California Golf Course

The experiments were conducted at the Center for Turf Irrigation and Landscape Technology (C-TILT), California State Polytechnic University, Pomona. The plots were laid out in a split plot design with three replicates where the main factor was the different Aquaboost treatments and the sub factor was the irrigation water quality (recycled and potable). Each individual plot was 10ft by 10 ft in dimension (Figure 1).

The following treatments were included in the trial;

Control
1. Aquaboost low rate (2000 ppm)
Aquaboost mid rate (4000 ppm)
1. Aquaboost high rate (8000 ppm)

Results and Discussion

Water conservation experiments

During a period of 5 months the amount of irrigation was slowly reduced to observe the effects of Aquaboost in maintaining turf quality under reduced irrigation regimes. In the month of May the irrigation system was set to 100% of the ETo replacement values. In the month of June the amount of irrigation water was reduced by 25% (75% ETo) followed by 33% reduction (67% ETo) in July, 50% reduction in August (50% ETo) and finally it was reduced to 75% reduction (25% ETo) in September. The data from the recycled and potable water experiments were combined as an overall average for the water conservation experiments. The plot layout for the experiments is shown below (Photo 1).

Photo 1. Layout of plots in the month of August 2009 when the plots received 50% of the ETo replacement values through irrigation.

Volumetric Moisture Content

The volumetric moisture content (VMC) reduced as the amount of irrigation reduced from 100% ETo to 75%, 67%, 50% and finally 25% ETo. The application of Aquaboost at all the three rates resulted in higher VMC but the difference was not significant at the 100% and 75% ETo levels. As the moisture stress increased the addition of the Aquaboost resulted in higher VMC in the soil. The difference in VMC between the Aquaboost rates was significant at the 67% and 50% ETo levels. There was no difference in VMC between the different rates of Aquaboost at the 25% ETo level (Figure 1).

Figure 1. Overall mean volumetric moisture content (VMC) as affected by the addition of Aquaboost under different irrigation regimes.

Turf Color and Quality

Addition of the Aquaboost helped in improving turf color and quality throughout the experiment. The turf color was highest when the highest rate of Aquaboost was applied. There was no difference between the medium and the low rate of the Aquaboost treatments (Figure 2).

Figure 2. Overall mean turf color of the plots as affected by the addition of Aquaboost under different irrigation regimes.

Overall the turf quality improved with the addition of Aquaboost throughout the water conservation part of the experiment. The turf quality declined as the amount of irrigation water was reduced. There was no difference in turf quality between the low and medium rate of Aquaboost treatments. The highest rate of Aquaboost resulted in highest turf quality throughout the experiment (Figure 3). The turf quality was adversely affected when the irrigation water was reduced to 25% of the ETo even with the Aquaboost treatments. Hence, based on these results a reduction of 25% to 50% of the irrigation water based on ETo replacement values could be achieved with Aquaboost in a heavy soil where the experiment was conducted. In light textured soils the percentage reduction of irrigation water with Aquaboost will be lower than observed in the experiments since the soil was a heavy clay loam soil with a higher water holding capacity.

Normalized Deviation Vegetation Index (NDVI)

The health, growth, and development of turf was monitored with a Greenseeker (N Tech Instruments, Ukiah, CA). The Greenseeker sends light from a source and records the reflectance from the turf canopy. Monitoring the reflectance in the near infrared (NIR) and red (R) wavelengths allows the determination of turfgrass quality and detection of early water stress (Park et al., 2005). The characteristics of healthy, live, green vegetation are that it has a low reflectance of light from the visual spectrum (R) as a result of the leaf pigments and has a high reflectance of NIR from the scattering of light in the leaf mesophyll cells (Park et al., 2005). On the other hand, dead, brown vegetation and the soil have the reflectance that increases from the visible spectrum to NIR (Park et al., 2005). The normalized difference vegetative index (NDVI) is strongly correlated with plant biomass, leaf area index, canopy photosynthetic capacity, and chlorophyll production (Park et al., 2005). Hence healthy dense turf stand has a higher NDVI value and the ratio of R/NIR is lower than the values observed in thin unhealthy stand of turf.

The highest rate of Aquaboost resulted in higher NDVI compared to the other treatments but there was no significant difference between the other treatments (Figure 4). There was no significant difference between the treatments in regard to the ratio of the red/NIR values between the treatments (Figure 5). Though the combined mean of the potable and recycled water treatments did not show significant difference in the NDVI and red/NIR values but the individual treatments had significant difference when they were compared within the recycled and potable water irrigation treatments.

100% ETo

During the month of May 2009 the irrigation system was set to deliver 100% of the ETo replacement. Overall the addition of Aquaboost did not affect turf growth and development when there was adequate irrigation water. The difference between the treatments was observed under moisture stress.

Turf Color

The plots were rated for turf color on a scale of 1-10 where 1 = brown dead turf and 10 = lush green color. A reading of 6.0 was considered as an acceptable turf color.

Recycled Water

All the plots which received Aquaboost had higher turf color compared to the untreated plots. There was no statistical difference between the three rates of Aquaboost in the recycled water irrigated plots under the 100% ETo irrigation regime (Figure 6).

Potable Water

The was no difference in turf color between the different rates of Aquaboost and the untreated control treatment when the plots were irrigated with potable water under the 100% ETo irrigation regime. Hence, no benefit of adding Aquaboost was observed when there was more than adequate moisture in the soil.

Figure 3. Overall mean turf quality of the plots as affected by the addition of Aquaboost under different irrigation regimes.

Figure 4. Overall mean normalized deviation vegetation index (NDVI) of the plots as affected by the addition of Aquaboost under different irrigation regimes.

Figure 5. Overall ratio of Red/NIR values of the plots as affected by the addition of Aquaboost under different irrigation regimes.

Figure 6. Turf color in the plots irrigated with recycled irrigation water throughout the experiment. The plots were visually rated on a scale of 1-10, where 1 = brown dead turf and 10 = lush green color.

Figure 7. Turf color in the plots irrigated with potable irrigation water throughout the experiment. The plots were visually rated on a scale of 1-10, where 1 = brown dead turf and 10 = lush green color.

Turf Quality

The visual quality ratings was conducted on a scale from 1-10 where 1 = thin stand while 10 = dense thick stand of turf. A reading of 6.0 was considered as an acceptable turf quality.

Recycled water

The addition of Aquaboost resulted in higher turf quality compared to the untreated plots. There was no significant difference in turf quality between the low mid and high rate of Aquaboost treatment.

Figure 8. Overall turf quality of the plots irrigated with recycled irrigation water. The plots were visually rated on a scale of 1-10, where 1 = brown dead turf and 10 = lush green color.

Potable Water

The turf quality was higher in the mid and high rate of Aquaboost compared to the untreated and the low rate of Aquaboost treatments.

Figure 9. Overall turf quality of the plots irrigated with potable irrigation water. The plots were visually rated on a scale of 1-10, where 1 = brown dead turf and 10 = lush green color.

Normalized Difference Vegetative Index (NDVI)

The health, growth and development of turf can be monitored using an instrument called the Greenseeker. The normalized difference vegetative index (NDVI) is strongly correlated with plant biomass, leaf area index, canopy photosynthetic capacity and chlorophyll production (Park et al. al., 2005). Hence healthy dense turf stand has a higher NDVI value and the ratio of R/NIR is lower than the values observed in thin unhealthy stand of turf.

Recycled Water

The highest normalized difference vegetative index (NDVI) was observed in the highest rate of Aquaboost followed by the medium and the low rate.

Figure 10. Overall normalized difference vegetation index (NDVI) of the plots irrigated with recycled irrigation water.

Potable Water

The difference between the treatments was highly significant in the plots irrigated with potable water. Highest NDVI was observed in the highest rate of Aquaboost treatment followed by the medium and low rates of Aquaboost.

Figure 11. Overall NDVI of the plots irrigated with potable irrigation water.

Red/NIR

A healthy dense turf stand has a higher NDVI value and the ratio of R/NIR is lower than the values observed in thin unhealthy stand of turf.

Recycled Water

The difference in Red/NIR was significant for the treatments in the plots irrigated with recycled water. The lowest Red/NIR ratio was observed in the highest Aquaboost treatment which indicated that the plots were least stressed. There was no difference between the mid and low rate of Aquaboost treatments.

Figure 12. Overall red/near infra red (R/NIR) value for the plots irrigated with recycled water.

Potable Water

The difference in Red/NIR ratio between the treatments for the mid and low rates was not significant. The Red/NIR ratio was lowest in the highest Aquaboost treatment in the plots irrigated with potable water.

Figure 13. Overall Red/near infra red (R/NIR) value for the plots irrigated with potable water.

Greenseeker readings indicated that optimum turf health was observed when Aquaboost was injected at the highest rate of 8000 ppm into the irrigation lines every week on bermudagrass.

Volumetric Moisture Quality (VMC)

Recycled Water

The volumetric moisture content (VMC) at 4 inches under the soil surface indicated that the highest moisture was observed in the medium rate of Aquaboost treatment followed by the high and the low rate.

Figure 14. Overall volumetric soil moisture content (VMC) for the treatments irrigated with recycled water.

Potable Water

The difference in VMC between the treatments was lower in the potable water irrigated plots compared to the recycled water irrigated plots. Highest VMC was observed in the highest rate of Aquaboost treatment but there was no difference between the mid and the low rate of Aquaboost treatments.

Figure 15. Overall volumetric soil moisture content (VMC) for the treatments irrigated with potable water.

75% ETo

During the month of June 2009 the irrigation system was set to deliver 75% of the ETo replacement values. Hence these treatments were actually saving 25% of the irrigation water in respect to the ETo replacement values. Taking the crop coefficient of bermudagrass as 0.75 this irrigation regime was the optimum amount of irrigation that should be applied to bermudagrass maintained under southern California growing conditions.

ETc = Crop coefficient x ETo

Turf color

Recycled Water

All the plots which received Aquaboost had higher turf color compared to the untreated plots. There was no difference between the three rates of Aquaboost applied in the recycled water irrigated plots under the 75 % ETo irrigation regime (Figure 16).

Figure 16. Overall turf color for the treatments irrigated with recycled water.

Potable Water

The highest rate of Aquaboost had higher turf color compared to the other treatments. There was no difference in turf color between the low and the medium rate of Aquaboost treatments.

Turf Quality

Recycled water

The addition of Aquaboost resulted in higher turf quality compared to the untreated plots. There was no significant difference in turf quality between the low, medium and high rate of Aquaboost treatment.

Figure 17. Turf color in the plots irrigated with potable irrigation water throughout the experiment. The plots were visually rated on a scale of 1-10, where 1 = brown dead turf and 10 = lush green color.

Figure 18. Overall turf quality of the plots irrigated with recycled irrigation water. The plots were visually rated on a scale of 1-10, where 1 = brown dead turf and 10 = lush green color.

Potable Water

The highest rate of Aquaboost had higher turf color compared to the other treatments. There was no difference in turf color between the low and the medium rate of Aquaboost treatments.

Normalized Difference Vegetative Index (NDVI)

Recycled Water

The highest normalized difference vegetative index (NDVI) was observed in the highest rate of Aquaboost followed by the medium and the low rate. There was no difference in NDVI between the low and the medium rate of Aquaboost.

Figure 19. Overall turf quality of the plots irrigated with potable irrigation water. The plots were visually rated on a scale of 1-10, where 1 = brown dead turf and 10 = lush green color.

Figure 20. Overall normalized difference vegetation index (NDVI) of the plots irrigated with recycled irrigation water.

Potable Water

RED/NIR

Recycled Water

The difference in Red/NIR was not significant for the Aquaboost treatments in the plots irrigated with recycled water.

Figure 21. Overall NDVI of the plots irrigated with potable irrigation water.

Figure 22. Overall red/near infra red (R/NIR) value for the plots irrigated with recycled water.

Potable Water

The difference in Red/NIR ratio between the treatments for the high, mid and low rates was not significant.

Volumetric Moisture Content (VMC)

Recycled Water

The volumetric moisture content (VMC) at 4 inches under the soil surface indicated that there was no significant difference between the treatments.

Figure 23. Overall red/near infra red (R/NIR) value for the plots irrigated with potable water.

Figure 24. Overall volumetric soil moisture content (VMC) for the treatments irrigated with recycled water.

Potable Water

The difference in VMC between the treatments was not significant in the potable water irrigated plots.

67% ETo

During the month of August 2009 the irrigation system was set to deliver 67% of the ETo replacement value. Hence these treatments were actually saving 33% of the irrigation water in respect to the ETo replacement values.

Figure 25. Overall volumetric soil moisture content (VMC) for the treatments irrigated with potable water.