Long-term field experiment for exploring effects of Biochar on soil processes in winter wheat-summer maize cropping system in Northern China

In June of 2009, a long-term field experiment was conducted in the Shang-zhuang Experimental Station of China Agricultural University (CAU) at Haidian District, Beijing (N 40° 08′ 21″, E116°10′ 52″). The soil is calcareous fluvisol and the field located on an alluvial plain at an altitude of 51 m and a shallow groundwater level of 1-1.5 m. The region has a typical continental monsoon climate with an annual average air temperature of 11.6 °C and an annual average precipitation of 400 mm. The typical cropping system is winter wheat (from October each year to June of the following year) and summer maize (from June to September each year).

There are 6 treatments in the experiment: chemical fertilization with returned-straws both of wheat and maize was as experiment control (CK, or B0); 30, 60, and 90 t/ha Biochar were applied on the base of CK, coding as B30, B60, and B90; meanwhile, returning straw of wheat and maize but no chemical fertilizer (WM) and only wheat straw returning (W) were also as a treatment. After application of Biochar in June of 2009, all other agronomic practices were same as local real production way.

Although the field experiment is going on, we have got important conclusions till now, that are, (1) About 40% biochar lost from the 0-20 cm soil layer during the first 5 years after Biochar application; (2) No more than 25% biochar located in the aggregates >53 um in the 5^th year after Biochar application; (3) Biochar decreased the turnover of C in the returned-straw to SOC by 11% to 31% during the first 5 years after Biochar application, and the main decrease occurred from the wheat straw; (4) Biochar decreased soil labile organic carbon pool about 50%; (5) Priming effect caused by Biochar was positive during the first 3 years but negative during the 3 to 5 years after Biochar application; (6) Biochar decreased wheat-straw-derived SOC in larger aggregates, but accumulated more in smaller aggregates; (7) Biochar increased soil pedogenic carbonate content in the 0-20 cm soil layer during the 8 years after Biochar application; (8) Biochar amendment significantly increased subsoil pH (0.3−0.5 units) during the 10 years after biochar application; (9) The transported Biochar in subsoil acted as nuclei to precipitate pedogenic carbonate; (10) Biochar amendment enhanced soil inorganic carbon pool by up to 80% in the 2m soil profile. All these results have been published on international journals such as Science of the Total Environment, Soil Tillage Research, CATENA, Journal of Soils and Sediments, Journal of Integrative Agriculture, Agricultural Ecosystems & Environment, Soil Use Management, and Environmental Science & Technology.