Corn Starter Fertilizer

Farmers use corn starter fertilizer to increase corn yields? True but the 25-36% increased growth at V6 (young corn, six true leaves) may only increase corn yield 2-3%. Weather and soil conditions after planting often have a greater influence on crop yield than starter fertilizer. However, farmers want to get their corn crop off to a great start so they have a chance at achieving those higher corn yields.

Where do farmers get a big boost from corn starter fertilizer? Generally, soils that are low in nitrogen (N), phosphorus (P), and potassium (K) respond the most to N-P-K starter. Corn after corn responds to added N. No-till fields with cover crops respond to early applied N due to a higher carbon: nitrogen (C:N) ratio in the soil. In no-till fields, 40-60# of N is suggested at planting to overcome the N deficient. Soil microbes need the N to break down cover crop roots and possibly higher crop residue. Poorly drained soils that are cold and wet also respond to starter fertilizer because the soil microbes are less active.

Where do farmers get their biggest yield increase? Both N and P generally give the biggest yield increases. In most cases, P is the most limiting when soils are cold and wet due to slow seedling growth and slow absorption of P to the root. In healthy soils, beneficial fungi help the plant get P, but this requires a plant investment in growing a mycorrhizal network, so corn plants may seem a little stressed in the spring. The benefits often come later in the summer when P is limited. Starter P fertilizer tends to give the biggest yield increases because soil P is slow moving and P is needed by plants for early cell multiplication and energy transfer.

A close second, is the response to starter N fertilizer. Often N may be lacking in the topsoil due to N leaching in the form of nitrates. Nitrate N is very mobile. Nitrate N stimulates early corn plant growth. Later in the growing season, the ammonium form of N promotes yield more than nitrate N fertilizer. N mineralization or plant available N is often limited in cold wet soils, so corn growth increases when adequate N is supplied. Adding a gallon of sugar to N starter fertilizer per acre supplies a readily available carbon source for microbes to make proteins. For Potassium (K), corn K starter fertilizer yield response is generally low unless K is soil deficient. K fertilizer has a high salt content and may injure germinating corn seeds. N and P starter fertilizer generally generates the biggest corn yield responses.

What about other nutrients? Every soil and plant nutrient is needed in balance. Most soil nutrients are needed to create amino acids to form proteins. Sulfur (S) is the next most limiting element. Historically, atmospheric S from acid rain gave farmers 20-30# of S/acre yearly, however that has decreased to 6-10# S/acre yearly. Every 1% soil organic matter gives about 2.5# S, so a 2% SOM generates 5# S/acre, so a farmer may count on 11-15# S/acre. A 250- bushel corn crop needs about 20# S, which may be a deficiency of 5-9#S/acre. Farmers often use ammonium thiosulfate (12% N, 26% S) in starter fertilizer at a rate of 10 parts N to 1 part S. It may be beneficial to increase the S fertilizer content slightly if S is deficient. Corn gets about 50% of its N from applied fertilizer through soil microbes, the other 50% comes from the soil microbes themselves. If S is soil deficient, soil microbes may need some extra S to make that other 50% N more plant available.

After N-P-K-S, zinc is often added to starter fertilizer. Slight zinc deficiency in corn is common. A lack of zinc may be responsible for 10-30% corn yield loss if it is not in adequate supply. Zinc is the central element in 300 plant enzymes. Adequate zinc keeps a plant healthy and reduces many corn diseases. Calcium and its carrier boron may also be beneficial. Calcium is needed in large amounts to promote root tillering, stalk strength, and early leaf growth. Boron moves calcium into the plant but can injure germinating roots, so apply in very small amounts away from germinating seeds. On sandy soils, magnesium is often lacking but it is a salt so apply it away from the seed. Iron is often lacking in cold wet soils and is responsible for the enzyme that makes chlorophyll. A little fulvic acid buffers salts in fertilizer and helps with plant absorption. Overall, a balanced micro nutrient package can promote higher crop yields when critical nutrients are lacking.