## 2 Materials and Methods  
### Study Area  
The study was conducted in two rice regions at sea level in Valencia and Seville (Spain). Rice is cultivated in the Albufera wetland in Valencia, a protected natural park near the city of Valencia, and in the Guadalquivir marshes, located south of Seville city, next to another critical wetland, the Donana National Park. In both regions, the rivers and the lakes provide the necessary ecosystem for the crop (surface water via canals). Approximately 15,000 ha of rice are cultivated in Valencia, while the potential area without drought in Seville is 35,000 ha. Fields are generally small (less than 2 ha) in Valencia and more significant in Seville (5-10 ha on average). The selected fields were carefully managed by the growers, where weed management is a mixture of herbicide spraying and manual weed removal, avoiding large spots of extreme weed growth. The area of the fields in location 1 (Valencia) was considerably low, less than 1 ha in a high number of fields; in location 2 (Seville), the field area increased but was still significantly lower than the average values in other countries, like the U.S. Consequently, fields were leveled more frequently and soil properties in the field were usually the same. [PERSON] agroclimatic classification system defines the climate in both areas as sub-tropical Mediterranean with hot and dry summers [52]. In both regions, the fields were sown under flooded conditions (broadcast sowing) in May, and the sowing date coincided with most farms. The water depth during sowing and the emergence stage is less than 5 cm. After emergence, the water depth is increased to a mean value of 8-10 cm. Fields are dried approximately two to three times during the vegetative stage for terrestrial treatments (herbicide spraying and top-dressing fertilization). For the rest of the season, the fields are flooded and only dry for the harvest in September and October. Common varieties, grower practices, and phenological stages are accurately described by [PERSON] [53], [PERSON] [54], and [PERSON] et al. [55]. Rice varieties are short-, medium-, and long-grain; but the medium grain 'JSendra' variety (cross between California 'M202' and Spanish 'Senia' in 2005 by Instituto Valenciano de Investigaciones Agriaries, IVIA) represents approximately half of the Valencian rice area and an important percentage in Seville (between 10% and 20%). This cultivar exhibits a high average yield (\(\approx\)8000 kg\(\cdot\)ha\({}^{-1}\)) and good culinary qualities, the season duration is \(\approx\)140 days. In Valencia, the other cultivars are less important (each cultivar represents an area less than 10%) because of their low yields (traditional varieties, e.g., 'Bomba' variety) or new cultivars from other Spanish regions or countries with problems in climatic, soil, and market adaptation. In Seville, the long-grain variety 'Puntal' is the most cultivated, but this cultivar is only grown in that region, being 'JSendra' the second variety in crop area. 'JSendra' is well adapted in both regions, and farmers are able to obtain its potential yield. The study fields were selected, covering the entire wetland rice area in Valencia and the east part of the Seville region, where a representative number of?Sendra' fields are grown, as shown in Figure 1. Thus, all the selected fields were commercial farms of the?Sendra' variety to compare both regions, avoiding the variety influence. All fields followed the standard grower practices described by [PERSON] [53]. The area, number of fields, and primary sowing date by year are shown in Table 1. The number of fields throughout the years depended on the crop area, cultivar rotation, and the availability of combine harvesters with yield monitors.