|In Alabama, cotton and corn are the primary crops that receive starter fertilizer applications. Simply defined, starter fertilizers are any fertilizers that are placed in a localized band near, but not in contact with, the seed at planting. In contrast, “pop-up” fertilizers are special fertilizers placed in the furrow in contact with the seed. While there is some risk of seedling injury from starter fertilizers, they are a good deal safer than applying pop-up fertilizers.
Most common liquid starter fertilizers include nitrogen and phosphorus, but other nutrients such as potassium, sulfur and micro-nutrients can be beneficial. Perhaps the most common starter materials are 10-34-0 and 11-37-0. These liquids are easily obtained and provide a good source of nitrogen and phosphorus. Some common liquid formulations include potassium and sulfur such as 9-25-3 with 3% sulfur. Other nutrients can also be added, but compatibility problems might be an issue with some materials such as poly-phosphates and magnesium salts.
Placement of the fertilizer is actually what makes it a “starter.” A band of fertilizer is placed close enough to the seed for the germinating seedling to reach it quickly without being so close as to cause injury to the plant. Perhaps the ideal location for the band of fertilizer is 2 inches to the side and 2 inches below the seed, or a 2X2 placement. Surface application of the band is also effective at improving yields.
There are several advantages to placing soluble plant nutrients close to young seedlings, and most are the result of slow uptake of nutrients caused by cold soil temperatures. Plants obtain nutrients by diffusion, root interception, and mass flow. A concentrated band of fertilizer close to seedlings aids in the diffusion of soluble nutrients, increases the likelihood of root interception by the crop, and increases the concentration of the soil solution as it moves through the band in the soil profile.
Phosphorus, which moves very little in soils and is not very soluble, is primarily taken up by plants by the process of root interception. In other words, the roots have to grow to where the phosphorus is positioned in the soil, hence the advantage of close placement to the seed. Phosphorus is also made unavailable for use by plants by soil reactions. Band placement of phosphorus containing fertilizers decreases fertilizer-to-soil contact, thus lowering the amount of phosphorus that is fixed in the soil.
Placing the fertilizer in a concentrated band increases the concentration of nutrients in the soil solution around the band. Diffusion and mass flow from the band create an area of high nutrient concentration that young seedlings can easily reach. Warm season crops such as cotton and corn are planted into cold soils early in the spring. These cold soil temperatures