Abstract
Phosphorus (P) is one of the most limiting macronutrients for crop productivity and P deficiency is a common phenomenon in agricultural soils worldwide. Despite long-term application of phosphate fertilizers to increase crop yields, P availability is often low, due to the high affinity of phosphate for the soil solid phase. It has been suggested that the accumulated (surplus) P in agricultural soils is sufficient to sustain crop yields worldwide for about 100years. In this paper, we try to clear up the potential for making use of legacy P in soils for crop growth potentially alleviating the global P resource shortage. Specifically, we try to clear up the potential of soil “P activators” for releasing fixed P. P activators accelerate and strengthen process which transform P into bio-available forms via a range of chemical reactions and biological interactions. They include phosphate solubilizing microorganisms, phosphatase enzymes and enzyme activators, low molecular weight organic acids, humic acids, lignin, crop residues, biochar and zeolites. Although reported performance is variable, there is growing evidence that P activators can promote the release of phosphate from soil and, hence, have potential for mitigating the impending global P crisis. Further basic and applied research is required to better understand the mechanisms of interaction of P activators with natural soils and to maximize activator efficacy.
Highlights
The aims of this review are to clarify our current understanding of the cycling and transformation of legacy P in agricultural soils and to present findings from the published literature about so-called “P activators”
We evaluate the contribution of P activators to soil legacy P availability, assess the advantages and disadvantages of different P activator classes and summarize the key mechanisms involved
It has been estimated that inoculation with arbuscular mycorrhizal fungi (AMF) might result in a reduction of approximately 80% of the recommended phosphate fertilizer rate under certain conditions, with similar crop yields (Liu et al, 2016)
Summary
Phosphorus (P) is a major limiting nutrient for crop growth in many agroecosystems and is indispensable in several physiological and biochemical processes (Simpson et al, 2011). P limitations are a major productivity constraint in many natural (Augustine et al, 2003) and managed (Bünemann et al, 2011) grassland systems. Other constraints may limit productivity, soil P often needs to be replenished repeatedly to satisfy plant demand, in part because it is quickly removed from the dissolved (plant available) form by sorption, precipitation and microbial immobilization (Roberts and Johnston, 2015) or is lost through surface runoff (in particulate and dissolved forms), subsurface flow (leaching and throughflow via the soil matrix and macropores), drain flow and even groundwater which may accelerate the eutrophication of P sensitive waters (Heathwaite and Dils, 2000; Hively et al, 2006; Holman et al, 2008; Sims et al, 1998)
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