Under the semiarid climate of the Southwest United States, accurate estimation of crop water use is important for water management and planning under conservation agriculture. The objectives of this study were to estimate maize water use and water productivity in the Four Corners region of New Mexico. Maize was grown under full irrigation during the 2011, 2012, 2013, 2014 and 2017 seasons at the Agricultural Science Center at Farmington (NM). Seasonal amounts of applied irrigation varied from 576.6 to 1051.6 mm and averaged 837.7 mm and the total water supply varied from 693.4 to 1140.5 mm. Maize actual evapotranspiration was estimated using locally developed crop coefficient curve and the tabulated United Nations Food and Agriculture Organization (FAO) crop coefficients, and from this maize water productivity was determined. Maize actual daily evapotranspiration (ETa) varied from 0.23 to 10.2 mm and the seasonal ETa varied with year and ranged from 634.2 to 697.7 mm averaging 665.3 mm by the local Kc curve, from 687.3 to 739.3 mm averaging 717.8 mm by the non-adjusted FAO Kc values, and from 715.8 to 779.6 mm averaging 754.9 mm with the FAO adjusted Kc values. Maize irrigation requirements varied from 758.4 to 848.3 mm and averaged 800.2 mm using the local developed Kc and varied from 835.5 to 935.6 mm and averaged 912.2 mm using FAO Kc. The net irrigation requirement varied from 606.8 to 678.6 using local Kc curve, and from 682.78 to 748.5 mm when adopting the FAO Kc values. Average irrigation requirement was 641 mm under the local Kc option and 730 mm under FAO Kc values option. Maize crop water use efficiency (CWUE) ranged from 1.3 to 1.9 kg/m³ and averaged 1.53 kg/m³, evapotranspiration water use efficiency (ETWUE) values were higher than CWUE and varied from 2.0 to 2.3 kg/m³, averaging 2.1 kg/m³. Maize irrigation water use efficiency (IWUE) was varied with years and averaged 1.74 kg/m³. There were strong relationships between maize CWUE and maize seasonal irrigation amounts of IWUE and the seasonal irrigation amounts with R² of 0.97 and 0.92, respectively. Maize CWUE increased linearly with maize IWUE with a coefficient of determination R² of 0.99, while IWUE showed a strong quadratic relationship with ETWUE (R² = 0.94). The results of this study can be used as a guideline for maize water management under the semiarid conditions in northwestern New Mexico and other locations with similar climate and management conditions. Irrigation requirements for maize should be adjusted to the local meteorological conditions for optimizing maize irrigation requirement and improving maize water productivity.

Limited water resources coupled with the increase of the human population calls for more efficient use of water in irrigated agriculture. Potato (Solanum tuberosum L.) is one of the most widely grown crops worldwide and is very sensitive to water stress due to its shallow rooting system. With the dilemma of potato sensitivity to drought and limited available water resources restricting crop production, researchers and crop growers have been investigating different approaches for optimizing potato yield and improving crop water use efficiency under different irrigation methods. While potato response to water is affected by other management practices such as fertilizer management, the present review is focused on the potato response to water under different environments and different irrigation methods and the impact on potato quality and potato diseases. Variable results obtained from research studies indicate the non-transferability of the results from one location to another as potato cultivars are not the same and potato breeders are still making effort to develop new high-yielding varieties to increase crop production and or develop new varieties for a specific trait to satisfy consumers exigence. This review is a valuable source of information for potato growers and scientists as it is not only focused on the impact of irrigation regimes on potato yield and water productivity as most reviews on water management, but it also presents the impact of irrigation regime on diseases in potatoes, tuber specific gravity, metabolite content of the tubers and the quality of the processed potato products.

A decrease in water resources, as well as changing environmental conditions, calls for efficient irrigation-water management in cotton-production systems. Cotton (Gossypium sp.) is an important cash crop in many countries, and it is used more than any other fiber in the world. With water shortages occurring more frequently nowadays, researchers have developed many approaches for irrigation-water management to optimize yield and water-use efficiency. This review covers different irrigation methods and their effects on cotton yield. The review first considers the cotton crop coefficient (Kc) and shows that the FAO-56 values are not appropriate for all regions, hence local Kc values need to be determined. Second, cotton water use and evapotranspiration are reviewed. Cotton is sensitive to limited water, especially during the flowering stage, and irrigation scheduling should match the crop evapotranspiration. Water use depends upon location, climatic conditions, and irrigation methods and regimes. Third, cotton water-use efficiency is reviewed, and it varies widely depending upon location, irrigation method, and cotton variety. Fourth, the effect of different irrigation methods on cotton yield and yield components is reviewed. Although yields and physiological measurements, such as photosynthetic rate, usually decrease with water stress for most crops, cotton has proven to be drought resistant and deficit irrigation can serve as an effective management practice. Fifth, the effect of plant density on cotton yield and yield components is reviewed. Yield is decreased at high and low plant populations, and an optimum population must be determined for each location. Finally, the timing of irrigation termination (IT) is reviewed. Early IT can conserve water but may not result in maximum yields, while late IT can induce yield losses due to increased damage from pests. Extra water applied with late IT may adversely affect the yield and its quality and eventually compromise the profitability of the cotton production system. The optimum time for IT needs to be determined for each geographic location. The review compiles water-management studies dealing with cotton production in different parts of the world, and it provides information for sustainable cotton production.