Soil Science and Fertilizers

HYV seeds stand for HEIGH YIELDING VARIETY. These are the good quality of seeds and produce a higher yield on a small piece of land but need plenty of water to produce the best results and they also increase the income of the farmers.

Biogas is produced by anaerobic degradation of biological materials such as food wastes, animal and plant wastes. Biogas is produced when organic matter decomposes without oxygen in a process which is called anaerobic decomposition. Biogas consists mainly of methane, carbon dioxide and small amounts of impurities/residues.

So the residue from biogas plant serves as organic manure.

Soil pH directly dictates the chemical form of various ions and elements in the soil, thereby strongly governing their solubility and availability for plant uptake. Extreme pH levels can render essential nutrients unavailable even if they are present in abundance.

• 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 '$CaCO _3$'.

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

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.

Calcium (Ca2+) is the most common cation associated with alkaline soils, often found in the form of calcium carbonate in calcareous soils.

The optimal pH range for cultivation is between 5.5 and 7.0

Porosity refers to the percentage of void space in soil. Higher porosity allows water to move more freely through the soil, thus enhancing the percolation rate.

Less porous soil (like clay) has smaller spaces, which increases the surface area for water to adhere to, leading to greater absorption/retention compared to highly porous sandy soil.

Animals living in the forest include herbivores and carnivores. The dung of these animals are decomposed by insects living in the soil. This contributes to the fertility of the soil by adding organic matter and nutrients, such as nitrogen, that is trapped by bacteria in the soil. This provides nutrients to the seedlings to grow in forests. Thus the correct answer is option C.

Mycorrhiza are symbiotic fungi that associate with plant roots, significantly improving nutrient uptake (especially phosphorus) and water absorption, which helps in the growth and survival of teak in denuded areas.

Chelating agents are organic compounds that can bind to metal ions, such as iron and aluminum, facilitating their mobilization and transport in the soil profile.

Soil erosion is the removal of top soil by the agency of water (water erosion) and wind (wind erosion). Soil erosion is of two types, natural and anthropogenic.