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Figure 1. Closely grazed bahiagrass pasture with patches of brunswickgrass in late September (toward end of growing season) in Levy County, Florida.

This information highlights the results of a 2-yr small plot study evaluating PGPR on stockpiled Coastal bermudagrass in Auburn, Alabama (2017-2019).

What is PGPR?

Plant growth-promoting rhizobacteria (PGPR) are non-pathogenic, soil-inhabiting beneficial bacteria that colonize the seeds and roots of plants. These bacteria benefit the host plants through increasing drought tolerance, insect resistance, nutrient uptake, and increasing top and root. Additionally, PGPR are antagonists toward pathogens through induced systemic resistance (ISR) by competing for nutrients, producing antibiotics, and secreting lytic enzymes that are important in the rhizosphere of the plant. Most research with PGPR has been conducted in agronomic crops; there are few studies evaluating the effects of PGPR on grasses, specifically forage-type grasses.

Why evaluate the use of PGPR?

Management practices have been affected by increased cost of N fertilization, and there is a need to evaluate alternative forms of N delivery. Auburn University’s Department of Entomology and Plant Pathology have developed blends and strains of PGPR that have produced similar DM yields, and comparable nutritive quality when compared with N fertilization.

What is stockpiling?

Stockpiling is often referred to as deferred grazing or standing hay, because it is allowed to grow and accumulate for later grazing during a time of forage deficit. Stockpiling for fall and winter grazing has the potential to reduce production costs by minimizing the amount of mechanically harvested and purchased feeds. Bermudagrass, a warm-season perennial, is widely used in the southeastern United States and is ideally suited for fall stockpiling.

What treatments were evaluated?

  • Control
  • Synthetic fertilizer
  • Blend 20
  • Blend 20 + synthetic fertilizer
  • DH44
  • DH44 + synthetic fertilizer

How were they applied and managed?

Established Coastal bermudagrass plots were mowed in mid-August and allowed to stockpile. Ammonium sulfate (21-0-0) was applied at a rate of 50 lbs N/acre, and PGPR was applied at a rate of 535 gal/acre. A second PGPR application was applied 30 days later. Plots were harvested in mid-November, December, and January in order to determine forage yield and nutritive value.

What are the key conclusions?

Forage DM yield was greatest for Blend 20 + fertilizer, but it was not different from that of the synthetic fertilizer treatment. Concentration of crude protein was least for DH44 and Blend 20 treatments. Concentrations of neutral detergent fiber and acid detergent fiber were similar among all treatments, except for the negative control. In vitro true digestibility was not different among treatments. Yield and nutritive value parameters were greater in Year 2 than Year 1, most likely due to differing weather conditions for each year.

Table 1a. Average Forage Yield and Nutritive Value for Treatments

TreatmentYield (lbs/acre)CP (%DM)NDF (%DM)ADF (%DM)ADL (%DM)IVTD (%DM)
Control1,13510.570.334.38.047.7
Synthetic Fertilizer1,57710.971.835.68.347.6
Blend 201,4589.273.636.28.143.9
Blend 20 + Synthetic Fertilizer1,70810.373.136.38.346.2
DH441,1349.073.035.57.745.5
DH44 + Synthetic Fertilizer1,37810.073.335.57.347.0

 

Table 1b. Average Forage Yield and Nutritive Value For Harvest Dates

HarvestYield (lbs/acre)CP (%DM)NDF (%DM)ADF (%DM)ADL (%DM)IVTD (%DM)
November1,39210.372.034.46.751.8
December1,3189.374.536.77.844.7
January1,45810.371.135.69.342.4

 

Implications

Although not yet commercially available, PGPR are a viable option for biofertilization that supports forage DM yield from stockpiled Coastal bermudagrass similar to that from synthetic fertilizer without materially affecting nutritive value. Blend 20 + synthetic fertilizer had the greatest DM yield compared with other treatments and warrants further investigation into PGPR + synthetic fertilizer combinations with a reduced N rate. Studies should also investigate PGPR in a grazing system to determine the effects on animal performance and forage palatability, and work with other bermudagrass hybrids and perennial grasses.

 

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