EVALUATION OF SOIL FERTILITY STATUS AND NITROGEN FERTILIZER ON TEA (C. sinensis L.) YIELDS IN TANGA REGION, TANZANIA

Abstract

Tea yields in Lushoto district, Usambara mountain northeast Tanzania have been declining over the years, affecting economic development of the district and the country at large. The decline has been attributed to among others, poor soil conditions. The objective of this study was therefore to identify the soil related causes of yield decline and suggest/provide corrective measures towards improvement of yields in small holder farmers' fields. The study was first carried out through a survey, conducted on smallholder tea farms to gather information from farmers on nutrient diagnosis. Thereafter soil and plant tissue samples were collected for analysis to determine whether the present low tea yields are related to the status of soil fertility on the farms. Soil and plant tissue samples collected from different smallholder tea farms in the district were subjected to chemical and physical analysis – (i) soil: pH, total N, available P, K, Ca, Mg, S, EC, CEC, %OC, Al, Cu, Zn, Fe, Mn and texture (ii) plant tissue: N, P, K, Ca, Mg, S, Cu, Zn, Fe and Mn. The resultant data was statistically analysed and overall mean values checked against the Tea Research Institute of Tanzania (TRIT)’s set critical levels required for optimum tea yield. Nitrogen in soil and plant tissue macronutrient analytical results from the farms was below the critical set values also Phosphorus and Potassium in soil were below the critical values. Copper in soil and plant tissue micronutrient analytical results from the farms was below the critical set values. A field experiment was then set up as a second study to determine plant responses to fertilizer application Urea, Triple super phosphate and Muriate of potash. The experiment was a Randomized Complete Block Design (RCBD) replicated three times, laid out in a 4 x 8 factorial arrangement. The treatments consisted of four clones (K 7, K 35, 282 and 207) and eight nitrogen fertilizer levels (0, 40, 80, 120, 160, 200, 240, 280 kg N ha-1). During the short rain season: clones K 35, K 5 and 282 at N application of 160 kg N/ha yielded the best. In the long rain season; clone 207 at N rate of 120 kg N/ha yielded the best. Annual mean yield indicates that two clones were superior; K 35 and 282 together with N application rates at 120 – 160 kg N/ha. It was concluded from the study farmers’ field in four schemes were identified that the most limiting nutrient. On top of the list is nitrogen followed closely by phosphorus potassium and copper.