Effect of washing biochar and chemical fertilizers
on rice yield and nutrient uptake

【Objectives】The beneficial effects of biochar on rice yield and nutrient uptake have been reported widely. This research will explore how washing will affect the goodness of biochar, to provide a support for the efficient use of biochar. 【Methods】 Bamboo biochar was washed with deionized water in laboratory first. Then, both the washed and un-washed bamboo biochar were used in a pot experiment. Six treatments were setup: no biochar and no fertilizer (CK), only bamboo biochar (B), washed bamboo biochar (WB), only chemical fertilizer (CKF), bamboo biochar with fertilizer (BF), washed bamboo biochar with fertilizer (WBF). The soil chemical and physical properties, rice straw and grain yields and N, P and K uptake were analyzed. 【Results】 After washing, the pH and K content of the bamboo biochar become lower, while the content of C, N, P, S, Ca, Na and Mg, the BET surface area, the total pore volume and average particle size keep unchanged. Whether with fertilizer application or not, the soil organic carbon, pH and available K are significantly improved by the addition of biochar, the effect in increasing soil available K of biochar is significantly better than that of washed biochar. When used individually, the increase in soil total N is similar in biochar of washing and not, the soil available P is significantly increased by the washing. The rice straw yields are significantly increased by 12.7% with washed biochar and 15.6% with unwashed ones, and the grain yield significantly increased by 15.7% with washed biochar, no significantly differences caused by washing. When combined used with chemical fertilizers, the rice straw yields with washed and unwashed biochar treatments are significantly increased by 33.1% and 18.7%, and the rice grain yields significantly increased by 18.4% and 16.7%, respectively. The N and K uptakes of rice straw and grain are both improved with the two biochar treatments, there are no significant differences between them, and the grain N increase with the washed biochar treatment is significant compared with CK. The effect in improving P absorption of grain is better in washed biochar treatment, but that in K uptake of rice straw is on the contrary, partly due to the substantially decreased K content in the washed biochar. 【Conclusions】 The washed bamboo biochar is superior to bamboo biochar for improving N use efficiency and rice yield. But lose some function of K supply. Taking environment protection,reducing nitrogen and saving water resource into account, washing is an alternative way for rice production in bamboo biochar application.