Effects of nickel fertilization on soybean growth in tropical soils

Although nickel (Ni) is recognized as plant nutrient since the turn of the 21st century, uncertainty remains about its optimum application rates and forms. This paper focuses on Ni application in soils, relating to its effect as a plant micronutrient. Specifically, the effect of Ni on the activity of urease in soybean plants is examined. The effects of applying four Ni rates in two different soil types were tested. A full factorial 2 x 4 blocked design experiment was established under controlled conditions. Ni rates (0, 0.25, 0.5 and 1.0 mg of Ni.kg(-1) of soil) were applied in two soils with contrasting clay contents. The addition of Ni increased the urease activity in soybean plants but was affected by soil textural differences. The highest urease activity was achieved by the application of 1.0 mg.kg(-1) Ni in the sandy soil. The absorption of Ni by the plants and its availability was found to be soil texture dependent. The rate of 0.25 mg.kg(-1) Ni increased the soybean dry matter production by 25% in the sandy soil. In conclusion, Ni was effective in promoting plant growth and biomass accumulation although depending on soil clay proportion. For soybean, there was no correlation between urease activity and biomass accumulation. The results of this study indicate a clear Ni effect in different type of soils in Sao Paulo state, serving as a solid initial doses indicator for soybean fertilization programs and future studies on nickel in Soybean.