Given current high fertilizer prices, producers are looking for ways to reduce fertilizer input costs wherever possible. It is now very critical to make sure you are receiving the maximum return possible for your fertilizer investment. Those of us in extension have been receiving many questions regarding fertilizer use strategies for many crops, particularly those that have high fertilizer requirements. The common question we are being asked by producers is how much I can reduce my application rates. There are many factors that come into play when trying to answer that question. In true extension fashion the answer is “It depends.” Let’s look at some of the factors that weigh into the decision regarding fertilizer application rates.
Have you had a soil test done within the past 3 years? To accurately assess the current fertility status of your soil you really need to know the current nutrient levels in the soil. Think of the fertility levels like the amount of gas in your truck’s gas tank. Suppose I told you to jump into a truck and drive from Exit 1 to Exit 7 on the turnpike with two conditions. The first condition was the fuel gauge was covered so you can’t see it, the second was you can’t stop for gas along the way. Under these conditions you really have no idea if you will be successful reaching your destination. The same can be said about reaching a crop yield goal. If you have no idea what the nutrient levels are in the soil, you don’t know if you will reach your yield goal. You may be under applying fertilizer, or worse yet in this time of high fertilizer prices you may be over applying fertilizer without any yield benefit. The small investment in a soil test may save you significant amounts of money, basically paying for itself.
If you have had your soil tested, check the P and K levels in the test report. Are the levels in the optimum or above optimum level? With high fertilizer prices you may want to consider deviating from a build and maintain approach to soil fertility where we recommend P and K crop removal applications. consider spoon-feeding the crop just what it will need to maintain itself and save the nutrient building for another year. Soils that are in the optimum range should have enough of these nutrients for the year without sacrificing yield. Keep in mind this approach should be considered for no more than a season or two, hopefully enough time for fertilizer prices to somewhat stabilize. This approach does not lend itself to long term stability. Soil P reserves could hold out for several years, while soil K reserves tend to be depleted faster, especially where forage crops are harvested. Be careful with a double crop small grain and soybean rotation where the straw is baled. This rotation can lead to depletion of soil K reserves more quickly, particularly in the sandier soils of the southern portion of the state.
Nitrogen management practices should consider what the most economical rate of N fertilizer is. This will be the rate of N where the crop yield gained from an additional unit of N fertilizer applied is equal in value to the cost of the N fertilizer. We need to remember that crop yields respond with diminishing returns to increasing rates of nitrogen. In simpler terms, are you getting a profitable return on your additional fertilizer investment? Make sure that additional yield is not costing you money. Are you making split applications of Nitrogen fertilizer when possible? This strategy can be especially useful where soils have a sandier texture such as in the southern portion of the state. Front loading nitrogen applications can be riskier if we should experience a wet spring which could promote leaching. It is critical to use best management practices for nitrogen fertilizer application timing and placement. The correct rate should be determined using a realistic estimate of yield potential. If you are fertilizing based on an estimate of 200 bushels per acre corn and the field never exceeds 180 bushels your optimism could be costing you money. Also, if using Urea N remember it is prone to volatilization losses when left on the soil surface unless it is treated with a urease inhibitor or incorporated into the soil with a timely rainfall or irrigation. Manure is a valuable source of N, P, and K. If you have access to manure incorporate it into your soil fertility program where appropriate. Hopefully, the information provided will assist with management decisions about the rate, source, timing, and application methods of fertilizers to maintain crop yields while reducing costs on fertilizers this year.