*6.7. Economic Irrigation Water Use Efficiency*

The parameter estimates for *EIWUE* equations of corn and soybeans are presented in Table 8. The results show that irrigation using water from on-farm surfaces only has a positive effect on corn *EIWUE*, compared to groundwater only. Higher water prices decrease *EIWUE* of corn, and higher energy expenses also decrease *EIWUE* of both crops. Combined with the results on water use and yield, these findings suggest that a higher efficiency cannot be achieved through increasing water prices. Higher labor payment also decreases *EIWUE* of corn.

Regarding farm characteristics, the number of wells shows a negative effect on both corn and soybean *EIWUE*. This indicates that fewer wells available on a farm can encourage an efficient use of irrigation water. The adoption of pressure irrigation increases the water use efficiency of both crops, indicating the effectiveness of achieving higher irrigation water use efficiency with the application of enhanced irrigation systems, and this is consistent with the results of water application and crop yield.

Similarly, irrigation efficiency is limited by factors related to the risk of reduced yield or poorer quality crop (on soybeans), limitation of physical field or crop conditions (on soybeans), cannot finance improvements (on corn), and will not be farming long enough (on corn). These findings can be true if water applications are limited by poor water distribution systems and/or farmers are resource-limited.

Effects of information sources are consistent for the two crops. Media reports show a positive effect, and variables showing a negative effect include local irrigation district employees and government specialists.

Regarding the state-level variables on climate variability, for soybean farms, compared with the average precipitation, a higher precipitation in 2011 and 2012 are positively associated with higher irrigation water use efficiency in 2013. The precipitation change in 2013 is positively associated with water use efficiency of both crops. The temperature change in 2011 decreases the *EIWUE* of corn and the temperature changes in 2013 increase *EIWUE* of both crops. These findings suggest that higher temperatures in the growing season lead to farmers using water more efficiently, while perceptions of precipitation are more effective to increase *EIWUE* than perceptions of temperature. Compared to farms in the Plains, both corn and soybean farms in the West have a lower *EIWUE*, while corn farms in the Midwest, South, and Atlantic states have a higher *EIWUE*.

**Table 8.** The results of multilevel models for the economic irrigation water use efficiency for corn and soybeans.



**Table 8.** *Cont.*

Significance levels: \* 10%; \*\* 5%; \*\*\* 1%.
