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HOT TOPICS IN TURF

Turf Hot Topics: Index of Nitrate Leaching Potential / Temperature Stress Tolerance

PRS™-probes, and ion-exchange resin in general (Kopp and Guillard, 2002), are new to turf grass research (Woods et al., 2006. We believe PRS™-probes are relevant to many aspects of turf grass research and the following are examples of how the PRS™-probes can be applied to current turf research.

PRS™-probes as an index of nitrate leaching potential
Numerous studies have been conducted to determine best management practices (BMP), in order to define the environmental conditions and turf management practices that have the potential to decrease nitrate leaching. PRS™-probes are useful tools for these types of studies because they can measure the soil supply rate of bioavailable nutrients. In contrast, a traditional soil test, based on a chemical extraction, provides a static measure of nutrient availability, which may not accurately reflect the nitrate leaching potential because it does not account for the dynamic components critical to supporting nutrient leaching.

Although PRS™-probes are a good fit for research pertaining to nitrate leaching in turf systems, they have only been used in this manner for agronomic research. For example, Whitley and Davenport (2003) used the PRS™-probes to develop a nitrate availability index which they related to the nitrate leaching potential, i.e. the lower the nitrate availability index the less nitrate available for leaching.

Related Literature:

Whitley, K.M. and J. R. Davenport. 2003. Nitrate leaching potential under variable and uniform nitrogen fertilizer management in irrigated potato systems. HortTechnology 13:605-609.

Temperature Stress Tolerance
In lawns and golf courses in temperate regions, the cool-season grass, Kentucky bluegrass (Poa pratensis L.), is commonly planted. However, in some temperate regions, summer temperatures can reach the upper limit of the ideal range for Kentucky bluegrass (15 - 23^º C) resulting in poor turf grass quality. This natural variability in growing season conditions has been the impetus for initiating turf grass breeding research programs for developing heat tolerance in cool-season grasses.

Research by Jiang and Huang (2001a,b) demonstrated that drought preconditioning of grasses, by exposing grass to periods of drought stress prior to hot summer months, can improve the heat tolerance of Kentucky bluegrass and tall fescue (Festuca arundinacea L.). Preconditioned cool-season grasses are more heat tolerant because of increased K⁺ and Ca²⁺ in the cytoplasm of plant cells. The high concentration of these ions inside plant cells help maintain turgor and relative water content in leaves. During heat stress, the K⁺ in grass cells accounted for 59 – 65% of the ions in solution (Jiang and Huang, 2001b). Additionally, the authors found that foliar applied Ca²⁺ increased the heat tolerance of Kentucky bluegrass. These results may warrant the investigation of the interactions of soil K⁺ and Ca²⁺ and the resulting physiological response of grasses to the relative supply rates of these two nutrients in soil.

PRS™-probes are an ideal tool for supporting research on the linkages between K⁺ and Ca²⁺ bioavailability in soil and the heat tolerance of cool-season turf grasses for several reasons:

The amount of K⁺ “available” for plant uptake depends on the quantity, but more importantly, on the activity (i.e., relative concentration) of K⁺ in the soil. Specifically, the K⁺ activity is strongly influenced by the activities of other cations in soil, such as Ca²⁺. Likewise, the PRS™-probes are sensitive to the differences in relative concentration of soil solution K⁺ and Ca²⁺, because they adsorb nutrient ions in proportion to their activity. Consequently, this selective adsorption mechanism of the PRS™-probe ensures data that reflects the bioavailability of the competing cations, thereby yielding a biologically meaningful measurement. Conversely, chemically-extracted soil tests extract total amounts of nutrient ions in soil regardless of their activity, which for K⁺, depending on the soil type, may greatly overestimate the quantity of K⁺ available for plant uptake.

PRS™-probes simultaneously adsorb all nutrient ions when placed in the soil. Concurrently measuring the relative supply rate of all essential nutrients provides you with the capability of assessing the entire 'nutrient picture' at once.

PRS™-probes measure the supply rate of nutrients as influenced by soil temperature and water content. Knowing how the physical soil environment influences the rate of Ca²⁺ and K⁺ supply may be important in determining the response of turf to heat stress.

PRS™-probes are inserted with minimal disturbance which should not interrupt play or turf maintenance, and are esthetically pleasing compared with collecting soil cores.

Related Literature:

Jiang, Y. and B. Huang. 2001a. Effects of calcium on antioxidant activities and water relations associated with heat tolerance in two cool-season grasses. J. of Exp. Bot. 52:341-349.

Jiang, Y. and B. Huang. 2001b. Osmotic adjustment and root growth associated with drought preconditioning-enhanced heat tolerance in Kentucky Bluegrass. Crop Sci 41:1168-1173.