Assessment of phosphorus availability in soil cultivated with ruzigrass

• Published in: Geoderma Vol. 312; pp. 64 - 73
• Main Authors: Almeida, Danilo S., Penn, Chad J., Rosolem, Ciro A.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.02.2018
• Subjects: adsorption; aluminum; bioavailability; calorimetry; corn; crop rotation; desorption; fallow; fractionation; grain yield; greenhouse experimentation; iron; Isothermal titration calorimetry; ligands; Organic phosphorus; phosphorus; Phosphorus pools; phytic acid; rhizosphere; soil; soil analysis; soil organic matter; solubility; titration; Urochloa ruziziensis; Zea mays; Organic phosphorus; Isothermal titration calorimetry; Phosphorus pools; Urochloa ruziziensis
• ISSN: 0016-7061; 1872-6259
• DOI: 10.1016/j.geoderma.2017.10.003

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 Ca-related P, greater P desorption, and less potential for P adsorption. Isothermal titration calorimetry is a useful semi-quantitative tool for understanding P sorption behavior. •The use of ruzigrass as cover crop may affect soil P availability in the long-term.•Decreased P uptake of maize grown after ruzigrass was observed.•Isothermal titration calorimetry was a useful tool to indicate soil P availability.•Ruzigrass may impact P forms and availability through increasing SOM.