黄土高原北部典型县域耕地土壤碳氮时空变异特征及影响因素

黄土高原生态环境脆弱，耕地质量的变化直接影响土地生产力的高低。选取其北部典型县域——天镇县，研究长时期耕地土壤有机质和全氮的时空演变规律及其影响因素，为黄土高原耕地质量提升和农业生态环境保护提供理论依据。基于1983年、2008年和2019年耕地质量数据，运用地统计学等方法分析天镇县有机质和全氮的时空演变特征。结果发现：（1）36年（1983—2019年）来，天镇县土壤有机质和全氮含量呈现整体上升、后期快速增加的变化特征。有机质和全氮含量的年均增加量前期（1983—2008年）较低，分别为0.20 g?kg-1和0.01 g?kg-1，在后期（2008—2019年）较高，分别为0.29 g?kg-1和0.03 g?kg-1。碳氮比呈现前期无显著变化，后期显著降低。（2）36年来土壤有机质和全氮的块基比均提升至高于25%，表明地形等自然因素影响逐渐减弱，施肥等人为因素影响增强。（3）土壤有机质和全氮的空间分布特征相似，呈现西部低、东部高的格局，西北部和中部的变化速度快。综上，36年（1983—2019年）来，施肥及秸秆还田等因素是导致天镇县有机质和全氮含量变化的主要因素，因此，结合当地条件增施有机肥、推广秸秆还田并合理施用氮肥能快速提升耕地土壤肥力。     

Influence of tree crown characteristics on the local PM10 distribution inside an urban street canyon in Antwerp (Belgium): A model and experimental approach

Apart from influencing the amount of leaf-deposited particles, tree crown morphology will influence the local distribution of atmospheric particles. Nevertheless, tree crowns are often represented very rudimentary in three-dimensional air quality models. Therefore, the influence of tree crown representation on the local ambient PM₁₀ concentration and resulting leaf-deposited PM₁₀ mass was evaluated, using the three-dimensional computational fluid dynamics (CFD) model ENVI-met^® and ground-based LiDAR imaging. The modelled leaf-deposited PM₁₀ mass was compared to gravimetric results within three different particle size fractions (0.2–3, 3–10 and >10 μm), obtained at 20 locations within the tree crown. Modelling of the LiDAR-derived tree crown resulted in altered atmospheric PM₁₀ concentrations in the vicinity of the tree crown. Although this model study was limited to a single tree and model configuration, our results demonstrate that improving tree crown characteristics (shape, dimensions and LAD) affects the resulting local PM₁₀ distribution in ENVI-met. An accurate tree crown representation seems, therefore, of great importance when aiming at modelling the local PM distribution.     

Effects of best management practices on dry matter production and fruit production efficiency of oil palm

Enhancing dry matter production with higher partitioning to fruit bunches is important for sustainable intensification of oil palm. A series of best management practices including site-specific nutrient management, canopy management, and harvesting has been developed for oil palm plantations. However, the effects of these practices on dry matter production and partitioning, and how the effects vary with climatic and soil conditions of plantation sites, remain largely unknown. We established a four-year field trial including 30 paired commercial blocks across Sumatra and Kalimantan, Indonesia. The paired treatments included site-specific best management practices, and standard estate practices as the control. The annual production of aboveground dry matter was 30.0 ± 0.5 t ha⁻¹ yr⁻¹ (mean ± se) under best management practices, higher than 28.8 ± 0.5 t ha⁻¹ yr⁻¹ under standard estate practices. The bunch index, an indicator of the fruit production efficiency, increased by 12% under best management practices compared to standard estate practices. Partitioning of dry matter to the fronds decreased by 8% under best management practices, compared to standard estate practices. The positive effect of best management practices on the annual production of total aboveground dry matter was stronger in the plantation site with higher annual rainfall. These results are useful for optimizing management practices to improve sustainable intensification of oil palm.     

Three decades following afforestation are sufficient to yield δ13C depth profiles

Vertical gradients in stable carbon isotope ratios (δ¹³C) in soil profiles can serve to approximate decomposition of organic matter under field conditions. This study tested the time (0, 30, and ≥ 150 y) required for the development of vertical δ¹³C profiles in topsoil by comparing arable, afforested and continuously forested sites, and showed that three decades following afforestation of former cropland are sufficient to develop distinct δ¹³C depth profiles.     

Can conservation tillage mitigate climate change impacts in Mediterranean cereal systems? A soil organic carbon assessment using long term experiments

Simulation models, informed and validated with datasets from long term experiments (LTEs), are considered useful tools to explore the effects of different management strategies on soil organic carbon (SOC) dynamics and evaluate suitable mitigative options for climate change. But, while there are several studies which assessed a better prediction of crop yields using an ensemble of models, no studies are currently available on the evaluation of a model ensemble on SOC stocks. In this study we assessed the advantages of using an ensemble of crop models (APSIM-NWheat, DSSAT, EPIC, SALUS), calibrated and validated with datasets from LTEs, to estimate SOC dynamics. Then we used the mean of the model ensemble to assess the impacts of climate change on SOC stocks under conventional (CT) and conservation tillage practices (NT: No Till; RT: Reduced Tillage). The assessment was completed for two long-term experiment sites (Agugliano – AN and Pisa – PI2 sites) in Italy under rainfed conditions. A durum wheat (Triticum turgidum subsp. durum (Desf.) Husn.) – maize (Zea mays L.) rotation system was evaluated under two different climate scenarios over the periods 1971–2000 (CP: Present Climate) and 2021–2050 (CF: Future Climate), generated by setting up a statistical model based on canonical correlation analysis. Our study showed a decrease of SOC stocks in both sites and tillage systems over CF when compared with CP. At the AN site, CT lost −7.3% and NT −7.9% of SOC stock (0–40 cm) under CF. At the PI2 site, CT lost −4.4% and RT −5.3% of SOC stocks (0–40 cm). Even if conservation tillage systems were more impacted under future scenarios, they were still able to store more SOC than CT, so that these practices can be considered viable options to mitigate climate change. Furthermore, at the AN site, under CF, NT demonstrated an annual increase of 0.4%, the target value suggested by the 4 per thousand initiative launched at the 21st meeting of the Conference of the Parties in Paris. However, RT at the PI2 needs to be coupled with other management strategies, as the introduction of cover crops, to achieve such target.     

磷影响大豆根系分泌有机酸总量和不同根区有机酸量

采用营养液培养的方法,设置由无磷转化为供磷(0-50)和由供磷转换为无磷(50-0)2个处理,分析了磷转换处理对不同根区有机酸的影响.结果表明:大豆生长对磷素的需求非常迫切,50-0处理根系可溶性磷含量相对较高,而0-50处理地上部可溶性磷含量相对较高;50-0处理根系有机酸分泌量较0-50处理大,而且分泌量随着距离根...     

Changes during winter in water‐stable aggregation due to crop residue quality

There is a need to develop practices that contribute to increased water‐stable aggregation (WSA) during winter in a humid temperate climate when soil is particularly prone to water erosion. Our objectives were to determine the effects of crop residue quality on WSA during winter and to relate these effects to biochemical indicators of fungal and bacterial biomass. Three graminae crop residues were selected for their different C/N ratios and biochemical characteristics (green oat residues, C/N = 18.8; wheat straw, C/N = 125.6; and mature miscanthus residues, C/N = 311.3). In October 2009, crop residues were added with an equivalent amount of C in the 0–10 cm layer to a Luvisol in north‐west France. WSA, expressed as mean weight diameter (MWD), amino sugar, soil mineral N and water contents were measured at regular intervals during 5 months. Aggregate MWD of the control soil decreased rapidly and remained low until the last sampling date in March which illustrates the structural vulnerability of bare soils in winter in this pedo‐climatic area. The incorporation of all three crop residues had significant positive impacts on aggregate MWD. Despite widely different C/N ratios, the maximum MWD under each treatment was similar (three times greater than the control soil). Maximum MWD occurred at times that clearly depended on residue quality. Maximum values occurred early for green oat (29 day), but were delayed to 50 day for wheat straw and to 154 day for miscanthus. Results from correlation analysis suggest that variations in WSA were partly mediated by microbial agents with a dominant effect of bacteria for green oat and a combined role of fungal and bacterial biomass for wheat straw. We suggest that the maximum MWD associated with the miscanthus late in the experiment is related to changes in the composition of the fungal community. Overall, our study shows that autumn application of crop residues increases WSA during winter with its effect being microbially mediated and determined by residue quality.