Does Planter Phosphorus Pay

Does Planter Phosphorus Pay
Phosphorus (P) is often applied at corn planting to improve crop yields. However, does it always pay for itself? Ohio State University Extension Research (E-Fields) investigated where applying P at planting is worthwhile.

Soil testing is critical. Past soil test recommendations were based upon Bray P1 but now they use Melich P. Bost methods are very similar. Under Bray P1, 15-30 Parts Per Million (ppm) P was considered good for attaining optimal crop yields on corn and soybeans. Under Melich P, 20-40 PPM for P is considered good. Most soils have a lot of tied up P but only the P that is plant available is considered usable. Only about 25-30% of the P that is applied that year is actually used by the plant. The other 70-75% become available in following years, depending on weather, soil type, humus levels etc. Cover crops and crop residue tie up many nutrients short-term, but they come available when they decompose. Residue from crops or cover crops are good P sources.

From 2016-2018, OSU Extension did replicated (3X) plots, 40 feet wide to test whether starter P was economical to apply in Fulton county, Ohio on conventional tilled fields. In all cases, soil test P was either in a good range (20-40 ppm P Melich) or higher (50-60 ppm P Melich). Two corn varieties were tested at each site (Pioneer, Dekalb). The control was zero P compared to 28# P/A applied at planting. On 6 tests, starter P had a significant yield difference 17% of the time (1/6 tests). Aerial photos were taken in July each year, and there was no significant difference in corn leaf color observed. Tissue tests were taken with no significant differences. In 2018, no starter P yielded 209 bu/A and the starter P (28 #/Acre) yielded 215 for a 6-bushel difference which was significant. The authors concluded that as soil test P approaches 15 ppm P (Bray P1) or 28 ppm P (Melich), then corn varieties will likely exhibit a greater response to P. It is important that farmers soil test each field and know what their soil test P numbers are to see if starter P is needed.

Henry County (Napoleon) in 2023 did two starter P tests using No starter P compared to 10 gallons of 10-34-0 on no-till fields. Soil test P (Melich P) was again adequate. The Starter P cost $46.50 to apply and yielded 4.6 bushels. Based on $4.50 a bushel corn and $800/ton for 10-34-0, the starter P plots lost about $25/acre. Another plot in Fulton county had similar results but the no starter P actually yielded 1 bushel more per acre (no significant difference). However, they only applied 5 gallons of 10-34-0 which cost $23.25/Acre. In no-till systems, especially with cover crops, good soil health due to beneficial microbes especially mycorrhizae fungi can supply 6X more P to the corn roots than the corn roots can themselves. The fungi stretch out 6-18 inches away from the roots, so they can gather in more P which is transported back to the plant. It’s not only P but also many other nutrients, micro-nutrients, and even water. In dry years, these beneficial fungus may help reduce drought stress.

In Lucas county, in 2020-2021, a farmer wanted to know if biologicals could help the plant attain more P. This farmer had relatively higher soil test P levels (56-62 ppm Melich P). He wanted to compare Zypro which is a biological product designed to optimize microbial mineralization to make P more plant available. He also wanted to try Nutrasyst, which is a blend of organic acids (fulvic, humic acids) that improve fertilizer uptake. He compared 28% UAN as a control to 28% UAN plus Zypro. The result was 8 bushels less corn with the Zypro added. He also compared a starter (control) to a starter fertilizer plus Nutrasyst which gained him 10 bushel of corn. There was a noticeable color difference in July in these plots with Nutrasyst plots considerably greener and healthier. The results were all significant. The following year, he dropped the Zypto but tested the Nutrasyst again. Different year, different results. No significant differences and only 3 bushel spread. Early on the Nutrasyst looked slightly better by aerial drone, but with good weather it made no significant difference in yield.

Again, the authors concluded that farmers need to test new products on their farms with their management practices to see if these biological products pay. In good weather years, probably little pay back, but with low soil test P levels and poor weather (too dry, too wet, too cold, too hot), some of these products may be beneficial.