High root zone pH reduces nutrient availability and high alkalinity water is strongly buffered around an alkaline pH. Soilless media can be altered to improve nutrient availability. This study was conducted to optimize the composition of soilless media for use with high alkalinity water. Mixes of peat and/or perlite or vermiculite in 50/50 and 33/33/33 volumetric ratios were tested. In some studies, mixes were also amended with up to 2.4 g/L of dolomite limestone to neutralize the initial acidity of the peat. Mixes containing vermiculite settled more, had higher water holding capacity (WHC) and percent plant available water (%PAW), and similar air filled porosity (AFP), compared to mixes containing perlite. Dry mass was measured in corn, peas, tomatoes, and soybeans, and chlorophyll content was measured in corn. The addition of dolomite increased pH and decreased dry mass in corn, soybean, and tomato, but peas were unaffected. Chlorophyll content in corn also declined with increased amounts of dolomite. After a week of daily irrigation, pH 7.8 nutrient solution neutralized the acidity of the peat, without the need for addition of dolomite. Mixes containing vermiculite improved growth and chlorophyll concentration compared to mixes with perlite. The higher cation exchange capacity (CEC) of vermiculite-containing mixes may have improved nutrient availability. A soilless mix of only peat and vermiculite, in approximately equal volumes, resulted in the greatest growth and chlorophyll content when watered with high alkalinity nutrient solution.
Tramp, Cody Alexander; Chard, Julie K.; and Bugbee, Bruce, "Optimization of Soilless Media for Alkaline Irrigation Water" (2009). Hydroponics/Soilless Media. Paper 2.