3.3 Mechanism of interaction of water and fertilizer on soil microbial biomass C and N and enzyme activity of Panax notoginseng in farmland
Vepslinen et al. suggested that chemical fertilizers affected soil enzyme activity by improving soil physical and chemical properties and microflora and that an appropriate ratio of water to fertilizer had an important effect on improving soil fertility and crop yield (Vepsalainen et al.,2001). Reasonable irrigation can improve soil enzyme activity. Too much or too low soil moisture is not conducive to the growth and reproduction of soil microorganisms, resulting in the reduction of soil enzyme activity. This study found different distribution characteristics of soil microbiomass carbon, nitrogen and enzyme activity optimal scheme fit under different optimal water and fertilizer management at different fertility periods.The Ci values under the same irrigation regime were F4, F3, F2, and F1 in descending order, and the benefits and drawbacks of the microbial biomass carbon, nitrogen, and enzyme activity of Panax notoginseng soil were F4, F3, F2, and F1 in descending order.; Under the same fertilization treatment, the Ci values decreased and then increased with the increase of irrigation, and the advantages and disadvantages of microbial biomass carbon, nitrogen and enzyme activity of Panax notoginseng soil were W2, W1 and W3 in descending order.The Ci value of the W2F4 treatment was the largest at 0.836 during the rooting period, followed by the Ci value of the W3F4 treatment at 0.794, and the worst treatments for soil microbial biomass carbon, nitrogen and enzyme activity were W1F2 and W1F1 with Ci values of 0.214 and 0.133, respectively.The maximum Ci value was 0.806 for the W3F4 treatment at the seedling period, followed by 0.801 for the W2F4 treatment, and the worst treatments for soil microbial biomass carbon, nitrogen and enzyme activity were W1F2 and W1F1 with Ci values of 0.263 and 0.111, respectively.The maximum Ci value for the W3F4 treatment was 0.733, followed by 0.568 for the W2F3 treatment, and the worst Ci values for soil microbiomass carbon and nitrogen and enzyme activity were 0.216 and 0.189 for the W2F1 and W1F1 treatments, respectively. The maximum Ci value for the W3F4 treatment was 0.835, followed by 0.766 for the W3F3 treatment. The worst soil microbial carbon, nitrogen and enzyme activity treatments were W2F1 and W1F1, with Ci values of 0.273 and 0.068, respectively.

4 Conclusion

The characteristics of soil microbial biomass C and N and enzyme activities of Panax notoginseng in farmland were studied through optimal management of water and fertilizer. The main conclusions were as follows:
(1) Under the same optimal management of water and fertilizer, the differences in soil microbial biomass C and N content and soil enzyme activity were significant with different growth periods (p<0.05). The soil microbial biomass C and N content and soil enzyme activity increased firstly and then decreased with time, and gradually increased from rooting period to flowering period; There were significant differences in soil microbial biomass C and N content and soil enzyme activity between the same growth period and different water and fertilizer optimal management (p<0.05), and soil microbial biomass C and N content and soil enzyme activity increased with the increase of irrigation amount and fertilizer application amount.
(2) The correlation coefficients of acid phosphatase and catalase with soil microbial biomass C and N were in the range of 0.90~1.00 under optimal water and fertilizer management, while those of urease and sucrase with soil microbial biomass C and N were in the range of 0.80~0.95. The C and N content of soil microbial biomass influenced soil enzyme activity.
(3) The comprehensive evaluation of soil microbial biomass C and N,and enzyme activities under optimal water and fertilizer management showed that the W2F4 treatment of Panax notoginseng at rooting period had the highest Ci value of 0.836 and the W3F4 treatments at seedling , flowering, and fruiting periods had the highest Ci values of 0.806, 0.733 and 0.835, respectively. The W2F4 treatment at the rooting period and the W3F4 treatment at the seedling, flowering, and fruiting periods were significantly effective in regulating soil microbial biomass C and N, and enzyme activities. That were beneficial to the growth and yield quality improvement of Panax notoginseng plants.
Foundation items: National Natural Science Foundation of China projects (51979134, 51779113); 2021 Joint Special Project on Agriculture in Yunnan Province(202101BD070001-077);Yunnan Province Fundamental Research Key Projects(CB22052C055A);Yunnan Provincial Education Department Scientific Research Fund Project (2021J0164); A study of terrestrial animal habitats in Li Ziping National Nature Reserve, Sichuan Province(2021ZD0125);Open Fund Project of Yunnan Provincial Key Laboratory of Highland Wetland Protection and Restoration and Ecological Services (202105AG070002); Provincial Innovation Team on Environmental Pollution and Food Safety and Human Health, Southwest Forestry University (2005AE160017); The construction project of key disciplines with advantages and characteristics (Ecology) in Yunnan universities; Research project of Key Laboratory of Soil Erosion and Control in Yunnan University.
Author Bio: Tuo Yunfei (1976-),Male,Associate Professor,Master Supervisor,mainly engaged in the research of agricultural water resources planning and utilization,E-mail:tyunfei@163.com.
Corresponding author: Tuo Yunfei (1976-),Male,Associate Professor,Master Supervisor,mainly engaged in the research of agricultural water resources planning and utilization,E-mail:tyunfei@163.com,College of Ecology and Environment,Southwest Forestry University,Kunming,650224,China,086+13888939641.

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