While many laboratory studies have focused on the short term effects of biochar addition to soil), there have been comparatively few tracing its longer term effects in the field. This study investigated the multiyear impact of biochar on crop performance and soil quality with specific emphasis on carbon (C) and nitrogen (N) cycling over a 3 y period. Biochar was added to an agricultural field at 0, 25 and 50 t ha(-1) and planted with maize (year 1) and grass (years 2 and 3). Biochar addition affected plant performance in the grass crop with significant increases in foliar N (year 2) and above-ground biomass (year 3). Below-ground, biochar increased soil respiration, fungal and bacterial growth rate and turnover in year 2. This change coincided with a shift toward a bacterial dominated decomposer community, suggesting a decrease in the potential for microbially mediated C sequestration. Biochar did not affect dissolved organic C (DOC) and N (DON), NO3- or NH4+ pool sizes. Similarly, biochar addition had limited effects on the turnover of C-14-labelled SOC (plant litter), DOC (sugars and organic acids) and DON (amino acids) and no long term effect on N mineralization, NH3 volatilization, denitrification and NH4+ sorption. After 3 years in the field, the alkalinity associated with the biochar had been fully neutralized and biochar lost most of its cations (K, Na, Ca) but had built up an associated microbial community. We conclude that biochar addition to soil causes small and potentially transient changes in a temperate agroecosystem functioning. Importantly, many of the short-term effects of biochar on plant growth and soil behavior reported from laboratory studies were not observed in the field emphasizing the need for long term field trials to help inform agronomic management decisions involving biochar. (C) 2011 Elsevier Ltd. All rights reserved. (Less)

Biochar-mediated changes in soil quality and plant growth in a three year field trial

Land degradation in the drylands, also called desertification, has affected the world for centuries, even millennia, in Africa, Asia, and Mediterranean Europe, for one or two centuries in the Americas, and 100 years or less in Australia. Among the principal degradation processes are vegetation degradation in rangelands, water and wind erosion, salinization of irrigated and certain semiarid lands, and soil compaction. Farmers, ranchers, and researchers, in general, are aware, from their personal experiences, of the environmental changes land degradation has brought. Unfortunately, there are little good research data on just how much damage has been done. Much of the evidence is from what can be seen, such as gullies, mobile sand dunes, and buried cities, as well as undocumented anecdotes of ancient and modern travelers. Given the uncertain data base, it is no wonder that there are radically different beliefs of the severity and the damage cost of land degradation in the drylands. This review attempts to an...

Land Degradation in the Drylands

Leadley, P., Pereira, HM., Alkemade, R., Fernandez-Manjarres, JF., Proenca, V, Scharlemann, JPW and Walpole, MJ. 2010. Biodiversity Scenarios: Projections of 21st century change in biodiversity and associated ecosystem services. Secretariat of the Convention on Biological Diversity, Montreal. Technical Series no. 50, 132 pages.

Biodiversity Scenarios: Projections of 21st century change in biodiversity and associated ecosystem services

Nutrient depletion in soils adversely affects soil quality and reduces crop yield and consequently poses a potential threat to global food security and agricultural sustainability. With an emphasis on human-induced nutrient depletion, this paper described the causality among soil nutrient depletion, soil quality, crop production, socio-economic variables, and environmental condition. Then, global soil nutrient budgets of nitrogen (N), phosphorus (P), and potassium (K) were estimated for wheat (Triticum aestivum L.), rice (Oryza sativa), maize (Zea mays L.), and barley (Hordeum vulgare) production for the year 2000. As a result, there were unbalanced fertilization with surplus N in some developing countries and insufficient inputs in many developing and all least developed countries. Globally, soil nutrient deficits were estimated at an average rate (kg ha−1 yr−1) of 18.7 N, 5.1 P, and 38.8 K, covering 59%, 85%, and 90% of harvested area in the year 2000, respectively, and annual total nutrient de...

Global Soil Nutrient Depletion and Yield Reduction

Review: Food loss and waste in Sub-Saharan Africa

Extent, severity and causative factors of land degradation in the Sudan

This paper examines the status of land resources in the Sudan after over half a century of unsustainable use. Several studies indicate that about 120 million ha of land, including 64 million ha of soils, are degraded to varying degrees. A remarkably high correlation seems to exist between human population densities and degraded soil in different aridity zones. The most degraded zones were the arid and semi-arid zones where 76% of the human population of the Sudan live. Wind erosion was the most widespread soil degradation type in the arid zone, while water erosion was dominant in the semi-arid zone. Chemical deterioration through nutrient loss was affecting all climatic zones. The central clay plains and the ironstone soils of south-west were the least degraded soil types. Overgrazing is the most widespread cause of soil degradation, particularly around permanent settlements and watering centres, affecting about 30M ha (47%) of the total degraded areas. Clearance of forests and woodlands cover for firewood and charcoal making and overexploitation of vegetation is the second cause of soil degradation affecting 22M ha. Cropping without appropriate nutrient inputs have degraded about 12M ha, particularly in small-scale farming on sandy and loamy soils. When these processes of resource mismanagement coincided with the recent recurrent droughts, collapse of the economic base of fragile areas took place.

Senna plants, native to the arid parts of the northern Sudan, were studied for mineral cation contents and salt tolerance. Plants tended to accumulate salts in tops, particularly when growing in saline soils. Highest concentrations of salts were in the leaves with a gradient from bottom to top leaves. Unde r high salinity and soil moisture stress in the field, plant growth was reduced without injury symptoms, but with shedding of some lower leaves. Lower leaf shedding could, therefore, be a physiological measure for reducing plant salt level and transpiration. Studies on the germination of senna seeds under controlled conditions indicated that they were highly tolerant of salinities up to 16.0 nimhos cm-1, and 50% reduction in germination occurred at about 20.0 mmhos cm-1. Air temperature significantly effected senna germination at substrate salinities between 10.0 and 25.0 mmhos cm-1. Studies in open air indicated that plants were more sensitive to salinity and alkalinity at seedling stage than t germination. Young plant survival and total pod yield were significantly reduced in soil salinities higher than 11.0 mmhos cm-1, being more pronounced at shorter than at longer irrigation intervals with saline waters.

Some features of salt tolerance in Senna (Cassia acutifolia), in Sudan

Soil fertility decline is occurring over large parts of the world, particularly the developing world. It occurs mainly through intensive cultivation and the inadequate application of replacement nutrients, and through deforestation and clearance of vegetation on sandy soils. Large amounts of soil nutrients are also lost to the terrestrial ecosystems through wind and water erosion. Low soil fertility is considered as one of the most important constraints on improved agricultural production. To sustain the future world population more fertilizers are required, which may become an environmental hazard, unless adequate technical and socio-economic measures are taken. It is estimated that, by the year 2020 at a global level, 70% of plant nutrients will have to come from fertilizers. Fertilizers are thus indispensable for sustained food production, but excessive use of mineral fertilizers has roused environmental concerns. Chief among these concerns are eutrophication of fresh water bodies, global warming and stratospheric ozone depletion, proliferation of algal blooms in coastal waters and contribution towards acid rain.

Fertilizers and the environment

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Extent, severity and causative factors of land degradation in the Sudan

Extent, severity and causative factors of land degradation in the Sudan

Some features of salt tolerance in Senna (Cassia acutifolia), in Sudan

Fertilizers and the environment