SOIL MOISTURE May 2 May 9 May 16 May 23 May 30 Jun 6 Jun 13 Jun 20 Aug 3 May 2 May 9 May 16 May 23 May 30 Jun 6 Jun 13 Jun 20 Aug 3


Figure 6. 70 kPa trigger May 2 May 9 May 16 May 23 May 30 Jun 6 Jun 13 Jun 20 Aug 3


Figure 8. UGA checkbook method May 2 May 9 May 16 May 23 May 30 Jun 6 Jun 13 Jun 20 Aug 3


Figure 7. SmartIrrigation Corn App


Figure 6 shows a very rapid utilization of soil moisture at all levels very early in the season. This is proof that if there is not adequate soil moisture the plants will work to access soil moisture where it is available. It can be assumed that the extra energy required to access moisture at these levels is most likely yield-reducing. It is also important to note that deep soil moisture was not recovered except during the three significant rainfall events mentioned earlier, but with a significant delay in recovery. The lagging graph lines for the deeper depths show this delay.


The SmartIrrigation Corn App (figure 7) keeps the soil moisture levels at an adequate range during the entire season and follows a similar pattern to the 40/50 kPa treatments. Past studies have shown that the app performs well. This is very good news showing that there is a tool that can perform even in “extreme” weather conditions without sensors in the field.


Overall, the checkbook method was designed to, and tends to, overirrigate. This can be seen up until mid-May. After this point, a general decline in overall soil moisture compared to some of the lower SWT treatments is present, especially the deep moisture, reinforcing the fact that the checkbook method was developed on a historical average and will miss the target in years that are not “average.” In this case, 2022 was hotter and drier than average and the checkbook method was not able to keep up with the total water requirements later in the season, since evapotranspiration was higher than average.


Figure 9 or the nonirrigated treatment rapidly depleted soil moisture by mid-May. As can be seen, all sensor depths reached a SWT of 150 (or higher) by mid-May, it should be noted that the


18 Irrigation TODAY | Winter 2023 Figure 10. Rainfall at SIRP since corn planting on March 29, 2022. irrigationtoday.org


Figure 9. Nonirrigated


sensors do not read over 200 kPa, showing that there is basically no moisture left at any of these depths. Even though there is some recovery of the soil moisture after the rainfall events, there was very little to no recovery in the deepest sensors even with higher rainfall events. This treatment will have a very low yield due to the lack of any moisture and heat during tassel.


As stated above, figure 10 shows the 9.5 inches of rainfall that has been received over the past 80 days. These intense hot and dry conditions during the testing time period allowed us to learn interesting things about soil moisture management using sensors in-season.


Wesley Porter, PhD, is an associate professor of crop and soil sciences at the University of Georgia.


Soil water tension (SWT kPa)


Soil water tension (SWT kPa)


Soil water tension (SWT kPa)


Soil water tension (SWT kPa)


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