Gao, Suduan

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    Carbon and Nitrogen Dynamics Affected by Drip Irrigation Methods and Fertilization Practices in a Pomegranate Orchard
    (Horticulturae, 2019-12-10) Tirado Corbalá, Rebecca; Gao, Suduan; Ayars, James E.; Phene, Claude J.; Phene, Rebecca C.; University of Puerto Rico at Mayaguez; College of Agricultural Sciences; Department of Crops and Agro-Environmental Sciences
    Knowledge of carbon (C) and nitrogen (N) dynamics under different irrigation practices in pomegranate orchards is novel and essential to develop sustainable production systems. The aim of this research was to determine the effect of high-frequency drip irrigation and different rates of N fertilizer on C and N distribution in the soil and N uptake by pomegranate fruit and leaves. The main treatments were surface drip irrigation (DI) and subsurface drip irrigation (SDI), and the sub-treatments used were three initial N rates (N1, N2, and N3). As trees grew larger, the N application rate increased. From 2013–2015, trees received the following rates of N: 62–113 (N1), 166–263 (N2), or 244–342 kg/ha (N3). Soil and leaf total C (TC) and N (TN), soil dissolved organic C (DOC), soil nitrate (NO3−), and total N uptake by fruit were evaluated between 2012 and 2015. Soil samples were collected to 120 cm depth at 15 cm increments. DI resulted in higher concentrations of TN, TC, NO3−, and DOC in the upper 75 cm depth than SDI. The N3 treatment resulted in higher concentrations of TN, TC, NO3−, and DOC under both DI and SDI. Neither DI nor SDI at the N1 or N2 levels increased TN and NO3− concentrations at 105–120 cm soil depth, indicating reduced leaching risk using high-frequency drip irrigation. Higher N uptake by fruit was observed in SDI than in DI in 2014 and 2015, and in N2 and N3 treatments compared with N1 in 2013 and 2014. The data indicate that the application rate at 166–263 kg/ha (N2) provided sufficient N for a 4–6-year-old pomegranate orchard and that high-frequency SDI is a promising technology for achieving higher N use efficiency and minimizing leaching loss of NO3− and DOC.
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    Subsurface Drip Irrigation Reduced Nitrous Oxide Emissions in a Pomegranate Orchard
    (International Journal of Environmental Science and Development, 2019-03) Gao, Suduan; Hendratna, Aileen; Cai, Zejiang; Duan, Yinghua; Qin, Ruijun; Tirado Corbalá, Rebecca; University of Puerto Rico at Mayaguez; College of Agricultural Sciences; Department of Crops and Agro-Environmental Sciences
    Soil fertilization is one of the major sources for nitrous oxide (N2O) emissions and soil moisture is among the most important factors affecting its production. Thus, one of the important mitigation strategies in semiarid or arid regions is through irrigation and/or fertigation management. The objective of this research was to evaluate the effects of different drip irrigation methods and N application levels on N2O emissions. Nitrous oxide emission flux and N2O concentration in soil profile were measured in a pomegranate field for two growing seasons under two irrigation systems [subsurface drip irrigation (SDI) at ~0.5 m depth and traditional surface drip irrigation (DI)], and three N application rates (50%, 100%, and 150% of current practice rate). Both years’ data showed that N2O emissions has a high and positive correlation with N fertilization events and application levels. Nitrous oxide emissions from DI at 100% and 150% N levels were over an order of magnitude higher compared to those from SDI based on the data of the first year. Data from the second year confirmed the first year’s findings of high emissions from DI. A positive linear correlation between the N2O emission flux and N2O concentration in soil-gas phase was identified that supported emission data. This research demonstrated that although N fertilization is a major cause for N2O emissions, subsurface drip irrigation/fertigation can lead to a significant emission reduction in addition to other benefits, such as increased water and nutrient use efficiencies, and reduced weed pressure.