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

Keywords: Mecanique des sols ; Drainage ; Ecoulement souterrain Reference Record created on 2004-09-07, modified on 2016-08-08

Applications of soil physics.

Sodic soils are characterized by the occurrence of excess sodium (Na+) to levels that can adversely affect soil structure and disturb availability of some nutrients to plants. Such changes ultimately affect crop growth and yield. There are large areas of the world that exist under sodic soils and need attention for efficient, inexpensive and environmentally feasible amelioration. Sodic soil amelioration involves increase in calcium (Ca2+) on the cation exchange sites at the expense of Na+. The replaced Na+ together with excess soluble salts, if present, is removed from the root zone through infiltrating water as a result of excessive irrigations. Records nearly a century old reveal the use of water, crop, chemical amendment, electric current, and tillage as amelioration tools for such soils. Among the amelioration strategies, chemical amendments have an extensive usage. Owing to gradual increases in amendment cost in some parts of the world during the last two decades, this amelioration strategy has become cost-intensive, particularly for the subsistence farmers in developing countries. In the meantime, phytoremediation with low initial investment has emerged as a potential substitute of chemical amelioration. Phytoremediation works through plant root action that helps dissolve native soil calcite (CaCO3) of low solubility to supply adequate levels of Ca2+ for an effective Na+−Ca2+ exchange without the application of an amendment. Although significant progress has been achieved in improving amelioration methods, a great deal of work remains to analyse the economics of such methods with focus on (1) the long-term sustainability of the amelioration projects and (2) the consequences of amelioration for the farmer himself, other growers and society as a whole. Computer modelling may help assess economic viability of different soil amelioration methods to extend results broadly to other similar locations. In addition, computer modelling to stimulate movement and reactions of salts in sodic soils has been a potentially useful complement to experimental data. However, such models need evaluation under field conditions. Copyright © 2001 John Wiley & Sons, Ltd.

Amelioration strategies for saline soils: a review

Environmental impacts of phosphogypsum

Impact of fly ash incorporation in soil systems.

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.

W. P. Miller

Papers

Use of Gypsum on Soils: A Review

Agricultural and industrial uses of by-product gypsums.