Pronounced effect of farmyard manure application on P availability to rice for paddy soils with low total C and low pH in the central highlands of Madagascar

T Rakotoson,Y Tsujimoto

doi:10.1080/1343943x.2020.1740601

Abstract

ABSTRACT Farmyard manure (FYM) – mixtures of animal droppings, crop residues, and fodder that are piled nearby homesteads – is a major nutrient source for smallholder farmers in Sub-Saharan Africa. However, its application effect has not been fully understood on typical P-deficient soils in tropics and in particular under anaerobic conditions. This study assessed the effect of FYM on irrigated rice in relation to soil properties – oxalate-extractable P (POx), pH, and total C (TotC) – that are important indicators of soil P deficiency in the region. The first pot experiment was conducted with a factorial combination of FYM (0 and 20 g kg–1) and mineral P (0 and 100 mg kg–1) applications using six paddy soils differing in the aforementioned soil properties. The second pot experiment was conducted in a factorial combination of FYM and mineral P using the isotope dilution technique. In both experiments, the effect of FYM application on biomass and P uptake of rice per P applied was nearly equivalent to that of mineral P and was greater in soils with lower TotC and lower pH with negligible effect of POx. The isotope tracing suggested that the FYM application might increase rice P uptake by solubilizing non-labile P pools in soils while mineral P was directly used by rice from labile P pools. The results indicated that the FYM should be most effective in soils with low TotC and low pH, and its application could enable the use of insoluble P pools in soils and enhance P uptake of rice under P-deficient and anaerobic conditions.

Highlights

Rice is the second largest source of caloric intake after maize (Zea mays) in Sub-Saharan Africa (SSA, hereafter)
The selected six fields were continuously under rice cultivation once a year from Nov–Dec to Apr– May with or without off-season upland crops in rotation. During this extensive soil survey, we interviewed to 42 farmers using farmyard manure (FYM) and identified that (1) the FYM was commonly produced in a pile nearby the homesteads by mixing organic materials and soils and left for 5–6 months during the off-season before rice cultivation and (2) cow dung was the most commonly used organic material followed by rice straw for developing FYM in the region
Results of Exp.1 confirmed that the effect of FYM application on both P uptake and biomass production of rice largely differed among soils under flooded conditions

Summary

Introduction

Rice is the second largest source of caloric intake after maize (Zea mays) in Sub-Saharan Africa (SSA, hereafter). Rice yields in SSA have remained low because of several biotic and abiotic stresses Among these various stresses, P deficiency is a major constraint for rice production in highly weathered soils in SSA (Dogbe et al, 2015; Saito et al, 2019). Our previous on-farm experiments demonstrated that the yield gap between P-fertilized and non-P-fertilized treatments could reach up to 2.5 t ha–1 in the central highlands of Madagascar (Andriamananjara et al, 2016). To alleviate this P-deficient stress in highly weathered soils, more effective use of organic matter (OM) such as farmyard manure (FYM) is expected because OM is the major available nutrient source for smallholder farmers. A recent survey showed that 16.3% of agricultural households use organic fertilizer, mainly FYM, whereas only 0.5% use mineral fertilizer in the central highlands of Madagascar (Tsujimoto et al, 2019)

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Results

Discussion

Conclusion