Changes in soil chemical properties and leaf nutrients content in tea due to nitrogen fertilizer rates and application intervals.

Abstract

Tea (Camellia sinensis (L.) O. Kuntze) plant, requires much more nitrogen than most of the other nutrients for its growth, development and sustainability of harvestable crop. Soil as a resource of plant nutrients, cannot continuously and adequately provide all the essential plant nutrients due to the high nutrient removal through harvesting and expected losses from erosion and leaching. Therefore, to sustain production, regular fertilizer application is essential. There has been speculation that the one year fertilizer application interval may be too close and that longer application intervals could give similar yields and reduce on high fertilizer expenditures. A study where nitrogen as NPK(S) 25:5:5:5 fertilizer was applied at the rates of 0, 60 120, 180, 240 and 300 kg N per hectare per year at 12 months and 24 months intervals at Michimikuru, Nyambene Hills and at Kangaita, Kirinyaga was conducted to verify the speculation. Physical and chemical characteristics of soils showed the Michimikuru trial site soil was medium textured (sandy loam), acidic (pH 4.57) with high organic matter accumulation and, exchangeable bases with low extractable manganese. The Kangaita trial site soil showed coarse texture (loamy sand), very acidic (pH 3.61), low exchangeable bases and organic matter content but high extractable manganese. The soil pH levels at Michimikuru decreased significantly (P≤0.01) with increase in nitrogen rates with 24 months application interval being less acidifying by 0.15 pH units compared with the 12 months interval. The levels of exchangeable cations were significantly (P≤0.01) high and manganese reduced in soil solution (P≤0.01) down the soil profile. There was adequate supply of all the required nutrients for uptake by tea in both application intervals. The results suggest that the soil and leaf nutrients, particularly, nitrogen was adequate for the growth, development and sustainability of the tea plant at the longer application interval at Michimikuru. Kangaita on the other hand indicated that soil pH and exchangeable cations decreased with increase in nitrogen rates, down the soil profile.