THE EFFECTS OF FERTILIZERS ON SOIL ECOSYSTEM HEALTH IN TOBACCO FARMS IN MIGORI COUNTY, KENYA

Abstract

Tobacco cultivation is associated with soil degradation because the crop is a heavy soilnutrients consumer. Due to this, there is a tendency of using excess inorganic fertilizers to curb the deficit, thus affecting the soil ecosystem health. Use of inorganic fertilizers in tobacco production may also affect the quality of the soil. This study was carried out to determine the effects of fertilizers on soil ecosystem health in tobacco farms in Migori County, Kenya. The specific objectives were: to determine the effects of fertilizers on soil biodiversity; to examine the effects of fertilizers on soil chemical characteristics; to assess the effects of fertilizers on tobacco yield; and to evaluate the soil ecosystem health of tobacco farms. A RCBD field-experimental study was laid in Mabera, Bondo, Kakrao, and Masaba sites on plots measuring 10 m2 with three replicates. Fertilizers used were: inorganic fertilizers (DAP and CAN) (T1) at a recommended rate of 60 kg P/ha and 30 kg N/ha and organic fertilizer (T2) at recommended rate of 4t/ha; and Control (T0) (0 kg P/ha and 0 kg N/ha). Tobacco variety 583V was grown. Data were collected on soil microbial count, weed count, soil pH, available P, total N, soil organic carbon, tobacco yield, Soil Quality Index, and on Ecosystem Health Index. Serial dilution method and microscopy were used to determine bacteria and fungi colony forming units respectively. A 1 m2 quadrat was used to identify and count weed species and their diversity determined by the Shannon Weiner Diversity Index (SDI). Soil was analyzed using the following methods; pH (1:2.5 H2O), total Nitrogen (Kjeldahl), soil organic carbon (Walkley and Black), and available Phosphorous (Olsen). Leaf priming method was used for harvesting tobacco leaves for yield determination. Soil ecosystem health was determined by Soil Quality Index and Ecosystem Health Index. Data were analyzed using GLM and subjected to ANOVA using GENSTAT, and means separated using Tukey’s (p≤0.05). Gram-positive level in VL samples was 3.354 CFU ml-1 in Bondo, while Masaba recorded 3.485 CFU ml-1 . The highest levels of Basidiomycetes species were recorded in Bondo (7.349 CFU ml-1 ) under T2 before harvest. Under virgin land across the sites, Digitaria scalarum was high with an SDI of 0.159 in Bondo. The highest number of Galinsoga parviflora counted was recorded in T2 (SDI = 0.154). Organic fertilizer (T2) improved soil available phosphorus in Kakrao (9.79 to 9.90 mg/kg of soil) before and after harvest. Treatment T2 recorded a significantly high (p≤0.05) tobacco leaf yield in Bondo (2.740 t/ha). Both Soil Stability Index and Microorganisms Community Dynamics Index values under T2 in Masaba and Mabera were greater than 40, indicating they are ecologically high functioning. Organic fertilizer had a positive effect on the soil microbial diversity and activities, while inorganic fertilizer (T1) resulted into the highest weed diversity. Application of organic manure exhibited high Soil Quality Index and Ecosystem Health Index. Organic fertilizer uses at 80 kg P/ha and 30 kg N/ha in tobacco cultivation improved and preserved soil ecosystem health, hence increased yield.