Research on the Symptoms and the Critical Value of Nickel Toxicity of Maize

Nickel (Ni) plays an important role in the growth of plants, but it is also a kind of heavy metal which can easily enrich in soil and exert toxic effect on plants. To evaluate the Ni stress on the maize growth, a pot experiment was conducted by black soils sampled from the field in the middle of Jilin province. And Ni was equilibrated in the soils to graded levels from 0 to 800mg kg^-1 soil. The main results were as follows: The concentration of Ni in maize had a negative correlation with the plant dry weight. The symptom of Ni toxicity was as follows: maize root was short and thin, leaf curled with barred vain and fade blade tip, and it was brown and rotten at the connection of the petiole and roots. In this study, the fitting equation of Y = 0.3071 + 0.0012X + -0.0001CX² described the extremely significant relationship between the amount of effective Ni in soil (when it was below 30mg/kg) and the dry matter weight of maize. The amount of effective Ni in soil (DTPA extracted) which could provide maize with the best growing state was 6.00mg/kg, the toxicity critical value was 11.48mg/kg, the range of Ni luxury absorption was 6.00-11.48mg/kg. 11.48-32.77mg/kg caused maize mild toxicity; 32.77-67.38mg/kg caused moderate toxicity and over 67.38mg/kg leaded to serious toxicity. When maize took place mild toxicity, the content of Ni in maize was 33.40-66.40mg/kg. Moderate toxicity was 66.40-111.40mg/kg. Serious toxicity was over 111.40mg/kg. The equations of Y = -0.0013X + 0.3126, Y = -0.0010X + 0.3364 could be used to express the relationship between effective Ni in soil, Ni in maize and the dry matter weight of maize when toxicity happened. The highest Ni fixed rate was 23.98% when the soil received 25mg/kg Ni.