Soil testing does not deliver an accurate assessment of the levels of soil Nitrogen that are available for plant growth. This is because they don’t sufficiently account for soil microbes, which mineralize organic nitrogen and make more of it available to a crop. As a result, farmers often apply more fertiliser Nitrogen than they need.
However, Richard Haney, a US Department of Agriculture (USDA) soil scientist in Texas, has developed a soil test that replicates some of the natural processes that occur in a field and accounts for that microbial activity, along with measuring nitrate, ammonium (NH4), and organic nitrogen.
The new soil test is known as the Soil Health Tool. It involves drying and rewetting soil to mimic the effects of precipitation. It also uses the same organic acids that plant roots use to acquire nutrients from the soil. The tool measures organic carbon and other nutrients, accounts for the effects of using cover crops and no-till practices, and will work for any crop produced with nitrogen or other types of nutrient fertiliser.
Haney has made it available to commercial and university soil testing laboratoriesand has worked with farmers to promote it. Growers who use it receive a spreadsheet that shows the amounts of nitrogen, phosphorus, and potassium available to crops. On average, they reduce fertiliser costs by about $10 to $15 per acre. Moreover, with less fertiliser applied, there is less of it running off into surface water.
Haney and his team have evaluated the tool in fields where they raised wheat, maize, oats, and grain sorghum at nine Texas sites over four years. They applied traditional fertiliser rates; no fertiliser; and the amounts dictated by the Haney soil tests. They planted and harvested on the same dates at each site, and kept track of fertiliser costs and application dates, crop prices, and overall profits.
They found that the tool reduced fertiliser use by 30-50% and reduced fertiliser costs by up to 39%. The enhanced testing methods had little effect on maize production profits, but increased profits by 7- 18% in wheat, oat, and sorghum fields.