EFFECTS OF SOIL TEMPERATURE ON MANGANESE AVAILABILITY TO PLANTS GROWN ON AN ORGANIC SOIL

The effect of soil temperature on the availability of manganese to wheat (Triticum aestivum ’Neepawa’) and barley (Hordeum vulgare ’Conquest’) from an organic soil was studied in a controlled environment growth chamber. Wheat and barley plants were grown in cylindrical pots placed in temperature-controlled water baths with soil (root) temperatures maintained at 10, 15, 20 and 25 °C. Air temperatures were maintained at 20/13 °C for the day/night intervals, respectively. Aerial plant parts were harvested at the three- to four-leaf stage and at the boot stage. Dry matter yields of wheat and barley tended to be greatest at soil temperatures of 20 or 25 °C when harvested at the three- to four-leaf stage. In contrast, yields obtained at the boot stage were usually greatest at a soil temperature of 15 °C. Concentrations of manganese in shoots of wheat and barley at both stages of growth increased significantly when soil temperatures were increased from 10 to 25 °C.In a second study, MnSO4∙H2O was supplied to barley plants grown at the four different soil temperatures. The MnSO4 increased Mn concentrations in shoots harvested at the three- to four-leaf stage at all soil temperatures. In contrast, MnSO4 was ineffective in increasing Mn concentration in shoots harvested at the boot stage. In addition to the plant growth studies, soil samples were extracted with 0.005 M DTPA or 1.0 M ammonium acetate (NH4OAc) at the different temperatures. Extractable Mn increased with increasing soil temperature and amounts extracted closely reflected the increases in amounts of Mn utilized by the plants in the growth chamber studies. Key words: Soil temperature, manganese, organic soil, availability