Effectiveness of Aspergillus japonicus in improving soil phosphate availability in cinnamon plantations

Abstract

Use of phosphate solubilizing microorganisms is an inexpensive strategy that can confer solubility of insoluble phosphates (P). Aspergillus japonicus, an effective native phosphate solubilizer identified by whole genome sequencing in a previous study was used to investigate the effectiveness of improving soil P in cinnamon (Cinnamomum verum Presl syn. Cinnamomum zeylanicum Blume) cultivations. A field experiment was conducted at Ekarella Estae, Opanayake, Sri Lanka. Randomized Complete Block Design (RCBD) with nine treatments and three blocks was employed. A total of 27 plots were accommodated with six plants/plot. The treatments were: Inoculum (I)+Carrier material (CM) [T1]; I+CM+Eppawala rock phosphate (ERP) Recommendation [T2]; I+CM+50% of ERP Recommendation [T3]; CM [T4]; CM+ERP Recommendation [T5]; CM+50% of ERP Recommendation [T6]; No ERP [T7]; ERP Recommendation [T8] and 50% of ERP Recommendation [T9]. Muriate of potash and urea were added to all the treatments. Pits (30 cm x 30 cm x 30 cm) were filled with compost and a mixture of ERP and 50 g of inoculum (spore density- 6.5×108 g -1 ) was applied. Then, four-month old seedlings were planted, four per pit. After six months, NPK fertilizers were applied as per the recommendations of the Department of Export Agriculture followed by a second inoculum application (50 g) after 2 months of NPK application. Soil sampling was done quarterly for a year and analyzed for available P by Bray method. The data were statistically analyzed by using SAS package. A significant difference was noted (p<0.05) between the three blocks at first and second sampling but not in the third and fourth samplings. Even though not significantly different (p>0.05), all inoculated treatments showed higher mean available P contents throughout the sampling period compared to the recommendation. At first sampling T3, T1 and T2 treatments had soil available P contents of 12.17±2.96, 11.44±3.94 and 8.28±3.45 mg Kg-1 soil, respectively while the recommendation (T8) showed only 5.82±1.19 mg Kg-1 soil. At second sampling the T3, T2 and T1 had 9.04±1.57, 8.52±0.84 and 7.85±0.64 mg Kg-1 soil while T8 showed only 7.56±0.92 mg Kg-1 soil. This trend was evident with third and fourth samplings. Interestingly, inoculum alone gave a higher soil P content than ERP alone treatment. Accordingly, it is evident that application of A. japonicus can improve the soil available P status of cinnamon plantations.