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Abstract
Response of plants to soil acidity is difficult to study under field conditions due to the complexity of soil systems. To circumvent this difficulty, it was thought that growth pouches, which have been used for nodulation and plant breeding studies, would be a practical method for studying the effects of acidity on alfalfa (Medicago sativa L.) growth, since single factors could be studied independently. Preliminary observations with commercial pouches showed that when pH 4.5 nutrient solutions remained in the pouches 5 h the pH increased to 6.5. Chemical analysis of the control solution (lacking Ca and Al) after remaining in the pouches 5 h contained Ca, Al and other ion contaminants. This indicated that the conventional pouch method is not reliable for studies with Ca, Al and pH. Because of the potential for using the pouch method for nutrient studies, modifications of commercial pouches were investigated. Acid washing of the original brown paper wick in the pouch was not adequate for removing ion impurities. The problem was corrected by replacing the brown paper with white filter paper. Chemical analysis of solutions from these modified pouches showed no impurities and pH levels remained constant, making this an adequate method for studies with Ca, Al and pH.