Effects of Urban Sewage Sludge Products on the Growth and Nitrogen, Phosphorus and Potassium Contents of Sophora japonica and Ginkgo biloba

In order to clarify the land use effect of urban sewage sludge products, this experiment selected the newly planted young forests of Sophora japonica and Ginkgo biloba as the research objects, which were commonly used afforestation tree species in Beijing. There were 5 sludge application gradients of 15 , 30, 45, 60 kg/plant, and 75 kg/plant, no sludge application was control, and a random block arrangement method was used to compare the effect of sludge application. The growth indicators, leaf chlorophyll content and nitrogen (N), phosphorus (P) and potassium (K) content of the leaves were regularly measured. The results showed that the annual growth value of the diameter at breast height and the annual growth value of the projected area of the crown of S. japonica increased significantly after the sludge was applied, and reached the maximum when the sludge application rate was 45 kg/plant. The application rate increased with the increase of the application rate, reaching the highest level at the application rate of 75 kg/plant, the N and K content in the leaves of S. japonica did not change significantly after applying the sludge, and the P content was significantly reduced under the high sludge application rate. After adding different amounts of sludge, the annual increase in diameter at breast height and the chlorophyll content of G. biloba were higher than those of the control group, and reached the maximum when a single plant was fertilized at 75 kg, the N, P, and K contents in G. biloba's leaves did not change significantly among the treatments. It can be seen that the rational application of urban domestic sludge products can promote the growth of diameter at breast height, crown width and the synthesis of chlorophyll, and to a certain extend the green period of S. japonica and G. biloba, but the accumulation of N, P and K in leaves is not significant.