Estimation of Deep Drainage below the Root zone of a Fertigated Tea Plant under High Rainfall Conditions.
Aruliah Anandacoomaraswamy, Tea Research Institute of Sri Lanka, Talawakele, Sri Lanka and Glendon W. Gee, Battelle, 3200 Q Ave., Richland, WA 99354.
Tea plant is a perennial crop from which the beverage tea is obtained. It is grown in well drained soil in an undulating terrain and under very high rainfall conditions (>2200mm annual rainfall). There are about 12500 plants in one hectare. The roots are mianly confined to the top 45cm. Though the annual rainfall is more than adequate for successful cultivation of tea, there are months with very low rainfall. Therefore, fertigation is practiced to improve the yield and reduce the fertilizer use. Two studies were conducted to estimate the deep drainage and amount of nutrients lost with the drainage. First study was at Somerset Estate, Nanuoya (1450m AMSL) and the second one was at. St Coombs Estate, Talawakele (1380 m AMSL). In the first study, deep drainage and nutrients leached were measured from 2002 to 2005. Water Balance for the study area was done at monthly interval taking into rainfall, irrigation, evapotranspiration and deep drainage. The nutrients mainly N , K and Mg leached were estimated from water samples collected from the water flux meter In the second study, a more detail measurements were made for soil evaporation (lysimeter), transpiration ( heat pulse method), rainfall and irrigation and deep drainage (Water Fluxmeter) and change in soil moisture storage. The results have shown that more than 50% of the rainfall is lost as deep drainage on annual basis. However, during dry weather, there was no deep drainage. Results also revealed that there is substantial loss of nitrogen as NO3-N and very little potassium.