SOIL PHOSPHORUS DYNAMICS OF SWEET POTATO-BASED CROPPING SYSTEM IN A RAINFOREST REGION OF NIGERIA

1 Department of Agronomy, University of Ilorin, Ilorin, Nigeria 2 Department of Agronomy, University of Ibadan, Ibadan, Nigeria 3 Institute of Tropical Agriculture, Universiti Putra Malaysia, Serdang, Selangor, Malaysia 4 Department of Agronomy, Ibrahim Badamasi Babangida University, Lapai, Niger State, Nigeria 5 Department of Biology, School of Secondary Education (Science Programme), Federal College of Education (Special), Oyo, Nigeria ABSTRACT. To guard against soil phosphorus (P) toxicity in tuber production and have optimum tuber yield at lesser cost of P-fertilization, better understanding of the dynamics of phosphorus release in sandy loamy soil is inevitable. Therefore, this work was carried out to investigate the trend of P-release from time of application to its optimum release and its effect on sweet potato growth and tuber production. To achieve this, a 5-week incubation study under laboratory conditions was carried out to study P-release dynamics using different P sources. Similar experiment was conducted on the field using the same P sources and application rate to monitor the influence P-release rate on sweet potato production. Data on number of leaves, vine length, tuber yield, soil extractable phosphorus and phosphorus uptake of the plants were taken. Relationships between P-uptake and tuber yield, number of leaves, vine length were also established. It was found that the trend of phosphorus release was a sigmoid shape. Leaf production and vine length were improved by P-application, while yield was suppressed. It is recommended that P-fertilizer should not be applied to the soil at short intervals to avoid nutrient toxicity.