Measured and simulated denitrification activity in a cropped sandy and loamy soil

Summary Denitrification activities were measured over a 3-year period in a coarse sandy soil and a sandy loam soil. In all years the crops were spring barley in combination with Italian ryegrass as a catch crop. The denitrification loss was measured using the acetylene inhibition technique on soil cores. Furthermore, a simple model was developed, based on daily values of soil moisture and soil temperature, to calculate the denitrification loss. Soil temperatures for the model were measured, whereas soil moisture was derived from a water-balance model. Measurements of denitrification gave an annual loss of 0.6 kg N ha^-1, and the model calculated a loss of 1–2 kg N ha^-1 in the coarse sandy soil. In the sandy loam soil annual losses were measured as 1.5, 3.0, and 13.0 kg N ha^-1 in 1988, 1989, and 1990, respectively. The corresponding values from the model simulation were 14, 9 and 14 kg N ha^-1.     

杂交稻和常规稻生育后期对NO_3~——N和NH_4~+-N的营养效应

利用~(15)N示踪技术研究了杂交稻和常规稻生育后期对不同N源的营养效应。结果表明,杂交稻对抽穗前追施的NO_3~--N的利用率比常规稻高7.8％,回收率高13.2％:追施NH_4~+-N时,杂交稻的N肥利用率比常规稻高6.1％,回收率高14.5％肥源之间比较,收获期NH_4~+-N的利用率和回收率都高于NO_3~--N。肥料N在穗中的分配率,杂交稻比常规稻大15.7—20.2％,但NO_3~--N与NH_4~--N处理间无明显差异。试验结果还表明,抽穗前追施NO_3~--N比追施NH_4~--N能更明显地促进水稻对Ca~(2+),Mg~(2+)的吸收,刺激浮根的生长,增加稻谷产量,而且杂交稻的这些效应大于常规稻。     

美国土壤信息系统的发展及其启示

考察了美国土壤信息系统的发展过程 ,总结了其发展的经验教训 ,在此基础上对我国土壤信息系统发展面临的问题进行了深入剖析 ,并提出了相应的发展建议     

岩溶区坡面土壤侵蚀特征研究

以重庆南川岩溶区为例,用137C s法研究了岩溶区坡面土壤侵蚀特征。结果表明,坡面上部侵蚀速率较小,平均侵蚀速率为400.8 t/(km2.a),最大侵蚀速率为1 138.4 t/(km2.a);坡面中部侵蚀加剧,平均侵蚀速率2 264.8 t/(km2.a),最大侵蚀速率可达3 760 t/(km2.a);坡面下部侵蚀减弱甚至堆积。土壤表层有机质、表层粘粒及水稳性团聚体含量在坡面上的变化与土壤侵蚀速率具有负相关趋势。     

大麦光合产物的分配、再分配与产量形成的关系

本试验以二棱形和六棱型两个大麦品种为材料,应用＾１４Ｃ示踪技术,对大麦各生育期＾１４Ｃ光合产物在各器官中的分配、财分配及其干物质积螺的关系进行了研究。试验表明：１．不同生育期光合产物的根本与再分配方式不同,分蘖和拔节期光合产物主要用于根系、茎叶的生长,只有１３．５％,８．９５％分配到籽粒中,抽穗和灌浆期光合产物主要用于籽粒育实和灌浆,分别有４７．２％和４８．１％,７２．１％和８８．１％分配到籽粒。     

The impact of sowing density of small grains on rill and ephemeral gully erosion in concentrated flow zones

Despite the fact that soil erosion by water causes considerable on-site and off-site problems, farmers in Europe are reluctant to adopt prevention and control measures when such measures require additional labour and material inputs. This paper documents the impact of multiple sowing of small grains on concentrated flow erosion rates and grain production for a winter triticale field (X Triticosecale Wittmack ex. A. Camus) in the Belgian loess belt. Multiple sowing refers to drilling more than once in zones of concentrated flow erosion in order to increase the total root mass in this zone. Multiple sowing strongly altered the morphology of erosion channels and reduced soil loss significantly. Statistical analysis confirmed that differences in channel dimensions could be explained by the seedling density. Doubling the root mass in the topsoil by multiple sowing, resulted on average in a reduction of soil loss by 42% for the whole growing season. For the winter period, soil loss reduction, mainly attributed to the triticale roots, amounted even to 53%, showing the tremendous impact of seedling roots on soil erosion by concentrated overland flow in the early stages of vegetation growth. Furthermore, total grain yield in the multiple drilled zones was not significantly smaller compared to the conventionally drilled parts of the field. Grain size of cereals was slightly smaller. The results of this case study indicate that double sowing in concentrated overland flow zones may be a viable soil erosion control technique.     

Nitrous oxide, methane and ammonia emissions following slurry spreading on grassland

In Sweden, 90% of ammonia (NH₃) emissions to the atmosphere originate from agriculture, predominantly from animal manure handling. It is well known that incorporation of manure into soil can reduce NH₃ emissions after spreading. However, there is a risk of increased nitrous oxide (N₂O) and methane (CH₄) emissions caused by bacterial activity and limited oxygen availability under these conditions. A full‐scale injector was developed and evaluated in a field experiment on grassland. Cattle slurry was either injected in closed slots 5 cm below ground or band spread on the soil surface above the crop canopy at a rate of 25 t ha^?1. In a control treatment, no slurry was applied. During a 5‐day period after application, NH₃ emissions were measured using an equilibrium concentration method. Gas samples for estimating CH₄ and N₂O emissions were also collected during 7 weeks following slurry application. Injection in closed slots resulted in no detectable NH₃ emissions. After band spreading, however, NH₃ emissions corresponded to nearly 40% of the total ammoniacal nitrogen in the applied slurry. The injection of slurry gave rise to a broad peak of N₂O emissions during the first 3 weeks after application. In total, for the measuring period, N₂O emissions corresponded to 0.75 kg N ha^?1. Band spreading resulted in only a very small N₂O release of about 0.2 kg N ha^?1 during the same period. Except for the first sampling occasion, the soil was predominantly a sink for CH₄ in all the treatments. The use of the injector without slurry application reduced grass yield during unfavourable growing conditions. In conclusion, shallow injection in closed slots seems to be a promising technique to reduce negative environmental impacts from NH₃ emissions with a limited release of N₂O and CH₄.     

Gully development in the Moldavian Plateau of Romania

Gully erosion has been recognized as an important environmental threat in the Moldavian Plateau of Eastern Romania. The main objective of this study was to define the process-based gully development by providing quantitative information from long-term field measurements in small catchments.Three main areas of monitoring gullies were explored: aerial photographs of flights in 1960 and 1970, classical leveling and repeated survey through a particular close stakes grid after 1980. The Caesium-137 technique has been used effectively in the areas of deposition of gully sediments to obtain reliable information on dating specific levels of sediments and to provide chronological measures of gully development.Most of the discontinuous gullies exhibit both proper gullying, mainly if not exclusively by gully head advance, and aggradation of the gully basin floor. Results indicated that the mean gully head retreat was 0.92 m year^− 1 and the mean areal gully growth was 17.0 m² year^− 1. Both values indicate a slow erosion rate for this area. The average annual regime of gullying is pulsatory, one that is best described by great fluctuations. Conventional measurements on sedimentation over the period 1987–1997 indicate a higher rate of aggradation in the upper half of the gully floor. Information on the Caesium-137 depth profile was used to provide estimates of a mean sedimentation rate of 4.4 cm year^− 1 over the period 1963–1996 and 2.5 cm year^− 1 after 1986 for the short successive discontinuous gullies. A new classification of the discontinuous gullies based on two criteria, respectively, the field patterns and the rate of aggradation within the gully basin floor was established.For continuous gullies, linear gully head retreat, areal gully growth and eroded material rates were quantified for three periods (1961–1970, 1971–1980 and 1981–1990). Results indicate that gully erosion has decreased since 1960. This gullying decline is due to the rainfall distribution, and the increased influence of soil conservation practices. The mean gully head retreat of 12.5 m year^− 1 between 1961–1990 was accompanied by a mean areal gully growth of 366.8 m² year^− 1 and a mean erosion rate of 4168 t year^− 1. As with discontinuous gullies, continuous gullies showed pulsatory development.The critical period for gullying over 1981–1996 covers 4 months from Mid March to Mid July in an area with mean annual precipitation around 500 mm. Another main finding of this 16-year stationary monitoring was that 57% of the total gullying occurred during the cold season, with the remainder during the warm season. Of the total gully growth, 66% results from only four years (1981, 1988, 1991 and 1996), when a greater amount of precipitation fell.     

以中国土壤系统分类为基础的土壤参比

为了土壤信息交流、知识共享 ,作者首先阐述了与世界土壤分类发展相伴随的中国土壤系统分类的发展 ,进而对中国土壤系统分类与美国土壤分类和WRB方案进行了参比 ,然后着重讨论了它与土壤发生分类之间的参比。今后拟建立土壤参比信息系统以实现计算机自动参比     

优质青贮玉米新青1号的选育及其栽培技术

新青1号是新疆农科院粮作所培育的优质高产青贮玉米新品种.该品种一般生物产量67 500～82 500kg/hm².春播生育期110 d左右,复播生育期90～100d,适宜≥10℃有效积温2400℃·d以上地区种植.全株粗蛋白含量10.07%,粗脂肪3.02%,总糖11.65%,粗纤维8.38%,无氮浸出物32.42%,干物质含量49.94%.子粒容重828g/L,子粒粗蛋白13.19%,粗脂肪5.55%,赖氨酸含量0.34%.通过适时播种、合理密植、加强田间管理和适时收获即可获得高产