Variation in Soil Organic Carbon and Total Nitrogen Content in Different Agroforestry Practices of Moshi Rural District, Northern Tanzania

The variation and amount of carbon and nitrogen sequestered in agroforestry systems depends on the type of agroforestry practices, its condition and its characteristics.This study aimed to examine variations in Soil Organic Carbon (SOC) and Total Nitrogen (TN) with soil depth across Agroforestry Practices.A total of 105 plots (quadrants) measuring 10 m x 10 m were established along transects in three villages (35 quadrats in each village) in Moshi rural district, northern Tanzania.Soil samples were collected at three points along the diagonal of the quadrat using a soil auger.Soil sampling cylinders with a diameter of 6 cm and a height of 4.5 cm were used to collect volumetric soil samples for the estimation of bulk density.Soil organic carbon and total nitrogen were determined by Walkley and Black wet oxidation and Micro-Kjeldahl methods and expressed in tCha-1 and percentage (%), respectively.Variations in SOC and TN in different AFPs were determined by ANOVA in R software.The ratios between SOC and N in different AFPs were determined by regression analysis and subjected to ANOVA for a multiple-means comparison test.Variation in SOC and TN in the different AFPs was determined by ANOVA in R software.The amount and vertical distribution of SOC and TN across soil depths among Agroforestry Practices differed significantly (P<0.05).Coffee Intercropped Agroforestry Practice had significantly higher SOC at 0-20 cm depth compared to other AFPs (P < 0.05).However, TN in Coffee Intercropping Agroforestry Practices (CIAP) differed significantly with only Boundary Planting Agroforestry Practice (BAP) (P < 0.05).The amount of SOC and TN in CIAP differed significantly (P<0.05) with BAP and MAP at 20-40 cm.Soil Organic Carbon (SOC) was positively related to Total Nitrogen (TN) in the 0 -20 cm and 20 -40 cm depths (P=0.049, = 0.26 and P=0.0003, =0.42)respectively and was significant.The current study confirms that integrating coffee into agroforestry practices has a direct positive contribution to SOC and TN.Management practices in agroforestry systems should thus aim to encourage the maintenance of coffee in farmlands to ensure a stable amount of organic carbon and nitrogen in the soil.