Chemical Characteristics of Soil SAQ's

What is the effect of adding organic matter to a soil with poor CEC, such as sand? ANSWER: Increases CEC What is the optimum pH range for most plants, and why is lime added to acidic soils? ANSWER: pH 5.5-7.5; to increase available Ca cations and reduce H⁺ ions What determines the acidity of a s...

What is the effect of adding organic matter to a soil with poor CEC, such as sand? ANSWER: Increases CEC What is the optimum pH range for most plants, and why is lime added to acidic soils? ANSWER: pH 5.5-7.5; to increase available Ca cations and reduce H⁺ ions What determines the acidity of a soil? ANSWER: Concentration of acidic ions (H⁺, Al³⁺) adsorbed onto the soil surface What is the effect of liming on soil pH and CEC? ANSWER: Increases pH and CEC by providing more Ca cations for exchange and increasing negative charges on soil colloids What is the primary reason why cations such as Ca2+ and Mg2+ are attracted to soil particles? ANSWER: Soil particles have a negative charge, and cations are attracted to these negative charges. How do polarised water molecules contribute to the formation of floccules? ANSWER: Polarised water holds soil particles together, trapping larger sand and silt in a floccule structure. What is the significance of Cation Exchange Capacity (CEC) in soil? ANSWER: CEC is the ability of the soil to adsorb cations onto its surface and exchange them for other cations. What is the benefit of humus having a higher Cation Exchange Capacity than clay? ANSWER: Humus can adsorb more cations, which are then available for exchange with other cations, making it a more fertile soil component. How do plant roots remove cations from the soil solution? ANSWER: Plant roots absorb cations from the soil solution, removing them from the soil. What is the significance of flocculation in soil structure? ANSWER: Flocculation improves soil structure by forming larger aggregates, allowing for better water infiltration and aeration. Why is high humus content more beneficial than high clay content in soil? ANSWER: Humus has a higher Cation Exchange Capacity, holds more water, is more fertile, encourages more earthworm activity, and has more negative charges, leading to a higher rate of flocculation. Why does the addition of organic matter, such as slurry or seaweed, to a sandy soil increase its Cation Exchange Capacity (CEC)? ANSWER: Because the organic matter increases the number of negative charges on the soil colloids, allowing more cations to be exchanged. Why is soil pH critical in determining the availability of cations for plant uptake, and what is the optimal pH range for most plants? ANSWER: Soil pH affects the availability of cations, as many are unavailable at low pH. The optimal pH range for most plants is 5.5-7.5, where most cations are available. How does liming a soil with low pH affect its Cation Exchange Capacity (CEC), and what is the primary benefit of doing so? ANSWER: Liming increases the pH, which increases the negative charges on soil colloids, thus increasing the CEC. The primary benefit is reducing \'acid leaching\' and making more cations available for exchange.