Changes characteristics of soil microbial biomass carbon,nitrogen and enzyme activity of Panax notoginseng under optimal management of water and fertilizer
Tuo Yunfei1,Liu Xiangning1,Zheng Yang1,Wang Qian1,Wang Fei1,Wang Zhaoyi1,Shi Xiaolan1,Ding Mingjing1,
Shen Fangyuan1,Xiang Ping1,Yang Qiliang2
College of Ecology and Environment, Southwest Forestry University, Kunming 650224
2.College of Modern Agricultural Engineering, Kunming University of Science and Technology, Kunming 650500)
Corresponding author: Tuo Yunfei,College of Ecology and Environment,Southwest Forestry University,Kunming,650224,China,
086+13888939641.
Abstract: There is a lack of understanding of the dynamic characteristics of carbon, nitrogen, and enzyme activity of soil microbial load of Panax notoginseng in water-fertilizer intercrops. In this study , we reveal that different water and fertilizer regulations affect microbial biomass carbon, nitrogen, and enzyme activities. As the study object, we set up 3 irrigations,4 fertilization levels, and 1 control in micro-sprinkler irrigated Panax notoginseng farmland, Luxi County, Yunnan Province from 2018 to 2020. The findings demonstrated that under the same water and fertilizer management, the carbon, nitrogen, and enzyme activities of Panax notoginseng’s soil increased and then decreased with increasing fertility time, in descending order of flowering, fruiting, seedling, and rooting periods.. The maximum value is reached during the flowering period ,while the minimum value is reached during the rooting period. The soil microbial carbon and nitrogen contents ranged from 0.49 to 1.05 g.kg-1 and from 14.98 to 66.21 mg.kg-1, respectively, and soil sucrose enzyme activity was the largest, ranging from 17.12 to 68.79 mg.kg-1.d.-1. The soil microbial carbon , nitrogen and enzyme activities of Panax notoginseng increased with the rate of water and fertilizer application under different water and fertilizer management. The soil microbial carbon , nitrogen and enzyme activities of Panax notoginseng at the flowering period were the largest. The soil microbial carbon and nitrogen activities of Panax notoginseng increased with the increase of irrigation and fertilizer application, whereas the soil microbial carbon and nitrogen activities of W3F4 increased by 0.41 g.kg-1 and 39.52 mg.kg-1 respectively compared with W1F1. Soil urease, sucrase, acid phosphatase, and catalase activities were the highest in W3F4, with increases of 44.26%, 61.51%, 42.56, and 32.25% respectively compared to W1F1. There was a significant positive correlation between soil microbiomass carbon and nitrogen and enzyme activity under different water and fertilizer management. Soil microbiomass carbon and nitrogen content determined soil enzyme activity. The entropy value method combined with the TOPSIS method was used to analyze the optimal program fit Ci of soil microbial biomass carbon, nitrogen, and enzyme activity under different water and fertilizer optimization management and at different fertility periods. The results showed that the Ci values were F4, F3, F2, and F1 in descending order under the same irrigation level treatment.The Ci values decreased and then increased with increasing irrigation water under the same fertilization level treatment. The carbon, nitrogen, and enzyme activities of the soil’s microbial biomass were successfully controlled when Panax notoginseng was treated with W2F4 during the rooting period and W3F4 during the seedling, flowering, and fruiting periods. This study is an essential guideline for water and fertilizer regulation of Panax notoginseng and its yield quality improvement.
Keywords: Panax notoginseng;Optimal management of water and fertilizer;Microbial biomass of Carbon and Nitrogen; Soil enzyme activity.
Soil microbial biomass (SMB), an active component of soil organic matter, plays a key role in the regulation of soil ecosystem and its function, serving as one of the most important biological indicators for the evaluation of the soil comprehensive quality(Raiesi et al.,2015;Evangelou et al.,2021).Soil MBC and MBN determine soil fertility and are important source of soil organic carbon and available nitrogen (Yu et al.,1999;Zhou et al.,2002). Soil enzyme activity is derived from soil microorganisms and plant root exudates and is sensitive to different fertilization responses(Yang et al.,2020). It is very active in soil ecosystems(Luo et al.,2014;Hill et al.,2012) and plays a vital role in nutrient cycling (nitrogen fixation, phosphorus adsorption and desorption, and potassium release, etc.) as well as in soil structure maintenance and crop yield(Burns et al.,2013;Zhao et al.,2016). It is a comprehensive soil fertility biological index(Zhang et al.,2015).As a catalyst for soil organic matter decomposition and nutrient conversion cycling, soil enzyme has a close relationship with soil nutrient content and microbial biomass carbon and nitrogen(Wang et al.,2016). Soil comprehensive fertility is determined by soil microbial biomass carbon and nitrogen and enzyme activity.
Fertilization and irrigation had significant effects on soil microbial biomass C and N and enzyme activity. The research by Jiang et al. showed that irrigation improved soil enzyme activity(Wang et al.,2017;Calderon et al.,2016), and the research on soil microbial characteristics, soil enzyme activity, and nutrient regulation in water-saving irrigation winter wheat fields by Ye Deling et al. showed that soil microbial characteristics and soil enzyme activity were regulated by irrigation and were closely related to the cyclic transformation of soil C and N nutrients(Ye et al.,2016). Li et al. found that nitrogen application significantly increased soil MBC and MBC: MBN(Li et al.,2018). Xu et al. studied the effects of fertilization on soil organic carbon (SOC) content, soil microbial biomass carbon (SMC), and soil microbial biomass nitrogen (SMN) and found that the yields of early and late rice treated with 30% organic matter +70% inorganic fertilizer, 60% organic matter +40% inorganic fertilizer and straw+inorganic fertilizer were higher than those of the early and late rice treated with inorganic fertilizer or no fertilizer(Xu et al.,2017). HAO et al. studied the effects of long-term application of inorganic fertilizer and organic fertilizer on the organic matter and microbial biomass of three subtropical rice soil, and the results showed that the mixed application of inorganic fertilizer with manure or straw improved the organic matter and microbial biomass of the subtropical paddy soil(Hao et al.,2008). Bach E.M. et al. showed that the microbial activity in the fertilized grassland was higher than that in the non-fertilized soil, and the addition of nitrogen in the fertilized grassland enhanced the soil microbial biomass and enzyme activity(Bach et al.,2015).
There have been many studies on the effects of various farmland management methods on soil microbial biomass C-N and enzyme activities, but none have been quantitative.Particularly, Notoginseng, a medicinal plant, has not received much study. The interaction of water and fertilizer has little effect on the rhizosphere secretion of Panax notoginseng and soil microbial biomass C-N and enzyme activities, thereby affecting the farmland soil microbiological properties of Panax notoginseng. At the moment, research on the interaction of water and fertilizer is primarily focused on regulating the improvement of soil saline-alkali land in dryland farmland in the north, as well as crop yield and quality(Li et al.,2016;Zheng et al.,2020). Panax notoginseng research is primarily focused on single factors such as cultivation mode,continuous cropping obstacle of Panax notoginseng, accumulation and adsorption of heavy metals in soil,and fertilizer element ratio(Tang et al.,2020). Few studies have been conducted to investigate the effects of optimal water and fertilizer management on soil microbial biomass C and N and enzyme activities of Panax notoginseng, as well as the regulation of the combination of irrigation and fertilization on plant growth, yield, and quality of Panax notoginseng. Soil microbial biomass C-N and enzyme activities characterized soil fertility. It was determined that optimal water and fertilizer management was conducive to the growth, yield, and quality improvement of Notoginseng by investigating the soil microbial biomass C-N and enzyme activities under optimal water and fertilizer management. In this study, a randomized zonal experimental design with different water and fertilizer interactions was used to optimize the management of Panax notoginseng through three years of growth from 2018 to 2020. In this experiment, the effect of different water and fertilizer management on soil microbial carbon, nitrogen and enzyme activities of Panax notoginseng was analyzed, and the mechanism of this management on soil microbial carbon, nitrogen and enzyme activity response was investigated. The results can provide technical support for the efficient use and management of water and fertilizer in Panax pseudoginseng farmland, as well as important practical significance for guiding the high yield and quality cultivation of Panax notoginseng.

1 Materials and methods

Test design and sample collection
The experiment was conducted in the typical planting area of Panax notoginseng in Dali Shu Village, luxi county City, Honghe Prefecture, Yunnan Province from 2018 to 2020. The growth period of Panax notoginseng was divided into the rooting period (November~January of the following year), the seedling period (February~April), the flowering period (May~July), and the fruiting period (August~October). Panax notoginseng was covered with a double-layer sun-shading net. To avoid the influence of natural rainfall on irrigation amount, plastic film was used to cover and discharge the rainfall, and the excess rainfall was timely discharged from the test area. Micro-sprinkler irrigation fertilization was adopted. Irrigation and fertilization were conducted simultaneously once a month. The fertilizer was soluble organic fertilizer. The micro-sprinkler flow was controlled according to the experimental design to meet the design criteria for fertilization and irrigation in different plots.According to the high-yield and high-efficiency fertigation system for planting Panax notoginseng in the local area, two factors (F) and (W) were applied in the experiment. The former includes four levels, namely, F1(3.20kg/667m2), F2(4.80kg/667m2), F3(6.20kg/667m2), and F4 (8.00 kg/667 m2); The latter three levels were W1(40% field water holding capacity),W2(60% field water holding capacity) and W3(80% field water holding capacity), one control. A total of 13 treatments were set, which were W1F1, W1F2, W1F3, W1F4, W2F1, W2F2, W2F3, W2F4, W3F1, W3F2, W3F3, W3F4 and CK, respectively. CK was the no-fertilization and no-irrigation control. Each processing three repeat, each community 16.70m long,1.50m wide, ditching ridging before planting, the groove depth of 30cm, the groove width of 40cm, to ensure that the water is not leaking, not diffuse groove, such as regular weed field management measures.
The sampling was conducted on the third day after irrigation and fertilization in December of each year, March, June, and September of the following year from 2018 to 2020. During the experiment, a 1m×1m sampling point was set in each residential area to remove soil surface litter and gravel around the sampling point at the sampling depths of 0~20~40cm and 20~40 cm, respectively. The soil samples were put into a self-sealing bag for labeling, sealed and stored, and then taken back to the laboratory. The fresh soil sample was divided into two parts. One part was used to measure soil water content and microbial carbon and nitrogen content. The other part was spread on kraft paper and air-dried naturally to remove roots, leaves, and gravel. Soil enzyme activity was tested after grinding and sieving. The German-American water-soluble organic fertilizers with N≥21%, P2O5≥21%、K2O≥21%, humic acid ≥6%, B≥0.1%, and Mo≥0.007% were selected. The basic physical and chemical properties of the soil before the test are shown in Tab.1.