Neco Model Questions Vol1 2022 Agricultural Science Question 2

A soil scientist is determining the water‑holding characteristics of a loamy soil using the gravimetric method. A 250 g oven‑dry soil sample is taken and the following weights are recorded: - Saturated soil (after soaking) = 400 g - Soil at field capacity (after draining for 2 h) = 340 g - Soil at wilting point (after drying at 105 °C until constant weight) = 280 g The bulk density of the soil is 1.3 g cm⁻³ and the effective rooting depth in the field is 15 cm. Answer the following: (a) Compute the gravimetric water content (%, w) at field capacity and at wilting point. (b) Convert these gravimetric values to volumetric water content (θ, %) using the bulk density. (c) Calculate the amount of water (in litres) that can be stored in 1 m² of soil at field capacity and at wilting point, and state the available water (difference) for plant use. (d) Briefly discuss how the obtained available water capacity influences irrigation scheduling for a rain‑fed crop. (e) Mention two possible sources of error in this gravimetric method and one precaution for each.