Effects of organic amendments on manganese toxicity in potatoes as measured by sand and soil culture studies

Abstract

Soil and sand culture studies were carried out in the greenhouse to investigate the influence of organic amendments on the rate of mineralization of manganese and iron in different soil types of Quebec. Potatoes (Early Rose variety which is resistant to manganese toxicity) grown in culture solution containing 100 ppm of manganese produced flowers two weeks in advance of those grown in 0.5 ppm. The yields of tubers were increased two-fold by the combined treatment of humic compounds and high concentration of manganese. Due to microbial competition, the introduction of carbohydrates, alcohols, etc, decreased the yields of tubers. The yields recorded with the Keswick variety (susceptible to manganese toxicity) and different organic amendments on St. Andre soil (low pH and organic matter and high manganese) were in the following order: humate > compost > compost and peat > peat > control. A somewhat different order was recorded on De l'Anse (low pH and manganese and high organic matter): compost > humate > peat > compost and peat > control. The presence of sodium humate in the nutrient solution reduced the manganese content of potato leaves but increased that of stems. The addition of carbohydrates slightly depressed the content of manganese in potato leaves. Glycerine favored the accumulation of high amounts of manganese in potato stems. The Ca/Mn ratio should be around 360 in the leaves and 400 in the stems of normal plants. Plants showed manganese toxicity symptoms when the Ca/Mn ratio fell below 70, or when the Mn/Fe ratio was about 0.2 in the leaves and 0.6 in the stems of normal plants. The sum of Mn/Fe and Ca/Mn ratios remained the same in potato stems regardless of the organic amendments and the soil types. As the Mn/Fe ratio increased, the manganese toxicity symptoms became more severe and the Ca/Mn ratio narrower. The addition of organic amendments generally decreased the Mn/Fe ratio as well as toxicity symptoms. Various regression equations are formulated to establish the correlations between plant and soil data. The most interesting findings are as follows: 1 Organic matter, total nitrogen and C/N ratio in the soil were found to be negatively correlated with exchangeable manganese. 2 A positive correlation was found between the Mn/Fe ratio of soil and that of plants, and also between the manganese content of potatoes and the manganese toxicity indexes. 3 Manganese toxicity indexes were positively correlated with Mn/Fe ratios and negatively with the Ca/Mn ratios in plants. 4 There was a definite tendency for the yields of the Keswick variety (susceptible to manganese toxicity) to decrease as the manganese content of the soil increased. However, the yields of Early Rose variety (tolerant to manganese toxicity) were higher with 100 ppm of manganese than with 0.5 ppm in the culture solutions. Therefore, Early Rose appears to be a good variety for acid soils containing high levels of exchangeable manganese.