稻草等有机物料腐解过程中酚酸类化合物的动态变化

采用湿润好气培养法 ,研究稻草等有机物料腐解过程中酚酸类化合物的动态变化。结果表明 ,稻草、锯木屑、猪粪均含有对羟基苯甲酸、香豆酸、阿魏酸等酚酸化合物。稻草、猪粪中香豆酸含量最高 ,阿魏酸次之 ;木屑中对羟基苯甲酸含量最高 ,香豆酸次之。稻草、猪粪在腐解过程中生成酚酸化合物主要是香豆酸和阿魏酸 ,木屑主要是对羟基苯甲酸和香豆酸 ;三种有机物料中酚酸化合物总量表现为稻草 >猪粪 >木屑 ,在腐解 2 0～ 30天时酚酸量为最高 ,40～ 5 0天时基本稳定 ,酚酸量为最少     

强还原处理配施枯草芽孢杆菌对百合土壤酚酸的影响

为研究不同有机物料强还原土壤处理(Reductive Soil Disinfestation, RSD)及枯草芽孢杆菌施用对土壤酚酸类物质的影响，以龙牙百合栽培土壤为研究对象，采用裂区试验设计，主区设置对照(CK)和以制糖发酵废液(MO)、植物残渣(SB)为主要有机物料的RSD处理，并于再植龙牙百合出苗后裂区添加枯草芽孢杆菌Y25(CK＿Y25、MO＿Y25、SB＿Y25)，分别在RSD处理后及龙牙百合生长期和收获期采集土壤样品，分析土壤中酚酸类物质的组成和含量变化。结果表明：与CK相比，SB处理显著(P<0.05)增加了土壤中丁香酸、对香豆酸、阿魏酸和总酚酸的含量，改变了土壤酚酸谱特征，而MO处理对土壤酚酸组成和含量的影响均不显著。龙牙百合再植能够提高RSD处理土壤中酚酸类物质含量，但不同处理随种植时间延长而呈现不同的变化规律。此外，添加枯草芽孢杆菌Y25能显著(P<0.05)降低SB处理土壤中酚酸类物质的含量(总酚酸降解率≥30%)，其中对香豆酸和阿魏酸在龙牙百合生长期和收获期的降解率分别高达39.2%～47.8%和32.3%～36.7%。本研究发现，以植物残渣为有机物...     

蒸汽爆破处理对麦麸的酚酸组成及其抗氧化活性的影响

该试验旨在研究蒸汽爆破处理对小麦麸皮的酚酸组成及抗氧化活性的影响.将麦麸在不同处理压力(0.5,1.5,2.5 MPa)和不同处理时间(30,90 s)条件下进行蒸汽爆破预处理.通过水解和碱提的方法,将得到的麦麸进行提取,得到游离酚酸和结合酚酸2部分,对其中的几种主要酚酸,如香草酸、丁香酸,4-香豆酸,阿魏酸进行研究.结果表明,4种主要酚酸的含量在蒸汽爆破处理后均有所提高,其中阿魏酸的含量最高,结合酚酸中由未处理时的57.232μg/g提高到了1454.092 μg/g.该试验还进行了总酚测定,抗氧化活性的测定.通过总酚的测定可以看出,蒸汽爆破处理后,总酚的含量高于未处理麦麸,且随着处理强度的增加,呈现先增加后减少的趋势,在处理条件为2.5 MPa,30 s,总酚含量最高,约为未处理时的9倍.抗氧化试验得到的变化趋势与总酚呈现相似的规律,与未进行蒸汽爆破预处理的麦麸相比,处理后的麦麸表现出了更高的1,1-二苯基-2-三硝基苯肼(DPPH)和2,2-联氮-二(3-乙基-苯并噻唑-6-磺酸)二铵盐(ABTS)自由基清除率,以及在亚油酸体系中的抗氧化活性和还原能力.当处理条件为2.5 MPa,30 s时,抗氧化活性表现最高.由此可得到,2.5 MPa 30s是蒸汽爆破处理麦麸的最佳条件,此时麦麸中酚酸含量和抗氧化活性均较优,为以后麦麸中酚类物质的深度开发利用提供理论支持.     

蒸汽爆破处理对麦麸的酚酸组成及其抗氧化活性的影响（英文）

该试验旨在研究蒸汽爆破处理对小麦麸皮的酚酸组成及抗氧化活性的影响。将麦麸在不同处理压力(0.5,1.5,2.5 MPa)和不同处理时间(30,90 s)条件下进行蒸汽爆破预处理。通过水解和碱提的方法,将得到的麦麸进行提取,得到游离酚酸和结合酚酸2部分,对其中的几种主要酚酸,如香草酸、丁香酸,4-香豆酸,阿魏酸进行研究。结果表明,4种主要酚酸的含量在蒸汽爆破处理后均有所提高,其中阿魏酸的含量最高,结合酚酸中由未处理时的57.232μg/g提高到了1454.092μg/g。该试验还进行了总酚测定,抗氧化活性的测定。通过总酚的测定可以看出,蒸汽爆破处理后,总酚的含量高于未处理麦麸,且随着处理强度的增加,呈现先增加后减少的趋势,在处理条件为2.5 MPa,30 s,总酚含量最高,约为未处理时的9倍。抗氧化试验得到的变化趋势与总酚呈现相似的规律,与未进行蒸汽爆破预处理的麦麸相比,处理后的麦麸表现出了更高的1,1-二苯基-2-三硝基苯肼(DPPH)和2,2-联氮-二(3-乙基-苯并噻唑-6-磺酸)二铵盐(ABTS)自由基清除率,以及在亚油酸体系中的抗氧化活性和还原能力。当处理条件为2.5 MPa,30 s时,抗氧化活性表现最高。由此可得到,2.5 MPa 30 s是蒸汽爆破处理麦麸的最佳条件,此时麦麸中酚酸含量和抗氧化活性均较优,为以后麦麸中酚类物质的深度开发利用提供理论支持。     

超微粉碎对青稞麸皮粉多酚组成及抗氧化活性的影响

为评价超微粉碎对青稞麸皮多酚、体外抗氧化活性和淀粉消化酶抑制活性的影响。该研究制备了3种粒径分别为335.94、72.52、22.69μm的青稞麸皮粉体,对3种粉体的多酚、黄酮含量及其组成、体外抗氧化活性与淀粉消化酶活性抑制率进行测定。结果表明:与粗粉相比,2种微粉的多酚(游离酚、结合酚)、黄酮和总酚含量均显著高于粗粉(P0.05)且粒径越小,含量越高;青稞麸皮粉共检出19种酚酸,其中游离酚以阿魏酸和藜芦酸为主,结合酚以阿魏酸和苯甲酸为主;随着粒径的减小,粉体多酚提取物的抗氧化活性(DPPH·自由基清除能力、FRAP还原能力、ABTS~+·自由基清除能力)及对α-葡萄糖苷酶、α-淀粉酶抑制率均显著增强(P0.05);粉体多酚组成及含量与体外抗氧化活性及淀粉消化酶活性抑制率存在一定的相关性。相关分析结果表明:青稞麸皮游离酚提取物中2,4-二羟基苯甲酸、藜芦酸是清除DPPH·自由基、抑制α-葡萄糖苷酶活性的主要贡献物质,阿魏酸是抑制α-葡萄糖苷酶及α-淀粉酶活性的主要物质;结合酚提取物中2,4-二羟基苯甲酸是抑制α-淀粉酶活性的主要物质。该结果显示超微粉碎一定程度上可提高青稞麸皮中多酚含量、体外抗氧化活性及淀粉消化酶抑制率,可作为青稞麸皮食品的一种有效前处理加工手段。     

三种因素对绿茶酒品质的影响

2016年7月,以采用烘青绿茶做原料酿制的绿茶酒为基酒进行调配,研究母液质量分数、糖添加量和酒精度三种因素作用下,绿茶酒茶多酚、总酸、茶氨酸、儿茶素和咖啡碱的含量变化。结果:随着母液添加量的增加,茶酒中茶多酚含量升高,A_3B_1C_3处理的茶多酚含量最高,为305.16 mg·kg~(-1);儿茶素含量在母液质量分数为2.0 g·L~(-1)(A_3)最高,为0.250 mg·m L~(-1);酒精度数越高,茶酒中的茶氨酸含量也越高。三种因素的共同作用降低了茶酒中的咖啡碱含量;母液添加量低、酒精度高的A_1B_2C_3处理咖啡碱含量最低,仅为0.33 mg·m L~(-1)。     

苹果皮渣固态发酵生产菌体蛋白饲料工艺优化及产物品质分析

为提高苹果皮渣中粗蛋白的含量,以黑曲霉为发酵菌种发酵苹果皮渣,通过单因素试验对影响苹果皮渣固态发酵的参数进行优化,在此基础上进一步采用响应面试验筛选最佳发酵工艺参数,并对最佳工艺条件下的发酵产物品质进行分析。结果表明,黑曲霉发酵苹果皮渣的最佳工艺条件为:黑曲霉接种量10%、发酵温度32℃、水料比3.5、发酵时间6 d。此条件下苹果皮渣经发酵后粗蛋白含量从7.05%提高到33.56%,粗脂肪含量从4.75%提高到5.57%,粗纤维含量从21.80%降低到13.53%,氨基酸总含量从45.10 mg·g~(- 1)提高到126.30 mg·g~(- 1),必需氨基酸含量从16.13 mg·g-1提高到50.40mg·g~(- 1)。综上,黑曲霉发酵可以显著提高苹果皮渣的营养价值,这为苹果皮渣资源化利用、缓解蛋白质供需矛盾提供了有效途径。     

盐城药用菊花连作障碍形成原因初步研究

以连作1年、3年、7年、15年的菊花田土壤和菊花为研究对象,考察各处理组菊花产量、发病率、土壤及菊花样品中的元素含量、土壤中可培养微生物数量及酚酸类化感物质的含量,进一步探讨不同浓度对羟基苯甲酸、香草酸、香豆酸、香豆素等化感物质对菊花组培苗生长的影响.结果表明:随着连作年限的增加,菊花的产量逐渐降低,发病率逐渐增加,连作15年的菊花产量仅为初茬菊花产量的19.80％,种植15年菊花的发病率达到100％.土壤中硼元素含量随连作年限的增加而逐渐减少.连作15年的菊花植株中的氮、磷、钾、铁、锰、铜、锌、硼8种元素含量,与其他组相比均有较大程度的降低.随着连作年限的增加,土壤真菌化严重,细菌和放线菌数量在3年达到最大,15年显著降低.土壤中香豆酸含量随着种植年限的增加而逐渐增加,连作7年后土壤中检测出香豆素残留.低浓度对羟基苯甲酸、香草酸及香豆酸对菊花组培苗生长发育影响不大,但香豆素、混合酚酸及高浓度的香豆酸显著抑制菊花组培苗生长和根的发育.酚酸物质积累、微生物区系的改变、土壤微量元素硼的减少可能是菊花连作障碍的主要原因.     

黄河三角洲盐渍土有机氮组成及氮有效性对土壤含盐量的响应

土壤盐分胁迫下有机氮组成及氮有效性对黄河三角洲盐渍土壤肥力的形成和生产力的提高具有重要作用。本研究采集黄河三角洲盐渍土壤区小麦-玉米轮作的3种盐渍土壤,分别为轻度盐渍土(含盐量2.28 g·kg~(–1), S1)、中度盐渍土(含盐量3.73 g·kg~(–1), S2)和重度盐渍土(含盐量6.69 g·kg~(–1), S3),分析不同盐分含量土壤的作物产量和土壤有机氮组分含量、无机氮含量、微生物生物量氮含量及相关酶活性等指标的变异特征,明确盐分含量对土壤有机氮组成及氮有效性的影响。结果表明:3种土壤中有机氮的酸解总氮含量是有机氮的主要组分,S1、S2和S3处理下分别占土壤总有机氮68.79%、61.60%和52.30%;不同处理下各形态含量酸解总氮为酸解铵态氮酸解未知氮酸解氨基酸氮酸解氨基糖氮,且各形态含量均以S1处理显著高于S2和S3处理(P0.05)。非酸解氮含量在3种处理间差异不显著,且均低于酸解总氮含量,其占全氮比例随土壤含盐量增加而提高。S1处理土壤硝态氮含量(22.08mg·kg~(–1))和微生物生物量氮含量(20.71mg·kg~(–1))最高,显著高于其他两种处理的土壤(P0.05);铵态氮含量在各处理下差异不显著。S1处理的小麦、玉米总产量分别是S2和S3的1.74倍和5.85倍。回归分析发现土壤可溶性全盐含量分别与土壤无机氮、微生物生物量氮含量呈显著的负指数关系,与小麦、玉米总产量、氨基酸态氮含量之间存在显著的负线性关系。土壤无机氮含量与土壤酸解总氮含量之间呈显著的正指数关系。土壤中较高含量的可溶性全盐抑制土壤酸解有机氮的形成及氮素有效性的提高。     

海伦黑土有机碳和养分含量30年变化特征

黑土是支撑东北地区粮食高产稳产的基础。近年来黑土质量退化、肥力下降,已严重威胁粮食的可持续生产能力。土壤有机碳和养分含量的演变特征是评价土壤肥力变化的重要指标。本文以位于黑土带腹地、具有代表典型黑土的海伦市为例,结合第二次全国土壤普查资料和实际调查数据,系统分析了30年来农田黑土有机碳和养分的变化规律及其相互关系,为改善黑土农田管理措施提供科学依据。结果表明,与80年代相比,黑土农田表层土壤有机碳含量下降了12%,其中厚层黑土下降幅度最大(22%)。土壤养分也呈现不同的变化趋势,表层黑土碱解氮和速效钾分别下降了33%和43%,有效磷增加了48%。碱解氮在厚层、中层和薄层黑土中的下降速率分别为3.25 mg·kg~(-1)·a~(-1),2.24 mg·kg~(-1)·a~(-1)和1.64 mg·kg~(-1)·a~(-1);速效钾的下降速率分别为4.11 mg·kg~(-1)·a~(-1),3.53 mg·kg~(-1)·a~(-1)和4.68 mg·kg~(-1)·a~(-1);不同类型黑土有效磷含量略有增加,增加速率分别为0.14 mg·kg~(-1)·a~(-1),0.53 mg·kg~(-1)·a~(-1)和0.22 mg·kg~(-1)·a~(-1)。相关性分析显示,土壤有机碳与碱解氮和速效钾含量显著正相关,与有效磷相关性不显著。针对当前黑土农田土壤碳和养分状况,应采取固碳、减磷、补钾和提高氮肥利用率的管理措施。     

Endogenous organic acid variations in different chickpea (Cicer arietinum L.) genotypes

Abstract

Changes in cropping systems during the past century have led to selective pressure on weed flora. Species and ecotypes with characteristics enabling them to survive in high-input farmland have increased in numbers, at the cost of plants lacking these characters. Since the 1950s, the perennial weed species Cirsium arvense (L.) Scop. and Sonchus arvensis L. have mainly been controlled by the herbicide group synthetic auxins like MCPA. During recent decades, C. arvense seems to have become less susceptible to MCPA in both Europe and North America but the reasons are unclear.

To study the importance of selective pressure on weed ecotypes, both short- and long-term studies were carried out in Uppsala, Sweden. The first consisted of two growth-characteristic greenhouse experiments. The hypothesis was that ecotypes of C. arvense and S. arvensis from high-input farmland were different and displayed a more competitive growth pattern than did ecotypes from low-input farmland.

The second study was a field experiment with four ecotypes of C. arvense from low-input farmland to study if selective pressure was in force, over a period of six years. The four ecotypes had different growth characteristics and herbicide sensitivity and they were exposed to crop competition and MCPA treatments during the experimental period. The hypothesis was that ecotypes with a more competitive growth pattern and MCPA tolerance would survive to a greater extent than would other ecotypes. For C. arvense, the results from the growth-characteristic experiment showed that the growth pattern of ecotypes from high-input farmland differed, showing a more directly elongated growth pattern with fewer spines on the leaves compared with ecotypes from low-input farmland, which usually were of rosette-type. Results from the field experiment with C. arvense showed that after six years MCPA-sensitive and/or rosette-type ecotypes had almost disappeared while ecotypes with a more directly elongated growth pattern and less sensitive to MCPA survived to a much greater extent. The conclusion was therefore that when exposed to selective pressure like crop competition and herbicide treatments, ecotypes of C. arvense with a more directly elongated growth pattern and less sensitive to herbicide treatment survived to a greater extent compared with ecotypes missing these traits. Ecotypes from high-input farmland had generally fewer leaf spines than did ecotypes from low-input farmland. This may suggest a trade-off between spine formation and rapid competitive growth. In the growth-characteristic experiment with S. arvensis, no differences between ecotypes from high- and low-input farmland regarding growth characteristics or leaf spines could be detected. This might partly be due to a lower exposure of S. arvensis to selective pressure compared with C. arvense, since S. arvensis generally is less sensitive to MCPA.     

有机酸处理条件对玉米秸秆热解特性的影响

酸洗预处理能有效改善K^+对生物质热解的影响,该文利用热重分析仪和裂解-气相色谱质谱联用仪进行了玉米秸秆的热解试验,研究了不同有机酸酸洗浓度(3%、5%和7%)、酸洗温度(25、50和75℃)和酸洗时间(1、2和3 h)对玉米秸秆热解特性的影响。结果表明:酸洗能显著降低玉米秸秆内在K^+的含量;经过不同条件的有机酸洗预处理后,玉米秸秆的TG/DTG(thermogravimetry/differential thermogravimetry)曲线均向高温段移动,最大热解速率随着酸洗浓度和酸洗温度的增加逐渐增大,随着酸洗时间的增加先增大后降低,在酸洗温度为75℃时,最大热解速率达到最大值15.49%/min;与此同时,玉米秸秆热解主要产物为酚类、酮类和呋喃类化合物,酸洗后,其酚类物质产率明显增加,在酸洗浓度为7%时达到最大值16.75%,而酮类和呋喃类化合物产率减少,分别在酸洗时间为1 h和酸洗浓度为7%时达到最小值0.10%和7.13%。酸洗后,焦炭产率减少,在酸洗浓度为3%时达到最小值18.79%。通过研究不同处理条件下有机酸对玉米秸秆热解特性的影响,为生物质预处理中酸溶液的选择提供了参考。     

Organic Acids and Diffusive Flux of Organic and Inorganic Phosphorus in Sandy-Loam and Clayey Latosols

This study evaluated the effects of organic acids on the diffusive flux of phosphorus (DFP) along time. Treatments were a factorial 2?×?2?×?2?×?2?×?5 design: two soils (clayey Red Latosol and a sandy-loam Red-Yellow Latosol), two organic acids (citric acid, CA, and humic acid, HA), and two phosphorus (P) sources [monopotassium phosphate (KH₂PO₄) and inositol hexaphosphate (IHP)] either with or without heating (100 °C) of the soil. The soil plus treatments, in all combinations, were placed in contact with an anion exchange resin and the P in the resin was measured after 2, 4, 6, 10, and 15 days. The DFP was greater when the soils were treated with CA than when treated with HA. Citric acid was more effective in increasing the DFP from KH₂PO₄, whereas HA was the organic ligand that promoted a larger DFP when the source was IHP.     

Interactive effects of organic acids in the rhizosphere

Organic acids released into the rhizosphere may perform many beneficial functions to the plant including metal detoxification and enhancement of nutrient acquisition. Typically, these organic acids are studied in isolation; however, roots simultaneously exude a cocktail of organic acids and other substances, and their combined impact on rhizosphere processes may be quite different. It has been hypothesized that some exudates may play secondary roles (e.g. inhibitors of microbial activity, blockage of sorption sites), which might enhance the longevity and nutrient-mobilization capacity of others. Here we investigated how the decomposition, sorption and P-solubilizing effects of citrate, malate and oxalate are affected by the presence of malonate and shikimate. We found that in a range of agricultural soils the decomposition of citrate, malate and oxalate was rapid, but not influenced by the presence of large quantities of shikimate or malonate. This suggests that the individual organic acids are taken up by different transport mechanisms or components of the microbial community. At large concentrations, malonate decreased sorption of citrate, malate and oxalate on the soil, whilst shikimate had little effect. The capacity of citrate, malate and oxalate to desorb P was significantly greater in cocktails containing malonate compared with the single organic acid; no effect was seen with shikimate. We conclude that neither malonate nor shikimate at realistic concentrations will significantly affect the biodegradation of citrate, malate or oxalate in the rhizosphere, and while malonate did enhance P desorption, this effect is additive rather than synergistic. Overall, we found little evidence that malonate and shikimate act as secondary regulators of citrate, malate and oxalate behavior in soil.     

Low pH and aluminum tolerance of Bradyrhizobium strains isolated from acid soils in Indonesia

Sixty-seven strains of Bradyrhizobium isolated from soybean plants growing on acid soils in West Java and Sumatra, Indonesia, were examined for the effect of the pH and aluminum concentration on their growth in nutrient media, compared with 61 strains of Bradyrhizobium from soils in Japan. The results in this study indicated that the indigenous population of Bradyrhizobium in the soils of Indonesia showed a large difference in acid- and Al-tolerance from that of Japan. Eighty-five and 48% of the isolates from Japanese soils and Indonesian soils, respectively, were unable to grow in YEM broth at pH below 4.5. The acid-tolerance was correlated with AI-tolerance of the isolates on YEM agar plates at pH 4.4. Seventy-five percent of the isolates that grew in YEM broth at pH 4.5 were also resistant to 400 µM Al on the YEM plates. Acetylene reduction assay of the root nodules revealed that 3 of the acid- and Al-tolerant isolates from Indonesian soils showed a significantly high nitrogen fixation activity.     

Effect of humic acid and fulvic acid based liquid and foliar fertilizers on the yield of wheat crop

Abstract

An organic-mineral liquid fertigation fertilizer containing humic acid, nitrogen (N)–phosphorus (P)–potassium (K), zinc (Zn), sulfur (S), manganese (Mn) and a liquid foliar fertilizer consisting of fulvic acid and gibberellic acids were formulated and applied to wheat. The purpose of this study was to develop an efficient and cost effective liquid and foliar fertilizer and compare their potential with commercially available urea and DAP. The fulvic acid and humic acids were obtained by alkaline extraction of lignite coal. All the treatments were significant over the control. The application of the liquid fertigation fertilizer and liquid foliar fertilizer along with 50?kg of urea per acre showed the best results biological yield (grain plus straw yield). It was found that the highest yield was obtained in T₆ treatment and the second best results were obtained with T₂ treatment, but has a high cost, while treatment T₆ was the most significant economical and yielded a high income when compared to other treatments.     

Plant defence inducers rapidly influence the diversity of bacterial communities in a potting mix

Plant hormones and their functional analogues are used in agriculture to combat plant diseases and pests. These chemicals are generally targeted at shoots, but soils inevitably receive a dose during application. In this study, we used 16S rRNA gene amplicon pyrosequencing to determine whether the diversity of bacterial communities in a potting mix (referred here as ‘model soil’) is influenced by exposure to salicylic acid (SA), methyl jasmonate (MeJA), ethylene (ET) and abscisic acid (ABA). The number of operational taxonomic units (OTUs; richness) and Simpson's Diversity Index values (evenness) associated with each sample was not influenced by the hormone treatments, but changes in community composition were observed. Relative to the control, all hormones more than doubled the abundance of a Limnobacter population, ABA led to a four-fold increase in a Cellvibrio population, ET led to a c. 70% decrease in an Algoriphagus population, and MeJA and ABA applications halved the abundance of a Massilia population. These changes may influence plant productivity.     

Chemical Composition of Ten Blackcurrant (Ribes nigrum L.) Cultivars

Abstract

Ten blackcurrant cultivars were evaluated for some quality components. On average, the sugar content was 9.0%, of which fructose made up 45%, glucose 40% and sucrose 15%. Soluble solids were 15.4% as an average for the ten cultivars in three years. The acid content was 5.1% of fresh weight, 88% was citric acid and 12% malic acid. The ascorbic acid content varied from 67 mg per 100 g fresh fruit in Hedda, to 204 mg per 100 g in Blackdown. Except for Hedda and Øjebyn, which both had low values of ascorbic acid and colour properties, the quality components of the cultivars were found to be within an acceptable range.     

不同来源腐殖酸的组成和性质的研究

本研究从三种有机物料草炭、褐煤、风化煤中提取腐殖酸,对其组成和性质进行了测定,同时对胡敏酸进行酒精沉淀分级。研究结果表明:褐煤胡敏酸氧化度和芳香度最高,其次为风化煤胡敏酸,最后是草炭胡敏酸;风化煤富里酸的氧化度和芳香度最高,其次为褐煤富里酸和草炭富里酸。胡敏酸各级分的回收率均随着级分数的升高而增加。回收率以风化煤胡敏酸最高,依次为褐煤胡敏酸、草炭胡敏酸。     

Soil Humic and Fulvic Acids from Different Land-Use Systems Evaluated By E4/E6 Ratios

Changes in land-use systems such as the introduction of trees on agricultural land can give rise to changes in the physicochemical properties of the soils, also affecting the quantity and quality of organic matter incorporated into the system. The present study assesses humic substances (HS) in the soil such as humic acid (HA) and fulvic acid (FA) by looking at the relationship between the optic densities determined at 465 and 665 nm (E4/E6 ratio). Topsoil samples (0–20 cm) from pine woodlands 60 years of age were compared with agricultural soils of similar age in the central-south region of the Province of Buenos Aires, Argentina. The pH of the topsoil from beneath the pine trees was highly acidic (5.0 vs. 6.2) and a significant increase in the level of organic carbon (OC) was registered. The carbon to nitrogen (C/N) ratio was also higher (by one order of magnitude) beneath the pine trees, although the humification conditions of the soil organic matter (SOM) were good in the soils of both studied land-use systems. The E4/E6 ratio was higher in the HA and FA 2º (second extraction) beneath the pines, indicating a smaller molecular size of the HS bound to the clay minerals. This fact can be attributed to the higher concentration of hydrogen ions beneath the pines and consequently the loss of polyvalent cations, mainly calcium. The most labile organic molecules (FA 1º – first extraction) were of a larger size in soils beneath the pines, most likely owing to a specific characteristic of the Pinus genus, although the fraction in question constitutes a minority fraction among the HS. Clear differences were established between the E4/E6 ratios in HA and FA, making this a highly useful method for determining molecular changes in HS as a result of changes in land use.