3.2.2. Light Interception and Leaf Area Index

Crop LAI during the 2016 season was impacted by irrigation, which reached a maximum of 2.47 at 1262 GDD (Figure 3). In 2017, LAI was similarly affected by irrigation and reached a maximum of 3.07 at 1203 GDD (Figure 3). Incidence of crop canopy light interception responded to changes in irrigation through time in 2016 only, reaching 74.6% interception at 967 GDD (Figure 3).

Light interception was influenced by row spacing though the 2016 season, which reached 74% in 19 cm and 65% in 76 cm at 1262 GDD (Figure 4). During 2017, LAI reached 2.87 in 19 cm and 2.59 in 76 cm at 1203 GDD (Figure 4). In both years, light interception and LAI were lower in wide row spacing. However, other work with pearl millet and row spacing has shown that in years where rainfall was less than the local average, wide row spacing outperformed narrow rows [36]. Weeds were not controlled either year of this field study and in 2016 rainfall was 11% less than the 30 year normal (Table 3), yet, row spacing had no effect on pearl millet DM.

During 2016, no differences for LAI nor light interception were observed between tillage treatments (Figure 5). Through 2017, mid-season LAI was different for the tillage treatments but there was no difference by harvest time, reaching a maximum value of 2.8 and 2.6 in till and no-till, respectively (Figure 5). Light interception was greater in no-till through the 2017 season, reaching 77 vs. 70% in till at end of season (Figure 5). For the 2017 season, light interception interactions were found for irrigation × tillage and row spacing × tillage. In the till treatment, there was an increasing trend following increasing irrigation and narrow row spacing, however, that trend was interrupted in the no-till where M had 6% less light interception than L, and 76 cm row spacing had 20% less than 19 cm.

**Figure 3.** Leaf area index (LAI) and percent light interception (PAR) for irrigation levels in 2016 and 2017 in pearl millet at Canyon, TX. Asterisks indicate treatment *p* < 0.05 on measurement date.

**Figure 4.** Leaf area index (LAI) and percent light interception (PAR) for row spacing in 2016 and 2017 in pearl millet at Canyon, TX. Asterisk indicate treatment *p* < 0.05 on measurement date.

**Figure 5.** Leaf area index (LAI) and percent light interception (PAR) for tillage levels in 2016 and 2017 in pearl millet at Canyon, TX. Asterisk indicate treatment *p* < 0.05 on measurement date.

## **4. Discussion**
