Interaction of Added Gypsum in Alkaline Soils with Uptake of Iron, Molybdenum, Manganese, and Zinc by Sorghum

Experiments with tomato plants ( Lycopersicon esculentum Mill.) in nutrient cultures indicated previously that Mo accentuated Fe deficiency at low levels of available Fe. This interaction may be important in alkaline soils where pH favors a low Fe availability and high Mo availability from native soil levels. When such interactions exist, this information will help interpret the relationship between response predicted by a soil test for available Fe and actual response. This interaction was confirmed in six soils where sorghum plants ( Sorghum bicolor L. Moench. var. RS‐610) increased in Fe uptake and/or Fe concentration as Mo was decreased by adding CaSO 4 at 30 ppm of S. The CaSO 4 decreased Mo from 2.33 to 1.26 ppm and increased Fe from 56 to 65 ppm in sorghum. An increase in Mo above native levels decreased the Fe concentration from 57 to 51 ppm and Fe uptake frmo 369 to 306 µg/pot in sorghum. Also, CaSO 4 consistently increased Mn concentrations from 70 to 90 ppm, and Zn from 56 to 80 ppm in sorghum. Knowledge of these interactions will help to interpret plant responses to natural levels of these micronutrient in soils and disturbed lands or to induced levels from sewage, other wastes, and fertilizers.