Nutrient management in low input grazing–based systems of meat production

Abstract. Low input grazing-based meat production is often practised on land where alternative land use is restricted and where high biodiversity warrants specific environmental payments. Although these systems are characterized by low external nutrient inputs, significant nutrient losses may occur per unit of produce, even though losses per unit area are low. If the aim is to have animal production without further eutrophication of watercourses, these losses should be minimized,. However, if nutrient-poor grasslands characterized by high biodiversity are the aim, some losses must be accepted to balance nutrient inputs by atmospheric deposition. The impact of grazing animals on nutrient dynamics in grasslands is reviewed in this paper, and options to further improve nutrient management are discussed. It is concluded that nutrient management should largely be addressed indirectly through management of animal behaviour in relation to grazing and supplemental feeding, as well as through optimization of the seasonal distribution of livestock size. A case study indicated that N losses from a cattle farm could be reduced considerably by these means, while animal production could actually be improved. Sustainability issues and trends in legislative and social pressures on low input grazing-based systems of animal production are discussed in relation to nutrient management and practical recommendations.     

Nutrient management for intensive animal agriculture: policies and practices for sustainability

Abstract. The intensity of animal production around the world has increased substantially during the last half-century, which has led to large problems with the disposal of manures and waste waters. The focus of this paper is on the development of national policies to improve the nutrient management of concentrated animal feeding operations (CAFOs), where nutrients are invariably in surplus. To create proper nutrient management strategies for CAFOs, and to avoid environmental problems when surplus nutrients enter air, soil and water, we need to know the number of animals/birds in the unit, the quantity of manure/slurry produced, how this material is stored and handled and how much land is available for manure spreading. In this paper, we discuss the development of nutrient management strategies for CAFOs in Europe and North America, and the voluntary measures and environmental regulations related to this. For the planning of nutrient management to be comprehensive and efficient, we need expertise from several disciplines. This planning includes development of: animal diets that reduce the amounts of excreted nutrients; efficient storage and land application technologies; land application programmes to optimize yields and reduce nutrient losses; and strategies for use of excess manure outside the farm. Also, large-scale efforts involving many stakeholders (farmers, governments and private industry) are needed to solve problems with nutrient imbalances over the long term. Efforts along these lines include manure relocation, alternative uses of manures, nutrient trading, and a general extensification of animal agriculture. The overall guiding principle for policies and planning should be a balance of nutrients, on farms as well as at larger scales.     

Soil community changes during secondary succession to naturalized grasslands

Succession to a naturalized grassland from former agricultural land and pastures is accompanied by changes in plant biodiversity and in the soil community. These changes are the result of a reduction or elimination of management, fertilizer applications and of grazing by large herbivores. We review soil biology studies on agricultural land that are in various successional stages towards naturalized grasslands, where interactions between plant species composition changes and the soil ecology affect each other. In many chronosequence studies, the soil microbial community tends to shift towards a less bacterial, and more fungal dominated food web energy channel following a reduction in fertilizer inputs and grazing intensity. Whereas changes in microarthropod communities are obscured, nematode trophic functional group (ecological guild) changes respond to both plant and soil community changes. There are opportunities to further study the feedback interactions between roots and soil organisms in grasslands. A better understanding of the molecular feedback mechanisms would be beneficial in long-term grassland management.     

Nitrogen and phosphorus management on Dutch dairy farms: legislation and strategies employed to meet the regulations

 The high input of nutrients through the use of fertilizers, manure and animal feed make it possible to reach high levels of agricultural production. However, high nutrient inputs may also result in large nutrient losses and thus have adverse effects on groundwater, surface water, and the atmosphere. To minimize nutrient emissions from agriculture, the Dutch government has introduced regulations on nutrient use. These include: (1) a ban on spreading animal manure on agricultural land during the winter, (2) the obligation to cover storage facilities for animal manure, (3) compulsory low-emission applications of animal manure to land, and (4) applying levies when the maximum permissible annual N and P surpluses for farms are exceeded. The nutrient surplus is the difference between nutrient input into the farm and nutrient output from the farm. The maximum permissible N surpluses for 2000 are 250 kg N ha^–1 year^–1 and 125 kg N ha^–1 year^–1 for grassland and arable land, respectively, and for P, 35 kg P₂O₅ ha^–1 year^–1 for both grassland and arable land. When the annual permissible levels are exceeded, farmers are charged with a levy. Results obtained at the experimental dairy farm "De Marke" showed that a reduction in nutrient inputs via fertilizers and purchased food, in combination with restricted grazing, reduced the N surplus in such a way that the NO₃ ^– concentration in the groundwater decreased to about the maximum permissible level of 50 mg NO₃ ^– l^–1. Since these results were obtained on a sandy soil that is very sensitive to NO₃ ^– leaching, it is suggested that all dairy farmers should be able to sufficiently reduce NO₃ ^– leaching by improving their farm management. Received: 13 July 1999     

The restoration and re-creation of species-rich lowland grassland on land formerly managed for intensive agriculture in the UK

Intensive agriculture has resulted in the loss of biodiversity and the specialist flora and fauna associated with the semi-natural grasslands of low-intensity pastoral systems throughout northwest Europe. Techniques employed to restore and re-create these grasslands on agricultural land in the UK are reviewed. Extensive cutting and grazing management have been shown to diversify improved swards and facilitate re-colonisation on ex-arable soils, although rates of re-assembly of plant communities with affinity to existing semi-natural grasslands have generally been slow. On former agriculturally improved swards, nutrient depletion has accelerated this process, especially where “gaps” for establishment have been created. Similarly, on ex-arable soils “nutrient stripping” and sowing with diverse seed mixtures has led to the rapid development of species-rich swards. On free draining brown earths such an approach may be required to restore grassland communities where soil phosphorous concentrations exceed semi-natural levels by more than 10 mg/l (using Olsen's bicarbonate extractant). However, the appropriateness of this threshold for other soil types requires further sampling. Although restored grasslands are likely to contribute to national biodiversity targets success will ultimately depend on the reinstatement of the communities and ecological functions of semi-natural references. Although this is technically feasible for a few plant assemblages, less is known about the re-assembly of microbial and faunal communities, or the importance of trophic interactions during grassland succession. As a consequence, more research is required on the functional attributes of semi-natural grasslands, as well as the methods required to restore localised types, novel nutrient depletion techniques, the “phased” introduction of desirable but poor-performing species and the performance of different genotypes during grassland restoration.     

Nutrients in the West African Sudano-Sahelian zone: Losses,transfers and role of external inputs

Crop growth on acid sandy soils of the Sudano-Sahelian zone is primarily limited by the low amounts of organic matter and available mineral nutrients in the topsoil. The shortening of fallow periods with population growth, the exploitation of fire wood, spatial nutrient transfers by wind and water and net nutrient exports with crop yields in the order of 15 kg nitrogen (N) 2 kg phosphorus (P) and 15 kg potassium (K) ha⁻¹ yr⁻¹ for traditional fields planted to pearl millet (Pennisetum glaucum L.) in the southern Sahel have exhausted these resources. Large productivity declines in the prevailing agro-pastoral systems are the consequence. Data are presented to show bow nutrient exports at the level of individual fields, through grain yields and biomass removal as forage, firewood, construction material, and also through run-off, wind and water erosion, leaching and volatilisation, are either losses for the ecosystem or sources of nutrients transferred within the ecosystem. Livestock is a vector of nutrients from rangelands to manured fields through forage intake and excretion and helps to shortcut nutrient cycles, but it is also a net consumer of organic matter and minerals. Through the effects of trampling on the soil and of grazing on the vegetation composition and production, livestock also indirectly affects the cycling and transfer of nutrients. Net nutrient inputs by heavy rains causing overland flow, dust deposition and through biological nitrogen fixation, are also unequally distributed and thus aggravate the fertility gradient from large nutrient ‘source’ areas such as rangelands to small ‘sink’ areas such as fallows, low lands, temporary lakes and river benches. At a finer resolution, shrubs and trees with their alternating periods of nutrient storage and recycling in leaves and wood, micro-depressions, termite mounts and ant nests become localised points of nutrient concentration and high crop productivity. To balance losses of nutrients in these integrated systems and to obtain sustainable increases in production, external inputs of nutrients are necessary. These may be introduced by two different pathways, either via mineral fertilisers applied to croplands or via externally produced supplements fed to livestock. These pathways are complementary and each one has direct effects on the other. Fertiliser application to croplands affect livestock through the increase in available forage and crop residue feed, whereas feed supplementation affects crop production through higher amounts and better quality of manure. The adoption of either strategy by farmers requires a high nutrient use efficiency at low cost. Data from regional field trials revealed increases in total dry matter (TDM) of cereals with broadcast annual P application at 13 kg ha⁻¹ ranging across three years from 19 to 88% for rockphosphate and from 34 to 102% for single superphosphate (SSP). Still, a low-external input approach seemed more advantageous to farmers. The placement of NPK fertiliser at 4 kg P ha⁻¹ with the seed at or shortly after planting caused average TDM increases of 70% for millet, sorghum, maize, cowpea and groundnut and showed an up to three-fold higher phosphorus use efficiency than broadcast P. On the other hand, late dry season supplementation of grazing steers with millet bran not only decreased animal weight losses but also increased N and P concentrations in the faeces. The larger nutrient concentrations in the manure increased millet grain yield by 28% and stover yield by 21% on a field manured at a rate of 3 t DM ha⁻¹. However, even with such approaches the current trends of declining soil productivity can only be reversed, if local policy makers are willing to support agricultural change through better terms of trade for agricultural products.     

Perspectives on nutrient management in mixed farming systems

Abstract. Changes in agricultural subsidies in Europe and the ready availability of fertilizers have allowed a spatial decoupling of livestock and crop production. This has increased the flow of nutrients that occurs between farms compared to within individual farms. In terms of nutrient cycling, mixed farms provide the opportunity to re-integrate aspects of agricultural production. The degree of integration between crop and livestock production is defined by the reliance on the use of home-produced feed compared to imported feed, and is independent of intensity. Management of inputs and/or internal flows offers the scope to improve nutrient use efficiency (NUE) on mixed farms. Greatest uncertainties in calculating NUE are associated with variation in yield and composition of home-produced feed, and consequent manure composition. Three key areas are addressed to highlight the interchange of nutrients (and risks for losses) between crop and livestock production; (i) the role of livestock diet in manipulating the amount and availability of manure nutrients; (ii) the impact of manure management on nutrient losses; and (iii) nutrient management through the integration of crops and livestock in rotations. While not all the associated issues are unique to mixed farming, these three areas all influence NUE.     

Modelling of soil nutrient budgets: an assessment of agricultural sustainability in Nepal

Abstract. Sustaining soil fertility under agricultural intensification and expansion onto marginal lands is a significant challenge in the Nepalese Middle Mountains. In a detailed watershed study it was shown that the overall soil fertility is poor, forest soils display the poorest conditions as a result of biomass removal, and sustaining agriculture is questionable due to the transformation from traditional to multiple cropping systems. Parent material is a significant factor influencing low phosphorus status while insufficient inputs create deficiencies in total carbon, nitrogen and bases. A nutrient budget model was developed to assess inputs, redistribution and losses relative to soil fertility. Yield, input and management data obtained from farm interviews, and soil analysis data were used in the calculation of nutrient budgets. Results from modelling indicate declining soil fertility under rainfed agriculture, forest and rangelands, and marginal conditions under irrigated agriculture subject to intensive cultivation. Nutrient deficits were relatively low for irrigated rice-wheat systems, which benefit from nutrient inputs via sediments and irrigation waters, but the introduction of triple cropping showed greater deficits. Nutrient balances were most critical under rainfed maize production where 94% of the farms were in deficit. Current shortages of organic matter make elimination of nutrient deficits problematic but improvement of composting, biological N-fixation and fertilizer efficiency and reducing erosion were found to be potential options.     

The Role of Nutrient Efficient Plants in Improving Crop Yields in the Twenty First Century

In the 21st century, nutrient efficient plants will play a major role in increasing crop yields compared to the 20th century, mainly due to limited land and water resources available for crop production, higher cost of inorganic fertilizer inputs, declining trends in crop yields globally, and increasing environmental concerns. Furthermore, at least 60% of the world's arable lands have mineral deficiencies or elemental toxicity problems, and on such soils fertilizers and lime amendments are essential for achieving improved crop yields. Fertilizer inputs are increasing cost of production of farmers, and there is a major concern for environmental pollution due to excess fertilizer inputs. Higher demands for food and fiber by increasing world populations further enhance the importance of nutrient efficient cultivars that are also higher producers. Nutrient efficient plants are defined as those plants, which produce higher yields per unit of nutrient, applied or absorbed than other plants (standards) under similar agroecological conditions. During the last three decades, much research has been conducted to identify and/or breed nutrient efficient plant species or genotypes/cultivars within species and to further understand the mechanisms of nutrient efficiency in crop plants. However, success in releasing nutrient efficient cultivars has been limited. The main reasons for limited success are that the genetics of plant responses to nutrients and plant interactions with environmental variables are not well understood. Complexity of genes involved in nutrient use efficiency for macro and micronutrients and limited collaborative efforts between breeders, soil scientists, physiologists, and agronomists to evaluate nutrient efficiency issues on a holistic basis have hampered progress in this area. Hence, during the 21st century agricultural scientists have tremendous challenges, as well as opportunities, to develop nutrient efficient crop plants and to develop best management practices that increase the plant efficiency for utilization of applied fertilizers. During the 20th century, breeding for nutritional traits has been proposed as a strategy to improve the efficiency of fertilizer use or to obtain higher yields in low input agricultural systems. This strategy should continue to receive top priority during the 21st century for developing nutrient efficient crop genotypes. This paper over views the importance of nutrient efficient plants in increasing crop yields in modern agriculture. Further, definitions and available methods of calculating nutrient use efficiency, mechanisms for nutrient uptake and use efficiency, role of crops in nutrient use efficiency under biotic and abiotic stresses and breeding strategies to improve nutrient use efficiency in crop plants have been discussed.     

Definition of sustainable and unsustainable issues in nutrient management of modern agriculture

Abstract. Sustainable management of nutrients in agricultural systems is critical for sufficient production of nutritious foods and to minimize environmental pollution. In this overview, we discuss some of the most important factors influencing nutrient cycling, and how practices for sustainable nutrient management can be optimized. In most cases, problems are associated with excessive use of nutrients (manures, other organic amendments, and inorganic fertilizers). Options for dealing with such problems at the farm level include: reducing nutrient inputs to balance exports, increasing the land area on which manures are applied, and export of excess nutrients from the farm in the form of value-added products. These strategies can be used singly, or in combination. Nutrients in the human food chain are often not recycled back to primary crop production. To manage such issues, and avoid regional nutrient accumulations, we need to develop a better understanding of large-scale nutrient flows, and develop policies to manage them. We stress the importance of scale when considering nutrient management in the future.     

Nitrogen Pollution from Swedish Beef Production based on Suckle-Cows

Measures to improve N-use efficiency and thus reduce N-pollutionare scrutinized in beef production based on suckle-cows. Measures in feed production, animal feed conversion and the use of animal manure are included and their economic opportunities are analysed. The resultssuggest that production based on non-N-fertilized grassgives very low losses of NO₃, NH₃ and N₂Oper ha. Production based on pastures and leys given 100 kgN ha^-1 results in considerably higher losses, especially perha but also per kg of produced beef. Beef productionwithout input of mineral fertilizers might be profitablein regions abundant in land with low opportunity cost,especially if environmental support is provided. Clover-basedbeef production gives relatively high N losses bothper ha and per kg of beef. The reason is unnecessarilyhigh N-content in the clover, resulting in high N-level inexcreta and increased losses from manure and pastures. Achange from a deep straw bed manure system to slurryspread only in spring and immediately incorporated canreduce N-losses considerably but is unprofitable insuckle-cow-production. Beef production has lower N-lossesthan pork production per ha but higher per kg of produced meat.     

Greenhouse gas mitigation potential of agricultural land in Great Britain

The aim of this paper is to assess the greenhouse gas (GHG) mitigation potential of croplands and grasslands in Great Britain under different management practices. We consider the feasible land management options for grass and cropland using county level land‐use data with estimates of per‐area mitigation potential for individual and total GHGs, to identify the land management options with the greatest cost‐effective mitigation potential. We show that for grasslands, uncertainties still remain on the mitigation potential because of their climatic sensitivity and also their less intensive management. For croplands in Great Britain, the technical mean GHG mitigation potentials for all cropland management practices range from 17 Mt CO₂‐eq. per 20 yr to 39 Mt CO₂‐eq. per 20 yr. There are significant regional variation in all cases, with the greatest potentials in England, negligible potential in Wales and intermediate potential in Scotland, with country differences largely driven by the areas of cropland and grassland in each country. Practices such as agronomic improvement and nutrient management are the most promising options because of their impact on N₂O emissions and also their larger potential at low cost. In terms of annual emissions from agriculture, calculated mitigation potentials are small, where the technical mitigation potential of agronomy and nutrient management strategies are ca. 4.5 and 3.8%, respectively (agricultural emissions account for ca. 9% or 47.7 Mt CO₂‐eq., of total Great Britain GHG emissions, Department of Energy and Climate Change, UK). However when compared with the land use, land‐use change and forestry sector (LULUCF) emissions, nutrient management would reduce further emission reductions by approximately half of the 2005 LULUCF sink (i.e. ?1.6 Mt CO₂‐eq. per year).     

EFFECT OF SOIL BUNDS ON RUNOFF,SOIL AND NUTRIENT LOSSES,AND CROP YIELD IN THE CENTRAL HIGHLANDS OF ETHIOPIA

The effects of soil bunds on runoff, losses of soil and nutrients, and crop yield are rarely documented in the Central Highlands of Ethiopia. A field experiment was set up consisting of three treatments: (i) barley‐cultivated land protected with graded soil bunds (Sb); (ii) fallow land (F); and (iii) barley‐cultivated land without soil bund (Bc). For 3 years (2007–2009), the effect of soil bunds on runoff, losses of soil and nutrients, and crop productivity was studied. Daily runoff and soil and nutrient losses were measured for each treatment using standard procedures while barley yield was recorded from the cultivated plots. The results showed that Sb brought about significant reduction in runoff and soil losses. Plots with Sb reduced the average annual runoff by 28 per cent and the average annual soil loss by 47 per cent. Consequently, Sb reduced losses of soil nutrients and organic carbon. However, the absolute losses were still high. This implies the need for supplementing Sb with biological and agronomic land management measures to further control soil erosion. Despite these positive impacts on soil quality, Sb do not increase crop yield. Calculated on a per‐hectare basis, Sb even reduce crop yield by about 7 per cent as compared with control plots, which is entirely explained by the reduction of the cultivable area by 8·6 per cent due to the soil bunds. Suitable measures are needed to compensate the yield losses caused by the construction of soil bunds, which would convince farmers to construct these land management measures that have long‐term beneficial effects on erosion control. Copyright © 2012 John Wiley & Sons, Ltd.     

黄花草木樨改良盐碱土的试验研究

在调查陕北地区不同地域作物(谷子)、人工草灌(苜蓿与柠条)和天然草地(退耕地)的生产力,土壤水分及耕层养分的基础上,对比研究了不同类型植物生产力的差异,并分析了引起差异的原因及限制生产力提高的因素。结果表明,作物地(谷子)生产力占据明显优势,但稳定性较差;人工草灌(苜蓿与柠条)及天然草地的生产力较谷子低;天然草地群落的生产力、稳定性、物种丰度指数和土壤养分含量均较优越。指出除水分不足是限制不同植物生产力发挥的主要因素外,土壤养分含量低和缺乏管理也是限制植物生产力提高的重要因素。同时指出,为达到正确评价不同类型植物的生产力和长期适应性,为该地区大范围植被建设提供依据和参考,应设立定位或半定位研究点进行长期测定与研究。     

Nutrient impoverishment and limitation of productivity after 20 years of conservation management in wet grasslands of north-western Germany

European wet grasslands are characterized by high diversity of plant and animal species but are threatened by intensive land use. Although preservation or restoration of species-rich wet grasslands requires low nutrient availability that could be achieved by long-term management, studies monitoring nutrient removal are lacking. Our objective was to assess the long-term effect of management (mowing twice a year without or with PK fertilization for 20 years) on (i) productivity and nutrient removal with the harvest, (ii) the type of nutrient limitation, and (iii) plant species richness in wet grasslands in north-western Germany considering the differences between organic and mineral soils.Initially low nutrient availability in soil led to decreased productivity and base cation removal with harvest particularly on mineral soils after six years of mowing twice a year without fertilization. On mineral soils, N:K ratios indicated limitation of plant growth by K. On organic soils, neither productivity nor K removal with the harvest changed with time suggesting additional K input probably caused by rising groundwater. On organic soils, K:P ratios and a significant decrease of productivity with increasing N:P ratios suggested P limitation. Plant species richness was maintained or even slightly increased by mowing twice a year without fertilization but mainly comprised species that were already present at the study sites.Productivity and N, P, K, and Mg removal with the harvest was significantly increased by mowing twice a year with PK fertilization while species richness was maintained. After 10 years, N:K ratios indicate K limitation even for mowing twice a year with PK fertilization. In case of initially low nutrient availability in soil, cautious PK fertilization and mowing can be recommended to meet demands of agriculture and nature conservation.     

Nutrient dynamics—wind and water erosion at the village scale in the Sahel

The loss of nutrients by wind erosion is generally attributed to losses by suspension, since suspension selectively removes the finest particles. However, because the main mass of sediment is moved by saltation during an event, the main mass of nutrients is also moved by saltation. Nutrient losses from one field during one wind erosion event can be as high as 73 per cent of the N and 100 per cent of the P needs for crop production. Vegetated areas have a higher dust deposition because of the filtering effect of the vegetation and the reduction of drag forces causing a higher deposition. This refutes the general assumption that deposition of suspended dust is homogeneous for a larger area. In the Sahel, two types of dust can be distinguished, the Harmattan dust is richer in nutrients and regarded as a real input of nutrients. The convectional storm dust has a nutrient content comparable with the nutrient content of the dust fraction of the topsoil and can't be regarded as input of nutrients. From research on nutrient losses by water erosion at the plot scale, it is concluded that nutrient erosion by water can cause serious losses of nutrients. But at the village scale, the losses are considerably smaller than at the plot scale. Measurement and subsequent nutrient budget analyses around the village Dangadé in Burkina Faso indicated that this area is especially vulnerable for wind erosion by saltation transport. This demonstrates that in the Sahelian environment, the effect of wind erosion at the village scale can't be ignored. Copyright © 2007 John Wiley & Sons, Ltd.     

Mitigation options for diffuse phosphorus loss to water

Abstract. Agriculture contributes significant loads of P to surface waters. The reductions in these diffuse P inputs necessary to help prevent eutrophication problems and/or assist in the restoration of water quality will require controls over both nutrient inputs and their subsequent transport in land runoff. Specific mitigation options include nutrient budgeting, input management, soil conservation, land use management and the establishment of riparian, and other buffer zones. The variable nature of diffuse P loss suggests that the best approach to control is through integrated management at a range of scales. Critical control concepts at the farm level include targeting source areas adequately, maintaining P input loading rates within recommended limits and avoiding high-risk management actions. Since eutrophication is a natural phenomenon and with potential conflicts with the need to meet production targets and/or minimize loss of other nutrients (N), some assessment of acceptable levels of P loss, of cost effectiveness of options and some prioritization of goals are necessary to find optimal solutions. As the requirements of individual waterbodies differ, these solutions need to be site specific and their successful adoption requires an appreciation by farmers of the importance of minimizing agricultural P loss both as individuals and collectively within a catchment.     

NUTRIENT UPTAKE AND USE EFFICIENCY BY TROPICAL LEGUME COVER CROPS AT VARYING PH OF AN OXISOL

Oxisols comprise large soil group in tropical America. These soils are acidic and have low fertility. Use of tropical legume cover crops in cropping systems is an important strategy to improve fertility of these soils for sustainable crop production. Data are limited on nutrient uptake and use efficiency of tropical cover crops under different acidity levels. The objective of our study was to evaluate growth and nutrient uptake parameters of sixteen tropical legume cover crops under three soil pH (5.1, 6.5, and 7.0) of an Oxisol. Shoot dry weight was influenced significantly by pH and cover crop treatments and their interactions, indicating that cover crops used had differential responses to changing soil pH levels. Overall, shoot dry weight decreased when soil pH was raised from 5.1 to 7.0, indicating acidity tolerance of cover crops. Nutrient concentration (content per unit of dry weight), uptake (concentration X dry weight), and nutrient use efficiency (dry weight of shoot per unit of nutrient uptake) varied significantly among cover crops. The variation in nutrient uptake and use efficiency among cover crop species was associated with variation in shoot dry matter production. Significant variation among crop species in dry matter production and low C/N ratios (average value of 14.25) suggest that cover crops which produced higher dry matter yield like white jack bean, gray mucuna bean, black mucuna bean, mucuna bean ana, and lablab are important choices for planting in tropical soils to recover large amount of macro and micronutrients, and to prevent such nutrient leaching in soil plant systems.     

Grazing as a management tool in dune grasslands: Evidence of soil and scale dependence of the effect of large herbivores on plant diversity

In nature management, the introduction of large herbivores into human-influenced grasslands is thought to be effective to maintain or enhance plant diversity. In order to test the validity of this assumption, we studied the effect of grazing by large herbivores on plant species richness and community heterogeneity across a soil acidity gradient at different spatial scales in dry coastal dune grasslands in western Belgium and north-western France. The effect of grazing on plant richness varied with scale and soil acidity. Grazing had a predominantly positive effect on plant species richness in all habitats at the small scale (0.25 × 0.25 m). However, at site scale (8 × 8 m) it had only positive effects in grasslands with higher soil pH (6-7.4). Similarly, grazing resulted in a homogenization of grassland vegetation at lower pH, while heterogeneity increased with grazing on soil with higher pH. In general, grazing increased the number of rare species, independent of soil pH. The results confirm that the impact of grazing on plant diversity depends on the scale considered and that the effects further depend on soil acidity which was correlated to biomass production at the given soil pH range in this study. Although grazing seems an appropriate management tool to maintain and even enhance plant biodiversity under many circumstances, it may negatively affect plant species richness, where soil resources limit plant biomass production.