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© 2006 Plant Management Network.
Accepted for publication 23 May 2006. Published 6 September 2006.

Hybrid and Planting Date Effects on Corn Response to Starter Fertilizer

Steven M. Cromley, William J. Wiebold, Peter C. Scharf, Division of Plant Sciences, University of Missouri, Columbia 65211; Shawn P. Conley, Department of Agronomy, Purdue University, W. Lafayette, IN 47907-1150

Corresponding author: William J. Wiebold. wieboldw@missouri.edu

Cromley, S. M., Wiebold, W. J., Scharf, P. C., and Conley, S. P. 2006. Hybrid and planting date effects on corn response to starter fertilizer. Online. Crop Management doi:10.1094/CM-2006-0906-01-RS.

Abstract

Previous research has identified several factors that may influence corn response to starter fertilizer including hybrid genetics and planting date. However research examining the influences of these management factors on corn response to starter fertilizer has produced inconsistent results. The objective of this experiment was to determine if hybrid maturity and planting date affect corn yield responses to starter fertilizer. The experiment was conducted near Columbia, MO in 2000 and 2001 and consisted of eight hybrids with and without starter fertilizer. Hybrids were selected for a range in maturity. Starter fertilizer was placed 2 inches to the side and 2 inches below the seed at a rate of 30 lb of N per acre and 30 lb of P₂O₅ per acre. Starter fertilizer increased plant height for four of the five planting date-year combinations and reduced the number of days from planting to midsilk for all five combinations. The magnitude of the changes in plant height and number of days from planting to midsilk due to starter fertilizer application were greater for April planting dates than for May planting dates. Starter fertilizer increased corn grain yield in two of the five planting date-year combinations. Planting date had no effect on the magnitude of the yield response from starter fertilizer. Hybrid maturity affected plant height and days to midsilk responses to starter fertilizer for several planting dates. In instances when hybrid maturity affected the response to starter fertilizer, later-maturing hybrids responded more than early maturing hybrids. There was no effect of hybrid maturity on yield response to starter fertilizer.

Introduction

Previous research has identified several factors that may influence corn (Zea mays, L.) response to starter fertilizer, including hybrid genetics and planting date. In several studies, hybrids responded differently to starter fertilizer, but it is unclear which plant characteristic accounted for this differential response (8,12,14). Gordon et al. (8) reported that for yield, two of five hybrids responded positively to starter fertilizer in all three years of a study performed in Kansas, and an additional hybrid responded positively in two of three years. The three hybrids that responded to starter fertilizer required more thermal units to reach midsilk (later maturing) than the two hybrids that did not respond. However, treatment with starter reduced the number of thermal units from emergence to midsilk for the three responsive hybrids. Conversely, research conducted in Iowa by Buah et al. (4) did not show a differential hybrid response to starter fertilizer. Buah et al. (4) concluded that the hybrid by starter fertilizer interactions were not significant for early-season dry matter production, nutrient concentration, or grain yield in the 12 hybrids studied.

Producers in Missouri and much of the Midwest are planting corn early in order to avoid corn plants silking during periods of hot dry weather that usually occur later in the growing season. Unfortunately, earlier planting usually means planting kernels into cooler soil. Cool soil temperatures reduce root growth (1,11) and nutrient uptake (9). Starter fertilizer often increases corn growth and grain yields in cooler soils (10,13), so it is often assumed that starter fertilizer exhibits greater responses at earlier planting dates. Research in Wisconsin by Bundy and Andraski (5) provided information that contradicts this assumption. They concluded that the probability of a response to starter fertilizer increased with later, not earlier, planting dates. They also observed that economic response to starter fertilizer increased with later hybrid maturity.

Research results examining management factors influencing corn response to starter fertilizer including hybrid and planting date have been inconsistent. Additional research is necessary in order to have a better understanding of what influences corn response to starter fertilizer so that appropriate recommendations can be developed. The objective of this experiment was to determine if planting date and/or hybrid maturity affect corn response to starter fertilizer in a no-tillage system.

Field Study Design and Analysis

This experiment was conducted in 2000 and 2001 on a Mexico silt loam soil (fine, smectitic, mesic Aeric Vertic Epiaqualf) at the University of Missouri Bradford Research and Extension Center near Columbia, Missouri. The experimental design was a randomized complete block with four replications. Treatments were randomized in a split plot arrangement. Whole plots consisted of three planting dates in 2000 and two planting dates in 2001. Split plots were sixteen combinations of eight hybrids planted with and without starter fertilizer. The experiment was planted without tillage following soybean.

Plots were planted with a four-row planter equipped with Yetter brand coulters and knives and a CO₂ -pressurized delivery system for starter fertilizer. The coulters and fertilizer knives were positioned to place the starter fertilizer 2 inches to the side and 2 inches below the seed. Plots were treated with and without starter fertilizer at 30 lb of N per acre and 30 lb of P₂O₅ per acre. This was a liquid fertilizer mixture of urea, ammonium nitrate, and ammonium polyphosphate. The seeding rate was 26,000 kernels per acre. Plots were 60 ft long and four 30-inch rows wide.

All plots received 165 lb of N per acre as broadcast ammonium nitrate after the second planting date. Weeds were controlled with labeled rates of metolachlor and atrazine. Eight hybrids (Pioneer brand 35N05, 33A14, 31B13; Asgrow brand RX505Bt, Rx799Bt; Dekalb brand 626Bty; NK brand 4640Bt, 7070Bt) were selected for a range in maturity using information provided by the seed companies. Planting dates in 2000 were 18 April, 15 May, and 25 May. In 2001, planting dates were 27 April and 17 May. Two replications from the 18 April planting date in 2000 produced poor stands because very dry soil conditions following planting caused poor emergence. Data for all plant characteristics from these two replications were recorded as missing.

At approximately V4 (four leaf collars visible) stand densities were determined and over populated plots were thinned to 24,000 plants per acre. Plant height (extended leaf) was recorded six weeks after planting. Midsilk date was recorded when 50% of the plants had emerged silks of at least 0.5 inch. Physiological maturity was recorded when 50% of the examined kernels exhibited black layer. Both midsilk date and black layer dates were converted to numbers of days after planting. The two middle rows were harvested for yield with a plot combine and corrected to 15% moisture. Harvest dates for 2000 were 8 September, 19 September, and 3 October. Harvest dates for 2001 were 11 September and 25 September. The magnitudes of the response from starter fertilizer for height, midsilk date, and yield were calculated by subtracting the value of the without starter treatment from the value of the with starter treatment and expressed as a percentage of the without starter fertilizer value. This calculation was made for each hybrid within each planting date within each replication.

Because of lack of homogeneity of variances among planting dates, plant height data were analyzed separately for each planting date. For all other characteristics, data were combined and data were analyzed using the General Linear Model procedure of SAS (SAS Institute Inc., Cary, NC). To assess the effect of hybrid maturity on corn response to starter, we calculated Pearson correlation coefficients between estimates of hybrid maturity and the magnitude of the response for each of the three plant characteristics we measured. We used midsilk dates recorded for plots that did not receive starter fertilizer as estimates of hybrid maturity.

Plant Height

Averaged across all hybrids, plant heights of plots treated with starter fertilizer measured six weeks after planting were greater than plant heights of plots without starter fertilizer for all planting dates except 17 May 2001 (Table 1). Our results are similar to results from many other studies that have reported starter fertilizer increased corn plant height or weight during vegetative growth stages (2,3,5,6,7,8,10).

Table 1. Height of eight corn hybrids six weeks after planting, planted with (yes) or without (no) starter fertilizer on three planting dates in 2000 and two planting dates in 2001.

 ^a Starter fertilizer treatments: No = none; Yes = 30 lb of N per acre and 30 lb of P₂O₅ per acre.

 ^b Averaged over hybrids and within a planting date and year combination "No" starter treatment significantly different from "Yes" starter treatment (F-test, P = 0.05).

The magnitude of the average increase in plant height ranged from 2.1 to 16.4% (Table 2). In both years, the April planting date exhibited a greater response to starter fertilizer than the May planting dates. We did not measure soil temperatures, but average air temperatures two weeks before through two weeks after planting were 54, 69, 70, 64, and 67°F for the 18 April 2000, 15 May 2000, 25 May 2000, 27 April 2001, and 17 May 2001 planting dates, respectively. Starter fertilizer has been shown to increase early growth if corn is planted in cooler soils (10,13).

Table 2. Magnitude of response of three plant characteristics to starter fertilizer for eight hybrids planted on three dates in 2000 and two dates in 2001.

 ^a Means within a row and within a planting date followed by the same letter are not different (LSD 0.05).

Correlation coefficients between hybrid maturity and the magnitude of height response to starter are presented in Table 3. Significant and positive relationships were found for the April planting date in both years. This indicated that later maturing hybrids responded more than early maturing hybrids when planted in April, but not in May. It is not clear why maturity of hybrids affects plant height response to starter fertilizer when corn is planted early.

Table 3. Simple correlations coefficients between the magnitude of height, midsilk date, and yield response to starter fertilizer to hybrid maturity for eight hybrids planted on three dates in 2000 and two dates in 2001.

 ^a Significant at P ≤ 0.10.

Plant Development

Previous studies have concluded that starter fertilizer often reduces the number of days required for silks to emerge (7,8,12). In our study, the number of days from planting to midsilk was reduced by starter fertilizer in both years at all planting dates (Table 4). In each instance, the effect was relatively small (2.2 days or less) and may not be biologically important.

Table 4. Midsilk date of eight corn hybrids planted with (yes) or without (no) starter fertilizer on three planting dates in 2000 and two planting dates in 2001.

 ^a Starter fertilizer treatments: No = none; Yes = 30 lb of N per acre and 30 lb of P₂O₅ per acre.

 ^b Averaged over hybrids and within a planting date and year combination "No" starter treatment significantly different from "Yes" starter treatment (F-test, P = 0.05).

The magnitude of the response from starter fertilizer on midsilk date was greater for the April planting dates than the May planting dates in both years (Table 2). This relationship among planting dates for midsilk date was similar to the relationship we found for plant height. Perhaps the acceleration of early vegetative growth by starter fertilizer affected plant development.

Significant and negative correlations were found between hybrid maturity and the magnitude of the response from starter fertilizer on midsilk date for the 15 May planting date in 2000 and the 27 April planting date in 2001 (Table 3). This negative relationship means that later maturing hybrids responded more than early maturing hybrids, but the relationship was significant for only two of the five planting date-year combinations.

The number of days to reach physiological maturity (R6) was not affected by starter fertilizer (data not shown). Gordon et al. (8) also observed that starter fertilizer had no effect on the number of days in the grain fill period. However, Bullock et al. (3) found that treatment with starter fertilizer resulted in an earlier black layer date

Yield

Starter fertilizer affected corn grain yield in three of the five planting date-year combinations. In 2000, starter fertilizer increased yield 9 and 8 bu/acre for the 18 April and 15 May planting dates (Table 5). Starter fertilizer decreased yield of the 27 April planting date 6 bu/acre. Bundy and Andraski (5) reported yield responses from starter fertilizer ranged from —10 bu/acre to +42 bu/acre in a study that examined data from 100 site-years. It is not clear why the two years in our study exhibited different results, but it is not uncommon to have zero or negative yield effects from starter fertilizer.

Table 5. Yield of eight corn hybrids planted with or without starter fertilizer on three planting dates in 2000 and two planting dates in 2001.

 ^a Starter fertilizer treatments: No = none; Yes = 30 lb of N per acre and 30 lb of P₂O₅ per acre.

 ^b Averaged over hybrids and within a planting date and year combination "No" starter treatment significantly different from "Yes" starter treatment (F-test, P = 0.05).

The magnitude of the response from starter fertilizer on grain yield did not differ among planting dates within either year (Table 2). Bundy and Andraski (5) reported that economic yield responses to starter fertilizer were most likely with later planting dates. Our data does not agree with their conclusion. We found no evidence that planting date affected yield response from starter fertilizer even though planting date affected starter fertilizer responses on plant height and days to midsilk.

We found no significant correlations between the magnitude of yield response from starter and hybrid maturity (Table 3). Bundy and Andraski (5) observed that responses to starter fertilizer were most likely with hybrids with longer relative maturity. In their study, hybrids with a relative maturity less than 100 days responded 33% of the time to starter fertilizer, whereas hybrids with a relative maturity greater than 100 days responded 53% of the time to starter fertilizer. We found no evidence to support this conclusion. Perhaps the differences in climate and corn management between Wisconsin and Missouri result in these different conclusions. In central Missouri, corn matures at least 30 days before average frost date. Quicker growth and development may not be as advantageous in Missouri as Wisconsin.

Conclusion

Starter fertilizer increased plant height for four of the five planting date-year combinations, reduced the number of days from planting to midsilk for all five of the planting date-year combinations, and increased corn grain yield for two of the five planting date-year combinations. The objective of this experiment was to determine if planting date and/or hybrid maturity affect corn responses to starter fertilizer. The magnitudes of the changes in plant height and number of days from planting to midsilk due to starter fertilizer application were greater for April planting dates than for May planting dates. Planting date had no effect on the magnitude of the yield response from starter fertilizer. Hybrid maturity affected the magnitudes of plant height and the number of days from planting to midsilk responses to starter fertilizer for several planting dates. In instances when hybrid maturity affected the response to starter fertilizer, later-maturing hybrids responded more than early-maturing hybrids. There was no effect of hybrid maturity on yield response to starter fertilizer.

Acknowledgments

Contribution from the Missouri Agriculture Experiment Station. Partial funding for this project was provided by Pioneer Hi-Bred, a DuPont Company.

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