Cellular Mechanisms of Aluminum Toxicity and Resistance in Plants

The effects of lime, fertilizer and manure applications on soil organic matter status and soil physical properties are of importance to agricultural sustainability. Their effects are complex and many interactions can occur. In the short-term, liming can result in dispersion of clay colloids and formation of surface crusts. As pH is increased the surface negative charge on clay colloids increases and repulsive forces between particles dominate. However, at higher lime rates, Ca2+ concentrations and ionic strength in soil solution increase causing compression of the electrical double layer and renewed flocculation. When present in sufficient quantities, both lime and hydroxy-Al polymers formed by precipitation of exchangeable Al, can act as cementing agents bonding soil particles together and improving soil structure. Liming often causes a temporary flush of soil microbial activity but the effect of this on soil aggregation is unclear. It is suggested that, in the long-term, liming will increase crop yields, organic matter returns, soil organic matter content and thus soil aggregation. There is a need to study these relationships on existing long-term liming trials. Fertilizers are applied to soils in order to maintain or improve crop yields. In the long-term, increased crop yields and organic matter returns with regular fertilizer applications result in a higher soil organic matter content and biological activity being attained than where no fertilizers are applied. As a result, long-term fertilizer applications have been reported, in a number of cases, to cause increases in water stable aggregation, porosity, infiltration capacity and hydraulic conductivity and decreases in bulk density. Fertilizer additions can also have physico-chemical effects which influence soil aggregation. Phosphatic fertilizers and phosphoric acid can favour aggregation by the formation of Al or Ca phosphate binding agents whilst where fertilizer NH4
+ accumulates in the soil at high concentrations, dispersion of clay colloids can be favoured. Additions of organic manures result in increased soil organic matter content. Many reports have shown that this results in increased water holding capacity, porosity, infiltration capacity, hydraulic conductivity and water stable aggregation and decreased bulk density and surface crusting. Problems associated with large applications of manure include dispersion caused by accumulated K+, Na+ and NH4
+ in the soil and production of water-repellant substances by decomposer fungi.

Influence of lime, fertilizer and manure applications on soil organic matter content and soil physical conditions: A review

Soil aggregate stability is a crucial soil property affecting soil sustainability and crop production A broad outline of the processes and agents of aggregate formation and aggregate stabilization are presented and discussed in this review Aggregate stability is difficult to quantify and interpret The aim of aggregate stability tests is to give a reliable description and ranking of the behavior of soils under the effect of water, wind and management Numerous methods have been used to determine aggregate stability with varying success The different methodologies complicate the comparison among aggregate stability data It is also difficult to obtain a consistent correlation between aggregate stability and other important soil properties such as soil erodibility or crusting potential This paper reviews the different methods of measurement of soil aggregate stability used in the literature, paying attention to the conditions of sample collection in the field and sample preparation and treatmen

Soil aggregate stability: a review

Experiments suggest that biodiversity enhances the ability of ecosystems to maintain multiple functions, such as carbon storage, productivity, and the buildup of nutrient pools (multifunctionality). However, the relationship between biodiversity and multifunctionality has never been assessed globally in natural ecosystems. We report here on a global empirical study relating plant species richness and abiotic factors to multifunctionality in drylands, which collectively cover 41% of Earth’s land surface and support over 38% of the human population. Multifunctionality was positively and significantly related to species richness. The best-fitting models accounted for over 55% of the variation in multifunctionality and always included species richness as a predictor variable. Our results suggest that the preservation of plant biodiversity is crucial to buffer negative effects of climate change and desertification in drylands.

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Plant Species Richness and Ecosystem Multifunctionality in Global Drylands

Invariably, many agricultural soils of the world are deficient in one or more of the essential nutrients needed to support healthy plants. Acidity, alkalinity, salinity, anthropogenic processes, nature of farming, and erosion can lead to soil degradation. Additions of fertilizers and/or amendments are essential for a proper nutrient supply and maximum yields. Estimates of overall efficiency of applied fertilizer have been reported to be about or lower than 50% for N, less than 10% for P, and about 40% for K. Plants that are efficient in absorption and utilization of nutrients greatly enhance the efficiency of applied fertilizers, reducing cost of inputs, and preventing losses of nutrients to ecosystems. Inter- and intra-specific variation for plant growth and mineral nutrient use efficiency(NUE) are known to be under genetic and physiological control and are modified by plant interactions with environmental variables. There is need for breeding programs to focus on developing cultivars with high NUE. Iden...

https://www.irrec.ifas.ufl.edu/IRSWS/History%20Publications/2/CSSPABaligar2001.pdf

Nutrient use efficiency in plants

Gypsum is a relatively common mineral that is widely available in agricultural areas and has a number of specialized agronomic uses, principally as a Ca source on legumes and as a soil conditioner on sodic soils. Recent research has suggest that the utility of gypsum may extend to a greater range of soils and crops than previously acknowledged. The purpose of this review is to document both current practices and potential new uses of gypsum in agriculture, in order to establish the state of the art in current gypsum use, and to point out needed research in this important area.

Use of Gypsum on Soils: A Review

Soil conservation in South Africa has historically focussed on preventing soil erosion Effective maintenance of the soil resource requires, in addition to erosion control, an understanding of how land use practices affect more subtle indicators of soil quality This review outlines how land use in South Africa can rapidly result in a marked reduction in soil organic matter (SOM) content and a greater tendency of soils to crust Removal of a cover of vegetation whether by ploughing, grazing or burning tends to reduce SOM due to reduced organic matter inputs and enhanced soil microbe activity Loss of SOM, particularly from the top few centimetres of soil (named here the pedoderm) has a disproportionately large effect on soil infiltrability and nutrient supply The mineralogy of the clay fraction also has great bearing on the response of soil to land use effects The unexpected role of quartz in soil dispersion and crusting in South Africa has only recently been unveiled Apart from SOM effects, land use c

Declining soil quality in South Africa: effects of land use on soil organic matter and surface crusting

Frequent fires intensify soil crusting: physicochemical feedback in the pedoderm of long-term burn experiments in South Africa.

Soils of South Africa is the first book in seventy years that provides a comprehensive account of South African soils. The book arranges more than seventy soil forms into fourteen groups and then provides, for each group:maps showing their distribution and abundance throughout South Africadescriptions of morphological, chemical and physical propertiesa detailed account of classification and its correlation with international systemsa discussion of soil genesis which includes a review of relevant research papersappraisal of soil quality from a land use perspective as well as for its ecological significanceillustrative examples of soil profiles with analytical data and accompanying interpretations.There is also a fascinating account of the special relationship that exists between South African animals and soil environments. Soils of South Africa should interest students and researchers in the earth, environmental and biological sciences, as well as environmental practitioners, farmers, foresters and civil engineers.

/pdf/soils-of-south-africa-45h5xfrm26.pdf

Soils of South Africa

Al-substituted goethites were prepared by rapid oxidation of mixed FeCl2-AlCl3 solutions at pH 6.8 in the presence of CO2 at 25°C. A combination of Al substitution and adsorption of CO2 reduced crystal size (except for an increase at small additions of Al) and produced unusual thin, porous particles. Product goethites had surface areas up to 283 m2/g and unit-cell expansions induced by hydration. Substitution of Al for Fe reduced the 111 spacing and increased infrared OH-bending vibrational frequencies. Al substitution split the goethite dehydroxylation endotherm during differential thermal analysis into a doublet and increased the temperature of all reactions. Both cold and hot alkali solutions dissolved Al from the goethite structure. After drying the product in vacuo at 110°C. X-ray powder diffraction data indicated minimal deviation from Vegard’s law for the goethite-diaspore solid solution up to about 30 mole % Al substitution. Goethite prepared in the presence of 40 mole % Al had a 111 spacing of 2.403 A corresponding to 36 mole % structural Al if Vegard’s law was obeyed. Rapid oxidation of mixed FeCl2-AlCl3 solutions appears to be conducive to a higher degree of Al substitution in goethite than alkaline aging of hydroxy-Fe(III)-Al coprecipitates.

Martin Fey

Papers

Use of Gypsum on Soils: A Review

Declining soil quality in South Africa: effects of land use on soil organic matter and surface crusting

Frequent fires intensify soil crusting: physicochemical feedback in the pedoderm of long-term burn experiments in South Africa.

Soils of South Africa

Synthesis and Properties of Poorly Crystalline Hydrated Aluminous Goethites