Abstract:
Most of the fields planted with clonal tea in Malawi are deficient in micronutrients. This was evident in leaf analysis data collected in 2007 from 170 mature clonal tea fields of some of the tea estates in Malawi, which showed very high incidences of B, Zn and Cu deficiencies. Current fertiliser recommendations have emphasised much on macronutrients, such as N, Pand K, but little attention has been paid to micronutrient elements despite continuous removal through harvesting. A study was therefore conducted to assess the effect of foliar applications of Cu, Zn and B containing fertilisers on yield and quality of mature clonal tea plants. Field experiments were laid out in randomised blocks in two fields planted with cultivars PC 105 and 108 at Mianga and Glenorchy estates in the Mulanje district in Malawi and were replicated four times at each site. The treatments were T1 (control, no spray), T2 [ 0.1% boric acid (190.8g B/ha)], T3 [1% copper sulphate solution (4.35kg Cu/ha)], T4 [1.25kg/ha zinc oxide (1kg Zn /ha)], T5 [0.1% boric acid, 1% copper sulphate solution, 1.25kg/ha zinc oxide], T6 [1% of Commercial micronutrient mix ( N 1.7%, P 2.3%, K 1.6%, Mg 0.25%, Fe 1288 mg/kg, Mn 1005 mg/kg, Zn 2182 mg/kg, Cu 732 mg /kg, B 8202 mg/kg, Mo 3681 mg/kg, kelp extract 75 mg/kg, amino acids 50 g/kg, phytofulvate 50 g/kg)], and T7 [2.48kg/ha zinc sulphate (1kg Zn /ha)]. Micronutrient foliar sprays affected yield significantly at Glenorchy tea estate, but had no significant effect on yield at Mianga estate. Copper sulphate solution applied at 1% concentration decreased yield, but the other foliar applications did not impact yield relative to the control at Glenorchy. Tea quality by taster’s scores was not affected at Mianga estate, whilst at Glenorchy quality was affected, with the commercial micronutrient mix giving the lowest total score. Individual parameters that contributed to the differences in total scores at Glenorchy estate included brightness, briskness, colour of liquor, colour of infusion and colour with milk. Thearubigin (TR) concentration was the only biochemical quality parameter that was affected by the micronutrient foliar sprays. The level of TR was increased in all treatments that received the foliar sprays and the control treatment gave the lowest amount of TRs at both sites. An increase in the Thearubigin/Theaflavin (TR/TF) ratio, obtained in all treatments that received the foliar sprays, provides evidence that more catechins were being converted to TRs than TFs during fermentation. Foliar levels of B, Zn and Cu were raised significantly by the application of the respective foliar sprays, except for the commercial micronutrient mix which did not significantly increase B and Zn levels at both sites, but raised Cu levels to the recommended level only at Mianga, but not at Glenorchy estate. Concentration of Cu was extremely high in tea leaves treated with copper sulphate either alone or in combination with boric acid and zinc oxide. Levels of other nutrient elements, namely N, P, K, S, Zn, Cu, Mg, Mn, Mo, Ca, Fe, B, Al and Na in the soils where different foliar sprays were applied were similar at both sites. Likewise, foliar levels of N, P, K, S, Zn, Cu, Mg, Mn, Mo, Ca, Fe, B, Al and Na were not different in all plots at Mianga, but at Glenorchy differences in foliar levels of Al and S were noted. High concentrations of Al and S in the leaves were observed in plots that received copper sulphate applied alone. High foliar concentrations of Al and Cu in leaves treated with copper sulphate could be the reason for the low yields obtained in the plots treated only with copper sulphate at Glenorchy estate. Foliar application of Cu, Zn and B in forms of 0.1% boric acid (190.8g B/ha)], 1% copper sulphate solution (4.35kg Cu/ha)], [1.25kg/ha zinc oxide (1kg Zn /ha)], 1% of a Commercial micronutrient mix (N 1.7%, P 2.3%, K 1.6%, Mg 0.25%, Fe 1288 mg/kg, Mn 1005 mg/kg, Zn 2182 mg/kg, Cu 732 mg /kg, B 8202 mg/kg, Mo 3681 mg/kg, kelp extract 75 mg/kg, amino acids 50 g/kg, phytofulvate 50 g/kg), and 2.48kg/ha zincsulphate (1kg Zn /ha) to mature clonal tea did not significantly increase yields and tea tasters scores, therefore their application to clonal tea with the aim of improving yield and quality may not be necessary. Results from this study indicated that clonal tea, specifically cultivars (PC 108 and PC 105), could not give positive results in terms of yield and quality of tea due to foliar application of Cu, Zn and B within the first season of application. However, if application is aimed at raising concentrations of Cu, Zn, and B, then boric acid, zinc sulphate, zinc oxide and the commercial micronutrient mix may be used without negatively affecting yield and quality of tea significantly. Copper sulphate however, at the application concentration and frequency used, should not be done because of the observed yield decline in copper sulphate treated plots. More prolonged research is required to determine if long term applications can correct perceived deficiencies and increase yield.
