Soil Science MCQ Question and Answer | Agriculture MCQ Question

An alkali soil must have a pH value of above 8.5.
Alkali soils are clay soils with high pH, a poor soil structure, and a low infiltration capacity. They also have a hard calcareous layer at 0.5 to 1 metre depth.
Alkali soils owe their unfavorable physio-chemical properties mainly to the dominating presence of sodium carbonate, which causes the soil to swell and is difficult to settle.

The cation exchange capacity is a measure of how many cations can be retained on soil particle surfaces. Negative charges on the surfaces of soil particles bind positively charged atoms or molecules (cations) but allow these to exchange with other positively charged particles in the surrounding soil water.
CEC of vermiculite is 150, kaolinite is 3 - 15, chlorite is 10 - 40 and for montmorillonite CEC is 60 - 100.

The extent of Zn-deficient soils is approximately 50%.
About 50% of soil samples analyzed for available Zn were found deficient in India. Significant improvement in crop yield and quality through the balanced application of Zn has been reported across India. Adequate Zn application to crops is important for the food and nutritional security of India.

Calcareous soil refers to calcisol with cemented carbonate layer near the surface in a desert environment. These often have more than 15% CaCO₃ in soil which are sparingly soluble salts that cause the soil to have high pH.
The pH of calcareous soil is generally 8 - 8.5.

If fertilizer prices go up the optimum close should come down.

The Olsen method is a chemical extractant (bicarbonate) that provides a reasonable estimate of the amount of plant-available P by measuring phosphate from the soil solution and exchange surfaces.
This procedure is suitable for all expected sodic soils, calcareous, alkaline, neutral and slightly acidic soils containing CaPO₄, since the calcium concentration in the solution is suppressed by the precipitation of CaCO₃, increasing PO₄ concentration in the solution.

The Chemical (Grigg & Tamn reagent) used for extraction of Molybdenum is Ammonium acetate at pH 3.3.
The Grigg or Tamn reagent (acid ammonium oxalate) is considered to be the best for the determination of available molybdenum. The reagent produces oxalate ions which replace the molybdate on soil colloids and clay. This exchange of oxalate and molybdate ions becomes irreversible by the formation of Mo-oxalic acid complexes.

In the minimum thermometer, the material used is Alcohol.
The minimum thermometer is one that automatically registers the lowest temperature attained during an interval of time. The alcohol in the glass minimum thermometer contains a dumbbell-shaped index that is kept on the bulb side of the meniscus by surface tension. The thermometer is installed in a horizontal mounting so that as the temperature falls, the index is pulled toward the bulb and remains at the minimum point as the temperature rises.

Gypsum block can measure water potential up to 1 - 15 bar.
A soil moisture block often referred to as gypsum block is a device for measuring soil moisture changes.
The amount of water in the soil is determined by the electrical resistance between the two electrodes within the gypsum block. More water present in the soil will reduce the resistance, while less water will increase it.

The mineral chlorite has an extra layer of Illite. The illite is abundant throughout the illite-chlorite predominant zone. Layers of illite and chlorite are semicoherent.
The chlorites are a group of phyllosilicate minerals common in low-grade metamorphic rocks and altered igneous rocks.