Tight budgets, fertility management

URBANA, Ill. — Balancing fertility input costs in times of lower commodity prices can be a conundrum for farmers.

“In general, setting yourself up by having a recent soil test pays dividends for understanding what are the potentials for prioritizing specific nutrients, cutting back, or looking at different fertilizer strategies,” John Jones, University of Illinois associate professor of agronomy and soil fertility Extension specialist, said in the latest Illinois Nutrient Loss Reduction Podcast.

“Phosphorous fertilizer prices have been staying fairly strong. Potassium may be fluctuating a little bit more, similar to nitrogen. Using the most recent soil test is really valuable.”

However, one factor to consider is the soil tests fertilizer recommendations are based on this fall may be based on tests conducted in the fall of 2022, for example.

“If you had dry conditions that year, it’s important to really put that into context, as well, because we may have two soil test years in a row if you’re skipping every other year or going every four years that you only have dry conditions for soil test data. That can bias numbers, specifically in potassium and pH. It shouldn’t affect phosphorous as much,” Jones said.

“When thinking about prioritizing nutrients, you can look at potentially only applying crop removal or a little under crop removal if you’re getting into a situation where you don’t need to build because your soil test levels are high enough for P and K. So, that’s an opportunity that usually comes.

“One of the important concepts is that even though we want to consider the prevailing yield of a given field or system when planning for removal for, let’s say, next year, depending on what seasonality you’re using for your P and K application, it’s important to note that even though the net returns to P and K are going to be lower and a little unpredictable at some low prices, the agronomic optimum soil test levels doesn’t change.

“So, if you’re focusing on obtaining or maintaining those agronomic optimum test levels, that also gives you a little bit of buffer when you have a need to back down on some inputs.”

Jones does not suggest the avoidance of soil tests during dry years. Even though it’s dry overall, if there was some rain to provide consistent soil moisture, the samples would “be just fine and probably provide adequate results,” he said.

Soil tests can also be delayed until spring.

“In most recent years we have had some dry periods into September, October, November, and the soil moisture is a little more consistent in the spring,” Jones said.

“So, there are options and that’s actually part of my ongoing research to look at providing fall soil sample interpretations and spring soil sample interpretations. But, in general, if you can get out there and grab samples, especially if you’re dealing with a four-year time span since your last soil test, it will have benefits picking up those areas that might not need fertilization for P and K.”

Nitrogen

Nitrogen recommendations in a lower commodity price scenario were also addressed in the podcast, hosted by Todd Gleason, media communications specialist, and produced by Rachel Curry, Nicole Haverback and Emma Eldridge, all of U of I Extension.

At press time, December 2024 corn was in the ballpark of $4.26 to $4.32 per bushel, while anhydrous was just below 50 cents per pound.

“When we think about the process of looking at an agronomic response to nitrogen and adjusting it for price considerations, which is what the (maximum return to nitrogen) process does, look at that ratio of prices between nitrogen and corn specifically that put you within that 0.1 ratio,” Jones said.

“Generally it’s kind of the middle of the road for the ratios that we usually put out from the MRTN calculator.”

When plugging information into the MRTN calculator, there are important factors to consider, including the specific region and what the previous year’s crop was which affects the next crop’s nitrogen demand.

“Those are two things that are baked into what we need to delineate between looking at summarizing nitrogen corn yield loss, but especially the corn price and nitrogen price are something you also will add,” Jones said.

“Then there’s a context essentially that considers those prices. For example, if we’re looking at corn a little over $4 a bushel, we’re looking at 40-cent to 50-cent nitrogen, generally in northern Illinois that should give you around 195 to 205 pounds of nitrogen per acre optimum rate following corn and around 165 to 178 following soybeans.

“That’s going to be a little different in central Illinois where it’s around 191 to 200 pounds of nitrogen per acre following corn and 173 to 181 following soybeans. Those numbers were updated from the 2023 growing season.”

The total pounds of nitrogen recommended by the MRTN calculator is a total of what should be applied overall within those data sets, whether it is split in the fall, spring or in-season or applied all at once.