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RALEIGH – Spring is a busy time on the farm with growers preparing equipment, working on lime and fertilizer applications, and making cropping decisions even as commodity prices are fluctuating daily.

Fertilizer prices, nitrogen, phosphorus, and potassium are through the roof this year, unprecedented since around 2008. Lime costs have also increased. Transportation and global supply chain concerns are all factors. How can farmers best manage high-cost nutrient inputs and maximize profitability this year?

It is most important for growers to first spend money on lime to ensure an adequate soil pH of 5.8 to 6.2 for mineral soils planned for corn and soybean production. For cotton, a pH of 6.0 to 6.2 is desired. North Carolina soils are naturally acidic and if not corrected, crop rooting is adversely affected plus availability of major nutrients is negatively impacted, said Dr. David Hardy, chief of soil testing with NCDA&CS.

Given high nitrogen prices, corn acreage may be down, and soybean acreage may be higher than usual. Soybeans fix their own nitrogen from the atmosphere with nitrogen-fixing soil bacteria that form nodules on roots; proper pH is very important for this process that we refer to as nitrogen fixation.

This past year, NCDA&CS soil testing lowered its fertilizer phosphorus recommendations for corn, soybeans, and small grains after careful research and review.
“This was very timely in helping farm profitability and further safeguarding our water resources across the state,” said Agricultural Commissioner Steve Troxler.

In high or very high phosphorus soils, growers who have used starter fertilizers in the past that contain phosphorus such as 19-19-0 should strongly consider switching to using a nitrogen-only starter such as 30-0-0.

“Studies support that much of the benefit of starter fertilizers is from nitrogen alone,” said Deanna Osmond, professor in Crop and Soil Science at N.C. State University. Phosphorus availability is highly controlled by soil pH, so again, liming soils will assure that phosphorus in the soil is available for plant uptake.

Potassium uptake and removal are typically very high in grain crops as compared to phosphorus. Cotton is also a high consumer of potassium.

In 2016 through 2018, NCDA&CS soil testing and N.C. State University conducted corn and soybean research trials at more than 50 locations that validated NCDA&CS soil test recommendations, even in very productive yield environments.

In addition to rate, timing of potassium applications, especially on sandy soils, should be given much thought this year. Our sandy soils have low ability to retain potassium, so applying close to planting or even splitting applications on extremely sandy soils could be beneficial, especially in cotton production.

“Knowing uptake/demand patterns of crops as related to growth stage is important in timing,” said Luke Gatiboni, extension specialist in Crop and Soil Science at N.C. State. Soybeans are late feeders of potassium, even into seed production, so applications may best be made just ahead of planting or even after planting. Corn utilizes potassium much earlier in the vegetative growth stages.

Nitrogen is not analyzed by the NCDA&CS soil testing lab since it is very unstable in our soils. The NCDA&CS soil report does provide a nitrogen recommendation based on studies conducted many decades ago. For a more finely tuned recommendation, growers are encouraged to base their nitrogen recommendations on realistic yields.

Some growers have documented yields through yield monitors. Growers can estimate nitrogen rates on a county-by-county basis for specific soil types at https://realisticyields.ces.ncsu.edu/ .

Research has shown that today’s corn hybrids are much more efficient in converting nitrogen to grain yield than older hybrids grown decades ago. Another important nutrient to ensure is adequate is sulfur, often considered a companion nutrient for nitrogen utilization by the plant.

For growers using private labs with often very high yield goal recommendations, Hardy said, “there is much uncertainty in the soil testing collegial community as to the basis for these recommendations. Neither my soil testing colleagues across the country, nor I have seen data to support these.”

Troxler encourages growers to use NCDA&CS soil test recommendations.

“Our soil test recommendations are tried and true and this is certainly not the year to be rolling the dice expecting high yields by applying excessive fertilizer,” he said.

If you have not soil sampled, the NCDA&CS soil testing lab has excellent turnaround time that is estimated to be about 7 to 10 working days. Yes, planting is just around the corner, but it may be best to wait a few days to determine lime and nutrient needs before just guessing.

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