Starter Fertilizer

Why Starter Fertilizer is Important for Cold, Wet Soils

• Starter fertilizers are particularly useful when crops are planted in cold, wet soils during spring or fall, regardless of soil fertility levels. They are especially beneficial in conservation tillage systems. Crops planted in late spring or early fall generally don’t require a starter fertilizer unless soil fertility is low.
• Starter fertilizers provide a small amount of nutrients near the seed, ensuring that the seedling has readily available nutrients until its root system develops. They also enhance the growth of emerging seedlings.
• Nitrogen (N) and phosphorus (P) are the key nutrients in starter fertilizers. Phosphorus is immobile in the soil, so developing seedling roots struggle to obtain the necessary amounts for proper growth. Phosphorus also promotes robust root growth.
• Corn is the most responsive crop to starter fertilizer use. The response of forage crops to starter fertilizers is less consistent. Sorghum usually doesn’t require a starter fertilizer. Small grains benefit from starter fertilizers, especially in low fertility soils and when planted in late fall. It is generally not recommended to use a starter fertilizer when planting soybeans.

Selecting the Right Starter Fertilizer Materials

• Any high-quality fertilizer containing nitrogen and phosphorus can be used as a starter fertilizer. For optimum effectiveness, the phosphate should be combined with ammonium nitrogen.
• If the soil has high phosphorus levels, an N-only starter fertilizer can provide a similar response without adding extra phosphorus to the soil.
• The specific fertilizer analysis is not critical for a starter effect alone, as long as it meets the criteria mentioned above. When phosphorus or potassium is recommended based on soil tests, choose an analysis that aligns with the recommendations.
• Ammonium sulfate (21-0-0-24S) and ammonium nitrate (34-0-0) are good choices for N-only starters.
• Both solid and fluid forms of starter fertilizer, applied at similar rates and placements, yield the same results.
• Monoammonium phosphate (MAP; 11-52-0) and ammonium polyphosphate (10-34-0) are excellent materials for starter fertilizers.
• Exercise caution when using starter fertilizers that contain diammonium phosphate (18-46-0) and urea (46-0-0), as they can cause seedling injury. Keep the rate low and avoid placing them directly with the seed.
• If micronutrients are necessary, they can typically be included in the starter fertilizer.

Determining the Right Rates and Placement

• For corn, a small amount of fertilizer (around 100 pounds per acre) is sufficient for an adequate starter response when soil fertility is good. If the fertilizer is placed approximately 2 inches away from the seed, do not exceed 70 pounds of N + K2O per acre. Reduce the rate if the starter is placed closer than 2 inches from the seed.
• Larger amounts of nitrogen can be applied as a starter, but the total N + K2O should not exceed the recommended limits. For forage crops, the rate should not exceed 60 pounds of N + K2O per acre.
• For oats, do not apply more than 20 pounds of N or 45 pounds of N + K2O per acre in the seed row.
• For winter wheat and barley, do not apply more than 15 pounds of N or 30 pounds of N + K2O per acre in the seed row.
• The recommended placement for corn or sorghum is 2 inches beside and 2 inches below the seed. Avoid using a starter if sorghum is drilled.
• Starter can also be applied directly with corn seed as a pop-up, but be cautious with urea and DAP, and keep the rate low.
• For forage crops, the starter should be banded 1 inch directly below the seeds.
• Small grains are typically drilled directly with the seed, including the starter fertilizer.

Starter fertilizer is a small amount of fertilizer nutrients applied close to the seed at planting. Its purpose is to enhance the development of emerging seedlings by providing essential nutrients in accessible locations near the roots. By promoting rapid crop establishment, starter fertilizers influence plant development, yield, resistance to insects and diseases, and weed competition. These readily available nutrients near young plants ensure rapid early growth, the formation of large leaves necessary for photosynthesis, subsequent growth processes, and earlier crop maturity.

A starter fertilizer is most beneficial when the crop is planted into cold, wet soils, regardless of the overall fertility status of the soil. These conditions hinder root growth, nutrient mobility, and the breakdown of nutrients into plant-usable forms. Cold, wet soils are commonly found in early spring and late fall, with reduced tillage systems exacerbating these conditions. Therefore, starter fertilizer is crucial in conservation tillage systems. Although warmer conditions in late spring may allow adequate plant growth and nutrient mobility, it is still recommended to use a starter fertilizer if soil fertility levels are low. In general, a starter fertilizer is not necessary for crops planted later in the spring unless soil fertility is low. However, including a fertilizer during planting to meet recommended maintenance fertilizer needs is acceptable.

The use of a starter fertilizer enhances crop growth primarily by providing a readily available supply of plant nutrients, especially phosphorus, in a position easily accessible to a seedling’s limited root system. Even in soils with high fertility, young seedlings may struggle to obtain necessary nutrients due to their small and sparsely distributed roots. Once a plant’s root system is established, it can extract nutrients from the bulk of the soil. The soil serves as the primary source of plant nutrients at this stage, as the plant has a well-developed and extensive root system with increased surface area to intercept nutrients and moisture throughout the soil.

Starter fertilizers composed of nitrogen and phosphorus provide the most favorable crop response. Phosphorus, in particular, is crucial for promoting vigorous root growth and preventing stunted, purple-colored plants. While phosphorus is the most critical nutrient in starter fertilizer, nitrogen in the starter can help plants overcome early-season nitrogen deficiency and enhance phosphorus uptake. Potassium, also known as “potash,” is not as critical as nitrogen or phosphorus in a starter, but a response is likely when soil potassium levels are marginal, especially under cold, wet conditions. Starter fertilizer response is typically reflected in increased early-season growth, slightly lower grain moisture at harvest, and higher grain yields. Rapid growth and earlier maturity are particularly important in regions where medium and short-season corn varieties are grown. Overall, the use of a starter fertilizer increases fertilizer efficiency and reduces costs.

In regions with high soil phosphorus levels, the necessity of using a starter fertilizer and potential environmental impacts have been questioned. Recent research suggests that there may still be benefits to using a starter fertilizer, even on high-testing soils, in certain instances. However, the response is seen in only about 20% of cases, and the size of the response is usually relatively small. Therefore, it is generally not necessary to use a starter on high phosphorus soils unless conditions are unfavorable, and soil test levels are only marginally high. If a starter is used on high phosphorus soils, management alternatives should be considered. Using a very low rate of starter fertilizer placed directly with the seed or using N-only starter fertilizers are viable options.

There has been a recent trend of incorporating secondary and micronutrients into starter fertilizers. However, in most cases, the addition of secondary and micronutrients does not provide economic benefits unless there is a specifically identified need and a high probability of a response. Regularly applying secondary or micronutrients as a starter without a specific need is not recommended. Pennsylvania, where this research is based, typically does not experience micronutrient deficiencies due to the soil’s texture, slightly acidic nature, and periodic applications of manure, which is rich in micronutrients. However, high phosphorus levels can reduce the availability of zinc (Zn) and high potassium levels can reduce magnesium (Mg) availability. Therefore, adding Zn or Mg to a starter containing high levels of P and K may not be very effective. Periodic broadcast applications of Zn fertilizer and Mg-containing dolomitic limestone are more effective alternatives when a need for these nutrients is identified. Boron (B) should not be added in a starter fertilizer.

The use of starter fertilizers in agronomic crop production, especially for corn, is well-established and beneficial for improving yields and profitability. The use of a starter greatly outweighs any disadvantages, such as slower planting due to refilling fertilizer boxes. However, using a starter fertilizer on other agronomic crops, such as soybeans, small grains, and sorghum, is less common. Soil testing is essential before applying any fertilizer to determine the field’s fertility status. A starter fertilizer can help meet a portion of the crop’s nutrient needs, complemented by additional fertilizer applications before or during the season to meet the remaining requirements. In some cases, a starter can fulfill the P and K needs of the crop, eliminating the need for a second fertilizer application later in the season. While using a starter fertilizer may slightly slow down the rate of planting, the benefits outweigh this minor disadvantage.

For corn, there are important considerations for managing starter fertilizer use, including selecting appropriate materials, determining rates, and placing the fertilizer correctly. The same considerations apply to corn grown for grain or silage. Any high-quality complete fertilizer containing nitrogen and phosphorus can be used as a starter fertilizer. For optimum effectiveness, choose a fertilizer with a high phosphate (P2O5) ratio and combine the phosphate with ammonium nitrogen. Several fertilizer analyses can be used, and the analysis is not critical as long as it meets the criteria mentioned earlier. However, if the soil tests recommend adding P or K, select an analysis that aligns with the recommendations. Ammonium sulfate (21-0-0-25S) and ammonium nitrate (34-0-0) are the best materials for N-only starters. Exercise caution when using diammonium phosphate (DAP; 18-46-0) and urea (46-0-0) containing materials to avoid seedling injury. The physical form of the fertilizer does not affect the performance of the starter. Both solid and fluid forms provide similar results.

For corn, the rate of starter fertilizer depends on soil fertility levels. Generally, a small amount of fertilizer is sufficient to achieve an adequate starter response when soil fertility is good. Higher rates of nitrogen can be applied as a starter fertilizer, but the total N + K2O should not exceed recommended limits. These limits become especially critical in no-till situations due to less accurate starter fertilizer placement. The planting method and soil fertility determine the typical range of starter fertilizer rates, with values ranging between 100 and 300 pounds per acre. Concerns usually revolve around using too much starter rather than too little.

The placement of starter fertilizer is crucial to ensure seedling access to nutrients. The standard placement for corn or sorghum is 2 inches beside and 2 inches below the seed. However, in no-till situations, it may be difficult to achieve the recommended depth for seed placement, let alone placing the fertilizer 2 inches below the seed. Alternative placements, such as placing the starter band 2 inches beside and at the same depth as the seed or dribbling the fertilizer over the seed row, can provide some benefit but may not be as effective as the standard method. Another alternative is pop-up placement, which places the fertilizer directly with the seed. Pop-up placement eliminates the need for a separate fertilizer opener and can achieve excellent results. However, care must be taken to avoid injury to the seedling. The rate should be kept below 10 pounds of N + K2O per acre, and the fertilizer must not contain urea or DAP. Determining the appropriate rate for pop-up placement can be more challenging with dry fertilizer systems, but fluid fertilizers can offer practical advantages in regulating lower rates and plumbing the fluid lines back to the seed units.

The response of forage crops to starter fertilizer is not as consistent as with corn. If soil fertility is already within the optimum to above-optimum range, a starter is not recommended. Forage species are planted at high seeding rates, allowing various seedlings to obtain nutrients from throughout the soil and establish the stand. Additionally, many modern drills lack a combination fertilizer unit for applying fertilizers. However, using a starter when feasible can be beneficial, especially in meeting small nutrient requirements indicated by soil tests, or under adverse soil conditions such as low fertility and cold-wet weather at planting.

For small grains, using a starter fertilizer is less critical for crop success compared to corn production. However, incorporating a starter can be important for winter grains grown on soils with marginal soil test levels or when planting occurs during cold, wet conditions. Depending on soil test recommendations, all the fertilizer can be broadcasted prior to planting, or a portion can be applied with the drill and the remainder broadcasted. Care must be taken to avoid fertilizer injury to the seedlings when applying too much starter with the seed. Guidelines for starter use with small grains include selecting a high-phosphorus, non-urea-containing fertilizer material, and following the recommended rates for each specific grain.

In general, using a starter fertilizer is not as common when growing grain or forage sorghum. Although similar starter fertilizers and rates to those used for corn can be applied when using a row planter, starter fertilizers in the row should be avoided when drilling sorghum to prevent injury.

Soybeans, like other crops, require sound fertility programs. However, due to soybean seedlings’ extreme sensitivity to fertilizer injury, it is generally not recommended to use a starter fertilizer at planting. Warm soil conditions during soybean planting usually facilitate adequate plant growth, nutrient mobility, and uptake from the bulk soil. If additional nutrients are recommended based on soil tests, it is best to apply the needed fertilizer before seeding. However, growers using a row planter can place a band of starter at least 2 inches to the side of the seed. Closer placement can severely injure the seedling. It is crucial not to drill fertilizer with the seed or use “pop-up” fertilizer with soybeans.

This article was prepared by Douglas B. Beegle, professor of agronomy, Gregory W. Roth, professor of agronomy, and Dwight D. Lingenfelter, assistant extension agronomist.