Abstract
ABSTRACT: Investment in soil phosphorus (P) capital in the tropics is often constrained by poor availability of mineral fertiliser to small-scale farmers. Consequently, new sustainable agricultural cropping strategies are required to maintain fertility and maximise crop yields. The co-application of Tithonia diversifolia (Tithonia) green manure and mineral fertiliser (KH2PO4) together (integrated nutrient management) in comparison to the addition of one or the other alone has been hypothesized to promote crop P uptake. The aim of this study was to critically evaluate the benefits of integrated nutrient management practices in laboratory experiments. Wheat was grown as a test crop in microcosms to which either 32P-labelled mineral fertiliser or 33P-labelled Tithonia was added either singly or in combination. Exclusion meshes were used to determine the role of arbuscular mycorrhizal (AM) fungi in P uptake from the different P sources. The rate of uptake of both 32P and 33P by mycorrhizas was similar, and the rate of mycorrhizal P capture was comparable to that of roots. Generally, there was little difference in wheat P acquisition under integrated nutrient management treatments in comparison to P acquisition from 32P-mineral fertiliser or the addition of 33P-Tithonia alone. Overall, Tithonia residues were not very effective in supplying P to wheat over a short time evaluation period, suggesting that mineral fertilisers will still be required to satisfy crop demand.
Highlights
Low-input agricultural systems typically result in low productivity and farm poverty, largely due to soil fertility constraints and including limited access to land, low financial capital, high vulnerability and low market participation (Kuivanen et al, 2016; Jama et al, 2000)
Both shoot and root dry matter weight (DW) were affected by the supplement of both Pi and Po sources in sub-compartments (Figure 2)
There was no effect on the amount of P uptake from the sub-compartment by wheat, or on the associated growth parameters arising from the exclusion of roots from the labelled sub-compartments
Summary
Low-input agricultural systems typically result in low productivity and farm poverty, largely due to soil fertility constraints and including limited access to land, low financial capital, high vulnerability and low market participation (Kuivanen et al, 2016; Jama et al, 2000). Large amounts of P fertiliser in tropical soils are needed to supply P demand (Roy et al, 2016), and the combined input of fertilisers, good soil/crop management and green manure plants can render degraded soils highly productive (García-González et al, 2018). It has long been recognised that the addition of OM to soils can increase plant P availability (Kolawole et al, 2013). Organic anions added directly via OM or formed during its mineralisation may become adsorbed to the soil sorption sites thereby reducing the P sorptivity of the soil (Iyamuremye et al, 1996), and increasing the availability of P for crops
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