长期施肥对红壤有机碳矿化及微生物活性的影响?

为评价不同施肥条件下红壤有机碳矿化和微生物活性及两者之间的关系,对长期定位试验施有机肥（M）、施用氮、磷、钾化肥（NPK）、有机肥配合化肥（NPKM）、秸秆配合化肥（NPKS）和不施肥（CK）共5个处理的红壤进行室内培养,分析不同施肥处理下红壤有机碳矿化的CO2释放量﹑微生物数量及微生物碳源代谢特征。结果表明,不同施肥处理的土壤有机碳矿化释放CO2量差异显著,由一级反应动力学方程拟合计算出土壤潜在有机碳矿化释放CO2–C量的大小顺序：M > NPKM > NPK ≈NPKS > CK,其值分别为180.3﹑88.5﹑47.6﹑43.4和34.5 mg/kg 。培养初期微生物活性较弱时CO2的释放速率最高,微生物数量的增长落后于有机碳矿化速率变化,但培养14﹑35和69 d 时3种微生物数量大小顺序为M > NPKM > NPK≈NPKS≈ CK,处理间差异显著且与CO2释放量显著相关。不同施肥处理间微生物群落结构差异显著,其趋势与有机碳矿化相符合。说明长期施肥特别是长期施用有机肥能影响微生物的群落结构,提高红壤微生物活性,进而促进微生物对有机碳的矿化。     

施用生物质炭对红壤有机碳矿化及其组分的影响

采用室内培养试验研究了生物质炭种类、土壤性状和氮肥施用对红壤有机碳矿化及其组分的影响。结果表明,添加生物质炭后红壤中有机碳的矿化速率随添加生物质炭制备温度的增加而下降;在有机质中等的土壤中,添加生物质炭可促进土壤有机碳的矿化;而对于有机质特别低或较高的土壤中,添加生物质炭降低了其有机碳的矿化;施用氮肥可明显增加生物质炭添加土壤中有机碳的矿化。研究认为,生物质炭类型、土壤性状和施用氮肥对添加生物质炭土壤有机碳矿化的影响差异可能与它们对土壤活性有机碳(微生物生物量碳和水溶性碳)的影响不同有关。总体上,施用生物质炭和氮肥若能促进土壤活性有机碳的形成,则相应地其也可促进土壤有机碳的矿化。生物质炭在土壤中的稳定性也受土壤性状和氮素状况的影响。     

生物质炭对土壤有机质活性的影响

为了解施用生物质炭对土壤碳组分的潜在影响,通过室内2年盆栽培养试验研究施用不同用量生物质炭对土壤有机碳积累、有机碳稳定性、微生物量碳和水溶性有机碳的影响,并与施用等碳量的小麦秸秆、酸洗生物质炭(去除生物质炭中的速效养分)及同时施用小麦秸秆与生物质炭的处理进行比较。结果表明,施用生物质炭可显著提高土壤有机碳的积累,增加土壤有机碳的氧化稳定性,降低土壤水溶性有机碳。施用生物质可在短时间内增加微生物量碳,但随着培养时间的增加,其微生物量碳逐渐下降,最终明显低于对照土壤(不施有机物料的处理)。土壤水溶性有机碳的下降可能与生物质炭对其吸附固定有关,而短时间内激发微生物量碳增加可能与施入生物质炭增加了土壤有效养分、改善土壤微生物生长环境有关。研究结果认为,长期单一施用生物质炭可能会引起土壤有机质生物活性的下降,但生物质炭与一般生物质有机肥配合施用可减免这些负影响。     

干湿处理对灰漠土土壤理化性质及微生物活性的影响

土壤风干．润湿过程可加剧土壤有机质矿化反应，其矿化来自于土壤非生物有机质分解和土壤微生物在干湿变化过程中死亡两个过程。因此，干湿变化可能对土壤有机质及养分循环产生重要的影响。国内外的相关研究主要集中于干湿变化过程中土壤对磷素的吸附作用及有机磷矿化作用微生物量碳的变化及有机碳矿化作用等等，实验对象多为肥沃或酸性土壤。灰漠土是干旱区的典型土壤类型之一，本文以阜康绿洲与其毗邻荒漠为研究对象，对干湿处理后土壤理化性质、土壤呼吸作用所发生的变化进行了初步研究，以期了解干湿变化过程对荒漠一绿洲土壤理化性质及微生物活性的影响，为荒漠土壤的演变机制和科学管理提供理论依据，同时也对干旱区土壤样品长期贮存后的再利用有一定指导意义。     

黑土中乙草胺残留和微生物变化的时间特征研究

通过黑土室外盆栽试验,研究了种植玉米和未种植条件下乙草胺在玉米生长苗期的残留变化规律及土壤微生物量碳的动态特征。研究表明:乙草胺在土壤中半衰期较短,土壤微生物活性是影响其降解的主要因素。但是,由于施用化肥极大地刺激了微生物活性,因而,乙草胺施用对土壤微生物量碳影响并不显著。然而,玉米的种植对土壤微生物量和土壤乙草胺残留数量有着显著的影响。种植玉米条件下土壤微生物量碳显著增加,同时,土壤中乙草胺残留量降低,说明种植玉米有助于微生物活性的提高和乙草胺生物毒害性的降低。     

长期施肥潮土在玉米季施肥初期的有机碳矿化过程研究

以黄淮海平原长期定位试验地2007年玉米播种期土壤为研究对象,通过室内37天的培养实验并选择4个应用比较广泛的方程对土壤有机碳矿化过程进行拟合,其目的主要是为了比较研究长期不同施肥土壤在玉米季施肥初期有机碳矿化过程及主要矿化参数的差异,并评估矿化参数和主要土壤性质之间的相关关系.结果表明,37天培养期内各施肥处理土壤CO2-C累积释放量与土壤有机碳、全氮含量和微生物活度均呈显著正相关,大小依次为OM＞1/2OM+1/2NPK＞NPK＞NP＞PK＞CK＞NK,有机碳矿化过程均呈曲线形式,与Jones(1984)改进的一级动力学方程拟合效果最好.拟合所得土壤潜在可矿化有机碳量(C0)、易矿化有机碳量(C1)和初始潜在矿化速率(C0k)均表现出有机肥处理高于化肥处理,施肥处理高于不施肥处理(NK处理除外),与土壤有机碳、全氮和土壤微生物活度均呈显著正相关;有机碳矿化速率(k)和土壤潜在可矿化有机碳占土壤总有机碳的比例在处理间差异均不显著,除k与有机碳呈显著负相关外,其他与土壤性质均无显著相关性.因此,我们推测有机肥和化肥的平衡施用均能显著增强土壤有机碳的矿化作用,有利于土壤无机养分的释放,同时使部分有机碳在土壤中积累.     

蚯蚓粪对豇豆土壤活性有机碳及微生物活性的影响

为探讨施用蚯蚓粪对豇豆土壤活性有机碳与微生物活性的作用效果,通过大田试验,研究CK(对照,不施肥)、CF(单施化肥)、VC(蚯蚓粪)和VC+CF(蚯蚓粪和化肥各提供50%的氮)等处理对豇豆土壤活性有机碳、碳库管理指数(CPMI)、微生物量碳氮及微生物呼吸、代谢熵的影响。结果表明,与CF相比,施用蚯蚓粪处理的活性、中活性和高活性有机碳含量均显著升高。VC+CF的活性有机碳含量与CPMI明显高于其它处理,较CF分别高出30.38%和36.69;同时,微生物量碳、氮含量亦显著高于其它处理。此外,VC+CF还明显增强了土壤微生物呼吸作用,但降低了代谢熵,其中土壤微生物呼吸分别比CK、CF和VC提高64.91%、36.23%和16.05%,而代谢熵分别下降10.85%、9.06%和5.32%。与VC+CF相比,VC对豇豆土壤的影响作用较小。相关性分析表明,土壤不同程度的活性有机碳、CPMI与微生物活性之间呈显著或极显著的相关性,各指标之间具有密切的内在联系。综上所述,蚯蚓粪与化肥配施能明显提高豇豆土壤的活性有机碳含量,且能显著增强土壤微生物活性。该研究为豇豆的合理施肥提供了理论依据。     

水稻秸秆施用后土壤溶解性有机碳的变化与土壤CO_2排放

为了进一步认识水稻秸秆还田后土壤有机碳固定机制,以浙江两种典型水稻土淡涂泥、青紫泥为研究对象,并以不加秸秆为对照,研究秸秆施用下土壤溶解性有机碳(Dissolved Organic Carbon,DOC)含量以及CO_2产生速率的动态变化,以及秸秆分解产生DOC在土壤中的吸附作用。结果表明,添加秸杆显著增加了土壤CO_2排放,总矿化碳量表现为10%>5%>2%>CK;土壤CO_2产生速率的变化与DOC含量变化具有高度一致性,都表现为先快速上升-急剧下降-缓慢下降-趋于稳定的变化模式,两者呈显著正相关(P<0.01),但在石英砂处理中两者则无明显相关性。DOC吸附实验表明随着秸秆分解时间延长,所产生的DOC在土壤中的吸附作用增强。pH和本底DOC较低的青紫泥对DOC具有更强的吸附作用,其CO_2排放速率和总矿化碳量均显著低于淡涂泥,青紫泥更有利于秸秆还田有机碳的保留和稳定。该结果表明秸秆分解前期产生DOC主要以CO_2形式释放,分解后期产生DOC更倾向于土壤有机碳固定,增加土壤对DOC的吸附作用有利于土壤固碳。     

互花米草控制技术对湿地土壤有机碳保留能力与微生物活性的影响

鉴于多种技术被用于控制崇明东滩互花米草的蔓延,为了选择更好的互花米草控制技术,首先比较不同控制技术作用下湿地土壤总有机碳（SOC）含量的差异,并对土壤中的微生物活性进行研究以分析土壤中总有机碳的输出能力,进而分析土壤总有机碳的保留能力。结果表明,经过刈割／翻耕、刈割／翻耕／水位调节、刈割／生物（芦苇）替代等控制措施后,湿地土壤中土壤总有机碳含量、可培养微生物菌落数、土壤转化酶活性和土壤呼吸强度均高于对照,而通过DGGE技术对微生物种群进行分析后发现,修复后的湿地土壤多样性显著低于对照。在几种不同的控制技术中,刈割／翻耕／水位调节模式由于增加了土壤的滞水时间,其土壤微生物活性相对较低,有机碳含量较高,表明采用该修复技术后土壤的碳代谢能力相对较弱,因此该修复技术更有利于湿地土壤有机碳的保留。相对其他控制技术而言,刈割／翻耕／水位调节模式可在控制互花米草蔓延的同时有效地保留土壤有机碳。     

露天煤矿区复垦土壤碳库研究进展

土壤是地球陆地生态系统中碳的重要贮藏库。露天煤矿区既是"碳源",也是"碳汇",研究其土壤碳的变化对区域碳平衡具有重要意义。本文梳理了当前世界范围内对露天煤矿区土壤碳库的构成、土壤有机碳库的区分测定方法、积累、转化和时空分布的研究。已有研究成果表明:(1)复垦与未复垦排土场中土壤无机碳含量无显著差异。(2)土壤有机碳的含量受复垦植被、年限、地形及土壤理化性质的影响。(3)不同因素通过影响土壤中的矿质态氮和微生物活性而影响有机碳的分解矿化率。(4)不同类型有机碳在土壤剖面中的分布呈不同规律,生物成因有机碳主要积累在土壤表层和亚表层,而地球成因有机碳积累在土壤底层。在此基础上提出深入研究方向:土壤无机碳和有机碳的相互转化关系、土壤碳循环与氮、磷、水循环的耦合关系及与生态系统生物多样性之间的内在联系。     

外源有机碳对黑土有机碳及颗粒有机碳的影响

为了阐释外源有机碳在土壤有机碳运转中的作用机制,以黑土为供试材料,进行了5年的室外培养试验,并结合室内全土及颗粒组分单独矿化培养试验,研究了不同外源有机碳对黑土有机碳(SOC)、颗粒有机碳(POC)含量及其矿化特征的影响。试验包括单施化肥、牛粪配施化肥、鸡粪配施化肥、秸秆配施化肥和树叶配施化肥5个处理。结果表明:(1)单施化肥黑土SOC的损失主要来源于POC的损失,外源有机碳有利于SOC和POC的累积,与对照相比,禽畜粪便处理的SOC和POC平均增加幅度分别为16.6%和27.8%,植物残体处理的SOC和POC平均增加幅度分别为27.0%和46.4%;(2)一级动力学方程能较好地描述SOC和POC的矿化动态(R~20.9),且POC比SOC易矿化,POC的60d累积矿化量是SOC的3倍以上;(3)禽畜粪便处理和植物残体处理的POC平均矿化率分别为31.5%和29.8%,禽畜粪便处理的POC更易矿化;(4)外源有机碳有效降低了黑土有机碳的矿化,尤其是牛粪,其SOC矿化率为1.9%,比对照低了3.4%,其POC矿化率为24.8%,比对照低17.4%;(5)外源有机碳在黑土中的碳累积能力表现为树叶秸秆牛粪鸡粪。     

添加牛粪对长期不同施肥潮土有机碳矿化的影响及激发效应

为了探讨长期不同施肥潮土有机碳矿化对添加牛粪的响应特征及添加牛粪对长期不同施肥潮土有机碳矿化的激发效应,以始建于1986年的长期定位试验为平台,通过室内恒温培养的方法研究添加等氮量牛粪后长期不同施肥(不施肥,CK;常量有机肥,SMA;常量化肥,SMF;常量有机无机配施,1/2(SMA+SMF))潮土有机碳矿化、土壤有机碳及活性碳库组分(微生物量碳、可溶性有机碳、颗粒有机碳和易氧化有机碳)含量的变化特征。结果表明:无论添加牛粪与否,长期不同施肥潮土有机碳矿化过程均符合一级动力学方程,而牛粪的添加显著增加了长期不施肥、长期单施化肥和长期有机无机配施土壤的有机碳矿化速率常数,增长幅度分别为21.74%、35.00%和45.00%;添加牛粪提高了长期不同施肥潮土有机碳、微生物量碳、颗粒有机碳和易氧化有机碳含量,却显著降低了可溶性有机碳含量;牛粪对长期不施肥、长期施用常量有机肥、常量化肥和常量有机无机配施潮土有机碳矿化的正激发效应分别达到了48.56%、3.60%、48.43%和3.92%,且对长期不施肥及长期施用常量化肥潮土的激发效应显著高于对长期施用常量有机肥及长期有机无机配施土壤;冗余分析显示添加牛粪对长期不同施肥土壤有机碳矿化的激发效应与土壤活性组分碳氮比呈正相关,与土壤养分含量呈负相关。该研究不仅为合理施用有机肥和实现农田生态系统的可持续发展提供理论依据,还有利于实现农业资源再利用及其效益最大化。     

黄淮海平原集约种植条件下土壤有机质动态模拟

A modified CQESTR model, a simple yet useful model frequently used for estimating carbon sequestration in agricultural soils, was developed and applied to evaluate the effects of intensive cropping on soil organic matter （SOM） dynamics and mineralization as well as to estimate carbon dioxide emission from agricultural soils at seven sites on the Huang-Huai-Hai Plain of China. The model was modified using site-specific parameters from short- and mid-term buried organic material experiments at four stages of biomass decomposition. The predicted SOM results were validated using independent data from seven long-term （10- to 20-year） soil fertility experiments in this region. Regression analysis on 1 151 pairs of predicted and measured SOM data had an r2 of 0.91 （P≤0.01）. Therefore, the modified model was able to predict the mineralization of crop residues, organic amendments, and native SOM. Linear regression also showed that SOM mineralization rate （MR） in the plow layer increased by 0.22% when annual crop yield increased by 1 t ha^-1 （P ≤ 0.01）, suggesting an improvement in SOM quality. Apparently, not only did the annual soil respiration efftux merely reflect the intensity of soil organism and plant metabolism, but also the SOM MR in the plow layer. These results suggested that the modified model was simple yet valuable in predicting SOM trends at a single agricultural field and could be a powerful tool for estimating C-storage potential and reconstructing C storage on the Huang-Huai-Hai Plain of China.     

绿肥压青对粉垄稻田土壤微生物量碳和有机碳累积矿化量的影响

绿肥压青还田是调控现代集约化稻田土壤逆境的重要手段,为评估绿肥压青下粉垄耕作对稻田土壤微生物量碳和土壤有机碳累积矿化量的影响,设置早稻粉垄耕作与常规耕作2种耕作模式,不施肥和同等肥力条件下施化肥、单倍绿肥配施化肥和双倍绿肥配施化肥4种施肥处理,晚稻免耕常规施用化肥,开展双季稻周年大田应用试验。结果表明:单倍绿肥压青下,粉垄耕作能提高稻田土壤微生物量碳含量,可达常规耕作的2倍,能有效增加微生物对土壤碳素的利用率。增加绿肥压青量会提高粉垄耕作稻田土壤有机碳累积矿化量和矿化潜力,与施用化肥相比,单倍绿肥压青下早晚稻分别增加1.6%～32.8%和0.6%～16.6%,双倍绿肥压青下分别增加58.6%～70.9%和29.6%～38.4%。粉垄单倍绿肥压青会降低免耕晚稻齐穗期、收获期土壤呼吸强度,较常规耕作分别降低33.4%和38.7%,较粉垄耕作其他处理降低8.5%～31.4%。单倍绿肥压青下粉垄稻田土壤代谢商较常规耕作累积降低65.5%,与常耕相比,粉垄双倍绿肥压青和粉垄单一化肥的土壤代谢商分别累积增加20.3%和159.2%,粉垄双倍绿肥压青可有效缓解土壤代谢商的提升。微生物量碳含量与有机碳矿化激发效应呈负相关,绿肥压青还田下相关系数达0.44;累积矿化量和代谢商呈极显著正相关,粉垄耕作下相关系数达0.59。可见,绿肥粉垄耦合的模式可作为一种增加稻田土壤微生物量碳含量、减少部分生育时期土壤呼吸强度,增强土壤碳库稳定性及碳固持的重要调控技术措施。     

长期施肥对黑土呼吸过程的影响

土壤呼吸是土壤有机C矿化分解,释放无机养分的重要生物化学过程。对公主岭地区长期有机肥(不施有机肥、施中量和高量有机肥处理)与化肥(不施化肥、施用N、NP、NPK化肥)配合施用的12个处理的黑土进行室内好气培养(196天),采用一级动力学方程模拟土壤的呼吸过程,结果表明,有机肥和化肥的施用能显著增加土壤呼吸释放的CO2 -C的累积量,提高土壤中潜在矿化的有机碳含量及其占土壤有机质的比例,促进土壤有机质中无机养分的释放,有利于提高土壤养分的有效性,改善黑土的供肥状况。有机肥与NPK化肥配合施用效果更为明显。     

Manure application followed by biochar application increases plant production regardless of soil dehydrogenase activity

Biochar is obtained by the pyrolysis of biomass, and contains abundant carbon and minerals. Biochar supplementation of soils can greatly improve soil health and quality, but these beneficial effects typically develop slowly over time. Depending on the quality of the biochar and the soil to which it is applied, it may take years before positive effects are apparent. This is because organic substances are slowly sorbed onto the biochar over time, and the biochar eventually becomes part of the sorption complex of the soil. It is therefore advisable to apply biochar together with some organic material. We examined the effect of co-application of different doses of biochar with manure on soil dehydrogenase activity (DHA), soil oxidizable carbon (COX), cumulative soil respiration, soil buffering capacity, the soil exchange reaction (pH/KCl) and the production yield of winter rape seeds. We also determined seed production when artificial granular fertilizers were added to biochar and manure. The results showed that the application of biochar and manure significantly increased grain yield, DHA, the soil exchange reaction and cumulative respiration. Thus, application of biochar with organic material can increase seed yield and some properties of agricultural soils. However, the positive effect of biochar on seed yield was not directly proportional to biochar dose, in that the seed yield was lower for a biochar dose of 45 t/ha than 30 t/ha.     

动物粪液中可溶性磷在土壤中的吸附和迁移特性研究

农田土壤施用动物粪肥引入了大量的可溶性有机物、有机磷和无机磷,了解这些可溶性物质在土壤中的相对移动性及它们之间的相互作用有助于指导农田养分管理。本研究从粪液中分离获得含水溶性无机磷、有机磷和有机物（碳）的溶液,选择了具不同质地和有机质含量的4个土壤（含高量有机质的黄筋泥、含低量有机质的黄筋泥、淡涂泥和清水沙）,应用等温吸附和土柱模拟淋洗方法研究了可溶性有机碳、无机磷和有机磷共存条件下,粪液中可溶性有机态磷和无机态磷在土壤中的吸附和迁移特性。吸附试验表明,可溶性有机物（碳）的存在大大降低了土壤对有机态磷和无机态磷的吸附,表明施用液态有机肥比施用化肥具有更大的磷流失风险。供试土壤对无机态磷的吸附强度高于有机态磷,但对二者的吸附量大小为:黄筋泥>淡涂泥>清水沙;并与粘粒含量、氧化铁含量呈正相关。有机质较高的土壤对有机磷的吸附明显低于有机质低的土壤。淋洗试验表明,在供试土壤中,这3种可溶性物质在土壤中吸持(包括生物吸持)的顺序为:可溶性无机磷>可溶性有机碳>可溶性有机磷;有机态磷比无机态磷更易在土壤中迁移。     

秸秆及其生物炭对土壤碳库管理指数及有机碳矿化的影响

以河南省粮食主产区壤质潮土和砂土为研究对象,通过盆栽试验和室内恒温培养试验,研究了生物炭与不同腐殖化程度的传统有机物料(秸秆和腐熟鸡粪)单施及配施对壤质潮土和砂土有机碳储量、活性及碳库管理指数的影响,并进一步比较了小麦秸秆直接还田和制炭还田对土壤有机碳矿化的影响,以及生物炭对土壤原有有机碳矿化的调控作用。结果表明:相同添加量下,生物炭对土壤有机碳含量的提升效果优于秸秆和腐熟鸡粪,在壤质潮土和砂土上分别较对照提升了63.15%和115.62%。另外,生物炭显著增加了土壤稳态碳含量和土壤碳库指数(CPI),但降低了土壤碳素有效率(SC)和碳库活度指数(AI),对土壤易氧化有机碳(POXC)和碳库管理指数(CMPI)无显著影响,添加秸秆显著增加了2种土壤POXC含量、基础呼吸和CPMI。进一步通过室内恒温培养试验发现,秸秆可在培养前期(0～37天)大幅度提升2种类型土壤有机碳矿化速率和累积矿化量,秸秆制炭还田对土壤有机碳矿化无显著影响。此外生物炭对土壤原有有机碳矿化的调控作用受其施用量、外源活性有机碳输入和土壤类型的影响,高量生物炭(2%)对非秸秆还田土壤有机碳矿化表现出较强的负激发效应,而低量生物炭(0.55%)对秸秆还田土壤有机碳矿化表现出较明显的负激发效应。因此,从"固碳减排"角度考虑,秸秆制炭还田是更合理的利用方式,且应根据土壤施肥管理措施和土壤类型考虑生物炭的施用量,添加质量比为2%的生物炭可显著抑制土壤原有有机碳矿化,降低CO_2排放,但应避开秸秆快速腐解期施用。     

Nitrogen and phosphorus constrain labile and stable carbon turnover in lowland tropical forest soils

Tropical forests contain a large stock of soil carbon, but the factors that constrain its mineralization remain poorly understood. Microorganisms, when stimulated by the presence of new inputs of labile organic carbon, can mineralize (‘prime’) soil organic matter to acquire nutrients. We used stable carbon isotopes to assess how nutrient demand and soil properties constrain mineralization of added labile (sucrose) carbon and pre-existing (primed) soil carbon in tropical forest soils. In a series of lowland tropical forest soils from Panama, we found that the mineralization of fresh labile carbon was accelerated foremost by phosphorus addition, whereas the mineralization of pre-existing soil carbon was constrained foremost by nitrogen addition. However, there was variation in the relative importance of these nutrients in different soils and the largest effects on the acceleration of sucrose metabolism and constraint of priming occurred following the addition of nitrogen and phosphorus together. The respiration responses due to sucrose or primed soil carbon mineralization were reduced at pH below 4.8 and above 6.0. We conclude that in these tropical forest soils, phosphorus availability is more important in promoting microbial mineralization of sucrose carbon, whereas nitrogen availability is more important in constraining the priming of pre-existing soil organic carbon. This response likely arises because nitrogen is more closely coupled to organic matter cycling, whereas phosphorus is abundant in both organic and inorganic forms. These results suggest that the greatest impact of priming on soil carbon stocks will occur in moderately acidic tropical forest soils of low nitrogen availability. Given long-term changes in both atmospheric carbon dioxide and nitrogen deposition, the impact of priming effects on soil carbon in tropical forest soils may be partially constrained by the abundance of nitrogen.     

Changes in chemical and biochemical soil properties induced by 11-yr repeated additions of different organic materials in maize-based forage systems

The repeated addition of organic materials to the soil greatly affects the physical, chemical and biological characteristics. In the present work, we analyzed changes in soil quality properties of the tilled layer caused by different agronomic managements of maize which supply different amounts of carbon (C) and nitrogen (N) through the addition of slurry, farmyard manure or plant residues. The agronomic history of the analyzed soils, which derived from a medium-term (11 yr) field experiment located in NW Italy, represents typical managements of maize for this region. The area is characterized by highly intensive agriculture, with consequent risks to soil degradation that could be limited by the efficient utilization of organic inputs and by recycling within cropping systems, the large amounts of manure that are produced from the many animal breeding farms in this region. We used a combination of both different chemical (soil organic C and total N) and biochemical indicators (potential soil respiration, potentially mineralizable N (PMN) and potential soil microbial biomass (SMB)). We considered the suitability of the selected biochemical indicators to describe the changes in soil characteristics resulting from the past management.The results showed that the application of the different organic materials, in addition to urea-N fertilizer, increased SOM contents and altered the selected soil biochemical properties compared with the unfertilized treatment, especially in the upper 15 cm of the 0?30 cm tilled soil layer. Farmyard manure applications caused the greatest increase in SOM content, PMN and potential SMB, whilst return of maize straw produced the largest increase in potential soil respiration, but had less effect on total soil organic C and SMB. The use of slurry only caused a moderate increase in SOM and showed intermediate changes in biochemical properties. Also, the rate of C accumulation in the soil per unit of C applied was higher for farmyard manure application than for slurry and straw incorporation in the soil. Fertilization with only mineral N did not induce an increase in C_org and N_tot and even reduces soil N mineralization potential.Because of the high variability in the data, potential SMB carbon could be considered as a less successful indicator for differentiating between past agronomic histories and effects on soil quality, whilst microbial activity (measured by potential soil respiration) and PMN, gave a more reliable and useful indication of the amount of easily decomposable organic carbon.