Nitrogenous Fertilizer Application Rates and Plucking Intervals on Tea (Camellia sinensis (L.) in Eastern Africa: Effects on Soil Nitrogen, Phosphorous, and Potassium
Robert O. Ombori *
Department of Chemistry, School of Physical and Biological Sciences, Maseno University, P.O. Box 333 - 40105, Maseno, Kenya.
P. Okinda Owuor
*
Department of Chemistry, School of Physical and Biological Sciences, Maseno University, P.O. Box 333 - 40105, Maseno, Kenya.
Bowa O. Kwach
Department of Chemistry, School of Physical and Biological Sciences, Maseno University, P.O. Box 333 - 40105, Maseno, Kenya.
David M. Kamau
Environment & Natural Resource Systems, KALRO Secretariat, P.O. Box 57811 – 00200, Nairobi, Kenya.
Wilson Dufitumukiza
Rwanda Agriculture and Animal Resources Development Board (RAB), Rwanda, P. O Box 5016, Kigali, Rwanda.
Solomon W. Msomba
Tea Research Institute of Tanzania, P.O. Box 2177, Dar Es Salaam, Tanzania.
*Author to whom correspondence should be addressed.
Abstract
Eastern Africa tea grows in high rainfall areas where nutrients depletion through leaching, surface run-off in addition to removal with crop can be high. Nutrients replenishment through fertilizer applications is therefore necessary. The recommended fertilizer application rates and harvesting intervals for tea in Eastern Africa are uniform despite varying environmental factors. These varying environmental factors, nitrogen fertiliser and plucking intervals caused variations in tea yields, quality and leaf nutrients. However, comparison of levels of macronutrients (N, P, K) levels and if the macronutrients levels and influenced by rates of nitrogen fertiliser and plucking intervals in the eastern Africa tea soils have not been documented. The effects of NPKS 25:5:5:5 fertilizer rates and plucking intervals on soil nitrogen, phosphorous and potassium in Eastern Africa were evaluated. Soil samples were obtained from fertilizer trials laid out as 5x3 factorial design replicated three times at each site (Timbilil, Changoi, Arroket (Kenya), Maruku, Katoke (Tanzania), Kitabi and Mulindi (Rwanda)) on clone TRFK 6/8 tea. The rates of nitrogen fertilizer were 0, 75, 150, 225 and 300KgN/ha/year while plucking intervals were7, 14 and 21 days. Soils were sampled at 0-10, 10-20, 20-30, 40-60 cm soil depths. Soil N was determined by Kjeldhal method while P and K using ICP-AES. These results demonstrate that although these soil are classified tea growing areas, soil nutrients levels vary widely. Plucking intervals had no influence on soil N, P, and K levels at all sites, demonstrating the plucking interval is not a major factor causing changes in soil nutrients levels. Increasing nitrogen rates increased (p≤0.05) soil N and P levels but lowered (p≤0.05) soil K. Continuous use of high rates of nitrogenous fertilizers may require remedial application of K to ensure optimal levels are available to tea plants. These results demonstrate that soil deficiencies in N and P can be corrected by application of NPKS 25:5:5:5. However, regular checks on soil K levels are necessary when using NPKS 25:5:5:5, as this may trigger K deficiency. The deficiency can be corrected by remedial K application. The levels of the nutrients varied (p≤0.05) with location of tea production. However, levels were optimal for tea production. The variations in the macronutrients with location of production demonstrate that it may be difficult to set soil nutrients norms to guide fertiliser use advisory systems.
Keywords: Nitrogen rates, plucking intervals, soil nitrogen, phosphorous and potassium