Research assessing the application of potash in Indiana found that corn yields weren’t affected by strip-till or conventional tillage, or by soil types, according to a study conducted by Purdue University agronomy professor Tony Vyn and supported by Pioneer Hi-Bred.

The key findings of the research were that:

• Grain yield of high-oil corn was consistently increased by potash applications, even though the average soil-test potassium concentration at the site exceeded the critical level for potassium.
• Yield increases resulting from applications of potash were independent of initial soil-test potassium level. This indicates that applications of potash had a larger effect on grain yield than initial potassium soil-test levels.
• Grain yield was unaffected by tillage method or soil type.
• Slightly lower ear-leaf potassium and grain-oil content were measured in no-till compared to chisel and strip-till plots.
• Year-to-year fluctuations in grain quality were many times larger than grain-quality differences resulting from potassium or tillage treatments.
• Decisions about potassium management are more important in obtaining optimum yields and quality of high-oil corn than decisions about tillage.

Many crop best-management practices are developed from small-plot research conducted on sites with uniform soils. But most commercial fields contain a variety of soil types that can differ widely in depth, texture, drainage and productivity characteristics.

Therefore, farmers may rightly wonder if recommendations from small-plot research conducted on uniform soils are applicable to more typical production conditions. Nutrient management may be particularly affected by soil differences, making selection of a uniform vs. variable-rate application strategy a key decision for farmers.

Potassium is an essential plant nutrient and is widely applied to soils used for corn production. However, different tillage systems are known to affect the distribution of available potassium in the soil profile. Lower tillage intensity generally results in greater stratification of fertilizer potash, with higher levels in the surface soil.

It’s unclear whether potassium should be managed differently across tillage systems or across different soil types. Adequate potassium nutrition may be even more critical in the production of high-oil corn vs. yellow dent corn. This is due to the role of potassium in the biosynthesis of oil in corn grain.

Primary Research Objective

The primary objective of Vyn’s study was to determine if tillage system or soil type affected the response of high-oil corn to potassium fertilization. Field experiments were conducted at the Davis-Purdue Agricultural Center in east-central Indiana in 2000 and 2001.

There are three major soil types in the study area, including the well-drained Blount and the more poorly drained Pewamo and Condit soil series.

Likewise, there was a range in soil-test potassium in the 2-to-6-inch layer, from 125 parts per million (ppm) by the ammonium-acetate extraction method. Averaged across years, the overall soil-test potassium level in the surface 10 inches of soil was 122 ppm of potassium. This compares to the critical level for corn production of 100 ppm of potassium.

Three tillage systems were evaluated: Fall chisel with spring cultivation; fall strip-tillage at an 8-inch depth (ST); and no-till following no-till soybeans (NT).

Three potash (sub-plot) treatments were also evaluated: Fall application of 90 pounds of potash per acre; fall application and an additional 50 pounds of potash spring banded; and no potash.

The fields had been in conservation-tillage systems for at least 5 years. Pioneer 34B25, a high-oil hybrid, was planted on May 12, 2000, and May 1, 2001, at 31,000 seeds per acre. Nitrogen and phosphorus starter fertilizer was applied to all plots at 38 and 25 pounds of nitrogen and phosphate per acre, respectively. An application of an additional 190 pounds of nitrogen per acre as anhydrous ammonia was sidedressed prior to the V6 growth stage in both years.

Research Results Q&A

Q. Was there a yield response to potash applications at this site even though the average soil test value was slightly above the critical level for potassium?

A. Yes. In both years, grain yields were increased (10% in 2000 and 5% in 2001) with the fall and spring potash treatment compared to the no potash treatment. Interestingly, yields increased nearly as much on the plots testing above 125 ppm of potassium as did yields from those plots testing below 90 ppm of potassium. In other words, potash fertilizer applications had a larger effect on grain yield than did initial soil test potassium levels.

Q. Did corn yields respond differently to tillage and potash treatments across the three contrasting soil types?

A. No. In these 2 years, tillage and potash fertilizer effects were the same regardless of soil type. In fact, overall yields were very similar across soil types (Table 1). This may not be the case in seasons with significant moisture stress. In a high-stress year, treatments with additional potash and a moisture-conserving tillage practice, such as no-till, might be expected to be higher yielding on upland soils more prone to drought.

Q. Which had the greatest impact on grain yields — tillage or potash fertility treatments?

A. In both years of the study, tillage had no significant effect on grain yield, while the fall and spring phosphate treatment increased yields an average of 11 bushels per acre compared to the check of no potash.

Q. Was grain quality affected by tillage or potash fertilizer treatments and did it differ across soil types?

A. In contrast to grain yield, grain quality was much less affected by the tillage and potash fertility treatments (Table 2). Year-to-year fluctuations and soil type produced the largest differences in oil content. There was a 0.35% increase in oil content for grain from the lower-lying Pewamo soil compared to grain produced in the well-drained Blount series. However, the average variation across years was nearly three times that, averaging 7.15% oil in 2000 vs. 8.18% in 2001.

Q. How might these results using high-oil corn compare to results with yellow dent corn?

A. The primary difference between these corn production systems is the number of plants producing pollen. Since the tillage and potash treatments had no particular effect on the pollinator plants in this study, it’s likely that responses of normal corn to these potash and tillage treatments would be similar to the results obtained with high-oil corn.

In fact, the researchers concluded that high-oil corn does not need to be grown only on productive, uniform soils as previously suggested. Their results found that, like normal corn, high-oil corn can be successfully grown under all tillage systems and on variable soils.