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Starter fertilizer acts to provide nutrients in close proximity to immature root systems that do not yet have the size and bulk density to access necessary nutrients from the soil, especially under less than ideal soil conditions. Specific planting circumstances that may benefit from the use of starter fertilizer include: soils that have tested low in phosphorus (P), cool soil temperatures associated with early planting, high residue cover associated with conservation, coarse textured (sandy) soils low in organic matter, poorly drained fields, soils with either high or low pH, and locations where substantial drought stress is likely.
Figure 1. Corn plant at growth stage V3, the period of transition from kernel reserves to nodal root uptake. Starter fertilizer helps to ensure the success of this transition.
Corn plant roots develop in two distinct phases: seminal and nodal roots. Seminal roots gather moisture from the soil while young seedlings use up the food reserves from the kernel. Once plants emerge from the soil, the nodal root system begins to develop which will become the primary route for water and nutrient uptake in the plant. During corn growth stages V1 through V5, preventing stress to the developing nodal root system is crucial because stunting during nodal root system development can slow the entire plant’s development and thus yield potential. Around stage V3, corn plants transition from dependence on kernel reserves to nodal root uptake (Figure 1). The success of this transition can be the key to a healthy, uniform crop. This is where starter fertilizer comes into play.
Uniform crop establishment and early vigor are ideal and important during early growth stages and can potentially impact plant development and yield. Not only are healthy, fast-growing young seedlings better able to compete with weeds, but they can also be more resistant to insects and diseases. Early rapid growth also helps to hasten the onset of large leaf formation which is necessary for photosynthesis.
When choosing a starter fertilizer system that works best for your specific field or operation, there are three main things to consider: the nutrients available/supplied by the material used, application rate, and placement options available.
Materials. When using a starter fertilizer that contains both nitrogen (N) and P, optimum results can be obtained when combining phosphate with ammonium nitrogen.
Monoammonium phosphate (MAP, 11-52-0) or ammonium polyphosphate (10-34-0) (liquid) based fertilizers are excellent choices. Nitrogen in ammonium form can help to enhance the use of P in the starter as well as P uptake from soil. Generally, starters should contain a high phosphate (P2O5) ratio and the phosphate should be highly water soluble. A fertilizer does not have to be labeled “starter65533;? to be used as such if it meets the needs for your situation and follows basic defined parameters of rate and placement. Depending on soil test results, micronutrients can also be provided in formulation to meet specific needs. Starter fertilizers can be applied in both solid and liquid forms as generally there is no difference in effectiveness. Liquid fertilizers may be more expensive than dry formulations, but when properly applied can require lower quantities and still be cost effective.
When a field has tested high in P, such as those on farms where manure is applied, there are a few options to gain effective starter response from fertilizer without adding significant amounts of P to already high testing soil. One option is the use of N only fertilizers such as ammonium sulfate (21-0-0-24S) or ammonium nitrate (34-0-0). Using an N only starter may provide an adequate response, but since P is immobile in the soil, sometimes additional P may still need to be added in very close proximity to the seed for an ideal response. This may be accomplished by the use of a very low rate of starter placed with the seed as a pop-up fertilizer. This allows the developing seedling access to P without adding much to the soil profile. Pop-up fertilizer will be discussed further in the placement section.
Table 1. Salt index for common starter fertilizer materials relative to 10-34-0 and expressed as pounds of salt effect per gallon.
Rates. Generally, only a small amount of fertilizer will be required for a starter response if soil fertility tests within the optimum range or higher. The appropriate rate of starter to use will depend on: proximity to the seed, salt content or index, and soil texture. Using rates above the recommended limit can cause a salt effect that can impede germination and early plant development. If starter fertilizer is placed 2 inches from the seed, do not apply more than 70 lbs N plus K2O per acre and reduce even further if placed in closer proximity to seed. If starter is placed with the seed (a pop-up fertilizer) the limit should be 10 lbs/acre. Salt index is estimated to be the sum of N + K + 0.5 x S. These values are provided in Table 1. Problems associated with salt damage may develop if soil moisture is limited within the first few weeks after planting or if fertilizer was placed too close to the seed. Soil texture also plays a role in that fertilizer rates must be lowered when placed within 1-2 inches on sandy soils. Table 2 shows the amount of 10-34-0 that can be safely applied per acre of corn in sandy versus non-sandy soils. It is especially important to follow rate limits in conservation tillage due to the less accurate placement of starter in relation to the seed.
Table 2. Amount of 10-34-0 that can be safely applied per acre for corn and grain sorghum in 30-inch rows.*
Placement. While N is mobile in the soil, P is bound and does not readily move through the soil, therefore having a lesser chance of contacting soil roots. Starter fertilizer allows close placement of P in order for the developing plants to take it in. Placement is crucial because seedling plants must be close enough to access nutrients, but not too close when used at higher rates. The ideal placement for starter fertilizer is in a band 2 inches to the side of and 2 inches below the seed (2x2). This allows the roots easy access to the fertilizer, but limits the potential for fertilizer burn. The 2x2 placement has an advantage over seed-placed starter because not only is the position relative to nodal root development more advantageous, but higher rates can be used without risk to the seed.
Alternatives to the 2x2 band include: placement at 2 inches beside and at the same depth as seed; dribbling fertilizer over the seed row in front of the no-till coulter; and pop-up placement. “Pop-up65533;? fertilizer which is placed directly in contact with the seed is an option, but requires extreme caution to avoid germination or seedling injury. The amount used should be very limited and depends on the formulation and soil properties. Possible advantages of pop-up placement include: no need for separate fertilizer opener on the planter, lower rate of fertilizer used, reduced amount of P on high P soils, and less fertilizer handling (fewer planter fill-ups). However, it should be used with extreme caution due to the potential for crop injury. No more than 10 lbs/acre N + K2O should be applied and neither diammonium phosphate (DAP, 18-46-0) nor urea (46-0-0) should be used because of risk for seedling injury. Pop-up placement can be a good option if the proper rate and materials rules are followed and equipment can be adequately set for pop-up placement.
Research has shown great variance in the ability of starter fertilizer to result in grain yield increases, meaning that environmental and management practices play a larger role in the crop’s final outcome. Studies have shown that situations most likely to experience yield response from the use of starter fertilizer include: areas in the Northern Corn Belt and areas within the Central Corn Belt that used reduced tillage or have poorly drained fields or soils testing low in P.
Beegle, D., Roth, G., and Lingenfelter, D. 2003. Starter fertilizer. Agronomy Facts 51. Penn State University. http://cropsoil.psu.edu. Hergert, G., and Penas, E. 2012. Using starter fertilizer for corn, grain sorghum, and soybeans. University of Nebraska–Lincoln. NebGuide. G361; Hoeft, R. 2000. Will starter fertilizer increase corn yield? University of Illinois Extension. The Bulletin; Nielsen, R. 2013. Root development in young corn. Purdue University Department of Agronomy. www.agry.purdue.edu. Web sources verified 01/19/2016. 140224070105