EFFECT OF POLYMER SEED COATING WITH MICRONUTRIENTS ON SOYBEANS IN SOUTHEASTERN COASTAL PLAINS

Polymer seed coating with micronutrients may affect soybean ( Glycine max (L.) Merr) growth and yields under dryland conditions. The objective of this study was to determine the effect of two seed application rates (265 and 395 mL 100 kg seeds - 1 ) of polymer based mixture of Copper (Cu), Manganese (Mn) and Zinc (Zn) micronutrients on dryland soybeans near Blackville, SC from 2011 to 2012. Soybeans were evaluated for plant Normalized Difference Vegetation Index (NDVI), Leaf Area Index (LAI), plant height, seed weight and grain yields. Compared to untreated control, polymer seed coating significantly increased grain yields by 8.1 and 14.0% with seed applications at 265 and 395 mL 100 kg seeds - 1 , respectively. Plant NDVI improved by 10.5% with application of polymer seed coating treatment at 395 mL 100 kg seeds - 1 . Seed coating at 265 and 395 mL 100 kg seeds - 1 significantly increased plant NDVI by 10.2 and 10.8% at 8 weeks after soybean planting and 4.6 and 4.2% at 12 weeks after planting. Based on significant linear relationships, grain yields increased by 179.2 kg ha - 1 with increasing plant NDVI by 0.1 unit at 6 weeks after planting soybeans and 99.4 kg ha - 1 with increasing weight by 1 g of 100 seeds. Treatment application did not affect plant NDVI at 4 through 6 and 9 weeks after planting, plant LAI at 8 and 12 weeks after planting and plant height. These results indicate that polymer seed coating may help to improve some growth parameters and grain yields of soybean under dryland conditions in Southeastern Coastal Plains.


INTRODUCTION
Micronutrient deficiency in the soil, enhanced by excessive rain or application of fertilizers, leads to drastically reduced yields (Konkol et al., 2012). Xie et al. (2011) noted that applications of Nitrogen (N), Phosphorus (P) and Potassium (K) fertilizers affected soil properties, where N increased corn shoot Cu concentration and P decreased availability of Copper (Cu) and Lead (Pb). Wozniak and Makarski (2012) reported that 90 kg N ha −1 improved uptake of K, Iron (Fe), Zinc (Zn) and Cu, while high rates at 150 kg N ha −1 increased concentrations of grain Manganese (Mn) in wheat (Triticum aestivum L.).
Although P may help increase grain yield, excess of this nutrient decreased Zn and enhanced Fe, Cu and Mn uptake in wheat biomass (Zhang et al., 2012). Hassan et al. (2012) observed increased P uptake in cereal crops planted after legumes.
Deficiencies of Zn, Fe and Fe decrease wheat yields in light soils, so application of these micronutrients may help to increase yields of susceptible wheat cultivars (Narwal et al., 2012). Micronutrients Fe and Mn are important to plants, but antagonistic relationship between these nutrients may occur during uptake (Moosavi and Ronaghi, 2011). Kobraee and Shamsi (2011a) noted that micronutrient concentrations changed during growing season of soybeans from R1 (beginning bloom) to R8 (full maturity) stages with Fe decreasing in leaves and stems faster than other nutrients. Micronutrients Zn, Fe and Mn were translocated from stems to leaves and

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Fe moved to seeds when soybeans were getting closer to R8 stage (Kobraee and Shamsi, 2011b).
Nutrient availability also depends on production practices. Ciolek et al. (2012) observed that wheat from organic farming had greater concentrations of Mn, Fe, Zn, calcium (Ca) and magnesium (Mg) than conventional program. The N, P, K, Mg, Mn, Zn and Cu nutrients in wheat were higher after inoculating grains with different bacteria (Eleiwa et al., 2012).
Deficiency of Zn is a common problem in different regions (Ghandilyan et al., 2012). Optimum soybean yield can be obtained when Zn and P concentrations in the soil are greater than extension recommendations (Anthony et al., 2012a). Han et al. (2011) added that soybean growth was mostly positively correlated with Zn fertilizer. Soybean yield increased with Zn fertilization, even in soils at above critical levels, so recommendations for Zn need to be revised (Inocencio et al., 2012).
Sulfur (S) and Fe affected Zn and Cu uptake in wheat grain (Wang et al., 2013). Nadim et al. (2012) pointed out that wheat production was improved with Boron (B) and Fe fertilization. Beside foliar sprays, seed coatings also improved Zn uptake and soybean yields (Han et al., 2011). Guareschi et al. (2011) reported that polymer coating of superphosphate and potassium chloride 15 days prior to planting increased dry matter and grain yields while no significant differences were reported with polymer applications at planting. According to De Additionally, seed coatings with temperature-activated polymer may help to protect seeds against cold soils (Gesch et al., 2012).
Growers need to better understand factors, which affect soybean yield variability (Anthony et al., 2012a). Anthony et al. (2012b) noted that fertilizer recommendations rely on estimating nutrients supplied and immobilized in the soil, which is important for sitespecific nutrient management. Micronutrients use in the fertilization program becomes a common practice on farms, but it is important to conduct more studies (Goncalves et al., 2011). There is a need to determine required micronutrient concentrations in soils and plants for soils with likely deficiencies (Hitsuda et al., 2010). Little research focused on seed polymer nutrient coating in soybeans under dryland environments and mostly insufficient rainfall. According to De Figueiredo et al. (2012), polymer-coated fertilizer need to be evaluated for improving efficiency of nutrients. Therefore, objective of this study was to evaluate polymer micronutrient seed coating on soybeans under dryland conditions in Southeastern Coastal Plains.

Site Preparation and Management
This study was conducted on Dothan loamy sand (fine loamy, kaolinitic, thermic Plinthic Kandiudult) at Clemson University, Edisto Research and Education Center (REC) near Blackville, SC (33° 21' N, 81°19' W) under dryland conditions in 2011 and 2012. These are deep, well drained soils with slow permeability and soil pH was 6.2. Treatments consisted of 2 rates of 45% seed coating formulations with Cu, Mn and Zn mixture on a polymer backbone at 265 and 395 mL 100 kg seeds −1 and an untreated control.
Prior to planting soybeans following winter wheat, soybean seeds were treated with polymer seed coating formulations. Soybean cv. 'Pioneer 97M50' was planted at 272,000 seeds ha −1 in strip-till using

Plant Measurements
Plant measurements were conducted in the center of each plot. Normalized Difference Vegetation Index (NDVI) was measured using handheld GreenSeeker TM (NTech Industries, Inc. Ukiah, CA) instrument once a week starting at 4 weeks after planting. The Leaf Area Index (LAI) LAI-2000 (Li-Cor, Lincoln, NE) meter was used to measure plant index at 8 and 12 weeks after soybean planting. Ten random plants were selected for height measurements from the ground to the top of the plant prior to soybean harvest.
Soybeans were harvested from the entire length of the plot using Kinkaid 8XP small plot combine (Kinkaid Equip. Mtg, Haven, KS) on 8 November 2011 and 29 October 2012. Grain samples from all harvested plots were evaluated for weight and tested for moisture using a Burrows Model 750 Digital Moisture Computer (Seedburo Equip. Co., Chicago, IL). Seed weight was determined after counting seeds using the Agriculex electronic seed counter model ESC-1 (Agriculex Inc., Guelph, Ont., Canada). Grain yield was converted to 15.5% moisture content. Additionally, weather data (air temperature and precipitation) were recorded during soybean vegetation using a weather station located near the experimental site.

Statistical Analysis
The study design was a Randomized Complete Block with six replications. Data were analyzed using the general linear models in SAS (SAS, 2011) by analysis of a variance and means were separated using Fisher's Least Significant Difference Test at p≤0.05. A linear regression model was fit using PROC REG (SAS, 2011) after contrast analyses indicated a significant (p≤0.05) response.

Weather Conditions
Monthly average temperature, precipitation and average from the 30-yr average are shown in Table 1. The average air temperature during the soybean growing seasons in each year was generally similar to the 30-yr average, except for June and July 2011 and August 2012 when temperature was 2.3, 1.3 and 1.1°C higher and October 2011 and June 2012 when temperature was 2.3 and 1.4°C lower, respectively.
Total precipitation was 151 mm higher during soybean growing season in 2011 and 15 mm higher in 2012. Insufficient precipitation was observed in June in two years and also July, September and October in 2012. Compared to multiyear rainfall data, higher precipitation was observed in August of 2011 and 2012 and July, September and October of 2011.

Normalized Difference Vegetation Index
(NDVI) Table 2 shows that plant NDVI at 7 weeks after planting significantly increased by 10.5% with application of polymer seed coating treatment at 395 mL 100 kg seeds −1 compared to control. Plant NDVI was also significantly greater at 8 (10.2 and 10.8%) and 10 (4.6 and 4.2%) weeks following planting with applications of seed treatments at 265 mL and 395 mL 100 kg seeds −1 , respectively. Polymer seed coating with micronutrients did not significantly affect plant NDVI at 4, 5, 6 and 9 weeks after soybean planting.

Plant Leaf Area Index (LAI), Height, Seed Weight and Grain Yield
Compared to the untreated control, application of polymer seed coating at 265 and 395 mL 100 kg seeds −1 significantly increased soybean yields by 8.1% and 14.0%, respectively ( Table 3).
Although there was no significant difference, plant LAI improved by 2.0 and 1.5% over control at 8 weeks after soybean planting and 6.9 and 5.3% at 12 weeks following planting with application of seed coating at 265 mL and 395 mL 100 kg seeds −1 , respectively. Compared to control, application of seed coating at 265 mL and 395 mL 100 kg seeds −1 increased plant height by 3.5 and 4.8%, respectively, but difference was not significant.

Relationships between Grain Yields and Plant Parameters
Significant relationships were observed between grain yield and plant NDVI at 6 weeks following planting and seed weight ( Fig. 1 and 2). Based on linear relationship, increasing plant NDVI by 0.1 at 6 weeks after planting soybeans increased yields by 179.2 kg ha −1 . Also, grain yields increased by 99.4 kg ha −1 with increasing weight of 100 seeds by 1 g.

DISCUSSION
Previous research on polymer seed coating with micronutrients was limited and not conclusive. Han et al. (2011) indicated that soybean growth was generally Science Publications AJABS positively correlated with Zn concentrations. Application of Zn also improved wheat growth (Nadim et al., 2012). Results from this study showed that polymer seed coating with micronutrients increased plant NDVI by 10.5% at 395 mL 100 kg seeds −1 , 10.2 and 10.8% at 8 weeks and 4.6 and 4.2% at 10 weeks after planting soybeans at 265 mL and 395 mL 100 kg seeds −1 , respectively.
Researchers reported that higher wheat Leaf Area Index (LAI) were obtained with Zn applications (Nadim et al., 2012) and production of sorghum and wheat was positively correlated with micronutrient levels in the soil (Nandapure et al., 2011). Inocencio et al. (2012) observed that Zn applications improved yields of soybeans, even when micronutrient availability in the soil was above the critical level. Wiatrak (2013) reported higher grain yields with application of polymer seed coating with micronutrients to winter wheat. According to Arshad et al. (2011), grain yield of wheat increased with Cu and Zn application. Applications of Zn, Fe and Mn improved yields of susceptible wheat cultivars (Narwal et al., 2012). This study showed that polymer seed coating at 265 mL and 395 mL 100 kg seeds −1 significantly increased soybean yields by 8.1 and 14.0%, respectively. However, plant height prior to harvest and LAI were not affected by seed coating.
A positive relationship between plant NDVI during crop vegetation and grain yields in this study agrees with Raun at al. (2001), who observed strong relationship between these parameters in winter wheat. Moreover, a positive relationship was observed between weight of grain and soybean grain yields.

CONCLUSION
This study investigated the effects of two polymer seed coating application rates on growth and yield of soybeans grown under dryland conditions. Application of seed coating to seeds at 265 mL 100 kg seeds −1 improved plant NDVI by 10.5% and applications of 285 mL and 395 mL 100 kg seeds −1 improved plant NDVI by 10.2 and 10.8% at 8 weeks after planting soybeans and 4.6 and 4.2% over control at 10 weeks after planting crop. Treatments did not affect plant NDVI at 4 through 6 weeks and 9 weeks after planting.
Grain yields significantly increased by 8.1% and 14.0% with application of polymer seed coating at 265 and 395 mL 100 kg seeds −1 compared to the untreated control. Although no significant difference was observed between treatments, applications of seed coating at 265 mL and 395 mL 100 kg seeds −1 improved plant LAI by 2.0 and 1.5% at 8 weeks following planting soybeans and 6.9 and 5.3% at 12 weeks after planting, respectively. Moreover, plant height increased by 3.5 and 4.8% over untreated control with application of seed coating at 265 mL and 395 mL 100 kg seeds −1 , respectively. Significant positive linear relationship showed that increasing plant NDVI by 0.1 increased crop yield by 179.2 kg ha −1 and weight increase by 1 g of 100 seeds −1 increased grain yield of soybeans by 99.4 kg ha −1 . Future research may focus on evaluating more micronutrients and different concentrations on crop growth and yields.

ACKNOWLEDGEMENT
I greatly appreciate a financial support from Specialty Fertilizer Products (SFP) for conducting field research.