Soil biological and physical measurements did not improve the predictability of corn response to phosphorus fertilization

Authors: GROEBNER, BEN - South Dakota State University; CLARK, JASON - South Dakota State University; SVEDIN, JEFFREY - Agri Northwest; Ransom, Curtis; CLAY, DAVID - South Dakota State University

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/13/2024
Publication Date: 6/10/2024
Citation: Groebner, B., Clark, J.D., Svedin, J., Ransom, C.J., Clay, D.E. 2024. Soil biological and physical measurements did not improve the predictability of corn response to phosphorus fertilization. Agronomy Journal. 1-12. https://doi.org/10.1002/agj2.21612
DOI: https://doi.org/10.1002/agj2.21612

Interpretive Summary: Farmers growing corn in South Dakota have relied on using soil tests to determine how much phosphorus (P) fertilizer to apply. Phosphorus fertilizer recommendations for corn were developed decades ago based on based on soil test P. These recommendations need to be updated to account for recent changes in farm management practices (e.g., cover crops and newer corn hybrids). The objective of this study was to first evaluate the current P fertilizer recommendations for corn in South Dakota, and second, determine if other soil properties (i.e., soil biological, physical, or chemical) should be considered in the current P fertilizer recommendations for corn. Data for this study was obtained across multiple farmers’ fields and years representing a range of soils and management practices in South Dakota. Results showed that the optimal soil test P critical value for South Dakota should be increased from 16 to 18 mg Olsen-P kg^-1. Efforts to improve the current P fertilizer recommendation by including other soil measurements not effective enough to warrant adjusting the current P fertilizer recommendation. These findings suggest that farmers may be under applying P fertilizer and could increase the probability of maximizing their yields by using an Olsen-P critical value of 18 mg kg^-1. Until additional data can be collected, these results suggest that soil test P is still the most reliable method of determining when additional P fertilizer is required regardless of the management practices being implemented.

Technical Abstract: Including soil health and physical measurements with traditional soil fertility measurements has the potential to improve corn (Zea mays L.) P fertilizer recommendations. The objectives for this study were to 1) evaluate the current South Dakota corn P recommendations and 2) determine the effect of including additional soil health, physical, and chemical measurements on the accuracy of P recommendations. This project was conducted in central and eastern South Dakota from 2019-2022 at 117 experimental areas that varied in management, landform, and soil type. A treatment of 112 kg P2O5 ha^-1 was compared to a control with no P fertilizer. Soil samples (0-15 cm) collected before fertilization were analyzed for soil physical, chemical, and biological parameters. Analysis suggested that the optimal soil test P critical value should be increased from 16 to 18 mg Olsen-P kg^-1. The increase is potentially due to the increased use of conservation tillage practices and new corn hybrids. Below 18 mg Olsen-P kg^-1 the application of P fertilizer increased corn yields by 10% at 78% of sites while above 18 mg Olsen-P kg^-1 P application only increased yield at 38% of the sites. The P recommendation model was not improved by including selected enzymes, permanganate oxidizable C, soil respiration, total C, or total N but was when including pH, soil organic matter, and apparent cation exchange capacity (CECa). Therefore, the use of typical soil fertility measurements without soil physical and biological measurements is the best option for making P fertilizer recommendations in South Dakota.