Selective application of farmyard manure to phosphorus-deficient soils improves rice yields in sub-Saharan Africa: Insights from field trials and literature review

Context

Farmyard manure (FYM) is an important nutrient resource for smallholder rice farmers in sub-Saharan Africa (SSA). However, optimal strategies for consecutive FYM application or its combination with mineral fertilizers on low-nutrient soils remain unclear.

Objective

This study evaluates the effectiveness of FYM in enhancing rice yields on phosphorus (P)-deficient soils in SSA.

Methods

The study comprises multi-year field trials and a supporting literature review. Field trials at four sites with varying soil P availability in Madagascar's central highlands tested FYM’s effectiveness under different fertilizer management; no fertilizer, nitrogen (N) only, P only and combined NP. Additionally, a literature review of FYM trials was also performed to compared yield responses to FYM on low- and high-P soils in SSA.

Results

In P-deficient soils with baseline yields of 1.8 t·ha⁻¹, application of FYM alone (8–12 t·ha⁻¹) increased rice yields by approximately 1.5 t·ha⁻¹ on average over four seasons—comparable to the yield gain of 2.0 t·ha⁻¹ achieved with inorganic NP fertilizers alone. Conversely, the impact of FYM was reduced in P-sufficient soils or when P fertilizer was supplied. In cool regions, where delayed flowering from P deficiency increases cold stress risk, FYM shortened the days to flowering, synchronizing the flowering period within optimal temperatures. Moreover, yield benefits further improved with repeated FYM application, particularly when combined with N fertilizer at P-deficient soils.

Conclusions

Field trials demonstrate the effectiveness of FYM for boosting yields, particularly under P-deficient conditions in Madagascar and the review suggests these finding apply broadly across SSA.

Implications

These findings highlight the need for site-specific FYM management. Due to the variability of soil P availability in SSA, precise soil P diagnostics are essential to optimize FYM use for yield enhancement.