Where do first symptoms of manganese (Mn) deficiency appear in soybeans?

The first symptoms of manganese deficiency in soybeans typically appear on the upper leaves of the plant. Manganese is a micronutrient essential for various physiological functions, including photosynthesis and enzyme activation. When there is a deficiency, the younger leaves are affected first because they are still actively growing and require higher amounts of nutrients. Symptoms usually manifest as interveinal chlorosis, where the tissue between the leaf veins turns yellow while the veins remain green. This pattern reflects the mobility of manganese within the plant, which tends to be limited, leading to deficiency symptoms starting at the upper, newer growth where nutrient demand is highest.

In contrast, deficiencies would not initially be observed on new leaves, lower leaves, or distributed evenly throughout the plant, as these scenarios are not consistent with the known behavior of manganese within soybean plants.