Illinois
Fertilizer Conference Proceedings
January 26-28, 2006
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J.D. Hernandez, S.A. Ebelhar, and E.C.Varsa
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 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. Many things have changed since 1980, for example, tillage practices, cropping systems, higher yielding varieties and cultivars have been introduced, and appreciable quantities of soil zinc have been removed in harvested crops without replenishment. This necessitates a re-examination of the zinc fertilization needs of corn. 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 1.5 mg Zn kg-1 (ppm), 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 1.5 mg Zn kg-1 and those specific sites were chosen for the 2004 and 2005 experiments. Data from 2004 showed no yield and crop performance differences in response to the addition of Zn to soil in areas with medium-low soil Zn test. For this reason a new approach was established for 2005 trials. The selected sites had relatively medium levels of zinc with and without manure management, and soil P high to very high. The four sites chosen for each experimental site were in 2005 as follows:
Table 1: Site descriptions and identification
| Site ID | Identification |
|---|---|
Farm manure |
F-1 |
Farm
no manure |
F-2 |
SIUC manure |
S-1 |
SIUC
no manure |
S-2 |
The 2005 experiments consisted of 4 locations, 2 of them in a farm site in Washington county southern Illinois, one had a history of manure application and relatively high soil phosphorus test (80 mg kg-1) and the other with no manure history with high levels of soil test P, both soils had pHs above 6.8. The other 2 sites were located at Southern Illinois University Agronomy Research center and there was also one with manure application history and relatively high soil P level and the other with no manure history. Two zinc sources were evaluated at 0, 1, 2 and 4 lb Zn/acre: granular zinc sulfate (31% Zn) and DTPA liquid a commercial product ( Table 2).
The resulting eight treatments were each replicated four times in a randomized block design. The treatments were applied in check plots (0-Zn), ZnSO4 at rates of 1, 2 and 4 lb/acre, Zn-chelate (DTPA) at similar rates, and a plot with potassium sulfate to check for sulfur response. Macronutrients were balanced in all the treatments based on commercial production requirements. 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. The two central rows were harvested. Young whole plant Zn and P content, biomass production, grain yield and Zn-DTPA and P (Bray P1) were analyzed, ear leaf Zn and P content, and soil will be analyzed.
Location and manure history effects on Zinc response
In this experiment location was the factor that resulted in the greatest difference in zinc response. A particular response was observed in biomass production on 10 plants (6 leave stage) where in each soil type the soil with manure history had more biomass production. In the area S-1 and S-2 there were no differences in Zn plant concentration. However in F-1 and F2 the amount of Zn plant concentration and Zn plant uptake were almost double under manure history management. Another important result was observed with corn yield performance. In area S-1 and S-2 there were differences in yield performance. However the response was due to the presence of manure and not to the addition of the treatments. Unfortunately, no comparison is possible in F-1 and F-2, because the farmer harvested half of the experimental plot area by accident. The location (farm vs. research center) had an effect on total phosphorus uptake by young plants, due to the initial content in each location. However, manure and non manure did not increase the amount uptake by plants (data not shown).
Zinc Effects on Corn Growth, Nutrient Composition, and Yield
The 2005 growing season was erratic and with prevalent drought days. Signs of heat stress were observed in all the plots throughout the growing season. At the end of the season, yield differences were observed across plots from SIUC and farm plots, with more yield decrease effects on the farm sites where the lack of water was more severe. The application of zinc source was significantly different due to the selected location manure and non manure. However the zinc treatments showed no impact on early corn growth and zinc tissue composition and zinc plant uptake. The locations manure and non manure had effect on increasing the biomass production of young plants (P>0.01) [6-leaf stage plants]. Places with manure history produced the greatest amount of biomass among all the treatments. Whole plant tissue concentrations of zinc increased at the highest Zn rate (4 kg ha-1) with zinc fertilization at all locations. The treatment with sulfate plus DTPA (control) did not show any advantage suggesting no effects for the presence of those components within the treatments.
There was a tendency to increase yield with the addition of zinc (the highest rate) at all locations but significant effects were not observed at any of them, due largely to variability on the field. There was no difference in the relative response whether the zinc was applied as ZnSO4 or as Zn-chelate.
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 Zn-DTPA. This chance resulted in more available Zn in soil solution. However it did not change the crop response.
When this study was initiated in 2004 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 that tested "low" or "marginally sufficient" for soil test zinc levels. Zinc was applied as two sources (ZnSO4 or Zn-chelate) at rates of 0, 1, 2 and 4.0 kg Zn/ha. Even though relatively low-medium testing sites were chosen, corn response to applied zinc was observed. In this experiment a response to Zn plant concentration and Zn plant uptake was not affected by either rate or source. Finally yields showed a tendency to increase at the highest rates of Zn application (P>0.11). However the response observed in yield had large variability and were not statistically different.
Data from grain and fully developed corn ear leaf are not included in the conclusion because they are in the process of being analyzed.
Table 1. Site descriptions and identification
Table 2. Analysis of zinc fertilizer sources used in the 2005 studies on corn.
Table 3. Site conditions and experimental details related to the zinc studies on corn in 2005.
1 E.C.Varsa, and J.D. Hernandez are Emeritus Professor and Assistant Professor 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.
