The use of cover crops in an integrated production system can provide many benefits, including biomass production to increase soil carbon and improve soil health. In addition, some researchers also hypothesize that cover crops may take up P from less available fractions in the soil and recycle it back to the soil through plant residues, resulting in better P use efficiency. However, there is currently limited field data to support this hypothesis and quantify the effects on soybean yields.

Optimum fertility management for new soybean genotypes and yield potential also required continuous evaluation and adjustment of diagnostic tools, including traditional soil tests and tissue analysis as well as novel methods. In addition to improved genotypes, changes in farming practices aiming to increase soil carbon and health can affect nutrient cycling and availability to crops.

Proper phosphorus fertility management can have significant economic and environmental benefits. The expected results from this project can inform soybean producers on the best management options integrating cover crops and fertilizer management to minimize cost, increase yields and reduce environmental risk.

The co-PIs are extension specialists with active programs on soybean production, soil fertility, and soil and water quality. The outcomes from this research will be shared as early and frequently as possible as reliable findings become available. Results will be communicated to Kansas producers and crop advisors in various ways. Information will be disseminated through field days, the regular KSU Soybean Production Schools, extension publications, and the KSU nutrient management webpage. Results of field experiments and any revised recommendations that arise will be summarized and distributed to the public via news releases. Brief articles will be prepared for publication periodically in the Kansas State University Agronomy eUpdates. Results will be shared with county/district extension agents in the state who provide information to soybean growers on a regular basis.

Finally, this work will be completed in close collaboration with the KSU soil testing laboratory. The results will be shared with the KSU soil testing lab and private laboratories that advise Kansas growers each year.

The overall objective of this project is to improve phosphorus (P) management for soybean production in Kansas, increasing yields using improved diagnostic tools and fertilization strategies, and leveraging opportunities for application timing and placement with cover crops in the rotation.

Specific objectives include:
• Determine agronomically efficient and cost-effective P fertilizer application time and placement to maximize soybeans yields.
• Assess the interaction of cover crops ahead of soybean and P availability from the soil fraction and fertilizer application to maximize P use efficiency and reduce environmental losses.
• Evaluate current soil test interpretations for accurate P fertilization rates with increasing soybean yields, including the evaluation of new chemical and biological soil test methods.

Update:
Studies were established at 3 locations during the 2022 season, including deficient and above optimum soil P levels. Soybean showed visual response to the combination of treatments, including fertilizer P application rates and placement as well as the integration of cover crops; this was particularly noticeable early season and affected soil cover and weed control.

The early season data collected for the first year of this project suggest some significant interaction of the three main components of the study (P fertilizer placement, P rate, and cover crops).

Phosphorus is the most limiting nutrient for soybean yields, and also poses a high environmental risk for surface water in Kansas. Integrating fertilizer placement, timing, and cover crops ahead of soybean may increase P use efficiency, soybean yields, and profitability while minimizing losses. Proper management can also improve overall soil health and soil carbon in production systems in the medium and long term.

This project will generate needed, applied knowledge for P management in the field. And the information will be transferred directly to soybean growers and agronomists through extension programs and regular soybean production schools.