On page 8 of this issue, Dr. Weirich discussed the importance and techniques for collecting a proper soil sample. The next step in developing a nutrient management plan for your farm is interpreting the soil test results.
Soil testing and nutrient management is not an exact science. Do not get lost in the numbers on your soil test report. Instead, pay attention to the soil test ratings or levels of each nutrient. If a nutrient level is very low on the soil test report there is a high probability that a positive yield response will occur from applying that nutrient to the planned crop. Likewise if a nutrient rating on the soil test is very high there is a low probability that the planned crop will respond to fertilizer applications of that nutrient. Soil tests are more accurate at determining pH, phosphorus and potassium levels then secondary or micronutrient levels. If a secondary or micronutrient is low on the soil test report consider using a plant tissue test to confirm a deficiency. You may also consider on farm trials by applying the secondary or micronutrient in question to a small area in the field.
Once you have determined which nutrients need to be applied to maximize yields, the next step is to determine an application strategy. Most fertilizer recommendations including MFA’s are based upon a build-plus-maintenance approach. The goal of a build-plus-maintenance strategy is to increase low-testing nutrients to optimal levels. If a nutrient level is below optimal the fertilizer recommendation, we’ll recommend more then is being removed by the crop. The idea is to build the soil test level up by applying more than is removed. Once the soil test is in the optimal range the recommendation will be to only apply maintenance or crop removal rates. This strategy works well on land that is owned or in a long term lease.
Another nutrient application strategy is the sufficiency approach. The goal of the sufficiency approach is to apply enough fertilizer to maximize yields in the year of application. This strategy may be appropriate for short-term lease farms. This approach requires annual applications of fertilizer, especially if soil test levels are below optimal. The lower the soil test level the more fertilizer is going to be needed in order to maximize yields. Some factors that will affect fertilizer rates required for optimal yield will be cropping history, soil type, nutrient placement and timing of application. Consult with your local MFA Agronomist to help fine tune nutrient applications.
With the drought and low yields this past year it is going to be tempting to reduce or eliminate fertilizer applications for the 2013 crop. I strongly recommend utilizing your soil test results to determine your nutrient application rates and not 2012 yields. If soil test levels are low, continue to apply recommended rates, you will be ahead of schedule and reach optimal levels sooner. If a nutrient is in the optimal or higher range then you can probably get by without applying a full rate or no fertilizer containing that nutrient.
Soil testing and interpretation is only a portion of a well developed nutrient management plan. A nutrient management plan should consider the 4R best management practices for each field. The 4R nutrient stewardship concept is to apply the right source of plant nutrients at the right rate, at the right time and in the right place. Visit with an MFA Agronomist to help develop a nutrient management plan that is tailored to your farm.
Steve Cromley is senior staff agronomist for MFA Incorporated. See related story about soil testing.