Rice is the world’s most important cereal crop which acts as a primary food source for more than half of the world’s population especially for people in Asia (Rohman et al., 2014). In Sri Lankan context, it is the staple food and 2.7 million tones of rough rice are produced annually to satisfy around 95 percent of the domestic requirement in the country.) Approximately 560, 000 ha are cultivated during maha and around 310,000 ha are cultivated during yala by assembling 34 percent (0.77 /million ha) of the total cultivated area in Sri Lanka. Rice grain rich with carbohydrates, fat, proteins, fibers, and minerals as it provides 45% total calorie and 40% total protein requirement of an average Sri Lankan. The per capita consumption of rice in Sri Lanka fluctuates around 100 kg per year. With that, the demand for rice will increase at 1.1% per year and to meet the demand for rice, production should grow at the rate of 2.9% per year (Rice, 2018).
To achieve respective yield level from the plant, external nutrient application as fertilizer is important with proper quantity. With respect to paddy, the supply of three major nutrients namely, Nitrogen (N) Phosphorous (P) and Potassium (K) are essential for successful cultivation (Ekanayake, 2009). But excessive and imbalanced uses of chemical fertilizers have adversely affected sustainability of rice ecosystems and ultimately affect the health hazards for human beings and animals (Naher et al., 2016).
The traditional alternatives for chemical fertilizers are the organic fertilizers. Those alternatives are bulky and not very attractive to farmers compared to granulated and/or liquefied chemical fertilizers. Their transport, storage, and field application would require additional labor, time and cost. Furthermore, organic fertilizers need time to decompose and provide nutrients to the targeted crop plants and this is not compatible with short-term crops.
Microbial biofertilizers (living microbial inoculants which continue live in close association with crop plants) are also considered as a supplement to reduce the use of inorganic fertilizers and can overcome some limitations related to organic fertilizers. The importance of conventional biofertilizers as monocultures or in combination with other beneficial microbes as mixed cultures has been reviewed. (Mahdi et al., 2010; Saharan and Nehra 2011). But their survival and function are inconsistent under field conditions due to the heterogeneity of biotic and abiotic factors and competition with indigenous organisms (Senanayake et al., 2016). However, microbial communities in biofilm mode and their soil application as the biofilm- biofertilizers (BFBFs) have shown their consistent potential (Buddhika and Senevirathne, 2015).
Assemblage of microbes that consist with microbial cells (algal, fungal, bacterial and/or other microbial) as well as extracellular biopolymer (known as an extracellular polymeric substance (EPS)) produced by the cells and that can adhere to the abiotic or biotic surface known as Biofilms. Those are differentiated to form complex and multicellular communities (Seneviratne et al., 2007; Kecskés and Kennedy, 2007). Those microbes undergo extreme changes during their transition from planktonic (free-swimming) organisms to cells that are part of a complex, surface-attached biofilm (Seneviratne and Zavahir, 2010). The density of naturally existing microbial communities in a biofilm mode in the soil is not satisfactory to gain expectedbeneficial effects (Seneviratne, 2007; Kecskés and Kennedy, 2007). So beneficial biofilms have been formulated in vitro, to be used as biofertilizers so called biofilm-biofertilizers (BFBFs) in agriculture (Senanayake et al., 2016).
The effect of invitro developed biofilmed biofertilizers (BFBFs) on crop growth and yield have been tested successfully for many crops, such as maize, rice, a wide range of vegetables and for plantation crops like tea and rubber, under greenhouse and field conditions with their cut down amount of recommended fertilizer applications (Seneviratne et al., 2011; Buddhika et al., 2012a; Buddhika et al., 2012b; Hettiarachchi et al., 2012; Weeraratne et al., 2012; Seneviratne and Kulasooriya, 2013).
Biofilm biofertilizer applications generate several outcomes by offering structural and functional benefits to the rice plant. BFBF influence on microbial activities of rice plant rhizosphere (Feng et al., 2006) and among rice plant microbial exophytes and endophytes, endophytes play a major role in promoting plant growth and resistance to pathogens (Feng et al., 2006). Beneficial biofilms in rhizosphere enhance nutrient cycling and availability for crop growth as well as a biocontrol of pest and diseases improving crop productivity (Seneviratne and Jayasinghearachchi, 2005). Furthermore, BFBFs are effectively involved in detoxification of heavy metals, converting them into non-toxic forms (Senanayake et al., 2016).
Applying BFBF is likely to be beneficial in agro ecosystems for sustainable cropping systems via minimizing extensive use of inorganic fertilizers with sustained crop production (Seneviratne et al., 2011) Generally, BFBF alone is not recommended since fungal counterpart in the BFBF acquires some nutrients from the soil system, thus reducing plant growth. Therefore BFBF can only be use as a fertilizer supplement (Buddhika et al., 2013).
Series of studies (Seneviratne et al., 2011; Buddhika et al., 2012a; Hettiarachchi et al., 2012; Weeraratne et al., 2012; Seneviratne and Kulasooriya, 2013) were shown BFBF application can cut down the 50% of CF from DOA 2001 recommendation for rice without hampering of grain yield. Since the DOA recommendations have changed there are no sufficient studies carried out on the effect of BFBF application with the new recommendations. Due to the altering of fertilizer levels in 2013 recommendation, with low N level compared to 2001 recommendation it is important to have the critical evaluation to find out most effective CF level of 2013 DOA recommendation to be coupled with BFBF. Therefore,
This study will be targeted to evaluate BFBF application with different doses of new fertilizer recommendation (2013) under farmer rice field level examining plant growth, yield, soil parameters, microorganism activities, nutrient level of the rice grain.