J.D. Hernandez, E.C. Varsa, T.D. Wyciskalla, and S.A. Ebelhar 1
Studies have been conducted periodically over the years in Illinois on the need of zinc (Zn) by agronomic crops such as corn and soybean. The last intensive surveys and studies throughout Illinois were conducted from 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. Large quantities of manure have been applied throughout the state increasing soil P levels. Additionally appreciable amounts of soil zinc have been removed in harvested crops without intentional replenishment. This requires a re-examination of the zinc fertilization needs of corn. In addition, reports from commercial labs suggest that the decrease of Zn in soil and plant tissue levels is becoming marginal.
A survey of soil test zinc levels in seven southern Illinois counties was conducted in March and April 2004 (Figure 1). In most fields soil test zinc levels (DTPA-Zn) were higher than 1.5 mg Zn kg-1 (3 lb/A); suggesting that the level of Zn-DTPA was above of any economic response to be expected (Handbook on Reference Methods of Soil Analysis, 1992). However, a couple fields had areas where soil test levels were slightly at or below 1.5 mg Zn kg-1 and those specific sites were chosen for this experiment in 2004. Data results from 2004 experiment showed no yield and crop performance differences to the addition of any Zn source to soil in areas with medium-low soil Zn test values. Therefore, a new approach was established for the 2005 and 2006 trials. The new selected sites had relatively medium levels (the most common level in the previous survey) of DTPA-Zn. The soils for the 2005-2006 experiments had a previous history of either manure or no manure application, and all of them high soil test P (Bray P-1).
The four sites chosen in 2005 and 2006 consisted of 4 locations, 2 of them at a commercial farm site in Washington County Illinois, and the other at the Southern Illinois University-Carbondale Agronomy Research Center. Both location soils had soil pH levels above 6.8 (Table 1). Two zinc sources were evaluated at 0, 1, 2 and 4 lb Zn/acre: granular zinc sulfate (31% Zn) and DTPA-Zn liquid formulation -commercial grade product (Table 2). Check treatments with no Zn application and only DTPA (provided by the Zn-DTPA manufacturer) were included. The resulting nine treatments were each replicated four times in a randomized complete block design. 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. The data collection consisted of young whole plant and at tasseling tissue for Zn and P concentration, and their biomass production. Also corn plots were sampled for ear leaf Zn and P concentration at corn tasseling. At the end of the season grain yield was collected and the data from grain was standardized to 15 % grain moisture. After harvesting the plots were soil sampled and analyzed for soil Zn-DTPA and soil P (Bray P1).
Objectives: i) To determine whether or not manure history has an impact on zinc application and corn yield performance ii) To determine if the high soil phosphorus concentration will have an effect on corn response to zinc fertilization, and iii) To determine if zinc fertilizer source type have any effect on corn response to zinc fertilization.
In this experiment, location was the factor that resulted in the greatest difference in zinc response among treatments in 2005 and 2006. A particular response was observed in biomass production on 10 plants (6 ‘leaf’ stage). 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 F-2 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 all the areas there were differences in yield performance. However the response was due to the presence of manure and not to the addition of the Zn treatments. 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 P uptake by plants (data not shown).
The 2005 and 2006 growing season was erratic and with prevalent droughty 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 manured vs. non manured locations. However the application of zinc showed no impact on early corn growth and zinc tissue composition and zinc plant uptake. The comparison of the locations with manure and no manure increased 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 lb A-1) with zinc fertilization at all locations. The treatment with sulfate plus DTPA (check plots) did not show any advantage suggesting no effects for the presence of those components within the treatments.
There was a numerical tendency to increase yield with the addition of zinc (at the Zn 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 crop relative response whether the zinc was applied as ZnSO4 or as Zn-chelate.
Application of zinc significantly increased soil test zinc (DTPA-extractable Zn) levels at all locations with the application of higher Zn rates. The increase in soil test zinc was about the same whether the zinc source was ZnSO4 or Zn-DTPA (Data not shown).
When this study was initiated in 2004, a survey of farm fields for soil test zinc (DTPA-Zn) 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 the initial trial in 2004, four field sites were chosen that had areas that tested “low” or “marginally sufficient” for soil test zinc levels. No response to either source or rate was observed in 2004.
In 2005 and 2006 soil with different manure management and high soil P tests were selected. Zinc was applied as two sources (ZnSO4 or Zn-chelate) at increasing application rates. Even though there was an increase of plant and soil zinc concentration with the addition of zinc in the experiment, yield effect was not observed. In this experiment a response to Zn plant concentration and soil Zn (DTPA-Zn) was the same using either Zn source.
Corn yields showed a tendency to numerically increase at the highest rates of Zn application (P>0.11). However the response observed in yield had large variability and was not statistically different. Soils with a high P test were not responsive to the addition of Zn, regardless of previous manure load management.
Plant Zn concentration increased with the addition of any Zn fertilizer. However, no plant yield response was clearly observed when Zn was added at any of the experimental locations.
*Data (2006) 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 Zn study.
1 J.D. Hernandez, E.C. Varsa, and T.D. Wyciskalla are Assistant Professor, Emeritus Professor and Instructor respectively, Plant, Soil, and Agricultural Systems Department, Southern Illinois University-Carbondale; S.A. Ebelhar is Agronomist at the Dixon Springs Agricultural Center, University of 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.