Assessment of phosphorus availability in soil cultivated with ruzigrass

Abstract

Growing ruzigrass (Urochloa ruziziensis) in crop rotation systems has been suggested as a strategy to increase soil phosphorus (P) cycling and P availability. However, despite increased P lability shown in routine soil analysis, decreased grain yields of crops grown after ruzigrass have been observed. The objective of this study was to evaluate soil P availability to maize (Zea mays) in low or high-P soil cropped to ruzigrass. Soil P lability was evaluated using Hedley fractionation and pearl resin extractions, and P desorption/adsorption was assessed by isothermal titration calorimetry (ITC). Phosphorus changes in soil-P fractions in the maize rhizosphere were studied in a greenhouse experiment. Growing ruzigrass resulted in higher resin-extractable P and soil organic matter (SOM) contents than fallow. However, in soil cropped with ruzigrass, maize P uptake and P desorption were lower, and P adsorption to soil was higher than soil under fallow. In general, organic P bound to Fe and Al was non-available. Phosphorus sorption as assessed with ITC was a better indicator of P bioavailability to maize than pearl resin and Hedley fractionation, and suggested that P was less bioavailable after ruzigrass due to increased SOM, which resulted in the formation of metal phytate and more effective organo-metal sites for ligand exchange. Greater P solubility and availability in fallowed soil appeared to be partly due to the dissolution of Carelated P, greater P desorption, and less potential for P adsorption. Isothermal titration calorimetry is a useful semi-quantitative tool for understanding P sorption behavior.

Nanophosphorus Fertilizer Stimulates Growth and Photosynthetic Activity and Improves P Status in Rice

“…In plants, P is an essential element required for development and reproduction, and it is one of the main components of the fertilizers necessary to sustain modern agriculture. In soils, the concentration of inorganic P (available to plants) ranges from 35 to 70% of the total P. This form of P shows low diffusion and high fixation rates in soils through ligand exchange by 1 : 1 clay minerals, Fe and Al oxides and hydroxides, and is thus precipitated as Fe, Al, and Ca phosphates [11,12]. Additionally, phosphate fertilizers are obtained from phosphoric rock, a nonrenewable resource, and whose reserves are running out [13].…”

Can tropical grasses grown as cover crops improve soil phosphorus availability?

“…According to Almeida et al . (), ruzi grass should result in the accumulation of recalcitrant P o forms in soil. In the present study, it was observed that tropical grasses and microorganisms may expose recalcitrant P o forms, resulting in increased concentration of these P o forms, and showing that a great improvement in P availability may depend not only on the release of P from grass residues, but also on the mineralization of recalcitrant P o forms such as phytate.…”

“…Despite the fact that residual–P may be considered as a combination of inorganic and organic stable P forms strongly associated with the mineral fraction, P remobilization was mainly observed in residual–P due to grass cultivation. Several studies have shown that residual–P can be depleted by plant uptake (Almeida et al ., ).…”

“…A closer look into P dynamics in the rhizosphere of tropical grasses revealed a depletion of labile P forms, which may result in higher P adsorption capacity and lower soil P desorption, as observed by Almeida et al . () and also here through a lower P E concentration in low‐P soil. According to Almeida et al .…”

“…The strong soil P adsorption capacity by Fe and Al oxides in highly weathered soils results in lower soil P solution concentration and reduces the P diffusion flux (Raghothama & Karthikeyan, ). However, growing adapted species in low‐P soils may affect the P resupply by the soil solid phase due to changes in the soil P pools (Almeida et al ., ).…”