2004, Issue #3

  from your Pioneer Sales Representative:  Kingston Feed & Farm

CROP INSIGHTS  

University/Pioneer Research¹ Update:

Corn Response to Potassium and Tillage Across Variable Soil Types

by Tom Doerge, Agronomy Research Manager

Key Findings of CMRA¹ Research Project

·   Grain yield of high-oil corn was consistently increased by K applications even though the average soil test K concentration at the site exceeded the critical level for K.

·   Yield increases resulting from applications of K were independent of initial soil test K level. This indicates that applications of K had a larger effect on grain yield than did initial K soil test levels.

·   Grain yield was unaffected by tillage method or soil type.

·   Slightly lower ear-leaf K 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 K or tillage treatments.

·   Decisions about K management are more important in obtaining optimum yields and quality of high-oil corn than decisions about tillage.

Introduction

Many crop best management practices (BMPs) are developed from small-plot research conducted on sites with uniform soils. However, most commercial fields contain a variety of soil types that can differ widely in depth, texture, drainage and productivity characteristics. Therefore, producers 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 versus a variable- rate application strategy a key decision for producers.

Potassium (K) 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 K in the soil profile. Lower tillage intensity generally results in greater stratification of fertilizer K with higher levels in the surface soil. It is unclear whether K should be managed differently across tillage systems or across different soil types. Adequate K nutrition may be even more critical in the production of high-oil corn versus yellow dent corn. This is due to the role of K in the biosynthesis of oil in corn grain.

Primary Research Objective

The primary objective of this study by Dr. Tony Vyn, Purdue University, was to determine if the response of high- oil corn to potassium fertilization is affected by tillage system or soil type.

Study Description

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 (Figure 1). Likewise there was a range in soil test K in the 2 to 6-inch layer, from <90 to >125 parts per million (ppm) by the ammonium acetate extraction method. Averaged across years, the overall soil test K level in the surface 10 inches of soil was 122 ppm K. This compares to the critical level for corn production of 100 ppm K.

Three tillage (main plot) systems were evaluated:

·         Fall chisel with spring cultivation (CT)

·         Fall strip tillage at eight inches depth (ST)

·         No-tillage following no-till soybean (NT)

Three K (sub-plot) treatments were also evaluated:

·         Fall application of 90 lbs K₂O/acre (Fall K)

·         Fall application plus an additional 50 lbs K₂O/acre spring banded (F&S)

·         No K (No K)

The fields had been in conservation tillage systems for at least five years previously. Pioneer® Brand 34B25, a high-oil hybrid, was planted on May 12, 2000 and May 1, 2001 at 31,000 seeds/acre. Nitrogen (N) and phosphorus (P) starter fertilizer was applied to all plots at the rates of 38 and 25 lbs N and P₂O₅ per acre respectively. An application of an additional 190 lbs N/acre as anhydrous ammonia was sidedressed prior to the V6 growth stage in both years.

Grain yield and moisture measurements were obtained from a combine-mounted yield monitor. Grain quality (oil and protein) was determined by near infrared analysis on grab samples taken from each sub-plot area.

Results

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

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

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

No. In these two years, tillage and K 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 K and a moisture-conserving tillage practice such as no-till, might be expected to be higher yielding on upland soils more prone to drought.

Which had the greatest impact on grain yields, tillage or K fertility treatments ?

In both years of this study, tillage had no significant effect on grain yield while the Fall & Spring K treatment increased yields an average of 11 bu/acre compared to the No K check.

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

In contrast to grain yield, grain quality was much less affected by the tillage and K 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 versus 8.18% in 2001.

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

The primary difference between these two corn production systems is number of plants producing pollen. Since the tillage and K treatments had no particular effect on the pollinator plants in this study, it is likely that responses of normal corn to these K 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.

References:

Vyn, T.J., B.J.Ball, D. Maier, and S.M. Brouder. 2002. High oil corn yield and quality responses to fertilizer potassium vs exchangeable potassium on variable soils. Better Crops Vol. 86, No. 4. Potash and Phosphate Institute, Norcross, GA.

¹The Pioneer Crop Management Research Awards (CMRA) Program provides funds for agronomic and precision farming studies by university and USDA cooperators throughout North America. The awards normally extend for three years and address crop management information needs of Pioneer agronomists, sales professionals and customers.

Table 1. Grain yield as affected by tillage, K fertilizer,  soil series, and soil exchangeable K in 2000 and 2001.

No K=no K, Fall K=fall applied K, F&S=fall and spring applied K. Data followed by the same letter, or no letter, within a row or within a column are not significantly different according to a protected LSD P = 0.05 or a t test (GLM model) at t_crit = 0.05.  Letters distinguishing differences among individual tillage and K treatment means within columns are italicized, and among SEK means within rows are shown in lower case. Overall means within a column are shown in upper case.

Table 2. Grain oil concentrations as affected by tillage, K fertilizer, soil series, and soil exchangeable K (2-6” depth) in 2000 and 2001.

No K=No K, Fall K=fall applied K, F&S=fall and spring applied K. Data followed by the same letter, or no letter, within a row or within a column are not significantly different according to a protected LSD P = 0.05 or a t test (GLM model) at t_crit = 0.05.  Letters distinguishing differences among tillage and K treatment means within a column are italicized. Overall mean differences resulting from soil series and SEK are shown as upper case.