Symbiotic effectiveness of arbuscular mycorrhizal technology and Azotobacterization in citrus nursery production under soil disinfestation and moisture conservation practices

The present study was carried out with the objective to exploit indigenous arbuscular mycorrhizal (AM) fungal symbiosis and Azotobacterization on citrus seedlings inoculated under solarized, chemical sterilized and natural soil conditions along with moisture conservation mulch practices. Two potent indigenous species of AM fungi namely, Glomus fasciculatum (Thaxter sensu Gerdemann) (AM₁) and G. macrocarpum Tul. & Tul. (AM₂), and two strains of Azotobacter chroococcum viz., A. chroococcum strain-I (AZ₁) and A. chroococcum strain-II (AZ₂) were inoculated at nursery stage under four different moisture conservation mulch practices viz., black plastic mulch (BPM), grass mulch (GM), cover crops (CC), green manuring+clean cultivation (Gm+Cc). The effects of AM fungi and A. chroococcum strains on mycorrhizal spore population, Azotobacter bacterial count, vegetative growth characteristics and soil microbial densities (bacteria, fungi and actinobacteria) were studied. Different AM fungi showed the difference in the effectiveness of inter-species in citrus seedlings. The observations on the individual effect of soil disinfestations and mulch practices on microbial density, percent root colonization, vegetative growth characteristics (plant height, stem diameter, leaf area and total root length) and nutrient content of leaf of the seedlings were also recorded. Inoculation with G. fasciculatum and AZ₁ showed greater positive effects in the seedlings compared to G. macrocarpum and AZ₂ strain recording highest AM colonization, plant height, stem diameter, leaf area, root length and had the density of soil borne bacteria, fungus and actinobacteria reduced drastically in the solarized soil plots. Solarization increased the maximum daily temperature to 48.5°C and the average minimum daily soil temperature to 28.8°C at 5–25cm depth. It is also noticed that the plants inoculated with G. fasciculatum and AZ₁ had improved vegetative growth characteristics, microbial consortium of the rhizosphere soil and nutrient content of leaf N, P, K and Zn under plots of solarization and black plastic mulching compared to chemical sterilized and natural plots under different mulch types. The present findings inferred that the combining soil solarization and inoculation of rhizosphere soil to AM fungi and A. chroococcum using black plastic mulching as moisture conservation practice could be considered as an efficient and feasible approach for excellent citrus nursery management under mid-hill rain-fed agro-climatic conditions of Himachal Pradesh.