Phosphorus availability and dynamics in soil affected by long-term ruzigrass cover crop

Danilo S Almeida; Daniel Menezes-Blackburn; Hao Zhang; Philip M Haygarth; Ciro A Rosolem

doi:10.1016/j.geoderma.2018.09.056

Phosphorus availability and dynamics in soil affected by long-term ruzigrass cover crop

Geoderma. 2019 Mar 1:337:434-443. doi: 10.1016/j.geoderma.2018.09.056.

Authors

Danilo S Almeida¹, Daniel Menezes-Blackburn^{2

3}, Hao Zhang², Philip M Haygarth², Ciro A Rosolem¹

Affiliations

¹ São Paulo State University, College of Agricultural Sciences, Department of Crop Science, Botucatu 18610-307, Brazil.
² Lancaster University, Lancaster Environment Centre, Lancaster LA1 4YQ, UK.
³ Sultan Qaboos University, Water and Agricultural Engineering, College of Agricultural and Marine Sciences, Department of Soils, PO Box 34, Al-khod 123, Oman.

Abstract

The use of grasses as cover crops in the off-season of cash crops under no-till has been largely adopted. However, soil phosphorus (P) uptake was previously shown to be reduced when ruzigrass is introduced in the rotation, affecting the viability and sustainability of this cropping system. The objective of this study was to assess the effect of ruzigrass on soil P availability and desorption kinetics under different P fertilizer application rates. A long-term field experiment where soybean (Glycine max) has been grown in rotation with ruzigrass (Urochloa ruziziensis) or fallow for 10 years, with the application of 0, 13, and 26 kg ha^-1 of P, was evaluated for two consecutive years. Soil P desorption kinetics was assessed using diffusive equilibrium (DET) and gradient in thin films (DGT) techniques, as well as the DGT-induced fluxes in soils model (DIFS). Microbial biomass P (MBP) was assessed to verify if soil solution P (P_DET) was reduced due to immobilization by microorganisms. Ruzigrass reduced MBP and P_DET especially when P fertilizer was applied. The concentration of labile P (P_DGT) was also lower after ruzigrass than in fallow. The soil ability to resupply P to soil solution was lower after ruzigrass regardless of P rates due to a slower desorption in response to the perturbation imposed by DGT. Growing ruzigrass as cover crop in the soybean off-season decreases soil P availability regardless of P fertilizer application rates by fundamentally reducing P mobility and P resupply from soil solid phase into soil solution.

Keywords: Crop rotation; DET; DET, diffusive equilibrium in thin films; DGT; DGT, diffusive gradient in thin films; DIFS, DGT induced fluxes in soils and sediments model; Fallow; Kd, equilibrium distribution coefficient between solid phase and soil solution; MBP, microbial biomass phosphorus; PDET, soil solution P concentration measured by DET; PDGT, DGT measured time average P concentration at the interface of soil and DGT device; PE, effective P concentration; Presin, soil phosphorus extractable with anion exchange pearl resin; R, ratio of PDGT and PDET; R-Rdiff, relative resupply from solid phase; Rdiff, ratio of PDGT to PE in the case where there is no P resupply from the solid phase; SOM, soil organic matter; Tc, response time of (de)sorption process; Urochloa ruziziensis; k−1, desorption rate constant.