Garry L. Grabow

Ammonia Adsorption in Five Types of Flexible Tubing Materials

Five different types of tubing materials, namely, polytetrafluoroethylene (PTFE), perfluoroalkoxy (PFA), fluorinated ethylene propylene (FEP), high density polyethylene (HDPE), and polyvinyl chloride (PVC) were evaluated for ammonia adsorption at two nominal ammonia concentration values (1 and 10 ppm) at ~24°C. All tubing sections were 2.5 m in length and 4.76 mm in i.d. except the HDPE which had an i.d. of 4.32 mm. Mass balance was used to determine ammonia (as ammonium-nitrogen (N)) adsorbed on the inside of the tubing versus the total N recovered in the tubing plus the gas scrubbers (primary and secondary). No tubing significantly differed in N adsorption. Averaged for both ammonia concentrations, N adsorption as percent of total N ranged from 0.15% (PVC) to 1.69% (FEP). Hence, the least expensive PVC tubing may represent the best option under conditions similar to those used in this study. The gas scrubber design used in this study had excellent trapping efficiency (>99%).

Subsurface Drip Irrigation: Status of the Technology in 2010

Subsurface drip irrigation (SDI), although a much smaller fraction of the microirrigated land area than sur- face drip irrigation, is growing at a much faster rate and is the subject of considerable research and educational efforts in the U.S. This article discusses the growth of SDI, highlights some of the research and extension efforts, and points out some of the challenges to SDI adoption and some of the future opportunities for SDI.

Water Distribution from a Subsurface Drip Irrigation System and Dripline Spacing Effect on Cotton Yield and Water Use Efficiency in a Coastal Plain Soil

A subsurface drip irrigation (SDI) system was installed in 2001 in the Coastal Plain of North Carolina. Initially, four zones were installed, each with 0.91 m dripline spacing. In 2002, a fifth zone with 1.82 m dripline spacing was added. This system irrigated a cotton (Gossypium hirsutum L.) and peanut (Arachis hypogea L.) rotation on a Norfolk sandy loam soil. Seed cotton yield data was collected from 2001 to 2004. In addition to SDI, overhead sprinkler irrigation was applied to cotton plots from 2001 to 2003. This study was concurrent with another study that evaluated the effect of irrigation system type, cotton growth regulator (mepiquat chloride), herbicide (glyphosate) treatment, and planting date on lint yield and quality. Although the soil is classified as a sandy loam, water moved laterally to the midpoint of the 1.82 m spaced dripline; this was likely due to the pan layer found at about 0.3 m just below the dripline depth of 0.23 m. There was no difference in lateral water movement between the two dripline spacings. Seed cotton yield and irrigation water use efficiency was not statistically different between irrigation system type or dripline spacing over all years in the study. Seed cotton yield averaged 3.44 Mg ha-1 for the 0.91 m dripline spacing and 3.22 Mg ha-1 for the 1.82 m spacing for the three-year period 2002-2004 compared to an unirrigated average of 2.58 Mg ha-1 for the same period. Average irrigation water use efficiency was greater for the 0.91 m dripline spacing but not statistically different from the 1.82 m spacing. For 2001-2003, when sprinkler-irrigated plots existed, seed cotton yield averaged 3.55 Mg ha-1 for the 0.91 m dripline spacing, 3.35 Mg ha-1 for the sprinkler-irrigated plots, and 2.56 Mg ha-1 for the unirrigated plots. Drought conditions existed in 2002, when 258 mm of rain occurred between planting and final irrigation. The other growing seasons received relatively high amounts of rainfall: 524, 555, and 643 mm in 2001, 2003, and 2004, respectively.

Swine anaerobic lagoon nutrient concentration variation with season, lagoon level, and rainfall.

Twenty swine anaerobic lagoons (8 finish, 6 nursery, and 6 sow) were monitored for lagoon liquid nutrient concentrations and liquid level above or below the stop-pump level. Weekly rainfall was also recorded. Significant differences in total nitrogen (N) concentrations existed between lagoons and also between types of farms. The N concentration varied within the same lagoon by a factor of two or more during the 4-yr study period and typically displayed a seasonal trend of decreasing during the summer and increasing during the winter. Years of operation (8 to 29 yr) were not a significant factor for mean N concentration over the 4-yr period. The lagoon liquid level was not a significant factor for N or total phosphorus (P) concentration. The finish farms displayed a decreasing trend of average annual nitrogen concentration with increase in annual rainfall.

EVALUATION OF EVAPOTRANSPIRATION-BASED AND SOIL-MOISTURE- BASED IRRIGATION CONTROL IN TURF

A study was initiated in Fall 2006 in Raleigh, North Carolina to compare two types of commercially available irrigation control technologies, one based on estimates of evapotranspiration (ET) and the other based on feedback from soil moisture sensors. Water applied and turf quality from one ET-based system and two sensor-based systems were compared to a system using a standard time-based irrigation schedule. The effect of irrigation frequency was also a part of the study. Estimates of turf ET were obtained from the Penman-Monteith equation using on-site weather data, and also from an atmometer. Results from the twenty week evaluation in 2007 showed that on average the “add-on” soil-moisture-based system evaluated applied the least amount of water while the ETbased system evaluated applied the most water. Weekly irrigation frequencies used the least amount of water, followed by bi-weekly and daily frequencies in increasing amounts when averaged across all technologies. Minimally acceptable turf quality was maintained by all technologies and frequencies through most of the study, but turf quality declined substantially the last month of the study for the add-on system and standard timer-based system. The “on-demand” sensor-based system resulted in the best combination of water efficiency and turf quality.

SDI Dripline Spacing Effect on Corn and Soybean Yield in a Piedmont Clay Soil

A subsurface drip irrigation (SDI) system was installed in the Piedmont of North Carolina in a clay soil in the fall of 2001 to test the effect of dripline spacing on corn and soybean yield. The system was zoned into three sections; each section was cropped to either corn (Zea mays L.), full-season soybean [Glycine max (L.) Merr.], or winter wheat (Triticum aestivum) double cropped to soybean representing any year of a typical crop rotation in the region. Each section had four plots; two SDI plots with dripline spacing at either 1.52 or 2.28 m, an overhead sprinkler irrigated plot, and an unirrigated plot. There was no difference in average corn grain yield for 2002–2005 between dripline spacings or between either dripline spacing and sprinkler. Irrigation water use efficiency (IWUE) was greater for sprinkler irrigated corn than for either SDI treatment and there was no difference in IWUE in soybean. Water typically moved laterally from the driplines 0.38 to 0.50 m. SDI yield and IWUE increased relative t...

Evaluation of Two Smart Irrigation Technologies in Cary, North Carolina

Decreasing the amount of water applied by residential irrigation systems without causing negative effects on turfgrass quality is a challenge. A variety of technologies are available in the market that seeks to reduce irrigation water use. These technologies include rain sensors, and soil moisture sensor (SMS) based and evapotranspiration (ET) based controllers. A study was conducted in Cary, North Carolina with the purpose of evaluating the effectiveness of two smart systems, based on the amount of irrigation applied and turf quality in residential settings. The study included 24 residential sites that were divided into six geographical regions, each group within a region receiving four different treatments. The treatments were: SMS) an irrigation controller with a soil moisture sensor, ET) an evapotranspiration based controller, ED) a standard irrigation controller using seasonal runtimes based on historical climate data and Control) irrigation controller with no intervention. Data was collected from May 2009 through September 2009. Maximum water savings were achieved by the SMS treatment followed by ET, ED and Control treatments. According to visual turfgrass rating, only the Control group was found to have turf quality below an acceptable level.

Leaching of Nutrients and Trace Elements from Stockpiled Turkey Litter into Soil

In addition to nutrients, poultry are fed trace elements (e.g., As) for therapeutic purposes. Although a large proportion of the nutrients are assimilated by the birds, nearly all of the As is excreted. Hence, turkey litter constituents can leach into the soil and contaminate shallow ground water when it is stockpiled uncovered on bare soil. This study quantified the leaching of turkey litter constituents from uncovered stockpiles into the underlying soil. Four stockpiles were placed on Orangeburg loamy sand in summer 2004 for 162 d; 14 d after their removal, four stockpiles were created over the same footprints and left over winter for 162 d. Soil samples at depths of 7.6 to 30.5 cm and 30.5 to 61 cm adjacent to and beneath the stockpiles were compared for pH, electrical conductivity, total C, dissolved organic C, N species, P, water-extractable (WE)-P, As, WE-As, Cu, Mn, and Zn. All WE constituents affected the 7.6- to 30.5-cm layer, and some leached deeper; for example, NH(4)(+)-N concentrations were 184 and 62 times higher in the shallow and deep layers, respectively. During winter stockpiling, WE-As concentrations beneath the stockpiles tripled and doubled in the 7.6- to 30.5-cm and 30.5- to 61-cm layers, respectively, with WE-As being primarily as As(V). Heavy dissolved organic C and WE-P leaching likely increased solubilization of soil As, although WE-As concentrations were low due to the Al-rich soil and low-As litter. When used as drinking water, shallow ground water should be monitored on farms with a history of litter stockpiling on bare soil; high litter As; and high soil As, Fe, and Mn concentrations.

Residential Irrigation Water Use in the Central Piedmont of North Carolina. II: Evaluation of Smart Irrigation Technologies

AbstractA study was conducted in Cary, North Carolina, in the spring and summer of 2009 with the purpose of evaluating the effectiveness of two “smart irrigation” controllers based on the amount of irrigation applied and resulting turf quality in residential settings. Twenty-four residential sites were selected, in clusters of four, representing six geographical areas within the town. Each geographical cluster included one site of each treatment. The treatments were standard irrigation controller with an add-on soil moisture sensor system (SMS); standard irrigation controller with an add-on evapotranspiration-based adjustment system (ET); standard irrigation controller using seasonal runtimes based on historical climate data (ED); and a control group which used a standard irrigation controller with no intervention (CON). Weekly water usage was obtained from irrigation meter readings and turf quality was characterized using a visual rating and a normalized difference vegetation index (NDVI) meter. Maximum ...

Subsurface Drip Irrigation Research on Commodity Crops in North Carolina

Subsurface drip irrigation (SDI) is relatively new to North Carolina. Subsurface drip, for purposes of this paper, means drip line installed at a depth below normal tillage operations, and used multiple years. There has been interest of the use of this technology on commodity crops (corn, wheat, soybeans, cotton, and peanuts) upon which much of the North Carolina agricultural economy is based. Research-scale SDI systems have been installed in the Piedmont of North Carolina, in clay loam soils, and in the Coastal Plain in fine sandy loam soils. One year of data has been collected for corn, winter wheat, and soybeans in the Piedmont, and for cotton and peanuts at the Coastal Plain site. The Piedmont site tested for impact of drip line spacing on corn, winter wheat and soybean yield, while the initial phase of the coastal plain site tested the effect of irrigation method (SDI, sprinkler, and rainfed) and pest strategies on cotton and peanut yield. Data from the Piedmont site indicated that a 5-foot drip line spacing (every-other-row between-rows) on corn was just as effective as a 2.5-foot spacing (every-row under-row). No increase in winter wheat yield was realized for any of the drip line spacings, however the wheat was replanted due to cold, dry weather, and was poorly established, complicating the comparison. SDI irrigated soybean yield was also not statistically different than rainfed yield for any of the drip line spacings. This may have been due to the combination of an early frost and indeterminate soybeans that negated potential irrigation benefits late in the pod filling stage. Data from the Coastal Plain site showed that SDI improved cotton yield as compared to sprinkler across Roundup. and Pix. treatments. Peanuts receiving various disease control strategies had similar results. Continued research is planned for both sites.