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Limited phosphate resources, increasing fertilizer prices and unsustainable methods of treating phosphates in wastewaters have resulted in the need for phosphate recovery technologies. One method involves the precipitation of a magnesium ammonium phosphate mineral called 'struvite' (MgNH 4PO4·6HO). Wastewaters often require an additional source of Mg2+ and a solution pH between 8 and 11 in order to achieve orthophosphate (OP) removal as struvite. This research examined 3 effluents to determine an ideal pH for producing the lowest residual values of OP. Two types of MgO were also tested for their ability to reduce OP concentrations: a pure chemical source and ground MgO refractories. Optimal pH levels were not determined, as it was likely that the supersaturation was too high to produce differences in OP removal. Chemical-grade MgO was more reactive than the refractories, and was therefore more effective in removing OP as struvite in wastes where Mg2+ was limiting. OP removal rates of >90% were achieved in each effluent.

Low availability of soil phosphorus (P) limits crop production in many areas of Zambia. The use of Chilembwe phosphate rock (CPR) from Zambia for direct application has not been successful on annual crops due its low solubility. The modification technique studied was a biological method to transform inorganic P from CPR into plant biomass of 'Tithonia diversifolia.' 'T. diversifolia' was grown in acidic soil treated with finely-ground CPR at rates of 0, 20, 40, 60 and 80 kg P ha-1. Applications of 40 kg P ha-1 or higher CPR significantly increased leaf P concentration after 16 weeks compared to the control. Application of CPR can enhance leaf P concentration and improve biomass quality of ' T. diversifolia.' 'T. diversifolia' was also grown under 'Faidherbia albida' treated with finely-ground CPR. Leaf P concentration was significantly higher under the 'F. albida' canopy compared to the open field after 8 weeks. Biomass from 'T. diversifolia' was used to prepare a leaf extract and evaluate its effects on biomass production of ' Arachis hypogeae.' Application of 750 liters ha-1 leaf extract did not significantly affect biomass production in 'A. hypogeae ' after 12 weeks, compared to the control, or application of 40 kg P ha-1 CPR.

Phosphorus deficiencies are limiting crop production in agricultural soils worldwide. Locally available sources of phosphate rock (PR) are being recognized for their potential role in soil fertility improvement. For applications of PR to be effective, the phosphorus must be made plant-available. Modification with acid-producing microorganisms has the potential to increase the agronomic effectivenss of PR. For this thesis, four strains of 'Aspergillus niger ' were screened for phosphate solubilization and acid production. Response surface methodology was used to optimize medium conditions for citric acid production. Lastly, PR solubilization from additions of PR to an ' A. niger' ATCC 9142 culture medium at cultivation onset, was compared with additions of PR to the acid-containing culture supernatant. The two treatments were found to solubilize equivalent PR, with solution P values ranging from 219-382 mg/l. Future research is necessary to optimize this process and to investigate the effects of such phosphorus mobilization on plant growth.

The Cretaceous Napo Formation in Ecuador contains a phosphate deposit of economic significance. The apatite in the phosphate deposit is a peloidal, fluorine rich carbonate fluorapatite, embedded in calcitic cement. It is a moderately substituted, reactive apatite with a unit-cell a-value of 9.334 A?. Sedimentary phosphates in E cuador were formed authigenically in discreet stages under anoxic conditions at the sediment-water interface, in a localized area. Chemical analyses using NAA and ICP-OE S revealed that Uranium and Rare Earth Elements are positively correlated with phosphorus indicating these elements are either incorporated into the apatite lattice, or adsorbed onto mineral surfaces. The uranium concentration of the Napo phosphate averages 100 mg kg-1, while the radioactivity ranges from 20 to 410 Bq kg-1. The overall radiation emanating from the static mine environment is 280.63 Bq kg-1 equating to a radiation dose of 1.85 mSv per year, resulting in a 0.01% risk of developing cancer.

This thesis investigates food security, intra household dynamics and changes in manure use in northern Malawi. Interviews were conducted with 56 people about food security and intra household dynamics. Available cash, labour and family supports all influenced food security. Agricultural labour was carried out by husbands and wives in 50% of households. Husbands controlled most decisions about income and agriculture. On-farm experiments using Brassica juncea and Brassica napus were conducted to compare manure extract (ME) with the local fertilizer, solid manure (SM). SM produced significantly higher yields than ME, but ME produced significantly higher yields than the control. Nitrogen uptake appeared to be one of the factors to cause this difference. ME was preferred by farmers for vegetables, due to performance and reduced labour. Farmer participatory research (FPR) helped to generate information about manure use, gaps in farmer knowledge and constraints to food security. Some drawbacks to FPR are noted.