A study of nutrient availability including nitrogen transformation on a chromium-contaminated site
Study of a former industrial land, which was contaminated with chromium, was the major research topic of this study. A survey study of the land was made to evaluate the pH, electrical conductivity ;and percentage of organic matter of soils, available nutrients, total nutrients, available and total chromium and total other heavy metals in the soils. The survey also includes the total nutrients, total chromium and some other heavy metals in the plants and root mat. Soils throughout the site had high total chromium concentrations, high pHs and low plant available nitrogen and low vegetation yields. However, chromium was not detected in the plants. The effects of fertilizer additions were evaluated in two pot experiment studies of these soils using ryegrass as a test crop. The first pot experiment was carried out to look at the response of the soil samples to different combinations of N, P and K fertilizers to determine which fertilizer is limiting the plant growth. The response was measured by dry matter production. Nitrogen was shown to be the limiting factor for growth of the grass in these soils. Alleviating the limiting factor resulted in a yield increase. Since the trend of this increase can not be fully applied to all types of soils and spoils due to differences in nature of the material a second pot experiment was carried out to look at the response of the vegetation to addition of the different rates of nitrogen fertilizer. The results showed that the application of 100 /50 /50 of N/P/K kg/ha fertilizer could obtain the maximum yield for the site except for a soil sample from the base of the east side (sample 4) which did not respond to more than 50 of N kg/ha. Since the changes in the yields from these experiments were not affected by soil extractable chromium in the two experiments the possibility of the direct effect of chromium on plant growth was discounted. The occurrence of the nitrogen turnover and possible toxicity effects of chromium on these processes was assessed during a number of incubation studies. First of all the nitrogen supply power of the soils was evaluated using an incubation test for the nitrogen mineralization rate of the soils from this site. This experiment was done under aerobic conditions. An attempt was also made to look at possible volatization of ammonia due to the pH of these soils.