Long term effects of nitrogenous fertilizers on tea yields, nutrients uptake and some soil chemical properties

Abstract

A field experiment was set up to determine long tenn responses of different rates of nitrogen fertilizers namely used in tea, N~KS 25:5:5:5 and NPK 20: 10: 10, on tea 'Ields, nutrient uptake and soil chemical properties. The experiment also aimed at establishing whether tea plant would benefit nKJrefrom NPK20: 10: 10 or NPKS 25:5:5:5 fertilizer formulation. Mean tea yields and eafnitrogen over the sixteen year period, 6 to 2001, were not affected by ferti lizer :ormulation. Similarly, leaf sulphur content ,as unaffected by fertilizer type. However, ,jf and soil phosphorus and potassium 1ntents were significantly higher in the WK 20: 1 0: 10 formulation compared to WKS 25:5:5:5. The NPKS 25:5:5:5 mnulation acidified the soil more than the WK20:1O:1O at up to the 60 cm depth. Soil ,iailable phosphorus and potassium were :i!her in the NPK 20: 10: 10 fertilizer at all dour depths. Nitrogen fertilizer rates gave significant Jadratic yield responses with peak yields .the 300 kgN ha-I rate in both fertilizer 'xs, Nitrogen uptake from the leaf nutrient :~had a similar pattern and indicated that :vond the 300 kgN ha.1 rate, the nitrogen ,elsdld not change implying that the extra qgenadded was not utilized as efficiently mttea plant. While leaf phosphorus and ,1,1ssJUm decreased in a quadratic manner :h mtrogen fertilizer rates, leaf sulphur lent was not affected. The implications Jsmg either of the two fertilizer "1ulations m tea production are discussed.