Parameter selection and testing the soil nitrogen dynamics model SOILN

Abstract. The SOILN model with a crop growth submodel for grass and cereal crops and the associated soil water and heat model SOIL were selected out of a number of similar models to simulate nitrogen cycling in a soil/crop system. The main parameter values required by the model were selected on the basis of a combination of field experiments and literature sources. Experimental data measured on grassland at Dumfries in the West of Scotland and on arable land at Bush Estate near Edinburgh were used to test the model. Simulated biomass yields and nitrogen contents of harvested biomass were in reasonable agreement with measured values for both grass and cereal crops. There were similar trends in accumulated leached nitrate between the simulations and experiments at the sites. Any discrepancy between simulated and measured nitrate leached appeared to correspond to similar discrepancies between simulated and measured water flow. The comparison between simulated and experimental results suggests that the model with the selected parameter values can simulate nitrogen and carbon cycling both in grassland and in arable land, and make convincing predictions about the effects of varying soil, crop, fertilizer and manure management practices. A basic sensitivity analysis carried out on the parameters determining the biological and biochemical processes showed the model predictions of annual N-leaching are relatively insensitive to all but two of the plant parameters. However, the model predictions of annual N-harvested and dry mass production are sensitive to numerous plant parameters.     

北京延庆县耕地整理潜力多因素综合评价数据模型

耕地整理潜力进行科学评价是土地整理潜力评价的重点。该文在综合分析了耕地整理潜力评价问题特点的基础上,提出了采用“组合法”评价耕地整理潜力的思路,并结合北京市延庆县进行了实证研究,在实证研究中采用了模糊评判模型和加权指数和法模型对耕地整理潜力进行组合评价,同时每种模型均采用基于成对比较法和灰色关联度法确定的综合权重。这种评价方法综合了各种评价方法的优点,避免了简单加权法中的缺点,使评价结果更科学、合理、可靠。研究结果可对耕地整理潜力评价研究有所借鉴。     

The spatial variability of soil nitrates in arable and pasture landscapes: implications for the development of geographical information system models of nitrate leaching

Abstract. In response to the European Community Nitrate Directive (91/676) a catchment scale Geographical Information System (GIS) model of nitrate leaching has been developed to map nitrate vulnerability and predict average weekly fluxes of nitrate from agricultural land units to surface water. This paper presents a pilot study which investigated the spatial variability of soil nitrates in order to: (1) define an appropriate pixel size for modelling N leaching; (2) quantify the within-unit variability of soil nitrate concentrations for pasture and arable fields; and (3) assist in the design of an efficient sampling strategy for estimating mean nitrate concentrations. Soil samples, taken from two 800 m transects in early September 1994, were analysed for water soluble nitrate. The arable soils had a mean nitrate-nitrogen concentration of 0.693 μg/g (S.E. 0.054 μg/g) and the pasture soils had a higher mean nitrate-nitrogen concentration of 0.86 μg/g (S.E. 0.085 μg/g). Spatial variability was investigated using variograms. The pasture data had a weak spatial relationship, whereas the arable data exhibited a strong spatial relationship which fitted a spherical variogram model (r² 0.87), with a range of 40 m. A pixel size of 40 m is suggested for nitrate modelling within the GIS based on the arable variogram and an improved sampling strategy for model validation is suggested, involving bulking sub-samples over a 40 m grid for estimating mean nitrate concentrations in combined land use and soil units.     

The effect of crop, N-level, soil type and drainage on nitrate leaching from Danish soil

Abstract. Nitrate leaching measurements in Denmark were analysed to examine the effects of husbandry factors. The data comprised weekly measurements of drainage and nitrate concentration from pipe drains in six fields from 1971 to 1991, and weekly measurements of nitrate concentration in soil water, extracted by suction cups at a depth of 1 m, from 16 fields in 1988 to 1993. The soils varied from coarse sand to sandy clay loam.
The model used for analysing the data was: Y = exp (1.136–0.0628 clay + 0.00565N + crop ) D^0.416, with R²= 0.54, where Y is the nitrate leaching (kg N/ha per y), clay is the % clay in 0-25 cm depth (%), N is the average N-application in the rotation (kg/ha/y) and D is drainage (mm/y). The most important factor influencing leaching was the crop type. Grass and barley undersown with grass showed low rates of leaching (17-24 kg/ha/y). Winter cereal following a grass crop, beets, winter cereals following cereals and an autumn sown catch crop following cereals showed medium rates of leaching (36-46 kg/ha/y). High rates of leaching were estimated from winter cereals following rape/peas, bare soil following cereals and from autumn applications of animal manure on bare soil (71-78 kg/ha/y). Estimates of leaching from soil of 5, 12 and 20% clay were 68, 44 and 26 kg/ha/y, respectively. Leaching was estimated to rise significantly with increasing amounts of applied N.
The model is suitable for general calculations of the effects of crop rotation, soil type and N-application on nitrate leaching from sandy soil to sandy clay loarns in a temperate coastal climate.     

湖北省耕地变化与粮食生产的特征分析

耕地资源是保障粮食安全及社会稳定的基石.在分析湖北省1978-2008年耕地面积和粮食产量变化的基础上,进一步分析了最小人均耕地面积和耕地压力指数的变化特点;采用GM(1,1)方法对未来10 a耕地、人口、粮食产量、最小人均耕地面积和耕地压力指数进行了预测.结果表明:(1)1978年来,湖北省人均耕地面积和人均粮食产量不断减少,最小人均耕地面积总体变化呈波浪式降低而耕地压力指数呈波浪式上升.(2)未来10 a,最小人均耕地面积将逐年降低而耕地压力指数将逐年升高,人均耕地面积降低速度快于实际最小人均耕地面积的降低速度,耕地面积难以保证粮食生产安全.并对此提出了相关建议.     

基于反现实情景模拟的耕地“进出平衡”政策绩效预测

探究情景模拟下耕地进出平衡政策实施绩效与影响,有助于完善该政策机制和促进耕地保护。该研究以广州市为例,通过构建现实情景（政策实施情景）和反现实情景（惯性发展情景）下的农用地内部转换决策效用函数、土地利用需求预测模型和基于元胞自动机（cellular automata,CA）的土地利用转换潜力综合模型,对比分析两种情景下的土地利用时空动态格局变化,对该政策未来实施绩效进行预测。结果表明：1）该政策实施有效减少了广州市耕地的流失,政策实施情景中2020—2030年耕地流向非耕农用地的面积减少了20.40km²;2）该政策实施对耕地和园地的景观格局影响较大,政策实施情景中耕地的聚集程度更高,但园地的破碎程度更大;3）政策实施情景中2020—2030年广州市农用地内部地类数量比例保持平衡,较多园地恢复为耕地,且各地类分布更加均匀。耕地进出平衡政策未来在广州市的实施绩效良好,有效减少了耕地流失,维持了农用地内部结构比例,促进了园地向耕地转换,对保持耕地数量动态平衡、保障国家粮食安全具有重要意义。     

How important is N2O production in removing atmospherically deposited nitrogen from UK moorland catchments?

Nitrate (NO₃⁻) leaching due to anthropogenic nitrogen (N) deposition is an environmental problem in many parts of the UK uplands, associated with surface water acidification and affecting lake nutrient balances. It is often assumed that gaseous return of deposited N to the atmosphere as N₂O through denitrification may provide an important sink for N. This assumption was tested for four moorland catchments (Allt a’Mharcaidh in the Cairngorms, Afon Gwy in mid-Wales, Scoat Tarn in the English Lake District and River Etherow in the southern Pennines), covering gradients of atmospheric N deposition and surface water NO₃⁻ leaching, through a combination of field and laboratory experiments. Field measurements of N₂O fluxes from static chambers with and without additions of NH₄NO₃ solution were carried out every 4 weeks over 1 yr. Wetted soil cores from the same field plots were used in experimental laboratory incubations at 5 and 15 °C with and without additions of NH₄NO₃ solution, followed by measurement of N₂O fluxes. Field measurements showed that significant N₂O fluxes occurred in only a very small number of plots with most showing zero values for much of the year. The maximum fluxes were 0.24 kg-N/ha/yr from unamended plots at the River Etherow and 0.49 kg-N/ha/yr from plots with NH₄NO₃ additions at the Allt a’Mharcaidh. Laboratory incubation experiments demonstrated that large N₂O fluxes could be induced by warming and NH₄NO₃ additions, with the top 5 cm of soil cores responsible for the largest fluxes, reaching 11.8 kg-N/ha/yr from a podsol at Scoat Tarn. Acetylene block experiments showed that while N₂ was not likely to be a significant denitrification product in these soils, reduced N₂O fluxes indicated that nitrification was an important source of N₂O in many cases. A simple model of denitrification suggesting that 10-80% of net N inputs may be denitrified from non-agricultural soils was found to greatly over-estimate fluxes in the UK uplands. The proportion of deposition denitrified was found to be much closer to the IPCC suggested value of 1% with an upper limit of 10%. Interception of N deposition by vegetation may greatly reduce the net supply of N from this source, while soil acidification or other factors limiting carbon supply to soil microbes may prevent large denitrification fluxes even where NO₃⁻ supply is not limiting.     

Impact of excreted nitrogen by grazing cattle on nitrate leaching

Abstract. At De Marke experimental farm, data on water and nitrogen flows in the unsaturated zone were gathered on two grazed pastures on sandy soils during the years 1991 to 1994. These provided a basis for calibration and validation of simulation models. The different levels of nitrate-N concentrations of the two plots could largely be explained by differences in crop uptake and simulated denitrification as influenced by different groundwater levels. The irregular distribution of excreta was taken into account by a simulation study quantifying the variability of nitrate-N concentrations under a grazed field. The resulting distribution of simulated nitrate-N concentrations explained the average and peak values of the measured concentrations. Temporal variability of weather was used to assess the nitrate leaching risk under urine patches deposited in either July or September. At site A the probability of exceeding the EC-directive by drinking water (11.3 mg/1 nitrate-N) under a urination deposited in either July or September was respectively 10 and 25%. The average field concentration at this site will hardly ever be a high risk for the environment under the current farm management. At site B the EC-directive will be exceeded under any urine patch in almost 100% of the years, affecting the field average concentration. In field B careful grazing management would result in less nitrate leaching, but the environmental goals would not be reached.     

县级土地类型划分替代耕地分等的可行性探讨

当前所进行的耕地分等工作过程较为繁复,并且至今在理论与实践上均无一个好的的指导操作规程。针对此情况,根据现有的结论性的资料,在系统科学思想的指导下,在县级水平上建立起了一个在理论上更符合土地实际情况和更能反映农业生产实际的三级土地类型分类系统,也为县级耕地分等提供一种新的思路,为能切实将其分类结果应用于耕地分等,从理论和实践上对其进行了论证。     

基于标准样地国家级汇总的耕地质量动态监测点构架研究

该文以黑龙江、吉林、辽宁、山西、河南、安徽、湖南、湖北、江西中部九省为研究区域,以农用地省级汇总成果为主要数据来源,首次将标准样地国家级汇总成果与耕地质量动态监测相结合,对基于标准样地国家级汇总的耕地质量监测点的选取进行初步探讨,完成中部九省标准样地国家级汇总数据库建设,并分析九省国家级标准样地在不同等别及二级区上的分布情况,在此基础上,进行基于标准样地的耕地质量动态监测点的选取,最后,对标准样地体系提出参考性建议。     

县域耕地的样地法评价

该文首先进行了县域耕地样地法评价的方案设计,该方法的核心是在耕地质量分计算中,将评价单元的特征与设置与评价区域内的标准样地进行对比后完成的。然后应用样地法将河南省南阳市卧龙区的耕地评价为Ⅰ～Ⅷ等。Ⅰ～Ⅲ等的耕地中,有87.6%的面积分布在冲积、湖积平原区;Ⅳ～Ⅵ等耕地中,有61.4%的面积分布在垄岗区;而Ⅶ、Ⅷ等耕地集中分布在丘陵区。样地法所划分耕地等别的分布在总体上合理地体现了不同地貌类型及土壤条件下耕地质量的差异。利用210个样点单元的标准粮产量与其对应样地法耕地质量分进行线性拟合,判定系数等于0.876的含义是指标准粮产量的变异中有87.6%是由耕地质量分引起。样地法耕地质量分的高低较好地反映了耕地的生物生产力水平。所以,所设计的样地法可为中国县域样地法耕地评价提供方法与模式参照。     

水力侵蚀作用下坡地土壤碳氮淋溶迁移特征

碳氮随壤中流淋溶下渗是土壤碳氮流失的主要路径之一,然而由于直接观测难度大,土壤碳氮淋溶相关研究相对滞后,特别是由于壤中流的复杂性,一些问题还未得到完全解释。本文基于文献总结分析土壤、环境及壤中流影响下土壤碳氮淋溶迁移特征和观测方法,系统总结碳氮淋溶的研究方法以及各自优劣。结果表明：影响碳氮淋溶的因素众多,最主要的是降水和土壤性质。现场测量方式能真实反映淋溶的自然过程,室内试验能有效便捷地定量研究各因素对淋溶的影响,数学模型通过模拟水和溶质在多孔介质中的流动和输移,能更好地理解碳氮淋溶的物理机理,未来研究可将这些方法有机结合,以实现更好的研究效果。本文旨在为碳氮在物质循环和养分转移过程中的作用提供一定认识,为未来更好地调控生态系统中碳和氮的矿化、固着、淋溶和植物吸收的动态变化提供依据。     

淮河流域农业生态系统中地下水体氮源追溯

淮河流域地下水体中的氮污染问题一直以来备受关注。为了从源头追溯氮污染物的来源,本文通过清单法收集淮河流域2002—2017年期间35个地级市的农业统计资料,首先构建基于化肥施用氮、人畜粪便返田氮、生物固氮、大气沉降氮、种子带入氮、秸秆带入氮为输入项和作物收获氮、反硝化脱氮、氨挥发脱氮为输出项的氮平衡模型,估算进入淮河流域农业生态系统内的氮盈余量和强度;然后利用氮盈余量与淋滤系数构建氮淋滤模型定量估算氮淋滤到地下水体中的量。研究发现：2002—2017年间淮河流域农业生态系统中氮年均输入量为1 005.01万t·a^-1,化肥施用氮是最大的氮输入源,占总输入量的52.76%;淮河流域农业生态系统中氮年均输出量为706.43万t·a^-1,作物收获氮在氮输出中所占的比例最大,达87.29%。随着时间的增加,氮盈余量和强度逐步降低。本次从地级市角度计算的氮源强度和其时间变化规律与以往从流域角度计算的氮源强度和其时间变化规律相差不大,保证了结果的准确性。从地区上分析,河南省各地级市的氮源强度最高,山东省和安徽省各地级市的最低。2002—2017年间,淮河流域农业区氮盈余量淋滤进入地下水中的氮污染物总量为26.22万~41.71万t·a^-1,淋滤进入到地下水体中的氮污染物平均量为31.41万t·a^-1,其中2006年最高。较大的氮淋滤值对水体环境造成了较大的污染负荷。采用SPSS 21.0中用F统计量和皮尔森相关系数（ρ）对地下水中的实际氮污染物浓度与估算值间的氮污染物量进行相关性检验,最终通过显著性检验且相关系数达到0.517,证实了本次模型选择的准确性。本文研究表示,2002—2017年淮河流域农业生态系统中地下水体中氮的来源主要为化肥输入,最主要的输出途径为作物收获,污染最严重年份为2006年,为解决农业面源污染问题提供了重要的前期资料,对地下水中氮污染的防控具有重要的现实意义。     

干旱区耕地景观格局碎化特征及社会经济驱动因素分析

为探讨干旱区耕地碎化特征与驱动机制,基于特克斯县1990年、1998年、2000年、2003年、2006年、2011年的遥感影像,利用遥感与GIS技术,分析了研究区20a来耕地景观格局变化特征。并运用偏最小二乘回归模型探讨了耕地景观格局指数变化的驱动因素。结果表明:1990—2011年,研究区斑块碎化程度在逐步增大,斑块密度呈现增加的趋势;平均最近邻体距离与面积加权平均分维数在2000年前后均呈现出先减小后增大的特点,且两者的变化率在1998—2000年和2006—2011年均为正值,在其他阶段则均为负值,而斑块密度变化率的趋势则与之相反。回归模型结果显示,影响耕地碎化的主要因素包括总人口、农业机械总动力、粮食作物产量、油料作物产量等,但在三个模型中,各影响因子作用力大小存在一定差异。人口的增长与城镇化水平的提高,使大量耕地改造为建设用地,从而导致了耕地的碎化。而农业机械化水平的提高促进了耕地的集约化,在一定程度上减小了耕地斑块的孤立程度。     

基于GIS的前哨农场耕地地力评价

准确地掌握区域耕地地力等级及其空间分布格局,对于提高耕地生产能力具有重要的参考价值。以黑龙江垦区的前哨农场为研究区,以耕地地块为评价单元,在GIS的支持下,应用层次分析法、模糊数学法、综合指数法定量评价了耕地地力,进而分析耕地地力空间地域分布特征与规律。结果表明:农场耕地地力划分为6个级别,旱地和水田都是三级地、四级地数量最多,呈现向五级地、二级地、六级地和一级地逐次减少的正态分布特征;大部分耕地的地力处于中上等水平,且水田地力水平略高于旱地;西南部的第一、第二和第九管理区土壤质地良好、养分丰富、管理措施得当,是该农场优质耕地的集中分布区域。     

土地整理分区研究——以北京市大兴区为例

在各级土地整理专项规划中,为明确区域土地整理的类型与方向,制订适合实际情况的土地整理标准,进而为土地整理潜力评价提供基础,需进行土地整理分区。该文以北京市大兴区为例,以乡镇为分区单元,采用经济社会指标与自然指标相关延伸的方法,确定10项指标进行星座聚类分析,将大兴区分成北部经济发达区、东部产粮区与中南部综合发展区三个区,并分别明确了三个区域土地整理的方向。