Biostimulants and Drought Tolerance – what have we learned over the two years.

Biostimulants and Drought Tolerance – what have we learned over the two years.

E.J. Nangle T. Morris, S. Cusack and D.P. Petrella

Introduction:

The use of biostimulants in turfgrass management is becoming more critical to the success of turfgrass managers as environmental stresses increase and limitations are continulaly expanded on what can be used in golf course settings. The consistency of the results obtained can however leave turfgrass managers with pause for concern . Issues such as variations in soil types, site specificity and variations in organic matter content, unclear pathways of plant uptake are components of the products that can impact the efficacy of these products. Results have been successful where products have had combinations of nitrogen included in the product and also in laboratory settings indicating there is potential for their use – however field applications have been where the conundrum arises.

One area that is going to be continually a concern for turfgrass managers is the ability to manage turfgrass surfaces with limited levels of moisture to sustain high quality turfgrass surfaces . Products such as wetting agents can help with soil issues that might arise but options for drought tolerance include breeding and potentially use of C4 grass species if conditions continue to deteriorate. The objective of this trial was to evaluate the use of a group of products that are commonly called biostimulants which offer potential solutions in regards to plant hormone changes, stress tolerances and a range of other issues. To compare these products against each other is a regular occurrence but evaluation of these products agaisnt an alternative approach such as the use of Urea also is required based on budget and potential return on investment.

Materials and Methods:

This trial was initiated in its second year at the Waterman Farm in Columbus Ohio on June 8th 2023 on a research green surface that contained a mixed stand of annual bluegrass Poa annua and creeping bentgrass Agrostis stolonifera. The green is mowed at 0.145″ 4x per week with clippings collected and received preventative applications of insecticides and fungicides. Applications were made on June 23rd, July 5th and July 19th using a back pack CO2 sprayer at high label rates for all products (Table 1).

Table 1. Treatments and rates for products used in evaluation of biostimulants for drought tolerance during Summer 2023 in Columbus, OH.

The treatments were replicated four times and laid out in a randomized complete block design (Figure 1). Drought stress was initiated on July 12 with the construction of a framed rainout shelter that was covered with polyethylene liner which was opened on the north and south end to allow for air movement. The drought period was completed on July 24th when hand watering was returned. Turf was evaluated for quality (1-9 scale), color (1-9 scale), percent stress on the plots, normalized difference vegetative index and volumetric water content at 3″ depth. Treatments will be made one final time and recovery will be evaluated through August 31st 2023.

 

Results:

Color ratings indicated some minor differences initially with treatments 3,4,6 and 8 having a slightly higher color rating but 0.2 difference overall would seem to be of limited consequence. At D27 variability increased but none of the treatments provided color rankings significantly higher than the check plot (9) (Table 2).

Table 2. Daily color ratings during evaluation of biostimulants for enhancement of tolerance to drought stress in Columbus OH, Summer 2023

Treatment	D0	D15	D27	D41	D48
1	7.0 a†	6.6 bc	6.8 abc	6.6 bc	6.8 ab
2	6.8 b	6.5 b	6.6 bc	6.4 c	6.4 abc
3	7.0 a	6.6 bc	6.9 ab	7.0 ab	7.0 a
4	7.0 a	6.9 ab	6.9 ab	7.0 ab	6.0 c
5	6.9 ab	6.6 bc	6.5 c	6.8 abc	6.5 abc
6	7.0 a	7.0 a	7.0 a	7.1 a	6.9 a
7	6.9 ab	7.0 a	6.9 ab	6.8 abc	6.1 bc
8	7.0 a	6.8 ab	6.9 ab	7.1 a	6.8 ab
9	6.9 ab	6.6 b	6.8 abc	6.5 c	6.1 bc
LSD	0.2	0.3	0.3	0.4	0.6

†Means followed by different letters are significantly different at p ≤ 0.05

Turf quality with the exception of the final rating date was found to be acceptable for all treatments. On the final date treatment 4 provided an overall ranking that was below acceptable and across all treatments there was some decline in quality. Highest rated treatments were 1,6 and 8 for the final date (Table 3).

Table 3. Daily Quality ratings during evaluation of biostimulants for enhancement of tolerance to drought stress in Columbus OH, Summer 2023

Treatment	D0	D15	D27	D41	D48
1	7.0 a†	6.5 a	6.8 abc	6.8 ab	6.6 ab
2	7.0 a	6.4 ab	6.8 abc	6.5 b	6.4 abc
3	6.9 ab	6.4 ab	6.8 abc	7.0 a	6.6 ab
4	6.9 ab	6.5 a	7.0 a	6.8 ab	5.9 c
5	6.6 b	6.6 a	6.8 abc	6.6 b	6.4 abc
6	6.8 ab	6.6 a	6.9 ab	7.0 a	6.9 a
7	6.9 ab	6.1 b	6.5 c	6.8 ab	6.0 c
8	7.0 a	6.6 a	6.9 ab	7.0 a	6.9 a
9	6.9 ab	6.1 b	6.9 ab	6.6 b	6.1 bc
LSD	0.3	0.4	0.3	0.3	0.5

†Means followed by different letters are significantly different at p ≤ 0.05

NDVI values showed some variability at D15 and that pattern continued through D48 when plots were under the most drought stress. Treatment 7 provided significantly lower values along with treatment 9 and 2 on D41 while treatments 3,6 and 8 were rated significantly higher than four other treatments on that date (Table 4).

Table 4. Daily NDVI Ratings during evaluation of biostimulants for enhancement of tolerance to drought stress in Columbus OH, Summer 2023

Treatment	D0	D15	D27	D41	D48
1	0.728 ab†	0.772 bc	0.758 bcd	0.776 ab	0.663 ab
2	0.722 b	0.772 abc	0.742 d	0.757 de	0.638 bc
3	0.736 a	0.788 a	0.762 abc	0.785 ab	0.690 a
4	0.737 a	0.780 ab	0.766 abc	0.771 bcd	0.600 cd
5	0.725 ab	0.777 abc	0.754 bcd	0.762 cde	0.653 ab
6	0.727 ab	0.787 ab	0.769 ab	0.783 ab	0.700 a
7	0.721 b	0.769 c	0.748 cd	0.747 e	0.585 d
8	0.731 ab	0.783 abc	0.775 a	0.791 a	0.703 a
9	0.726 ab	0.777 abc	0.753 bcd	0.762 cde	0.638 bc
LSD	0.014	0.016	0.018	0.017	0.052

†Means followed by different letters are significantly different at p ≤ 0.05

Stress did not develop until D41 which was 7 days after drought was initiated and on both dates (D41 and D48) percent of stressed turf increased. Treatments of Urea att he highest rate provided plots with the lowest levels of stress and this was significantly lower than many of the other treatments. The lower rate of urea also began to show stress at D48 while plots receiving treatments 2,7 and 9(UTC) showed greater stress to the drought (Table 5).

Table 5. Daily stress ratings (% plot) during evaluation of biostimulants for enhancement of tolerance to drought stress in Columbus OH, Summer 2023

Treatment	D0	D15	D27	D41	D48
1	0.0 a†	0.0 a	0.0 a	3.1 a	7.5 bc
2	0.0 a	0.0 a	0.0 a	2.5 ab	27.5 a
3	0.0 a	0.0 a	0.0 a	0.0 b	8.1 bc
4	0.0 a	0.0 a	0.0 a	0.0 b	10.0 ab
5	0.0 a	0.0 a	0.0 a	1.3 ab	7.5 bc
6	0.0 a	0.0 a	0.0 a	0.0 b	8.1 bc
7	0.0 a	0.0 a	0.0 a	2.5 ab	26.3 ab
8	0.0 a	0.0 a	0.0 a	0.0 b	4.4 c
9	0.0 a	0.0 a	0.0 a	1.9 ab	21.3 ab
LSD	0.0	0.0	0.0	2.9	19.3

†Means followed by different letters are significantly different at p ≤ 0.05

 

Conclusions:

In 2022, treatment #7 provided turf quality as high as the urea treaments but this did not happen in 2023. The additional rate of urea showed a dose response in the sense that the lower rate showed increased stress during the drought period. Recovery data will be collected and analyzed for both years to complete this study. The products used other than urea currently cannot form a stand alone program for drought stress and should only be used in combination with other agronomic practices.