Production of Pinus radiata is a major contributor to New Zealand's economy and new plantings are a valuable carbon sink. Phosphorus (P) deficiency and high P fixing capacity of some volcanic ash soils (e.g. Allophanic Soil) may constrain radiata productivity. This thesis investigates the role of ectomycorrhizal (ECM) root processes in the acquisition of P by P. radiata fiom native soil and soil fertilised with two reactive phosphate rock (RPR) fertilisers. The application of finely-divided RPRs to a P deficient Allophanic Soil significantly increased P. radiata seedling growth and P uptake in 10 month pot trials. RPR dissolution was high in this soil, and it was further enhanced by the radiata rhizosphere processes. The development and formation of ECM in radiata seedlings was stimulated by low rates of RPR application but was hindered in unfertilised soils and high rates of RPR application. The P. radiata ECM roots induced acidification and increased oxalate concentration and phosphatase activities in the rhizosphere soil. These changes in rhizosphere biochemical properties were associated with enhanced solubilisation of fertiliser and soil inorganic P and increased mineralisation of organic P, leading to increased P bioavailability in the rhizosphere. ECM inoculation of P. radiata roots with Rhizopogen rubescens and Suillus luteus stimulated production of phosphatase enzymes and oxalate and induced acidification in the rhizosphere. The extent of root-induced changes in the rhizosphere soils was associated with ECM hyphae length density. A technique using pulse labelling of radiata shoots with 14CO2 showed promise in estimating the active ECM hyphae density. The 14C activity was highly correlated with ECM hyphae density measured by an agar film technique. Overall, observations made in this thesis indicate that sparingly soluble forms of organic and inorganic P in soils low in plant-available P are readily solubilised and utilised for P. radiata growth through ECM rhizosphere processes.

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)