|ALMEIDA, DANILO - Sao Paulo State University (UNESP)|
|ROSELEM, CIRO - Sao Paulo State University (UNESP)|
Submitted to: Geoderma
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/5/2017
Publication Date: 2/15/2018
Citation: Almeida, D.S., Penn, C.J., Roselem, C.A. 2018. Assessment of phosphorus availability in soil cultivated with ruzigrass. Geoderma. 312:64-73.
Interpretive Summary: Growing ruzigrass in crop rotations is often encouraged to improve phosphorus (P) availability to plants. However, even though soil tests indicate that soil P should be more plant available after ruzigrass cultization, decreased yields of the crop following ruzigrass is often observed. The objective of this study was to explore how ruzigrass changed soil P forms, and compare this to measured P uptake by corn planted in soil that was previously cultivated with ruzigrass. Isothermal titration calorimetry (ITC) was also used to assess P sorption and desorption mechanisms of P onto soil. Growing corn in soil that was previously cultivated with ruzigrass resulted in less plant uptake of soil P, even though soil extractable P (resin-P) and soil organic matter was higher compared to soils that were not previously cultivated with ruzigrass. The P fractionation test combined with plant uptake indicated that organic P bound to iron and aluminum was non-available, and that this form of P increased from ruzigrass cultivation. The ITC technique indicated that P was less sorbed with greater strength in the ruzigrass cultivated soil, which likely decreased bioavailability to corn. The results of this study indicate that certain types of crop rotations can decrease soil P availability to the following crop. This research has a direct impact on agricultural producers and researchers.
Technical 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 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.