CARROT RESPONSE TO SOIL TEMPERATURE AND COPPER, MANGANESE, ZINC AND MAGNESIUM

Carrots grown under greenhouse conditions in a medium-decomposed, acid organic soil showed a significant yield and carrot length response to soil temperature and copper fertilization. Root lengths at 16 C were significantly greater than lengths at 12 and 20 C, which in turn were significantly greater than lengths at 8 C. Root and leaf yields at 8 C were significantly inferior to yields at 12, 16 and 20 C. The total native copper content of 10 ppm in soil, and leaf concentrations of 12 ppm in the tissue, were insufficient for normal carrot development under these experimental conditions. Application of copper at the rate of 25 ppm in soil significantly increased yields. Leaf concentrations of 145, 125 and 4440 ppm of Mn, Zn and Mg, respectively, in tissue, and soil concentrations of 60, 80 and 1300 ppm for Mn, Zn and Mg, respectively, were sufficient for normal carrot plant development. Increasing soil temperature significantly increased Cu and Mn concentrations in the leaves, and this occurred irrespective of whether the source of the respective nutrient was native or applied. In the case of Zn, leaf concentrations increased with increasing temperatures only when zinc was applied to the soil. With soil temperature above 12 C, magnesium concentrations in the leaves were significantly decreased and this was so for native or applied magnesium in the soil.