Phosphorus Cycling and Use Efficiency in Intensified Smallholder Cropping Systems of South East Nigeria

This study quantifies phosphorus cycling dynamics and use efficiency in intensified smallholder cropping systems of South East Nigeria, addressing a critical gap in understanding of phosphorus management in one of Africa's most densely farmed agricultural landscapes. South East Nigeria's highly weathered ultisols have inherently low phosphorus availability due to strong sorption, yet the high agricultural productivity demands of the region's dense farming population require intensive phosphorus management. This study combines soil phosphorus fractionation, plant phosphorus uptake monitoring, and stable isotope oxygen-18 labelling of phosphate to trace phosphorus cycling pathways in six contrasting management systems across Enugu, Imo, and Abia States. Systems range from intensive vegetable production to cassava monoculture and maize-legume intercrop. Phosphorus input-output budgets and apparent phosphorus use efficiency are computed for each system over two years. Rhizosphere processes including mycorrhizal colonisation and phosphatase enzyme activity are quantified. Findings reveal that phosphorus use efficiency in South East Nigerian smallholder systems averages only 16 percent, significantly below the theoretical maximum, with the majority of applied phosphorus accumulating in non-labile organic and mineral-bound fractions. Mycorrhizal colonisation rates are significantly lower in intensively managed vegetable systems compared to cassava, explaining differences in phosphorus acquisition efficiency. Phytase enzyme activity is the strongest predictor of organic phosphorus mineralisation rate across systems. The study contributes original phosphorus cycling data for South East Nigeria and recommends mycorrhizal inoculant evaluation for vegetables and phosphorus-efficient variety selection as priority management improvements.

Keywords: phosphorus cycling, use efficiency, South East Nigeria, mycorrhizal colonisation, smallholder systems.