SOIL pH DECREASE IN THE HERBICIDE STRIP OF GRASSED-DOWN ORCHARDS

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Abstract
In an orchard in which apple trees were grown for 10 years in 160-centimeter-wide, weed-free, unmulched herbicided strips separated by grassed-down mown alleyways, I found that the pH of the surface soil (0 to 10 cm), whether measured in distilled water or 1 N KCl, was significantly lower in the herbicide strip than in the grassed alley. The difference in soil pH between the strip and alley areas was slightly reduced when the pH was measured in 1 N KCl rather than water. Levels of soluble salts in saturation paste extracts of the surface soil were significantly higher from the herbicide strip than the grassed alley. The decrease in pH in the surface soil of the herbicide strip was also accompanied by a large decrease in the percentage base saturation and a consequent significant increase in exchange acidity. In the 0− to 5-cm depth increment, the exchangeable Ca percentages for the grassed alley and the herbicide strip were 71 and 40, respectively; the corresponding values for exchangeable Mg percentage were 14 and 9. The difference was attributed to leaching of exchangeable Ca2+ and Mg2+ ions out of the surface soil of the herbicide strip, while, in the grassed alley, base saturation was maintained by the cycling of these cations through ion uptake by the growing sward and subsequent returns upon the mowing of the sward. In an orchard in which apple trees were grown for 10 years in 160-centimeter-wide, weed-free, unmulched herbicided strips separated by grassed-down mown alleyways, I found that the pH of the surface soil (0 to 10 cm), whether measured in distilled water or 1 N KCl, was significantly lower in the herbicide strip than in the grassed alley. The difference in soil pH between the strip and alley areas was slightly reduced when the pH was measured in 1 N KCl rather than water. Levels of soluble salts in saturation paste extracts of the surface soil were significantly higher from the herbicide strip than the grassed alley. The decrease in pH in the surface soil of the herbicide strip was also accompanied by a large decrease in the percentage base saturation and a consequent significant increase in exchange acidity. In the 0− to 5-cm depth increment, the exchangeable Ca percentages for the grassed alley and the herbicide strip were 71 and 40, respectively; the corresponding values for exchangeable Mg percentage were 14 and 9. The difference was attributed to leaching of exchangeable Ca2+ and Mg2+ ions out of the surface soil of the herbicide strip, while, in the grassed alley, base saturation was maintained by the cycling of these cations through ion uptake by the growing sward and subsequent returns upon the mowing of the sward. © Williams & Wilkins 1981. All Rights Reserved.

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