Soil water supply is another major determinant of tall fescue growth and survival. In the PRISM Species Suitability Model, mean annual precipitation values of 625, 450, and 300 mm were used to set limits to the well-suited, moderately suited, and marginally suited zones (Figures 3-4a and b). The model also calculates a water balance function for estimating mean annual relative yield based on soil water balance for each grid location. The functions composited in this calculation include monthly calculations of total available water, readily available water, root-zone water depletion, evapotranspiration, and relative yield production, using precipitation, air temperature, and soil information for each grid location. Water balance yield boundaries were set at 80, 70, and 60% for well-suited, moderately suited, and marginally suited zones (Table 3-1).

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Table 3-1. Limit input values in the PRISM Species Suitability Model for setting tall fescue suitability categories. Grid locations for which values fall outside the threshold extremes are mapped as unsuited for tall fescue.

 

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Fig. 3-4a. Tall fescue suitability map for the conterminous US based on mean annual precipitation tolerance values of 625, 450, and 300 mm were used to set limits to the well-suited, moderately suited, and marginally suited zones.

   Fig. 3-4b. Tall fescue suitability map for the PRC based on mean annual precipitation tolerance values of 625, 450, and 300 mm were used to set limits to the well-suited, moderately suited, and marginally suited zones.

 

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