07944nam a2200169 a 450000100080000000500110000800800410001910000190006024501450007926000590022430000110028350000740029452073570036865300100772565300270773565300120776210615152020-11-23       2019    bl uuuu  m   00u1 u    #d1 aCARRACELAS, G.  aRice irrigation management effects on water productivity, grain quality and food safety.  [Thesis of Master Science].h[electronic resource]  aAustralia: Deakin University, 2019. OPEN ACCESS.c2019  a123 p.  aSupervisors: John Hornbuckle (Deakin University); Alvaro Roel (INIA).  aAbstract: The rice sector is facing great challenges in the coming years of not only achieving high yields to meet global food demand but also to use less water, energy, and other inputs per unit of production. This also needs to be achieved without compromising the environment and maintaining food safety. Rice farming systems in Uruguay are at the leading edge of productivity and fields are fully irrigated and continuously flooded. Water is becoming increasingly scarce due to environmental concerns, climate change reducing water availability and competition from other sectors. New irrigation techniques need to be developed to use less water. These techniques will also need to minimize off-site impacts while preserving grain yield, quality and food safety. Increases in water productivity would allow rice production to expand and/or allow the allocation of water to irrigate other crops and/or other users such as urban and industrial. In addition, increases in water productivity will reduce pumping costs, improving the economic results and sustainability of the rice industry. The focus of this study was to determine irrigation techniques that increase water productivity (WP), allowing a reduction in water input without negatively affecting grain yield in Uruguay. Between 2009 to 2015, a total of ten experiments were conducted in the northern, central and eastern rice growing regions of Uruguay. Treatments included: early continuous flooding (C), alternate wetting and drying (AWD), intermittent flooding until panicle initiation (IP) and intermittent flooding during all crop growth periods (I). The irrigation treatments were investigated in a delayed flood, drill-seeded rice production system. All treatments were planted on dry soil. In treatment C which represents the traditional irrigation management regime (i.e., control), flooding started 15-20 days after emergence and a water layer of 10 cm above the soil surface was maintained throughout all the crop cycle. In treatments IP and I, the water level alternated between 10 cm and 0 cm and was reestablished when the soil was still saturated. The AWD treatment allowed the soil to dry periodically (water depletion of 50% of soil available water) until panicle initiation. After this period, the field was continuously flooded as the control  treatment. IP and I led to significant savings in irrigation water inputs in the North and Central regions (averaged 35% or - 3986 m3 ha- 1 ) in relation to C. In the East region, AWD allowed for a 29% (-2067 m3 ha-1 ) water saving in relation to the control but resulted in a significant yield loss of 1339 kg rice ha-1 (15% reduction) in relation to C. WP was increased by 0.25kg m-3 (23%) in IP and 0.68 kg m-3 (62%) in I, in relation to the control C. The whole grain percentage was significantly reduced with I in the North region only. Techniques that maintained the soil at saturated water conditions like intermittent flooding, allowed a reduction of water input with no significant effects on grain yield, which led to a significant increase in WP in relation to the control C treatment. A second objective of this study was to determine the inorganic arsenic (iAs) accumulation in rice grain in two contrasting soils commonly used for rice production in Uruguay. This research project also aimed to identify alternative irrigation management techniques to traditional flooding that could be used to limit or reduce the inorganic arsenic accumulation in the grain and to determine differences in the iAs levels within the most commonly planted rice varieties in Uruguay. To this end, five experiments were conducted with a split plot design with four blocks over three rice growing seasons from 2014 until 2017. The experimental sites included two irrigation treatments: continuous flooded (C) and alternate wetting and drying (AWD). The split plots included different varieties: Indicas and Japonicas. Average iAs accumulated in rice grain was 0.07 mg kg-1 , well below international limits, even under the C irrigation technique. It was found that iAs accumulation in rice grain can be further reduced by the implementation of AWD in certain soils. Japonica varieties had a lower accumulation of iAs in rice grain, in comparison with Indicas at both sites. In summary, this study identified irrigation techniques that used significantly less irrigation water while maintaining rice grain yield and therefore increasing water productivity, across a range of typical irrigated rice growing environments in Uruguay. Intermittent irrigation until panicle initiation was found to be the lowest risk technology that allowed a reduction in irrigation water used without negatively affecting rice yield, leading to a significant increase in water productivity. Grain yield was not reduced with irrigation techniques that maintained soil moisture above or near saturated conditions. When the soil moisture dropped below saturation even during the vegetative period, yield was found to be affected negatively. Alternate Wetting and Drying techniques allowed soil moisture to drop below saturation and yield was affected negatively. Inorganic Arsenic levels (iAs) in two experimental rice growing sites evaluated in Uruguay were found to be well below the limit proposed by the international standards CODEX of 0.20 mg kg-1 (FAO and WHO, 2019). Alternative irrigation management techniques such as AWD, resulted in lower levels of iAs accumulated in rice grain in relation to continuous flooded treatment at one of the evaluated experimental sites in Uruguay. Rice variety was found to significantly affect iAs uptake and accumulation in rice grain. Japonica varieties were found to accumulate lower amounts of iAs in grain relative to Indicas. Based on the results obtained using @risk, an average income loss of implementing IP in relation to C of -53.7 US$ ha-1 was expected, considering the average rice price of 217 US$ ha -1 and a water price of 0.017 US$ m-3 with 90% of probability. It was found in most cases that a loss in profitability occurred by implementing alternative irrigation technologies such as IP, I, AWD in relation to the control treatment continuous flooding (C) using @risk modelling. Higher economic loss was registered in the East followed by the Central site. However, in the North, a lower net economic loss of implementing alternative irrigation management was found and the economic difference of implementing alternative irrigation managements could be negative or positive depending on water and rice prices variations. Traditional continuous flooding irrigation technique the most adopted practice in Uruguay in order to achieve the highest yield potential. As water payment in Uruguay is currently based on a fixed cost per irrigated hectare not by volume of water used, changes beyond flood management practices would likely be necessary in order for producers to be incentivized to implement alternative irrigation techniques that increase water productivity while improving the economic results. New irrigation technologies, geolevelling, automation of rice irrigation systems and rice breeding to develop cultivars that tolerate non-flooded conditions, could also play an important role for the successful implementation of alternative irrigation techniques on rice fields in the future.  aARROZ  aRICE (ORYZA SATIVA L.)  aURUGUAY