Yield gap analysis and resource footprints of Irish potato production systems in Zimbabwe

Irish potato is the third most important carbohydrate food crop in Zimbabwe after maize and wheat. In 2012, the Government of Zimbabwe declared it a strategic national food security crop. In this study, we examine the country's potential for increasing Irish potato yield and help ease the nation's food security challenges. The magnitude of food production increase on already existing croplands depends on the difference between the current actual yields and the potential yield of the crop in the given agro-ecological environment, also called the yield gap. We used three already well-understood types of yield gap: (1) the gap between actual farmer yields, Ya, and the maximum (potential) yield, Yp, achieved when a crop is grown under conditions of non-limiting water and nutrient supply with biotic stress effectively controlled; (2) the gap between Ya and the water-limited yield, Yw, which is the maximum yield attainable under rainfed systems; and (3) the gap between Ya, and the highest yield, Yh, achieved by the best farmers in an agro-ecological area. A grower survey was conducted on the different potato production systems in the country in order to establish the actual yields and input application rates used in potato production. The actual potato yields were used to calculate efficiencies of natural and synthetic resources use. Potential and water-limited yields, and planting times of potato were established for the different agro-ecological regions using the LINTUL-POTATO model, a model based on interception and utilisation of incoming solar radiation. The mean actual yield observed ranged from 8 to 35% of the potential yield, translating to a yield gap of 65 to 92%, hence there is a huge potential to increase production. Simulated potential water use efficiency based on evapotranspiration range was 19–27 g potato/l against the actual water use efficiency of 2–6 g potato/l based on irrigation and rainfall. The current high fertiliser application rates and low actual yields we report, suggest inefficient fertiliser use in potato production in Zimbabwe. The average actual fungicide and insecticide use efficiencies were 0.7 and 13 kg potato/g active ingredient, respectively, across all production systems. All sampled growers lacked knowledge on integrated pest management, a concept which could possibly improve the biocide use efficiency through lowering biocide application rates while maintaining or even improving yields. Our analysis suggests that there is opportunity to improve water, nutrients and biocides resource use efficiencies and increase potato actual yields in Zimbabwe