Biochar input to reduce trace greenhouse gas emission in paddy field.

Biochar application to the paddy field may be an effective method to deal with global climate change for the mankind. The effect of four different application rates of biochar made from bamboo added to the paddy field on soil quality, rice yield and trace greenhouse gas emissions was investigated by a field experiment to provide a scientific basis for biochar agricultural application. The experiment was carried out in a rice farm from Tai Lake Region and consisted of four treatments, biochar at 10 t/hm2 (T1), biochar at 20 t/hm2 (T2), biochar at 40 t/hm2 (T3), and paddy field without biochar application as a control (T0). Each treatment had three replicates arranged in a completely randomized block design. Changes in soil chemical and physical properties, rice yield and trace greenhouse gases (CH4, N2O) emissions with biochar addition were investigated during a whole rice growing season of 2013. The results showed that, comparing with the control treatment, soil pH value and organic carbon content were significantly increased (P<0.05) after biochar application, and the increase of organic carbon content was proportional to biochar application amount (r=0.78, P<0.01). Soil bulk density was significantly decreased with the increasing biochar application rate (P<0.05). Biochar application had no significant effect on soil cation exchange capacity, total nitrogen, available phosphorus and quick-acting potassium content (P>0.05). Rice yields of four treatments were respectively (8 120.6±468.2), (8 313.5±221.8), (8 505.4±381.2) and (7 996.8±285.6) kg/hm2, and had no significant difference with biochar application amount (P>0.05), and the same result was obtained by the experiment of 2014, which showed biochar application cannot increase rice yield effectively, but can stable rice yield sustainably. CH4 emission flux decreased gradually with the increase of biochar application amount. Meanwhile, CH4 cumulative emission decreased effectively with biochar application. There was a negative correlation between CH4 cumulative emission and biochar application amount (r=-0.24, P<0.01).However, CH4 cumulative emission cannot decrease significantly by excessive biochar application (P>0.05). Comparing with the control (T0), N2O emission flux decreased significantly within a week after biochar application (P<0.05), and rose slightly during the drainage of the paddy field, and finally reached a steady value (about 9.80 mg/(m2·h)) for three biochar application treatments (T1, T2 and T3). However, there was no significant difference with CH4 cumulative emission between the treatments of biochar at 20 t/hm2 (T2) and 40 t/hm2 (T3) (P>0.05), implying that CH4 cumulative emission cannot decrease effectively by excessive biochar application (>20 t/hm2 for the purple clay soil in the Tai Lake region). N2O cumulative emission decreased significantly with biochar application (P<0.05), but there was no significant difference among the treatments with different biochar application rates (P>0.05). CH4 and N2O emission fluxes and cumulative emissions showed the similar changes according to the preliminary experiment results of 2014. In this experiment, considering the effect and cost comprehensively, biochar application amount at 20 t/hm2 could be a technical option to reach low carbon emission intensity and stable rice producitivity in the rice paddy agriculture. It also provided a viable way to realize the enhancement of carbon sequestration and the mitigation of greenhouse emissions in the Tiaoxi Watershed of Tai Lake region. [ABSTRACT FROM AUTHOR]