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Impact of green manure crop species on rhizosphere soil phosphorus

Phuong Nguyen , Richard McDowell , Leo Condron

Abstract

Context: Green manure crops have the potential to improve phosphorus (P) use efficiency in agroecosystems by enhancing the mobilisation of soil P reserves. Aims: This study investigated and quantified the short-term mobilisation and uptake of soil P in the rhizosphere of several green manure crops. Methods: Five plant species/varieties (Lupinus angustifolius (lupin - early and late flowering varieties), Pisum sativum (pea), Cicer Arietinum (chickpea), and Fagopyrum escolentum (buckwheat)) were grown in two contrasting soils, pumice (1100 mg total P kg-1, anion storage capacity 39%), and volcanic ash (2800 mg total P kg-1, anion storage capacity 95%) in rhizosphere study containers. After 40 days, rhizosphere (0-5 mm) and bulk (>5 mm) soils were sampled and subjected to P fractionation. Organic anions were collected from the rhizoplane using an anion exchange membrane. Key results: Dry matter yield, P uptake and rhizoplane organic anion exudation were affected by plant species, soil type and their interaction. Rhizosphere P changes of labile inorganic organic P, and stable inorganic P were influenced by plant species and soil type, while moderately labile inorganic P was affected by only plant species. Interaction between plant species and soil type had no effect on rhizosphere P depletion or accumulation. The quantities and composition of organic anions determined in rhizoplane exudates were highly variable (0.01-0.1 µmol cm-2 h-1). However, significant correlations were observed between the depletion of moderately labile and stable soil inorganic P and concentrations of malate in exudates. Conclusions: The findings of this study clearly demonstrated the capacity of green manure crops (esp. blue lupin) to rapidly mobilise and deplete different forms of soil P across the soil types.

SR22257  Accepted 13 May 2024

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