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Illinois Fertilizer Conference Proceedings
January 26-28, 1998

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Starter Fertilizers for Reduced-Till Corn

K.B. Ritchie, R.G. Hoeft, E.D. Nafziger, L.C. Gonzini, and J.J. Warren 1
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Introduction
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Illinois research has shown that starter fertilizer frequently increases corn yield in no-till systems (Ritchie et al., 1996), but yield increases are rare when tillage has buried most of the crop residue (Bretzlaff and Boone, 1970; Bullock et al., 1993). There is inadequate data to predict whether starter fertilizer might be effective in reduced tillage practices that leave more residue than intensive tillage, but less residue than no tillage.

There is very little information available regarding how effective S, Zn, or Agricultural Crop Additive (ACA) might be in starter fertilizer, because most of the published research has evaluated broadcast applications of S and Zn, and additions of ACA to NH3. Sulfur deficiencies of corn have been reported on soils with coarse texture and low organic matter (Hoeft et al., 1985). Zinc deficiencies are most evident when soils are cool, and problems from Zn deficiency may be compounded when soil P test levels are high (Tisdale et al., 1985). In Illinois studies, Hoeft et al. (1985) measured a grain yield increase from S application at 5 of 82 site-years; all 82 sites were either low in organic matter, sandy in texture, and/or in areas where apparent S deficiency had been reported. Vanden Heuvel et al. (1989) reported yield increases from Zn at 3 of these same sites. Soil tests for S and Zn were not reliable indicators of whether yield responses to these nutrients may occur (Hoeft et al., 1985; Vanden Heuvel et al., 1989).

Agricultural Crop Additive, which is commonly called ACA and contains zinc ammonia acetate, has not significantly increased grain yield when added to NH3. Christensen and Bricker (1980) reported that although ACA tended to increase corn grain yields in a 3-year study, the yield increases were not statistically significant. Randall (1980) found that although ACA increased silage yields more than did NH3 alone, grain yields were not increased by the addition of ACA. In a greenhouse study, Liu et al. (1997) found that plant height, leaf area, and dry weight of 3-week-old seedlings were increased by ACA.

The objectives of our research were to evaluate the effect on early plant growth and yield of 1) 2X2-banded starter fertilizer containing combinations of N, P, and K, 2) starter N placement, and 3) S, Zn, or ACA added to a 2X2-banded starter fertilizer containing N and P.

Materials and Methods
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Two experiments were conducted side-by-side in 1996 and 1997 at 6 locations (6 locations X 2 years = 12 site-years) varying in existing fertility, soil type (Table 1), crop rotation (Table 3, Table 4, Table 5 and Table 6), and climate. With the exception of 1 site-year in Experiment 2 (Table 5 and Table 6), the previous crop was either corn or soybean. Cooperating farmers were the same throughout the experiment at 5 of the 6 sites, but the plot area was in a different location on the farm each year. The 4-inch soil temperature was monitored for 30 days after planting (Figure 1) with a Hobo® temperature logger (Spectrum Technologies, Plainfield, IL). The early 1996 season was wet, followed by a relatively cool summer, and yields were above average. In 1997, soils were cool for an extended period after planting, but the weather during pollination was hot and dry (Figure 2). Yield results are not reported for the Ogle and Pike county sites in 1997 because severe yield reductions occurred.

Cooperating farmers typically used primary tillage (e.g. chisel plow) in the fall and secondary tillage (e.g. field cultivator) in the spring. Actual amounts of surface residue were not measured, but calculations based on values provided by Hill (1995) suggested that about 15% of the soybean residue and about 35% of the corn residue would have remained on the soil surface after the seeds were planted.

Soil samples were taken in the early spring at 7-inch depths. The samples were analyzed for pH (deionized water), P (Bray-Kurtz P1), K (ammonium acetate exchangeable), and extractable S and Zn (Mehlich III extractant). Nitrogen was applied to all sites at planting time by injecting UAN solution (28% N) according to the University of Illinois recommendations of 1.2 lbs of N per bushel of proven yield, minus 40 lb/acre legume credit when soybean was the previous crop (Hoeft and Peck, 1997). In addition to nutrients supplied in the starter fertilizer, DAP and potash were applied about 5 months before planting by many of the cooperating farmers (Table 2).

Corn was planted at rates near 40,000 seeds per acre (planting dates and hybrid are listed in Table 2) in research plots 10 feet wide and 30 feet long. Plant populations were thinned to 30,200 plants/acre at the V5 growth stage, and above-ground plant samples were taken to measure weight. Grain was hand-harvested from an area in the middle of the plot measuring 5 by 15 feet, and yields were adjusted to 56 lbs/bu at 15.5% moisture.

Experiment 1

Starter fertilizer was applied in factorial combinations of N (0, 12.5, or 25 lbs/acre), P (0 or 30 lbs P2O5/acre), and K (0 or 20 lb K2O/acre) in a 2X2 band. Fertilizer sources were ammonium nitrate, concentrated superphosphate, and potassium chloride. In addition, UAN was dribbled on the soil surface 2 inches to the side of the seed furrow at rates supplying 12.5 or 25 lb N per acre. All treatments were replicated 4 times.

Experiment 2

The purpose of this experiment was to determine whether S, Zn, or ACA improved the performance of a 25-30-0 starter. Fertilizer sources were UAN (28-0-0), ammonium polyphosphate (10-34-0), ammonium thiosulfate (12-0-0-26), Zn-EDTA, and ACA. Sulfur was supplied at a rate of 10 lb/acre, Zn at 0.25 lb/acre, and ACA at 0.5 pint/acre (0.17 lb Zn/acre). In 1996, instead of soybean being the previous crop at a Champaign county site, grass was the previous crop because the plot area was previously enrolled in the Conservation Reserve Program (CRP). Treatments were replicated 4 times at 2 locations (Effingham, Champaign corn following CRP), and 8 times at the other 4 locations. Plant tissue from the first 3 replications at each location was analyzed for S and Zn. In 1997, ACA was not used, plant tissue was not analyzed for S or Zn, corn or soybean was the previous crop at all sites, and all treatments were replicated 8 times.

Results
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Experiment 1

Plant weights at the V5 growth stage were increased in 11 of 12 site-years by 2X2-banded 25-30-0 and 25-30-20 (Table 3). Nitrogen increased plant growth at 11 of 12 site-years, and P increased plant growth at 5 site-years. Increasing the amount of starter N from 12.5 to 25 lb N/acre further increased plant weight in 3 site-years at the Ogle and McLean sites. Soil temperatures were cool (Figure 1) at these sites, and corn was the previous crop. In both of these conditions, plants would be expected to benefit from additional starter N.

Placement of starter N was influenced more by cool soil temperatures than was the amount of starter N. Plant growth was increased when starter N was placed in a 2X2 band instead of on the soil surface at 6 site-years (Table 3). In 1996, N placement influenced response to starter N at the Ogle (both 12.5 and 25 lb N/acre) and McLean (25 lb N/acre) sites, which were the sites where early-season growth was greater when supplied with 25 than with 12.5 lb N/acre. In 1997, growth increases due to banded N were measured at the Effingham (both 12.5 and 25 lb N/acre), Champaign continuous corn (both 12.5 and 25 lb N/acre), Champaign corn following soybean (12.5 lb N/acre), and McLean (12.5 lb N/acre) sites. Soil temperatures were substantially cooler at both Champaign sites and the Effingham location in 1997 (Figure 1). These results demonstrate that placing N in a 2X2 band was more effective at increasing early plant growth than was surface-dribbled N, particularly in cooler soils where root growth is slowed. However, none of the increases in early plant growth due to starter N placement resulted in yield increases (Table 4).

Grain yields were increased in 2 of the 10 site-years by 2X2-banded treatments that contained N (Table 4). Starter fertilizer increased yields at Effingham more than at any other location in 1996, and starter N, P, and K each increased yield response at this site. The only significant yield increase from starter fertilizer in 1997 was the 25-30-20 treatment at McLean.

Based on only 1 site-year, it is difficult to explain why so many yield increases from starter fertilizer occurred at Effingham in 1996. The soil at Effingham has low water holding capacity, and drought stress typically occurs. It seems likely that plants receiving starter fertilizer may have pollinated sooner in better soil moisture conditions.

The lack of yield response to starter fertilizer in 1997, even though early growth was increased by an average of 50 percent, may have been largely due to unfavorable weather conditions at pollination time (Figure 2). Cold, wet conditions slowed early season growth, and delayed pollination until late July, when soil moisture was depleted due to several days of hot, dry weather. This unfavorable environment likely neutralized any positive effects the starter fertilizer may have contributed from increased early plant growth. In unrelated experiments conducted on corn planted in mid-April in Champaign county, plants whose early growth was 2 stages slower (i.e. V4 instead of V6) had larger grain yields (about 20 bu/acre) than did those with vigorous early growth; the plants with slow early growth were still pollinating when substantial rainfall was finally received in mid-August (Hoeft et al., 1997, personal communication).

Experiment 2

Sulfur, Zn, or ACA did not enhance the efficacy of a starter containing N and P. Although the 2X2-banded 25-30-0 starter fertilizer treatment increased V5 plant weight at all 12-site years, plant weight was increased only at Ogle in 1996 by adding S or S plus Zn to the 25-30-0 starter (Table 5). Grain yield was increased at 3 of 10 site-years by the 25-30-0 treatment (Table 6), but was not further increased by adding S or Zn (10 site-years), or ACA (5 site-years). Adding S or Zn to the 25-30-0 treatment decreased V5 plant weight (Table 5) and tended to decrease yield (Table 6) at Effingham in 1996, but it is not known why this occurred.

There was no consistent effect of S, Zn, or ACA on the V5 plant tissue concentrations of S and Zn measured in 1996 (data not shown). The S and Zn levels measured in the V5 plants in 1996 were above the "critical concentrations" listed for S of about 0.20 percent (Hoeft et al., 1985) and 16 ppm for Zn (Carsky and Reid, 1990). In this study, tissue S concentration ranged from 0.22 to 0.34 percent, and Zn concentration ranged from 23 to 33 ppm (data not shown).

Conclusion
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Starter fertilizer consistently increased early growth of corn in the reduced-tillage systems, but grain yields were not consistently increased. Early-season growth was increased by N in 11 of 12 site-years, while P increased growth in 5 of 12 site-years. Treatments supplying 25 lb N/acre increased plant growth more consistently than did 12.5 lb N/acre, and placing N fertilizer in a 2X2 band increased plant weight more than did dribbling N on the soil surface. Grain yields were increased in 2 of 10 site-years by 6 of 8 banded starter fertilizers that contained N.

When starter fertilizers containing N and P increased grain yields, adding S, Zn, or ACA did not further increase yields, nor did these additives consistently increase plant weight.

Purchase of equipment to apply starter fertilizer would not be justified by the inconsistent results obtained in this study. Those already equipped to apply starter fertilizer should consider including N in the starter fertilizer, as well as applying starter fertilizer on soils that have low productivity indices, low fertility, or cool temperatures.

Acknowledgments
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We thank the cooperating farmers and industry agronomists, Illini FS, Brandt's Pleasant Plains, Cole Growers Supply, and the Fertilizer Research and Education Council.

Tables and Figures
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Table 1. Average soil test values at experimental sites. Cropping sequences are corn following soybean (C-S) or corn following corn (C-C).

Table 2. Planting dates, hybrid used, and broadcast fertilizer applied at experimental sites. Cropping sequences are corn following soybean (C-S) or corn following corn (C-C).

Table 3. Effect of starter fertilizer applied as 2X2-banded combinations of N, P, or K, or surface-banded N, on the V5 plant weight of reduced-till corn in Experiment 1. Cropping sequences are corn after soybean (C-S) or corn after corn (C-C).

Table 4. Effect of starter fertilizer applied as 2X2-banded combinations of N, P, or K, or surface-banded N, on the grain yield of reduced-till corn in Experiment 1. Cropping sequences are corn after soybean (C-S) or corn after corn (C-C).

Table 5. Effect of S, Zn, or ACA added to a 2X2-banded starter fertilizer containing N and P on the V5 plant weight of reduced-till corn. Cropping sequences are corn following soybean (C-S), corn following corn (C-C), or corn following grass (C-CRP).

Table 6. Effect of S, Zn, or ACA added to a 2X2-banded starter fertilizer containing N and P on the grain yield of reduced-till corn. Cropping sequences are corn following soybean (C-S), corn following corn (C-C), or corn following grass (C-CRP).

Figure 1. Average soil temperature at the 4-inch depth for 30 days after planting.

Figure 2. Soil moisture at 3 depths (6, 18, and 30 inches), rainfall, and timing of silking at a site in Champaign county, 1997.

Footnotes and References
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1 K.B. Ritchie is a Research Assistant, R.G. Hoeft and E.D. Nafziger are Professors, and L.C. Gonzini and J.J. Warren are Senior Research Specialists, Dept. of Crop Sciences, University of Illinois. Research funded by the Illinois Fertilizer Research and Education Council (FREC).

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*Department of Crop Sciences
*University of Illinois Extension
*College of Agricultural, Consumer, and Environmental Sciences
*University of Illinois at Urbana-Champaign
*Illinois Fertilizer & Chemical Association
*Illinois Department of Agriculture
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