nutrient cycle

While non-point nutrient loads are important determinants of biological productivity in Southeastern Piedmont impoundments, productivity can be attenuated by concomitant sediment loads that reduce the biological availability of these nutrients. A biogeochemical model is proposed ...

African animal trypanosomiasis constrains agricultural production in areas of Africa that hold the continent’s greatest potential for expanded agricultural production. Compared to animals kept in trypanosomiasis free areas, animals kept in areas of moderate risk of trypanosomiasis have lower calving rates, lower milk yields, higher rates of calf mortality, and require more frequent treatment with preventive and curative doses of trypanocidal drugs. At the herd level, trypanosomiasis reduces milk offtake, live animal offtake and the work efficiency of oxen used for cultivation. Herds of trypanosusceptible livestock can be devastated by sudden exposure to high levels of trypanosomiasis risk. Trypanosomiasis also affects where people live, the way they manage their livestock and the number of animals that they keep. In the tsetse-infested areas as a whole, trypanosomiasis reduces the offtake of meat and milk by at least 50%. And by generally constraining farmers from the overall benefi...

The amounts and proportions of dry matter and macronutrients were measured in overstory trembling aspen (by tissue), understory vegetation, woody detritus, the forest floor, and the mineral soil in duplicate stands of 8, 14, 18, and 32 years and in a single stand of 63 years on an Entic Haplorthod in northern Wisconsin. The following changes occurred during secondary succession: (i) above- and below-ground aspen biomass increased, (ii) aboveground aspen production peaked between the ages of 18 and 32 years, (iii) the root to shoot ratio (R/S) of overstory aspen declined, (iv) the amounts and ecosystem proportions of macronutrients (N, P, K, Ca, and Mg) in the aspen overstory increased, and (v) the ecosystem proportions of nutrients in the understory declined. As the relative abundance of nutrients in overstory aspen increased, the labile nutrient pool in the mineral soil, particularly Mg and Ca, declined. The study suggests that understory roots play an important role in nutrient re...

East and Southern Africa have soils that are still relatively fertile, notably those in the Highlands, associated with the Rift valley area. The lower areas are less well-endowed when it comes to soil fertility. At low agricultural intensity, this does not matter as nutrients cycle ...

For several decades, a diverse literature has claimed that urban agriculture has the potential for hunger and poverty alleviation. This article reviews empirical data from equatorial Africa that touch on this assertion, updating the work on the subject published in the mid-...

Abstract: The term “stability ” has many different meanings and its interpretation and application in various sciences is not absolutely identical. Historically, stability has been first formally defined in mathematical form by Lyapunov to describe equilibrium behaviour of the solar system. Lyapunov stability considers the behaviour of a system solution if its initial state is in the neighbourhood of an equilibrium point. Conceptually, it states that the equilibrium point is stable if all solutions originating in its neighbourhood forever remain “close enough ” to equilibrium. Due to its precise definition and well-established mathematical technique, Lyapunov stability has found a widespread application outside its original context, particularly to analyse solutions of mathematical models of biological communities in order to determine conditions they must satisfy to be stable. Research of this kind has been a dominating trend and, in words of Justus (2006), set much of the agenda o...

The mixed prairie represents the most arid region of the Northern Great Plains in Canada. Approximately 6.5 M ha of the original total of 24 M ha have retained their native character. The native prairie supports about 5.3 M animal–unit–months or about 15% of all beef cattle present on the Canadian prairies. A large portion of the area is dominated by either needle-and-thread (Stipa comata Trin. + Rupr.) or western wheatgrass (Agropyron smithii Rydb.), both cool season grasses, and associated with blue grama [Bouteloua gracilis (H.B.K.) Lag. ex Steud.] a warm season grass. These species define the major plant communities of the mixed prairie and determine their production potential. However, their production is limited by available water during the growing season and by soil nutrients; factors which also influence their species composition. Grazing imposes a significant impact on the grasslands by altering the water and nutrient cycles, through defoliation and reduced plant litter, a...

Lake Superior, one of the largest lakes in the world, is an ecosystem where nitrate (NO3 −) concentration has risen almost fivefold in the last century. Recent studies suggest that this increase may be due to lack of a significant nitrogen (N) sink, such as sedimentary denitrification or burial, because of low organic matter supply to the lake bottom. In

Ecosystem services are benefits that humanity obtains from ecosystems. These are conditions and ecological processes through which ecosystems and the species within them sustain life. Through processes that regulate and support primary ecosystem functions, such as soil formation, oxygen production, water and nutrient cycling, pollination and regulation of pests, diseases, erosion and climate, humans derive an important service and that is to produce goods, such as food, fresh water, fuel and genetic resources. In addition there are also cultural services that are essential to human well being, such as spiritual attachments, diversity of cultures, aesthetic and inspirational values and recreation. Biodiversity can be both, a response affected by ecosystem changes as well as a factor that modifies ecosystem processes and services. Biodiversity represents the foundation of ecosystems that, through the services they provide, affect human well-being. It reflects the number, variety and v...

The industrialization of agriculture and the concurrent increase in societal concerns on environmental protection and food quality have put the focus on agricultural management and its impact on soil quality. Soil quality involves the ability of the soil to maintain an appropriate productivity, while simultaneously reducing the effect on the environment and contributing to human health. This development has changed society's expectations of science and there is an urgent need to improve the communication among researchers from different scientific disciplines. The interaction of scientists with decision makers is a topic of utmost relevance for future developments in agriculture. Reflexive objectivity denotes the exercise of raising one's consciousness of the cognitive context, i.e. societal priorities, and the values and goals of the researcher. The term sustainability comprehends the priorities in the cognitive context and thus constitutes a valuable tool for expressing th...