EFFECT OF HARVESTING METHODS AND NPK FERTILIZER ON SOIL pH, SOIL AND LEAF MAJOR NUTRIENTS CONTENTS AND YIELD OF TEA IN TANZANIA

Abstract

Tea (Camellia sinensis, (L), O. Kuntze crop in Tanzania has been traditionally harvested by hand. In recent years, high cost and shortage of labour have compelled tea growers to opt for mechanical harvesting. Mechanical harvesting is becoming very important and is considered vital for survival of the tea industry. However tea growers have reported decline in yield after some years of mechanical harvesting and there is a notion that nutrients lost through the harvested crop differ from hand harvested tea. Thus there is need to replenish nutrients lost through harvested crop which is different from hand harvested tea, however to replenish soil nutrients in mechanical harvested tea, growers are applying the same fertilizer rates as in hand harvesting method. The objective was to determine the effect of tea harvesting methods (hand and mechanical) and NPK fertilizer on soil pH, major nutrients (NPK) uptake, tea yield components (shoot weight, shoot type composition) and yield. The study had two parts. First a survey was conducted on tea estates (Ngwazi, Itona and Itambo) where both hand and mechanical harvesting had been practiced for more than three years. Soil and leaf samples were collected for soil pH, soil and leaf major nutrients (NPK) analysis. Yield data were used to compare yield trend in hand and mechanical harvesting. In the second part, two experiments were set at the Tea Research Institute of Tanzania stations (Marikitanda and Ngwazi) using randomized complete block design (RCBD) with split-plot arrangement. Experiments were conducted for 10 and 8 months at Marikitanda and Ngwazi respectively. Hand and mechanical (shear) harvesting formed the main plots and the six fertilizer rates (0, 50, 100, 150, 200, 250 kg N/ha) the sub-plots. NPK 25:5:5 fertilizer was applied once. Soil and leaf samples were analyzed for soil pH, soil and leaf major nutrients (NPK) contents. Yield, shoot count and shoot weight data were recorded. Results showed that, tea in mechanical method had higher soil pH and K uptake by tea plants. Tea plants in hand method had higher uptake of N and P. Mechanical method had significantly (p<0.05) lower shoot weight and had higher proportions of mature leaf and broken leaf (low quality greenleaf). Yield was significantly (p<0.05) higher in mechanical than hand method. The interaction between harvesting methods and fertilizer rates on shoot weight was not significant. Effects of fertilizer rates showed that, soil pH decreased with fertilizer rates, soil nutrients uptake increased with fertilizer rates but declined at high rates: At Marikitanda Tea Research Station, nitrogen declined at 250 kg N/ha, phosphorus at 250 kg N/ha and potassium at 150 kg N/ha. At Ngwazi Tea Research Station, nitrogen declined at 250 kg N/ha, phosphorus at 200 kg N/ha and potassium at 200 kg N/ha. Shoot weight increased with fertilizer rates but not significantly. At both experimental sites, shoot weight declined at 250 kg N/ha. Yield increased with fertilizer rates but declined at high rates: At Marikitanda Research Station, the yield declined at 200 kg N/ha, at Ngwazi Tea Research Station it declined at 250 kg N/ha. Only at Marikitanda did fertilizer rates showed significant (p<0.05) difference. There was no significant difference in fertilizer rates between hand and mechanical harvesting. The interaction between harvesting methods and fertilizer rates on yield was not significant. It is recommended that during the first few years (≤ 3) same rate of fertilizer should be applied in both hand and mechanical harvesting, this study should be continued in order to further assess the effects of harvesting methods on soil pH, nutrients uptake and yield