3.2 Effect mechanism of water and fertilizer optimal management on soil enzyme activity of Panax notoginseng
Soil enzymes were key components for catalytic decomposition of soil nutrient conversion, and their activity in soil could be used as a measure of soil health index(Ashraf et al.,2020;Kotroczo et al.,2014). this study found significant differences in soil urease, sucrase, acid phosphatase, and catalase activities at different growth periods under optimal management of that same water and fertilizer (p<0.05), and the increasing and then decreasing trends were observed with the prolongation of growth period of Panax notoginseng, which ranged from large to small in flowering period, fruiting period, seedling period and rooting period. This was consistent with the findings of Peibing et al. that soil enzyme activities had obvious seasonal variation characteristics, with the soil sucrase activity in summer > autumn > spring > winter, and urease activity in summer > spring > autumn > winter. The results showed that the two soil enzyme activities were the highest in summer and the lowest in winter similar (Pei et al.,2018). Zhu et al. believed that soil enzyme activities had obvious seasonal variation characteristics, with the peak values of soil catalase, phosphatase, and urease of reed community appearing in the exuberant growth period, and the trough value appearing in the germination period and the leaf developing period (Zhu et al.,2017). In this study, the flowering period of Panax notoginseng was in summer and it grew vigorously, while the root increasing period was in winter, which was the germination period. Therefore, the flowering period of soil enzyme activity of Panax notoginseng was the largest, and the root increasing period was the smallest. The reason was that summer was the rainy season, with plenty of rainfall. The soil temperature and humidity were suitable for the growth and reproduction of microorganisms, and the enzyme activity in the soil was increased by the increase of microbial activity. This study found that under different water and fertilizer optimal management, soil urease, sucrase, acid phosphatase, and catalase showed significant differences in the same growth period (p<0.05). The contents of soil urease, sucrase, acid phosphatase, and catalase increased with the increase of irrigation amount and fertilizer application amount, and the treatment of soil urease, sucrase, acid phosphatase, and catalase W3F4 at the flowering period was the largest.
This study found a significant correlation between soil microbial biomass C and N and soil enzyme activities (p<0.05), a very significant positive correlation between soil acid phosphatase and catalase and soil microbial biomass C and N (P<0.01), and a significant positive correlation between urease and sucrase and soil microbial biomass C and N (P<0.05). This was similar to the finding by Eivazi, F. et al. that the activities of soil urease, sucrase, and alkaline phosphatase had a very significant positive correlation with the soil microbial biomass of carbon, nitrogen, and phosphorus (Eivazi et al.,1996). Yang et al. found a highly significant positive correlation between soil microbial biomass C, N, and P and soil urease, sucrase, and alkaline phosphatase activities(Yang et al.,2015). The study also reveals that soil invertase, acid phosphatase, and catalase were the main factors affecting the regulation of microbial biomass c and n, while urease was an important factor affecting microbial biomass C and N.