Alternate micro-sprinkler irrigation and organic fertilization decreases root rot and promotes root growth of Panax notoginseng by improving soil environment and microbial structure in rhizosphere soil

It is a challenge to improve Panax notoginseng production and soil environment in arid area of Southwest China. Therefore, the objective of this study was to propose a new and promising alternate micro-sprinkler irrigation (D2) to cope with the challenge based on moderate deficit micro-sprinkler irrigation (D1) and slight deficit micro-sprinkler irrigation (D3). A two-year greenhouse experiment was conducted to evaluate the root rot incidence of Panax notoginseng among of the D1, D2 and D3 treatments by analyzing the soil water content (SWC), soil microbial biomass carbon (SMBC), nitrogen (SMBN), total phosphorus (TP) and total potassium (TK), soil available nutrients(AN, AP and AK), soil enzyme activity, soil microbial structure, plant growth parameters, plant dry matter, nutrients uptake (N, P and K), and root rot incidence. Experiment treatments consisted of three irrigation amounts (D1, D2 and D3) and four organic fertilizer levels [500 (F1), 1000 (F2), 1500 (F3), and 2000 (F4) kg hm−2] in 2017 and 2018, respectively. All treatments were designed using a randomized complete block with three replications. The results indicated that no significant differences in growth parameters [PH (plant height), SD (stem diameter), and LAI (leaf area index)] of Panax notoginseng were found among of the D1, D2 and D3 treatments in 2017 and 2018. Compared with the D1 and D3, the D2 treatment significantly increased shoot dry weight (SDW), root dry weight (RDW), total N, P, K uptake and decreased SMBC, SMBN, TP, TK, AN, AP, AK and root rot incidence in 2017 and 2018. The result suggested the D2 treatment had greater production advantages than the D1 and D3 treatments. In addition, compared with the F3 treatment, other F treatments (F1, F2, and F4) in the D2 treatment significantly enhance total plant dry matter, total N, P and K uptake. However, root rot incidence significantly increased with the increase of application F levels, and D2F3 can significantly decrease fungi/bacteria and fungi/actinomycetes in rhizosphere soil of healthy Panax notoginseng in 2018. According to analyzing the root rot incidence of different application F treatments, we found that 1500 kg hm−2 in the alternate micro-sprinkler irrigation might be recommended as an appropriate application F level to decrease root rot incidence of Panax notoginseng in the semi-arid area of Southwest China.