秸秆生物炭对可变电荷土壤表面电化学性质的影响及磷肥增效作用及其机制

Large areas of variable charge soils are distributed in tropical and subtropical regions of southern China. Generally, soil acidification and Al/Mn toxicity in this area is serious due to intensive weathing and leaching processes. In addition, low nutrient-retaining capacities, low contents of organic matter and phosphorus (P) utilization efficiency in these soils lead to their critical food productivity. Recent studies indicated that crop straw biochars can ameliorate soil acidity and improve soil CEC, and finally increase crop yields. However, little information is available on the impact of biochars on the surface electrochemcial properties of variable charge soils and P utilization efficiency. In this project, variable charge soils collected from southen China and biochars derived from different crop straws, will be used to investigate the impact of biochars on surface electrochemical properties of variable charge soils. The interaction of crop straw biochars with these soils and the effects of biochars on positive charge, negative charge and zero point of charge (ZPC) of the soils and their colloids will be examined with batch experiments. The electrokinetic potential and isoelectric point (IEP) of the bulk soils and the soil colloids, the overlapping of the electrical double layer between oppositely charged soil particles in presence and absence of biochars will be compared. Furthermore, the effect of the crop straw biochars on adsorption of P by these soils, along with P species distributions in the amended soils will be examined. Based on these theoretical propositions, a series of pot and field experiments will be conducted to investigate the effects and involved mechansisms of biochars on enhancing the chemical activity as well as biological availability of P in the soils. The achievements of this project will provide references for improving the physical-chemical properties of highly weathered soils, increasing the bioavailibility and utilization efficiency of P in tropical and subtropical regions of China.

我国南方热带和亚热带地区分布着大面积的可变电荷土壤，由于遭受强烈风化淋溶，这类土壤酸化、铝锰毒害严重，有机质、阳离子交换量（CEC）低，磷肥利用率差，因此土壤生产力水平低下。研究发现添加秸秆炭可以改良土壤酸度，提高土壤CEC，增加作物产量，然而生物质炭影响土壤表面电化学性质及磷肥利用率的研究很少。本项目拟选择南方典型可变电荷土壤，研究秸秆生物炭对土壤表面电化学性质的影响：生物质炭与土壤颗粒表面作用机制，对土壤表面正、负电荷量、电荷零点（ZPC）的影响，以及生物质炭对原土和胶体动电电位和等电点（IEP）及土壤颗粒双电层重叠作用的影响；进而评估生物质炭对磷在可变电荷土壤表面吸附和赋存形态的影响。在这些理论研究的基础上，结合盆栽与田间小区实验，阐明生物质炭提高磷在可变电荷土壤中的化学活性和生物有效性的机制。本研究可为通过生物质炭改善南方可变电荷土壤的理化性质，提高磷肥有效性和当季利用率提供依据。

磷（P）是作物生长必需的大量元素，我国南方热带和亚热带地区分布着大量酸性可变电荷土壤，这类土壤富含铁铝氧化物，P肥利用率（PUE）较低。秸秆生物炭可提高土壤pH，缓解植物铝毒，改良酸化土壤，但是秸秆生物炭提高这类土壤PUE，改善供P状况效果如何，以及其中所涉及的机制尚不明确。.本项目针对以上问题开展研究，发现：氯化铵替代Mehlich 3（改进M3）法作为可以测定各类土壤，尤其是生物炭改良红壤中有效磷（AP）含量的方法，证明添加生物炭可以显著提高改良红壤中AP水平。.添加秸秆生物炭可以提高P在安徽和广东红壤中的有效性。吸附解吸热力学实验结果表明，外源P浓度为2 mM时，添加稻草（RB）和大豆秸秆炭（SB）使安徽红壤P吸附量从20.37 mmol kg-1分别降低到18.55和18.38 mmol kg-1；使广东红壤的吸附量从31.65 mmol kg-1分别降低到28.65和24.81 mmol kg-1。因此，土壤固P能力下降，P有效性提高。搅流池吸附动力学实验中，280 min解吸试验结束时，添加RB和SB处理的安徽红壤对P解吸量分别提高了21.05%和0.55%；对广东红壤P解吸量分别提高24.39%和44.83%。另外，随着RB和SB的加入，改良土壤P饱和度（DPS）明显增加。.秸秆生物炭可以促进水稻生长，提高土壤PUE。与安徽和云南红壤相比，添加秸秆生物炭提高了安徽和云南土壤的pH、电导率，氮、P、钾含量，水稻植株的生物量和PUE。譬如，添加生物炭使安徽红壤和云南红壤的水稻植株生物量分别增加1.22–47.05%和37.53–57.57%。而2%的花生生物炭提高PUE效果最佳，使安徽和云南红壤PUE分别增加了24.70和5.07倍。.秸秆生物炭同样可以提高旱地土壤PUE，促进玉米生长。盆栽实验结果表明，来自不同作物秸秆的生物炭显著提高红壤和砖红壤CEC，增加土壤表面对磷酸根的排斥力，同时生物炭表面酸性官能团与磷酸根竞争土壤表面吸附位点，提高磷回收率。但形成不溶性的Ca-P和Mg-P降低了磷的回收率。较低Ca2+和Mg2+含量的稻草生物炭比油菜和花生秸秆生物炭更明显提高磷回收率。因此，施用秸秆生物炭可以提高可变电荷土壤PUE。