Tom Kilcer’s online monthly newsletter for February (Advanced Ag Systems Crop Soil News) recently landed in my inbox. Kilcer is a Certified Crop Advisor whom I’ve known for 45 years. The last 10 of those years, I’ve not been shy to ask him questions in the agronomy arena. Both of us are very concerned with helping growers optimize crop production while attempting to rein in runaway fertilizer costs.
Kilcer stated that with the price/supply squeeze becoming tighter during spring fertilizer purchases, particularly this year, farmers must look for options that support high yields while minimizing input costs. He stressed the importance of soil testing to see what is needed in our soils, thus avoiding guessing what they need. Studying soil samples over the past 40 years, he’s observed that fields with regular manure applications tend to test high to very high in phosphorous (P). This is especially true for fields that are daily spread or spread without immediate incorporation. The nitrogen (N) fractions volatilize and are lost while the P mostly remains. Thus, more manure is applied to meet corn’s N needs; as a result, excess P, above and beyond the maximum needs of the crop, accumulates. The high to very high soil test in P means that the odds of getting an economic return on applying starter P is zero. Kilcer stressed P can achieve rapid early growth for high yields but does not guarantee it. If your soil is already high to very high in P, there is no economic return for applying P starters.
With global energy/fertilizer crises still very problematic, I wanted T’s advice, asking him a question specifically addressing N needs: Would it be a good idea, as soon as ground is dry enough to fit the soil and drill a seeding, to plant some clover with oats as a nurse crop? My hope was that the farmer could amass a nice build-up of N in the clover’s noduled root system, then harvest the oat/clover crop as silage or baleage. Then they’d most likely kill any regrowth with herbicide, following taking off the first cutting. He said that there would be a well-yielding first cutting, but that nitrogen-fixing bacteria will not have had any enough time to build up N reserves on the nodule biomass. This N source, had it existed, would have then become available during the following rotation to corn, or the hot climate summer annuals – sorghum, sudangrass (or their hybrids) and millets.
He told me the most effective, and now economical, way to get N to these non-legumes is to inject liquid manure into soil; this procedure minimizes the volatilization of the ammonia fraction of the manure. Equally effective at getting the liquid manure’s N to the next crop in the rotation is the method of broadcasting the slurry on the sod, then lightly disking the slurry in soon after broadcasting it (within an hour). Manure left uncovered for hours or more loses most of its volatile N.
Kilcer told me there are at least two good things resulting from the fertilizer cost crisis. First, many growers are forced to soil test – folks who until recently have been flying blind with their crop recommendations. Second, more and more growers are forced to acknowledge the nutrient values of manure rather than just considering it a waste product needing disposal. Kilcer pointed out that about half of the N in the slurry is in the ammonia (highly available) form; the other half is in the organic (carbon-centered) form, which is slower-releasing. It’s good that the N isn’t all rapidly released.
When asked if corn growers should still use starter fertilizer – when P tests medium to very high – he answered “definitely,” just recommending an N starter. He said cold, wet soil has very slow organic matter breakdown and the crop will respond to N – plus sulfur – in the 2×2 band. Add 30 lbs./acre of N in the band (two inches over, two inches down) to carry the plant well into the end of June, when soils are assured warmth and root systems are big enough to receive manure or side-dressed N. Folks injecting manure and planting over the injection zone have effectively banded fertilizer and more is not needed. Farms rarely have uniform soil tests across all fields. Quoting Kilcer directly, “Utilizing an N (only) starter on high phosphorus-testing fields, and a starter with phosphorus on medium/low P-testing fields, may be a bit of a hassle but it can make a big difference on the cost of the crop you are growing this year. For those with liquid fertilizer systems, having two nurse tanks, one with P and one just N, allows you to make a mix for the field you are planting. It’s not exact, but it will get you the majority of the fertilizer savings.”
The need to soil test is spotlighted by costly soil amendments. Not soil-testing in so-called normal times was a bad idea. Not soil-testing today earns less flattering terms. Testing for nitrates and total N in soil is particularly critical since the current energy-based N costs are so painful. I believe that when soil organic matter (SOM) drops below 4%, soy and corn should not be planted: these two crops, lacking fibrous systems, build soil poorly. Lost SOM means that nitrogen-storing ability is reduced in proportion to the carbon volatilization – think greenhouse gas. Ag lime is too often ignored: the biggest regulator of the return on one’s fertilizer investment is raising the pH up to 6.2 for corn and 7.0 for alfalfa. Proper pH makes the fertilizer most available, making plant growth better able to use it. As the pH drops, fertilizer efficiency drops 30% – 50% in supporting crop yield – spending more, getting less. In the last two years, ag lime costs have gone up less than 10%.