and 20cm). The experiment on time of introducing sweet potato in mixture, treatments comprised two cropping systems (sole and intercrop) and five times of introduction (sweet potato planted 6 weeks before, 3 weeks before, same day as, 3 weeks after and 6 weeks after mungbean planting). Treatments in the experiment on integrated nutrient management comprised two cropping systems (sole and intercrop) and four levels of nutrient management (0, 4kg/ha agrolyser, 10t/ha organomineral fertilizer and 10t/ha organomineral fertilizer + 4kg agrolyser). Generally, intercropping significantly reduced sweet potato vine length and leaf area index at 9WAP and storage root yield in 2017. Intercropping also reduced mungbean leaf area index in both years and seed yield in 2016. In both sweet potato and mungbean, the closest intra-row spacings resulted in highest leaf area index, but the closer spacings of 100 x 30cm or 100 x 15cm gave significantly higher root yield in sweet potato than the wider spacing 100 x 60cm in 2017. However, the spacing of 100 x 15cm produced higher seed yield in mungbean than the spacing of 100 x 10cm in 2016. Land equivalent ratio (LER) and land equivalent coefficient (LEC) showed yield advantages but economic analysis indicated monetary yield disadvantages due to intercropping. The most profitable systems were obtained from sole sweet potato at the narrowest intra-row spacing of 15cm, followed by 30cm. In both years, sole sweet potato had statistically similar root yields with sweet potato introduced 6 weeks before mungbean but higher yields than other planting schedules except when sweet potato was planted 3 weeks before mungbean in 2016. Root yield reductions when sweet potato was introduced before and after mungbean plantings were 9.8 – 39.6% and 60.0 – 65.2% respectively. Seed yield reductions in mungbean when sweet potato was planted before and after mungbean were 39.8 – 54.4% and 13.6 – 28.2% respectively. Except for when sweet potato was introduced 3 weeks after mungbean and simultaneous planting in 2016, sole mungbean had significantly higher seed yield than intercropping at different times of introduction of sweet potato in mixture in both years. Although LER and LEC showed yield advantages due to intercropping, the highest profit was obtained from sole sweet potato, followed by planting sweet potato 6 weeks before the introduction of mungbean. Intercropping reduced sweet potato root yield and mungbean seed yield while 10t/ha organo mineral fertilizer + 4kg agrolyser or 10t/ha organo mineral fertilizer alone produced significantly higher root yield than 4kg/ha agrolyser or the control on average. LER and LEC indicated yield advantages accrued to intercropping but the highest profit was achieved in sole sweet potato with combined use of 10t/ha organo mineral fertilizer + 4kg agrolyser, followed by application of 10t/ha organo mineral fertilizer alone.