Residual Effects of Manganese Sulfate on Growth and on Manganese Uptake in Soybean

A significant portion of manganese (Mn) chemical fertilizers applied to calcareous soils is not absorbed by the first crop and may, therefore, affect the growth as well as chemical composition of the subsequent crops, this being called the residual effect of Mn, Soil tests may be employed to predict such effects. The present experiment was conducted to study the residual effects of manganese sulfate on the subsequent crop of soybean (Glycine max L.). Twenty soils of northern Iran (5-39% calcium carbonate equivalent), previously treated with two levels of Mn (0 and 30 mg Mn kg-1 as MnSO4) and under a single crop of soybean, was used in greenhouse to grow a second subsequent crop of soybean with no additional Mn fertilizer but with a uniform application of nitrogen, phosphorous and potassium. Soils were sampled before the subsequent crop and extracted through Mn extractant DTPA. Dry weight of plant tops as well as Mn concentration and uptake after eight weeks under the greenhouse conditions were used as the plant responses to residual Mn in soil. Statistical analyses showed that manganese sulphate application significantly increased the dry matter from 16.56 to 20.29 g/pot. Manganese application also increased leaves' Mn content as well as Mn uptake from 115 to 120.20 mg/kg vs. from 1.98 to 2.45 mg/ pot., respectively. The overall effects of previously applied Mn on dry matter were not significant, whereas seed yield, as well as Mn uptake were significantly increased. In all the soils, grain yield increased by 7.67% in comparison with control. The residual effects of Mn on dry matter and seed yield of the third crop on these soils were non-significant, but Mn uptake increased by 8.19% in comparison with control. In the fourth crop, the residual effects of Mn on dry matter , seed yield , Mn concentration and Mn uptake were found to be of no significance .