Abstract
Abstract Soils within the Te Kauwhata Irrigation Scheme were sampled to determine the extent of soil acidity and aluminium (A1) and manganese (Mn) toxicity. Most soils belonged to yellow-brown earth or brown granular loam soil groups. Forty-one soil profiles were sampled at 20 cm intervals to 80 cm. Samples were analysed for pH, and A1 and Mn extracted by 1M KC1 and 0.02M CaCl2. Mn was also extracted using 1M NH4OAc, and 0.2% hydroquinone in 1M NH4OAc (easily reducible Mn). The results show that the soils have strongly acid subsoils. Toxic levels of extracted Al were common in most subsoils and some topsoils. The toxic levels of Mn are likely in many topsoils and soil horizons with Mn concretions. Incorporation of lime into the subsoil to increase soil pH and reduce Al toxicity and potential Mn toxicity may be necessary for some crops.
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