Soil Chemical Analysis

Positive ions that are available in soils absorb on grain surfaces. The total sum of cations that can be absorbed bij a soil/sediment at a certain PH is defined by the cation-exchange capacity (CEC, in meq g-1: mol equivalents per gram). The uptake of cations is an important parameter in agriculture and the larger the CEC, the more cations can be absorbed to the soil. The CEC depends highly on the pH of soil and sediments, where the CEC decreases with decreasing PH (increasing acidity). The exchange of ions on sediments occurs commonly fast on geological time scales, but the kinetics of adsorption in natural environments is still poorly understood. The strength of the bonding between the cations and the sediments varies from weak Van der Waals bondings (physical adsorption) to strong chemical bonds. The CEC is widely used for agricultural assessment because it is a measure of general soil fertility as well as an indicator of structural stability because CED is capabel of enhancing development of shrinkage cracks. The list below shows the CEC for different types of minerals. The data indicate that the CEC can vary over 2 orders of magnitude for various types of , minerals and can vary one order of magnitude within one soil type. Cation exchange capacity for different types of sediment (Eisma, 1992; Locher and de Bakker, 1990):

Cation exchange capacity.

Sodicity-induced soil degradation is a major environmental constraint with
severe negative impacts on agricultural productivity and sustainability in arid
and semiarid regions. As an important category of salt-affected soils, sodic soils
are characterized by excess levels of sodium ions (Naþ) in the soil solution
phase as well as on the cation exchange complex, exhibiting unique structural
problems as a result of certain physical processes (slaking, swelling, and
dispersion of clay) and specific conditions (surface crusting and hardsetting).
Saline-sodic soils, another category of salt-affected soils, are generally grouped
with sodic soils because of several common properties and management
approaches. Sodic and saline-sodic soils occur within the boundaries of at
least 75 countries, and their extent has increased steadily in several major
irrigation schemes throughout the world. The use of these soils for crop
production is on the increase as they are a valuable resource that cannot be neglected, especially in areas where significant investments have already been
made in irrigation infrastructure. It is imperative to find ways to improve sodic
and saline-sodic soils to ensure that they are able to support highly productive
land-use systems to meet the challenges of global food security.

/pdf/phytoremediation-of-sodic-and-saline-sodic-soils-3k3e40blaf.pdf

Phytoremediation of Sodic and Saline‐Sodic Soils

Soil degradation in India is estimated to be occurring on 147 million hectares (Mha) of land, including 94 Mha from water erosion, 16 Mha from acidification, 14 Mha from flooding, 9 Mha from wind erosion, 6 Mha from salinity, and 7 Mha from a combination of factors. This is extremely serious because India supports 18% of the world’s human population and 15% of the world’s livestock population, but has only 2.4% of the world’s land area. Despite its low proportional land area, India ranks second worldwide in farm output. Agriculture, forestry, and fisheries account for 17% of the gross domestic product and employs about 50% of the total workforce of the country. Causes of soil degradation are both natural and human-induced. Natural causes include earthquakes, tsunamis, droughts, avalanches, landslides, volcanic eruptions, floods, tornadoes, and wildfires. Human-induced soil degradation results from land clearing and deforestation, inappropriate agricultural practices, improper management of industrial effluents and wastes, over-grazing, careless management of forests, surface mining, urban sprawl, and commercial/industrial development. Inappropriate agricultural practices include excessive tillage and use of heavy machinery, excessive and unbalanced use of inorganic fertilizers, poor irrigation and water management techniques, pesticide overuse, inadequate crop residue and/or organic carbon inputs, and poor crop cycle planning. Some underlying social causes of soil degradation in India are land shortage, decline in per capita land availability, economic pressure on land, land tenancy, poverty, and population increase. In this review of land degradation in India, we summarize (1) the main causes of soil degradation in different agro-climatic regions; (2) research results documenting both soil degradation and soil health improvement in various agricultural systems; and (3) potential solutions to improve soil health in different regions using a variety of conservation agricultural approaches.

/pdf/soil-degradation-in-india-challenges-and-potential-solutions-mp765nht8k.pdf

Soil Degradation in India: Challenges and Potential Solutions

Soil salinity (high levels of water-soluble salt) and sodicity (high levels of exchangeable sodium), called collectively salt-affected soils, affect approximately 932 million ha of land globally. Saline and sodic landscapes are subjected to modified hydrologic processes which can impact upon soil chemistry, carbon and nutrient cycling, and organic matter decomposition. The soil organic carbon (SOC) pool is the largest terrestrial carbon pool, with the level of SOC an important measure of a soil's health. Because the SOC pool is dependent on inputs from vegetation, the effects of salinity and sodicity on plant health adversely impacts upon SOC stocks in salt-affected areas, generally leading to less SOC. Saline and sodic soils are subjected to a number of opposing processes which affect the soil microbial biomass and microbial activity, changing CO fluxes and the nature and delivery of nutrients to vegetation. Sodic soils compound SOC loss by increasing dispersion of aggregates, which increases SOC mineralisation, and increasing bulk density which restricts access to substrate for mineralisation. Saline conditions can increase the decomposability of soil organic matter but also restrict access to substrates due to flocculation of aggregates as a result of high concentrations of soluble salts. Saline and sodic soils usually contain carbonates, which complicates the carbon (C) dynamics. This paper reviews soil processes that commonly occur in saline and sodic soils, and their effect on C stocks and fluxes to identify the key issues involved in the decomposition of soil organic matter and soil aggregation processes which need to be addressed to fully understand C dynamics in salt-affected soils. © 2009 The Authors. Journal compilation

Soil carbon dynamics in saline and sodic soils: a review.

The study was carried out in sodic lands of Sultanpur District, Uttar Pradesh, India. The barren soils and the soils supporting 3-, 6- and 9-year-old plantations of Prosopis juliflora (Swartz) D.C. and Dalbergia sissoo Roxb. Ex. D.C. plantations were examined to assess the rate and extent of changes undergone by physical and chemical properties of the soil. The study brought out that these species indicated the process of soil rehabilitation from the early stages of growth and the extent of rehabilitation increased with the age of the plantation. P. juliflora was found to be more efficient in reclaiming the soil in comparison to D. sissoo. The decline in soil pH and exchangeable sodium percentage (ESP) indicates the desodification and enrichment with organic C, N, P and K indicates improvement in nutrient status of the soil. After 9 years of planting the surface soil was completely desodified as indicated by pH (<8ċ5), ESP (<15) and sodium adsorption ration (<15). A significant increase in organic C, exchangeable Ca2+ and Mg2+ and decrease in exchangeable Na+ reveals that the nutrient status is attaining suitable balance. The physical attributes of the soil also underwent improvement in terms of increase in porosity, water-holding capacity, field capacity and decline in bulk density. The flocculation of dispersed soil surface and improvement in soil structure was indicated by increased infiltration rate (cm h−1) and soil permeability (cm2). Copyright © 2003 John Wiley & Sons, Ltd.

Leguminous trees for the restoration of degraded sodic wasteland in eastern Uttar Pradesh, India

The ameliorative effect of Dalbergia sissoo, planted on sodic land at Sultanpur (26° 10′–26° 40′N, 81° 45′–82° 30′E), India, in a tropical environment, was studied at 3, 6 and 9 years of age. The soil properties of the sites improved significantly, showing marked reduction in pH, electrical conductivity (EC) and exchangeable sodium percentage (ESP) and an increase in organic carbon, nitrogen and availability of nutrients in the soil. The significant reduction in Na ion was found in all the age groups. Results showed an improvement in the soil moisture regime due to increased infiltration rate (cm hr−1), soil permeability (cm2), water-holding capacity, field capacity and pore space whereas, the bulk density decreased significantly after successive years of planting. The effect on soil attributes was confined to surface soil in the young plantation and deeper in older plantation. Therefore, the study clearly indicated that the sodic soil could be desodified by growing D. sissoo plantations on these degraded sites. Copyright © 2002 John Wiley & Sons, Ltd.

Rehabilitation of degraded sodic lands during a decade of Dalbergia sissoo plantation in Sultanpur District of Uttar Pradesh, India

A study was carried out to compare the impact of 6-year-old plantations of Prosopis juliflora (Swartz) D.C., Dalbergia sissoo Roxb. Ex. D.C. and Eucalyptus tereticornis Sm. on the physical and chemical properties of sodic soil in the Indo-Gangetic alluvial plains of Uttar Pradesh, India. Soil properties under the three tree species showed significant improvement through a reduction in the pH, electrical conductivity, exchangeable sodium percentage, CaCO 3 and gypsum requirement, and by increase in organic C, total N, and available P and K. The six years of reclamation had achieved a marked reduction in exchangeable sodium (from 11.5 to 4.5 cmol c kg -1 ) to a depth of 1.5 m in the soil profile, whereas the levels of exchangeable calcium, magnesium and potassium had increased. There was also a significant reduction in soil bulk density (from 1.66 to 1.24 gcm -3 ) and increases in porosity, water holding capacity, field capacity, permeability and infiltration rate. The equilibrium infiltration rate after 455 min increased from 0.03 cm h -1 in the control to 0.13 cm h -1 under P juliflora and D. sissoo and 0.10 cm h -1 under E. tereticornis. It is concluded that salt-tolerant tree species have a significant impact on soil properties, which could help to rehabilitate the sodic wastelands in the region.

Amelioration of a highly alkaline soil by trees in northern India

Tree plantation is a proven strategy to improve the salt-affected soils. However, the efficiency of trees to reclaim the soil varies from species to species. This study was therefore, carried out with the objective of assessing the efficiency of 3-yr old plantations of Prosopis juliflora (Swartz) D.C. (Mesquite), Eucalyptus tereticornis Sm. (Forest Red Gum) and Dalbergia sissoo Roxb. Ex. D.C. (Indian Rosewood) to improve the sodic soil characteristics in Sultanpur districts of Uttar Pradesh, India (26°10'-26°23'N, 81°50'-82°5'E). Soil samples collected from six depths; 0.0-0.1, 0.1-0.3, 0.3-0.6, 0.6-0.9, 0.9-1.2 and 1.2-1.5 m below the surface, were analysed for chemical and physical properties by following standard methods. The infiltration rate (IR) was determined by double concentric infiltrometer and the permeability by constant head permeameter. The trees were measured for their girth at breast height (at 1.33 m from ground) and crown area within a 100 x 100 m sector at each of the sites selected. There were decreases in soil pH (from 10.06 to 9.64) and exchangeable sodium percentage (from 70.6 to 26.9) at the P. juliflora plantation relative to the E. tereticornis and D. sissoo plantations. The organic carbon and nitrogen content increased from 2.0 and 0.18 g/kg to 3.9 and 0.45 g/kg under P. juliflora at the surface (0.0-0.1 m) layer. There was also more exchangeable Ca 2+ , Mg 2+ and K + at exchange sites and a reduction in exchangeable Na + 3 yr after establishing the plantations. There was a significant decrease in surface soil (0.1 m) bulk density from 1.66 to 1.37 (t/m 3 ) but an increase in porosity from 41.2 to 46.3% and water holding capacity from 4.3 to 4.8 g/kg. The IR and soil permeability also increased after 3 yr of tree growth. Prosopis juliflora proved more effective than E. tereticornis and D. sissoo in its ability to enrich a sodic soil with organic matter and establishing better soil-water characteristics.

Influence of forest tree species on reclamation of semiarid sodic soils

Amelioration of sodic soils requires the supply of Ca2+ to replace the excess Na+ present on the soil exchange complex. Tree planting on sodic soil produces CO2 that enhances the solubility of CaCO3 present in the sodic soil, and thus releases an appreciable amount of soluble Ca2+ that replaces Na+ from the exchange complex. The study indicates that the sodic soil gets desodified and becomes suitable for plant growth. The study was carried out in 9-year-old rehabilitated plots in the Sultanpur district of Uttar Pradesh, India, to evaluate the relative effects of Prosopis juliflora, Dalbergia sissoo, and Eucalyptus tereticornis plantations on sodic soil and their tolerance of sodicity. The study showed that the saturated soil paste extract Ca2+ and Mg2+ concentrations increased significantly in all the plantations, whereas Na+ concentration decreased from the surface to lower layers. Due to the reduction in Na+ concentration and increase in Ca2+ and Mg2+ concentration, the Sodium Adsorption Ratio (SAR) als...

Amelioration of Degraded Sodic Soil by Afforestation

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