Effects of Different Copper Concentration on Growth and Nodulation of Green Gram (Vigna radiata L.)

An investigation was conducted to study the influence of copper (Cu) on the growth of shoot, root, and nodulation of green gram (Vigna radiata L.). A field pot experiment was designed in a Completely Randomized Design with six treatments and four replicates at Palachcholai, Faculty of Agriculture, Eastern University, Sri Lanka from September to November 2023. Six levels of copper concentration (control, 50, 100, 150, 200, 250 mg copper/kg soil) was applied to the soil in the form of copper sulphate (CuSO4.5H2O) in which the green gram plants were grown. Exposure to copper at concentrations ranging from 100-250 mg copper/kg soil reduced total chlorophyll content, shortened root length, decreased plant biomass, and produced fewer leaves, and a lower number of nodules. Conversely, exposure to copper at 50 mg copper/kg soil increased the fresh shoot biomass, soil microbial respiration and soil pH. Additionally, the positive effects of copper were observed on tap root length, leaf area, and root volume. The copper at 50 mg copper/kg soil concentration enhanced the shoot biomass, the number of nodules and soil microbial respiration by 25% ,14%, and 22% respectively compared to the control while the copper concentrations ranging from 100 mg copper/kg soil to 250 mg copper/kg soil significantly inhibited the overall growth and nodule formation of green gram. The results clearly indicate that Cu is an important micro-nutrient, only it should be added in trace amount to induce plant growth and other physiological processes. However, copper at higher concentrations can act as a heavy metal and cause phyto-toxicity on plants.