Water balance implications of switching from continuous submergence to flush irrigation in a rice-growing district

Abstract

Studies conducted at the field scale report significant reductions in the irrigation requirements of rice when continuous submergence (CS) is replaced by less water-demanding regimes such as flush-irrigation (FI, i.e. intermittent irrigations of rice growing in non-submerged soils). However, the effects of their extensive application in paddy areas with shallow groundwater is much less studied. We present a scenario analysis investigating the impacts on irrigation requirements induced by a shift from CS to FI in an irrigation district of Northern Italy where rice is the main crop, followed by maize and poplar. The area is characterised by a shallow water Table whose depth fluctuates between two meters (in winter) and less than 1 m (in summer). We applied a three-stage procedure, where we first analysed present state conditions using the SWAP (Soil, Water, Atmosphere, Plant) model to simulate irrigation deliveries and percolation fluxes. Then, we calibrated an empirical relationship between estimated percolation fluxes and measured depths to groundwater. Finally, we applied this relationship, in combination with the SWAP model, to predict the variation of district irrigation requirements due to a widespread shift from CS to FI. Results show that neglecting the feedback between groundwater recharge due to irrigation and groundwater depth led to overestimating the reduction of irrigation requirements of rice, which decreased from around 80% when no feedback was considered to around 60% when it was accounted for. Moreover, increased groundwater depths resulted in higher irrigation requirements for maize with an estimated growth of more than 50% due to the need of shortening the irrigation turn. These results demonstrate the importance of considering the impacts on the hydrological processes at larger scales when planning the conversion of CS into more efficient field irrigation methods.

Water Management Options for Rice Cultivation in a Temperate Area: A Multi-Objective Model to Explore Economic and Water Saving Results

“…A strong orientation to agriculture characterizes the area, with the 0.59 hectares of utilizable agricultural area available per With more than 80,000 ha in 2015 [39], the province is the first area in Italy for rice production, though other irrigated crops are also present, from maize to permanent grasslands and short rotation forestry (i.e., poplar groves). This combination in the production pattern may determine conflict in the use of water resource [25], given the specific water demand during the cropping season and the weather-climate trend; despite this, the largest part of irrigation water is here required by rice, since it is the most spread irrigated crop. In this sense, interventions targeted to this sector would have strongly repercussions on regional agriculture as a whole.…”

“…The irrigation volume applied actually consists in providing more water than the amount needed, which means draining the excess [25,46]. Such water outflow from the field should not be however considered a loss; rather, water surplus is reused in either downstream or adjacent fields, and thus contributes in their irrigation, either by flooding irrigation or not.…”

Towards a smart automated surface irrigation management in rice-growing areas in Italy

“…Although the main objective of the rice farms is productive, areas in which the prevailing crop is rice create a peculiar agro-ecosystem characterised by the presence of water in the fields for several months each year (Leibundgut and Kohn, 2014). This extensive water presence endows these areas with significant landscape and natural heritage values, ranging from the preservation of traditional rural landscapes to the safeguarding of different animal and plant species typical of wetland areas (Cesari de Maria et al, 2016). The prolonged presence and circulation of water due to continuous flooding of fields from wet-sowing until close to harvest represent a distinguishing feature of these rice areas, some of which have also been included in the European ecological network NATURA 2000 and on the official list of the European Special Protected Areas (Habitat Directive, 92/43/EEC; European Commission, 1992) (Chiaradia et al, 2013).…”

Prospects for Improving Gravity-Fed Surface Irrigation Systems in Mediterranean European Contexts

“…The pedo-climatic conditions are favorable for extensive cropping, but farming is strongly dependent on irrigation due to the high water requirements of these crops. By studying twelve years of meteorological data (from 1993 to 2013) from 10 agro-meteorological stations located in the district, Cesari de Maria et al [2] found that during the agricultural season (April to September), the average temperature was approximately 20.2 • C, while the total rainfall was approximately 360 mm, with marked variability from year to year. The relative humidity was always high (>80%) and implies the presence of foggy months during the winter and hot and muggy months in the summer.…”

“…In sizeable areas of the southern Member States, especially in Catalonia, Northern Italy and Portugal, gravity-fed surface irrigation remains the dominant form of irrigation, being used in 51%, 70% and 63% of farms, respectively [1]. The main cultivated crops are cereals, particularly maize and rice, which require approximately two to three times the amount of water compared with other extensive crops [2]. The utilized agricultural area (UAA) in these states accounts for approximately 40% of the total land area, resulting in an average size of 16.1 ha per agricultural holding.…”