Localized phosphorus application via P-dipping doubles applied P use efficiency and avoids weather-induced stresses for rice production on P-deficient lowlands

Abstract

To achieve higher production with minimal environmental impact in sub-Saharan Africa (SSA), it is crucial to make technical transitions from low-input to nutrient-use-efficient production systems. P-dipping, a localized phosphorus (P) application on seedling roots, is a potential approach to enable such a transition for lowland rice production. However, empirical evidence on the effectiveness of this approach in smallholders’ heterogeneous field conditions is lacking. Therefore, 18 on-farm trials were implemented by applying three P application treatments (zero P; P broadcasting at 13.1 kg P ha−1; P-dipping at 13.1 kg P ha−1) with and without N top-dressing (60 kg N ha−1) under a range of topographic, edaphic, and climatic conditions in the highlands of Madagascar. The P-dipping had consistently greater yields vs. zero P, with an average increase of 1.1 ± 0.7 t ha−1 and 1.8 ± 0.7 t ha−1 under non-N-applied and N-applied conditions, respectively. These yield gains by P-dipping corresponded to substantially high agronomic P-use efficiency (AEP: kg yield gain per kg P applied) of 82 ± 52 kg kg−1 in the non-N-applied plots and 136 ± 51 kg kg−1 in the N-applied plots that were both twice as large as those obtained from P broadcasting. The effect was particularly prominent in fields at high elevation and late-transplanted fields at the low elevation site where P-dipping alleviated not only P deficiency but also late-season low-temperature stress by shortening days to heading. The P-dipping effect was also increased when the fields had erratic water levels after transplanting, which was associated with vigorous initial growth and avoidance of submergence stress. No significant correlations were detected between AEP values and any of the soil properties except for P availability. This study revealed that the effect of P-dipping is consistent in various P-deficient soils and is enhanced by combining with N topdressing and when fields are prone to late-season cold stress or early season submergence stress. The finding of this study provides a practical insight for smallholder rice farmers how and where P fertilizer is effectively applied toward sustainable intensification and resilience to weather-induced stress in SSA.