Mexico is currently the largest exporter of beer and the second largest importer of barley (Hordeum vulgare L.) malt in the world (FAO, 2020¹). Barley in Mexico is mainly produced in irrigated agriculture in the Bajío region, specifically in Guanajuato and Queretaro states (SIAP, 2020). However, the region is increasingly suffering from water stress, which hampers agricultural production. The agricultural sector uses 84% of the state's water to irrigate ~3,36,000 ha of crops and is the largest water consumer in the state (Hoogesteger and Wester, 2017; SIAP, 2020). Water for irrigation in Guanajuato comes mainly from aquifers (69% of water used), while the remaining 31% comes from surface water. As a result of the intensive agriculture in the region, 19 of the 20 aquifers in the state are now overexploited, and the groundwater level is dropping at a rate of up to 3 m year⁻¹ (Wester et al., 2011; Romero et al., 2017; Flores et al., 2018). In order to assure the continued production of barley in the region, it is thus important to drastically reduce agricultural water consumption.

Irrigated barley in the Bajío is grown between December and May, with the optimal planting date being around the 15th of December. Water is provided through furrow irrigation in 3 to 4 heavy (100–300 mm) irrigations. Between May and December, maize (Zea mays L.) is generally grown, and this may receive 1 or 2 furrow irrigations depending on the amount of rainfall in the particular growing season. Precipitation is projected to decrease under all climate change scenarios, which will increase the need for irrigation to maize production in the region (Murray-Tortarolo et al., 2018). There are several options for reducing water use in this barley-maize production system. Water use in irrigation is commonly reduced by investing in advanced irrigation systems such as sprinklers or drip irrigation (Yadvinder-Singh et al., 2014; Sandhu et al., 2019); however, the costs of the necessary equipment are high and may not be cost effective in the barley-maize production system. Ideally, in a system with low profitability, like the maize-barley system, less costly interventions that increase water use efficiency are identified. For example, the laser leveling of unleveled fields, which can save up to 50% of irrigation water and increase crop yields (Jat et al., 2009, 2015), or the training and incentivizing of irrigators, who currently have no incentive to make irrigation more efficient, to reduce water use. Well-executed furrow irrigation can be relatively efficient compared to advanced irrigation systems, with irrigation efficiencies of 45–80% depending on the configuration, while sprinkler irrigation systems can reach 65–90% efficiency, and drip irrigation systems 80–95% (Postel et al., 2001; Irmak et al., 2011), so improving the furrow irrigation system may be the most economical option.

In furrow irrigation, irrigation efficiency depends mainly on inflow rate, cut-off time, furrow length and runoff (Eldeiry et al., 2005). Infiltration rate and surface roughness also determine irrigation efficiency, but are often considered as constants in a field; however, increasing infiltration and surface roughness to increase advance rate could be achieved by agronomic interventions such as implementing conservation agriculture (CA) (Verhulst et al., 2011). Jat et al. (2009) reported a 12–20% reduction in water use by implementing zero tillage, which was combined with a higher soil aggregate stability and infiltration rate. Wagger and Cassel (1993) found no difference in water use efficiency between tilled and direct seed maize production in a experiment in the southeastern USA, while Sidhu et al. (2019) and Choudhary et al. (2020) found increased water use efficiency with zero tillage in the rice-wheat system in India. In a long-term experiment in San Luis Potosi, CA led to increased soil health, resulting in an increase in infiltration rate, improved irrigation, and a higher maize yield (Fonteyne et al., 2019; Martínez Gamiño et al., 2019), but a study across 20 sites in Mexico indicated that CA generally increased maize yields, while improvements in infiltration rate were site-specific (Fonteyne et al., 2021). The combination of improved irrigation systems and CA could potentially reduce water consumption even more (Sidhu et al., 2019). Although CA could potentially increase irrigation efficiency, the relationship between water use in furrow irrigation and tillage has not been studied thoroughly (Bryant et al., 2020).

To evaluate potential water saving practices, we set up a field experiment in Guanajuato, Mexico, to compare water use with two tillage systems [conventional tillage (CT) and CA] and two irrigation systems (furrow irrigation and drip irrigation) in barley and maize production from 2016 to 2020. Additionally, we compared water use in CT and CA in 20 side-by-side comparisons in farmer's fields. Our hypothesis was that drip irrigation, CA and the combination of these can reduce water use in barley and maize production in the Mexican Bajío in compared with the conventional practice of furrow irrigation and CT.

Substantial reductions in irrigation water use are possible in the barley-maize production system in the Mexican Bajío. CA reduced water use by ~20% in comparison with the conventional production system; drip irrigation reduced water use by about 30% in comparison to furrow irrigation, while combining both practices reduced water use by ~40% on a yearly basis. In farmer's fields, the irrigation quantity and the management factors depended on the conditions of each field and preferences of each farmer. However, even though the conditions in the farmer's fields were less controlled, similar results were observed under those conditions as under controlled conditions in the field experiment. The effect of CA on WUE was even greater in farmers' fields than in the field experiment, probably because the farmers' fields were larger and therefore less precisely irrigated, while the shorter furrows in the field experiment allowed for more efficient irrigation (Zerihun et al., 1997). If CA could be applied in the 60,000 ha of irrigated barley in Guanajuato and Querétaro (SIAP, 2020), the ~1,000 m⁻³ ha⁻¹ of irrigation water saved per hectare that was observed in the farmers' fields would amount to ~60 Mm³ in irrigation water saved per growing season, while simultaneously reducing greenhouse gas emissions by ~11,520 t CO₂ equivalents. The reduced irrigation requirements would bring substantial savings in pumping costs and aquifer depletion, but might also be used to increase production by increasing irrigated cropland (Fishman et al., 2015). However, according to Jägermeyr et al. (2016), if farmer-implementable practices such as CA or water harvesting could be implemented on a global scale, this would substantially increase agricultural production by 18–41% through the expansion of irrigated land, while simultaneously reducing groundwater withdrawal rates; thus, the implementation of CA could both increase agricultural output and reduce water use in the Bajío. Our water-use findings were similar to those found in studies in the double-cropped intensive production systems in northwestern India, where CA reduced irrigation water use by about 20% in comparison with CT, while increasing maize, wheat and rice yields and improving profitability (Das et al., 2014; Parihar et al., 2016; Jat et al., 2019). In the same region, drip irrigation can reduce water use by 32% in wheat and 65% in maize (Sandhu et al., 2019). The similarity between the results from our dedicated field experiment, the farmers' fields and the scientific literature shows that the implementation of CA is a viable option for reducing agricultural water use.

Drip irrigation increased barley yields, which may have been an effect of reduced flooding of the root zone that creates anoxic conditions. After furrow irrigation the soil is saturated completely with water, and the plant suffers anoxic conditions for several days. With drip irrigation the soil is not completely saturated, and plants suffer no stress from flooding. The soil moisture sensors indicated that soil under CA retained moisture for longer; this helps the crop to overcome periods of drought stress, which is common with surface water irrigation that is available according to schedule and not according to crop needs because distribution is decided centrally for the whole irrigation district. In irrigated wheat under CA, Verhulst et al. (2011) found that yields were similar under full irrigation, but under reduced irrigation CA yielded 19–26% more. In our experiment the soil under barley in CA had a higher moisture content at each irrigation, which may have led to a lower irrigation requirement. With maize, drip irrigation had no significant effect on yield because maize is mostly rainfed, and there was little difference in moisture conditions between treatments. Both CA and drip irrigation increased maize yields by ~1 t ha⁻¹ in our field experiment, although the difference was not statistically significant. In farmer's fields, CA also increased barley and maize yields, even though a range of different varieties, fertilizations and crop management practices were applied by the cooperating farmers.

The lower water use in CA compared to the CT system is likely due to several factors, such as increased infiltration rate through improved soil structure, less evaporation as a result of using residues for soil cover (Zhang et al., 2005; Ranaivoson et al., 2017), and higher moisture retention with increased organic matter (Govaerts et al., 2007; Basche and DeLonge, 2019). Since the relationship between tillage and irrigation water use has been little studied, it is unclear which aspects of CA contribute the most to water saving, whether it is the soil cover, the improved soil health, increased infiltration rate, or another aspect. Further study of the factors that lead to water use reduction and yield increases under CA with furrow or drip irrigation, as well as further studies in different production systems, is desirable to further develop CA as a water-saving practice. Reduced irrigation costs and higher yields make both CA and drip irrigation attractive options for farmers. However, while CA reduced production costs, drip irrigation required a high initial investment. In the long term, it is likely that yields would increase further due to improved soil health, while production costs may be reduced through the reduction in tillage and weed management (Fonteyne et al., 2019, 2020; Wall et al., 2020). Drip irrigation was evaluated in one farmer's field but was discontinued because it was not profitable due to the high costs. Experience with drip irrigation for cereals in the region is lacking however, it is likely that a well-managed drip fertigation system could increase yields and reduce fertilization costs enough to offset the investment in drip irrigation, especially for maize (Sidhu et al., 2019). Additionally, the dropping aquifer levels make pumping ever more costly, so saving water becomes more profitable every year. Drip irrigation would be most beneficial for farmers with the use of subterranean pumped water, while when using surface water there is no incentive to save water as it does not reduce costs, even though collective action could increase water availability for everyone. Overall, to reduce water use in grain production, CA appears the most rapidly scalable option as it reduces costs and increases profits, while drip irrigation needs further improvement to be a profitable option.

Conservation agriculture with both furrow irrigation and drip irrigation could be further improved to increase water savings and profitability. In furrow-irrigated CA, improved irrigation methods such as surge irrigation or irrigating alternate furrows should be evaluated in terms of savings in water use. Since furrow irrigation is already generally done using gated pipes, these practices could be implemented relatively easily. Drip irrigation could be made more attractive to farmers by optimizing drip fertigation for the barley-maize system in the region. Drip fertigation can reduce fertilizer use and increase yields through more timely application of the nutrients where they are needed (Sidhu et al., 2019). Drip fertigation for maize increases the efficiency of applying nutrients compared to the flood irrigation system (Sampath Kumar and Pandian, 2010). In the Bajío, maize yields of 20 t ha⁻¹ and barley yields of 8 t ha⁻¹ are possible given optimal management (Saldivia Tejeda et al., 2020). Drip fertigation could help to attain those yields consistently, which would make the investment economical. Furthermore, the use of sensors, weather data and modeling could improve irrigation scheduling and consequently reduce irrigation water use. Conservation agriculture, in which the soil is not tilled, could allow the installation of buried drip lines, which would drastically reduce the costs of replacing drip lines and improve water use efficiency (Sidhu et al., 2019). Problems with rodent damage and leakage should be resolved first however. An increased use of sensors to inform the optimal irrigation moment could reduce water use, as we observed in the 2019 barley season. Production systems vary widely across Mexico, and the effects of the evaluated treatments could be different in other water-stressed regions, for example in the northwest where only one crop is grown per year, or the Laguna area, where tillage is performed two or three times per year (Fonteyne et al., 2021). There is thus probably a large potential to reduce water use, but research is necessary to adapt the technologies to the conditions of the diverse cropping systems across Mexico.

Water use in the barley-maize production system of the Mexican Bajío can be reduced by the implementation of conservation agriculture or drip irrigation or the combination of both by 20 to 40%. Conservation agriculture retained moisture longer resulting in less moisture stress, which may have resulted in a higher yield in barley. Furthermore, in farmers' fields it improved soil health and reduced fuel consumption. While conservation agriculture has generally been promoted as a soil-conserving and labor-reducing practice mainly in rainfed areas, our study indicates that the promotion of conservation agriculture in irrigated regions is advisable in order to reduce irrigation water use.

The datasets presented in this study can be found in online repositories. The names of the repository/repositories and accession number(s) can be found below: CIMMYT Research Data and Software Repository Network, https://hdl.handle.net/11529/10548578.

ÁFG and SF contributed to the conception and design of the study. ÁFG performed the investigation and curated the data. SF wrote the first draft of the publication. NV supervised the project and reviewed and edited the draft. All authors contributed to revision of the manuscript, and read and approved the submitted version.

The experiments were funded by the Cultivando un Mexico Mejor project funded by Heineken. The data analysis and writing of the article was funded by CCAFS and MasAgro Guanajuato. The work of CCAFS is supported by CGIAR Fund Donors and through bilateral funding agreements. For details please visit https://ccafs.cgiar.org/donors. MasAgro Guanajuato is funded by the Secretaría de Desarrollo Agroalimentario y Rural of the state of Guanajuato. Any opinions, findings, conclusion, or recommendations expressed are those of the authors and do not necessarily reflect the view of the donors.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.