Turfgrass Establishment Using a Liquid Source of Phosphorus

Grady L. Miller

This study was conducted to assess establishment, root growth, turfgrass shoot quality and plant stress tolerance of cool-season grasses following application of a liquid phosphorus (P) fertilizer (31% P2O5). Quicker establishment is beneficial to the turf manager trying to minimize disruption in course conditions. Due to the significant fluctuations in precipitation and fall and winter temperatures, heat and drought stress tolerance is important in the establishment and maintenance of consistent, healthy turf. For this study plant drought stress tolerance was thoroughly evaluated to determine influence of fertilizer treatments on stress responses over a wide range of water deficits.

To evaluate the liquid product, greenhouse studies were initiated at the Turfgrass Envirotron in Gainesville, Florida. The study was conducted using perennial ryegrass, creeping bentgrass, and rough bluegrass (Poa trivialis) established from seed. Treatments consisted of application of 32 oz per 1000 square feet the P fertilizer and humic acid solution following germination with a sequential at the same rate. Control treatment consisted of an application 18-9-18 with a sequential using the same timing as the other treatment. Nitrogen rates were approximately 2 pounds per 1000 square feet for both treatments.

Results from these evaluations indicate that cool-season turfgrasses may be improved with early fertilization with the liquid P solution compared to a more traditional fertilizer such as 18-9-18 applied to the soil surface. Previous experience has shown that P fertilizer in close proximity to germination seeds had a beneficial effect in the early stages of seedling establishment. Improvement in percent cover (density) was most improved with bentgrass compared to perennial ryegrass or Poa trivialis. No improvement was detected in establishment of Poa trivialis. More noticeable in these evaluations were the differences in color and tissue dry weight (yield) when comparing plants fertilized with liquid P solution to those fertilized with 18-9-18 fertilizer. Turf treated with liquid P had a 14% higher color (quality) ratings at 7 weeks and 31% higher rating at 14 weeks despite using slightly lower N rates. Liquid P fertilized plants also had lower dry matter production┬ż 48% lower at 7 weeks and 9% lower at 14 weeks. This means that quality can be maintained or improved with slightly lower N rates and less biomass produced resulting in reduced N waste and less frequent need for mowing.

Drought stress damage at 14 weeks after seeding indicated less overall injury in plants fertilized with liquid P. This was not expected due to the lower tissue K concentration of liquid P treated plants. A lower tissue K concentration often results in increased drought stress. Plants with higher tissue K concentrations were able to maintain turgor longer than those with lower tissue concentrations. In general, P tissue concentrations were similar in plants regardless of treatment. This indicates that a more balanced P and K fertilizer would provide a better combination of drought tolerance and drought avoidance. Fertilizer treatments did not have a consistent effect on root length density evaluations with respect to grass species.

To evaluate physiological water stress, stomatal closure was carefully modeled. A plant with the ability to hold its stomata open longer should be more efficient at avoiding severe drought stress. In general stomatal closure data indicated that plants fertilized with 18-9-18 may be more drought resistant than those fertilized with liquid P. This is most likely due to the better P/K ratio applied to the turf. There are similarities in wilt data between the two treatments, but wilt data and transpiration decline data do not always agree since transpiration decline data does not evaluate plant efficiency during periods when available water is high.

In summary, it appears that liquid P application may improve seedling growth of cool season grasses. These data indicate that for early-season drought tolerance the P/K ratio is important. Additional studies are currently underway to evaluate P placement of traditional granular P fertilizers prior to establishment. In these studies, subsurface application of various P sources are being compared to broadcast applications to determine placement influences of similar fertilizer sources.