Is the Lack of Response of Maize to Fertilization in Soils with Low Bray1-P Related to Labile Organic Phosphorus?

The usual soil test phosphorus (P) neglects the P supply from labile organic P (Po) fractions, which could explain the nonresponse of maize (Zea mays L.) in sites with soil P testing below the critical level. We aim to determine Po and inorganic P (Pi) in NaHCO3 extracts and in the coarse soil fraction (hereinafter, CF) from responsive and nonresponsive sites to P fertilization in maize. We then compare the classification errors of the Cate and Nelson method by comparing the relationship between maize relative yield and the soil Bray1-P concentration vs. the new proposed indices. The study included responsive and nonresponsive sites to P fertilization carried out across the Pampas Region in the center-east of Argentina. Treatments included four P fertilization rates: 0, 12, 24, and 36 kg P ha(-1). The experiments were laid out in a randomized complete block design with three replicates. We determined Bray1-P, Pi, and Po in NaHCO3 extracts and in the coarse soil fraction. Sites non-responsive to P fertilization and with Bray1-P concentrations below the critical level showed 70% more Po in the coarse soil fraction (Po-CF) than sites with high crop response and similar Bray1-P level. However, Po-Bic alone did not improve the relationship with maize relative yield. Po-CF and Bray1-P included in a soil integrative P index improved the prediction of crop response to P fertilization and reduced classification errors, which suggests that Po-CF is a source of available P for the crops. The novelty reported in this study was to demonstrate the organic P contribution to relative yield by including it into an integrative soil testing. We find that nonresponsive sites to P fertilization, with low Bray1-P, were correctly classified when including Po-CF in a new soil test P. Improvements in the P fertilization diagnostic prescription tool contribute to an increase in economic profit and reduce environmental impact.

Automated summary

This study investigates the impact of different soil phosphorus levels on maize yield and finds that labile organic phosphorus in the coarse soil fraction could be a potential source of available phosphorus for crops, leading to improved prediction of crop response to phosphorus fertilization and reduced classification errors when included in a soil testing regimen.