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Effect of Rice Straw Biochar Application on the Dynamics and Balance of Nitrogen on Clay and Sandy Loam Soils Planted to Rice (Oryza sativa L.)
Dissertation Abstract:
This study was conducted at the International Rice Research Institute (IRRI) in Los Baños, Laguna, Philippines. The first experiment aimed to determine the soil nitrogen supply capacity in Binangonan clay and Sariaya sandy loam soils. An anaerobic incubation experiment was conducted in the greenhouse to determine the soil nitrogen (N) mineralization and the N-supplying ability of paddy soil without N fertilization. The second experiment aimed to evaluate the effects of biochar made from rice straw on the N dynamics and balance on lowland rice soils. The pot experiment was conducted in a screenhouse under anaerobic condition during two rice growing seasons. The experiment was arranged in a completely randomized design (CRD) in three replications with two biochar levels (10 and 40 ton ha-1). Two dosages of biochar were applied once in the wet season. The basic characteristics of selected rice soils showed that the Binangonan clay soil had higher cation exchange capacity (CEC) and clay content. The Sariaya sandy loam soil, on the other hand, had higher total N and total C. The amount of N mineralized during cropping season of rice was estimated to be between 51.9 mg N kg-1 to 141.7 mg N kg-1 in Binangonan clay soil and between 62.7 mg N kg-1 to 77.83 mg N kg-1 in Sariaya sandy loam soil. The N mineralization was related to total N and NH4+-N contents. Under anaerobic condition, the Sariaya sandy loam soil had higher N supplying capacity than the Binangonan clay soil. N-supply measured as NH4+-N in sandy loam soil was higher at 0-30 days and observed at adequate level for N uptake during vegetative stage, while the Binangonan clay soil was higher at 0-60 days and very poor in N supplying capacity. The second experiment showed that rice straw biochar increased the soil pH, CEC, total organic carbon, and total N contents, and decreased the soil bulk density, particularly with higher application rate. Application of biochar was greatly pronounced on NH4+-N during anaerobic condition in biochar-amended soil at 40 ton ha-1 in combination with chemical fertilizer and cow manure in both soils. In clay soil, plant N uptake and grain yield significantly increased by biochar rate at 40 ton ha-1 with chemical fertilizer and the use of chemical fertilizer alone in both cropping seasons. In sandy loam soil, the added biochar at 10 and 40 ton ha-1 in combination with chemical fertilizer and cow manure had markedly increase N uptake in both seasons. However, the added biochar at 10 ton ha-1 in combination with chemical fertilizer showed higher yield during the WS cropping while a lower yield was observed in the DS cropping as affected by added chemical fertilizer. The nitrous oxide emission between treatments was statistically significant with urea having the highest peak, however, the amount was negligible when compared to nitrogen output. Results from the estimation of N balances had guided the appropriate biochar application rate based on higher yield and less N losses. For clay soil, the use of straw biochar rate of 40 ton ha-1 with chemical fertilizer together with N management significantly improve the N output from residual N is recommended. For sandy loam soil, the application of rice-straw biochar at 10 ton ha-1 in combination with chemical fertilizer and cow manure need additional 64.3 kg ha-1 N to meet the target yield.