More and more, farmers are looking for help in determining correct nutrient management strategy.
High fertilizer prices and grain market volatility have raised many questions from farmers and agronomists regarding nutrient rate management. Last year, the economics of corn, wheat and soybean production was very good. Fertilizer prices were high but grain prices also were at record highs. Now with grain prices down 40 to 50 percent, growers are looking at crop budgets and asking the question, "What is the right fertilizer program for my farm?" In some situations, farmers may not have the funds to fertilize the crop to optimal levels. Many times, given this situation, farmers are tempted to shift the majority of their fertilizer funds to nitrogen alone. If other nutrients are yield limiting, this strategy may reduce yield and profitability.
Farmers are also looking for help in determining the correct nutrient management strategy. Developing that strategy will be especially challenging. Farmers who tag up with agronomists who follow the basics will be the most successful in creating a nutrient management plan. When visiting with farmers or agronomists, our approach is to focus on the science of soil fertility and crop production to optimize yield and economic return.
Soil testing is the cornerstone of any fertility program. Soil test results help in estimating the availability of nutrients and plant response to applied fertilizer. Having a history of fertility levels of a field can help determine the right rate. It is very important that the soil sample be taken correctly. In order for the sample to be useful, it must be taken so that it is representative of the area being sampled. It also must be accurately taken so the test results can be properly interpreted.
Soil sampling is often the weakest link in the recommendation process. Because of the labor involved in sampling, the farmer or the agronomist will take short cuts that limit the usefulness of the sample. One common source or error is the sampling depth. Proper sampling depth for soil pH, organic matter (OM), phosphorus (P), potassium (K) and zinc (Zn) is the surface 6 to 8 inches, since this is the depth that the soil tests were calibrated for in university research. Sampling deeper or shallower than this will provide misleading results.
For available nitrogen (N), chloride (Cl) and sulfur (S), samples should be collected to 24 inches, since these nutrients are mobile in soils.
Setting a realistic yield goal is important in determining a correct nutrient management plan. Yield goals should be set on a field-by-field basis or for various management zones within a field. There are many opinions on how realistic yield goals should be determined. Some suggest averaging the past five years, excluding atypical low yields caused by factors such as drought or hail, and adding 5 to 10 percent to account for continuous yield improvement. It is important to have realistic, but aggressive yield goals.
Another important step is determining the most limiting nutrients. When faced with limited budgets, growers are often tempted to spend all of their fertilizer dollars on N. The farmer may forget that nutrients often interact to produce a greater crop response than if one nutrient is applied alone. If some other nutrient is yield limiting and not going to be applied, the yield goal should be adjusted to optimize the economic response.
If nutrient rates are reduced below optimum, increasing nutrient efficiency is very important. Consideration of nutrient source, placement and potential loss is key in optimizing yield. Placing nutrients close to the growing plants, especially with immobile nutrients such as P, K and Zn, will be very important if rates and soil test are low. With mobile nutrients, consideration of potential loss should be incorporated in the nutrient management plan. If only a low rate of a needed nutrient on a responsive soil can be afforded, consider banding where the roots can intercept it early in crop development. Using products that stabilize nutrients should also be considered to increase their efficiency.