eChapters

Family: Solanaceae

Flowering: July-September

Fruiting: October-December

Botanical description: The plant is an erect, branched herbaceous weed that grows up to 60cm tall. The leaves are alternate, ovate or oblong, deep green in colour with an indented margin and acuminate at the tip. Flowers are small, white in colour with 5-1.5 mm across. The berries are globose in shape, green at early stage and turn to orange or black when ripened.

Family: Solanaceae

Flowering: November-December

Fruiting: January-March

Botanical description: The potato plant is a leafy, tufted herb with tuberous underground stems growing up to 2 ft tall and spreading out a little more. The leaves are compound, long and the leaflets are 7-15 in number, with about 3 inch in long. The tubers are not roots, but modified stems or rhizomes, and the “eyes” are really leaf buds.

Family: Chenopodiaceae

Flowering: November-December

Fruiting: January-March

Botanical description: The leaves of the plant are alternate, lower most and middle one is long petioled, ovate-oblong, obtuse or acute, entire or dentate and higher one is small. Flowers are dioecious. Male flowers in arranged in spicate clusters combined into a leafy terminal panicle and female flower in axillary clusters. Ovary enclosed by tepal like bracts that developed into a globose or pyramidal, 2-4 spined structure in fruiting.

Family: Talinaceae

Flowering: September-October

Fruiting: November-December

Botanical description: The plan is an erect, stout, fleshy herb, growing up to 0.5-1 m in height. Leaves are elliptic to obovate, 5-15 cm long, 1.5-5 cm wide, tip pointed to tapering. The flowers are borne in 2-5-branched, raceme like clusters, 3-20 cm long with a stalk about 8-11 mm long. Petals are pink, obovate, up to 1 cm long. Capsules are pale yellow, ellipsoid, 6-7 mm long. Then plant flowers and bears fruits during September-December.

Family: Apiaceae

Flowering: November-January

Fruiting: February-April

Botanical description: The plant is an erect, freely branching annual herb with finely dissected, lacy, blue-green leaves. The leaves are about 1 ft long and divided pinnately three or four times into thread like segments each about 1 in long. The dill plant grows about 3-5 ft tall.

Family: Aizoaceae

Flowering: July-September

Fruiting: October-December

Botanical description: The plant is a succulent herb with prostrate forked branches, growing up to 20-45 cm long. Stems are prostrate or rising, somewhat succulent, up to 50 cm long or more, smooth or sparsely velvety. Leaves are flat, elliptic to obovate, 1-2 cm long, 0.4-2 cm wide, margins entire, tip blunt with rounded base. Leaf stalks are 0.5-2.5 cm long, expanded into a sheath joined with leaf base to form a cup. Flowers are pinkish or white in colour, borne solitary, stalkless, largely hidden in leaf axils. Capsule with a lower scarious or membranous portion and an upper brown. Seeds are black in colour with muricate concentric lines.

Family: Fabaceae

Flowering: September-October

Fruiting: November-January

Botanical description: Thye plant is a small diffused herb, with erect to creeping habit. Leaflets are 1-4 cm long, 8-35 mm broad, obovate to oblong-wedge-shaped, tip rounded to notched. The flowers of the plant yellow in colour, bloom in 8-20-flowered clusters, with a stalks 3 mm long and sepals nearly equal, shorter than or as long as the tube. The fruit is 1-2 cm long, 2-3 mm broad, linear, sharp tipped, curved and 4-8-seeded.

Family: Fabaceae

Flowering: December-January

Fruiting: February-March

Botanical description: The plant is an erect, annual and strongly smelling herb growing up to 10-50 cm in height. The Leaves are trifoliate with leaflets 1-3 cm long, 5-15 mm broad, obovate to inverted-lanceo shaped. Flowers are cream or yellowish-white, in colour, 1-2 together in leaf axils and 1.2-1.8 cm long. Pods are oblong, straight or falcate with age, 7.5-10 cm long with a long beak and 20 seeded.

Family: Fabaceae

Flowering: December-January

Fruiting: February-March

Botanical description: The plant is a scrambling and climbing herb, with stems almost hairless, up to 3 ft tall. The leaves are compound with 5-6 pairs of opposite leaflets and 1 terminal tendril. Leaflets are narrow, linear, 2.5-3.0 cm long, 2-3 mm wide. Flowers are borne singly or in pairs on short stalks arising at the base of the leaves, blue to purple in colour, large, up to 2 cm long. Seed pods are mainly black, linear, 4-6 mm broad, containing 10-12 round or angulated small seeds. The plant flowers and bears fruits during December-March.

Family : Rutaceae

Flowering: March-April

Fruiting: (Next Year) April-June

Botanical Description: The plant is a medium sized tree with spines of 1-2 cm long. The leaf is composed of three leaflets. The leaflets are oval, elliptic with 2.5-6.5 cm petiole, terminal one is larger. Flowers of the tree are white or greenish-white. The fruits are ovoid, hard and about 5-7.5 cm in diameter. The flowers appear during March-April and the tree bears fruits towards October, ripening in April.

Family : Moraceae

Flowering: December-January

Fruiting: June-July

Botanical Description: The plant is an evergreen tree that grows up to 20-30 meter tall and 80-200 cm in diameter with evergreen, alternate, glossy and leathery leaves reaching up to 9 inch long. Leaves are oval on mature trees. All parts of the plant contain sticky and white latex. Inflorescence is solitary, borne axillary on special lateral short leafy shoots arising from older branches. Fruits are large arising from the tree trunk and weighting about 10-50 kg. the exterior of the fruit is green or yellow when riped and composed of numerous hard, cone like points attached to a thick and rubbery, pale yellow or whitish wall.

Family : Oxalidaceae

Flowering: July-September

Fruiting: October-December

Botanical Description: The plant is a small evergreen tropical tree that grows upto 25 feet in height. The compound leaves are soft, medium green, spirally arranged around the branches in an alternate fashion. The leaflets are sensitive to light and fold inward at night. The flowers are small and bell shaped, with five petals that have whitish edges. The fruit is fleshy, have a thin and waxy skin, five lobbed, ovate to ellipsoid with attractive yellow-orange in colour.

Family : Arecaceae

Flowering: February - March

Fruiting April - August

Botanical Description: The plant is a large tree and grows upto 30-40m. in height. The trunk may have a circumference of 1.7 m at the base. The leaves are palmate, leathery, gray green and 1-3 m in wide with folded along at the midrib. Flowers are 90-150 cm long and branched. Fruits are ovoid, 15-20 cm in diameter with fibrous and fleshy mesocarp.

Family : Cucurbitaceae

Flowering & Fruiting: Most part of the year

Botanical Description: The plant is a climbing herb with angular stem and long tuberous root. The leaves are classified as palmately simple with five lobes while the shape varies from the heart to pentagon form. The size of the leaves is approximately 5-10 cm in width and length. The tendrils are long, elastic with coil-like springy character that can wrap around the host to the entire length. The flower is large and white about 4 cm in diameter and contains five long tubular petals. The fruit is oblong, narrowed apically or at both ends. The raw fruit is green in color and turns bright red when ripened. The seeds of the plant are oblong and compressed.

Family : Cucurbitaceae

Flowering: September-October

Fruiting: October-November

Botanical Description: The plant is an procumbent annual climber growing to 1.5m. The leaves are oval to kidney shaped with five to seven shallow lobes. Plants produce trailing vines and yellow flowers similar to cucumbers, but flowers may be male, female, or perfect. Fruit is spherical or ovoid, large, and can reach the size of a football, although it is generally more flattened. It is striped green or pale green in colour, ultimately turning yellow.

Family : Dilleniaceae

Flowering: May- June

Fruiting: September-February

Botanical Description: The plant is a moderate sized evergreen tree growing up to 15m tall. The leaves are deep green in colour, oblong to lanceolate and 15-36 cm in long. The flowers are white, large, up to 5 inches across. The fruit is rounded, 5-12 cm in diameter aggregate of 15 carpels with each carpel containing 5 seeds embedded in the pulp.

Family : Dioscoreaceae

Flowering & Fruiting: Throughout the year

Botanical description: The plant is a vigorous, perennial, climbing plant, producing annual stems up to 15 metres long from a very large tuberous rootstock. Tubers of the plant are one to several, polymorphic, variously branched or lobed and hairy with small rootlets. The stems scramble over the ground, or twine into the surrounding vegetation. The stem is quadrangular, winged, and twines right-handed. Leaves are opposite, 7-18 x 4-10 cm, broadly ovate, base cordate with acuminate apex. Flowers are laxly arranged, sessile with 1-1.5 mm long and ovate bracts and fleshy tepals.

Family : Dioscoreaceae

Flowering & Fruiting: September-October

Botanical description: Aerial yam is a glabrous-leafed, non-spiny, perennial climbing plant producing annual stems up to 10 metres long from a woody, tuberous rootstock. These stems scramble over the ground, or twine into the surrounding vegetation. The stems twine left-handed and produce aerial axillary bulbils. The plant produces tubers; however the bulbils which grow at the base of its leaves are more important food products. They are about the size of potatoes (hence the name air potato) weighing from 0.5 to 2 kg. The flowers are whitish or pinkish in colour.

Family : Dioscoreaceae

Flowering & Fruiting: August-October

Botanical description: Stem twining to the left, terete, tomentose. Leaves 3-foliolate, palmately divided into 3-5 subequal leaflets, broadly ovate, oblique at base, abruptly acuminate; petiole 15-18 cm long. Spikes are 30 cm long, densely tomentose, distantly flowered fascicles at nodes on long peduncle. Female flowers sessile; bracts 4 mm long, ovate; tepals 2 x 1 mm, oblong, acute, hairy. Capsule 25 x 15 mm, oblong, tomentose. Male flowers not seen.

Family : Dioscoreaceae

Flowering & Fruiting: July-December

Botanical description: The plant is a perennial climbing plant. Tubers are irregular, usually long ovoid, transverse section white when fresh, becoming brown. Roots fibrous. Leaves are compound, palmately divided into 3-5 leaflets, and alternately arranged on the twining stems. Male flowers are nearly stalkless and Female spikes are simple or branched. Capsules are thinly leathery, sparsely hairy and turns black at maturity.

Family : Ebenaceae

Flowering: March-April

Fruiting: March-April (Next Year)

Botanical Description: The plant is an evergreen tree with a spreading crown. It can grow up to 37 m tall, with a trunk girth of 2 m. The bark is black, smooth, and the inner bark turns bluish on exposure to sunlight. Leaves are oblong and glossy. The male flowers are formed in 3-5 flowered cymes in leaf axils. Female flowers are solitary. Fruits are round, up to 3.5 cm in diameter, yellow when ripe with a juicy pulp.

Family : Ebenaceae

Flowering: April-May

Fruiting: (Next Year) March-April

Botanical Description: The plant is a medium-sized tree growing up to 25 m, height and 1.9 m girth. The bark is black in colour, peeling in rectangular scales, which is an identifying feature. The leaves are eliptic-oblong, opposite or alternate, leathery, up to 35 cm long, velvety on both sides when young, becoming smooth above when fully grown. Male flowers are mauve in colour, sessile or nearly sessile in short peduncles, mostly 3-flowered. Female flowers mauve, mostly extra-axillary or sometimes solitary, axillary, opposite to each other, larger than the male flowers. Fruits olive green in colour, ovoid or globose 3-4 cm across, 1-8 seeded berries. Seeds are compressed, oblong and shiny.

Family : Moraceae

Flowering: Round the year

Fruiting April - June

Botanical Description: The tree is very large, growing up to 30 m tall, with many aerial roots that develop in to new trunks, so that the tree goes on spreading laterally. Indefinitely a single tree can cover a very wide area. The leaves are leathery, entire, ovate or elliptic, which grow up to 20-30 cm long with prominent lateral veins. The fruits are 1 to 2 cm in diameter, rounded in shape, without stalks arranged in pairs at leaf axils and it changes to bright red colour when ripens. The plant flowers round the year and bears fruits during April-June.

Family : Moraceae

Flowering: March-June

Fruiting June-July

Botanical Description: It is a large sized tree with few short areal roots. Leaves are ovate or elliptic with 7-20×3.5-9 cm in size. The most distinctive aspect of this tree is the red, furry figs in short clusters, that grows directly out of the trunk of tree. The figs do carry hundred of flowers in it.

Family : Rutaceae

Flowering: February-April

Fruiting: November-January

Botanical Description: The plant is an erect, slow-growing tree with a few upward-reaching branches. The bark is ridged, fissured and scaly with sharp spines. The leaves are alternate, 3 to 5 in long, dark-green in colour, leathery, often minutely toothed, blunt or notched at the apex, are dotted with oil glands and slightly lemon-scented when crushed. Flowers are greenish or reddish in colour, 1/2in across, are borne in small, loose, terminal or lateral panicles. The tree is mostly known for its hard woody fruit, size of a tennis ball, round to oval in shape. The pulp is brown, odorous, resinous, acid or sweetish, with numerous small, white seeds scattered through it.

Family : Sapotaceae

Flowering: February-April

Fruiting: May-July

Botanical Description: The plant is a large or moderate-sized tree, smooth and brown bark with pubescent or tomentose branchlets. The leaves are clustered near the ends of the branches, elliptic, oblong or ovate and acuminate. The flowers are cream coloured, fleshy, on rusty tomentose pedicel and clustered at the end of the usually leafless branches. The fruits are fleshy, green berries, quite large and containing from one to four shiny, brown seeds.

Family : Sapotaceae

Flowering: November-January

Fruiting: March-June

Botanical Description: The plant is a tree growing up to 3-12 m tall, with gray bark and smooth branchlets. The leaves are alternately arranged often closely clustered towards the end of branchlets, obovate to obovate-elliptic leaf blade with 0.8-2 cm leaf-stalks. Flowers are white or light yellow in colour, about 4 mm in size and arise in fascicles in leaf axils. Berry is oblong to ellipsoid, 1- 2 seeded and yellow when ripe.

Family : Cucurbitaceae

Flowering: August-September

Fruiting: September-November

Botanical Description: The plant is a large perennial climber which grows up to 3-5 m. The leaves are simple, alternately arranged, ovate and 3-5 lobed. The flowers are yellow, 4-6 cm across, solitary on axillary stalks. Fruit is an ellipsoid, 3-6 cm long, densely covered with soft spines.

Family : Musaceae

Flowering & Fruiting: Most parts of the year

Botanical description: Banana is a tropical small size tree, with large leaves which overlapping bases from the trunk. The leaves are oblong and 1.2-1.5 m in length. The stem reaches a height of about 10-30 feet. Flower develops from the centre of the crown. Only female flowers develop into a banana fruit that varies in length from 4 to12 inches. Each banana plant bears fruits only once. The plant bears flowers and fruits in most parts of the year.

Family: Nelumbonaceae

Flowering & Fruiting: July-December

Botanical description: It is a perennial aquatic plant, growing from a tuberous rootstock lying in mud at the bottom of water bodies, lakes and ponds. The plant produces large leaves which float on the surface of the water. Leaves are large, simple, glabrous, solitary, beset with scattered hard minute papillae and rounded in shape and covered with a network of microscopic hairs. Flowers are large, pink or white in colour with expanding and emerging above water. Fruit is 1-2 cm across with flat-topped seed pod divided into compartments. Seeds globose, 1 mm across and brown in colour

Family : Nymphaeaceae

Flowering: Throughout year

Fruiting: Throughout year

Botanical description: It is an aquatic perennial herb, having erect perennial root stocks that anchor it to the mud in the bottom of the water bodies. Leaves vary from being elliptic-oval to almost circular 15-26 cm across, fine hairs on upper side and always remain at floating stage. Flowers are mostly white, occasionally pink or red reaching up to 15 cm in diameter.

Family : Arecaceae

Flowering: February-March

Fruiting: April-May

Botanical Description: The plant is a moderate sized dioecious tree which grows up to 4-10 m. in height and 30 cm diameter with a large crown and rough trunk covered with persistent leaf bases. The leaves are 3 m. long, gently recurved on 1 m petioles with spines near the base. The leaf crown grows to 5 m wide and 7-10 m tall containing up to 100 leaves. The inflorescence grows upto 1 m with white flowers. The single seeded fruit ripens to orange-yellow.

Family : Phyllanthaceae

Flowering: May-June

Fruiting: June-September

Botanical Description: The plant is a small deciduous tree reaching about 25-30 ft in height. Leaves are compound, 14-25 inches long, crowded at the ends of the branches leaflets 2-3.5 inches long, alternately arranged along the rachis, ovate or obliquely ovate, acute with rounded or wedge-shaped base. Flowers are very minute, in short dense spike-like clusters arising from nodules along the branches. Fruit is pendulous, in small clusters from the branches, round or slightly flattened at the poles, with shallow or deep ribs (usually 5) 0.75 inch across.

Family : Phyllanthaceae

Flowering: March-May

Fruiting: November-February

Botanical Description: The plant is a small to medium sized deciduous tree, reaching 8 to 18 m in height. It is known for its edible fruits of the same name. The tree has crooked trunk and spreading branches. The leaves are simple, nearly stalkless and closely set along slender branchlets. The leaves are often mistaken for leaflets of pinnate leaves. The flowers are small, greenish-yellow or pinkish, having six segments, but no real petals. The fruit is nearly spherical, light greenish yellow, quite smooth and hard on appearance, with 6 vertical stripes or furrows.

Family : Mimosaceae

Flowering: January-March

Fruiting: April-June

Botanical Description: The plant is a large, nearly evergreen perennial tree that grows up to 20 m or more in height. It has a broad crown, up to 30 m across, and a short trunk, up to 1 m thick. Leaves are deciduous but foliage is persistent, as the new leaves appear while the old ones are being shed, so that the tree looks like an evergreen. Flowers yellowish-white in colour and are borne in small spherical glomerules of about 1 cm in diameter, forming short axillary panicles of 5-30 cm in length. Pods are greenish-brown to red or pinkish, rather thin with 10-15 cm long with irregular shape and flattened. There are about 10 seeds per pod, shining black in a white pulpy aril.

Family : Myrtaceae

Flowering: April-May

Fruiting: July-August

Botanical description: The plant is an evergreen tropical tree, 50 to 100 ft. tall, with oblong opposite leaves that are smooth, glossy and having a terpentine smell. It has fragrant white flowers in branched clusters at stem tips and purplish-black oval edible berries. The leaves are antibacterial, and are used for strengthning the teeth and gums. The fruit is ellipsoid or oblong, variable in size and shape, usually up to 2.5 cm long, black, shining and juicy when fully ripe. Seeds always one, with thick rounded fleshy cotyledons, closely appressed on their inner faces.

Family : Lythraceae

Flowering: August-September

Fruiting: November-December

Botanical description: The water chestnut is an annual aquatic herb with a rosette of floating leaves and submerged, anchored into the mud by very fine roots. It has two types of leaves, finely divided, feather-like submerged leaves borne along the length of the stem, and undivided floating leaves borne in a rosette at the water’s surface. The floating leaves have saw-tooth edges and are ovoid or triangular in shape, 2-3 cm long, on inflated leaf-stalks 5-9 cm long, which provide added buoyancy for the leafy portion. Flowers are white in colour, with Four petals and are borne for a long period. The fruit is a nut with barbed spines. Seeds can remain viable up to 12 years, although most germinate within the first two years.

Family : Rhamnaceae

Flowering: July-September

Fruiting: October-January

Botanical Description: Jackal Jujube is a very thorny straggling shrub with rusty-velvety young branches with paired thorns. Thorns are, one straight and the other recurved. Alternately arranged simple leaves are ovate to ovatelancelike, often oblique, with three prominent nerves and numerous transverse nervules. Tiny green flowers are borne in nearly stalkless velvety cymes in leaf axils. Fruits are spherical or obovoid drupes, black, shining, seeds woody.

Soil sample collection is the first and most important step for soil quality analysis. A soil sample collected with due care and proper procedure is essential for getting reliable result of the analysis. The sample should represent the field and for practical purposes, an area of about 0.5 hectare is considered as one sampling unit. In case of conspicuous variation observed in the field in terms of texture, colour, slope etc, separate samples should be collected from areas differing in these attributes. In other words, sample should be collected from an area in the field with similar characteristics as seen through normal visual observation. Sampling should thus be avoided from areas like near trees, permanent vegetations, manure pits, manure piles or recently fertilized fields.

Soil Sampling procedure

1. For a particular field unit, one composite soil sample is prepared out of the samples collected from 7-8 spots distributed across the field unit. The entire field is covered by moving in a zig-zag manner from each sampling spot.
2. For each sampling point or spot, scrapping off the surface litter such as grasses or crop residues is done. Then, a “V” shaped pit of 15-20 cm length and of equal width is made. Depth of sampling depends upon the requirement and on the type of crop. For field crops like paddy, wheat etc, samples are collected from 15 cm depth. From the “V” shaped pits, take outslice of ½ inch thickness from both sides of the exposed pit surfaces from top to bottom.
3. The soil samples so collected from the 7-8 points are mixed thoroughly by hand and then is reduced to about 500 g by quartering process. The quartering process consists of a procedure in which the entire soil mass is divided into four quarters; the two opposite ones are discarded and the remaining two are remixed. This process is repeated till about 500g soil is obtained.

Soil pH is the measure of hydronium ion (H₃O⁺) or more commonly hydrogen ion (H⁺) activity in the soil suspension. Soil pH can be measured in soil-water suspension, saturation extract or in 0.01 M CaCl₂ solution. Saturation extract is used to identify specific soil problems such as salinity or sodicity. Measurement of pH using 0.01 M CaCl₂ solution gives more reproducible results than measured through soil-water suspension. It also provides a good approximation of field conditions as the electrolytic composition of 0.01 M CaCl₂ is considered similar to that of soil solution. However, among the three methods, soil-water suspension is most commonly used in research laboratories as well as for fertilizer recommendation as it is simpler and more convenient.

Electrical conductivity (EC) is a useful indicator of soil salinity. Relationships have been developed between EC and salinity classes for a 1:1 soil: water suspension. With increase in salt content in a soil, the EC increases. Thus, for salt affected soils, measurement of EC is vital as accumulation of salts in the root zone is detrimental to plant growth. EC is a measure of the ability of a soil solution to conduct electrical current.

Equipment and Reagents

1. Digital Conductivity meter
2. 0.01 M potassium chloride (KCl) solution: Dissolve 0.7456 g dry KCl in distilled water and make up the volume to 1.0 litre. This solution has an electrical conductivity of 1.413 dS m_-1 at 25ºC.

Ion exchange is a reversible process by which a cation or anion held on the solid phase is exchanged with another cation or anion in the liquid phase. Soil mineral and organic colloidal particles have negative valence charges that hold dissociable cations. The power to retain cations at the surface of soil colloids is referred to as the cation exchange capacity (CEC). Cation exchange is a reversible reaction in soil solution, dependent upon negative charges of soil components arising from permanently charged or pH-dependent sites on organic matter and mineral colloid surfaces. The CEC is the sum of cations held by a kilogram of soil and is expressed in Cmol (p₊)/kg soil. In most agricultural soils, the cation-exchange capacity (CEC) is generally higher than the anion exchange capacity (AEC).

Exchanges sodium (Na+) is animportantparameter forsalt affected soils. This is estimated by extraction with ammonium acetate and then measuring the extract inflamephotometer.

Reagents

1. Neutral normal ammonium acetate solution (1 N CH₃COONH₄ of pH 7): Dissolve 77.09 g of ammonium acetate in distilled water and make up the volume to one litre. Adjust the pH of the solution to 7 with ammonia solution or acetic acid.
2. Standard solution of Na (500 mg/L Na): Dissolve 1.271 g of NaCl in distilled water and make up the volume to one litre.
3. Working standard solution of Na (100 mg/L): Dilute 200 ml of 500 mg/L stock solution to 1000 ml.

Soil bulk density (BD) or apparent density is determined in -situ by core method. Stainless steel or metallic cores of cylindrical shape with known height and diameter are inserted into the soil till the rim of the core. The soil core is then excavated and the soil sample is oven dried to get the dry weight. The ratio of the oven dry weight to the total volume of the core gives the bulk density of the soil.

Aggregation is a direct indicator of soil structure. Ahealthy soil is considered to have well aggregated structure. Though not routinely followed during soil testing and chemical analysis, aggregation is one of the major indicators of soil physical health. Wet sieve method (Yoder, 1936) is usually followed for soil aggregate analysis. This involves gently raising and lowering a nest of sieves in water to assess the stability of aggregates to rapid wetting. However, the Yoder’s wet sieving method has been modified to make it simpler and currently, the method of Kemper and Rosenau, 1986 is being commonly used in research laboratories. One of the pre-requisites in these methods is the availability of wet sieving apparatus and further, these methods are laborious and time consuming. On the other hand, the method described by Cambardella and Elliott (1993) is considered very ideal because of its simplicity and is being widely used for aggregate bound soil carbon fraction study. The soil sample is wet sieved with a series of three sieves (2000, 250 and 53 micron size).

Aggregation is one of the basic physical characteristics of soil. Under natural conditions, primary soil particles, particularly clays, tend to join together to form secondary units called aggregates. Size distribution of soil aggregates is important because the size of the aggregates determines their susceptibility to water and wind erosion. Also, their size is important in determining the pore size distribution and regulating pore space in cultivated soils.

There are a variety of procedures being in use to test the stability of aggregates and aggregate size distribution. However, choice of the method for analysis of aggregate size distribution is determined by the purpose of analysis. The developed measures are relative and purpose specific. This chapter discusses dry aggregate analysis.

Thisprocedure estimates aggregatestabilitytoimpact ofraindropsand water erosion. Wet sieving procedure was originally proposed by Yoder, 1936. Later, the procedure was modified byKemper and Rosenau, 1986.

Equipment

1. Yoder type sieve shaking electrically operated machine (3/4 inch stroke at 30 strokes per minute)
2. Concentric sieves of various sizes of pores to fit properly into the machine.
3. Weighing balance

In dry combustion technique, the combustion of soil sample (about 250 mg and mm sieved) is carried out at high temperature (about 1000 ºC) through feeding in an inert boat in the electric furnace. The CO₂ produced from the oxidation of carbon present in the soil sample at high temperature is carried towards non dispersive infrared detector (NDIR) by a carrier gas where it is quantified and total carbon content is determined.

This is one of the commonly used method to estimate organic carbon content in soil. In this wet digestion method, soil organic matter is oxidised with a mixture of K₂Cr₂O₇ and concentrated H₂SO₄ utilizing the heat of dilution of H₂SO₄. The unused K₂Cr₂O₇ is back titrated with ferrous sulphate or ferrous ammonium sulphate.

Labile fractions of soil carbon (C) refer to the fraction of soil carbon that are easily altered by microbial activities. These fractions serve as sensitive indicators to changes in management induced soil quality and are grouped under active soil C pool. The method described by Weil et al. (2003)estimates changes in biologically active soil C using a dilute KMnO . This is an improvement over the method used by Blair et al (1995), where a very high concentration (0.333 M) of KMnO₄ was used.