12 September 2023

Deep soil testing reduces fertilizer spending


A study from Texas quantified the average savings associated with reducing fertilizer use after soil testing. For a 1,000-acre U.S. farm, it exceeds $130,000 per year

by Matteo Cavallito


An analysis of soil composition can reduce fertilizer use and result in significant savings. This is reported in a study by the Texas A&M AgriLife Extension Service, a research and training agency based in College Station, USA. The study, quoted in an article published on No-Till Farmer website, quantified the positive economic returns by highlighting how small investments can generate significant results.

“By deep soil testing before planting corn, cotton, or wheat, the AgriLife Extension analysis found projected savings from $13 to $189 per acre are possible when taking advantage of the residual nitrogen in the soil and accounting for it when making growing-season decisions,” the article states.

Soil test is crucial

According to experts, in particular, farmers should focus on depth analysis to better assess the abundance nutrients. “Many producers only soil sample the top 0-6 inches (the first 15 centimeters, ed.),” said Jourdan Bell, agronomist at A&M AgriLife. “But deep soil sampling to depths of 6-24 inches or deeper, if feasible, should be done whenever possible (about 61 cm, ed.).”

Bell, in particular, mentioned how residual plant nutrient levels in the soil can vary greatly from year to year depending on many factors. These include fertilizer use but also rainfall frequency and irrigation, cropping system, and the plants’ ability to absorb the element in the previous year.

The study

In the High Plains of Texas, the region surveyed in the research, local farms manage an average of 1,000 acres. Twenty percent of the land is typically planted with wheat; the remainder is divided equally between corn and cotton (400 acres each). Researchers estimate that nitrogen fertilizer expenditures amount to about $190 per acre in corn fields, $118 in cotton fields, and $54 in wheat fields. The variability is obviously related to the different amount needed for each crop.

The study evaluated five possible scenarios based on different levels of nitrogen application following soil testing: 100 percent of the recommended amount, 75 percent, 50 percent, 25 percent and 0 percent.

For corn the benefits ranged from $47 to $189 per acre, for cotton they ranged from $30 to $118 while for wheat they ranged from $13 to $53. Soil testing, moreover, is relatively cheap. That means net savings forfertilizer can exceed $130,000 per year for each farm, according to the authors.

Fertilizer price and environmental impact remain an issue

Interest around the potential of soil testing as a cost-saving strategy in the use of chemical products has grown in past years in correspondence with the boom in fertilizer prices. The phenomenon boomed starting in 2021 and then scaled back more recently. The current numbers, in any case, are still high. In August, the fertilizer price index compiled by the World Bank was around 157.6 points, 30 percent lower on an annual basis.

This is far from the record high of April 2022 when the index had been close to 300 points, but today’s value, at the same time, is twice as high as that recorded at the end of 2020. The problem with costs, in short, has not been solved.

Reducing the use of nitrogen-based substances, in any case, does not only provide economic benefits. Excessive use of the element, in fact, can have a negative environmental impact by contaminating waterways and causing phenomena such as soil eutrophication (i.e., excessive nutrient enrichment) and endangering animal and human health.