Abstract
Use efficiency of N fertilizers in lowland rice cultivation is very low. Biochar can be used to modify the N releasing rates of fertilizers and increase their efficiency. Maximum amount of urea that can be intercalated into biochar (BC) and the effects of biochar based slow-release urea fertilizer (SRF) on soil solution N contents and growth of rice (<em>Oryza sativa</em>) were investigated. Two feedstock materials (sawdust and tea waste) were slow pyrolysed at 500°C to produce BC and N were intercalated into BC using urea solutions with seven concentrations (U1=0% <U2<U3<U4<U5<U6<U7=100% w/v). The maximum intercalated N contents in sawdust BC and tea waste BC were 28% and 22%, respectively. Five treatments: two SRFs at 17.25 mg N kg<sup>–1</sup> soil (75% recommended N) and three urea levels (0, 75, and 100% N) were applied to rice plants (Bg 251) in a pot experiment. Application of SRF significantly improved the greenness and growth of rice plants when compared with 0% N control and were comparable with 100% urea-N treatment. The apparent recovery of N (ARN) was significantly (p<0.05) improved in SRFs (60-71%) compared to urea only treatments (38-52%). Nitrate-N contents in soil solution were not significantly different (p<0.05) among treatments while NH4<sup>+</sup>-N content in 100% urea treatment was significantly (p<0.05) higher throughout. Based on urea intercalation efficiency and the ARN, we concluded that SRF made using sawdust biochar is having a higher potential than SRF made using tea waste biochar to improve the efficiency of urea in lowland rice cultivation.
Highlights
Rice cultivation in Sri Lanka uses about 60% of the urea imported to the country and the nitrogen use efficiency (NUE) of added urea is less than 30% in rice growing soils (Sirisena et al, 2013)
Hemicellulose in feedstocks will be escaped as it subjected to volatilization during the pyrolysis process (Keech et al, 2005, Watkins et al, 2015) and is higher in sawdust compared to tea wastes (Akgül et al, 2018; Joshua, 2016)
From the two biochar types used in this study, the saw dust biochar is having a higher potential than tea waste biochar to intercalate urea
Summary
Rice cultivation in Sri Lanka uses about 60% of the urea imported to the country and the nitrogen use efficiency (NUE) of added urea is less than 30% in rice growing soils (Sirisena et al, 2013). Resource conserving agricultural technology with integrated farming and intercropping, application of nitrification inhibitors and urease inhibitors, introduction of improved varieties and use of efficient fertilizer technologies are few such approaches commonly used (Montemurro and Diacono, 2016). These practices have shown to be agronomically effective, most farmers are reluctant to adopt them due to lack of resources and high costs incurred for materials and labour. There is a necessity to introduce technologies as adoptable and costeffective products in soil fertility management
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