Residual Effects of Soil Profile Modification on Water Infiltration, Bulk Density, and Wheat Yield
Fine-textured soils of the Southern High Plains, of which Pullman (fine, mixed, thermic Torrertic Paleustolls) is the dominant series,/ have inherently low water infiltration rates. Pullman soils have a moderately permeable surface horizon overlying and slowly-permeable Bt horizon, which limits deep water penetration, thus hampering water conservation efforts and reducing water-use efficiencies Ibr crop production. In 1964, Pullman clay loam was profile-modified (PM) to 0.9- and 1.5-m depths. The objective of the 1990–1991 study was to compare soil bulk density (Db), water infiltration, plant available water (PAW) content, and winter wheat (Triticum aestivum L.) yield on PM and unmodified soil. Soil Db values were similar near the surface, but decreased with increasing depth of PM at depths greater than 0.3 m, except for the deepest increment (1.50–1.80 m), were Db values were 1.56 Mg m−3 for all treatments. Time required for 240 mm of applied water to infiltrate was 28.6 h on unmodified soil, and 8.,I h with 0.9- m and 6.3 h with 1.5-m PM. The PAW contents in October and March were significantly greater for the mean and at some depths in PM plots than in unmodified plots. The differences were attributed to greater evaporative losses from the unmodified soil. After wheat harvest in June, mean PAW contents were not significantly different, but water extraction occurred to greater depths on modified than on unmodified soil Wheat grain yields tended to increase with PM (2.81 Mg ha−1 on unmodified and 3.07 mg ha−1 with 0.9-m and 3.37 Mg ha−1 with 1.5-m deep PM). This study showed that PM imposed on the Pullman soil in 1964 is still highly effective for increasing water infiltration. Although wheat yields were not significantly increased, grain sorghum [Sorghum bicolor (L.) Moench] and alfalfa (Medicago sativa L.) responded favorably to PM in previous studies. Considering the long-term benefits, PM should be cost-effective if the cost is prorated over the lifetime of the benefits and if crops that respond favorably to PM are grown.
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