ABSTRACT

Soil organic carbon and main nutrient stocks play key roles in maintaining soil fertility and yields of agricultural crops including cocoa (Theobroma cacao). The amount of nutrients removed from the soil by the cocoa trees could be influenced by its physiological growth stage. A study was carried out to examine the changes in some soil physical and chemical properties with main nutrients availabilities under cocoa plantations at the Cocoa Research Institute in the Eastern Region of Ghana. Cocoa plantations of different ages (5, 10, 14, 18 and 23 years) were chosen based on similar land history. Soils at the study sites are classified as Xanthic Ferralsol (WRB series). On each plantation, one acre (0.4ha) plot was demarcated and divided into three blocks for soil sampling. Five core samples were taken at 0–15 cm depth per block, bulked together and subsample taken to the laboratory for analyses. Particle size analyses showed that all soils were of sandy loam texture. All soils were acidic with pH below 5.5, relatively low exchangeable K and Ca. Bulk density values varied with ages at highest in 18 years. Soils under 23 years old plantations had relatively lower bulk density than those of the other ages. Total nitrogen content under the 5, 10, and 18 years of cocoa plantations was below the critical values considered adequate for good cocoa growth. Soil carbon stock and available phosphorus content of the soil generally tend to increase with age of the cocoa plantations. These differential variations in the soil nutrients, namely, total N, available P, exchangeable K, Ca, and Mg among five different cocoa plantation ages suggest that total nitrogen, available P, and exchangeable Mg were higher than the critical levels for good cocoa growth under 23 years of cocoa plantations only, but exchangeable K and Ca were lower the critical levels for all ages of cocoa plantations.

摘要

土壤有机碳和主要养分库在维持土壤肥力和包括可可（Theobroma cacao ）在内的农作物产量方面发挥着关键作用）。可可树从土壤中带走的养分量可能受其生理生长阶段的影响。在加纳东部地区的可可研究所进行了一项研究，以检查可可种植园下一些土壤理化性质与主要养分有效性的变化。根据相似的土地历史选择不同年龄（5、10、14、18 和 23 年）的可可种植园。研究地点的土壤被归类为 Xanthic Ferralsol (WRB 系列)。在每个种植园中，划定一英亩（0.4 公顷）的地块，并划分为三个块进行土壤采样。在每块 0-15 厘米深度处采集五个岩心样品，将其散装在一起，然后将子样品带到实验室进行分析。粒度分析表明，所有土壤均为砂壤土质地。所有土壤均为酸性，pH 值低于 5.5，交换性 K 和 Ca 相对较低。体积密度值随年龄而变化，最高为 18 岁。23 年林龄以下的土壤容重低于其他林龄。可可种植园 5、10 和 18 年的总氮含量低于可可良好生长的临界值。土壤碳储量和土壤有效磷含量通常随着可可种植园的年龄而增加。这些土壤养分的差异变化，即总氮、速效磷、交换性钾、钙和镁在五个不同的可可种植年龄之间表明，总氮、速效磷和交换性镁高于可可良好生长的临界水平仅可可种植园不到 23 年，