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.