Evaluating a Soybean Fertility Program

Historically, many soybean fertility programs are based on the philosophy of “make do with what’s left.” But progressive growers are finding it’s important not to forget this crop’s primary job is to pull nutrients out of the soil, and that those nutrients need to be replenished.

Soybeans have long been known for their efficient use of residual nutrients, but today’s higher-yielding varieties demand closer attention to ensure essential nutrients are available for proper nutrition. As with other crops, growers should begin forming a long-term soybean fertility program only after conducting a thorough soil sampling of planned acres.

The most important variable in managing soil fertility in soybean production is a soil’s pH. Soybeans thrive in a pH range of 6.0 to 6.8, allowing for maximum efficiency of crop inputs, and potentially decreasing the risk of yield losses. Beyond protecting yield, adequate soil fertility helps lower the impacts from stresses such as weather, disease and nematodes. Soybeans require large amounts of crop nutrients, especially phosphorus (P) and potassium (K). For example, a 60-bushel-per-acre yield removes 48 pounds per acre of P and 84 pounds per acre of K in the grain.

Micronutrients are equally crucial for plant yield and growth, although in smaller quantities. Shortages of even one essential nutrient can shortchange soybean yields, so growers should look beyond carryover macronutrients and consider possible micronutrient deficiencies in soybean crops as well.

Manganese (Mn), one of the most common micronutrient deficiencies in soybeans, plays a vital role in photosynthesis by aiding in chlorophyll synthesis. Manganese deficiencies are often associated with high-pH soils, which may result from an imbalance with other nutrients such as Calcium (Ca), Magnesium (Mg) and Iron (Fe). Deficiency symptoms are most severe in high organic matter soils during cool spring months, when soils are waterlogged. Symptoms disappear as soils dry and temperatures warm.

Manganese deficiencies can be corrected in several ways:

· If liming caused the deficiency, keep soil pH below 6.5.

· Mix soluble salts, such as Mn sulfate (MnSO₄), with starter fertilizer, and apply in bands. High P starter fertilizer helps move Mn into the plant.

· A field deficiency symptom can be corrected by foliar application.

Micronutrients such as iron (Fe), boron (B) and molybdenum (Mo) can also play a key role in achieving proper nodule formation. As soybean yields edge higher, the likelihood for nutrient deficiencies to hinder top yields also increases. Make sure you’re getting the most from your soybean investments: Rather than relying on carryover nutrients, begin planning a well-balanced fertility program before the first seed goes in the ground.

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