Biodissolution of silicate minerals by silicon solubilizing bacteria (ssb) in wetland rice

Abstract

ABSTRACT The present study entitled “Biodissolution of silicate minerals by silicon solubilizing bacteria (SSB) in wetland rice” was carried out to evaluate the effect of silicate solubilizers on the solubility and availability of native Si and its impact on crop growth and yield of test crop rice (var. Uma). The study was undertaken in three parts viz; a survey, an invitro study and a field experiment. Geo-referenced soil samples from the wetlands of southern laterites (AEU 8) were collected to identify the silicon deficient locations for further study. The lowest available Si (15.20 mg kg-1) was recorded from Integrated Farming System Research Station (IFSRS), Karamana and hence the wetland at IFSRS, Karamana was selected as the experimental site for further study. A laboratory incubation study was carried out for a period of three months using two sources of silica viz; calcium silicate (S1) and paddy husk ash (S2) at different doses: D1 (100 kg ha-1 of silica), D2 (75 kg ha-1 of silica) and D3 (50 kg ha-1 of silica). The soil was incubated and silicon solubilizing bacteria (SSB) was inoculated at two doses viz; 2 kg ha-1 (I1) and 5 kg ha-1 (I2). From the study it was observed that the availability of P, K and Si nutrients were significantly increased through the application of Si sources and SSB. However the availability of Fe, Mn and Al were reduced when the soil was incubated with SSB and Si sources. Application of 100 kg ha-1 of silica as calcium silicate along with 5 kg ha-1 of SSB (D1S1I2) significantly increased the availability of major nutrients and Si, and while the availability of heavy metals like Fe, Mn and Al were reduced. A field experiment was also carried out at Integrated Farming System Research Station, Karamana to evaluate the effect of silicate solubilizers on the solubility and availability of native Si and its impact on crop growth and yield in rice (var. Uma). The treatments imposed were the various combinations of Si sources (calcium silicate and paddy husk ash) and SSB at the dose of 5 kg ha-1. It was observed from the study, that the grain and straw yield were found to increase with the soil application of SSB at 5 kg ha-1 along with 75 kg ha-1 silica as calcium silicate (T4). In the case of yield attributes, soil application of SSB @ 5 kg ha-1 along with 50 kg ha-1 silica as paddy husk ash (T6) recorded the highest value for number of panicles/m2 and panicle length. Thousand grain weight was found to increase with the soil application of SSB @ 5 kg ha-1 along with 75 kg ha-1 silica as calcium silicate (T4). The application of SSB and Si sources significantly improved the available Si content in the soil. From the present study, it is evident that the application of SSB and Si sources also had a synergistic effect in improving the availability of N, P, K, Ca, Mg, S, Zn and B content in the soil. Soil application of SSB at 5 kg ha-1 along with 75 kg ha-1 silica as calcium silicate (T4) was also effective in reducing metal toxicities by decreasing available Fe, Mn and Al content in the soil. The grain and straw uptake of N was significantly higher in soil application of SSB at 5 kg ha-1 along with 75 kg ha-1 silica as paddy husk ash (T6) than the other treatments. However, soil application of SSB @ 5 kg ha-1 along with 75 kg ha-1 silica as calcium silicate (T5) was found to increase the uptake of P, K and Si in grain and straw With regard to soil enzymes viz; deaminase and dehydrogenase activity, soil application of SSB @ 5 kg ha-1 along with 75 kg ha-1 silica as paddy husk ash was found to be the superior (243.41 nmol mg−1 h−1 and 408.92 μg of TPF hydrolysed g-1 of soil 24 hrs-1 respectively). Root characters like, root volume and root weight were found to the highest with the soil application of silica at 100 kg ha-1 (T2) and soil application of SSB @ 5 kg ha-1 along with 75 kg ha-1 silica as paddy husk ash (T6) respectively. With respect to the economic analysis, soil application of SSB at 5 kg ha-1 along with 75 kg ha-1 silica as calcium silicate (T4) recorded the highest value for net income. However, soil application of SSB at 5 kg ha-1 alone (T7) was found to be the best with respect to B: C ratio (1.63). From the study it is concluded that the application of SSB and Si sources significantly enhanced the availability of nutrients as well as alleviate the metal toxicities of Fe, Mn and Al in lateritic wetland soils. The soil application of SSB at 5 kg ha-1 along with 75 kg ha-1 silica as calcium silicate significantly improved yield and yield attributes and there by the net income while the soil application of SSB at 5 kg ha-1 alone recorded the highest B: C ratio. With respect to soil attributes, the treatment with soil application of SSB at 5 kg ha-1 along with 75 kg ha-1 silica as calcium silicate (T4) was found to be the best.