Water needs and production of asparagus in the arid zone of northwestern Mexico

In arid and semi-arid areas, water is a scarce and expensive resource for agriculture. This becomes environmentally critical when irrigation water is extracted from overexploited aquifers. Despite this problem, there is intensive agriculture with perennial crops, which consume significant volumes of water. One of these crops is green asparagus (Asparagus officinalis L.), with records of irrigation applications around 2,000 mm annually for high-density plantations. In order to assess feasibility for reducing the irrigation water application, an Eddy covariance system was installed in 2019-2020 on a commercial asparagus plot to determine evapotranspiration and the potential for atmospheric carbon fixation. Additionally, other sensors were installed to monitor the soil water tension and its impact on yield. The results show that the reference evapotranspiration did not change significantly during both years and it was about 1,849 and 1,929 mm year-1; while the crop evapotranspiration was about 1,188 and 1,146 mm, respectively. The irrigation applications were 1,949 and 1,517 mm, with a reduction of 432 mm year-1, keeping a dry biomass production of 1,920 and 1,917 g m-2 during 2019 and 2020, respectively. On the other hand, gross primary productivity and net carbon exchange were 1,905 and -733 g m-2 in 2019, while in 2020 they were 2,066 and -874 g m-2. The soil water tension at 0.6 m depth during the growing period from May to November in 2019 ranged between -5 and -15 kPa, while in 2020 it ranged from -10 to -25 kPa. Plant area index measurements in both years did not change and their maximum was between 8 and 9. These results indicate that it is possible: 1) to reduce irrigation water, 2) to improve root system oxygenation, 3) to obtain similar values of gross primary production, net carbon exchange, dry biomass, and 4) to maintain quantity and quality of asparagus spears.