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Darby S. Kellum, Manoj K. Shukla, John Mexal and Sanjit Deb

Greenhouse gas (GHG) emissions are fueling global climate change, with methane and nitrous oxide being the primary agricultural gases emitted. It has been shown that N2O emissions correlate to moisture content fluctuations; however, emissions from agricultural fields in the semiarid regions of the Southwest where rewetting events occur regularly are not well established. The scope of this study was to quantify GHG emissions in correlation to soil moisture fluctuations and fertilizer application. The study was conducted continuously in two pecan [Carya illinoinensis (Wangenh.) K. Koch] orchards between Aug. 2010 and Aug. 2011 on a sandy loam soil (La Mancha) and a silty clay loam soil (Leyendecker), both under normal management practices. The small chamber technique was used to measure GHGs. Emissions varied greatly throughout the year. The largest flux of CO2 at La Mancha and Leyendecker both occurred during a drying event immediately following an irrigation event: 84,642.49 μg·m−2·h−1 and 30,338.24 μg·m−2·h−1, respectively. The net CH4 flux at Leyendecker and La Mancha was close to zero with the largest emissions occurring during wetting events. Results showed that N2O emissions were maintained near the baseline except for the few days following an irrigation event. The largest emission peak at La Mancha occurred after irrigation and nitrogen application: 322.06 μg·m−2·h−1. The largest emission peaks of 26.37 and 1.13 μg·m−2·h−1 at Leyendecker and La Mancha, respectively, occurred after irrigation, nitrogen application, and tillage. Nitrogen application was the driving factor affecting N2O emissions at La Mancha, whereas soil moisture content was the driving factor at Leyendecker. Emission factors (EFs) at La Mancha and Leyendecker were 0.49% and 0.05%, respectively. A thorough accounting of GHG emissions is necessary for budgeting and identifying mitigation policy.

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S. Shukla, C.Y. Yu, J.D. Hardin and F.H. Jaber

Continuous monitoring of hydraulic/hydrologic data for managing water for horticultural crops has been a challenge due to factors such as data loss, intensive resource requirements, and complicated setup and operation. The use of state-of-the-art wireless spread spectrum communication technology and wireless data acquisition and control (WDAC) systems for agricultural water management is discussed in this paper. The WDAC technology was applied to a research project where lysimeters were used for water quantity and quality studies for vegetables. Two types of WDAC networks, master–slave and peer-to-peer WDAC networks, are discussed. The WDAC system linked the wireless dataloggers to a network to make real-time data available over the Internet. The use of WDAC made it possible to collect real-time data and control the experiment (e.g., frequency of data collection) remotely through the Internet. The WDAC system for the lysimeter study was compared to a commonly used manual system with regard to potential instrument damage, data loss, ease of data collection and analyses, and total cost of monitoring. The advantages of the WDAC include: reduced equipment losses from natural disasters (e.g., lightning), improved equipment maintenance, reduced data loss from faulty equipment, higher project personnel efficiency, and real-time involvement by a dispersed team. The total cost of the WDAC system ($65,750) was about half that of the manual system ($130,380). The WDAC system was found to be an effective tool for agricultural water management projects.

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S. Shukla, B.J. Boman, R.C. Ebel, P.D. Roberts and E.A. Hanlon

Despite efforts to optimize water and nutrient inputs to Florida's vegetable and fruit crops, the sandy soils, shallow water table, and tropical climate of Florida result in nutrient leaching losses that are unavoidable. Water quantity and quality management strategies that can reduce these nutrient losses from Florida's horticultural crops were reviewed and research needs for quantifying their effectiveness were identified. The water quantity management strategies included water table management for irrigation, drainage management, detention of runoff and drainage, and summer flooding. In addition to the expected water quality benefits of these practices, potential effects on crop production and farm economics were also discussed. Watershed-scale adoption of stormwater harvesting has the potential to not only reduce the nutrient loadings but also become a source of additional income for landowners through water trading. The water quality practices included structural and managerial practices (e.g., vegetative filter strips and ditch cleaning). Key research needs for reducing the unavoidable nutrient discharges included the development of a crop-specific drainage management tool; quantification of farm and watershed-scale benefits of stormwater detention and its reuse with regards to nutrient loadings, water supply, crop production, and farm income; enhancement of hydraulic efficiency of detention areas; and effects of summer flooding and ditch maintenance and cleaning on nutrient discharges.

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Gregory S. Hendricks, Sanjay Shukla, Kent E. Cushman, Thomas A. Obreza, Fritz M. Roka, Kenneth M. Portier and Eugene J. McAvoy

Watermelon (Citrullus lanatus) production is concentrated in southern Florida where growers often use seepage irrigation. According to a recent survey, growers believe that nitrogen (N), phosphorus (P), and potassium (K) rates recommended by the University of Florida Institute of Food and Agricultural Sciences (UF-IFAS) are low. A study was conducted during Spring 2004 and 2005 at a UF-IFAS research farm to compare three nutrient and water management systems: high rate [HR (265, 74, and 381 lb/acre N, P, and K, respectively)], recommended rate [RR (150, 44, and 125 lb/acre N, P, and K, respectively)], and recommended rate with subsurface irrigation (RR-S). Irrigation was managed to keep soil moisture content at 16% to 20% for HR and 8% to 12% for RR and RR-S. The experimental design was a randomized complete block design with two replications and three subsample areas within each 0.25-acre plot. The HR management approach produced ≈60% to 80% higher yields (cwt/acre) during 2005 than RR or RR-S. The HR treatment produced larger watermelons than RR or RR-S in 2005. Triploid watermelon prices had to be at least $3.74/cwt to cover all costs associated with HR. The HR approach increased the grower net returns by $590/acre and $1764/acre under conservative and higher yield and price expectations, respectively. Soluble solids content and hollowheart ratings were unaffected by treatment. Total biomass, recorded during 2005, followed a similar trend as yield, with HR producing 105% and 125% greater total dry weight than RR and RR-S, respectively. Total N content of HR biomass was 56% higher than that of RR and RR-S. Total P content was 29% and 50% higher than that of RR and RR-S, respectively. Leaf and petiole tissue from the HR treatment exhibited consistently higher N and K leaf tissue values during 2005 than RR and RR-S. In conclusion, trends in the data consistently showed greater plant performance with higher rates of fertilizer and soil moisture content. Our ability to detect differences in 2005 was probably enhanced by higher rainfall during 2005 compared with 2004.