田间陈化生物质炭提高稻田土壤团聚体稳定性和磷素利用率

  【目的】  生物质炭因其巨大的比表面积和稳定的结构而被用作土壤改良剂。然而关于田间陈化生物质炭对土壤肥力和养分利用效率影响的研究相对缺乏。通过定位试验，分析田间不同陈化年限的生物质炭对水稻产量和养分利用效率的影响。  【方法】  田间定位试验设在江苏南京，供试土壤为粘质水稻土。共设置5个处理，分别是不施磷肥对照 (CK)、施用磷肥 (P) 及磷肥配施新鲜生物质炭 (PB_0y，2017年施入)、2年陈化生物质炭 (PB_2y，2015年施入) 和5年陈化生物质炭 (PB_5y，2012年施入)。在水稻收获后采集土壤样品进行团聚体分级，测定大团聚体 (250～2000 μm)、微团聚体 (53～250 μm)、粉粒 (2～53 μm)、粘粒 (< 2 μm) 含量以有效磷含量和基本理化性质，同时测定水稻产量和磷素利用效率。  【结果】  与P处理相比，PB_2y和PB_5y处理显著提高250～2000 μm大团聚体的比例 (69.2%～107.8%) ，降低2～53 μm粉粒 (13.1%～14.7%) 和 < 2 μm粘粒 (6.9%～41.9%) 的比例，而PB_0y与P处理相比各粒级比例均无显著差异；PB_0y、PB_2y和PB_5y处理土壤有机碳 (SOC) 提高了18.5%～58.5%，全磷含量提高了5.7%～17.1%，但2～53 μm粒级SOC含量无显著差异。与P处理相比，PB_0y处理对水稻产量和磷素利用效率影响不显著，PB_2y和PB_5y处理均可显著提高水稻产量 (13.7%和16.3%) 和磷素利用率 (35.4%和45.5%)。由结构方程模型可知，陈化生物质炭 (PB_2y和PB_5y) 通过改善土壤养分状况 (SOC、全磷含量、碳磷比等) 和土壤结构 (250～2000 μm大团聚体比例增加)，保证了水稻产量和磷储量。  【结论】  与新鲜生物质炭相比，陈化生物质炭可有效增加250～2000 μm大团聚体比例以及土壤有效磷和全磷的保护，从而促进植物对磷的吸收利用，达到增加产量和磷素利用效率的目的。5年陈化生物质炭的改良效果好于2年陈化生物质炭。

Field-aged biochar improves soil aggregation stability and phosphorus use efficiency in paddy field

  【Objectives】  Biochar has been widely used as soil amendment because of its large surface area and stable structures. However, the long-term effects of field-aged biochar on soil fertility and nutrient availability are relatively lacking. Therefore, we compared the effects of field-aged biochars at different years on rice crop yield and nutrient use efficiencies through in situ long-term field experiments.  【Methods】  The long-term field experiment was established in Nanjing, Jiangsu, which belongs to clayey paddy soil. Five treatments were carried out in triplicates as following: control without phosphate fertilizer (CK), phosphate fertilizer (P), P with fresh biochar amended in 2017 (PB_0y), P with 2-year field-aged biochar amended in 2015 (PB_2y) and with 5-year field-aged biochar amended in 2012 (PB_5y). Soil samples were collected after rice harvest, and the contents of soil aggregate size classes of macro-aggregate (MacroA, 250–2000 μm), micro-aggregate (MicroA, 53–250 μm), silt fraction (SiltF, 2–53 μm) and clay fraction (ClayF, < 2 μm), available P content and basic physicochemical properties were measured. The rice yields and P uptake by rice were determined.  【Results】  The PB_2y and PB_5y treatments significantly increased the content of MacroA (250–2000 μm) by 69.2%–107.8%, decreased that of SiltF (2–53 μm) by 13.1%–14.7% and ClayF (<2 μm) by 6.9%–41.9%, while PB_0y did not, compared with the P treatment. The PB_0y, PB_2y and PB_5y treatments significantly increased SOC by 18.5%–58.5% and total P by 5.7%–17.1%, but did not significantly increased in SOC content of 2–53 μm fraction, compared to the P treatment. Similarly, both the PB_2y and PB_5y treatments significantly increased rice yield by 13.7% and 16.3% and phosphorus use efficiency by 35.4% and 45.5%, respectively, while PB_0y did not, compared to the P treatment. Based on the structural equation modeling, the field-aged biochar (PB_2y and PB_5y) increased the rice yield and P storage by improving soil nutrient status (SOC, TP, SOC/TP, etc.) and structure (increasing the ratio of soil MacroA).  【Conclusions】  As compared to the fresh biochar amendment, the field-aged biochar at different years effectively increased the ratio of soil macro-aggregates of 250–2000 μm and the protection of soil available phosphorus and total phosphorus, thus facilitating the absorption and utilization of phosphorus by plants and improving yield and phosphorus use efficiency. The improvement effects of field-aged biochar at 5-year is greater than field-aged biochar at 2-year.