## 4 Discussion  
### Effects of Irrigation Methods and Management Practices  
Better irrigation management is key to increasing alfalfa water productivity in the desert environment. The data presented here provide ET estimates, the possibilities of water savings at different times of year, and potential yield impacts of deficit strategies targeted to conserve water.  
The results showed that changes in irrigation technology itself is not a fix-all solution to improving hay yields and water productivity. For instance, the seasonal ETa was 1450 mm at site E and 1481 mm at site F (both sites under subsurface drip irrigation) in the 2020 season. These amounts were lower than the measured ETa at the surface irrigated sites over this season (Figure 4). The seasonal WP values were also lower, 15.9 kg ha\({}^{-1}\) mm\({}^{-1}\) at site E and 15.5 kg ha\({}^{-1}\) mm\({}^{-1}\) at site F, than all of the surface irrigated sites in the 2020 season (Figure 10). Maintenance and gopher strikes were among the major challenges at sites E and F which impacted irrigation management and as a result influenced the total hay yields per season. This has been commonly observed in production alfalfa fields utilizing SDI [36]. Eventually, the farmer reseeded these two fields and converted them to alfalfa seeds from alfalfa hay in the 2021 season to reduce the number of irrigation events per season and to mitigate the negative impacts of drip tape damages and leaks from rodents.  
In this study, the greatest alfalfa crop coefficient values were obtained during the harvest cycles of April-June, the period that alfalfa yield productivity is considerably higher than the remainder of crop season. According to the seasonal trends of alfalfa crop coefficient values (Figure 13), the average crop coefficient values for the various harvest cycles are as follows: 0.82 for the March harvest cycle, 0.95 for the harvest cycles of April-May, 0.89 for the harvest cycles of June-July, 0.84 for the harvest cycles August-September, and 0.75 for the fall harvest cycles. Thus, more efficient irrigation systems could incorporate different Kc values for the different times of year to reflect differences in water demand.  
Figure 12: The amounts of water conserved by implementing the deficit irrigation strategies D1 (elimination of three irrigation events) and D2 (elimination of two irrigation events) at the different experimental sites of A–D over the 2019–2021 crop seasons.  
These crop coefficient values reflect local desert environments in terms of climate, soil, and water and crop management and may assist farmers in more accurate and effective irrigation scheduling. It is particularly important that farmers ensure that fields have a full profile of water at the beginning of the season and irrigate fields fully by early- to mid-July following the proposed crop coefficient values for the individual harvest cycles. Early season irrigation to fill the crop root zone will produce healthy roots in the lower root zone to take full advantage of the soils water holding capacity and the plants long root system. This could be one reason why site C had a lower seasonal crop water use (1433 mm) and DM yield (23.5 Mg ha\({}^{-1}\)) in the 2019 season (Figures 4 and 8). Alfalfa DM yield at this site was nearly 9% lower than the average DM yield achieved at all experimental sites during the same crop season.