Jeffrey G. White

Long-Term Variable Rate Lime and Phosphorus Application for Piedmont No-Till Field Crops

Variable rate (VR) fertilizer application is a paradigm with potential to improve input efficiency and farm profitability. It is widely marketed by commercial applicators in the southeastern US. However, field studies comparing VR with traditional management have not demonstrated consistent, positive results. The objectives of this study were: (1) to determine the soil impact, crop response and economic potential of VR phosphorus (P) and lime application in a North Carolina Piedmont no-till field crop system using intensive soybean [Glycine max (L.) Merr.] production and (2) to economically evaluate alternatives to standard commercial grid soil sampling for directing VR P and lime. A 23-ha long-term no-till field in the SE Piedmont was divided into 0.4ha plots assigned to either VR or uniform P and lime application. Grid soil sampling and VR P and lime application were done prior to four crops over 3 years: full season soybean, wheat (Triticum aestivum L.)–double cropped soybean, and full season soybean. Soil test P, pH and crop yield response to VR P were inconsistent. Soil pH in areas with low pH initially did increase in response to VR lime, but it took two to three applications to bring all of these areas to the target pH. Once VR-liming raised initially low soil pH to levels close to target, yield of soybean, but not wheat, were up to 0.74Mg ha−1 higher than with uniform lime. Even with significantly higher soybean yields associated with VR lime, 3 years of grid sampling and VR application were not profitable compared to uniform application. The results indicated that VR lime could be profitable if the initial grid sampling data were used either for 2 consecutive years, or if it was used to restrict future grid sampling to specific areas requiring further VR lime.

Characterizing Soil Physical Properties for Soil Moisture Monitoring with the North Carolina Environment and Climate Observing Network

AbstractSoil moisture has important implications for meteorology, climatology, hydrology, and agriculture. This has led to growing interest in development of in situ soil moisture monitoring networks. Measurement interpretation is severely limited without soil property data. In North Carolina, soil moisture has been monitored since 1999 as a routine parameter in the statewide Environment and Climate Observing Network (ECONet), but with little soils information available for ECONet sites. The objective of this paper is to provide soils data for ECONet development. The authors studied soil physical properties at 27 ECONet sites and generated a database with 13 soil physical parameters, including sand, silt, and clay contents; bulk density; total porosity; saturated hydraulic conductivity; air-dried water content; and water retention at six pressures. Soil properties were highly variable among individual ECONet sites [coefficients of variation (CVs) ranging from 12% to 80%]. This wide range of properties sug...

Determination of Biosolids Phosphorus Solubility and Its Relationship to Wastewater Treatment.

In North Carolina (NC), biosolids land application rates governed by crop nitrogen (N) requirements typically surpass crop phosphorus (P) needs, increasing surface water pollution potential. The NC Department of Environmental Quality (NCDEQ) is considering P-based biosolids application guidelines for some nutrient-impaired watersheds using the P Loss Assessment Tool (PLAT), but important biosolids information is lacking: total P (TP), water-extractable P (WEP), and percent water-extractable P (PWEP). In each of three seasons, we sampled 28 biosolids from 26 participating water resource recovery facilities (WRRFs) and analyzed for TP, WEP, and percent dry matter (DM), from which PWEP and nonsoluble P were calculated. Based on descriptive statistics and an online survey of treatment processes, biosolids were divided into Class A-alkaline, Class A-heat, Class B-slurry, and Class B-cake. The average TP in Class A alkaline stabilized biosolids was more than five times less than the average of the other biosolids, 5.0 vs. 26.6 g/kg, respectively. Averaged over biosolids, WEP and PWEP were 1.4 g/kg and 5.0%, respectively. Stabilization processes appeared to reduce WEP substantially, so biosolids potential soluble-P loss is low. Our data will allow PLAT to be used for biosolids P-loss risk assessments.

APPLICATION OF GROUND PENETRATING RADAR TO AID RESTORATION PLANNING FOR A DRAINED CAROLINA BAY

Clayey subsurface strata in precipitation-driven wetlands act as aquitards that retain water and can affect wetland hydrology. If the aquitard layers have been cut through by drainage ditches, then restoring wetland hydrology to such sites may be more difficult because of the need to fill ditches completely with low hydraulic conductivity material. Ground penetrating radar (GPR) surveys were conducted to determine the depth and continuity of shallow clay layers and identify those that have been pierced by drainage ditches at Juniper Bay, a 300-ha drained Carolina bay in North Carolina, USA that will be restored. Carolina bays are a wetland type that occur as numerous, shallow, oval-shaped depressions along the Atlantic Coastal Plain. The GPR interpretations found that moderately fine-textured (clay loam, sandy clay loam, silty clay loam) and fine-textured (sandy clay, silty clay, clay) aquitards underlay coarser-textured horizons in most of the bay at an average depth of 1.6 m. Extensive ground truthing showed that, on average, GPR predicted the depth to these aquitards to within 16% of their actual depth. An atypical GPR reflection in the southeast sector of the bay was interpreted as a fluvial deposit without aquitards until a depth of 3 to 5 m. This area may require different restoration strategies than the rest of the bay. By comparing the depths of aquitards and drainage ditches, several areas were identified as likely locations of ditch-induced aquitard discontinuity that may require filling or lining of suspect ditches to prevent potential water losses if there are downward hydraulic gradients. Cost estimates by two professional firms indicated that GPR could provide large volumes of data with cost and time efficiency. GPR surveys are proposed as a useful tool for characterizing potential wetland restoration sites on the Atlantic Coastal Plain and other regions with similar soils.

Effects of rotational infrastructure within pasture-raised pig operations on ground cover, soil nutrient distribution, and bulk density

Interest in pasture-based pork products has increased significantly in recent years. However, nitrogen (N) losses resulting from these systems are common due to importation of feed, high stocking rates, and pig behavior. This study was conducted to evaluate soil inorganic N, soil-test phosphorus (STP), ground cover, and compaction changes as impacted by rotational shade, water, and feed structures in a pasture-raised pig operation over two 12-week pig occupations. Shade and watering structures were rotated weekly for 12 weeks within a rotational (mobile) scheme; data were compared to a stationary structure system as well as to a managed hay operation with no pigs. Soil samples were acquired from subplots and analyzed for distribution of inorganic N concentrations among main plot treatments, including nitrate (NO3), ammonium (NH4), and STP values. Soil inorganic N concentrations were higher in exterior subplot positions than in interior positions. This pattern was not maintained after a second pig group occupied the plots. Soil test phosphorus was unaffected by either pig occupation. Ground cover percentages were higher in control (hay) treatments than for pig treatments, however no difference was found between mobile and stationary structure treatments in either pig occupation. Soil compaction, as measured by soil bulk density, was found to be higher under permanent shade structure locations as compared to mobile and control treatments. Mobile and control compaction levels were not different for the second occupation, utilizing a more intensive sampling scheme, suggesting a benefit to the rotation of shade, water and feed infrastructure. The weekly rotation of infrastructure performed during both occupations was both labor intensive and time consuming. The observed lack of improvement in nutrient distribution to a rotational infrastructure may limit its utility in pastured-pig systems. However, further options are available that would allow the production of pasture-raised pigs while minimizing associated nutrient loading and pasture degradation.