Deep soil testing for determining complete soil nutrient status
Common knowledge dictates that testing soil for nutrient status should be a common practice to sustain crop yield potential and support soil health. Click here for a White Paper on this website that provides details/links to information about proper soil sampling to ensure that the soil’s nutrient status is correctly determined by soil test.
Soil samples for nutrient testing are commonly collected from the top 6 in. of the soil profile. Now comes information from Texas A&M Univ. that deep soil testing offers the potential to reduce fertilizer costs by determining if there are available plant nutrients below the usual sampling depth. In an April 2023 article titled “Deep Soil Testing Offers the Potential to Reduce Fertilizer Costs”, authors Jones and Bell provide results from research conducted in Texas that indicates that deep soil testing–i.e. 6-24 in. or deeper–is a management tool that provides the potential for significant cost savings related to nitrogen [N] fertilizer applications to crops such as corn, wheat, and cotton. Pertinent points from the cited article follow.
• Deep soil testing allows producers to measure and take advantage of N and other soluble nutrients that are in the deeper soil profile so they can apply less fertilizer and save money.
• Knowing the amount of residual N and other essential nutrients in the crop’s rooting zone below the 6-in. sampling depth allows producers to customize their fertilizer applications based on a crop’s needs.
• The results reported in this article demonstrate 1) how deep soil sampling and subsequent testing can allow producers to take advantage of the available N that is present in the entire soil profile that is utilized by crop plants, and 2) the potential cost savings that can be realized when accounting for the amount of N that is in the deeper soil profile.
It is recognized that the results reported in the above-cited article may not be directly related to soybean production, but it is also recognized that soybeans are often rotated with corn, rice, and cotton in the Midsouth. Thus, costs associated with N fertilization of these crops that may be rotated with soybeans will affect long-term profitability of most farm operations in the Midsouth.
Deep soil testing can play an important role in the measurement of essential plant nutrients that may have leached below the usual 0-6 in. soil sample depth. This leaching is more likely to occur in coarse-textured soils; thus, sampling coarse-textured soils at depths below the usual sampling depth can provide insight into the total amount of an essential nutrient element that may be available to growing plants. This will be especially important when sampling sites that have received excessive rainfall that will increase percolation of water with soluble nutrients to depths below the usual 0-6 in. sampling depth.
Producers are encouraged to consider periodic deep soil sampling and testing to ensure that they are measuring the total soil content of a necessary plant nutrient. If they are uncertain about the necessity of this added chore, they should consult with their state’s soil fertility specialist or with the laboratory that conducts nutrient analysis tests on their soil samples. This additional sampling is especially important in today’s production environment with high fertilizer prices.
Composed by Larry G. Heatherly, June 2023, larryh91746@gmail.com