Infuence of Seed Coating with Micronutrients on Growth and Yield of Winter Wheat in Southeastern Coastal Plains

Polymer seed coating with micronutrients may provide important nutrients during plant growth and improve yields. The objective of this study was to determine the effect of three seed application rates (265, 395 and 530 mL 100 kg seeds −1 ) of polymer based mixture of Copper (Cu), Manganese (Mn) and Zinc (Zn) micronutrients on dryland winter wheat (Triticum aestivum L.) near Blackville, SC from 2010 to 2012. Compared to untreated control, seed coating significantly increased grain yields by 5.0 and 2.1% with seed applications at 530 and 395 mL 100 kg seeds −1 , respectively. Dry matter yield improved over control by 13.4, 22.6 and 20.7%, N uptake by 13.9, 24.6 and 19.3% and P in plant biomass by 16.0, 23.3 and 21.3% with seed applications at 265, 395 and 530 mL 100 kg seeds −1 , respectively. Coating application of 265 mL 100 kg seeds −1 increased grain N content by 5.0% compared to control. Grain P uptake was greater with seed application rates of 265 and 395 mL 100 kg seeds −1 (0.415 and 0.399%, respectively) than 530 mL 100 kg seeds −1 (0.385%). Significantly higher grain Cu uptake was observed at rate of 395 mL 100 kg seeds −1 than 265 and 530 mL 100 kg seeds −1 . Based on significant linear relationships, increasing dry matter yield and N uptake by 1 kg ha −1 , Zn content in plant biomass and grain Cu content by 1 ppm and plant height by 1 cm, increased grain yields by 2.6, 369.3, 27.8, 18.3 and 58.3 kg ha −1 , respectively. Grain yields improved by 706.4, 357.4 and 436.2 kg ha −1 with increasing plant Normalized Difference Vegetation Index (NDVI) by 0.1 unit at 16, 18 and 21 weeks after planting. These results indicate that polymer seed coating may help improve some nutrient uptake and production of dryland winter wheat in Southeastern Coastal Plains.


INTRODUCTION
Micronutrient deficiency in the soil can reduce crop yield and quality (Konkol et al., 2012). They reported that micronutrient deficiency may occur due to excessive irrigation or excess application of chemical fertilizers. Nandapure et al. (2011) showed that application of chemical fertilizers at optimum rates helped to improve uptake of micronutrients by crops and yields were positively correlated with micronutrient status in the soil. According to Xie et al. (2011), Nitrogen (N) application improved shoot Copper (Cu) uptake in corn, but not in soybean (Glycine max L.). They observed that phosphorus application decreased copper (Cu) uptake. Zhang et al. (2012a) showed that adequate N supply can improve uptake of iron (Fe), Zinc (Zn), Manganese (Mn) and Cu in wheat grains. Standard N rate of 90 kg ha −1 increased potassium (K), Fe, Zn and Cu and 150 kg N ha -1 improved Mn uptake in grain of spring wheat (Wozniak and Makarski, 2012). McBeath et al. (2011) pointed out that Phosphorus (P) should be applied in early wheat growth to provide essential P and improve grain yields. According to Hassan et al. (2012), legumes improved P uptake of the following cereal crops. Wheat grain had higher concentrations of Calcium (Ca), Fe and Zn in cropping system after pea (Pisum sativum L.) and improved K and Mn content after soybeans (Wozniak and Makarski, 2012).
Applications of P increased yield, but decreased Zn in shoot and grain while improving uptake of Fe, Cu and Mn in plant biomass (Zhang et al., 2012b). Therefore, they recommended applying Zn to soils high in P to improve yield and grain Zn concentration. Narwal et al. (2012) noted that Zn, Fe and Mn insufficiencies affect wheat grown on light soils. Their results showed that applying Zn, Fe and Mn increased yields of susceptible wheat genotypes. Researchers emphasized that plant Zn deficiency is common in the world (Ghandilyan et al., 2012) and critical Zn soil status should be revised (Inocencio et al., 2012). Pandey et al. (2012) reported that Zn deficiency decreased tissue Zn content and dry matter yield of pea. Soybean growth and yields were positively correlated with Zn applications in soils deficient in this micronutrient (Han et al., 2011). Moreover, Zn and Cu uptake in the wheat grain may be affected by Sulfur (S) and Fe (Wang et al., 2013). Moosavi and Ronaghi (2011) reported that high applications of essential nutrients like Fe and Mn decreased absorption of other nutrients by roots or transportation from roots to plant shoot. However, soybean root or dry matter yield was not affected by Fe or Mn application.
Compared to conventional practices, wheat grain from organic farming had greater concentrations of Mn, Fe, Zn, Ca and Mg (Ciolek et al., 2012). However, lower uptake of grain Fe and Zn was determined in organically grown barley and oat. Kobraee and Shamsi (2011a) showed that micronutrients varied in different parts of soybean plant during the growing season from R1 to R8 stages. Nutrients Zn, Fe and Mn were transferred from stem to leaves when soybeans were approaching the full maturity stage (R8) (Kobraee and Shamsi, 2011b).
Fertilizer placement is important in improving nutrient availability (Fernandez and White, 2012), which may also be affected by tillage system. According to Wozniak and Makarski (2012), ploughless tillage system increased content of Zn and Cu, while ploughing improved uptake of K, magnesium (Mg) and Mn in the wheat grain. Zhao et al. (2012) reported that both origin and genotype affected contents of Mn, Fe, Cu, Zn and other micronutrients in wheat grain. Higher uptake of N, P, K, Mg, Mn, Zn and Cu and grain yields were reported following wheat grain inoculation with different bacteria (Eleiwa et al., 2012). Abedi-Koupai et al. (2012) emphasized that coating with polymer significantly decreased the release rate of iron. Seed coatings with temperature-activated polymer may help protect soybean seed from cold and wet soils and improve emergence (Gesch et al., 2012). Guareschi et al. (2012) reported that application of superphosphate and potassium chloride coated polymer 15 days before planting increased dry matter and grain yield of soybeans, but application at planting did not produce higher yields.
Not all soils require application of micronutrients to improve soil fertility and crop yields (Mubarak et al., 2012). However, it is becoming a more common practice to use micronutrients in the fertilization programs and more research is needed to develop good program (Goncalves et al., 2011a;. Anthony et al. (2012) pointed out that fertilizer recommendations depend on nutrients supplied and immobilized by soil and these recommendations are important for nutrient management. Additionally, critical micronutrient status in soils and plants has not been determined for soils with expected nutrient deficiencies.
Very little research focused on seed polymer nutrient coating under dryland environments and limited repors are not conclusive on the effect of seed treatments on wheat crop under insufficient rainfall. Figueiredo et al. (2012) emphasized a need to evaluate polymer-coated fertilizer to improve efficiency of nutrients. In the Southeastern Coastal Plain, wheat is mostly grown under dryland conditions. Soils in this region are mostly light and sandy with low holding capacity for water and nutrients. Moreover, precipitation is unpredictable and mostly insufficient, which contributes to lower yields. Therefore the objective was to evaluate polymer micronutrient seed coating on winter wheat under dryland conditions in Southeastern Coastal Plains.

Site Preparation and Management
This study was initiated on Faceville loamy sand (Fine, kaolinitic, thermic Typic Kandiudults) at Clemson University, Edisto Research and Education Center (REC) near Blackville, SC (33° 21' N, 81°18' W) under dryland conditions in the fall of 2010. These are well drained soils with moderate permeability and soil pH was 6.6. Treatments consisted of 3 rates of 45% seed coating formulations with Cu, Mn and Zn mixture on a polymer backbone at 265, 395 and 530 mL 100 kg seeds −1 and an untreated control.
Prior to planting winter wheat following soybean previous crop, the seed coating formulations were applied to wheat seeds. Wheat cv. 'Pioneer 26R12' was planted at 59 seeds per 1 m of row and 19 cm row spacing using a

Sample Collections and Analyses
Plant tissue samples were collected from above the ground for biomass production and nutrient concentration at Zadoks 21 wheat stage on 19 January 2011 and 9 February 2012. Plant Normalized Difference Vegetation Index (NDVI) was measured in two center rows using handheld GreenSeeker TM (NTech Industries, Inc. Ukiah, CA) instrument once a week starting in late January. Plant height, based on 10 random plants in each plot, was measured from the ground to the tip of the grainhead prior to wheat harvest.
Wheat was harvested from the full length of the plot using Kinkaid 8×P small plot combine (Kinkaid Equip. Mtg, Haven, KS) on 16 May 2011 (about a week earlier that normally due to possibility of the hailstorm damage in the area) and 24 May 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 from each plot to 135 g kg −1 moisture content. Additionally, weather data (air temperature and rainfall) were recorded during wheat vegetation using a weather station located near the experimental site.

Statistical Analysis
The experimental design was Randomized Complete Block with six replications. General linear models in SAS (2011) were used to analyze data and means were separated using Fisher's Least Significant Difference Test at p≤0.05. A linear or quadratic regression model was fit using PROC REG (SAS, 2011) after cotrast indicated a significant response.

Weather Conditions
Monthly average temperature, precipitation and average from the 20-year average are shown in Table 1. The average air temperature was mostly similar to the 20-year average, except for March 2012 when temperature was 3.3°C higher and December 2010 and January 2011 when temperature was 6.0 and 3.2°C lower, respectively.
Precipitation varied between years and affected plant growth. Precipitation was 182 mm lower in 2010/2011 season and 145 mm lower in 2011/2012 season. Insufficient precipitation was recorded for November, December, January and April in both seasons and also May in the first growing season and February in the second season. Slightly higher precipitation was observed in February in the first season, March in both seasons and May in the second season. Table 2 shows that application of seed coating treatments significantly increased dry matter production, N and P uptake compared to the untreated seeds. Seed treatment applications at 265, 395 and 530 mL 100 kg seeds −1 increased dry matter production by 13.4, 22.6 and 20.7%, N uptake by 13.9, 24.6 and 19.3% and P uptake by 16.0, 23.3 and 21.3% over control, respectively. However, Cu, Mn and Zn content in plant biomass was not affected by the seed coating treatment.

Plant height, Yield and Grain Nutrient Uptake
Application of seed coating at 395 and 530 m 100 kg seeds −1 produced significantly higher grain yields of winter wheat (Table 3). Compared to control, grain yields increased by 2.1% at 395 ml seed application and 5.0% at 530 mL 100 kg seeds −1 of seed coating application. Grain N significantly increased by 5.0% with seed application treatment of 265 mL 100 kg seeds −1 . Highest grain P content was recorded at 265 mL and 395 mL 100 kg seeds −1 and for untreated control, while the highest seed treatment application had lower P content. Grain Cu content was highest for the control and treatment with seed coating application at 395 mL 100 kg seeds −1 . Seed coating treatment did not significantly affect plant height, grain weight and Mn and Zn content in grain.

Relationships between Grain Yields and Plant Parameters
Significant relationships were observed between grain yield and plant biomass, N uptake in plant biomass, plant tissue Zn content, Normalized Difference Vegetation Index (NDVI) at 16, 18 and 21 weeks after planting, plant height and grain Cu content ( Fig. 1-8). Based on these linear relationships, grain yield increased by 2.6 kg ha −1 for every 1 kg ha −1 increase in plant biomass, 369.3 kg ha −1 for 1 kg increase in N uptake, 27.8 kg ha −1 for 1 ppm increase in Zn tissue content and 706.4 kg, 357.4 kg and 436.2 kg ha −1 with NDVI increase by 0.1 at 16, 18 and 21 weeks after planting, respectively. Additionally, increasing in plant height by 1 cm and grain Cu content by 1 ppm, increased grain yields based on linear relationships by 58.3 kg and 18.3 kg ha −1 , respectively. Month

DISCUSSION
Previous research on seed coating was very limited and not conclusive. Pandey et al. (2012) reported that Zn deficiency in the pea crop decreased dry matter yield and tissue Zn concentration. According to Han et al. (2011), growth of soybean was generally positively correlated with Zn concentrations. However, Kobraee and Shamsi (2011a) observed that Zn and Mn concentration in leaf and stem at different growth stages of plant were lower than the untreated control. Another study showed that application of Mn did not affect soybean dry matter yield (Moosavi and Ronaghi, 2011). Results from this study indicated that application of polymer seed coating formulations with Cu, Mn and Zn mixture increased dry matter production, N and P uptake of winter wheat compared to untreated seeds. Arshad et al. (2011) observed that grain yield and grain Cu and Zn concentrations of wheat increased with Cu and Zn applications. They also reported significantly increased Zn concentrations in wheat plants with Cu applications. Inocencio et al. (2012) added that Zn fertilization increased soybean grain yield. However, Kobraee and Shamsi (2011a) pointed out that Zn, Fe and Mn concentrations in soybean seed were lower than control. This study showed that seed coating application improved grain yields, grain N and P concentrations and affected grain Cu content.
A positive relationship between plant NDVI and grain yields in this study agrees with Raun et al. (2001), who also observed a strong relationship between plant NDVI of winter wheat and grain yield. Additionally, positive relationships existed between grain yields and plant biomass, N uptake in plant biomass, plant tissue Zn content, plant height and grain Cu content.

CONCLUSION
This study investigated the effects of three polymer seed coating application rates growth, yield and nutrient uptake of winter wheat grown under dryland conditions. Application of seed coating to seeds at 265, 395 and 530 mL 100 kg seeds −1 improved dry matter production by 13.4, 22.6 and 20.7%, N uptake by 13.9, 24.6 and 19.3% and P uptake by 16.0, 23.3 and 21.3% over control, respectively. Higher application of seed coating treatment produced significantly higher grain yields. Grain yields increase of 5.0% was obtained with seed coating rate of 530 mL 100 kg seeds −1 and 2.1% at rate of 395 mL 100 kg seeds −1 . Seed coating rate of 265 mL 100 kg seeds −1 significantly improved N uptake in grain of winter wheat. Grain P uptake was lower with highest seed coating rate to seeds, but grain Cu was highest for the control and treatment with seed coating application rate of 395 mL 100 kg seeds −1 . Seed coating application did not significantly affect Cu, Mn and Zn content in plant biomass, plant height, grain weight and Mn and Zn content in grain. Significant positive linear relationship showed that for every unit increase in plant biomass, N uptake, Zn in plant tissue, plant height and grain Cu content, grain yields increased by 2.6, 369.3, 27.8, 58.3 and 18.3 kg ha −1 , respectively. Increase in plant NDVI by 0.1 at 16, 18 and 21 weeks after planting improved grain yields by 706.4, 357.4 and 436.2 kg ha −1 . More research may be needed in the future to evaluate the effect of more micronutrients on wheat growth, nutrient uptake and wheat production.

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