Soil degradation: I. Basic processes

This paper examines soil and land degradation. It describes basic processes and factors responsible for degradation, illustrates the cause-effect relationships and differentiates between natural and man-induced regressive effects. The ‘critical limit’ concept is described in terms of properties beyond which the soil will not support an economically-viable agriculture. This paper is not an exhaustive literature review but emphasizes the scientific principles involved and highlights natural against man-induced processes. Important natural processes are: laterization, hard-setting, fragipan and clay pan formation, and geologic erosion. In comparison, man-induced processes consist of: soil compaction, accelerated erosion, desertification, salt accumulation and leaching and acidification. One of the principal constraints is the problem of data reliability. A reliable database and precise criteria are definitely lacking and hinder the assessment of the extent, type and degree of soil degradation and establishing the cause-effect scenario. Improving our database is, therefore, of a high priority if we are to adopt land use policy for sustainable soil management and long-range resource management. Also outlined, are vital research and development strategies. Judicious resource management policy should emphasize managing prime agricultural land to produce to its maximum potential so that there is no need to cultivate marginal and easily-degraded fragile ecosystems. A strict code of conduct is needed for utilizing marginal/fragile lands. Methods of restoring the productivity of degraded lands must be researched so as to minimize the need to clear and develop new lands.     

生活污泥焚烧灰的重金属含量及其浸出特征

针对生活污泥灰中的重金属种类、重金属含量及其浸出特征进行研究,并进一步探究该污泥处理处置的可行方法。研究表明:在生活污泥灰中主要含有Fe、Pb、Cu、Ni、Zn、Mn、Cr、Cd,其中Fe的含量最多。污泥灰中重金属在酸性条件下的浸出率明显高于碱性条件下的浸出率,Cr、Ni和Cd的最佳浸提剂pH值均为2,其中Cu和Zn随浸提剂pH变化的浸出特征不明显。     

包膜缓/控肥氮释放特性比较研究

[目的]比较包膜缓/控肥氮释放特性,为改善白洋淀及周边地区农业耕作施肥习惯和减轻白洋淀污染状况提供理论依据。[方法]采用＂土柱淋溶法＂室内模拟试验,研究了5种肥料在白洋淀地区土壤中铵态氮和硝态氮释放淋溶情况。[结果]树脂包衣和硫包衣尿素在试验前期淋溶液中铵态氮含量较普通尿素分别减少了98.5%和98.7%,在试验中期分别减少了96.5%和97.4%,在试验后期分别减少了38.7%和76.7%;而硝态氮含量在试验前期较普通尿素分别减少了59.1%和81.8%,在试验中期分别增加了414.7%和40.7%,在试验后期分别增加了1702.8%和642.3%。[结论]树脂包衣和硫包衣尿素明显减少了易挥发的铵态氮含量,有效控制了作物易吸收利用的硝态氮在前期的释放,并增加了在中后期易吸收氮的供应。     

不同腐熟稻草基质的理化性质及淋溶液养分变化研究

为研究稻草秸秆资源化利用方法,提高稻草作草坪基质的价值,通过向秸秆中添加不同比例的动物粪便、尿素和秸秆腐熟剂,测定不同腐熟处理基质的理化性质及养分淋溶情况.结果表明:尿素腐熟稻草基质的运输成本最低,动物粪便腐熟基质的保水能力较强.各资源化处理稻草基质的pH值差异不显著,有机质含量为1.7～1.9g/kg,均高于对照.动物粪便腐熟稻草基质的各种养分含量均高于对照,尿素腐熟稻草基质的碱解氮、速效钾和全钾含量高于对照,添加秸秆腐熟剂的尿素腐熟稻草基质的全氮含量降低.资源化处理稻草基质淋溶液的pH值随草坪草生育期的推进逐渐下降,后期下降缓慢且高于对照.动物粪便腐熟的稻草基质比尿素腐熟的稻草基质抗淋溶,秸秆腐熟剂可提高猪粪腐熟的稻草基质的抗淋溶作用,但抑制尿素腐熟的稻草基质抗淋溶作用.     

设施菜地夏季休闲期甜玉米经济产量及环境效益分析

在北京市门头沟、房山、大兴和通州等4个区选择15个典型设施菜地,设置田间观察对比试验,研究在北方设施菜地夏季甜玉米作为填闲作物的实际经济、环境综合效益。试验结果表明,种植甜玉米有较好经济效益,经济产量达15 168.0～20 332.8kg/hm2。在环境效益方面,种植甜玉米后可有效减少浅层土壤中的硝态氮含量,降低淋溶风险。与常规休闲(休闲期不种植作物)相比,种植甜玉米可使设施菜地0～100cm土层中的硝态氮含量平均减少290.4kg/hm2。在夏季休闲期种植甜玉米是北方设施菜地兼顾经济和环境效益的有效种植措施之一。     

Systems analysis of wheat production on low water-holding soils in a Mediterranean-type environment: II. Drainage and nitrate leaching

In Mediterranean-type environments, the concentration of rainfall in winter months results in average winter rainfall that is in excess of evaporative demand. Cropping coarse textured soils in such regions results in a risk of drainage below the root zone, and associated with this, nutrient leaching. We used the APSIM-Nwheat simulation model to quantify the magnitude and variability of drainage and nitrate–N leaching under wheat crops for six locations and three soil types in the northern sandplain region of the Western Australian wheat belt and to assess the impact of varying crop management on drainage and leaching. Overall, the combination of a high concentration of rainfall in the winter months and coarse soil types resulted in a significant risk of drainage and leaching events of considerable magnitude even at the driest sites considered: the assumption that leaching and drainage are low in areas of low rainfall is an over-simplification. For some locations, simulated drainage was high, exceeding 100 mm for two locations on two soils; the sand and the acid loamy sand. Across the six locations considered, drainage was linearly related to average growing season rainfall. Leaching varied markedly between the soil types, with loamy sand having only one fifth the leaching that was calculated for the acid loamy sand or the sand. This emphasises the importance of small differences in soil type for the risk of drainage and leaching, and hence the potential for negative off-site effects, when cropping light soils in a Mediterranean-type environment. Although sandy soils are held to present the most scope for reducing drainage through agronomic management, the analysis suggested the potential improvements are likely to be small. Consistent with experimental results from other parts of the Western Australian wheat belt, modification of rooting depth appears to present the best option to reduce drainage beneath annual crops.     

模拟条件下生物腐殖酸肥对土壤磷素淋失及流失的影响

通过模拟淋溶和径流实验,考察单施生物腐殖酸肥(BHA)后磷在竖直及水平方向的迁移能力,并通过室外小白菜种植实验进一步开展淋溶和径流中磷的行为研究,考察单施BHA对小白菜长势、产量的影响及对受纳水体水质的污染风险。实验以施化肥(CF)和不施肥(NOP)为对照。结果表明,(1)在模拟淋溶及径流实验中,经过8次浇水,BHA处理组的淋溶液及径流液中TP含量的最高值及平均值均高于CF及NOP处理组,在磷淋失量及淋失率上,3个处理间均无显著差异;在磷流失量及流失率上,BHA与CF无显著差异,二者均显著高于NOP处理组,其磷流失量分别比NOP高208.96%、147.01%,流失率分别比NOP高1.98%、1.39%。(2)室外小白菜种植的淋溶及径流实验中,在对小白菜长势的影响方面,BHA与CF无显著差异,二者均显著高于NOP处理组;在对小白菜产量及植株吸磷量的影响方面,CF处理组显著高于BHA及NOP。在磷淋失量上,BHA与CF无显著差异,二者均显著高于NOP处理组;在磷流失量上,BHA处理组显著高于CF及NOP,分别高78.52%、82.48%。研究表明,尽管BHA中的磷不如CF易被小白菜吸收利用,但是二者对小白菜长势的影响无显著差异;BHA施用后磷更易随径流液流失,而不易随淋溶液淋失,因此,施用BHA后应避免立即灌溉,尤其是大水漫灌。     

淋洗法测试肥料氮素释放性能研究

分别采用水浸泡法、间歇淋洗法和连续淋洗法测试肥料氮素释放性能,考察了不同模拟土壤介质的淋洗结果,并从介质饱和含水率、水分张力和阳离子交换量等方面综合分析了模拟土壤效果。实验表明:水浸泡法与无介质连续淋洗法结果具有良好的相关性,都符合y=ax+b释放模型;相同介质间歇淋洗法和连续淋洗法结果具有良好的相关性,都符合N=N0/[1+exp(A-kt)]释放模型;蛭石+土壤(体积比1∶1)能更好地模拟土壤性能。模拟土壤连续淋洗法可用于肥料生产企业在线检测。     

稻田土壤氮素矿化的几种方法比较

结合盆栽实验,对稻田土壤氮素矿化的几种方法进行了比较,结果表明:KC I煮沸法和碱解氮法是很好的测试土壤供氮能力的方法,淹水培养法矿化氮量与植物全氮含量相关性不高;而采用淹水培养间歇淋洗法和淹水密闭连续培养法对稻田土壤进行土壤氮素矿化的淋溶试验,结果表明:淋洗有利于土壤氮素的矿化过程。     

云南哀牢山中山湿性常绿阔叶林的降水化学

为了分析大气降水的化学物质输入及其降水淋溶对云南哀牢山森林生态系统生物物质循环产生的影响。通过观测大气降雨过程中大气降水、穿透雨及树干茎流在１９９１年５月￣１９９３年４月间的变化并测定其相应的水质特征。发现①大气降雨和穿透雨是养分输入的主要形式。其中以穿透雨养输入为主。树干茎流养分输入很小，可忽略不计。Ｎ、Ｐ、Ｋ、Ｃａ、Ｍｇ养分元素的输入量是穿透雨：６．０９９，０．４２３，５．９１５，１．７８９和