Title : Impact of varied rates of NPK fertilizer on the essential and non-essential mineral elements of indigenous tea (Jatropha zeyheri) of South Africa under field conditions
NPK fertilizer application on plants could have adverse effects on test crops when applied inappropriately. Fertilization of NPK is a key factor influencing tea's physiological, physical and chemical qualities. However, the influence of NPK on essential and non-essential mineral elements of J. zeyheri indigenous tea has not been documented. Therefore, the objective of this study was to assess NPK fertilizer’s effect on essential and non-essential mineral elements in J. zeyheri leaf tissues under field conditions. At a two-leaf stage, J. zeyheri seedlings were transplanted into 25 cm diameter plastic pots. Each pot was filled with heated-pasteurised sandy soil and Hygromix at a 3:1 (v/v) ratio and placed in a spacing of 0.30 m × 0.30 m inter-and intra-row spacing. Six treatments constituting NPK fertilizer rates (0, 2, 4, 8, 16 and 32 g) were arranged in a randomized complete block design, with 5 replications. The samples were prepared using a microwave digestion system. Essential minerals (Fe, P, K, Mg, Ca, Cu, Mn, and Zn) and non-essential mineral elements (Al, Co, Cr, Cd, Na, Pb, Ni and As) were determined using an Inductively Coupled Plasma Emission Spectrometer (ICPE-9000). Treatments were initiated a week after transplanting, and 130 days after that, NPK fertilizer rates had significant effects on essential mineral elements NPK fertilizer rates had significant effects on Ca, Fe, Mn and P contributing 49, 63, 62 and 72% in TTV, respectively. However, NPK fertilizer rates did not have significant effects on K, Mg, Cu and Zn. Significant effects were observed on non-essential mineral elements, Al, Na, Cd, Co, Cr, As and Ni contributing 50, 71, 62, 70, 61, 49 and 63% in TTV, respectively. However, NPK fertilizer rates did not affect Pb in J. zeyheri leaf tissues. The results of the current study indicated that J. zeyheri is a great source of essential and non-essential nutrient elements. This study found that moderate NPK application was sufficient for enhanced accumulation of J. zeyheri tea leaf mineral elements. Fertilizer requirements for J. zeyheri tea leaf tissues were optimized at 4.10 g fertilizer mixture/plant for essential mineral elements and 2.71 g for non-essential mineral elements, which translates to 41 and 27 kg NPK fertilizer mixture/ha, for essential and non-essential mineral elements, respectively. The results suggested that NPK fertilizer should be applied at low rates to enhance the accumulation of mineral elements in leaf tissues.
Keywords: Fertilizer, indigenous tea, Jatropha zeyheri, mineral elements, tea quality