Changes In Fractions Of Cobalt In Calcareous Soils And The Influence Of Cobalt On The Growth And Yield Of Tomato

Calcareous soils are widely distributed in chief agricultural areas of China. The state and transform of nutrient elements are important to plant nutrition and environmental quality in calcareous soils. Cobalt, as one of the beneficial elements, contributes to the development of plants. Pot and germination experiments were conducted to study the fractionation of cobalt element in calcareous soils and the effect of cobalt fertilizer on the growth and yield of tomato. The main results were summarized as follows: Existent state variations of cobalt in calcareous soils were studied in selective sequential extraction method. Results showed cobalt added into soils existed mainly in state of residual and iron/manganese oxide bound, whose percentage ranged from 83.5 percent to 95.9 percent. The contents of various fractionation decreased in order of residual> readily reducible Mn bound>carbonate bound>organics bound>exchangeable. Contents of each forms of cobalt are well related to the total cobalt contents. The cobalt contents of different states generally increased with its increased addition. But carbonate bound cobalt contents had little change at lower concentration of cobalt. Various forms had different changes in the soil: the content of exchangeable decreased obviously, while that of organics bound increased a little, and that of the other three states hardly altered. The test was applied in an incubator at 25℃temperature. The results showed that 10mg/L CoSO₄ could slightly promote the growth of hypocotyls and increased the fresh weights of hypocotyls and cotyledons. But in contrast to the control, the difference was not significant. The solutions whose concentrations were higher than 20mg/L all manifested inhibited effects on the growth of tomato seeds. It was observed that the inhibition of CoSO₄ strengthened with its concentration. Results related to the effect of cobalt on the growth and yield of tomato were shown that Co significantly increased the contents of chlorophyll and the numbers of flowering and...