Abstract
The use of substandard agronomic practices accompanied by climate variability under smallholder farming settings exacerbates the low production and productivity of potatoes. Hence, a holistic approach that combines different practices to enhance plant growth and optimize yield will be valuable in smallholder settings. This study aims to evaluate the capacity of integrated management practices centered on cultivar selection, and the application of mulch and fungicide to improve potato production in rainfed production systems. Field trials were conducted for two consecutive seasons in 2022/23 and 20223/24 under two different agroecological zones (Swayimane and Appelsbosch) that have five localities (Mbalenhle and Hlathikhulu are from Appelsbosch, Gobizembe, Mbhava and Stezi are from Swayimane). Factors that were tested included four cultivars (Electra, Panamera, Mondial, and Sababa), two levels of mulching (mulch and not mulch), and fungicides (sprayed and unsprayed), which were laid out in a randomized complete block design replicated three times. The collected data such as potato yield, harvest index, days to reach maturity, plant height, soil water content, disease severity, the area under the disease progress curve (AUDPC), the relative area under the disease progress curve (rAUDPC), calculated potato actual evapotranspiration and water productivity were analyzed using GenStat statistical software (GenStat® 64-bit version 23.1, VSN International Ltd, UK). Means were separated by Tukey at a probability level of 5%.
Localities with low atmospheric water demand and humid environments, dominated by sandy soils and located in high altitudes, resulted in higher yields for the Electra cultivar with the highest of 64.22 t ha-1. The Electra cultivar showed a greater proportion of the biomass allocated to tubers resulting in large tuber size contributing to a high harvest index of 90.2%. Mbhava is located on a south-facing slope, with the lowest altitude, and clayed soils had the lowest yield of 13.4 t ha-1 from the Mondial cultivar which had no application of fungicide and mulch. Electra cultivars showed consistent performance under different practices and yielded more than other cultivars across localities. Hence, it is recommended that effective management practices such as fungicide (spraying or unsprayed) and mulch (mulch or not mulch) and selection of Electra can be adopted to increase potato yield under rainfed conditions. Furthermore, integration of late maturing cultivars (Panamera) with mulch and fungicide spraying improved tuber quality, also tubers that had higher dry matter content resulted in higher starch, carbohydrate content, and energy.
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However, the main interaction cultivar x mulch x fungicide x locality showed an insignificant effect (p>0.05) on potato tuber quality traits Sababa cultivar had the lowest nutritional profile for all traits across localities.
Disease severity on the cultivars Sababa and Mondial with mulch and unsprayed was higher at the Hlathikhulu, Gobizembe, and Mbalenhle localities than at Stezi and Mbhava. The cultivar Mondial with mulch application and unsprayed showed high AUDPCs at the Hlathikhulu, Gobizembe, and Mbalenhle localities. The cultivar Electra with an application of mulch and fungicide resulted in low AUDPC (196%-day) at the Mbhava. Mondial with an application of mulch and unsprayed treatment had a rAUDPC seasonal average of 0.44 to 0.74% across high altitude localities (Mbalenhle, Hlathikhulu, and Gobizembe), whereas the Sababa cultivar with mulch and without fungicide application had the highest average of 0.45 to 0.70%. The treatment sprayed with fungicide and with mulch showed low disease severity at the Mbhava and Stezi localities. Localities that had lower vapor pressure deficit (VPD), high relative humidity, and sandy soil had a higher potato water productivity for all cultivars, with the highest of 18.38 kg m-3 from Electra.
The model was calibrated to aid in the understanding and better use of the crop model using minimal data input for calibrating new cultivars that have not been calibrated before to improve the accuracy and precision of the model. Moreover, the model satisfactorily predicted canopy cover, soil water content, actual evapotranspiration, biomass, and yield. The addition of canopy growth and decline coefficients, and normalized water productivity to the minimal input data calibration resulted in higher accuracy and robustness of the model. The simulation outputs obtained from the current study will contribute to future research that will be conducted to test how well AquaCrop predicts yield and water productivity by comparing simulated outputs with independent observed data from Stezi and Mbhava localities. The results suggest that low minimal data inputs can calibrate the model successfully and obtain high levels of accuracy. The findings suggest that localities that have less atmospheric dryness were able to give higher yields for potato cultivars. Electra and Panamera showed a delay in disease incidents compared to Mondial and Sababa, showing signs of late blight tolerance. The important integration management practices for Mbalenhle, Hlathikhulu, and Gobizembe were the application of fungicide and without the application of mulch and the selection of Electra cultivar, whereas at Stezi and Mbhava both the
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application of fungicide and mulch were found as important holistic approaches for improving potato productivity, with the selection of Electra cultivar.