Occurrence and Sustenance of Arbuscular Mycorrhizae in Selected Dry Zone Agricultural Lands in Sri Lanka

Arbuscular mycorrhizae (AM) are one of the important symbiotic micro-organisms that provide a primary natural pathway for soil/plant nutrient transfer. The prevalence of AM on Reddish Brown Earth soils in the dry zone was determined under three agronomic management regimes: least-, moderate- and well-managed at Kiralogama, Puliyankulama, and Medawachchiya, respectively, in the Anuradhapura District. Arbuscular mycorrhizae interactions were evaluated with varieties each; sesame (Sesamum indicum L.), bitter gourd (Momordica charantia L.), cowpea (Vigna unguiculata (L) Walp.), chilli pepper (Capsicum annuum L.) and tomato (Solanum lycopersicum L.), and locally-common four weed/non-crop species; akmella (Synedrella nodiflora (L.) Gaertn.), balathana (Eleusine indica (L.) Gaertn.), kurakkan (Eleusine coracana (L.) Gaertn.), and wal-rubber (Euphorbia heterophylla L.) in pot experiments. Rhizosphere soils at the well-managed Medawachchiya site recorded the highest number of average live (1312) and dead (2637) spores per 100 g of soil retained on 125 μm sieve compared to the lowest live (459) spores at the least-managed site at Kiralogama. At both Kiralogama and Puliyankulama, live spore counts significantly increased with the progress of Maha rainy season. Increases in plant P and Zn concentrations showed strong positive correlations with AM colonisation. Significant differences of both AM colonisation and spore counts were observed in pot experiments depending on the weed/non-crop species and the variety of crops. Akmella (51.2 %), bitter gourd (var. Black - 69.1 %), Sesame (var. Mali - 76.7 %) and wal-rubber (76.8 %) were associated with high levels of AM colonisation as well as soil spore counts.