Nitrogenous Fertilizer Application Rates and Plucking Intervals on Tea [Camellia sinensis (L.)] in Eastern Africa: Changes in Soil Calcium, Magnesium and Manganese Levels

Tea production requires high rainfall areas that cause nutrients depletion through surface run-off, leaching, and removal with crop. This makes application of fertilisers mandatory to replenish the nutrients. However, such applications could cause soil nutrients imbalance. Harvesting frequency cause variations in yields. Despite variations in environmental factors recommended fertilizer use is similar while harvesting frequency varies between 7 to 14 days. Fertilizer use and plucking are major agronomic inputs that may influence crop yields and soil nutrients removal. The objective of this study was to determine the influence of rates of NPKS 25:5:5:5 fertilizer and harvesting intervals on soil calcium, magnesium and manganese levels in Eastern African tea soils. Samples were obtained from fertilizer trials on clone TRFK 6/8 at three, two and three sites in Kenya, Tanzania, and Rwanda, respectively, from a 5 nitrogen rates by 3 harvesting frequency factorial trials replicated three times at each site, at 0-10, 10-20, 20-30, 40-60 cm soil depths. The nutrients were determined using ICPAES. Higher rates of nitrogen fertilizer increased (p≤0.05) soil Mn levels but reduced (p≤0.05) Ca and Mg soil levels. Thus, long term use of nitrogenous fertilizers could cause nutrients imbalance that may make tea production uncertain as these nutrients are not controlled through supplementation. Harvesting frequency did not influence soil Ca, Mg and Mn levels at all sites. The nutrients levels varied (p≤0.05) with location of production. Despite the variations the nutrient levels were still optimal and therefore not constraining tea production. These results suggest need for proper management of these nutrients to ensure continued high tea production.