PPSC-PMS Paper Agriculture 2017 MCQs

The L-value, representing labile phosphorus, was proposed by Larsen in 1952. Colwell (1967) pioneered the integrated soil test approach for fertilizer recommendations. Desai and Biswas (1975) demonstrated biogas production from cow dung in India. However, the Law of Limiting Factors was formulated by F.F. Blackman in 1905, not Lundegardh. Lundegardh is primarily known for his work on plant respiration and ion absorption.

According to the international system of soil particle classification, silt particles are defined as those having a diameter between 0.02 mm and 0.002 mm. Sand particles are larger (typically 2.0 to 0.02 mm), while clay particles are the finest, with diameters less than 0.002 mm. This size classification is fundamental to soil science.

Nitrogen is a fundamental macronutrient required for plant growth and development. It serves as a vital component of amino acids, which form proteins like glycoproteins, and is a key element in the structure of nucleic acids (DNA and RNA). Furthermore, nitrogen is a central atom in the chlorophyll molecule, which is essential for photosynthesis. Adequate nitrogen supply is critical for optimizing plant metabolic processes and overall crop yield.

Muck soils are organic soils that have undergone significant decomposition, resulting in a dark, friable material. They are distinguished from peat soils (which have higher, less decomposed organic content) by having an organic matter content typically ranging between 20% and 50%. These soils are highly productive for specific vegetable crops when properly managed and drained.

Granite and basalt are classified as igneous rocks. Since igneous rocks are formed from the cooling and solidification of molten magma or lava, they do not fall under the categories of sedimentary, stratified, or aqueous rocks, which are formed through different geological processes.

Pulse seeds are inoculated with rhizobia bacteria to facilitate biological nitrogen fixation. This symbiotic relationship allows the bacteria to colonize the plant roots and form nodules. Within these nodules, the bacteria convert atmospheric nitrogen into ammonia, which the plant can readily assimilate for growth. Proper seed coating ensures sufficient contact between the bacteria and the emerging roots, significantly enhancing the nitrogen supply to the legume crop.

The standard DTPA (Diethylene triamine pentaacetic acid) extracting solution used for micronutrient analysis has a concentration of 0.005 M. This chelating agent is widely used to estimate the bioavailability of cationic micronutrients like zinc, copper, manganese, and iron in soils. The extraction process typically involves a buffered solution at pH 7.3, which effectively mimics the ability of plant roots to absorb these essential nutrients from the soil matrix.

Smectite is a group of expanding lattice clay minerals, such as montmorillonite, known for their high capacity to shrink and swell upon wetting and drying. This physical property is due to the expansion of the interlayer space within the crystal structure as water molecules are adsorbed. This behavior significantly impacts soil structure, permeability, and engineering properties, often leading to the formation of deep cracks in dry conditions.

The Hartig net is a specialized network of fungal hyphae that develops within the intercellular spaces of the root cortex in ectomycorrhizal associations. This structure facilitates the exchange of nutrients between the fungal symbiont and the host plant. It is a defining characteristic of ectomycorrhizae, distinguishing them from endomycorrhizae, which typically penetrate the cell walls to form arbuscules or vesicles within the root cells.

Soil texture is determined by the relative proportions of sand, silt, and clay. Fineness increases as the clay content increases. The sequence Loamy Sand (LS) < Sandy Loam (SL) < Loam (L) < Sandy Clay Loam (SCL) < Clay Loam (CL) represents an increasing gradient of clay particles. Clay particles have a much higher surface area and water-holding capacity compared to sand, significantly influencing soil physical properties, nutrient retention, and overall workability for agricultural purposes.