Use of Starter Fertilizers in Corn Production
Stresses that impede nodal root development may be caused by living (biotic) organisms such as insects or diseases or by non-living (abiotic) physical or chemical factors such as soil obstructions, soil moisture conditions, cool temperatures, or fertilizer placement. Stresses may be continuous in the field, or may occur sporadically in microenvironments throughout the field.
Continuous or uniform stresses that affect plants equally often include cold or wet soil conditions or below optimum air temperatures. Although detrimental to crop growth and sometimes yield, these stresses are generally less damaging than sporadic stresses that affect one plant and not its neighbors. This is because individually affected plants are likely to fall behind in physiological growth stages if conditions remain unfavorable.
Once a plant begins to fall behind by two or more growth stages, it becomes increasingly difficult for the plant to catch up. This is commonly thought to be a consequence of shading by its competing neighbors. Shading slows the plant's growth rate, further reducing root elongation and nutrient uptake. Thus, the problem of competing for limited resources is compounded, likely for the remainder of the plant's life cycle.
Sporadic or variable stresses in a field can be more detrimental to grain yield than continuous stresses. Sporadic stresses include: uneven residue distribution, dry or cloddy soils, wet spots, diagonal anhydrous ammonia bands, fertilizer salt injury, wheel traffic compaction, seed furrow (sidewall) compaction, insect or herbicide damage to roots, and soilborne diseases.
Uneven stands have been reported to suffer corn grain yield reductions from six to as much as 23 percent depending on the severity. This yield loss could be significantly reduced by starter fertilizer applications in cases where the primary cause of uneven stands is the inability of the young nodal root system to access sufficient soil nutrients.
Application of Starter Fertilizers in Corn
Solid and fluid forms of starter fertilizer exist and if applied at similar rates and placement, provide the same results. Liquid fertilizers can be applied at lower quantities than dry forms and the effect of the nutrients when they are applied at the same rate per acre is the same. While liquid forms are more expensive than dry materials, if applied accurately and at the lower quantity, they can be cost effective. An economical, high-quality, complete fertilizer containing N and P can work as a starter fertilizer. In general, a fertilizer with a high P ratio (1-2-1, 1-3-1, etc.) in a highly water-soluble form and combined with ammonium nitrogen can be used. If applying in-furrow, recommended rates are 4 to 5 gallons per acre. Formulations may change based on availability and if other nutrients are added. Monoammonium phosphate (MAP 11-52-0) based materials are good choices, and ammonium polyphosphate (APP 10- 34-0) is also a widely used liquid starter fertilizer. Starter fertilizers containing only N may be sufficient for soils regularly applied with livestock or poultry manure, as those soils may already contain high levels of P. Diammonium phosphate (DAP; 18-46-0) and especially products containing urea (46-0-0) may cause injury at higher rates and if placed close to the seed.
Soil Analysis
Soil testing is the best tool for growers to make fertilizer decisions. Samples can be taken any time after harvest, but should not be completed after a fertilizer, lime, or manure application. Samples should also be taken prior to tillage to increase sample reliability. Soil testing is recommended at least once every three years.5 However, annual testing is more accurate to help determine what nutrients should be applied and at what rates. The amount of N and/or P used as a starter fertilizer can be deducted from the total recommended nutrient requirement for the season.6
Key Learnings from a Meta-Analysis of Starter Fertilizer Application7
Responses of corn to starter fertilizer can vary across production systems and environments. A large meta-analysis of 474 studies conducted in the United States from 1990 to 2019 on starter fertilizer indicated the following7:
Across all 474 comparisons, grain yield was increased by 5.2% with a starter fertilizer application compared to corn without starter fertilizer. Of the 474 comparisons of corn with starter vs corn without starter, 74% of the fields had a yield increase from the starter application.
When N was not limiting, the impact of a 2 x 2 application (Figure 1) had similar results to in-furrow applications when most of the N was applied at planting or before. However, when the majority of N was applied as a sidedress application, the 2 x 2 application increased yield almost 9% compared to no starter or when the starter was applied in furrow.
Regardless of previous crop (corn, soybean, cotton, sorghum, or wheat) yield was higher with the use of a starter fertilizer. This was perhaps a result of most studies applying N either pre- or at planting. Additionally, many producers increase N applications at pre- or at planting when corn follows a non-legume crop (corn, cotton, wheat) as compared to a legume crop (soybean, alfalfa).
Surprisingly, of the previous studies included in the meta-analysis, the impact of starter fertilizer was the same in no-till and tilled systems. Soil temperatures can be lower in no-till systems at planting thus reducing the rate of nutrient mineralization. However, tillage related differences in soil conditions like soil moisture and temperature may not justify changes to fertilizer management. Keep in mind this result maybe a result of the studies included in the analysis and the impact for a particular field may be different.
Yield increases were similar when the starter contained N and P as compared to products containing K as well. As most starter products contain a combination of nutrients with the recent inclusion of S in many products, the response documented in this study, by using combinations, appears well justified.
The impact of starter on yield was similar across different levels of soil organic matter, texture and planting month soil temperature and moisture conditions. This is contrary to the current opinion that starter fertilizer is more beneficial in course soils with low organic matter and under cool and wet soil conditions.
The analysis showed that while the response to starter fertilizer decreased when P and K were above recommended levels, a positive yield response was still found for both P and K when both were above the critical level. This suggests that starter fertilizer containing P and K may improve corn yield even when soil tests would not warrant it. A study in Ontario, Canada supported the finding of the mega-analysis, that a starter fertilizer increased yield both when P and K were both below and above recommended levels.1
At higher seeding rates, the benefit of starter fertilizer was limited when compared to a broadcast application. The researchers speculated that starter fertilizer may cause increased root growth thus increasing competition for available nutrients later in season.
As yield level increases, the benefit of starter fertilizer increases. The authors speculated that as yield potential increases, nutrient uptake also increases and reflects a greater crop demand and lowering risk of other limitations in the higher yield situation.
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