| This thesis is an investigation of livestock's contribution to phosphorus (P) cycling in smallholder agriculture in Kenya. One of the main problems in smallholder agriculture is P deficiency which is attributed to the inherently low level of P in the soil parent rock, the high fixation of P by Al and Fe oxides and the intensive cropping with low nutrient input The first experiment examined the potential for using phosphate rocks as a P supplement for Napier grass (Pennisetum purpureum) to prevent or correct P deficiency in cattle. The results showed that up to 33% of Busumbu phosphate rock (BPR) was absorbed. Because of the relatively high concentration of fluoride (F) (16.6 mg kg−1) in the BPR, the effects of replacing dicalcium phosphate (DCP) in chick rations with graded levels of BPR on the feed intake (FI), average daily gains (ADG), and tibia breaking strength (TBS) was examined. The BPR linearly (P < 0.05) reduced Fl, ADG, and TBS. There was a positive (P < 0.05) correlation (R 2 = 0.945) between the F in the diet and the F accumulated in the bone and a negative (P < 0.05) correlation (R2 = 0.984) between F in the bone and TBS implicating F toxicity as the cause of the reduced performance. As an alternative to feeding BPR to cattle, the effect of phospho-composting on P release from BPR and P uptake by corn (Zea mays L.) was investigated. The effects of organic verse mineral acids, pH, and temperature on P release from BPR were also examined. Acetic and lactic acid were superior (P < 0.05) to HCl on resin extractable P from BPR. Composting enhanced (P < 0.05) P release from BPR by up to 20% for NaHCO3, NaOH, and HCl extracted P. Compost supported higher (P < 0.05) corn dry matter yields and P uptake than triple superphosphate. Animals consuming P-adequate forages would therefore not suffer P-deficiency. |
