Making Choices

The Appropriate Nutrients For Your Crops

By John Leif, Field Agronomy Manager

Seed and crop protection selection has changed dramatically over the past 20 years, but crop nutrition planning is sometimes based on past history rather than on knowledge of the soil and needs of the crop (“it’s what I’ve always done”). The agricultural economy can make it tempting to take a few shortcuts and not purchase inputs or services that were purchased in the past. The challenge is making the best use of financial resources but not cutting inputs that will make money. As growers consider their crop nutrition needs it is tempting to forgo something as basic, and important, as soil testing.

Soil testing allows the grower to determine the current condition of the soil, including imbalances, deficiencies, and excesses. It also helps identify how much nutrition is already available in the soil so that fertilizer applications can be optimized. A multi-year testing program allows the grower to monitor changes in the soil over time.

Yes, soil testing does cost money – around $25 per sample for a complete test that includes soil characteristics, nutrient levels and base saturation. However, if one soil sample represents 20 acres in a field and the field is sampled every three years, the cost of soil sampling averages out to be about $0.41 per acre per year. Not a bad investment, considering the amount of information received from that test.

Nutrient levels in soil will change over time. Nutrient level reductions can be the result of crop removal, changes in fertilizer use, and loss through erosion or leaching. Nutrients that weren’t well managed 20 years ago, such as sulfur or micronutrients, have become more prominent as nutrients that can be limiting to yield. Soluble nutrients such as manganese and boron are difficult to build up in the soil, and higher crop yields of today take more crop nutrition than the yields of 20 – 30 years ago. “Free” sulfur from manufacturing and power generation facilities is not as available as it was before the Clean Air Act was implemented. Simply applying the same fertilizer mix you have always applied may not provide the best production or economic return.

The soil test report can be used to develop a complete nutrient management program for a field, including soil amendments to adjust nutrient imbalances as well as determine the fertilizer application needs for the crop. Using products that can be mixed to address the needs of a field will provide the best opportunity for economic return.

An excellent example of using soil test information to optimize crop nutrition choices is a field experiment conducted by MGS Farms (formerly AgroSpray Research Farm) near Innerkip, Ontario. The soil test report for the field showed low levels of both phosphorus and potassium. A common, standard program in the area is an application of 5 gallons/acre of 6-24-6 liquid fertilizer that provides phosphorus and a small amount of potassium. That treatment was compared to 2.5 gallons/acre of Pro-Germinator to meet the phosphorus need or 2.5 gallons per acre each of Pro-Germinator and Sure-K to meet the phosphorus and potassium need. Addressing the phosphorus and potassium need as indicated by the soil test provided higher yield and higher net return compared to either no phosphorus or phosphorus fertilizer alone.

In addition to selecting nutrients needed to grow the crop, a soil test report will show relationships among nutrients in the soil. If one nutrient is in excess, other nutrients may not be available to the crop, even if the values of those nutrients are high. An excellent example of this is manganese and iron. If the manganese level is higher than the iron level, there is a risk that iron will be less available to the crop and supplemental iron nutrition is recommended. Excess levels of calcium can reduce the availability of several nutrients, including phosphorus, potassium and manganese, among others. Mulder’s Chart graphically describes some of those relationships.

If you have any questions about soil testing and developing a crop nutrition program, contact your AgroLiquid representative.