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Starter fertilizer provides 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.
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 (one leaf collar) through V5 (5 leaf collars), preventing stress to the developing nodal root system is crucial because stunting at this time can slow the entire plant’s development and thus yield potential. Around V3 growth stage, 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 how starter fertilizer may be beneficial.
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.
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.
Starter fertilizers help mitigate slower or sub-optimal growth rates, decreased mineralization in soil, and lack of nutrient mobility common in cool, wet soils.1 Low soil temperatures at planting can slow root growth, preventing young roots from taking up nutrients outside of the immediate root zone. Additionally, low soil temperatures can reduce the rate of microbial release of nitrogen from soil organic matter. In addition to mitigating effects of cool soil temperatures, starter fertilizer applications may also respond positively with the following field conditions:
Conservation tillage. No-till corn may respond to starter fertilizer more than conventional tillage corn systems as no-till soils may retain more moisture and have cooler soil temperatures at emergence compared to conventionally-tilled soils.
Soil compaction. Starter fertilizer may help reduce the negative impact soil compaction may have on seedlings.
Soil type and fertility. Corn planted in sandy soils with low organic matter, sandy soils with irrigation, some high pH soils, soils with low levels of available nutrients, and clay soils with high nutrient fixing capacities may benefit from starter fertilizer application.2
Placing starter fertilizer near the seed may help increase early growth in corn, which may or may not translate into increased yield potential. Early growth may be beneficial resulting in plants that are larger, more uniform, earlier flowering, and/or mature earlier. Establishing a uniform stand can help give the crop a boost toward pollination and tolerance to heat stress. In addition, established early plant growth can help improve water use efficiency, improve yield potential in years with a late spring frost, help hasten canopy closure, and reduce weed development.3,4 These characteristics can indirectly help maintain yield potential.
The macronutrients used in large amount by the plant are nitrogen, phosphorous, and potassium. Generally, a starter fertilizer is used to supply nitrogen and possibly phosphorous. The addition of other nutrients should be based on the response of a corn product to starter fertilizers and soil nutrient needs driven by a soil test recommendation.
Nitrogen (N). Nitrogen is the most limiting element in corn production and can be a beneficial part of starter fertilizer. Nitrogen is highly mobile in soil, especially under high precipitation conditions, and can easily leach if N availability is not synchronized with crop uptake. Applying N as part of a starter fertilizer program in addition to splitting applications can help decrease potential for N loss through leaching and denitrification in the soil.
Phosphorus (P). Phosphorus is another macronutrient found in starter fertilizers. Phosphorous is immobile or has limited movement within the soil profile, which may lead to deficiency symptoms. This makes the close proximity of starter fertilizer to the seed ideal for P applications. Starter P is especially important in soils with low P levels; however, soils with high levels of P have also shown a response to starter fertilizers.3,4
Research has shown that response to starter fertilizer application was more consistent for N alone than for P alone but the combination of N and P was generally the most desirable option.2
Potassium (K). Potassium is also involved with early plant growth, but is less common in starter fertilizers. Seedling nutrient requirements are relatively small for K, which reduces the need for K to be added in starter fertilizer applications.
The most common and recommended placement of starter fertilizer is 2 inches to the side and 2 inches below the kernel at planting (2-by-2 band) (Figure 2). Placed in this manner, the fertilizer is close to the seed but reduces the possibility for fertilizer injury. However, applying a 2-by-2 band may require additional investment to equip planters and slow down planting.
Figure 2. The 2-by-2 band placement for starter fertilizer.
These drawbacks, plus the availability of low-salt fertilizers, have led to an interest in furrow-placed fertilizers. Direct placement of starter fertilizer with the seed, also known as in-furrow or pop-up placement, is practical and economical for growers with a corn or corn-cotton system because growers typically use in-furrow equipment for insecticide and fungicide applications. As the seed will have direct contact with starter fertilizer, care must be taken to keep rates low enough to avoid fertilizer injury to the seed.
Sources: 1 Brouder, S. 1996. Starter fertilizer for Indiana corn production. Purdue University. http://www.agry.purdue.edu/. 2 Zublena, J.P., and Anderson Jr., J.R. 1994. Starter fertilizers for corn production. North Carolina Cooperative Extension Service. AG-439-29. http://content.ces.ncsu.edu/. 3 Hergert, G.W., Wortmann, C.S., Ferguson, R.B, Shapiro, C.A., and Shaver, T.M. 2012. Using starter fertilizers for corn, grain sorghum, and soybeans. University of Nebraska-Lincoln. G361.
http://ianrpubs.unl.edu/. 4 Hoeft, R. 2000. Will starter fertilizer increase corn yield. University of Illinois Extension. The Bulletin. http://bulletin.ipm.illinois.edu/. Beegle, D., Roth, G., and Lingenfelter, D. 2003. Starter fertilizer. Agronomy Facts 51. Penn State University. http://cropsoil.psu.edu. Nielsen, R. 2013. Root development in young corn. Purdue University Department of Agronomy. www.agry.purdue.edu. 180122052217 Web sources verified 01/19/2018.