Availability of phosphorus by maize crop in crop-livestock integration system

Abstract

The objectives of this study were to assess the concentrations of available P extracted using the Mehlich-1 (M1), ion exchange resin (IER) and modified Morgan (MM) methods in different soil layers after 36 months of experimentation with the application of phosphates in a crop-livestock integration system (CLIS). Moreover, this study aimed to assess which extraction method provides the best correlation of P concentrations with the maize crop attributes. The treatments consisted of applying annual doses (0, 60, 120 and 180 kg ha^-1 of P₂O₅) on the soil surface of the total area during the sowing of winter forage crops (black oats or annual ryegrass) in the form of triple superphosphate (TSP), rock phosphate (RP) or magnesium thermophosphate (MTP). After 36 months of experimentation (April 2012) and following the maize harvest, soil samples were collected from the 0-5, 5-10, 10-15 and 15-20 cm layers to assess the concentrations of available P using the M1, IER and MM extraction methods. The dry matter yield (DMY), the grain yield (GY), the accumulation of phosphorus in the dry matter (P-DM) and the export of phosphorus (P-Ex) were quantified in maize following the harvest to predict the effects of the different extraction methods on P availability. The IER method extracted greater amounts of available P, followed by the M1 and MM extractions. The treatments that included the application of TSP and either the M1 or IER extractions had similar efficacies when correlated with the DMY, GY, P-DM and P-Ex attributes of maize. The P extracted by the ion exchange resin was most correlated with P-DM and P-Ex for the water-insoluble P sources (RP and MTP). The MM solution was ineffective at predicting the bioavailability of P for maize grown in a soil with high clay content and iron and aluminum oxides that had received varying doses and sources of P applications in a CLIS.