Lower Mondego Valley Irrigation Distric (Portugal)
The Lower Mondego Valley Irrigation District (LMID) is a state initiative, located in the Centre of Portugal, which is managed by a local Water Users Association; the area is served by a full gravity irrigation system. The area comprises about 13,000 ha of irrigated agricultural land, of which 7000 ha are dedicated to rice, which is a crop of great tradition in the area, involving 6300 farmers and an annual production of about 30,000 tons. Soils are dominantly modern alluvial soils, of high agricultural value. However, near the coast, in the lower lands, heavy soils are found, that are typically poorly drained. These areas are mainly rice cultivated, due to the problems of drainage and soil salinization risks. Elsewhere in LMID, other dominant crops are maize and horticulture.
LMID has a temperate climate, with hot and dry summers and mild and rainy winters, typically Mediterranean; it is a Csb climate under the Köppen climate classification. The mean annual precipitation is approximately 900 mm. The wet semester is from October to March, registering about 70% of the annual precipitation. The driest months are July and August, with a mean monthly precipitation of around 15 mm. In the dry season, months often register zero-precipitation.
Dedicated infrastructures implemented in the Mondego River guarantee the supply of irrigation water to the agricultural fields in the Lower Mondego, namely to produce rice. The majority of the existing hydraulic infrastructures and solution dates back to the middle 1980’s. The water flows by gravity in the main irrigation canal to the irrigated fields, guaranteeing irrigation water to the majority of the agricultural area, including rice-producing areas. The irrigation water tariff paid by the farmers depends on the area of their irrigated land and is presently 81,5 €/ha. Laser land levelling is a common practice applied on rice fields: the rice basins are precise zero land levelled after soil ploughing. The rice agronomic practices are the traditional ones used in Portugal. After the initial flooding, sowing is made mechanically by centrifugal spread and is carried out usually in the beginning of May. The basins are drained before herbicide or pesticide applications. The basins are maintained flooded until the last crop phase, close to 2 or 3 weeks before harvest, usually in the beginning of October. The variety of rice produced in the region is Carolino rice and belongs to Oryza sativa L. ssp. japonica.
The main problems faced by rice irrigation in the study area include: 1. Limitations in irrigation water availability due to water source scarcity; 2. Constraints of the conveyance hydraulic system; 3. Water management problems at distribution and on-farm levels; 4. Environmental risks related with soil salinization and pollution with nitrates.
This case study focuses on a downstream irrigation sector, representative of the rice production in LM; the investigation will be complemented with experimental trials to assess the water productivity of plant varieties, which will be conducted at an experimental station of the DRAPC, and laboratory experiments to investigate the effect of irrigating using treated wastewater on selected rice varieties. This case study aims at contributing to the following objectives: 1. Improving irrigation management at conveyance level, aiming at water saving; 2. Improving irrigation water use at farm level, focusing on the optimization of water productivity related to upgrading soil and crop management techniques, including land levelling; 3. Decreasing putative health and environmental risks related to irrigation and drainage; 4. Assessing yield impacts and ecotoxicological risks of irrigating with treated wastewater; 5. Improving farmers’ economic outcomes.