Neco Model Questions Vol1 2017 Agricultural Science Question 2

A student collects three soil samples from a field (1 ha) at depths 0‑15 cm, 15‑30 cm and 30‑45 cm. For each sample the pH is measured with a calibrated pH meter and the organic carbon is determined by the Walkley‑Black method using 0.5 N ferrous sulphate (FeSO₄). The volume (ml) of FeSO₄ required for each titration is recorded. The dry weight of each soil subsample used for the titration is 10 g. Data obtained: | Depth (cm) | pH | Volume of 0.5 N FeSO₄ (ml) | |------------|----|----------------------------| | 0‑15 | 5.2| 12.5 | | 15‑30 | 5.8| 9.0 | | 30‑45 | 6.1| 6.5 | The bulk density of the topsoil (0‑15 cm) is 1.3 g cm⁻³. Using the data, answer the following: (a) Calculate the percentage of organic carbon (% C) in each depth layer. (b) Convert the % C values to percentage of organic matter (% OM) using the factor 1.724. (c) Identify which depth layer, if any, requires liming (pH < 5.5). For that layer, calculate the lime requirement (kg CaCO₃ ha⁻¹) using the formula: Lime = (5.5 – pH) × 2 × bulk density × depth (cm). State the result and give a brief recommendation.