Abstract:

Objective: Explore the effect of glyphosate herbicide application on soil physicochemical properties of Eucalyptus plantations and provide reference for the rational application of glyphosate. Method: Six experimental plotsin size of 20 m×20 m were set up in a 4a Eucalyptus plantations in the state-owned forest farm of Zhangzhou City, Fujian Province, 3 plots were applied with the glyphosate, and the other 3 plots were not. The glyphosate was applied to remove shrubs and weeds in May and September of 2015, 2016. The composition was41% glyphosate isopropylamine saline and water, formulated at a mass of 1:50, the dosage was 1 500 kg·hm^-2 every time. For the control plots, the glyphosate was not applied and manual weeding was used instead, other tending was kept the same as those for the treatment plots. Soil samples were collected in May 2017 to determine the glyphosate residues and soil physicochemical properties. Result: After application of glyphosate, the soil density of the layers of 0-10, 10-20, 20-40 cm was 1.23, 1.27, 1.34 g·cm^-3, which increased by 0.02, 0.02, 0.01 g·cm^-3 compared to the control. The total soil porosity was 49.79%, 48.23%, and 46.64%, which were0.49%, 0.32%, and 0.47% lower than the control plots, respectively. But the differences were not significant. Glyphosate residues were mainly concentrated in the surface layer of soil, and the residue of 0-2 cm soil layer was 4.43 mg·kg^-1 with significant difference (P < 0.05). The pH values in 0-2, 2-5, and 5-20cm soil layers were 5.26, 4.63, and 4.57, respectively, which increased by 0.90, 0.24, and 0.07 compared to the control plots, but the soil layers from 20-40 cm decreased from 4.53 to 4.34, a decrease of 0.19, and the difference between the two treatments was only significant in 0-2cm soil layer (P < 0.05). The electrical conductivity of each soil layer decreased, and the soil layers at 0-2, 2-5, 5-20, and 20-40 cm were 61.83, 42.77, 34.20, and 38.17 us·cm^-1, respectively, which were lower than the control plots by 4.27, 8.26, 9.20, 1.00 us.cm^-1, the differences were not significant.The soil electrical conductivity of the two treatments had different trends with the depth of the soil layer. The control plots showed a gradual decrease, while the treatment plots decreased first and followed by am increase. The content of organic matter in 0-2, 2-5, 5-20, and 20-40 cm soil layers were 40.38, 36.62, 28.08, and 18.99 g·kg^-1, respectively, which were 16.70, 9.90, 0.90, and 3.89 g·kg^-1 lower than those of the control plots, and only 0-2 cm soil layers was significantly different (P < 0.05). The available P content of each soil layer was increased to varying degrees. The soil layers of 0-2, 2-5, 5-20, and 20-40 cm were 5.29, 2.89, 1.51, and 0.93 mg·kg^-1, respectively, compared with the control plots, it was increased by 2.39, 0.98, 0.26, and 0.22 mg·kg^-1, and only the soil layer of 0-2 cm had significant difference (P < 0.05). The contents of total N, hydrolyzed N and total P decreased, but the contents of total K and available K increased, and the differences were not significant. Conclusion: After 2 years of application of glyphosate in the Eucalyptus plantations, the physical properties of the soil deteriorated but the impact has not yet reached a significant level. The glyphosate residual concentration was concentrated in the 0-2 cm soil layer, and the content was 4.43 mg·kg^-1, which was significantly different from the control plots(P < 0.05); The effects on soil chemical properties are mainly concentrated in the surface layer. The pH value of the 0-2 cm soil layer increased by 0.90, the organic matter content decreased by 16.70 g·kg^-1, and the available P content increased by 2.39 mg·kg^-1, which were significantly different from the control plots(P < 0.05).

Key words: glyphosate, Eucalyptus plantations, soil physicochemical properties