• بخشی از ترجمه:

چکیده
یکپارچه سازی درختان، به ویژه درختان برای تثبیت نیتروژن (NFTs)، در جنگل زراعی و سیلویو – سیستم های دامداری می تواند کمک بزرگی در جهت کشاورزی پایدار توسط بازسازی و حفظ حاصلخیزی خاک، و در مبارزه با فرسایش و بیابان زایی و همچنین ارائه سوخت باشد . مزیت خاص NFT تثبیت نیتروژن بیولوژیکی (BNF)، توانایی خاص آنها برای ایجاد نیتروژن در خاک و نیتروژن ثابت (و ماده آلی اضافی) می باشد که موفقیت آمیز می باشذ . اهمیت NFT این پرسش را به دنبال دارد که چگونه ما می توانیم به حداکثر رساندن و یا بهینه سازی اثرات BNF را مدیریت کنیم و انتقال نیتروژن به گیاهان مربوط به این موفقیت می باشد . برای اینکه قادر به دستیابی به این اهداف باشیم ، ارائه روش مناسب برای اندازه گیری BNF در درختان ضروری است. روش تفاوت ازت کل (TND) ساده ترین روش می باشد ، اما این روش برای نیتروژن بالای خاک مناسب می باشد . استفاده از روش استیلن کاهش (ARA) یافته ، اگر چه حساس و ساده است، بسیاری از محدودیت های فنی ویژه برای NFT و برآورد BNF به طور کلی بسیار کم است، در مقایسه با روش های دیگر ، برای NFT، تکنیک های نیتروژن هنوز در حال توسعه می باشد ، اما در حال حاضر با توجه به برخی از نتایج امیدوار کننده خواهد بود (به عنوان مثال، اندازه گیری تنوع ژنتیکی زیادی در BNF و NFT مختلف انجام شده است). عوامل گوناگون BNF را در درختان تحت تاثیر قرار می دهند . آنها شامل سن درختان، جزء میکروبی، رطوبت خاک، دما، شوری، pH محلول، سطح N خاک و کمبود مواد مغذی گیاهی می باشند . برخی از عوامل، به عنوان مثال درجه حرارت، بر همزیستی بیشتر از رشد گیاه، و اختلاف در اثر این عوامل در BNF در ژنوتیپ های مختلف NFT تاکید دارند . این عوامل و نیازهای تحقیقاتی برای بهبود BNF در درختان مورد بحث می باشد .

• بخشی از مقاله انگلیسی:

Abstract

acetylene especially methods. promising NFTs). Various The integration of trees, especially nitrogen fixing trees (NFTs), into agroforestry and silvo-pastoral systems can make a major contribution to sustainable agriculture by restoring and maintaining soil fertility, and in combating erosion and desertification as well as providing fuelwood. The particular advantage of NFTs is their biological nitrogen fixation (BNF), their ability to establish in nitrogendeficient soils and the benefits of the nitrogen fixed (and extra organic matter) to succeeding or associated crops. The importance of NFTs leads to the question of how we can maximise or optimize their effects and how we can manage BNF and the transfer of nitrogen to associated or succeeding plantings. To be able to achieve these goals, suitable methods of measuring BNF in trees are necessary. The total nitrogen difference (TND) method is simple, but is better suited for low than high soil N conditions. The reduction assay (ARA), although sensitive and simple, has many technical limitations for NFTs, and the estimates of BNF have generally been very low, compared to other For NFTs, the ~SN techniques are still under development, but have already given some results (e.g., has been used to measure large genetic variability in BNF within different factors affect BNF in trees. They include the age of trees, the microbial component, soil moisture, temperature, salinity, pH, soil N level and plant nutrient deficiencies. Some of the factors, e.g. temperature, affect the symbiosis more than plant growth, and differences in the effects of these factors on BNF in different NFT genotypes have been reported. These factors and research needs for improving BNF in trees are discussed.

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نوشته دانلود ترجمه مقاله اکوسیستم کشاورزی و تثبیت نیتروژن بیولوژیکی – نشریه اسپرینگر اولین بار در ترجمه فا پدیدار شد.

فهرست مطالب:

چکیده
۱ مقدمه
۱ ۱ امنیت غذایی در نیمه شمالگان
۱ ۲ کشاورزی نیمه شمالگان
۱ ۳ آگروفارستری
۱ ۴ اهداف مطالعه
۲ روش ها
۲ ۱مطالعه موردی: فیرست نیشن آلبانی
۲ ۲ طرح آگروفارستری
۲ ۳آنتخاب محل آگروفارستری
۲ ۴ ترکیب گونه های گیاهی
۲ ۵ طرح نمونه برداری خاک
۲ ۶ روش های جمع اوری نمونه های خاک
۲ ۷ آنالیز های خاکی
۲ ۸ انالیز داده ها
۳ نتایج
۳ ۱ ترکیب گونه ای
۳ ۲ تولید بالقوه ی باغچه ها
۴ بحث
۴ ۱ ترکیب گونه ای
۴ ۲ تولید بالقوه ی باغچه
۴ ۲ ۱ بافت خاک
۴ ۲ ۲ حاصلخیزی خاک(N, P, K, Mg, pH )
۵ نتایج
۵ ۱ توصیه هایی برای باغچه های جوامع آگروفارستری در آلبانی
۵ ۲ اجرایی بودن AFCGs در دیگر جوامع شمالی

بخشی از ترجمه:

اجرایی بودن AFCGs در دیگر جوامع شمالی
توصیه های مدیریت پوشش گیاهی و خاک منطقه مورد مطالعه به طور مستقیم به دیگ مناطق فیزست نیشن به خصوص مناطق بدون تاریخچه مدیریت قابل اعمال است. در این مناطق دهه ها شخم و تبدیل ارضی موجب تهی شدن عناصر مغذی خاک شده است. با این حال اسپیگلر و سوجی گزارش دادند که منطقه البانی با حاصلخیزی متوسط و بافت خوب برای تولید همراه با شخم و زهکشی مناسب است/. از این رو اجرای AFCGs ها در مناطق سالم شمالگان عملی بوده و می توان انتظار داشت که با گرمایش جهانی عملی تر هم شود.
مناطق محلی جنگل های شمالگان را می توان برای استفاده از درختان موجود در AFCGs، حفظ ارتجاع طبیعی و سازش بهره بردار ی کرد. طرح اکروفارستری و گونه های درختی در جوامع شمالی بستکی به نیاز های منطقه بر اساس میکرو کلیمای محلی، شرایط خاک، عوامل فرهنگی و اجتماعی اقتصادی علاو بر خدمات حیات وحش و ترسیب کربن دارد. با بیش از 500 گونه بید در سراسر جهان به خصوص در مناطق معتدله و حاره، استفاده از بید در دیگر جوامع توصیه می شود. این واریته های بید با طیف وسیعی از اقلیم ها و مکان ها سازکار می باشند و توسط قلمه قادر به تکثیر بوده و دارای سرعت رشد بالایی می باشند.
در نهایت این که، معرفی بزرگ مقیاس سیستم های اکروفارستری با گونه های بومی و سنتی در فیسرت نیشن می توان وابستکی به واردات نفتی را به حداقل رساند. AFCGs ها مطابق با استاندارد های امنیت غذایی می باشند و به امنیت غذایی کمک می کنند. روش های مناسب کشت در سیستم های بومی سنتی، حفظ روش های قبلی و کلاسیک و ازادی جوامع نیز بستکی به تولید کننده ها و توزیع کننده های غذاهای ایمن دارد.

بخشی از مقاله انگلیسی:

1. Introduction 1.1. Food Security in Sub-Arctic First Nations The Euro-Canadian Roman Catholic Mission developed agrarian settlements in remote First Nations of Northern Canada in the early 20th century [Vezina, unpublished manuscript, Historical Notes on the Village of Attawapiskat, Roman Catholic Church: Attawapiskat, Ontario], forcing nomadic indigenous peoples to settle and displacing traditional aboriginal ways of acquiring food [1,2]. In a previous study [2], Spiegelaar and Tsuji discuss extensively pre- and post- settlement socio-ecological and cultural conditions in remote First Nations communities. The Mission was somewhat successful in producing diverse foods within a challenging environment and short growing season, but their departure and subsequent closing of residential schools in the late 20th century ended local agricultural production and left remote First Nations dependent on an unreliable, import-based food system [2]. Modern food systems in these remote First Nations often lack nutritional quality [3–6], bear high transportation costs, and perpetuate the loss of traditional Aboriginal food systems and associated knowledge [7], ultimately impacting individual and community health [8]. This import-based system is also extremely resource-intensive, while it simultaneously perpetuates reliance on the unstable fossil-fuel industry and global food economy [9,10]. Modern First Nation food systems, therefore, prevent these vulnerable populations from becoming food secure [8]. Food Security can be defined as follows: the ―access by all people at all times to enough food for an active, healthy life…[including] the ready availability of nutritionally adequate and safe foods, and an assured ability to acquire acceptable foods in socially acceptable ways‖ [11]. 1.2. Subarctic Agriculture A re-introduction of local agriculture to augment traditional Aboriginal foods in northern communities has been suggested as a means to partially substitute imports, enhance food freshness, variety and nutrition, increase local control over food availability, and ultimately, increase food security [2]. While productivity in northern ecosystems is relatively limited, the capacity for food production in subarctic and arctic zones continues to increase with a warming climate; researchers predict an increase in the length of the growing season, enhanced plant growth rates, and greater soil nutrient availability in the north, and in turn, more hospitable conditions for growing a greater variety of edible plants [12]. Although increased productivity will subsequently increase carbon sequestration in biomass of high-latitude systems, the net effect will be a positive feedback towards warming due to significant levels of carbon release from permafrost thawing in the north [12,13]. While promising for northern food production, these rapid climatic and ecological changes are threatening wildlife and traditional ecological resources in these regions [14,15]. Wide-scale spread of conventional agriculture to the north could perpetuate the climate change problem. Modern agricultural methods release large amounts of CO2 and N2O through heavy use of industrial machinery and chemical fertilizers [16]; they also require extensive forest clearing followed by intensive land management, resulting in losses of carbon stores from both above-ground biomass and soil organic carbon [17]. Conventional agriculture has also been associated with short-term returns and long-term land degradation. Strategies used in this modern farming practice focus on increasing yield Sustainability 2013, 5 4059 through high use of pesticides and herbicides, and are dependent on expensive, resource-intensive technology [9,17]. Throughout North America, conventional agriculture has resulted in vast displacement of native biodiversity, land degradation and pollution of land and water [17,18]. Our previous study [2] on food security in the remote First Nation of Fort Albany, located in the James Bay Lowlands of subarctic Ontario, explored the successes, failures and long-term impacts of the Roman Catholic Mission’s agricultural program (1940–1970) on the local land and food system. In sum, a somewhat reliable food source was developed, but land cultivation introduced invasive species and resulted in significant soil quality loss, while the program aggressively displaced the traditional aboriginal harvest [2]. The agrarian program left with the Mission in the 1970s, when the residential school closed. As a result, First Nation people became more dependent on unhealthy store imports because neither the agrarian settlement nor the fragments of a nomadic indigenous tradition could support them. In a region with limited arable land that is vulnerable to rapid climatic, ecological and social change, conventional agricultural and food assistance programs are short-term solutions that ultimately degrade community culture and land resources. Yet, as First Nation populations continue to increase at a rate greater than the general Canadian population [19], and climate change provides more hospitable temperatures for northern crop production [12], import-substitution strategies other than conventional agriculture need to be explored. 1.3. Agroforestry Agroforestry is an alternative land-use system to conventional agriculture that has been utilized as a socioeconomically and ecologically sustainable means to establish long-term food security in impoverished areas, mainly within the sub-tropic and tropic regions [20,21]. Simply, it is a relatively recent term for an ancient practice of agriculture, which by definition, is a land-use system that combines woody perennials (e.g., trees, shrubs) with crops in spatial and temporal arrangements that optimize beneficial biological interactions and economic outputs [17,18]. In contrast to conventional agriculture, the use of multiple components and multiple species in agroforestry systems maintains ecological diversity [17]. Agroforestry systems in the tropics, sub-tropics and temperate regions (e.g., China) have played a substantial role in enhancing food security, as low input systems with diverse and complementary food products [17,22–24]. The reduced mechanical intervention allows for maintenance of soil integrity and more closed nutrient-cycling [18], subsequently, reducing the need for expensive and ecologically-damaging chemical inputs [25] and the emissions of N2O and CO2 [16]. As potential carbon sinks, northern agroforestry systems may act as an adaptive response to climate change in contrast to conventional agriculture, in both mitigating carbon dioxide and adapting to anticipated ecological changes [25,26].

نوشته دانلود ترجمه مقاله بهبود امنیت غذایی با باغچه های جوامع جنگل زراعی اولین بار در ترجمه فا پدیدار شد.

فهرست مطالب:

چکیده
۱ مقدمه
۲ روش
۲ ۱ مناطق مورد مطالعه
۲ ۲ جمع آوری داده ها
۲ ۳ پردازش تصاویر و متریک ها
۲ ۴ روش های آماری
۳ نتایج
۳ ۱ تعریف فضای حالت و فاز های اکولوژیکی
۳ ۲ تفسیر مسیر های انتقال
۳ ۳ تهیه نقشه مدل حال و انتقال
۴ بحث
۴ ۱ کاربرد های دیگر

بخشی از ترجمه:

مطالعه ما در خصوص گراسلند T. triandra  در شمال غرب استرالیا بیانگر یک سیستم نسبتا ساده است: یک مونوکالچر(تک کشتی) که سریعا به رویداد های محرک پاسخ می دهد و هم چنین یک قرق آزمایشی چرا در آن انجام شد. در صورتی که چرا یک فاکتور باشد، تغییرات در شدت چرا را می توان به عنوان یک محرک دینامیک سیستم با استفاده از شدت چرا به عنوان یک متغیر همراه در طبقه بندی درختی با فرض موجود بودن داده ها در نظر کرفت. علاوه بر سیستم های خشک و نیمه خشک، روش را  می توان به دینامیک های الگوی دیگر سیستم های چند فازی رویداد محور نظیر جوامع جلبک ها- ماکرو آلگ ها(جلبک های ماکرو) اعمال کرد((Fourqurean and Rutten, 2004),)که تغییرات زیاد در الگو بندی را بتوان با تصاویر هوایی در مقیاس های زمانی کوتاه پوشش داد. سیستم های پوشش گیاهی پیچیده تر نظیر جنگل های سوزنی برگ که دنیامیک رویداد محور آن  در مقیاس های دهه ای( ده ساله) تکامل می یابند، مستلزم پایش چندین سایت با تفکیک تاریخچه رویداد ها بین سایت ها می باشند( پیکت 1989).برای مثال سایت های Ridge و Cattlewell از نظر مکانی به اندازه کافی دور از هم بودند  تا در معرض آتش سوزی های طبیعی مجزا قرار گرفته و این خود امکان شناسایی اثرات متقابل بین آتش سوزی و خشک سالی را در سری های تصاویر T. triandra می دهد( شکل 5 و 6). دینامیک های برگرفته از تصاویر  قابلیت کاربرد را در طیف وسیعی از سیستم های پوشش گیاهی دارد.

بخشی از مقاله انگلیسی:

1. Introduction The state-and-transition model (STM) is a conceptual tool to organize our understanding of how the dynamics (or temporal change) of vegetation communities are driven by complex interactions among events (e.g. fire, grazing and flooding), processes (e.g. mineralisation and drainage) and biological factors (e.g. invasive species). STMs were originally developed to explain limitations in Clementsian linear succession models in predicting the consequences of land management on rangeland vegetation dynamics, including: irreversible vegetation change; grazing catastrophe; episodic plant recruitment; and, alternative stable vegetation states (Westoby et al., 1989). As a management tool, the STM illustrates the potential impacts, nonlinearities and uncertainties inherent under different environmental conditions or management scenarios (Bestelmeyer et al., 2004). Consequently, STMs are a key component of the proposed framework for science-based land management (SBLM) of rangelands in the western United States and elsewhere (Herrick et al., 2006). However, a science-based, quantitative implementation that goes beyond current qualitative methods of deriving STMs is constrained by: (i) a lack of long term data encompassing the breadth of different possible ecosystem behaviours; (ii) the need to derive STMs indirectly by collating a range of often disparate data sources; and, (iii) system and geographical specificity, thereby creating an inequity in terms of which systems and localities will be investigated first (Bestelmeyer et al., 2003, 2004). Data in the form of aerial imagery would ameliorate the above difficulties in STM modelling, as imagery is spatially extensive and may be reliably captured, georeferenced and processed at a range of geographical scales. A methodology to arrive directly at a STM from temporal sequences of imagery that capture vegetation pattern dynamics is therefore proposed. In its simplest form the STM identifies the possible vegetation communities that can occur in a particular system or locale, labelling them as different meta-stable phases (i.e. these vegetation communities may vary from being transient to persistent; Westoby et al., 1989; Stringham et al., 2003). The system may then experience a transition (or pathway) from one phase to another that was triggered (or driven) by the interacting effect of different events and processes. Hence, some of the nonlinearities observed in the field that confound linear succession models may be described, a list including: ecological thresholds and irreversible transitions; multiple stable states; historical contingency; cross-scale interactions, and lagged effects (Friedel, 1991; Rietkerk and van de Koppel, 1997; Peters et al., 2004). The dynamics of a system are therefore an observed sequence of nonlinear transitions between different phases (Fig. 1). A key concept of the STM is the ecological threshold, a boundaryin space and time between different phases of the system (or domains of stable system behaviour; May, 1977; Friedel, 1991). Transitions across ecological thresholds can occur along a continuum from irreversible to immediately reversible pathways (Stringham et al., 2003; Briske et al., 2005). Irreversible transitions are triggered by events that are typically unprecedented and which lead to a degraded state that is constrained by a different set of biological and soil processes (e.g. soil erosion, overgrazing, introduction of exotic plant species, altered fire regimes or a combination of such events). The typology of Stringham et al. (2003) uses irreversible transitions to define „states‟ of the system, whereas reversible transitions separate „phases‟ or „communities‟. Collections of phases, connected by a network of transitions are visualize as the phase dynamics nested within each system state (Fig. 1; Stringham et al., 2003). Science-based land management (SBLM) is defined by four core elements: (1) a method of land classification to describe „ecological‟ sites; (2) a data storage and management facility; (3) conceptual models of ecosystem dynamics, including site specific STMs; and (4) a methodology to evaluate the status of the ecosystem, be it qualitative or quantitative (Herrick et al., 2006). To date, SBLM has been applied to arid lands of western United States, where episodic events such as rainfall drive often dramatic shifts in ecological processes. In arid lands, intensive assessment is necessary to match and capture the frequency of driving events, otherwise important factors leading to vegetation change will likely be missed and long term trends will be confounded by temporary responses to recent events. Consequently, the need for long term monitoring is implicit in SBLM, and is akin to adaptive management (Holling, 1978): data from long term monitoring is used to update models and knowledge that assists management decision making in dynamic and uncertain ecological systems.

نوشته دانلود مقاله ترجمه شده اشتقاق مدل حال و انتقال از سری های زمانی دینامیک الگوی علفزار – مجله الزویر اولین بار در ترجمه فا پدیدار شد.

فهرست مطالب:

 چکیده
مقدمه
توصیف منطقه مورد مطالعه
کشاورزی دامنه ای
نگاهی بر مدل حوزه ای WEPP
روش
داده های هواشناسی
داده های هیدرولوژیک
اندازه گیری میدانی خواص خاک
مدل ارتفاع رقومی برای تعیین خصوصیات ابخیز
داده های ماهواره ای
کاربرد مدل wepp
ورودی های مدل
ارزیابی عملکرد مدل
معیارهای ارزیابی مدل
نتایج و بحث
شبیه سازی رواناب
آنالیزهای حساسیت
شبیه سازی تولید رسوب
ارزیابی سناریوهای مدیریت ساختمان و پوشش بنیان
مدیریت کارامد حوزه
ارزیابی عملیات مدیریت زراعی
تیمار شخم
مدیریت ساختمانی
اثر مجموعه بهترین عملیات مدیریتی و ساختارهای حفاظتی
نتیجه گیری

بخشی از ترجمه:

مدل WEPP تولید رسوب و رواناب را به طور رضایت بخشی در شرایط شیب و بارش زیاد حوزه با ضریب ناش سات کلیف بیش از 0.87 درصد و انحراف معیار 5.23 شبیه سازی کرد. مقایسه بین مقادیر شبیه سازی و اندازه گیری شده تولید رسوب و رواناب نشان داد که مدل مقادیر بالا را کم تر از مقدار واقعی براورد می کند. مطالعات بیشتر در خصوص اجزای زیزسطحی پارامتر های مدل می تواند برای بهبود قدرت براورد مدل مفید باشد.
نتایج شبیه سازی نشان می دهد که سویا و بادام زمینی پتانسل تعویض با برنج دیم برای کاهش تولید رسوب به ترتتیب تا 29.60 و 27.70 دارند.
نتایج شبیه سازی نشان می دهد که جایگزینی عملیات شخم سنتی با سیستم بدون شخم و کولتیواتور زارعی می تواند منجر به کاهش تولید رسوب تا 21.88 و 13.14 % شود.
نتایج شبیه سازی نشان می دهد که نصب 26 سد سنگی متخلخل و موانع رسوب گیر در حوزه امروی می تواند تولید رسوب را تا 54.6درصد کاهش دهد.
نتایج به وضوح نشان داد که مدیریت شخم وزراعی و کنترل سازه ای به تنهایی قادر به کاهش تولید رسوب ورواناب نمی باشند. شبیه سازی مجموعه روش های کنترلی بیولوژیکی، شخم و سازه ای دارای پتانسیل کاهش تولید رسوب تا 78.40% می باشد. تناوب کشت ذرت با سویا در ارتفاعات برای کاهش فرسایش خاک و رفع نیازهایی غذایی لازم است.
مدل واسنجی و اعتبارسنجی شده WEPP می تواند به طور موفقیت آمیزی برای توسعه راهبرد های بیولوژیک و ساختمانی در شرایط با شیب و بارش زیاد شرق هیمالیا مورد استفاده قرار گیرد.

بخشی از مقاله انگلیسی:

1. Introduction Food security and environment protection are the most challenging task the world is facing today. Land and water resources are important components of environment. Degradation of the quality of these resources will affect the quality of the environment. Major portion of the food consumed by human being comes from the land. Due to demographic pressure land use is intensified and erosion prone area is brought under subsistence agriculture leading to land degradation. Soil erosion is an irreversible phenomenon causing land degradation and deterioration of surface water quality. It is caused due to inappropriate land use and poor management. Soil degradation is responsible for making 0.3–0.8% of the world’s arable land unsuitable for agricultural production every year and an additional 200 million ha of cropped area would be required over the next 30 years to feed the increasing population (den Biggelaar et al., 2004; Lafond et al., 2006). Therefore, this precious finite resource must be safeguarded against all kinds of degradation and deterioration for sustainability of agricultural production and environment protection. In India, out of the total geographical area of 329 million ha, approximately 145 million ha of the total land resource is subjected to various degrees of wind and water erosion, which cause a loss of 5.3 million Mg of soil every year. In eastern Himalayan region of India, soil erosion by water is a major factor causing land degradation. About one third area of the region suffers from various forms of land degradation problems (Sehgal and Abrol, 1994). Practice of traditional slash-and-burn agriculture on steep slopes, intense rainfall, undulating and sloppy land surface compounds the problem many folds. About 386 900 ha area in the region is affected by shifting cultivation and as high as 76.6 Mg ha1 yr1 of soil is lost due to this system of farming (Satapathy, 1996). Eighty percent area is under threat of moderate to severe erosion. To combat the threat of land degradation, we need to understand physical process of erosion in relation of topography, land use and management. Watershed being a natural drainage unit should form the basis for planning various land uses and conservation measures to optimize the use of soil and water resources to increase and sustain agricultural production. In order to develop a comprehensive plan for soil and water conservation, it is essential to estimate runoff and soil loss resulting from different crop and structure-based management practices. Among the available tools for soil erosion assessment, simulation models are quite important because appropriate models can be used to evaluate a variety of management scenarios without costly and time consuming field tests (Pieri et al., 2007). In recent past a trend of testing and using physical process based runoff and soil erosion prediction models both at field as well as at watershed scales has gained momentum. These physical process based models, often with an explicit attempt to describe runoff and erosion processes, are better equipped to evaluate the impacts of management interventions and help make management decisions aimed at preserving land productivity and environment quality (Yu and Rosewell, 2001). Before application, such models need to be properly calibrated and validated using measured hydrologic data of the watershed. Lack of reliable field-measured data for calibration and validation of models is the major limitation for their application. Runoff and soil loss data can be obtained through field measurements and watershed attributes could be derived using remotely sensed data and digital elevation model of the watershed (Amore et al., 2004; Baigorria and Romero, 2007). In hilly watersheds spatial and temporal variability in terms of soil, land use/land cover, topography, rainfall and biotic interventions are large. The runoff, sediment, fertilizers, pesticides and other pollutants, resulting from the agricultural activities cause deterioration of quality of surface and ground water. Methods for identification of sources of pollutants and their quantification are essential for their control. Distributed parameter watershed models are applicable for this type of assessment. Review of literatures revealed that CREAMS (Knisel, 1980), ANSWERS (Beasley et al., 1982), SWRRB (Arnold et al., 1990), AGNPS (Young et al., 1989), EPIC (Sharpley and Williams, 1990) and SWAT (Arnold et al., 1998) are probably the most important models and widely used worldwide for hydrologic and pollutants transport modeling. The main erosion components of these models are based on concepts originally formulated in the Universal Soil Loss Equation (USLE) model (Wischmeier and Smith, 1978), which relate the total amount of soil loss to six factors: rainfall erosivity, soil texture, slope length and grade, soil cover and conservation practice. Runoff components of these models use the SCS–CN method to predict runoff (Bingner, 1990; Schröder, 2000). Among these models only SWAT, AGNPS and ANSWERS are the distributed parameters physically based watershed scale models mostly used for low slope conditions (Arnold et al., 1998; Bingner et al., 1992; Schröder, 2000). Any model used for computing potential soil loss from an area must deal with a large number of parameters concerning vegetation, management, soil, topography and climate (Amore et al., 2004). Performance of a model depends upon number of parameters it is considering for runoff and soil loss computation based on scientific theory. Performance of such model may not differ much on different scales. Topography and nature of rainfall are quite dominant parameters in generation of runoff and soil erosion particularly in hilly watersheds. Water Erosion Prediction Project (WEPP) is one such process based model developed for estimating soil loss, and selecting catchment’s management practices for conservation planning for field and small catchments (Flanagan and Nearing, 1995; Lane et al., 1997). The model was used successfully world wide (Yu and Rosewell, 2001; Huang et al., 1996; Amore et al., 2004; Pieri et al., 2007; Baigorria and Romero, 2007; Shen et al., 2009; Shen et al., 2010) including India (Pandey et al., 2008) for estimating runoff and soil loss from different land use and crop management practices. Performance of the WEPP model was compared with the ANSWERS (Bhuyan et al., 2002), EPIC (Bhuyan et al., 2002), and SWAT (Shen et al., 2010). They found that the performance of the WEPP model was at par with the ANSWERS and better than the EPIC and SWAT in simulating different management scenario for reduction of sediment yield.

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فهرست مطالب:

چکیده
۱ مقدمه
۲ جریان سطحی و انتقال رسوب در سطوح زبر
۳ مدل فرسایش استانه ی سطحی
۴ نتیجه گیری

بخشی از ترجمه:

چنین استدلال می شود که اثرات متقابل حین خصوصیات طحی به خصوص میکرو توپوگرافی و سله بندی بر کمیت و الگوی مکانی رواناب سطحی تاثیر می گذارند.این اثرات متقابل در همه ی مقیاس از مقیاس های زبری فردی تا مقیاس های حوزه ای دیه می شود.اگر چه پارامتر سازی زبری می تواند به صورت وابسته به مقیاس و بارندگی باشد اما مفهوم ظرفیت ذخیره ی موثر وی ا استانه ی رواناب در دامنه های مقیاس های مربوطه بسیار مهم است و در بسیاری از موارد به شدت بستگی به خواص سطحی خاک و توزیع ان ها دارد.
تغییرات تصادفی هم در شدت باران و هم در ذخیره و خصوصیات نفوذ بر مقدار و توزیع رواناب تاثیر می گذارد و اثرات متقابل بین این تغییر پذیری ها ایجاد وابستگی های قوی بین اندازه ی یمانگین قطه باران و طول دامنه برای یک طح معین می کنند.همه ی این روابط درونی هنوز به اندازه ی کافی خوب درک نشده اند که ما بتوانیم از ان ها برای ایجاد مدل های مناسب فرسایش و رسوب و چشم انداز استفاده کنیم. همچنین ان ها اصول و قواعد مفهومی مهم را برای تنظیم و واسنجی پلات ها تا مقیاس حوزه ای در اختیار می گذارند و به این ترتیب درک بهتر از نتایج تجربی و کاربرد ان ها در سطوح بزرگ تر حاصل خواهد شد.

بخشی از مقاله انگلیسی:

1. Introduction Soil erosion models commonly include parameters based on fixed soil properties or moisture–tension curves, but rarely take account of the dynamics linking soil and surface properties with water erosion processes, which are relevant at a range of time and space scales. The four sub-systems of Soil, Vegetation, Atmosphere and Surface interact dynamically with one another within each site, and sites are linked by lateral transfers of water, sediment and solutes in a downslope direction Fig. 1 . Ž . Over short within-storm periods, soils properties influence erosion mainly through their hydrology, aggregate stability, and cation dispersion. Over periods of decades, erosion can lead to profile truncation and armouring of the surface, and these changes then influence subsequent rates and patterns of erosion. Over the still longer periods of soil evolution, the balance between mechanical and chemical denudation determines the entire weathering profile and its variation downslope to create hillslope catenas, which in turn also influence the distribution of erosion rates. Similarly, erosion interacts with soil properties at a wide range of spatial scales. Macro-pores and crusting are examples of dominant influences at the finest 10 –10 Ž y3 y1 m scales, and give way in importance to spatial patterning produced by cultivation or . natural vegetation location at moderate 1–10 m scales, to catena differences at the Ž . Ž 2 3 . Ž 4 5 hillslope 10 –10 m scale, to major soil series at the catchment 10 –10 m scale and . Ž 6 8 to climatically based major soil groups at continental 10 –10 m scales. In all cases, . there are also strong links with soil via the vegetation cover, so that the direct importance of the soil is greatest under sparse covers. The direct links with the soil are therefore strongest under arid and semi-arid climates for uncultivated areas. Under conditions of global change, relatively slow changes in soils and erosion rates are giving way to much more rapid modifications under the impact of climate and landuse change. Under these strongly non-equilibrium conditions, many ‘natural’ inter-relationships between the soils and the associated pattern of erosion will be broken down, demanding a more fundamental assessment of cause and effect in highly disturbed systems and making it difficult to use analogue studies with any confidence. On natural semi-arid surfaces, microtopography evolves through sediment transfers and through the dynamics associated with mounds around perennial shrubs, with a time scale of decades to hundreds of years. On cultivated fields, microtopography is created by tillage operations and destroyed by sediment transfers over an annual cycle. These two systems have rather different dynamics but a number of important features in common. This paper explores developments with respect to one set of processes which are believed to be important, and have been relatively neglected—the interactions between overland flow, water erosion and surface microtopography. This theme is being explored through research in a number of related erosion models, which are concerned with the wide range of relevant spatial and temporal scales. Some are primarily related to hydrology, others to soil erosion under global change while others are concerned with the evolution of soils and landforms over geological time spans. These include the MEDALUS and MEDRUSH models Kirkby et al., 1997, 1998 , the Regional Degrada- Ž . tion Index RDI Ž . rCSEP: Kirkby and Cox, 1995 and a number of models for long-term landscape evolution e.g. Kirkby, 1991, 1992, 1994 . Ž . 2. Overland flow and sediment transport on rough surfaces Roughness due to random irregularities on a soil surface is usually well represented as a normal distribution of elevations relative to a mean, and is characterized by its standard deviation, or RMS roughness. There may also be various forms of systematic roughness due to tillage operations or, at a coarser scale, to terracing. Their orientation with respect to the slope direction is vitally important, particularly for long linear features like plough ridges. The scale dependence of roughness is not fully understood, but it is clear that roughness occurs at a number of scales, and natural roughness may well have a fractal or similar structure, with larger RMS roughness as it is measured with a coarser grid of points. At sufficiently coarse scales, roughness of natural surfaces merges into landscape elements such as ephemeral gullies and stream valleys. Cultivated areas also show systematic roughness elements, most strikingly at the scales of plough furrows and terrace systems.

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فهرست مطالب:

چکیده
مقدمه
مواد و روش ها
نتایج
عملکرد دانه
وزن هزار دانه
وزن آزمایش
محتوی پروتین
حجم SDS
همبستگی بین پارامترهای افزایش یافته
بحث
نتیجه گیری

بخشی از ترجمه:

نتیجه گیری
تاثیر مدیریت بقایای گیاهی پنبه بر عملکرد دانه،TW،PC،SDS معنادار نبود با این حال Srem دارای tgw بالتر و معنادارتری از Slev بود. تیمارهای ترکیبی شخم و روش کاشت پشته ای تاثیر معناداری بر عملکرد دانه،TGW-TW داشت با این حال به طور معناداری بر PC و SDS تاثیر نگذاشت. شخم حفاظتی با بذرپاشی منجر به کم ترین عملکرد دانه شد در حالی که هیچ اختلاف معناداری میان دیگر تیمارهای شخم وجود نداشت. عملکرد دانه همبستگی مثبتی با TGW داشت با این حال هیچ رابطه ای با دیگر پارامترهای دانه نشان ندادند. حتی تحت شرایط آبیاری، تغییر شرایط آب و هوایی به خصوص مقدار و توریع بارندگی طی فصل رشد تاثیر معناداری بر عملکرد دانه گندم و پارامترهای کیفیت علی رغم آبیاری های مکمل اعمال کردند. عملکرد دانه و TGW د ر2003-2004 در کم ترین مقدار خود بودند.TW در 2004-2005 نسبت به 2 سال دیگر بالاتر بودند.PC و SDS در 2004-2005 بالاتر بود که دارای مقدار بارندگی کم تری نسبت به 2005-2006 بود. به طور کلی، شخم سنتی با بذرپاشی کم ترین تاثیر در عملکرد دانه گندم داشت و د رمیان تیمارهای شخم دیگر، عملکرد مشابه دیده شد.مدیریت بقایای گیاهی هیچ تاثیری بر تولید گندم و کیفیت آن به جز TGW نداشت.

بخشی از مقاله انگلیسی:

1. Introduction In irrigated areas of the South East Anatolia Region of Turkey, cotton and wheat are the main arable crops. Cotton is usually grown in monoculture agriculture or in rotation with wheat. Cotton harvesting continues every year by November or December depending upon the weather conditions. Seedbed preparation is relatively hard for planting wheat following cotton because autumn rainfall results in wet soil conditions. In the region, wheat planting after cotton harvest is characterized by chopping or collecting stalks after cotton harvest, intensive tillage and broadcasting the wheat seed on leveled soil surface and then incorporating it by means of a shallow tillage operation. But, this system results in soil degradation and erosion, and in addition the production costs are very high and yield is low (Gemtos et al., 1998; Husnjak et al., 2002; Fahong et al., 2004; Hobbs et al., 2008). Besides, lateness of cotton harvesting leaves very limited time for land preparation for ‘on-time’ planting of wheat. Therefore, it is important to develop tillage and residue management technologies that allow more timely planting, and prevent yield reduction and soil degradation in wheat agriculture following cotton. Many researchers have reported that conservation tillage protects soil from wind and water erosion and improves soil physical, chemical and biological properties, and reduces production costs (Gemtos et al., 1998; Chan and Hulugalle, 1999; Lithourgidis et al., 2006; Thomas et al., 2007; Mann et al., 2008). However, yield of wheat under conservation tillage is inconsistent, depending on soil-climatic conditions, and it is dependent on a number of interacting factors, including weed control level, residue management, cultural practices and drill performance (Dawelbeit and Babiker, 1997; Gemtos et al., 1998; Carefoot and Janzen, 1997). Under irrigation, Karlen and Gooden (1987), Hemmat and Taki (2001), Li et al. (2008) reported lower wheat yield for conservation tillage as a result of poor stands, while Hao et al. (2001), Jalota et al. (2008), Mann et al. (2008), Schillinger et al. (2010) found that conservation tillage was equal to or better than conventional tillage. Javadi et al. (2008) reported that reduced tillage using chisel plow, or disk and toothed harrows could provide an efficient alternative to conventional tillage in order to maintain high productivity in irrigated conditions. However, they stated that no-tillage did not show promising results due to lack of appropriate equipment. The adoption of conservation tillage practices is very slow due to lower crop yields in such systems, and also differences in management that farmers may not be familiar with (Cosper, 1983). A study by Sayre and Hobbs (2004) showed that permanent raised beds were an excellent option and offered potential benefits in terms of higher crop yield and quality, lower production costs, improved soil structure through controlled traffic and minimum tillage, and the possibility that furrow-irrigation may be more efficient than flood irrigation. Also, the bed planting system offers opportunity for initial weed control prior to planting, facilitates access to crop for timely nutrient (especially N) application, uses lower seed rate, allows better stand establishment, and reduces crop lodging, herbicide dependence, soil erosion by irrigation water if crop residues are left on the surface in furrows and field compaction by restricting machinery traffic (Hobbs et al., 1998; Reeves et al., 1999; Sayre and Hobbs, 2004). Jin et al. (2008) stated that a permanent raised bed cropping system had the potential to make an important contribution to agricultural productivity, but ongoing research is needed on several aspects of this cropping system, including the suitability of current wheat varieties and relationships between tillage and water management practices, productivity and environmental conditions. Under rainfed conditions, the developed technologies and practices have resulted in similar or higher crop yields from conservation tillage than those from conventionally tilled fields (Hunt et al., 1997). They also reported that no yield loss was found when notill system was used in winter wheat agriculture after cotton. But, Ishaq et al. (2001) reported that the effect of tillage on wheat grain yield differed among years, and wheat grain yields were lower for minimum tillage than for conventional tillage, or deep tillage. They stated that wheat following cotton requires plough-based seedbed preparation to alleviate surface soil compaction and improve soil tilth. Also, Gwenzi et al. (2009) determined that tillage effects on crop yields in an irrigated wheat–cotton rotation were inconsistent throughout a 6-year period and the higher weed infestation and poor crop stand under minimum and no-tillage resulted in reduced wheat yield. They stated that minimum tillage and notillage were more sustainable tillage systems for semi-arid regions than conventional tillage because of limited adverse impacts on crop productivity, and improved soil structural stability. Dawelbeit and Babiker (1997) reported that the disk harrow and seed drill could be recommended for profitable wheat cultivation in irrigated Vertisols of Rahad. They determined that seed drilling and ridging after broadcasting resulted in significantly greater yields than broadcasting alone.

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فهرست مطالب:

چکیده
۱ مقدمه
۲ ایده عمومی در خصوص تاثیر درختان روی حاصلخیزی خاک
۳ درختان و کربن خاک
۴ درختان و تنوع زیستی خاک
۵ درختان در خاک های حاره ای
۶ درختان در کشاورزی امازون
۷ نتیجه گیری

بخشی از ترجمه:

مقاله حاضر به بحث در خصوص اثرات درختان روی حاصلخیزی خاک با تاکید بر سیستم های کشاورزی در آمازون می پردازد. بررسی منابعی خصوص اثرات درختان روی خواص فیزیکی و شیمیایی خاک در مناطق حاره ای،نیمه حاره ای و معتدله انجام شده که شامل اکوسیستم های طبیعی و اکوسیستم های زراعی می شود. کربن خاک در شکل ماده آلی به عنوان شاخص فعالیت بیولوژیک و نیز مشکلات سیاسی نظیر ترسیب کربن و تغییر اقلیم مطرح است. در رابطه با خاک های حاره ای و آمازون، اطلاعات در خصوص اثرات درختان روی خاک در سیستم های زراعی سنتی علاوه بر توسعه راه کارهای جایگزین کشاورزی پایدار تر برای منطقه مورد بحث قرار می گیرد . در نهایت مطالعه موردی در منطقه ساوانا رورامیا شمال برزیل معرفی می شود که توالی زمانی سیستم های آگروفارستری بومی اثرات مبرهن عملیات مدیریتی از جمله اثر درختان روی حاصلخیزی خاک را نشان می دهند. استفاده از گونه های مختلف درختی و دیگر عملیات به کار گرفته شده در سیستم های آگروفارستری می تواند یک راهکار جایگزین برای افزایش باروری خاک و حفظ تولیدات کشاوری با اهمیت کاربردی برای پایداری کشاورزی حاره ای تلقی شود.

۱ مقدمه

بر اساس مطالعه انجام شده توسط مرکز آگروفارستری جهانی ICRAF، ۴۳ درصد اراضی زراعی زمین(بیش از ۱ میلیارد هکتار) دارای پوشش درختی بیش از ۱۰ درصد می باشد. سطح وسیعی از اراضی زراعی یعنی ۱۶۰ ملیون هکتار دارای پوشش درختی بیش از ۵۰ درصد هستند. پتانسیل درختان برای بهبود تغذیه، درامد، مسکن، سلامتی و بهداشت، رفع نیاز های انرژی و پایداری زیست محیطی در چشم انداز های کشاورزی موجب شد تاICRAF حضور درختان را به عنوان ممولفه اصلی کشاورزی همیشه سبز معرفی کنند. در میان طیف وسیعی از مزایای ناشی از درختان، یک عنصر مهم اثر مثبت درختان روی خواص خاک و در نتیجه مزایای آن برای گونه های زراعی می باشد. این مقاله به بررسی دانش فعلی در خصوص رابطه بین درخت و خاک بر اساس تحقیقات سیستم های اگروفارستری علاوه بر مطالعات در محیط های طبیعی و غیر زراعی که اثرات درخت را روی خاک اثبات کرده اند می پردازد.

بخشی از مقاله انگلیسی:

This paper discusses the effects of trees on soil fertility, with a focus on agricultural systems in Amazonia. Relevant literature concerning the effects of trees on soil physical and chemical properties in tropical, subtropical, and temperate regions is reviewed, covering both natural ecosystems and agroecosystems. Soil carbon, in the form of organic matter, is considered as an indicator of biological activity as well as in relation to policy issues such as carbon sequestration and climate change. In the case of tropical soils and Amazonia, information on the effects of trees on soils is discussed in the context of traditional agriculture systems, as well as in regard to the development of more sustainable agricultural alternatives for the region. Lastly, attention is given to a case study in the savanna region of Roraima, northern Brazil, where a chronosequence of indigenous homegarden agroforestry systems showed clear effects of management practices involving trees on soil fertility. The use of diverse tree species and other practices employed in agroforestry systems can represent alternative forms of increasing soil fertility and maintaining agricultural production, with important practical applications for the sustainability of tropical agriculture. 1. Introduction According to a study by the World Agroforestry Centre, ICRAF, 43% of the planet’s agricultural lands (more than a billion hectares) has more than 10% tree cover [1]. A lesser but still significant area of agricultural land, 160 million hectares, has more than 50% tree cover. The potential of trees to bring improvements in nutrition, income, housing, health, energy needs, and environmental sustainability in the agricultural landscape has guided ICRAF’s mission, with the presence of trees being the principal component of an “evergreen agriculture” [2]. Within the array of benefits brought by trees, an important element is the positive effect of trees on soil properties and consequently benefits for crops. This paper explores current knowledge as to this relation between trees and soil, based on agroforestry systems research, as well as studies innon-agricultural or natural environments that demonstrate effects of trees on soil. Although we consider information from various ecosystems and biomes, the focus will be on Amazonia, where the authors have most of their experience. This focus on Amazonia is also due to the strong policy demands for the development of more sustainable agricultural systems in the region, as alternatives to forms of land use that have shown significant and negative impacts on natural resources and ecosystem services, such as deforestation for extensive cattle ranching. In this scenario, agroforestry systems have been indicated as one of the more promising alternatives to achieve a more sustainable agriculture, in greater equilibrium with the environment [3]. The presence of trees in farming systems, although an ancient practice, began to gain institutional attention during the 1970s and 1980s, with the beginning of studies on “agroforestry systems”. One of the principal definitions employed in this context was that proposed by Lundgren and Raintree in 1982: “Agroforestry is a collective name for landuse systems and technologies where woody perennials (trees, shrubs, palms, bamboos, etc.) are deliberately used on the same land-management units as agricultural crops and/or animals, 2 Applied and Environmental Soil Science Figure 1: Agroforestry system with rubber (Hevea brasiliensis), cacao (Theobroma cacao), and ac¸a´ı (Euterpe oleracea) in Tome-ac ´ ¸u, Para, showing the litter layer that is typically found in such ´ multistrata systems. Figure 2: Agroforestry system in initial phase, with black pepper (Piper nigrum) as principal cash crop, interplanted with cupuac¸u (Theobroma grandiflorum) and ac¸a´ı (Euterpe oleracea) for future fruit production, as well as timber trees (mahogany—Swietenia macrophylla and ipe—ˆ Tabebuia sp.) and Brazil nut (Bertholletia excelsa) as long-term products. in some form of spatial arrangement or temporal sequence. In agroforestry systems there are both ecological and economical interactions between the different components” [4] (Figures 1, 2, and 3). While trees in general can provide a number of environmental benefits in both rural and urban landscapes, and play key roles in ecosystem services provided by natural areas, in this paper we will restrict our focus to the effects of trees on soil fertility, in the specific context of agricultural systems. Although the benefits that trees can provide on rural properties such as food security, household income, economic stability, and thermal comfort (shade) are most often associated with their products, such as fruit, timber, or other items, the inclusion of trees in agricultural systems can also optimize nutrient cycling and have positive effects on soil chemical and physical properties. This process is especially important in tropical soils, where a high degree of weathering has created deep, leached soils that are poor in Figure 3: Multistrata agroforestry system in Tome-ac ´ ¸u, Para, with ´ harvest of hogplum (Spondias mombin) grown as the upper canopy over cacao and ac¸a´ı. plant nutrients [5, 6]. Although poor in nutrients, tropical soils are very rich in biodiversity, with higher diversity and biomass of microorganisms than temperate soils, with these being the principal agents mediating the supply of nutrients to the soil by means of the decomposition of organic matter, derived from the vegetation [7–9]. In the humid tropics, the removal of surface litter or organic matter generally results in the depletion of soil fertility in a few years [10, 11]. In agricultural systems practiced by traditional peoples, this limitation is circumvented by using the land for a short period (generally 2- 3 years), after which the cultivated areas are left to fallow with natural regeneration of secondary vegetation. The associated ecological interactions reestablish nutrient cycling and recuperate soil qualities, after which the area can once again be used for agriculture [12, 13]. This is the basis for shifting cultivation in Amazonia, a system that has permitted native populations to manage their natural resources over centuries, with small-scale environmental impacts that do not exceed the support capacity and resilience of ecosystems. However, the present-day situation of population growth and increasing pressure on agricultural lands lead to situations where there is demand for more intensive land use. This most often implies in repeated burning, the cheapest way to prepare land for planting, which can interrupt processes of nutrient cycling and accumulation, leading to loss of soil fertility and consequently slowing the recuperation of natural vegetation during fallow cycles [14]. In light of the present-day situation of Amazonia, where there are now good reasons and policy demands to balance conservation with development, it is necessary to think in terms of agricultural systems that optimize nutrient cycling and permit permanent or semipermanent production, as well as minimize dependence on external inputs and have low environmental impact. The inclusion of diverse tree species is a key element in maintaining the production of organic matter and generating other positive benefits, as well as allowing the diversification of products. However, before we discuss topics specific to tropical soils and Amazonia, Applied and Environmental Soil Science 3 the following sections will review general information about the influence of trees on soil and their role in accumulation of soil carbon stocks. 2. A General View of the Influence of Trees on Soil Fertility One of the pioneer studies to measure the effects of individual trees on soils was that by Zinke [15], who looked at pines growing on dunes in northern California, USA. His study found that under trees, certain soil properties exhibited a pattern of radial symmetry, with changes in pH, nitrogen, cations, and cation exchange capacity varying according to distance from the tree trunk, with a peak in these characteristics at a certain distance. Subsequent studies also demonstrated patterns in the variation of soil characteristics as influenced by trees, such as in tropical savannas [16, 17], deserts [18], and areas of temperate forests [19–23]. In analyzing soil characteristics under individual tree crowns in Kenyan savannas, Belsky et al. [16] found greater levels of mineralizable N, microbial biomass, P, K, and Ca underneath the crowns when compared to open savanna. Burke et al. [17] explain that in dry savannas the strong limitation on water availability permits only punctuated establishment of trees and shrubs but that under crowns cycling occurs in a different form than in open grasslands, with the possibility of soil enrichment in a scale of decades. However, such soil changes can be reverted with the death of the tree or by fires. Belsky et al. [16] also point out the effect of nutrients deposited in dung by birds and large mammals that utilize trees as resting places or roosts. Such patterns form what have been called “islands of fertility” or “resource islands” created by trees or bushes, generally in savannas or desert areas. The microenvironment of these “islands” can also influence the composition of the herb stratum [16, 19], soil density [19, 20], and earthworm activity [20, 23] among other factors, allowing the creation of positive feedbacks that favor plant establishment and productivity [23, 24]. At the same time, these patterns can be important indicators of stability or risk of desertification in such areas [17, 18]. Studies of forests in temperate climates indicate variations in soil that can be related to individual tree species. Besides the expected correlations, such as greater levels of N under legumes [20] or lower pH under species that produce acidifying litter, such as Pinus spp. [20, 23], other interesting interactions show that different species can alter soil in distinct ways, with variations in the increment of soil carbon [20], exchangeable Ca and Mg and per cent base saturation [21, 23]. In a study of 14 tree species in Poland, Reich et al. [23] found varied effects on soil characteristics; however, these effects were significantly related to the level of Ca in litter, independent of the species. Trees producing litter rich in Ca were associated with soils with greater pH, exchangeable Ca, and per cent base saturation, as well as greater rates of forest floor turnover and greater diversity and abundance of earthworms. Dijkstra [22] emphasizes that the rate of mineralization of organic Ca is a fundamental factor in this process, since it determines the immediate availability of this nutrient in the soil and can vary between species. The study of vertical patterns of the distribution of nutrients in soil can indicate other phenomena that are not detected when only the horizontal distribution of nutrients is examined. In an evaluation of more than 20,000 globally distributed soil profiles, the greater part in temperate climates, Jobbagy and Jackson [ ´ 25] found that cycling mediated by plants exerts a marked influence on the vertical distribution of nutrients in the soil, especially in the case of more limiting nutrients such as P and K. Patterns of greater concentration of these nutrients in surface layers (0– 20 cm) were attributed to the fact that since these are more important to plants, they are subject to greater uptake and cycling, being absorbed from deeper layers and returned to the soil surface through litterfall and rain water throughfall. This process of uptake functions in opposition to leaching, which moves nutrients downward and acts more strongly on those nutrients that are in lessdemand by plants. If a nutrient is not limiting, its movement in the soil profile will be more influenced by leaching than by cycling and it will present higher concentrations at greater depth, as occurs with Na, Cl, and Mg [25].

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