No abstract

The effects of increasing rates of lime and ammonium sulphate on French beans were studied on an acid red basaltic soil (pH 4.5-4.8), rich in manganese, on the north coast of New South Wales. Addition of lime resulted in an increased plant yield, a higher soil pH, and a marked reduction in available soil manganese and plant manganese. Applications of 2 or more tons lime per acre corrected manganese toxicity. Ammonium sulphate applications acidified the soil, increased manganese levels in both soil and plant tissue, and increased the frequency of manganese toxicity symptoms at less than 2 tons lime per acre. At pH 4.7-4.8, exchangeable and water-soluble manganese levels were sensitive to slight changes in reaction. Changes in pH between 5.2 and 6.0 caused only slight alterations in manganese levels in soil and plants. Two tons lime per acre reduced the level of manganese in the soil to about half that in the untreated soil, whereas 3 tons lime was necessary to halve the level of manganese in plants. Close linear relationships were found between rates of lime application and pH, between exchangeable and water-soluble manganese, and between both water-soluble and exchangeable soil manganese and plant manganese. Hyperbolic relationships were found between lime and manganese in soil and plants and also between pH and manganese fractions. Toxic levels of manganese in soil and leaves varied seasonally and yearly, and symptoms usually appeared when the manganese content of the first mature leaves was greater than 600 p.p.m. in the winter crop. Symptoms were more closely related to high levels of plant manganese than to soil manganese. The results of this trial indicate that soil and plant analyses are useful for predicting manganese toxicity in acid soils.