半干旱黄土丘陵区牧草叶片的解剖学研究

对宁夏固原地区引种的19种牧草叶片的形态及解剖学观察,并根据旱生结构特征,将19种牧草分为旱生结构一般,旱生结构比较明显和旱生结构明显3种类型.     

Designing cropping systems for efficient use of limited water in southern Australia

There has been continuous change in the systems of cereal production in southern Australia where the climate is semi-arid with moderately wet winters and hot dry summers. At the outset wheat (c. 1840) was grown in continuous culture as the land was gradually cleared for cropping, but yields declined to uneconomic levels by 1900. That system was then replaced with fallow-wheat rotations, and using phosphorus fertilizer, yields recovered, but not to the original level. From 1945, the high profitability of sheep production encouraged improvement of legume-based pastures and the introduction of pasture-crop sequences – ley-farming. Productivity was greatly increased and the yield of wheat crops regained the original level. But such were the rates of acidification and salinization of soil that reduced productivity and, in the case of salinity, reduced stream quality and threatened adjacent natural ecosystems. This ley-farming system was used until the late 1980s when prices for wool fell dramatically, and farmers reduced sheep numbers and intensified cropping. The thrust since then has been to design cropping systems that are economically as well as environmentally acceptable with salinity control as the major objective. There is now a search for systems that use more water to reduce drainage through the soil and lower saline water tables. A major contribution is the much restricted use of fallow but summer active plants are also required to provide a soil water storage buffer to retain autumn–winter rainfall. New systems under evaluation include herbaceous perennials such as lucerne that are readily integrated into a crop-livestock system and agroforestry combinations with various trees. The design and appropriate distribution of the new systems is aided by remote sensing techniques to locate areas of saline discharge and linkages to zones of groundwater recharge, geographical information systems to arrange the data for land system analysis, and computer models of crops and cropping systems. There is a substantial challenge for farmers, agronomists and others to identify and assess suitable new systems and to bring the public into the debate and into the solution.     

亚高山半干旱地带植被恢复保水剂试验研究

在亚高山半干旱地带采用四种不同类型的保水剂材料对油松、岷江柏、刺槐、山桃进行了持续三年的田间试验。试验结果表明，采用CMS吸水材料、植物生长调节剂、生长素等配制的复合保水剂对亚高山半干旱地带造林树种进行处理，可提高苗木成活率、保存率并促进幼苗生长。造林第二年针叶树和阔叶树的平均成活率提高5．9％，造林第三年针叶树和阔叶树的平均保存率提高5．2％，针叶树和阔叶树的苗木高生长量平均增加61．7％。经统计检验，确认了复合保水剂的不同剂型对苗木成活和生长的影响之差异。     

Tree leafing phenology and crop productivity in semi-arid agroforestry systems in Kenya

The hypothesis that temporal separation of resource use between trees and crops minimises competition for wa ter in agroforestry systems during the cropping period and increases utilisation of annual rainfall was tested at Machakos in semi-arid Kenya. Four popular tree species were chosen to provide a range of leafing phenologies. These included Melia volkensii, which sheds its leaves twice a year, Senna spectabilis and Gliricidia sepium, which shed their leaves during the long dry season, and the evergreen Croton megalocarpus. All four species retained their foliage during the long rains, offering little scope for temporal separation of resource use. Maize (Zea mays) yields were reduced by 50–70% in the agroforestry treatments. Reductions in crop yield were strongly correlated with tree growth (r ² =0.94) and available soil moisture (r ² =0.88). G. sepium remained leafless for much of the short rains despite the presence of available soil water, and was least competitive with the bean crops (Phaseolus vulgaris) grown at this time. Reductions in crop yield in the agroforestry treatments were closely correlated with tree growth (r ² =0.99) and available moisture (r ² =0.79) during the 1996/97 short rains (158 mm), but not during the much wetter 1997/98 season (608 mm). Shading by trees or shade nets reduced crop yield, in contrast to previous studies in the semi-arid tropics. Low off-season rainfall during the study period (9% of annual rainfall compared to the long-term average of 20%) limited the potential for temporal separation of growing periods. Where the prospects for temporal or spatial separation in resource use are limited, shoot and/or root pruning may be necessary to manage competition between trees and crops. This revised version was published online in June 2006 with corrections to the Cover Date.     

Organic carbon pools in a Luvisol under agroforestry and conventional farming systems in the semi-arid region of Ceará, Brazil

Many environmental benefits have been attributed to agroforestry systems in various ecosystems around the world. However, there is a limited amount of information to evaluate this agricultural system in the semi-arid region, specifically in the region of Ceará, Brazil. The objective of this work was to evaluate five agricultural (four agroforestry and one conventional) systems in order to test the hypothesis that the agroforestry systems promote an increase in the soil organic carbon stocks and organic carbon pools, thus improving soil quality. The following treatments were tested: agrosilvopasture (AGP), silvopasture (SILV), traditional agroforestry (TRAG), intensive cropping (IC), and native forest (NF). The soil samples were collected at four depths: 0–6, 6–12, 12–20 and 20–40 cm. Total soil organic carbon stocks and the organic carbon pools (microbial biomass-C, mineralizable-C, oxidizable-C, free, occluded light fraction organic matter, and C in the humic substances) were analyzed. After 5 years of experimental cultivation, the soil under the SILV system presented the best results for the attributes studied, preserving, and in some cases, improving these attributes, when compared to the other conditions. The traditional agroforestry system (TRAG) reduced total organic carbon stocks and, consequently, C in some organic matter compartments, indicating that the fallow period was not sufficient to maintain soil quality. The AGP and IC systems presented significant losses in some of the soil organic matter (SOM) pools, suggesting that the soil environment had been degraded. The most labile SOM components were considered sensitive indicators of change in the soil quality. The silvopasture system can, therefore, be recommended as an alternative soil management strategy for food production and for the maintenance of soil quality and agricultural sustainability in the semiarid region of Ceará state.     

Spatial heterogeneity provides organic matter refuges for soil microbial activity in the Patagonian steppe, Argentina

In arid and semi-arid ecosystems that are frequently classified as water limited, it is unclear how spatial and temporal variability of vegetation and climate could affect microbially-mediated soil processes. Our objective was to determine how aboveground spatial heterogeneity creates characteristic soil conditions that modulate microbial growth and activity in a semi-arid Patagonian steppe. In particular, we explored how micro-environmental and biogeochemical soil characteristics generated by the native vegetation could control soil β-glucosidase activity. Both life-form (shrubs, grasses, mosses and bare soil) and season exerted strong controls on all measured abiotic (soil temperature and gravimetric soil water content, inorganic nitrogen, pH and total C and N) and biotic (microbial biomass C and β-glucosidase activity) soil characteristics. Partial correlation between β-glucosidase activity and extracellular organic C (EOC) was high across seasons (r = 0.5; P < 0.001) while soil water content did not correlate with soil enzymatic activity (r = 0.09; P > 0.05). We postulate that labile soil carbon rather than water availability functions as a principal limitation of microbial activity in this semi-arid ecosystem, and the distribution of this carbon is, in large part, determined by the patchy distribution of vegetation.     

Effect of long-term conservation tillage on soil biochemical properties in Mediterranean Spanish areas

In semi-arid Mediterranean areas, studies of the performance of conservation tillage systems have largely demonstrated advantages in crop yield, soil water storage and soil protection against wind and water erosion. However, little attention has been given to interactions between soil biochemical properties under different tillage practices. Biochemical properties are useful tools to assess changes caused by different soil tillage systems in long-term field experiments. This study deals with the effect of long-term tillage practices (reduced tillage and no-tillage vs. traditional tillage) on soil chemical properties and microbial functions in three different sites of Spain (two of them located in the Northeast and one in the Southwest) under semi-arid Mediterranean conditions. Soil biological status, as index of soil quality, was evaluated by measuring microbial biomass carbon (MBC) and dehydrogenase (an oxidoreductase) and protease (a hydrolase) activities at three soil depths (0–5, 5–10 and 10–25 cm). In the three experimental areas, increases in soil organic matter content, MBC and enzymatic activities were found at the superficial layers of soil under conservation tillage (reduced tillage and no-tillage) in comparison with traditional tillage. Values of the stratification ratio of some biochemical properties were significantly correlated with yield production in Northeast sites.Conservation tillage has proven to be an effective strategy to improve soil quality and fertility in Mediterranean areas of Spain.     

地膜覆盖对半干旱地区土壤环境及作物产量的影响研究综述

地膜覆盖作为半干旱地区一项重大的旱作农业技术,具有保墒、增温、增产作用,截至2005年,已推广超过1 300万hm2。综述了覆膜对土壤水分、温度、养分、微生物及作物产量的影响。     

围栏封育下华北半干旱草原植物生态位研究

为查明围栏封育条件下华北半干旱草原植物生态位格局及变化,于河北坝上地区红松洼国家级自然保护区设置100 m×100 m围栏监测固定大样地,采用样方法对封育区和放牧区植被生长状况进行调查,运用生态位理论对围栏内外主要植物的生态位宽度、生态位重叠值和生态位相似比例进行测算.结果表明:披针叶苔草(Carex lanceolata)在围栏内外的生态位宽度均为最大.披针叶苔草、裂叶蒿(Artemisia tanacetifolia)、地榆(Sanguisorba officinalis)、毛茛(Ranunculus japonicus)、珠芽蓼(Polygonum viviparum)等生态位宽度较大物种之间具有较高程度的生态位重叠.这些物种的生态位相似比例也较高;而生态位宽度较小的物种其生态位相似比例较小.表明生态位宽度与生态位重叠值、生态位宽度与生态位相似比例之间存在一定的线性关系.     

Nitrapyrin decreased nitrification of nitrogen released from soil organic matter but not amoA gene abundance at high soil temperature

Water pulses have a significant impact on nitrogen (N) cycling, making management of N challenging in agricultural soils that are exposed to episodic rainfall. In hot, dry environments, wetting of dry soil during summer fallow causes a rapid flush of organic matter mineralisation and subsequent nitrification, which may lead to N loss via nitrous oxide emission and nitrate leaching. Here we examined the potential for the nitrification inhibitor nitrapyrin to decrease gross nitrification at elevated temperature in soils with contrasting soil organic matter contents, and the consequent effects on ammonia oxidiser populations. Soil was collected during summer fallow while dry (water content 0.01 g g⁻¹ soil) from a research site with two management treatments (tilled soil and tilled soil with long-term additional crop residues) by three field replicates. The field dry soil (0–10 cm) was wet with or without nitrapyrin, and incubated (20 or 40 °C) at either constant soil water content or allowed to dry (to simulate summer drying after a rainfall event). Gross N transformation rates and inorganic N pools sizes were determined on six occasions during the 14 day incubation. Bacterial and archaeal amoA gene abundance was determined on days 0, 1, 7 and 14. Nitrapyrin increased ammonium retention and decreased gross nitrification rates even with soil drying at 40 °C. Nitrification was likely driven by bacterial ammonia oxidisers, as the archaeal amoA gene was below detection in the surface soil layer. Bacterial ammonia oxidiser gene abundances were not affected by nitrapyrin, despite the decrease in nitrifier activity. Increased soil organic matter from long-term additional crop residues diminished the effectiveness of nitrapyrin. The present study highlights the potential for nitrapyrin to decrease nitrification and the risk of N loss due to mineralisation of soil organic matter under summer fallow conditions.