Physico-chemical properties of commercial composts varying in their source materials and country of origin

Composting is a partially controlled bio-oxidative process through which highly heterogeneous organic matter (OM) in its solid-state transforms into a humified material. The variability of the OM undergoing composting makes compost research a great challenge. Our purpose was to define chemical and plant response characteristics of a variety of composts, grouped based on their major source materials. Thirty-seven commercial composts were collected from France, Greece and the Netherlands. When grouped by country of origin, significant differences were found in %OM, %C, %N, dissolved organic carbon (DOC) concentration, electrical conductivity (EC) and NO₃ concentration. These differences may be attributable to source materials or local regulations and quality control measures. When the composts were classified into 7 groups by their source materials: wood, green, manure, grape marc (GM), oilcake, spent mushroom substrate and municipal solid waste-based composts, significant differences between groups were found in %OM, %C, %N, DOC, pH, EC, NO₃ and soluble sugars. Extracts of composts from all groups, except GM and oilcake had absorbance in the UV and visible range that was linearly correlated with DOC. GM and oilcake compost extracts had lower absorbances and distinctly lower specific UV absorbance (SUVA). Diffuse reflectance infrared Fourier Transform (DRIFT) spectra of the composts from different source groups also exhibited distinct group features (e.g. the ratio of polysaccharide to aliphatic peak intensity), whereas NMR spectra did not. Cucumber plants grown on manure-based composts had greater fresh weight than those grown on other composts. Plants grown on oilcake and GM composts exhibited low fresh weight. The difference in characteristics of the oilcake and GM composts may be a result of their unique chemical composition which slows their degradation. It may also be related to their relatively low degree of maturity, which is a consequence of their slow degradation.     

Export rate of dissolved organic matter from paddy fields during cultivation-activity events

The aim of this study is to quantify the dissolved organic carbon (DOC) of drainage water from paddy fields in agricultural areas of Tottori prefecture, Japan. In four experimental paddy fields, DOC concentration varied much from 1.1 to 10.1 mg C l⁻¹, and was the highest during heavy runoff that occurred in April when there was a non-agricultural period. However, variation in DOC concentration did not always correspond to rainfall, but depended more on cultivation-activity events such as tilling, planting, draining in summer, and final draining in autumn. The water discharge rate from each experimental field was estimated by using a hydrologic model (the Tank Model and a genetic algorithm). Daily DOC export rate per unit area of three experimental paddy fields was calculated to be 0.0074, 0.0052, and 0.0081 kg a⁻¹ day⁻¹, respectively. The daily DOC export rate showed large seasonal variation with the highest value in May and June. It can be concluded that DOC export from paddy fields can be a substantial source of DOC in receiving waters, and the export rate depends much on cultivation method practice. It might be suggested that DOC export from paddy fields can be controlled by a better water management practice of farmers.     

土地耕作后微生物量碳和水溶性有机碳的动态特征

采用野外观测与室内模拟试验相结合的方法,研究了湿地土壤和垦殖10年的农田耕作后土壤呼吸通量、微生物量碳、土壤基础呼吸、土壤qCO2值、水溶性有机碳的动态特征。研究结果表明:小叶章湿地耕作后,土壤含水量明显下降(p<0.05);土壤CO2通量在最初的1~2 d形成一个排放高峰,农田耕作土壤CO2通量一直显著高于未耕作土壤(p<0.01)。农田土壤微生物量碳含量显著低于小叶章湿地(p<0.001)。在耕作后最初的1~3 d,湿地和农田土壤微生物量碳均没有显著的变化;之后,土壤微生物量碳迅速增加,显著高于未耕作土壤。观测时间内,耕作农田土壤微生物量碳含量始终显著高于未耕作土壤(p<0.01)。垦殖10年农田土壤耕作后,对土壤水溶性有机碳含量无显著影响。湿地耕作后,土壤水溶性有机碳迅速增加。在耕作后80 d内,土壤水溶性有机碳含量显著高于未耕作土壤(p<0.01)。之后,则低于未耕作土壤。     

红壤稻田土壤溶解有机碳含量动态及其生物降解特征

本通过田间采样分析和室内培育试验,研究了不同利用年限的3种红壤水田土壤中溶解有机C(DOC)的含量动态和生物降解特征。结果表明：土壤DOC的含量随土壤深度而降低,二具有显负相关性。0-30cm土壤DOC的含量及其占总C比例随土壤有机C含量的升高而增大。DOC的季节变化明显,主要与气候因素有关：降雨和灌水可显提高DOC的含量,是落干时含量的1．44-2．50倍。淋溶试验结果表明,从试验开始,淋滤液中DOC的浓度呈增加趋势,至2l天时达到最大,其后又趋下降。在49天的培养期内,DOC的分解速率为3l％-58％,其中低分子量组分能在数天内降解掉。不同土壤间DOC的分解速率有明显差异。     

How important is plant litter to the regulation of mineral‐N leaching to streams in winter? An observations‐led experimental approach

Ammonium‐N concentrations were frequently observed to exceed nitrate‐N concentrations in an intermittently flowing stream draining acid grassland in North Yorkshire. This prompted the design of a soil microcosm experiment to investigate the role of litter in the leaching of ammonium and nitrate from soil profiles during winter. Drainage water was analysed weekly for N species, pH, mineral acid anions and dissolved organic carbon (DOC) for a period of 11 weeks, while extractable mineral‐N was determined after 5 and 11 weeks. The results demonstrate that litter plays an important role in reducing mineral‐N leaching in winter months. They also suggest that DOC from the litter participates in mineral‐N retention in the soil profiles in winter. Ammonium‐N and nitrate‐N concentrations measured in the microcosm drainage water are similar to those of the stream.     

Clear-cutting reduces nitrate leaching in a pine plantation of high natural N status

Following the tree harvest, the biogeochemistry of a catchment is modified by changes in soil temperature and moisture, and nutrient cycling. We monitored soil-solution and stream-water chemistry, and soil properties in a Pinus radiata D. Don plantation in New Zealand before and after clear-cutting and replanting in 1997. The annual rainfall during the study was 1440–1860 mm. The soil was a 1800-year-old pumice soil of high natural N status; the catchment had received large inputs of volcanic N in rain, probably over the 1800 years since the pumice had been deposited. The leaching loss of nitrate-N was 28 kg ha⁻¹ yr⁻¹ in 1996, and then decreased sharply after clear-cutting to 3 kg ha⁻¹ yr⁻¹ in 1998 and <1 kg ha⁻¹ yr⁻¹ in 1999. Weed growth and soil microbial biomass increased during this time, and would have removed much of the N from soil solution in the upper soil layers. Although the catchment was small (8.7 ha), there was a 2-year lag until N decreased in stream-water; the losses of dissolved organic N to stream-water were low. There was no change in soil pH over the 4 years, but spring-water pH appeared to increase, which was consistent with the increase in bicarbonate that accompanied grass/weed growth. The export of cations (mmol_c l⁻¹) in the spring-water was Na>Ca>Mg=K as expected for rhyolitic pumice, and the total concentration was probably controlled by the accompanying anions. The export of anions was NO₃=Cl>SO₄=HCO₃ before harvest and HCO₃=Cl>SO₄=NO₃ after harvest.     

Dissolved organic carbon and nitrogen leaching from Scots pine, Norway spruce and silver birch stands in southern Sweden

The effects of three common tree species - Scots pine, Norway spruce and silver birch - on leaching of dissolved organic carbon and dissolved nitrogen were studied in an experimental forest with podzolised soils in southern Sweden. We analyzed soil water collected with lysimeters and modeled water fluxes to estimate dissolved C and N fluxes. Specific UV absorbance (SUVA) was analyzed to get information about the quality of dissolved organic matter leached from the different stands. Under the O horizon, DOC concentrations and fluxes in the birch stands were lower than in the spruce and pine stands; annual fluxes were 21 g m⁻² y⁻¹ for birch and 38 g m⁻² y⁻¹ and 37 g C m⁻² y⁻¹ for spruce and pine, respectively. Under the B horizon, annual fluxes for all tree species ranged between 3 and 5 g C m⁻² y⁻¹, implying greater loss of DOC in the mineral soil in the coniferous stands than in the birch stands. We did not find any effect of tree species on the quality of the dissolved organic matter, as measured by SUVA, indicating that the chemical composition of the organic matter was similar in leachates from all three tree species. Substantial amounts of nitrogen was leached out of the soil profile at the bottom of the B horizon from the pine and birch stands, whereas the spruce stands seemed to retain most of the nitrogen in the soil. These differences in N leaching have implications for soil N budgets.     

连续6年施用生物炭和炭基肥对棕壤生物活性的影响

为了明确生物炭与传统土壤培肥方式对土壤中生物活性的影响,通过连续6年微区定位试验,以传统的土壤培肥方式作为对照,探究较长时间施用生物炭和炭基肥对土壤酶活性的影响,以更好地揭示施用生物炭对农业土壤微生态环境的影响,为生物炭农用提供理论参考。定位试验于2009年开始,连续6年进行了花生微区田间试验(2 m2)。试验设4个处理,分别为秸秆还田+NPK(CS)、施用猪厩肥+NPK(PMC)、生物炭+NPK(BIO)和炭基肥(BF)处理。测定了2014年播前以及花生各生育时期土壤中过氧化氢酶、蔗糖酶、脲酶以及微生物量碳和可溶性有机碳含量等指标。结果表明,连续施用6年后,BIO处理中土壤过氧化氢酶活性除播前和成熟期与CS及PMC处理相近外,其他生育时期均显著(P0.05)低于这2个处理;土壤蔗糖酶活性除成熟期外其他时期均高于CS和PMC处理。BF处理中土壤过氧化氢酶活性除播前处于较高水平,其他生育时期与CS和PMC相比均处于较低水平;土壤蔗糖酶活性除结荚期外其他生育时期均接近或者低于CS和PMC处理。与CS和PMC处理相比,BIO和BF处理对脲酶活性的影响没有表现出明显的规律性。BIO和BF处理除成熟期外,其他生育期中土壤微生物量碳含量均低于PMC处理。在花针期相对于CS和PMC处理,BIO处理中可溶性有机碳含量提高,BF中处理可溶性有机碳含量降低。与CS和PMC相比,施用生物炭会抑制土壤过氧化氢酶活性,提高蔗糖酶活性,提高了土壤可溶性有机碳含量;施用炭基肥抑制了过氧化氢酶、蔗糖酶活性,降低了可溶性有机碳含量,生物炭和炭基肥对脲酶活性的影响没有表现出明显规律性,对微生物活性提高的作用在秸秆还田和施用猪厩肥之间。     

不同可溶性有机碳对铜在土壤中迁移的影响

土壤中可溶性有机碳（DOC）的存在被认为是能促进重金属在土壤中迁移的重要因素之一,但不同DOC的作用效果可能不同。本研究以Cu为研究对象,利用饱和土壤恒定流条件下的混合置换实验,试图阐明：不同DOC（胡敏酸（HA）和柠檬酸（CA））在土壤中的迁移过程,及其对Cu在土壤中迁移的促进作用。结果表明CA在砂土和红壤性水稻土中的移动能力高于HA;而HA和CA均有促进Cu在土壤中迁移的趋势,但CA的促进效果更为明显,这可能与CA比HA更能提高环境pH值及HA的分子比较大有关;尽管Cu在供试的两种土壤中的迁移能力均很弱,但其在质地粘重的红壤性水稻土中的迁移潜力似乎大于其在砂土中的迁移潜力。上述结果表明,当土壤中加入DOC含量较高的溶液时,Cu在土壤中迁移能力的增强可能主要与土壤溶液中存在可移动的Cu-有机质络合物有关,为验证这一研究结果,进一步的田间和长期试验十分必要。     

Soil biology and warming play a key role in the release of ‘old C’ from organic soils

A radiocarbon approach was used to investigate the roles of temperature and soil fauna activity in the turnover of ‘old’ non-labile carbon in a peatland ecosystem. We investigated the impacts of enchytraeids on carbon turnover in two different soil layers, with different incorporation of the ‘bomb’ peak, when incubated at two different temperatures. Results showed that, in agreement with previous studies, warmer temperatures promoted reproduction rates of enchytraeids, with the top layer supporting higher animal densities and biomass. With independence of the animal treatment, soil respiration in the top 5 cm was four times higher than in the deeper layer suggesting that decomposition was greater in the upper layer, with the response being greater at the highest temperature treatment. Furthermore, independent of temperature, the presence of enchytraeids in the top layer significantly enhanced the release of non-labile C as DOC. Similarly, at the bottom layer, ‘older’ C sources were mobilised in response to warming and a greater amount of pre-bomb carbon was released into the soil solution at 20 °C when the worms were present. A strong positive link between the ages of the C assimilated by the animals and released through mineralization suggests an important role of soil biology in the mobilisation of the older C pools in soils and should be taken into account in developing global C models to predict the response of soil C dynamics to climate change.