Illinois
Fertilizer Conference Proceedings
January 24-26, 2005
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E.C.Varsa, J.D. Hernandez, S.A. Ebelhar, and T.D. Wyciskalla
1
Studies have been conducted periodically over the years in Illinois on the need of zinc (Zn) by agronomic crops. However, an in–depth evaluation of the need for and response to zinc by corn and soybean has not been conducted in southern Illinois for over 24 years. The last intensive survey and study throughout Illinois was conducted in 1977 to 1979 in which a total of 85 sites were evaluated, including about 20 sites in southern Illinois (Brinkman et al., 1980). In these statewide studies only three sites responded significantly to applied zinc and only about one-fourth of the sites responded economically positive to the zinc treatments. Because tillage practices have changed, higher yielding varieties and cultivars have been introduced, and appreciable quantities of soil zinc have been removed in harvested crops without replenishment, a re-examination of the fertilizer zinc needs of corn and soybean is warranted. In addition reports from commercial laboratories suggest that an increasing number of soil and plant tissue analyses are marginal with respect to zinc sufficiency.
A survey of soil test zinc levels in seven southern Illinois counties was conducted in March and April 2004 (Table 1). In most fields soil test zinc levels were higher than 3.0 lb Zn/ac, the suggested level of DTPA extractable zinc above which an economic response to fertilizer zinc would usually not be expected (Handbook on Reference Methods of Soil Analysis, 1992). However, several fields had areas where soil test levels were at or below 3.0 lb Zn/ac and those specific sites were chosen for the 2004 experiments. The four sites chosen and the soil test zinc levels at each experimental site were as follows:
| Initial Site ID | Site Name | lb Zn⁄ac |
|---|---|---|
#2 |
MW⁄2 |
2.8 |
#3 |
TW⁄3 |
1.6 |
#4 |
MW⁄4 |
1.5 |
#6 |
DP |
2.8 |
Two zinc sources were evaluated at 0, 2.5, and 5.0 lb Zn⁄ac: granular zinc sulfate (31% Zn) and MicroPel (1.6% Zn), a commercial pelleted limestone by Bay Chemical Company that was formulated to contain a number of micronutrients including zinc ( Table 2). The resulting six treatments were each replicated six times in a Latin Square design to give a total of 36 plots per location. The two check plots (0–Zn for zinc sulfate and MicroPel) were each treated with an amount of granular elemental sulfur (90% S) that balanced the sulfur that was applied as sulfate–S in the 5.0 lb Zn⁄ac treatments. Also pelleted lime was applied to the 0–Zn MicroPel plots that was equal to the calcium equivalent (limestone) applied in the 5.0 lb Zn⁄ac treatment as MicroPel. The size of the individual plots was 20 ft. by 30 ft. All fertilizers were broadcast applied after corn emergence and were incorporated by a shallow cultivation. Additional experimental details and site conditions are given in Table 3.
Zinc Effects on Corn Growth, Nutrient Composition, and Yield
The 2004 growing season was nearly ideal for corn. Warm and relatively dry conditions in March and April allowed earlier than normal land preparation and planting. Favorable moisture and cooler than normal summer temperatures continued to result in nearly ideal conditions for crop development. In the end, record yields were observed across Illinois and especially high yields were observed in southern Illinois.
The impact of zinc on early corn growth and zinc tissue composition was minimal (Table 4). Zinc had no effect on the dry weight of immature (6–leaf stage) whole plants at any of the four experimental sites. Whole plant and ear leaf tissue concentrations of zinc tended to increase with zinc fertilization at all locations. However, significant zinc composition increases were observed at only two of the four sites for ear leaf zinc. At the DP site zinc concentrations of both immature plants and ear leaf tissue were considerably lower than those found in similar tissues at the MW–2, TW–3, and MW–4 locations. Soil type differences (Cisne versus Bonnie silt loam) were probably responsible for the zinc composition differences.At most all locations slight yield increases were observed with the applied zinc but significant effects were observed at only one location (Table 4). There was no difference in the relative response whether the zinc was applied as ZnSO4 or as MicroPel. When averaged over all sites and the two zinc sources, mean yields were as follows: 0–Zn = 206.5 bu⁄ac, 2.5 lb Zn⁄ac = 209.1 bu⁄ac, and 5.0 lb Zn⁄ac = 210.8 bu⁄ac. If the price of zinc were assumed to be $1.00 per pound, a slight economic benefit would be realized with its use. However, it should be cautioned that these study sites were in portions of fields where some of the lowest soil test zinc values were observed. A smaller zinc response would probably have been recorded if the sites were on soils with a higher zinc soil test level.
Effect of Applied Zinc on Zinc Soil Test Levels
Application of zinc significantly increased soil test zinc (DTPA-extractable Zn) levels at all locations (Table 5 ). The increase in soil test zinc was about the same whether the zinc source was ZnSO4 or MicroPel. On average, an application of two to three lbs Zn⁄ac was required to increase DTPA–extractable Zn by one lb⁄ac. Some of the sites had relatively high soil pH values (ex: TW–3 and DP) and may have caused a reduction in observed soil test values.
A survey of farm fields for soil test zinc in seven southern Illinois counties found most fields had levels that were at or above sufficiency for most crops. Considerable variability in zinc soil test values was found within any one field. No particular soil characteristic or morphological feature could be attributed to the variability. In a study to determine the responsiveness of corn to zinc, four field sites were chosen that had areas which tested "low" or "marginally sufficient" for soil test zinc levels. Zinc was applied as two sources (ZnSO4 or MicroPel) at rates of 0, 2.5, and 5.0 lb Zn/ac. Even though low testing sites were chosen, corn response to applied zinc was mostly non-significant. A significant yield response to zinc was observed at only one location. Soil samples collected for extractable zinc after harvest revealed that test values increased as a result of the applied zinc fertilizers. The magnitude of the soil increase was about the same whether the fertilizer source was ZnSO4 or MicroPel. In 2005, the response of soybean to the residual zinc from the 2004 treatments will be evaluated, as well as, new locations to be identified and established for zinc studies on corn.
Table 1. Survey of fields in southern Illinois for soil extractable zinc.
Table 2. Analysis of zinc fertilizer sources used in the 2004 studies on corn.
Table 3. Site conditions and experimental details related to the zinc studies on corn in 2004.
1 E.C.Varsa, J.D. Hernandez, and T.D. Wyciskalla are Emeritus Professor, Assistant Professor, and Researcher, respectively, in the Plant, Soil, and Agricultural Systems Department, Southern Illinois University-Carbondale. S.A. Ebelhar is an Agronomist at the Dixon Springs Agricultural Center, University of Illinois, Simpson, Illinois.
Brinkman, G.S., J.E. Sawyer, and R.G. Hoeft. 1980. Zinc and sulfur status of Illinois soils. In 1980 Illinois Fertilizer Conference Proceedings. Pp. 27–39.
Handbook on Reference Methods for Soil Analysis. 1992. Council on Soil Testing and Plant Analysis. Omaha, NE.
