Integrated Cropping System Nutrient Management
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The primary focus of this Hatch project is to improve understanding of the underlying mechanisms of soil processes and plant nutrition that regulate nutrient cycling, identify nutrient management that optimizes rice crop yield, and decrease environmental impacts from nitrogen use. Climate change, food and energy security, population pressure, and limited natural resources are critical challenges facing agroecosystems (CCSP, 2008; FAO, 2009; GCRP, 2009; Müller et al., 2009). Nutrient cycling is a fundamental component of agroecosystem functions. The main goal of integrated cropping system nutrient management is to improve nutrient use efficiency and decrease negative environmental impacts. To fully explore the benefits of integrated cropping system nutrient management requires a better understanding of the underlying mechanisms of nutrient biogeochemistry cycling.A major component of this proposal focuses on management practices affected rice production in southeast Texas and surrounding rice production regions, as well as other crops produced in this area. Numerous studies have been conducted to investigate the effects of different management practices (i.e. water, fertilizer, tillage, rotation, and planting time) on rice nutrient biogeochemical cycling. Of particular interest in this proposed research and extension program is flooded agricultural ecosystems.Flooded water management is one of the most significant characteristics in irrigated rice agroecosystems and fundamentally modifies soil physical, chemical, and biological properties (De Datta, 1981). Soil physical properties are primarily affected by the saturated soil moisture, and the heat capacity of water is greater than that of other soil components (mineral or organic matter). Thus, the soil temperature of a flooded rice field fluctuates less than soils from an upland crop field. Flooding also creates a more or less continuouslanaerobic environment.Chemically, the following soil properties are affected by flooding: 1) depletion of molecular oxygen, 2) chemical reduction of the soil, or a decrease in redox potential, 3) increase in pH of acid soils and decrease in pH of calcareous and sodic soils, 4) increase of specific conductance, 5) reduction of Fe(III) to Fe(II) and Mn(IV) to Mn(II), 6) reduction of SO42- to S2-, 7) increase in supply and availability of nitrogen (N), 8) increase of availability of phosphorus (P), silicon, and molybdenum, 9) decrease in concentrations of water-soluble zinc and copper, and 10) generation of CO2, CH4, and toxic reduction products such as organic acids and hydrogen sulfide (Ponnamperuma, 1972). Along with the modified soil physical and chemical properties, the soil microbial community changes as well (Pet-Ridge and Firestone, 2005). Accordingly, nutrient availability changes spatially and temporally (Norman et al., 1990; Wilson et al., 1989). For example, Ponnamperuma (1965) reported that more nitrogen is available under flooded soil than unflooded soil. The author explained that the lower N immobilization under flooding results in increased net N mineralization.The nutrient-use efficiency is also affected by the interactions between the rice crop and soil processes a regulated by management practices (Samonte, et al., 2006; Wu and Wilson, 1998). The interactions between soil properties, root development, and management practices are important aspects for integrated cropping system nutrient management. Roots of the rice crop are responsible for mineral nutrition (Yoshida, 1981)..........