Indigenous nutrient supply, weeding and fertilisation strategies influence on-farm N, P and K use efficiency in lowland rice

Abstract

Enhancing use efficiency of applied fertiliser increases farmers’ returns on fertiliser investment through reducing nutrient inputs and improving yields. We investigated on-farm how indigenous nutrient supply and management practices affected N, P, and K uptake, agronomic efficiency and recovery efficiency of fertiliser, and physiological efficiency of nutrients taken up, under irrigated lowland rice conditions in Uganda. Treatments included recommended agronomic practices (RAP) without fertilisation, farmers’ practice (FP), farmers’ selected intensification practice (FIP), and RAP with NPK fertilisation (RAP + NPK). Indigenous N, P, and K supply varied greatly among farmers’ fields. N, P, and K uptake were significantly higher under RAP + NPK than under RAP, FP, and FIP; however, physiological efficiency (PE; kg grain kg−1 nutrient uptake) was significantly lower under RAP + NPK by 19% (N), and 12% (P/K), due to a larger effect of NPK application on uptake than on yield, leading to higher tissue concentrations. Indigenous available N reduced apparent N recovery, and agronomic and physiological N efficiencies independent of treatment. Also, P and K PEs decreased with increasing indigenous supply. Delaying weeding beyond recommended time, in interaction with indigenous N supply, decreased agronomic N efficiency, but increased PE of N. Interaction between P rate and timing reduced its PE; K rate and weeding time interaction reduced its PE. The decrease in efficiencies at high indigenous supply and delayed weeding indicates a need for site-specific fertilisation strategies based on naturally available nutrient levels and proper weeding. Weeding and fertilisation timing directly affect nutrient use efficiency, and therefore, fertiliser use efficiency in rice production systems.