Estimation of Runoff,Peak Discharge and Sediment Load at the Event Scale in a Medium‐Size Mediterranean Watershed Using the Annagnps Model

In this paper, the Annualized Agricultural Non‐Point Source (AnnAGNPS) model has been used to estimate runoff, peak discharge and sediment load at the event scale in a Mediterranean watershed. The study area is the Carapelle torrent, Southern Italy (area = 506 km²), where continuous rainfall, streamflow and sediment load data are available. Nineteen flood events have been registered in the period 2007–2009 and were used for the application of the model. The aim of the paper is to evaluate the predictive accuracy of the model at the event scale, in a medium‐size watershed, given the specific conditions of the semi‐arid environments. A sensitivity analysis has been carried out to assign the correct parameterization: the mean normalized output variation of the most meaningful input parameters pointed out the influence of the curve number on runoff, peak discharge and sediment load predictions (values greater than 1); the MN Manning's roughness coefficient and K, C and P factors of the universal soil loss equation showed a moderate influence on sediment load simulations (values between 0·5 and 1). The selection of the Soil Conservation Service synthetic storm types has been based on the observed storm events analysis to improve the peak discharge simulations. The model prediction has proved to be good for runoff (R² = 0·74, NSE = 0·75, W = 0·92) and peak discharge (R² = 0·85, NSE = 0·70, W = 0·94), and satisfactory for sediment yield (R² = 0·70, NSE = 0·63, W = 0·91). The relative error is lower for high events; this result is quite interesting in semi‐arid environments, where most of the annual sediment yield is concentrated in a few, severe events. Copyright © 2013 John Wiley & Sons, Ltd.     

Changes in Physical Properties of Soils with Land Use Time in the Brazilian Savanna Environment

Soils from central Brazil have been intensively used over the last decades because of the rapid conversion of savannas ( Cerrado ) into corn/soybean fields. The objective of this work is to study modifications in the physical properties of soils in the Rio Verde watershed, as a function of the land use time for agriculture, determined from classification of Landsat satellite images between 1980 and 2010. Soil samples were collected at surface (0–20 cm) and subsurface (20–40 cm) horizons for the different classes of land use time (<10, 10–20, 20–30, and >30 years). The following physical properties were measured: bulk density (BD), air permeability (K_a), penetration resistance (PR), microporosity (MI), macroporosity (MA), and total porosity (TP). Results showed a strong expansion with time of agriculture that occupied 35·3% (1980), 37·4% (1990), 51·3% (2000), and 60·9% (2010) of the watershed area. When properties were compared with those from the reference areas (preserved soils under native vegetation), significant differences were observed for all the physical attributes of soils for a land use time higher than 20 years. Overall, BD and PR increased with land use time, and the opposite was verified for K_a, MA, and TP. Some physical properties presented values (e.g., 1·54 g cm⁻³ for BD and 0.06 cm³ cm⁻³ for MA) close to the critical ones reported to affect crop development, but they were not still impacting on local soybean yield. Copyright © 2013 John Wiley & Sons, Ltd.     

Impact of Land Use and Land Cover Changes on Organic Carbon Stocks in Mediterranean Soils (1956–2007)

During the last few decades, land use changes have largely affected the global warming process through emissions of CO₂. However, C sequestration in terrestrial ecosystems could contribute to the decrease of atmospheric CO₂ rates. Although Mediterranean areas show a high potential for C sequestration, only a few studies have been carried out in these systems. In this study, we propose a methodology to assess the impact of land use and land cover change dynamics on soil organic C stocks at different depths. Soil C sequestration rates are provided for different land cover changes and soil types in Andalusia (southern Spain). Our research is based on the analysis of detailed soil databases containing data from 1357 soil profiles, the Soil Map of Andalusia and the Land Use and Land Cover Map of Andalusia. Land use and land cover changes between 1956 and 2007 implied soil organic C losses in all soil groups, resulting in a total loss of 16·8 Tg (approximately 0·33 Tg y⁻¹). Afforestation increased soil organic C mostly in the topsoil, and forest contributed to sequestration of 8·62 Mg ha⁻¹ of soil organic C (25·4 per cent). Deforestation processes implied important C losses, particularly in Cambisols, Luvisols and Vertisols. The information generated in this study will be a useful basis for designing management strategies for stabilizing the increasing atmospheric CO₂ concentrations by preservation of C stocks and C sequestration. Copyright © 2012 John Wiley & Sons, Ltd.     

收获期木薯地耕作层土壤硬度的试验研究

采用田间物理测定和数理统计分析方法,测定了收获期木薯种植地耕作层不同深度的土壤硬度,建立了耕作层深度与土壤硬度的数学模型,分析了土层深度对土壤硬度的影响规律。结果表明:建立的木薯地耕作层土壤硬度与深度的数学模型精度高,硬度与深度基本上成3次方的非线性关系;采用盖膜方式种植的木薯地,其土壤硬度先随土层深度的增大而增大,后随土层深度的增大而缓慢增大或减小;不采用盖膜方式种植的木薯地,其土壤硬度先随土层深度的增大而减小,后随土层深度的增大而增大,最后又随土层深度的增大而减小。     

基于RAGA的PPC模型在黑土区玉米调亏灌溉评价中的应用

调亏灌溉作为一种行之有效的节水灌溉方式,对黑土区农业水资源的可持续高效利用具有重要意义。而调亏灌溉方案的优劣取决于它的综合效果,难以直观评价。以2013年在黑龙江省红星农场进行的玉米调亏灌溉技术效应的试验研究为基础,选取了8个评价指标,采用投影寻踪分类模型(PPC),利用基于实数编码的加速遗传算法(RAGA)优化其投影方向,根据投影函数值得到各评价指标对综合评价的贡献大小对不同调亏处理的各项指标进行排序。结果表明:苗期水分调亏程度为田间持水量60%的处理为最佳调亏灌溉方案,产量和水分利用效率比适宜调亏灌溉处理分别提高了2.11%和6.42%。研究结果可为黑土区玉米灌溉管理提供科学依据。     

制种玉米密度对土壤水分及产量构成的影响研究

通过田间试验,就制种玉米密度对土壤水分、农艺性状、产量构成及产量的影响进行了研究分析。结果表明:1在拔节期以前,低密组的土壤含水量比高密组的高;在拔节期到灌浆期,高密组的比低密组的高。在整个生育期,拔节期前土壤含水量比较高,而后逐渐降低,吐丝期达到最低,然后又逐步上升。2在一定密度范围内,制种玉米株高、亩产量随着密度的增大而增加单株产量产量相反;叶长、穗粗、穗粒数先随着密度的增大而减小,后随着密度的增大而增大;叶宽、穗长、百粒重、出籽率先随着密度的增大而增加,后随着密度的增大而减小;叶面积、茎粗、穗位先随着密度的增大而减小,后随着密度的增大而增加,然后又随着密度的增大而减小,秃顶变化规律相反。     

基于HYDRUS-2D的地下滴灌下水分运移数值模拟研究

利用HYDRUS-2D软件模拟了地下滴灌条件下滴头周围黏壤土的土壤水分动态,并与田间观测进行对比;通过分析不同滴头流量对试验地土壤湿润模式的影响,明确了最佳灌水技术参数。结果表明,HYDRUS-2D软件模拟结果与观测值一致,体积含水率均方根误差为1.2%~4.5%,湿润范围均方根误差变化范围为2.1~3.87cm。     

玉米秸秆残茬覆盖对大豆田土壤水温效应的影响

研究了传统耕作、玉米原垄留茬耕作、玉米原垄留茬全覆盖、玉米留茬条带覆盖、浅松覆盖和深松覆盖6种耕作方式下土壤含水率、棵间蒸发量和地温的变化。结果表明,条带覆盖对大豆不同生育期土壤剖面含水率影响最大;其他耕作方式对棵间蒸发的抑制作用均小于传统耕作;日平均地温在苗期变化明显;保护性耕作对日平均地温影响较大,传统耕作最高,留茬全覆盖最低。     

放牧管理模式对高寒草甸草原土壤养分特征的影响

为探讨不同放牧管理模式下高寒草甸草原土壤养分特征的变化,对青藏高原东缘禁牧(NG)、全生长季休牧(RG)、传统夏季休牧(TG)和连续放牧(CG)4种放牧管理模式下高寒草甸草原土壤有机质、全氮、全磷、全钾、速效氮、速效磷和速效钾含量进行测定和分析。结果表明:(1)NG显著增加了0~30cm土层有机质含量,RG和TG显著增加了0~20cm土层有机质含量;(2)NG,RG和TG显著提高了高寒草甸草原0~30cm土层全氮含量和20~30cm土层速效氮含量,而降低了0~10cm土层的速效氮含量;(3)NG,RG和TG显著提高了高寒草甸草原0~30cm土层全磷和速效磷含量;(4)不同模式放牧对高寒草甸草原土壤全钾含量无显著影响,但总体上,NG,RG和TG高于CG;NG,RG和TG降低了0~10cm土层速效钾含量,而显著增加了10~30cm土层速效钾含量。连续放牧使土壤养分流失严重,从而导致土壤肥力降低,而禁牧和季节性休牧能有效增加青藏高原东缘高寒草甸草原土壤的养分含量,是该区和类似区域草地放牧管理的理想选择。     

放牧管理对西藏高寒沼泽植物群落结构和土壤碳氮的影响

对西藏当雄县3种不同放牧管理模式(冬季放牧、冬春季放牧和全年放牧)下的高寒沼泽的植物群落结构和土壤碳氮进行了调查。调查发现,3种放牧管理模式下的高寒沼泽植物群落总盖度差异不显著,而优势物种藏嵩草的高度和盖度差异显著;放牧管理对沼泽群落结构和物种多样性影响较大,随着放牧强度的增加,物种丰富度增加;放牧利用显著降低了高寒沼泽湿地群落优势物种藏嵩草的高度和盖度,其优势度也显著降低,使得高寒沼泽逐渐退化。冬季放牧、冬春季放牧和全年放牧沼泽地上生物量和地下生物量依次降低。同时,随着放牧强度的增加,高寒沼泽表层土壤有机碳氮的含量也显著降低,且高寒沼泽表层土壤碳氮与地上和地下生物量显著正相关。通过对比分析,冬季放牧是当前西藏高寒沼泽较好的放牧管理模式。