In North Florida field corn production, starter fertilizers commonly include liquid blends such as 28-0-0-5 (urea ammonium nitrate and ammonium thiosulfate mixture), 10-34-0 (ammonium polyphosphate), or a combination of 28-0-0-5 and 10-34-0, resulting in a 23-9-0. These fertilizers are usually applied at planting as a surface dribble, or as a 2 by 2 band meaning the fertilizer is placed 2 inches to the side and 2 inches below the depth of the seed. These fertilizers provide plants with nitrogen and phosphorus for early season growth. The 28-0-0-5 also contains sulfur via ammonium thiosulfate. Chelates provide crops with micro-nutrients and can be added to starter liquid fertilizers but are only advised when needed based on soil test results.
Yield response to starter fertilizer is variable but is more likely in situations where soil test indicates deficiency of one or more nutrient supplied by the starter fertilizer. There is more likely to be a yield response to starter fertilizer in cool coarse textured sandy soils (containing low organic matter and mineralization rates). That is why starter fertilizer is generally recommended for north Florida field corn production due to our sandy soils and potential cool soil temperatures during planting time from late February through early April. Some of the benefits of using starter fertilizer include improved early-season growth and root development, faster dry down of crops, and potential for increased yield.
Include or exclude Phosphorus in starter fertilizer?
Whether phosphorus should be included in starter fertilizer applications is a common question in the Suwannee Valley area of North Florida. Phosphorus is a macronutrient that plays an important role in plant energy transfer, photosynthesis, and early season root development. Soils in the Suwannee Valley region often test in the high range for phosphorus according to UF/IFAS recommendations using the Mehlich 3 extraction. For irrigated field corn planted at a population of 30,000 plants or above, the current UF/IFAS recommendation is 175 lbs. of P2O5 for low (≤ 25 mg kg-1) P soils, 80 lbs. of P2O5 for medium (26 – 45 mg kg-1) P soils, and 0 lbs. of P2O5 for high (>46 mg kg-1) P soils. However, the UF/IFAS Field corn production guide states that 15 lbs. of phosphorus via starter fertilizer is adequate when soils test in the high range for phosphorus. Research is on-going to review UF/IFAS phosphorus fertilizer rate recommendations across various crops including field corn. For now, note that yield response to the addition of phosphorus in starter fertilizer is variable but is more likely in sandy textured soils and cool/wet conditions. These conditions can cause corn to exhibit phosphorus deficiency symptoms (stunted growth and purple leaves) even when phosphorus tests high based on soil test recommendations. This is due to lower mineralization rates of cool sandy soils and the fungi responsible for helping corn absorb phosphorus being less active at cold temperatures.