Thesis (M.Sc. (Soil Science)) -- University of Limpopo, 2019 / Phosphorus (P) deficiency has been reported in 30- 40% of global arable land, which poses a huge threat in potato production because of its critical role in the early vegetative development and tuber formation. The use of low cost ground phosphate rock (GPR) as an alternative P fertilizer source has gained recognition. Although GPR contains high P percentage, its direct application is less beneficial immediately due to its low reactivity which makes P unavailable for plant uptake. In this experiment, GPR was co-composted with cattle and poultry manure in order to enhance P acquisition by the potato crop. The aim of this study was to evaluate the potential of phosphocompost application as a cheaper alternative P-source for potato production. The experiment was conducted on Mondial and Valor… potato cultivars at the University of Limpopo Syferkuil Experimental farm in 2015 and 2016. Poultry (PM) and cattle manure (CM)-based phospho-compost mix ratios of 8:2 and 7:3 were applied at 0, 20, 40, 80 and 120 kg P/ha. The trial was laid out in a split plot arrangement fitted into a randomised complete block design with treatments replicated three times. Results indicated statistically significant effects of phospho-compost types on soil pH and available P content at both flowering and harvesting growth stages in 2015 and 2016 with the higher available P content found in the PM-based phospho-composts. In both seasons, highly significant differences in fresh and dry leaf samples among phospho-compost types were obtained. Highly significant season x compost type interaction effects were also recorded on leaf biomass as well as the 2015 tuber weight, with highest tuber weight obtained in plots that received PM7:3-based phospho-compost at 80 t/ha rate. Notwithstanding the non-significant effect of compost type on tuber yield in 2016, higher yield was obtained from PM8:2. Although the grading of tubers showed no significant response to phospho-compost application; the difference between small and medium tubers obtained from 2016 trial was significantly affected by phosphocompost application rates. The CM8:2 mix ratio gave the highest baby tubers (16.87%) while PM7:3 mix ratio gave the highest (36.32%) medium tubers. The grading of the potato tubers revealed a mostly class 1 dominated by baby, small and medium size tubers in the 2015 harvest while the 2016 harvest was also mostly class 1 but dominated by small, medium and large-small size tubers. Tuber size and class were vi most favored by the PM-based phospho-compost applications in both planting seasons. None of phospho-compost types and application rates had significant effect on the measured nutrient concentrations of both plant parts. However, the differences in nutrient concentrations across seasons and plant parts were significant except for Ca. The measure tissue P concentration from the 2016 trial was within the required range suggesting that phospho-compost utilization, particularly the poultry manure-based, in potato production can be beneficial in addressing P deficiency. The PM8:2 mixed ratio resulted in increased soil available P content, potato tuber yield in 2016 and the P concentration across the two plant parts evaluated. The concentration of soil available P and tissue P showed increases with higher application rates albeit non-significance. Future research on the optimum application rate is suggested on a wide range of soils for the various phospho-compost types. / Potato SA and the National Research Foundation (NRF)