Temporal variability of tree litter fall, soil carbon stocks and hydrology of soils under different agricultural land uses

Abstract

The research was conducted at the crop plantations of Akenten Appiah Minkah University of Skill training and Entreprenuarial Development (AMUSTED – Mampong in the forest-savannah transition agro-ecological zone of Ghana. The objective of the research was to assess the seasonal variations in litter fall, soil carbon accumulation and hydro-physical properties of soils under different agricultural land use. The experiment was a 5 × 6 factorial, laid in a randomized complete block design, with 5 different land uses and 6 distinct seasons. The land uses were forest stand, cocoa plantation, coffee plantation, cashew plantation and mango plantation while the seasons were dry season 2016, major rainy 2016, minor rainy 2016, dry season 2017, major rainy 2017 and minor rainy 2017. A field test was conducted to measure soil bulk density, volumetric moisture content, total porosity, air-filled porosity, degree of saturation and aggregate stability of soils under the different land uses. Cumulative infiltration, infiltration rate, sorptivity, steady state infiltrability and saturated hydraulic conductivity were also evaluated. For carbon accumulation, quantity of litter fall, soc, soil carbon stocks and soil carbon sequestration were measured. A laboratory analysis was carried out to measure total nitrogen, phosphorus, pH, exchangeable bases like calcium, magnesium, potassium. Microbial biomass (Cmic, Nmic and Pmic), microbial quotient (qCmic, qNmic and qPmic) and microbial biomass ratios (Cmic/Nmic, Cmic/Pmic and Nmic/Pmic) were all measured. The bulk densities of soils under the different land uses were significantly different (p<0.05) from each other, in the order mango > cashew > coffee > cocoa > forest. Both the soil gravimetric and volumetric moisture content differed significantly among land uses, with cashew and coffee recording the highest and lowest values in both instances, respectively. Significant (p<0.05) seasonal variations in soil moisture were observed in the order MNRS2017 > MNRS2016 > MRS2017 > MRS2016 > University of Education,Winneba http://ir.uew.edu.gh xv DS2017 > DS2016. The study showed, significant difference in total porosity, airfilled porosity and degree of saturation of the different land uses and seasonal variations, with aeration decreasing with increased rainfall amount. Aggregate stability was significantly different among the different land uses and season. Aggregate stability gradually improved over seasons by 1.5 % to 11.1 % from season DS2016 to MNRS2017. Hydrological and hydraulic properties of soils under the different land uses were significantly different from each other. Seasonal cumulative infiltration amount and hydraulic conductivity of soils ranged from and 90.2 to 154.1 mm and 0.036 to 0.077 mm s-1, respectively. Litter fall significantly differed among the different land uses, forest stand (3.28 t/ha) and mango plantation (2.27 t/ha) recorded the highest and lowest. Significant seasonal variations of litter fall were recorded, with DS2017 (4.06 t/ha) and MRS2016 (1.80 t/ha) recording the highest and lowest, respectively. Soil carbon stocks and soil carbon sequestration was highest (48.04 Mg C/ha and 179.2 CO2 Mg/ha) and lowest (45.7 Mg C/ha and 167.7 CO2 Mg/ha) in mango plantation and forest stand, respectively. Total nitrogen, available phosphorus, potassium, magnesium, calcium and pH were significantly different among the different land uses. Soil microbial biomass (Cmic, Nmic and Pmic) which ranged from 151.3 to 323.8 mg/kg, 22.28 to 47.32 mg/kg and 7.89 to 25.5 mg/kg, respectively differed significantly among the different land uses and seasons. Microbial quotients (qCmic, qNmc and qPmic) decreased in the dry seasons (DS2016 and DS2017), while it was highest in the minor rainy reasons (MNRS2016 and MNRS2017). It is recommended that, mango, cashew, cocoa and coffee could be used to store and sequester as much carbon as the forest when they are properly managed. Coffee > cocoa > cashew > mango improved soil hydrological and hydraulic properties in this order of efficiency.