EVALUATION OF NITROGEN APPLICATION METHODS AND RATES WITH NUTRISPHERE -N ON SOIL NITRATE-NITROGEN IN SOUTHEASTERN COASTAL PLAINS

Nitrogen (N) application with Nutrisphere-N polymer may affect soil Nitrate-Nitrogen (NO 3-N) movement in the soil. The objective was to evaluate two N appli cation methods (all at planting and split applicati on) and five N rates (0, 45, 90, 135 and 180 kg N ha ) with Nutrisphere-N polymer on soil NO 3-N in dryland corn (Zea mays L.) near Blackville, SC from 2010 to 2012. Soil sa mples were collected from the soil depth of 90 cm and divided into 15 cm increments following corn harvest. Compared to uncoated fertilizer, Nutrisph ere-N improved NO3-N concentration by 29.8% with 180 kg N ha −1 in split applications at 0-15 cm depth and by 44.7% at 90 kg N ha −1 applied at planting at 15-30 cm depth. Soil NO 3-N content increased with NutrisphereN by 26.2, 36.1, 28.0 and 17.3% at 45 kg, 90 kg, 13 5 kg and 180 kg N ha −1 in split applications at 15-30 cm depth, respectively. Nutrisphere-N improved soil NO 3-N concentration by 40.1 and 31.6% at 90 kg and 135 kg ha over uncoated treatment for N applied in split app lications at 30-45 cm depth, respectively. Soil NO 3-N content improved with Nutrisphere-N by 36.9% at 135 kg N ha applied at planting, while NO 3-N concentration improved by 33.9 and 34.9% at 135 kg and 180 kg N ha −1 with Nutrisphere-N applied in split applications at 45-60 cm depth, respectively. At 60 -75 cm depth, Nutrisphere-N decreased soil NO 3content by 22.0% at 180 kg N ha −1 applied at planting and increased content by 37.5 and 59.9% with split N applications of 90 kg and 135 kg ha , respectively. Soil NO3-N concentration increased with Nutrisphere-N by 30.6% over untreated fertilizer at 135 kg N ha −1 in split applications at 75-90 cm depth. Generally , N applications with Nutrisphere-N helped to reduce so il NO3-N losses.


INTRODUCTION
Fertilizer recommendations depend on estimating supplied and immobilized nutrients in the soil (Anthony et al., 2012). More applied fertilizers to sustain crop production may lead to environmental issues (Ni et al., 2011) and soil and groundwater Nitrogen (N) pollution, which is a concern for animals and humans (Hubbard et al., 2004). Franzen et al. (2011) noted that nitrification and ammonia volatility are vital in improving N use efficiency. Leaching of NO 3 -N and NO 2 -N to groundwater are important issues, especially in the southeastern Coastal Plain due to warm temperatures and relatively high rainfall (Hubbard et al., 2004). Luo et al. (2011) observed some differences between NO 3 -N and NH 4 -N losses. In poorly drained soils, N lost through denitrification may contribute to soil Nitrous Oxide (N 2 O) emissions and therefore to global warming and ozone depletion (Nash et al., 2012). Pelster et al. (2011) reported that conversion from conventional to no tillage may increase emissions of N 2 O, especially with N applications. Producers need to optimize agricultural production to reduce negative impact of these emissions on environment (Nash et al., 2012). Vaio et al. (2008) expressed concerns of negatively impacting environment from N loss. Optimum N management is important to Science Publications AJABS reduce NO 3 -N leaching below the root zone (Martinez-Alcantara et al., 2012). In field trials, controlled release fertilizers may help to conserve environmental quality through increased N Use Efficiency (NUE) and reduced N application rates (Shoji et al., 2001). Therefore, the objective of this study was to evaluate the effect of Nutrisphere-N polymer on soil NO 3 -N movement under two application methods and five N rates in dryland corn.

Site Preparation and Management
This study was conducted on Dothan loamy sand Nitrogen treatments consisted of two N application methods (all at once at planting and as a split application with 35 kg N ha −1 applied at planting and the rest as a side-dress application at V6 corn stage) and five nitrogen rates (0, 45, 90, 135 and 180 kg N ha −1 ).
Liquid fertilizer 25-S (formulation of 25 N and 3.5% S) was applied on both sides of corn rows to selected plots using a Reddick fertilizer applicator (Reddick Equipment Co., Inc., Williamson, NC) following corn planting. Corn in selected plots was side-dressed with different N rates at V6 stage using a Reddick fertilizer applicator on 14 May Soil samples were collected for NO 3 -N following corn harvest from the soil depth of 90 cm using Giddings hydraulic soil probe (Giddings Machine Co. Inc., Windsor, CO) mounted on a tractor. These soil samples were divided into 15 cm increments and analyzed for NO 3 -N content.
Additionally, weather data (air temperature and precipitation) were recorded during corn vegetation using a weather station located near the experimental site.

Statistical Analysis
The study design was a Randomized Complete Block with four replications. Data were analyzed using general linear models in SAS (2011) and means with standard error bars were shown for N rates by N application methods.

Weather Conditions
The average monthly air temperature was generally similar to 30-yr average, except for  Table 1).
Precipitation was 169 mm greater during corn growing season in 2012 and 24 and 34 mm lower in 2010 and 2011 than 30-yr average, respectively ( Table 1)

Soil Nitrate-Nitrogen (NO 3 -N)
Soil NO 3 -N content varied for application methods and N rates ( Fig. 1 and 2). Application of 180 kg N ha −1 in split with Nutrisphere-N polymer improved soil N content by 29.8% over untreated fertilizer at 0-15 cm soil depth. Similar or slightly higher NO 3 -N content was observed with Nutrisphere-N polymer for other N application rates and also similar for N applied at planting.
At 15-30 cm soil depth, NO 3 -N content was 44.7% greater with Nutrisphere-N polymer at 90 kg N ha −1 applied at planting (Fig. 3). At 45 kg, 90 kg, 135 kg and 180 kg N ha −1 in split applications, Nutrisphere-N increased NO 3 -N content by 26.2, 36.1, 28.0 and 17.3% compared to untreated N, respectively (Fig. 4).   For N applied at planting, soil NO 3 -N content at 30-45 cm was similar for treatments with and without Nutrisphere-N polymer (Fig. 5). However, Nutrisphere-N improved soil NO 3 -N concentration by 40.1 and 31.6% at 90 kg and 135 kg ha −1 over uncoated treatment at the same soil depth for N applied in split applications (Fig. 6).
At 45-60 cm depth, Nutrisphere-N polymer improved soil NO 3 -N content by 36.9% at 135 kg N ha −1 applied at planting, while NO 3 -N concentration improved by 33.9 and 34.9% at 135 kg and 180 kg N ha −1 with Nutripshere-N in split applications, respectively ( Fig. 7 and 8).
The NO 3 -N content in soil at depth of 60-75 cm decreased with Nutrisphere-N polymer by 22.0% at 180 kg N ha −1 applied at planting (Fig. 9). With split N applications of 90 kg and 135 kg ha −1 , Nutrisphere-N increased soil NO 3 -N by 37.5 and 59.9%, respectively (Fig. 10).
At 75-90 cm depth, similar soil NO 3 -N concentrations were observed for N applied at planting with and without Nutrisphere-N (Fig. 11). However, at the same depth soil NO 3 -N concentration increased with Nutrisphere-N polymer by 30.6% over untreated fertilizer at 135 kg N ha −1 in split applications (Fig. 12).

DISCUSSION
Results from previous studies generally showed reduction in soil N loss and improved N use efficiency with products slowing N release. Wen et al. (2001) reported greater N recovery from coated than regular fertilizer, because N release better matched crop N demand and uptake. Controlled release fertilizers, especially polymercoated urea helped to reduce NO 3 -N leaching in potato (Solanum tuberosum L.) and may allow reduction of split N applications (Wilson et al., 2009).
Slow release products reduced nutrient losses and improved water use efficiency under insufficient rainfall (Ni et al., 2011) and polymer-coated urea was very effective under higher soil moisture conditions due to reduced N 2 O emissions (Drury et al., 2012).
This study showed that compared to uncoated treatment, Nutrisphere-N polymer improved NO 3 -N concentration by 29.8% with 180 kg N ha −1 in split applications at 0-15 cm depth. Soil NO 3 -N content increased with Nutrisphere-N by 44.7% at 90 kg N ha −1 applied at planting and by 26.2, 36.1, 28.0 and 17.3% at 45 kg, 90 kg, 135 kg and 180 kg N ha −1 in split applications at 15-30 cm depth, respectively.
For N applied in split applications at 30-45 cm depth, Nutrisphere-N improved soil NO 3 -N concentration by 40.1 and 31.6% at 90 kg and 135 kg ha −1 over uncoated treatment, respectively. Soil NO 3 -N content improved with Nutrisphere-N by more than 30% at 135 kg N ha −1 applied at planting and 135 kg and 180 kg N ha −1 applied in split applications at 45-60 cm depth.
At 60-75 cm depth, Nutrisphere-N decreased soil NO 3 -N content by 22.0% over control at 180 kg N ha −1 applied at planting and increased NO 3 -N content by 37.5 and 59.9% with split N applications of 90 kg and 135 kg ha −1 , respectively. Compared to untreated fertilizer, soil NO 3 -N concentration increased with Nutrisphere-N by 30.6% at 135 kg N ha −1 in split applications at 75-90 cm depth. Similar concentrations for treatments with and without Nutrisphere-N were observed at 0-15 cm, 30-45 cm and 75-90 cm depth for N applied to corn at planting.

CONCLUSION
This study investigated the effect of two N application methods and five N application rates with Nutrisphere-N polymer on soil NO 3 -N movement in corn grown under dryland conditions. Compared to untreated N, application of 180 kg N ha −1 in split applications with Nutrisphere-N improved soil N content by 29.8% at 0-15 cm soil depth. At 15-30 cm depth, Nutrisphere-N increased soil NO 3 -N content by 44.7% at 90 kg N ha −1 applied at planting and Science Publications AJABS 26.2, 36.1, 28.0 and 17.3% at 45 kg, 90 kg, 135 kg and 180 kg N ha −1 in split applications, respectively. Nutrisphere-N improved soil NO 3 -N concentration by 40.1% and 31.6% at 90 kg and 135 kg ha −1 over uncoated treatment at 30-45 cm soil depth for N applied in split applications. At 45-60 cm soil depth, soil NO 3 -N content improved with Nutrisphere-N by 36.9% at 135 kg N ha −1 applied at planting, while NO 3 -N concentration improved by 33.9 and 34.9% at 135 kg and 180 kg N ha −1 with Nutripshere-N applied in split applications, respectively. At 180 kg N ha −1 applied at planting, soil NO 3 -N content decreased with Nutrisphere-N by 22.0% at depth of 60-75 cm. At the same depth, Nutrisphere-N increased soil NO 3 -N by 37.5 and 59.9% with split N applications of 90 kg and 135 kg ha −1 , respectively. At 75-90 cm depth, soil NO 3 -N concentration increased with Nutrisphere-N polymer by 30.6% over untreated fertilizer at 135 kg N ha −1 in split applications. Similar soil NO 3 -N concentrations were observed for treatments with N applied at planting with and without Nutrisphere-N at 0-15 cm, 30-45 cm and 75-90 cm soil depth. More research is needed to evaluate NO 3 -N movement in the soil after fertilizer application with Nutrisphere-N under different soil types and irrigation.

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