Plants grow best in neutral or slightly acidic pH. Slight acidity favours tree growth and forms forests. Slight alkalinity is however, helpful in growth of grasslands and some crop plants like legumes. Hence, for most plants a pH value of 6 to 7 is favourable.

• Lime is a valuable soil amendment that helps plants and lawns flourish by raising soil pH.
• Most vegetables grow best in a slightly acidic to neutral soil, with a pH between 6.0 and 7.0 hence acidic soils having low pH is added with lime for raising its pH.
  
• Hence Lime is added to soil which is acidic.
• So, the correct answer is 'Lime'.

Petroleum products are used as transportation fuels, fuel oils, for generation of electricity, road oils etc. major use of  petroleum is in transport.

Pedology refers to study of soil in their natural environment. Demography refers to study of human population. Paleontology refers to the study of fossils. Hydrology refers to the study of water.

• When a plant's soil pH increases the plant's ability to absorb certain nutrients is disrupted.
• A pH of 6.0 to 7.0 (slightly acidic to neutral) range is most suitable for the best growth of plants. 
  
• A most economical and effective method to control the pH of the soil is the addition of $CaCO _3$ because it increases the pH level of acidic soil, thus reducing the acidity and increasing the alkalinity of the soil.
  
• Hence the most economical and effective method to control the pH of the soil is $CaCO _3$.
• So, the correct answer is '$CaCO _3$'.

• The water holding capacity of a soil is a very important agronomical  characteristic. 
• small particles have a much larger surface area than the larger sand particles.
  
• large surface area of particle allows the soil to hold a greater quantity of water. so , option A is correct.
  

Edaphic factor is an abiotic factor relating to the physical or chemical composition of the soil found in a particular area. For example, very alkaline soil may be an edaphic factor limiting the variety of plants growing in a region.

Oxalophytes are the plants that grow in acidic soil that maintained at pH 5.5 as this enables the plant to absorb nutrients required for the growth.

A good soil is that which allows the water to percolate slowly into groundwater. These soils can remove pollutants and they promote the growth of healthy vegetation, which in turn reduces soil erosion. 

Soil pH is in the range of 6 to 7 for most plants but some prefer acid or alkaline conditions. At this pH soil organic matter and structure is very good. A lot of micro-organisms, that support plant growth can live in the soil at this pH.

Plants and animals aid in the development of a soil through the addition of organic matter. Fungi and bacteria decompose this organic matter into a semi-soluble chemical substance, known as humus. Larger soil organisms, like earthworms, beetles, and termites, vertically redistribute this humus within the mineral matter found beneath the surface of a soil. Humus is the biochemical substance, that makes the upper layers of the soil become dark. It is coloured as dark brown to black. 

Soil pH is important because it influences several soil factors affecting plant growth, such as :

Loam is considered ideal for gardening and agricultural uses, because it retains nutrients well and retains water, while still allowing excess water to drain away. 

Soil water is often referred to as soil moisture. Soil is the amount of water present in the interparticle spaces in the soil and is available to plants. When soil moisture gets depleted, enough water is not available for plants. So they have to apply more pressure in obtaining water from around the soil particles. 

Soil pH is important because it influences several soil factors affecting plant growth, such as (1) soil bacteria, (2) nutrient leaching, (3) nutrient availability, (4) toxic elements and (5) soil structure. Bacterial activity that releases nitrogen from organic matter and certain fertilizers is particularly affected by soil pH, because bacteria operate best in the pH range of 5.5 to 7.0. Plant nutrients leach out of soils with a pH below 5.0 much more rapidly than from soils with values between 5.0 and 7.5. Plant nutrients are generally most available to plants in the pH range 5.5 to 6.5. For most plants, the optimum pH range is from 5.5 to 7.0.

Soil particles vary greatly in size, and soil scientists classify soil particles into sand, silt, and clay. Starting with the finest, clay particles are smaller than 0.002 mm in diameter. Some clay particles are so small, that ordinary microscopes do not show them. Silt particles are from 0.002 to 0.05 mm in diameter. Sand ranges from 0.05 to 2.0 mm. Particles larger than 2.0 mm are called as gravel or stones. Most soils contain a mixture of sand, silt and clay in different proportions.

A physiologically dry soil is a soil in which the concentration of oxygen is very less and that of salt is very high. Normal plants cannot grow in such soil and only halophytes are found in them. The Sunderbans in West Bengal are rich in physiologically dry soil. Thus the correct answer is option C.

• The process of absorption of water by the soil is called percolation. It is different for different soil types and depends upon the soil compositions. It is calculated by the formula i.e., percolation rate = amount of water/percolation time.

In the steppes and deserts, evaporation greatly exceeds precipitation. The products of rock weathering are brought by intermittent flowing streams during a flood and left behind on the basin floor. This soil has clay, silt and sand are the dissolved mineral salts and is called halomorphic soil. Thus the correct answer is option B. 

• The topsoil is darker because it contains dead organic material in many stages of decomposition. 
• This degradation produces a substance called humus that is composed of carbon-rich compounds and imparts a dark color. Thus, the correct answer is option D.

Humus is organic matter containing nutrients from the soil. It is nothing but dead and decaying organic matter where saprophytes convert complex organic material into simple nutrients. These nutrients are then available to the plants through humus.

Black cotton soil is rich in clay, which has very small sized particles. These small sized particles obstruct water movement and hence, this soil has high water holding capacity and low percolation.

There are different systems constructed to increase the amount of water which is present in the groundwater reserves. The percolation tanks are constructed in the land which is highly permeable. The water from the runoff which gets collected in the tank is then percolated in the ground. This system helps to recharge the groundwater system. These are one of the methods which are used for the conservation of the water resources.

Soil porosity is percentage and type of soil pores or interstices. It is of two types - microspores and macrospores. Macrospores are  non capillary pores of more than 20 micrometer diameter. Gravitational water flows through macropores greater than 50 micrometer. Macropores hold air. In good soils,their number is 20 percent. Micropores are capillary pores with diameter of less than 20 micrometer. They hold capillary water. Good soil contain 30 percent microspores. Solubility and availability of plant nutrients depends on porosity because if the pore size is more water will wash away all the nutrients to water table as gravitational water and if porosity is less there will not be any air, respiration of roots and hence, absorption of nutrients will suffer.

Field capacity is the capacity of field. The amount of water retained by a unit weight of undisturbed soil after complete drainage under controlled conditions is called as field capacity.
Water held up in capillary space between soil particles is called as capillary water.
Gravitational water is the water that seeps down the surface of earth and makes up the water table.
Storage water is normally not used to describe soil water.

Venaparthy is a small village which is situated in the state of Andhra Pradesh. The village is known for being an area which is free from the problems due to groundwater pollution and water crisis. There are percolation tanks which are set up in the village and the nearby locales. These percolation tanks help in the collection of water in the earthen dams and recharge the groundwater in these regions. 

Soil salinity is the presence of excess salts especially those of sodium, potassium and magnesium. 

There are different systems constructed to increase the amount of water which is present in the groundwater reserves. The percolation tanks are constructed in the land which is highly permeable. The water which gets collected in the tank is then percolated in the ground. This system helps to recharge the groundwater system. These are one of the methods which are used for the conservation of the water resources.

The percolation tanks are constructed on the land which is highly permeable. The constructs may be performed using earthen materials which will allow the water to pass through it. This type of tank is also called as the earthen percolation tank. The water which gets collected in the tank is then percolated in the ground. This system helps to recharge the groundwater system. 

There are different systems constructed to increase the amount of water which is present in the groundwater reserves. The percolation tanks are constructed in the land which is highly permeable. The water which gets collected in the tank is then percolated in the ground. This system helps to recharge the groundwater system. 

Venaparthy is a small villages situated in the state of Andhra Pradesh. The village is known for being free from the problems due to groundwater pollution and water crisis. There are percolation tanks which are set up in the village and the nearby locales. These percolation tanks help in the collection of water in the earthen dams and recharge the groundwater in these regions. 

Percolation tanks are the most prevalent structures as it is a measure to recharge the groundwater reservoir both in alluvial as well as hard rock formations.The size of percolation tank should be governed by percolation capacity of strata in the tank bed. Normally, the capacity of percolation tank is 7.87 mm/day.

The percolation tanks are constructed on the land which is highly permeable. The water which gets collected in the tank is then percolated in the ground. This system helps to recharge the groundwater system. The water can be used by constructing borewells for domestic purpose. Canals can be constructed which can be used for the purpose of irrigation and cultivation of crops. 

Percolation rate of a soil is the water absorption rate of the soil. It depends on the composition of the soil. It is different for different types of soil. Hence, it helps in selection of proper soil for the crop growth. Soil with lower percolation has high water retention capacity whereas soil with high percolation has low water retention capacity. Lower percolation rate refers that the soil can hold water for more time while higher percolation rate refers that the soil can hold water for less time. 

Percolation rate of a soil is the water absorption rate of the soil. It depends on the composition of the soil. It is different for different types of soil. Hence, it helps in selection of proper soil for the crop growth. Soil with lower percolation has high water retention capacity whereas soil with high percolation has low water retention capacity. Lower percolation rate refers that the soil can hold water for more time while higher percolation rate refers that the soil can hold water for less time. 

Percolation rate of a soil is the rate of water absorption by the soil. It depends on the composition of the soil. It is different for different types of soil. Hence, it helps in selection of proper soil for the crop growth. Soil with lower percolation rate has high water retention capacity whereas soil with high percolation rate has low water retention capacity. 

The optimal pH range for cultivation is between 5.5 and 7.0

• Alkaline soils are clay soils with high pH, a poor soil structure and a low infiltration capacity.pH of alkaline soil is  > 8.5, 
• The principal cation in alkaline soil is Ca2+ because alkaline soils are primarily caused by a calcium carbonate-rich parent material weathering (developing) in an arid or dry environment.
  
• Hence the principal cation in alkaline soil is  Ca2+.
  
• So, the correct answer is 'Ca2+'.

Soil salinity can be measured by conductivity meter, it is a device which measures electrical conductivity in a solution due to presence of salts or impurities

• Irrigation is the application of controlled amounts of water to plants at needed intervals. 
  
• Prolonged liberal irrigation of agricultural fields is likely to create a problem of salinity, loss of nutrients from the soil. as more amount of water enters through the xylem vessels of the plants the soil becomes waterlogged, vegetations and crop die due to insufficient supply of oxygen.
• Hence Prolonged liberal irrigation of agricultural fields is likely to create a problem of salinity.
• So, the correct answer is 'Salinity'.

Forest Biomes represent the largest and most ecologically complex systems.  They contain a wide assortment of trees, plants, mammals, reptiles, amphibians, invertebrates, insects and micro-organisms which vary depending on the zone's climates.  Sadly, boreal and rainforest biomes are being cut down at an alarming rate, with hundreds of species of plants and animals disappearing from the planet on a daily basis. In forests temperature is generally lower in summer and higher in winter. The days are cooler and nights are warmer than in the surroundings. The floor of the forest is carpeted with lichens and mosses. Moisture content of the soil remains stable for longer periods because of absence of evaporation.

Explanation: Water content or moisture content is the quantity of water contained in a material, such as soil (called soil moisture), rock, ceramics, fruit, or wood. The water content of soil is defined as the ratio of weight of water to weight of solids of given mass of soil.

Explanation: Clay can have a very high porosity. Because its grains are very small, there are a lot of (small) pore spaces in between them. What clay does not have is good permeability, which is a measure of how "connected" these pore spaces are. Clay can hold a lot of water, but it doesn't let it flow very well.

The process of turning and loosening of soil is called ploughing or tilling. Harvesting is the process of cutting the crop and gathering them to transport it to the market. Threshing is the process of separating the chaff from the grain. Irrigation is the process of watering the plants in a field.

Sand is a naturally occurring granular material composed of finely divided rock and mineral particles. The composition of sand varies, depending on the local rock sources and conditions, but the most common constituent of sand in inland continental settings and non-tropical coastal settings is silica (silicon dioxide, or SiO2), usually in the form of quartz making it most friable.