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Fig. 3-5. Growth response of tall fescue to pH: Y=106.97exp{-0.5[(x6.68)/1.54]2};R2=0.99; optimum is 6.7.

 

Tall fescue grows on soils that vary from strongly acidic (pH 4.5) to alkaline (pH 9.0) (USDA-NRCS, 2006b). Best growth occurs, however, when soil pH is maintained between 5.5 and 7.5 (Belesky and Fedders, 1995) (see Chapter 4).

The pH response function shown in Figures 3-5a and b are based on zero growth at pH 3.0 and pH 11.0 and optimum relative growth (100%) from pH 6.0 to 7.0 (Wilkinson and Mays, 1979). Using this function, boundaries were set at 5.4 to 8.0 for the well-suited areas (>75% growth), 4.8 to 5.4 and 8.0 to 8.6 for the moderately suited areas (50-75% growth), 4.1 to 4.8 and 8.6 to 9.3 for the marginally suited areas (25-50% growth), and <4.1 and >9.3 for the unsuited areas (<25% growth) (Table 3-1).

Different measuring methods were used for the United States and China datasets, and both had to be equalized and assigned an appropriate discrete value for each grid cell. For polygons that were assigned a range of pH values, the lowest acid and the highest alkaline values were used (e.g., for the 4.5-5.5 category a pH of 4.5 was used).

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Fig. 3-5a. Tall fescue suitability map for conterminous US based only on soil pH tolerances where marginally suited values are 4.06-4.78 and 8.58-9.30, moderately suited are 4.78-5.38 and 7.98-8.58 and well suited values are 5.38-7.98.

      Fig. 3-5b. Tall fescue suitability map for PRC based only on soil pH tolerances where marginally suited values are 4.06-4.78 and 8.58-9.30, moderately suited are 4.78-5.38 and 7.98-8.58 and well suited values are 5.38-7.98.

 

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