Response of orange-fleshed sweetpotato varieties to artificial defoliation and fertilisation under Zimbabwean conditions

Orange-fleshed sweetpotato (Ipomoea batatas L.) has become a popular source of beta-carotene, a precursor for Vitamin A, in sub-Saharan Africa (SSA); in addition to other important dietary components. The objective of this study was to establish the optimum rate of artificial defoliation and compensatory NPK fertilisation for tuber yield of orange-fleshed sweetpotato varieties under Zimbabwean conditions. A field experiment was conducted during the 2020/2021 and 2021/2022 cropping seasons, at Chinhoyi University of Technology in Zimbabwe. Treatments included five orange-fleshed varieties (Alisha, Delvia, Irene, Namanga and Victoria) and one standard white-fleshed variety (Chingovha); three NPK fertiliser regimes [normal practice (124.5 kg N + 42 kg P + 21 kg K ha-1), and compensatory fertilisation at 25% (155.6 kg N + 42.5 kg P + 26.5 kg K ha-1) and 50% (186.8 kg N + 63 kg P + 31.5 kg K ha-1) above normal practice]; and three defoliation intensities (zero, two and three times). The treatments were laid out in a randomised complete block design, with three replications. Varietal differences were significant in marketable tuber yield, with Chingovha, Delvia, Irene and Namanga outperforming Victoria by up to eight times. Chingovha and Delvia responded positively to compensatory NPK fertilisation under intensive and moderate defoliation, with total tuber yield increases of 170% when supplemented with 25 and 50% NPK fertiliser, respectively. To maximise Delvia tuber yields, we recommend two defoliations coupled with high compensatory fertilisation. Other orange-fleshed sweetpotato varieties can be defoliated thrice without requiring investment in extra fertiliser to prevent yield penalties.