Wheat, canola and grain legume access to soil phosphorus fractions differs in soils with contrasting phosphorus dynamics

Abstract

Despite the high phosphorus (P) mobilizing capacity of many legumes, recent studies have found that, at least in calcareous soils, wheat is also able to access insoluble P fractions through yet unknown mechanism(s). We hypothesized that insoluble P fractions may be more available to non-legume plants in alkaline soils due to increased dissolution of the dominant calcium(Ca)-P pool into depleted labile P pools, whereas non-legumes may have limited access to insoluble P fractions in iron(Fe)-and aluminium (Al)-P dominated acid soils. Four crop species (faba bean, chickpea, wheat and canola) were grown on two acid and one alkaline soil under glasshouse conditions to examine rhizosphere processes and soil P fractions accessed. While all species generally depleted the H 2 O-soluble inorganic P (water Pi) pool in all soils, there was no net depletion of the labile NaHCO 3 -extractable inorganic P fraction (NaHCO 3 Pi) by any species in any soil. The NaOH-extractable P fraction (NaOH Pi) in the alkaline soil was the only non-labile Pi fraction depleted by all crops (particularly canola), possibly due to increases in rhizosphere pH. Chickpea mobilized the insoluble HCl Pi and residual P fractions; however, rhizosphere pH and carboxylate exudation could not fully explain all of the observed Pi depletion in each soil. All organic P fractions appeared highly recalcitrant, with the exception of some depletion of the NaHCO 3 Po fraction by faba bean in the acid soils. Chickpea and faba bean did not show a higher capacity than wheat or canola to mobilize insoluble P pools across all soil types, and the availability of various P fractions to legume and non-legume crops differed in soils with contrasting P dynamics.

Phosphorus fractions depletion in the rhizosphere of young and adult maize and oilseed rape plants

“…Already in 1971 Riley and Barber (1971) but even more recently Rose et al (2010) obtained rhizosphere soil by separating the soil adhering to roots that had been separated carefully from the bulk soil. The soil obtained in this way is partly actual rhizophere soil but will also contain some bulk soil.…”

Enhanced biological N2 fixation and yield of faba bean (Vicia faba L.) in an acid soil following biochar addition: dissection of causal mechanisms

“…Declining levels of organic matter in soils results in a reduced capacity to supply N for crop growth (Dalal and Mayer 1986) and, as a result, crop, fodder and shrub legumes continue to play a critical role in maintaining or improving soil N status (Peoples et al 1995). In addition to fixing N, legumes contribute to soil carbon (C) via release of root exudates and tissue residues, act as a disease-and pest-breaks in cereal-based rotations, and can enhance the phosphorus (P) nutrition of subsequent crops through undefined mechanisms (Karpenstein-Machan and Stuelpnagel 2000; Nuruzzaman et al 2005;Rose et al 2010).…”

Strategies and agronomic interventions to improve the phosphorus-use efficiency of farming systems

“…Limited work to date has shown that organic anion exudation and P uptake by chickpea and lupin was variable across a range of low P soils from Western Australia (Veneklaas et al 2003). In another study and contrary to expectation, faba bean and chickpea grown in other low-P soils did not mobilise P from sparingly-soluble soil pools, pointing to a need for a better understanding of how and when these crops gain access to sparingly-available P (Rose et al 2010a, b).…”

“…However, farming systems that have lower P-fertiliser requirements because they export less P in products are also possible (e.g. Rose et al 2010a;.…”