A Comparison of the Responses of Mature and Young Clonal Tea to Drought

Abstract

To assist commercial producers with optimizing the use of irrigation water, the responses to drought of mature and young tea (Camellia sinensis) crops (22 and 5 years after ®eld planting respectively) were compared using data from two adjacent long-term irrigation experiments in southern Tanzania. Providing the maximum potential soil water de®cit was below about 400±500 mm for mature, and 200±250 mm for young plants (clone 6/8), annual yields of dry tea from rainfed or partially irrigated crops were similar to those from the corresponding wellwatered crops. At de®cits greater than this, annual yields declined rapidly in young tea (up to 22 kg ha 71 mm 71 ) but relatively slowly in mature tea (up to 6.5 kg ha 71 mm 71 ). This apparent insensitivity of the mature crop to drought was principally due to compensation during the rains for yield lost in the dry season. Differences in dry matter distribution and shoot:root ratios contributed to these contrasting responses. Thus, the total above-ground dry mass of well-irrigated, mature plants was about twice that for young plants. Similarly, the total mass of structural roots (>1 mm diameter) to 3 m depth was four times greater in the mature crop than in the young crop and, for ®ne roots (<1 mm diameter), eight times greater. The corresponding shoot:root ratios (dry mass) were about 1:1 and 2:1 respectively. In addition, each unit area of leaf in the canopy of a mature plant had six times (by weight) more ®ne roots available to extract and supply water than did a young plant. These results show that young tea should be irrigated in preference to mature tea, especially where the maximum soil water de®cit is likely to exceed 250 mm. introdutionThe irrigation of commercial tea (Camellia sinensis) estates in the Mu®ndi district of the southern highlands of Tanzania was initiated in the 1970s. It followed the demonstration of yield and other advantages to be gained by applying water during the annual six months of dry weather (Carr, 1974). Currently about

Ecophysiology of tea

“…Accordingly, tea yield would also reduce below this threshold as observed, for example by Carr (1971b). Reduction of tea yields during prolonged dry periods have been observed by many workers in several tea-growing regions of the world (Carr, 1974;Carr et al, 1987;Stephens and Carr, 1991a;Othieno et al, 1992;Burgess and Carr, 1993;Nixon et al, 2001;De Costa and Surenthran, 2005).…”

“…In a detailed study, Nixon et al (2001) showed a clear difference between young (i.e. five-year-old) and mature tea (22-year-old) in their susceptibility to drought and response to irrigation.…”

“…The lower sensitivity of annual yields of mature tea was primarily because it was able to compensate for part of the yield loss that occurred during the dry period by having a substantially higher yield during the wet period of the year. Nixon et al (2001) related the differential responses of young and mature tea to variation in their root systems and shoot-root dry matter partitioning. Interestingly, mature tea had four times more structural roots (> 1 mm diameter) and eight times more fine roots (< 1 mm diameter) than young tea.…”

High Fertilizer Rates Increase Susceptibility of Tea to Water Stress

“…Yield losses due to drought vary with location, but available data gives a range of 14-20% in Kenya (Ng'etich 1999;Ng'etich et al, 2001), 33% in Ngwazi in Tanzania (Nixon et al, 2001), 26% in Sri Lanka (Wijeratne, 1996), 17% in Siligur and 31% in Tezpur, both in India (Panda et al, 2003). Besides the yield loss, drought frequently leads to plant deaths.…”

Effect of Total Solar Radiation and Rainfall on Yield of Different Tea (Camellia sinensis [L.] O. Kuntze) Clones at Two Sites in Kenya

“…For solar radiations above 350 Wm -1 require 700-800 Wm -1 , a value equivalent to full sunlight in the cooler seasons of many high altitude tea areas, and account for 75% of full sunlight in the warmer rainy seasons. The factors that have been documented to limit yield include: removal of young shoots (Tanton, 1979), air temperature (Ng'etich, Stephens, & Othieno, 2001); Tanton, 1982a;, soil temperature confounded with dry air (Tanton, 1982a;Odhiambo, Nyabundi, & Chweya, 1993;Chen & Fong, 1994;Nixon, Burgess, Sanga, & Carr, 2001), hail (Ng'etich et al, 2001;Othieno et al, 1992), day-length (Tanton, 1982b), soil temperature (Ng'etich et al, 2001) and solar radiation (Squire, 1977). Falling temperatures and soil physical and chemical conditions greatly limits tea yield (Ng'etich et al, 2001).…”