Mojor inorganic nutrients in soil from small scale tea farms and water and sediments from Sulal river, Bureti sub-county, Kericho county, Kenya.

Abstract

In a bid to increase tea yields, small scale tea growers do annual application of a blend of inorganic fertilizer containing nitrogen, phosphorous and potassium (NPK 26:5:5). The application is normally done on the onset of the short rainy seasons. These nutrients can get into the streams, rivers, lakes and oceans through surface run-off contributing greatly to water degradation and pollution problems. Thus, a study was conducted to assess the levels of chemical fertilizer nutrients in soils from small scale tea farms, water and sediments from the Sulal River. The samples were collected from an area stretching a distance of 12 Km to cover the source of nutrients application along Sulal River catchment area. Sampling was done during dry (January-February 2019) and rainy (October-November 2019) seasons. Samples were analyzed for nitrogen, phosphorous, potassium and selected physicochemical parameters of soil, water and sediments. Nitrogen, as nitrate-nitrogen (NO3–N) and phosphorous, as phosphate-phosphorous (PO4 ˉ P) were analyzed calorimetrically using Salicylic acid and Olsen methods, respectively. Potassium was determined using flame photometer. The levels of water and sediment quality parameters were compared with recommended levels for drinking water and likelihood for eutrophication set by Kenya Bureau of Standards, World Health Organization and Water Service Regulation Board, Kenya. Results were analyzed using IBM SPSS 20. The average levels during the dry and rainy seasons in soil samples for pH were 4.64±0.26 and 4.41±0.1, electrical conductivities were 187±45.79 and 253±23.76 μS/cm, % moisture content were 20.91±3.11and 36.38±2.20, nitrate-nitrogen were 0.68±0.20 and 0.58±0.20 mg/kg, phosphate-phosphorous were 0.14±0.08 and 0.38±0.17 mg/kg and potassium were 1.22±0.31 and 2.63±0.70 mg/kg. The average levels during dry and rainy seasons in water samples for pH were 6.72±0.00 and 6.38±0.21, dissolved oxygen levels were 6.78±0.59 and 9.58±0.64mg/L, electrical conductivities were 174±5.02 and 205±20.14 μS/cm, total dissolved solids were 92±4.59 and 120.70± 19.57 mg/L, nitrate-nitrogen were 0.58±0.21 and 1.19±0.22 mg/L, phosphate-phosphorous were 0.00±0.00 and 0.13±0.84 mg/L and potassium were 0.26±0.08 and 0.84±0.19 mg/L. The average results during the dry and rainy seasons in sediment samples for pH were 6.62±0.20 and 6.75±0.17, electrical conductivities were 67±6.66 and 52±10.19 μS /cm, % water contents were 116.96±3.95 and 129.84±5.00 %, nitrate-nitrogen were 0.70±0.35 and 0.42±0.23 mg/kg, phosphate-phosphorous were 0.49±0.25 and 1.14±0.40 mg/kg and potassium were 1.53±0.45 and 2.86±0.31 mg/kg. The levels of pH, electrical conductivity, dissolved oxygen, nitrogen and potassium in water and sediments in both seasons were within the maximum permissible limits set by KEBS, WHO and WASREB while phosphorous in water during rainy season were however, above the WHO (0.025 mg/L) and KEBS (0.030 mg/L) recommended limit for drinking and domestic use and WASREB (0.005 mg/L) level for likelihood of eutrophication. The study revealed the pollution status of Sulal River due to high levels of phosphorous of phosphorous. Availability of excess phosphorus can accelerate eutrophication in water bodies causing a reduction of dissolved oxygen, followed by death of aquatic organisms. The water from Sulal River may be used for irrigation purpose but not drinking and domestic purposes. Seasonal variation revealed significantly (p<0.05) higher nutrients in the rainy season than the dry season except for nitrogen and phosphorous in soil and nitrogen in sediment samples. This indicates that the seasonal changes are the major factors in the fluctuation of most of the analyzed physicochemical parameters in soil, water and sediments.