喀斯特坡面表层土壤含水量、容重和饱和导水率的空间变异特征

表层土壤水分物理性质对深层土壤水分的动态变化具有重要的作用,研究其空间变化特征有助于深入理解坡地降雨入渗及产流规律,实现土壤水资源的合理利用.基于网格(10m×10 m)取样,用地统计学方法研究了桂西北喀斯特地区典型灌丛坡地90 m×120 m(投影长)表层(0~10 cm)土壤含水量、容重和饱和导水率的空间变异特征.结果表明:研究区土壤含水量、容重和饱和导水率均具有明显的空间依赖性和空间结构.土壤水分含量半变异函数用高斯模型模拟较好,土壤容重与饱和导水率用指数模型拟合较好.土壤含水量表现为强烈的空间自相关性,土壤容重和导水率表现为中等的空间自相关性.土壤含水量与饱和导水率空间连续性的尺度范围较小,而土壤容重空间连续性的尺度范围较大.总体上土壤含水量沿坡向下呈递增趋势,土壤容重呈递减趋势,而土壤饱和导水率沿坡面没有明显变化规律,斑块小而多,表现为高异质性.土壤含水量与土壤容重、饱和导水率均呈极显著负相关,而土壤容重与饱和导水率之间没有明显的相关性.     

有机物料对喀斯特地区石灰土有效N、Fe、Zn含量的影响

为研究不同有机物料对喀斯特石灰土元素有效性的影响,采用40 d的室内培养实验,比较了单独添加不同比例（1%、3%、5%）的生物质炭、鸡粪肥、羊粪肥对喀斯特石灰土有效N、Fe、Zn含量的影响。结果表明：添加生物质炭提高了喀斯特石灰土的pH值,而添加鸡粪肥和羊粪肥降低了喀斯特石灰土的pH值;添加3种有机物料均增加了喀斯特石灰土的有机质含量,大小关系为：生物质炭 > 鸡粪肥 > 羊粪肥,但添加鸡粪肥和羊粪肥土壤有机质的化学活性和微生物活性更高。受pH、有机质活性、碳氮比等因素的影响,添加鸡粪肥和羊粪肥能增加土壤有效N含量,但两种有机肥对土壤有效N的提高效果相差不大,而添加生物质炭反而降低了土壤有效N的含量;3种有机物料均能提高土壤的有效Fe和有效Zn含量,其中鸡粪肥效果最佳,其次为羊粪肥和生物质炭。当3种有机物料的添加比例为5%时,生物质炭处理土壤的有效N、Fe、Zn含量分别是对照处理的0.92、1.13、1.21倍;鸡粪肥处理土壤的有效N、Fe、Zn含量分别是对照处理的1.22、1.63和3.39倍;羊粪肥处理土壤的有效N、Fe、Zn含量分别是对照处理的1.27、1.34和2.59倍。所以,相对于生物质炭,有机粪肥对喀斯特地区的石灰土有更好的改良效果。     

生物质炭添加对红壤性水稻土重金属有效性及土壤质量的影响

通过田间定位试验探讨了不同生物质炭添加量对红壤性水稻土理化性质、重金属有效性和土壤质量的影响。生物质炭于2017年水稻种植前一次性添加于耕作层(0~17cm),分别设置5个不同处理:CK:0 t·hm^-2,A10:10 t·hm^-2,A20:20 t·hm^-2,A30:30t·hm^-2和A40:40 t·hm^-2,经种植两季水稻后于2018年9月采集耕作层(0~17 cm)和犁底层(17~29 cm)土壤,计算土壤质量指数(SQI),评价土壤质量。结果表明:在耕作层(0~17 cm)和犁底层(17~29 cm),随着生物质炭添加量的增加,土壤容重逐渐降低;土壤孔隙度、pH值、有机质和可溶性有机碳含量增加,铵态氮和有效磷分别在添加量为20和30 t·hm^-2时达到最大值;土壤中脲酶、过氧化氢酶和蔗糖酶的活性降低;生物质炭能够降低有效态Cd、As和Pb的含量,在生物质炭添加量为40 t·hm^-2时最低;在土壤耕作层(0~17cm),有效态Cd、As和Pb含量分别与脲酶、土壤pH值和蔗糖酶呈显著线性相关;在土壤犁底层(17~29 cm),有效态Cd、As和Pb含量分别与脲酶、过氧化氢酶和有效磷含量呈显著线性相关;各处理的SQI由高到低依次为A40>A30>A20>A10>CK,对应的指数值分别为0.641、0.638、0.579、0.533和0.464。这表明,红壤性水稻土的土壤质量在生物质炭添加量为40 t·hm^-2时,达到最佳。综上所述,生物质炭在添加第二年后,能够显著降低红壤性水稻土的有效态重金属含量,提高土壤质量。     

永定河流域官厅水库南岸典型林分土壤饱和导水率研究

为研究永定河流域官厅水库南岸生态水源保护林土壤饱和导水率(K_(fs))的特征,科学评价水源保护林功能,选取水源保护林典型林分与当地成林和非林地作对比,采用方差分析、相关分析和因子分析的方法研究土壤理化性质对饱和导水率的影响并根据因子得分排名探究土壤通透性最好的林分。结果表明:(1)土壤饱和导水率随土层深度增加而减小,水源保护林中混交林的饱和导水率大于纯林接近于成林,侧柏×山杏混交林的饱和导水率最高;(2)因子分析结果表明,影响饱和导水率最主要的因素为饱和含水量、容重和有机质含量;次重要因子为土壤砂粒、粉粒和粘粒含量,土壤毛管孔隙度和非毛管孔隙度对本区域饱和导水率影响不大;(3)综合因子得分排名分析,以侧柏×山杏混交林的土壤通透性最好,油松×山杏混交林次之。目前生态水源保护林对土壤通透性的改善优势明显,造林颇具成效。     

生物质炭添加对喀斯特地区坡耕地黄壤水分入渗过程的影响

为探究生物质炭添加对喀斯特地区土壤水分入渗特性的影响,本研究以坡耕地黄壤为对象,采用室内土柱模拟的方法,研究不同添加量(质量分数为0、1%和2%)和不同粒径(粒径大小为<0.25、0.25～1和>1 mm)生物质炭添加下土壤水分累计入渗量、入渗速率及湿润锋进程的变化特征,并对入渗过程进行模拟。结果表明: 在定容重条件下,添加生物质炭后土壤的入渗过程明显受到抑制,添加生物质炭土壤的累计入渗量和入渗速率显著低于未添加生物质炭土壤,生物质炭添加量为1%和2%土壤的累计入渗量和入渗速率无显著差异。不同粒径生物质炭添加下,土壤累计入渗量从大到小依次表现为<0.25、0.25～1和>1 mm。与CK相比,当添加量为1%时,土壤300 min累计入渗量分别下降20.9%、35.2%和45.0%;当添加量为2%时,分别下降21.5%、37.5%和44.2%,说明大粒径生物质炭对土壤入渗的抑制作用显著强于小粒径生物质炭。土壤湿润锋进程对不同含量和不同粒径生物质炭添加的响应趋势与累计入渗量的变化趋势基本一致。Horton和Kostiakov模型能够用于模拟本研究中的土壤水分入渗过程,Horton模型拟合精度高,R²最大(0.91～0.98),均方根误差(RMSE)最小(0.14～0.21),而Kostiakov模型拟合得到的初始入渗速率更接近实测结果。研究结果可为生物质炭的合理施用提供科学依据,也可为喀斯特坡耕地土壤改良和水土保持提供有益参考。     

施用生物质炭对红壤中硝态氮垂直运移的影响及其模拟

为研究在红壤中施用生物质炭后硝态氮的垂直运移规律,采用室内土柱模拟的方法,分别按照炭土比为0、2.22%(5 t·hm^-2)、4.45%(10 t·hm^-2)、8.95%(20 t·hm^-2)、13.37%(30 t·hm^-2)和17.80%(40 t·hm^-2)设置混合土壤,并采用CXTFIT 2.0模型对试验结果进行拟合.结果表明： 在饱和条件下,不同生物质炭添加比例下,硝态氮运移的穿透曲线发生明显变化.不同处理的硝态氮相对浓度(C/C_o)峰值、淋溶速率和累积淋失量随生物质炭添加量的增加而显著降低.各穿透曲线尾部均存在一定的拖尾现象,且随生物质炭添加量的增加拖尾现象越显著.对硝态氮穿透曲线的影响因素分析可知,生物质炭影响了土壤的容重、有机碳、孔隙度、阳离子交换量(CEC)等物理性质,进而导致各处理硝态氮穿透曲线发生了变化.采用CXTFIT 2.0数学模型模拟硝态氮在土壤中的运移,硝态氮的穿透曲线拟合值与实测值呈显著正相关,相关系数均>0.850,能够很好地对土壤硝态氮运移和运移参数进行预测,试验结果可为预测生物质炭施用对地下水体环境硝态氮的影响提供科学依据.     

生物质炭添加对毛竹林土壤呼吸动态和温度敏感性的影响

为探讨生物质炭添加对森林原位土壤呼吸动态及温度敏感性的影响,于2014年5月至2016年4月对浙江省杭州市富阳区庙山坞林区毛竹(Phyllostachys edulis)林进行了为期两年的生物质炭添加试验,生物质炭施加量分别为0(CK)、5(LB)、10(MB)和20 t·hm~(–2)(HB)。利用LI-8100土壤碳通量系统测定土壤呼吸速率时空动态。结果表明:添加生物质炭会降低毛竹林土壤呼吸速率且呈现明显的季节动态,土壤呼吸速率在6–7月最高(林分1中LB处理除外),1月或2月最低,添加生物质炭对毛竹林土壤呼吸的影响显著;CK、LB、MB和HB处理的年平均土壤呼吸速率分别为3.32、2.66、3.04和3.24μmol·m~(–2)·s~(–1);与对照相比,LB、MB和HB处理下年平均土壤呼吸速率分别降低2.33%–54.72%、1.28%–44.21%和0.09%–39.22%。添加生物质炭使LB、MB、HB处理的土壤水分含量分别增加了0.97%–75.58%、0.87%–48.18%和0.68%–74.73%。土壤呼吸速率与5 cm土壤温度呈现显著的指数相关关系,与5 cm土壤水分含量没有显著相关性,但与温度和水分呈显著相关关系。生物质炭添加影响土壤呼吸温度敏感性,LB、MB处理明显增加土壤温度敏感性。LB、MB和HB处理下年平均累积土壤呼吸CO_2排放分别降低7.98%–35.09%、1.48%–20.63%和–4.71%–7.68%。添加生物质炭显著降低毛竹林土壤碳排放和土壤温度敏感性,对缓解气候变化具有一定意义。     

苹果酸和草酸对两种植物吸收土壤中Cd、Zn 的影响

向受Cd、Zn 复合污染土壤中添加5.51、11.0、16.5 mmol·kg^–1(干土)苹果酸和草酸, 研究天然小分子有机酸对土壤Cd、Zn 的形态转化及小飞扬草(Euphorbia thymifolia L.)和三叶鬼针草(Bidens pilosa L.)积累Cd、Zn 的影响。结果显示: 添加苹果酸、草酸处理, 土壤中酸提取态Cd、Zn 含量比对照分别增加0.13%-1.30%、4.25%-13.4%, 有机酸对土壤中Cd 和Zn 有一定的活化作用。苹果酸和草酸促进小飞扬草和三叶鬼针草对目标重金属的积累、强化效果: 苹果酸≈草酸。添加11.0 mmol·kg^–1 苹果酸处理使小飞扬草对Cd+Zn 的总积累量达63.9 mg·kg^–1, 添加11.0 mmol·kg^–1 草酸处理使三叶鬼针草对Cd+Zn 的总积累量达128mg·kg^–1。有机酸促进三叶鬼针草向地上部转运Cd 和Zn, 促进小飞扬草向地上部转运Cd, 仅添加11.0 mmol·kg^–1 苹果酸、草酸和添加16.5 mmol·kg^–1 草酸处理促进小飞扬草向地上部转运Zn。有机酸处理下, 小飞扬草和三叶鬼针草地上部Cd 含量与地上部Zn 含量显著正相关, 相关系数分别为0.533 和0.813。添加一定浓度的有机酸可以活化土壤重金属, 促进植物地上部对Cd、Zn 的富集, 提高植物对重金属的积累, 加快重金属污染土壤的修复。     

花岗岩崩岗不同部位土壤饱和导水率特征及其影响因素

崩岗是我国南方花岗岩丘陵区普遍存在的水力-重力复合土壤侵蚀现象。为探究崩岗的土壤水力学性质与侵蚀机理的内在联系及其与影响因素之间的关系,选择桂东南活动型、半稳定型和稳定型3种花岗岩崩岗为对象,研究不同部位土壤饱和导水率的空间变化及其影响因素。结果表明:1)崩岗土壤饱和导水率在不同部位呈波动分异,其中崩壁中部为最小值,崩积堆上部为最大值,其次为洪积扇顶端。2)选取Cosby、Compbell、Julià、Hypre 4种土壤饱和导水率传递函数对该区土壤饱和导水率进行拟合,结果预测值与实测值均存在偏差。3)相关性分析表明,土壤饱和导水率与毛管孔隙度、黏粒含量呈极显著负相关关系,与非毛管孔隙和砂粒含量呈极显著正相关关系。4)通径分析表明,砂粒含量为崩岗土壤饱和导水率的主要影响因素,其次为非毛管孔隙度和土壤容重,其中砂粒含量与非毛管孔隙度对土壤饱和导水率呈正效应,容重呈负效应。研究结果可为揭示崩岗侵蚀机理和防治提供理论依据。     

丛枝菌根真菌和生物质炭对连作西瓜土壤肥力的影响

【背景】作为土壤改良剂生物质炭能够改善土壤条件,促进丛枝菌根(arbuscular mycorrhizal,AM)真菌侵染和植物生长发育。【目的】探究接种AM真菌配合施加生物质炭对连作土壤肥力和西瓜生长的效应。【方法】盆栽‘圆佳’西瓜(Citrullus lanatus)嫁接苗[砧木为‘全能铁甲’南瓜(Cucurbita maxima×C. moschata)],栽培基质为西瓜连作土壤,试验设接种或不接种AM真菌变形球囊霉(Glomus versiforme)并施加0%、1%、2%和4%的生物质炭,共8个处理,测定土壤理化特性、土壤酶活性、土壤微生物数量和植株生长量。【结果】接种AM真菌并施加生物质炭,可显著促进土壤大颗粒团聚体的形成和有机质的矿化,稳定土壤pH,增加土壤细菌和放线菌数量,降低真菌数量,提高土壤蔗糖酶、过氧化氢酶和脲酶的活性,活化土壤矿质养分,最终促进西瓜植株的生长发育。其中,以接种变形球囊霉并施加2%?4%生物质炭组合的效应最大。两者互作在一定程度上提高了连作土壤的pH、饱和含水量及孔隙度,降低了土壤容重,有利于土壤大颗粒团聚体的形成,提高了土壤酶活性,改善了根围土壤微生物组成。【结论】 AM真菌接种配合施加2%?4%的生物质炭可以显著改善连作土壤的肥力状况。     

Effectiveness of biochar and compost on improving soil hydro-physical properties,crop yield and monetary returns in inceptisol subtropics

Organic manures in combination with biochar might improve efficacy of biochar in improving soil functions related to hydro-physical properties and a field experiment was conducted over the course of two years with two levels of biochar @ 0 and 2tha⁻¹ and four levels of compost (100% recommended dose of N through farm yard manure, 100% recommended dose of N through vermicompost, 50% recommended dose of N through farm yard manure, and vermicompost each, and unfertilized control). Each treatment was replicated three times in factorial randomized block design (RBD). The objective of this research was to determine the effects of biochar and compost on soil hydro-physical properties, water use efficiency, monetary returns and yield of knolkhol (Brassica oleracea var. gongyloides L.) under sub-tropics of North West India. Compared with no-biochar, application of biochar significantly increased knolkhol yield by 7.8% and soil properties (infiltration rate, aggregate stability, maximum water holding capacity and hydraulic conductivity). Similarly, integration of compost significantly enhanced the soil water retention, aggregate stability, hydraulic conductivity and crop yield and gave highest infiltration rate, water retention, hydraulic conductivity and crop yield under M3 (50 % N through farm yard manure, +50 % N through vermicompost) treatment. Furthermore, synergetic positive effect of biochar and compost were noted for soil infiltration rate (4–38%), water retention (0.9–13.7%), aggregate stability (6–10.7%) and yield (6–11.9%) over the sole application of compost. Combined use of farm yard manure, and vermicompost accompanied by biochar resulted in highest net returns and B:C ratio. Biochar in combination with farm yard manure, and vermicompost can enhance soil hydraulic properties resulting in increased crop yield and maximum monetary returns under subtropical conditions.     

施用生物炭和聚丙烯酰胺对海涂围垦区盐碱土水力性质的影响

通过圆盘入渗试验,探讨不同改良剂施用量下土壤入渗特性的变化,揭示添加生物炭和聚丙烯酰胺(PAM)对海涂围垦区盐碱土水力学参数、孔隙特征及不同级别孔隙水流贡献率的影响.结果表明: 单施2%生物炭,土壤饱和导水率比对照增加46.4%;盐碱土饱和导水率随PAM施用量增加而减小.单施2%生物炭使土壤总有效孔隙度和半径>100 μm的有效孔隙度分别增加8.3%和10.2%.单施PAM时,土壤总有效孔隙度和不同半径孔隙有效孔隙度均有减小趋势,其中,PAM梯度为1‰时最明显,减幅高达88%以上.施用生物炭和PAM后,半径<100 μm的孔隙的水流贡献率呈下滑趋势,半径>500 μm的孔隙对土壤水流运动起主导作用.     

海涂土壤结构改良对水稻叶绿素荧光参数和产量的影响

为探索添加生物炭和聚丙烯酰胺(PAM)改良海涂围垦区土壤结构对水稻叶片叶绿素荧光特性和产量的影响,开展测坑栽培试验.试验供试土壤分别设置3个水平生物炭(0%、2%、5%,分别表示为B₁、B₂和B₃,占表层0~20 cm土重比)和PAM(0‰、0.4‰、1‰,分别表示为P₁、P₂和P₃,占表层0~20 cm土重比)添加量处理.3年试验结果表明: 添加适宜生物炭和PAM有利于改善水稻叶片荧光特性,而高浓度生物碳和PAM对其影响不明显,甚至出现抑制现象.各生育期水稻叶片最大光化学量子产量(F_v/F_m)、实际量子产量(Φ_PSⅡ)、光化学淬灭(q_P)和非光化学淬灭(NPQ)均在B₂P₂组合处理下达到峰值.生物炭添加量处理间水稻叶片叶绿素量(SPAD值)无明显差异,而PAM添加量不同导致水稻叶片SPAD值差异显著,添加0.4‰PAM(P₂)下水稻叶片SPAD值最高.添加生物炭和PAM改良盐渍土对水稻产量影响显著,在B₂P₂组合处理下产量最高,达到7236 kg·hm^-2;与对照组(B₁P₁)相比,产量提高了28.5%.添加生物炭和PAM改良海涂盐渍土对水稻产量的影响主要是通过对水稻千粒重、每穴穗数、每穗粒数和结实率的影响而实现的.添加适量生物炭和PAM改良滩涂围垦区土壤结构有利于提高水稻叶绿素荧光特性和产量.     

蚯蚓堆肥与生物炭对瓜草复合系统土壤及植株的影响研究

为探究蚯蚓堆肥与生物炭对西瓜-白三叶草生境系统的作用机制,采用温室栽培试验,设置空白对照（西瓜植株）、生物炭、覆盖三叶草、蚯蚓堆肥、覆盖三叶草+蚯蚓堆肥、生物炭+蚯蚓堆肥、覆盖三叶草+生物炭和覆盖三叶草+生物炭+蚯蚓堆肥8个处理,比较分析蚯蚓堆肥与生物炭对西瓜-白三叶草复合系统的土壤养分、微生物群落结构与主栽作物西瓜代谢组学特征。结果表明：(1)复合处理下,土壤容重降低,肥力提高,西瓜植株对氮、磷、钾养分的吸收能力增强,覆盖三叶草+生物炭+蚯蚓堆肥处理（WBV）处理综合表现最优;(2)WBV处理中微生物菌群丰富度下降,Shannon指数、Chao 1指数排序为BV＞WB＞CK＞WV＞WBV处理,与对照相比,WBV处理土壤中微生物菌群放线菌门（Actinobacteria）、变形菌门（Proteobacteria）、厚壁菌门（Firmicutes）细菌以及被孢霉门（Mortierellomycota）真菌的相对丰度明显提升,而绿弯菌门、酸杆菌门和芽单胞菌门的相对丰度下降;(3)WBV处理西瓜果肉中检测到亚麻酸（alpha-linolenic acid）、裂解型磷脂酰胆碱(17:0)（LysoPC(17:0)）、磷酰肌醇酸(18:1(11Z)/0:0)（CPA(18:1(11Z)/0:0)）等脂质化合物,以及丙氨酸、天冬氨酸与谷氨酸等氨基酸。研究发现,覆盖三叶草+生物炭+蚯蚓堆肥复合系统可显著提高速效氮、速效磷,速效钾等土壤营养含量,促进西瓜对氮、磷元素的吸收,改善土壤微生物环境,改变西瓜植株脂质、有机酸及氨基酸的代谢水平,提升西瓜植株生物膜受保护能力和细胞渗透调节能力,增强其抗逆能力。     

施用生物炭基肥对喀斯特石灰土磷元素特性的影响

以贵州省喀斯特山地石灰土为研究对象,采用盆栽试验方法,研究施用生物炭(稻壳炭)、猪粪堆肥和NPK肥3种肥料制成的生物炭基肥,测定土壤中不同形态磷含量、碱性磷酸酶活性及刺槐幼苗生物量。试验共设10个处理,分别为CK、M、F、MF、RH1MF、RH2MF、RH4MF、RH8MF、RH4M、RH4F(其中CK代表对照,M代表堆肥,F代表化肥,RH代表稻壳炭,数字代表生物炭按炭土质量比计算在生物炭基肥中的配比)。结果表明,施用生物炭基肥可显著提高喀斯特石灰土中总磷、有效磷、有机磷、微生物量磷含量及刺槐幼苗生物量,生物炭高施用量下处理(RH8MF)的效果更好,且4种不同形态的磷含量相互之间呈极显著正相关(P0.01);生物炭中等用量配比下生物炭基肥处理(RH2MF、RH4MF)的土壤碱性磷酸酶活性最高,分别比CK提高82.7%、63.4%。综上所述,施用生物炭基肥,尤其在生物炭较高施用量下,可以显著改善喀斯特石灰土中磷素含量,可改善石灰土中磷素含量较低状况,提高喀斯特山地人工幼林地生态恢复的成效。     

Effects of compost produced from town wastes and sewage sludge on the physical properties of a loamy and a clay soil

Organic fertilizer produced by composting 62% town wastes, 21% sewage sludge and 17% sawdust by volume, was applied at the rates of 0 (control), 75, 150 and 300 m³ ha⁻¹ to loamy and clay soils, in order to investigate its potential for soil improvement. The experiments were conducted in areas characterised by a semi-arid climate. The chemical properties of the soils were affected directly by the amendment compost. The physical properties of the amended soils were improved in all cases as far as the saturated and unsaturated hydraulic conductivity, water retention capacity, bulk density, total porosity, pore size distribution, soil resistance to penetration, aggregation and aggregate stability, were concerned. In most of the cases the improvements were proportional to the application rates of the compost and they were greater in the loamy soil than in the clay soil.     

Influence of biochar and compost on phytoremediation of oil-contaminated soil

The use of pyrolyzed carbon, biochar, as a soil amendment is of potential interest for improving phytoremediation of soil that has been contaminated by petroleum hydrocarbons. To examine this question, the research reported here compared the effects of biochar, plants (mesquite tree seedlings), compost and combinations of these treatments on the rate of biodegradation of oil in a contaminated soil and the population size of oil-degrading bacteria. The presence of mesquite plants significantly enhanced oil degradation in all treatments except when biochar was used as the sole amendment without compost. The greatest extent of oil degradation was achieved in soil planted with mesquite and amended with compost (44% of the light hydrocarbon fraction). Most probable number assays showed that biochar generally reduced the population size of the oil-degrading community. The results of this study suggest that biochar addition to petroleum-contaminated soils does not improve the rate of bioremediation. In contrast, the use of plants and compost additions to soil are confirmed as important bioremediation technologies.     

Efficiency of different types of biochars to mitigate Cd stress and growth of sunflower (Helianthus; L.) in wastewater irrigated agricultural soil

Cadmium contamination in croplands is recognized one of the major threat, seriously affecting soil health and sustainable agriculture around the globe. Cd mobility in wastewater irrigated soils can be curtailed through eco-friendly and cost effective organic soil amendments (biochars) that eventually minimizes its translocation from soil to plant. This study explored the possible effects of various types of plants straw biochar as soil amendments on cadmium (Cd) phytoavailability in wastewater degraded soil and its subsequent accumulation in sunflower tissues. The studied biochars including rice straw (RS), wheat straw (WS), acacia (AC) and sugarcane bagasse (SB) to wastewater irrigated soil containing Cd. Sunflower plant was grown as a test plant and Cd accumulation was recorded in its tissues, antioxidant enzymatic activity chlorophyll contents, plant biomass, yield and soil properties (pH, NPK, OM and Soluble Cd) were also examined. Results revealed that addition of biochar significantly minimized Cd mobility in soil by 53.4%, 44%, 41% and 36% when RS, WS, AC and SB were added at 2% over control. Comparing the control soil, biochar amended soil effectively reduced Cd uptake via plants shoots by 71.7%, 60.6%, 59% and 36.6%, when RS, WS, AC and SB. Among all the biochar, rice husk induced biochar significantly reduced oxidative stress and reduced SOD, POD and CAT activity by 49%, 40.5% and 46.5% respectively over control. In addition, NPK were significantly increased among all the added biochars in soil–plant system as well as improved chlorophyll contents relative to non-bioachar amended soil. Thus, among all the amendments, rice husk and wheat straw biochar performed well and might be considered the suitable approach for sunflower growth in polluted soil.     

Performance of subsurface flow constructed wetland taking pretreated swine effluent under heavy loads

Subsurface flow constructed wetlands (SSFCW) subjected to changing of loading rates are poorly understood, especially when used to treat swine waste under heavy loads. This study employed a SSFCW system to take pretreated swine effluent at three hydraulic retention times (HRT): 8.5-day HRT (Phase I), 4.3-day HRT (Phase II), and 14.7-day HRT (Phase III). Results showed that the system responded well to the changing hydraulic loads in removing suspended solids (SS) and carbonaceous oxygen demands. The averaged reduction efficiencies for four major constituents in the three phases were: SS 96-99%, chemical oxygen demand (COD) 77-84%, total phosphorus 47-59%, and total nitrogen (TN) 10-24%. While physical mechanisms were dominant in removing pollutants, the contributions of microbial mechanisms increased with the duration of wetland use, achieving 48% of COD removed and 16% of TN removed in the last phase. Water hyacinth made only a minimal contribution to the removal of nutrients. This study suggested that the effluent from SSFCW was appropriate for further treatment in land applications for nutrient assimilation.     

Effects of microplastics and biochar on soil cadmium availability and wheat plant performance

Biochar is a promising amendment to promote cadmium (Cd) sorption and fixation in agricultural soil, where microplastics are emerging contaminants in soil. Herein, a greenhouse pot experiment was conducted to elucidate the effects on Cd availability in a soil–plant system by biochar and fresh/aged microplastics application. The fresh microplastics led to an obvious increase in soil Cd availability and Cd uptake by wheat plant, while the aged microplastics increased the available Cd in soil but had no effect on Cd uptake by wheat plant, which was likely attributed to the blocking effect of the aged microplastics on Cd transportation from the soil to the wheat plant. Unexpectedly, biochar had increased Cd availability and Cd uptake. The increased soil soluble Cd was because of both decreased soil pH and elevated dissolved organic matter (DOM) content resulted by biochar addition. Also, the unchanged Cd adsorption of the soil was likely responsible for the increased tested soil Cd availability. In addition, the combined effects of a greater decrease in soil pH, an increase in soil DOM content, and a reduction in Cd adsorption after the addition of microplastics to biochar-amended soil resulted in a significant increase (ranging from 2.63% to 47.73%) in Cd availability compared to soil treated with biochar alone. Moreover, fresh microplastics inhibited wheat growth, and greater inhibition effect was observed for their aged ones. The biochar elevated the wheat biomass; however, the coexistence of microplastics and biochar decreased the wheat plant biomass compared with biochar alone, due to the negative influence of microplastics in plant growth.