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Starter Fertilizers for Corn Production

Table of Contents

Why Use a Starter Fertilizer?

Starter Fertilizer Elements

Optimum Nitrogen and Phosphorus Rates in Starter Fertilizers

Starter Fertilizer Placement

Corn Response to Placement Methods

Other Benefits from Starter Fertilizers

Response of Hybrids to Starter Fertilizers

Factors that Influence Plant Response to Starter Fertilizers



Prepared by
J. P. Zublena, Department Extension Leader, Soil Science Extension

Published by
North Carolina Cooperative Extension Service

Publication AG-439-29 
October 1994 (DWD)

Last Web Update:
December 1997 (DBL)

Corn starter fertilizers have been used successfully to increase early plant growth, nutrient uptake, and yields in research trials and on the farm. They also promote earlier maturity, improve southern corn billbug control, and help suppress weeds through earlier shading. Use of starter fertilizers is increasing in North Carolina and the southeastern United States. This fact sheet presents the principles of successful starter fertilizer use, research results relevant to North Carolina, and management suggestions for corn producers.


Why Use a Starter Fertilizer?

Cool air and soil slow corn plant and root growth in the spring. When root growth is restricted, corn plants often turn purple. Early season purpling varies with variety, but most often it is a symptom of an induced phosphorus (P) deficiency. The deficiency is described as induced because it may occur on soils that test high for phosphorus. It occurs because phosphorus moves slowly in the soil. If roots do not grow enough to reach soil phosphorus reserves, the plant begins to starve for that nutrient.

In most cases, phosphorus deficiencies are temporary, and symptoms disappear as soon as soil temperatures rise to a point where root growth is stimulated and the plant can reach more phosphorus. Grain yields are not reduced every year by root stunting, but yield losses can be significant in years when temperatures are low. Additional factors that limit root growth can also induce phosphorus deficiencies. Some common causes include soil compaction, herbicide injury, and insect or nematode damage to the root system.

Starter fertilizers may be used to overcome slow root growth and the potential for reduced nutrient uptake. Starter and "pop-up" fertilizers involve at-planting placement of a small supply of nutrients near the seed (for starter fertilizer) or in the seed furrow (for pop-up types) so seedling roots can rapidly reach the nutrient source. These fertilizers are not intended to supply all nutrients needed by the crop. Their primary purpose is to provide an accessible nutrient source for root and plant growth when adverse conditions occur soon after planting.


Starter Fertilizer Elements

A field's yield potential, soil nutrient reserves, and fertilizer management programs will dictate the best combination of nutrients for use in a corn starter fertilizer. It is best to fine tune your starter needs by comparing various nutrient combinations and starter rates on your own farm. The best tools for evaluating starter fertilizer performance are a comprehensive plant tissue analysis program and comparison of final yields.

Most research in the Southeast supports the practice of including nitrogen and phosphorus in corn starter fertilizers. Research in South Carolina compared several elements in corn starter fertilizers applied 2 inches below and 2 inches to the side of the seed position (known as a "2-by-2" placement) on coastal plain soils. The results showed that nitrogen in combination with phosphorus was superior to both broadcast and banded nitrogen alone.

Furthermore, the addition of micronutrients, potassium, or sulfur to the starter did not improve yields over the nitrogen-phosphorus combination. Soil tests at these experimental sites did not call for micronutrient applications. If soil tests, field history, or past tissue analyses predict a micronutrient deficiency, adding a suitable micronutrient source to the starter fertilizer may be warranted. Lower micronutrient rates are needed for banded starters than for broadcast applications. The most common micronutrients needed on corn are manganese and zinc. Recommended starter rates are 0.75 to 1 pound of actual manganese or zinc per acre when soils are deficient. If boron is needed, do not exceed 0.5 pound per acre of boron in a 2-by-2 band.

Support for including both nitrogen and phosphorus in starter fertilizers has come from several southeastern states. Participants in a regional workshop on corn starter fertilizers observed positive yield responses to starter fertilizers in 78 percent of research and on-farm tests.

Conclusions from the workshop stated that, over time, positive responses to starter fertilizers appear to be more consistent for nitrogen alone than for phosphorous alone. However, combining nitrogen with phosphorus in a starter fertilizer is generally the most attractive option.


Optimum Nitrogen and Phosphorus Rates in Starter Fertilizers

Materials commonly used in starter fertilizers include diammonium phosphate (DAP 18-46-0), monoammonium phosphate (MAP 11-48-0), and ammonium polyphosphate (APP 10-34-0). All of these materials have higher phosphorus than nitrogen contents. In a preliminary study of starter materials, researchers compared two commercial liquid starter fertilizers with analyses of 10-34-0 (nitrogen, phosphate, and potash) and 3-18-18 to a blended 10-10-0 starter. The commercial starters were applied at a rate of 8 gallons per acre and the experimental blend at 30 gallons per acre. In that one-year study, the blended starter delivered 30 pounds of nitrogen and 30 pounds of phosphate per acre and produced yields 10 bushels per acre higher than the other materials.

Two later studies in South Carolina and Alabama examined nitrogen and phosphorus rates in corn starter fertilizers. Both programs were conducted on Norfolk soils with high to very high phosphorus levels. Results from six tests were similar for the two states. Corn responses to starter fertilizers were more consistent for nitrogen alone than for phosphorus alone, and yields were generally greater at all nitrogen rates with the addition of 10 to 20 pounds of phosphate (P2O5) per acre (Figure 1). From these studies, it appears that there is an advantage on high-phosphorus soils to decreasing the amount of phosphorus in the starter fertilizer and increasing the amount of nitrogen. Optimum levels in these studies were achieved with 10 to 20 pounds of P2O5 and 30 to 40 pounds of nitrogen per acre. At this increased concentration, the starter nitrogen can eliminate the need for all preplant broadcast applications of nitrogen.

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Figure 1. Effect of nitrogen and phosphorus rates in corn starter fertilizers on grain yields.
(Note: Data are averages for six tests obtained on sites in South Carolina and Alabama.)

This fertilization management scheme would improve nitrogen use efficiency, reduce potential nitrogen leaching losses, and provide a mechanism for reducing phosphorus application rates on soils that test high in phosphorus. The desired starter fertilizer analysis can be achieved by blending dry granular materials such as DAP with ammonium nitrate or urea. Another option is to use fluid starter fertilizers by blending products such as a 10-34-0 fertilizer with 30 percent urea ammonium nitrate (UAN) solution. In areas where sulfur is needed, ammonium sulfate can be used in dry blends and fluid sources such as S-25 can be substituted for 30 percent urea ammonium nitrate solution. Before large-scale mixing, always test fertilizer materials for compatibility.

On soils testing medium or low in phosphorus, higher phosphate rates may be needed in the starter fertilizer. On medium-phosphorus soils, adding 30 to 40 pounds per acre of phosphate should be adequate. As a rule of thumb, use about two-thirds of the recommended broadcast rate. On low-phosphorus soils, consider a combination of starter and broadcast phosphorus because the majority of the root zone is likely to be deficient in phosphorus.


Starter Fertilizer Placement

The adoption of starter fertilizers on the farm is often hampered by problems that arise when installing application equipment. The following section offers several placement options.

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Figure 2. Placement alternatives for corn starter fertilizer.

Two-by-Two Placement. The most common starter placement is 2 inches to the side and 2 inches below the kernel at planting (Figure 2a). This precision placement method, called 2-by-2 placement, requires specialized equipment generally consisting of either reverse knives, double-disk openers, or courters with drop tubing behind them. Each of these equipment packages has advantages depending on the tillage system used (for example, no-till planting or conventional tillage).

All 2-by-2 placement units should be mounted in a manner that will allow them to "float" with the planter. Planter bar and unit spacings often make it difficult to install additional fertilizer attachments; thus, many are placed on forward-mounted tool bars. Forward mounting of starter fertilizer equipment decreases the precision of the placement on rough or rolling ground. These mechanical constraints and the expense of application equipment for placement has prompted researchers and producers to try the alternative placement methods, as described in the following paragraphs.

Below-seed placement (Figure 2b) is suited for in-row subsoiling units. When fluid fertilizer materials are used, a drop nozzle or stainless-steel tube can be attached to the subsoil shank with adjustable locking collars that allow a fixed placement at any depth below the seed.

With liquid application units, care should be taken to prevent the liquid fertilizers from adhering to the subsoiler shank. When this occurs, the liquid starter drips down to the subsoiler shoe and is unavailable for early plant growth. Splatter shields can be welded at specified depths on the subsoiler, or a K-3 or K-5 flood nozzle can be mounted on the end of the drop nozzle with a 45-degree elbow directing the nozzle spray away from the subsoiler shank. Either method will prevent the fluid from dripping down to the subsoiler shoe.

When granular fertilizers are used, materials should be allowed to fall freely into the subsoil track from a height 6 inches above the soil surface. Soil movement prevents granular materials from dropping all the way down to the subsoiler shoe. Below-seed placement is not as precise as a "floating" 2-by-2 placement or any surface placement because of draft bar movement.

In-furrow placement (Figure 2c) of fertilizer with the seed requires simple equipment but may result in fertilizer injury (Table 1). Fertilizers applied with this technique are commonly referred to as "pop-up" fertilizers. Pop-up fertilization is not recommended in North Carolina. However, some growers working with organic soils have used 5 gallons of 10-34-0 fertilizer per acre placed in the furrow, and researchers in Tennessee have found that little injury occurs when small amounts of pop-up fertilizers are used in clay soils.

Table 1. Effect of Starter Fertilizer Placement Methods on Corn Grain Yields in Florida
Placement Year 3-Year
1984 1985 1986
Check 142 169 130 147
In-furrow 107 173
2-by-2 172 2101 163 182
Surface dribble 170 186 168 175
2 inches below 122 178 162 154
5 inches below 137 177 152 155
8 inches below 139 189 162 163
Source: D. Wright 1991. In: Technical Bulletin 1991.1, Starter Fertilizers for Crops in the Southeast. PPI, FAR, Atlanta, Ga.

1 Planted four days after other test. Comparable check = 186 busels per acre.

Surface banding over the row (Figure 2d) may be more effective on sandy soils than on clay soils. Placement can be accomplished with conventional banding equipment. Starter fertilizer solutions may be sprayed over the seed furrow with nozzles placed behind the press wheel. Band widths of 6 to 12 inches can be obtained with nozzle height adjustments.

Surface dribble (Figure 2e) may also be most effective on sandy soils. It can be set up with conventional banding equipment oriented to deliver a stream of starter fertilizer to be offset 2 inches on one or both sides of the seed furrow. Most often, an appropriately sized orifice is used to meter the starter fertilizer. If a fan nozzle is used, it must be turned parallel to the seed furrow direction.

Banding under the row (Figure 2f) is done with a T-shaped PVC manifold with orifices extending along a specified band width and mounted on a disk bedder. Precision with this method of starter fertilizer placement depends on the action of the bedder. Abrasive action of soil during bedding may reduce the life of the PVC manifold.


Corn Response to Placement Methods

Plant growth and nutrient uptake can be influenced by placement method (Figures 3, 4, and 5). In general, placing the fertilizer closer to the seed gives the greatest plant response. To prevent fertilizer salt injury, the total amount of nitrogen or nitrogen plus potash (K2O) should not exceed 80 pounds per acre, especially if the fertilizer is placed within 2 inches of the seed. It is also important to ensure that application equipment is aligned uniformly so that starter fertilizers are placed the same distance from each row. Large plant growth variations between rows may be observed with placements differing by only 1/2 inch.

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Figure 3. Effect of starter placement on corn plant height.


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Figure 4. Effect of starter placement on phosphorus uptake


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Figure 5. Effect of starter placement on nitrogen uptake.

Final grain yields can also be affected by starter placement. In Florida, the 2-by-2 and surface dribble methods appeared to be superior to other placement methods (Table 1). In South Carolina, all starter placements resulted in higher corn yields than no starter when managed with irrigation for maximum yields (Table 2).

Table 2. Effect of Starter Placement on Corn Yields
Placement Year
1985 to 1988 1986 to 1988 1987 to 1988
(bushels per acre)
Check 205 206
2-by-2 217 220 213
2 inches below 220 229 229
4 inches below 217 225 214
6 inches below 217 224 221
14 inches surface blend 227 229
Surface dribble 231
Source: J. Zublena. 1991. In: Technical Bulletin 1991.1, Starter Fertilizers for Crops in the Southeast. PPI, FAR, Atlanta, Ga.


Other Benefits from Starter Fertilizers

Starter fertilizers do not always increase corn yields. They do, however, offer agronomic advantages that are often overlooked. A North Carolina study showed that applying 15 gallons of 10-34-0 starter fertilizer per acre increased corn yields by 11 bushels per acre and reduced grain moisture at harvest by 2.7 percent (Table 3). Gross returns because of drying savings were $25.78, and the returns generated by the yield response were $23.38, for a total return of $49.16 per acre. As indicated by the fact that grain moisture is lower, starter fertilizers hasten corn maturity. Thus, corn that has received a starter fertilizer may also be harvested earlier so that it can be sold when prices tend to be higher. The higher selling price would have to be weighed against the increased dockage for selling grain at a higher moisture contents.

Table 3. Starter Fertilizer Use on Irrigated Corn
Treatment Yield
(bushels per acre)
Grain Moisture
at Harvest
($ per acre)
With starter 202 18.04 29.24
Without starter 191 20.73 80.09
Difference   11   2.74   9.16
Difference for yield: 23.38
Difference for moisture: 25.78
1Starter fertilizer (10-34-0) was applied 2-by-2 at a rate of 170 pounds per acre on soil that tested very high for phosphorus. Study conducted by J. R. Anderson, Jr., North Carolina State University.

Starter fertilizers also contribute to improved insect and weed control. In the North Carolina coastal plain, the southern corn billbug can be a major problem. When starter fertilizers are used, early-season plant growth is rapid, and stand loss to billbug injury may be reduced because larger plants are more tolerant of the insect's attack. Improved weed control may be another benefit of using a starter fertilizer. The rapid, early-season growth stimulated by starter fertilizers helps corn to compete more effectively with weeds and may reduce the need to apply herbicides (Figure 6). Thus, starter fertilizers may contribute to reduced pesticide use and help minimize the environmental impact of corn production.

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Figure 6. Effect of fertilizer placement on early corn growth versus weed growth.
Source: J. R. Anderson, Jr., Gates County, North Carolina; 1991.


Response of Hybrids to Starter Fertilizers

Few states have tested the response of different hybrids to starter fertilizers. The most comprehensive study in the Southeast, conducted in Florida, compared 21 commercial hybrids. The hybrids were positively, negatively, or neutrally responsive to starter fertilizers. Hybrids responding positively to starter fertilizers included Funks G 4733, Asgrow Rx 777, Sunbelt 1880, Northrup King PX 9581, Pioneer Brand 3320, Jacques JX 247, Jacques 8400, and Coker 8680. The most consistent negatively responding hybrid (three out of three years) was Northrup King 508. Other negatively responding hybrids (two out of three years) included Dekalb DK 748, AgraTech GK 900, Paymaster 7990, McCurdy 7800, Dekalb XL 71, and Coker 21.

The Florida researchers also looked at the influence of starter fertilizers on plant lodging. They concluded that lodging was reduced with starters regardless of the hybrid used. Thus, it is important to know that hybrids do respond differently to starter fertilizers. To determine which hybrids are responsive, you may want to conduct simple tests on your own farm.


Factors that Influence Plant Response to Starter Fertilizers

Other factors that may influence corn response to starter fertilizers include the tillage method, soil type, soil fertility status, and yield potential. In general, if conditions promote soil compaction and prevent early-season soil warming, corn will respond positively to the starter fertilizers. For example, no-till corn appears to be more responsive to starter fertilization than corn grown in conventional tillage systems. Corn grown on clay soils with high phosphorus fixing capacities and soils with low levels of plant-available phosphorus are also likely to respond more favorably to starters containing phosphorus. It is also important to note that conditions that limit growth or yield potential may reduce plant responses to starter fertilizers. Poor stands, insect or nematode damage, or drought may nullify the effects of starter fertilizers.



Starter fertilizers provide another management tool that may increase yields or improve the profitability of corn production. Starter fertilizers can be applied several ways, depending on producer preference and the mechanical flexibility of the equipment. A starter fertilizer should contain nitrogen and possibly phosphorus. Nitrogen and phosphorus rates can be adjusted to optimize starter response on individual sites.

The addition of other elements should be based on site-specific soil nutrient needs. The various corn hybrids respond differently to starter fertilizers: some positively, some negatively, and some not at all. Many physical and environmental conditions that reduce nutrient uptake can be offset, in part, by the use of a starter fertilizer. Starter fertilizers promise to be a valuable tool for minimizing the environmental impact of corn production.


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