Optimize Yield by Soil Testing

Optimize Yield by Soil Testing


Conservation Tillage & Technology Conference (CTTC) last week had several good speakers. Clint Nester, Nester Ag, consults on about 200,000 acres in Ohio, Michigan and Indiana since 1992. All that data drives their soil test recommendations. They start by soil testing, determine nutrient rates, variable apply nutrients and then evaluate crop yields. They follow the 4R’s (Right Source of fertilizer, Right Rate, Right Place, and Right Time). By following the fundamentals, they strive for optimal yields with the highest profit margin while protecting the environment (improve water quality). 

Soil testing can be done many ways. They emphasize getting core samples that are representative. Some farmers and retailers sample by soil type, 2.5-acre grids, or zones. Nester’s use zone soil sampling, taking numerous representative soil samples down to 6.67 inches. Zones allow for good N-P-K soil recommendations, help determine pH and lime levels, starter fertilizer rates, side-dress N rates, hybrid selection, and even crop population levels. Nester’s track soil test over several years to identify trends and to solve agronomic problems. That helps them make informed decisions about what inputs to apply to improve the farmer’s bottom line. It also improves water quality because they are not guessing and putting on too much expensive fertilizer or not enough when needed. 

Nester Ag strive to optimize calcium (Ca) and magnesium (Mg) soil levels. Ideally, their goal is a 70% Ca base saturation and a 12-15% Mg base saturation. Soils in Northwest Ohio (clay soils) tend to be high in Mg which makes soils tight, sticky, hard and dense. Air and water can not move in tight soils which tend to have poor drainage. Soils that are Ca and Mg balanced are open, have stable soil aggregates (soil crumbles), good drainage, oxygen rich for deeper roots, and have higher microbial activity. It’s not only pH, its good soil structure which allows healthy plants to grow. Good Ca levels attract the clay particles together to form good soil aggregates while high Mg causes soil to be structureless, like a concrete slab, so air and water cannot move freely. On sandy soils and ridges, Mg levels may be too low, and these soils may need more Mg fertilizer. 

On Nitrogen (N) fertilizer, it’s all related to the cost of fertilizer, crop prices, and crop yields. Modern corn hybrids need less N per bushel but also, N fertilizer is expensive. Generally, added N may raise yields, however due to the cost of N, the highest net profit occurs before the highest yield. Farmers need to determine the best N rate for their fields by doing some N plots and N strips. With lower crop prices, N rates should decrease simply because the extra N applied does not pay for itself, even though yields improve slightly. 

On potassium (K), Nester’s find that the added K tends to help improve yields. Generally, K base saturation should be between 2-5%, but Nester Ag pushes the higher end, 4-5%. Potassium (K) soil test levels have been dropping but Tri-state fertilizer recommendations have eliminated K build up. Why are K soil test levels dropping? Nester Ag says growing more soybeans (a high K remover), higher crop yields, more wheat with straw removal, and even less corn borer means crops are producing better yields and thus removing more K. Nester Ag thinks K rates may be a little too low based on their data. Fall application of K Fertilizer may also get tied up in the clay soil structure when soils are wet and fall tillage occurs. Adequate soil K improves N uptake in plants. Based on 32 years of soil test and yield data, Nester Ag says keep your K soil test levels at 4-5% K base saturation. 

Due to the passage of the 1908’s Clean Air Act, free atmospheric Sulfur (S) has declined from 24# S/acre in 1985 to about 4# to 7#/acre in 2022. Sulfate forms in the spring when crops need the S. Building soil organic matter by growing cover crops may help. Adding spring applied gypsum (calcium sulfate) is more beneficial than fall applications. Calcium and sulfate are mobile and may be lost or tied up deep in the soil. 

Phosphorus (P) is more soluble than it was 20-30 years ago. MAP and DAP fertilizer have highly soluble P plus with less soil inversion, the top 2 inches are more acid, leading to soluble P. Potassium (K) soil levels may be too low, while P soil levels may be too high. Using cover crops, employing the 4R’s to place P close to the roots (2”X2” or 4”X4”) helps crops get adequate P. Lot’s of good soil advice at CTTC this year!