No abstract

A study on the relationship between latex yield and antecedent environmental data was undertaken for five clones (RRII203, RRII118, RRIM600, RRII105 and GT1) of Hevea brasiliensis (rubber) in Agartala, northeast India, a region in which rubber is not traditionally cultivated. The explained variance for the regression equations based on parameters determined on the day of tapping and up to 3 days prior to it, varied from 72% to 37% during the NWT period and 94-83% during the WT period. Soil moisture storage, 1 and 3 days prior to tapping, was found to be the primary parameter affecting yield for the NWT and WT periods, respectively. It was observed that the clone RRII105, with a comparatively lower yield to that of RRIM600, was more susceptible to daily WD conditions during the non-winter season. RRIM600 and RRII105 being high-yielding clones were also found to be fairly dependent on the AT of the day prior to tapping. The mean lag period correlation of this parameter with yield was also found to be higher during the WT period than during the NWT period. As a whole, the mean lag period based on prior measurements of environmental variables showed optimum correlation with yield at 15-20 days prior to the day of tapping. The study also confirms that varied responses of yield with environmental factors in this non-traditional region of rubber cultivation depend on clonal character.

<div><table cellspacing="0" cellpadding="0" align="center"><tbody><tr><td align="left" valign="top"><p>Climate change   analysis has been conducted using daily surface meteorological datasets in   respect of nine parameters from five rubber growing locations in the East and   North-East India. Monthly, seasonal and annual variability in meteorological   parameters showed decreasing trends in relative humidity, sunshine hours and   pan evaporation rates coupled with increasing temperature extremes. Rise in   mean temperature was seen to be highest (0.34 0C per decade) for Dhenkanal   which experiences dry sub-humid type of climate. The data on relative humidity   and temperature also revealed the fact that warm surface temperatures, along   with limited moisture availability, may lead to lower relative humidity in   the future, since all the stations are away from the moist coastal belts.   Decreasing trends in sunshine hours were mainly observed during winter and   post monsoon seasons with decreasing number of days even with the optimum   required daily sunshine hours. The fact that there were no significant   changes in the amount of rainfall or the number of rainy days was in   conformity with several earlier reports in the northeast. Mean monthly   decadal variations have also been tested with earlier and recent sets. With   long term trends in most of the weather parameters, being lesser when   compared to that of the traditional rubber growing regions in India, it is   imperative that for rubber cultivation to thrive in this non-traditional   belt, future policy inputs will have to be based depending on the magnitude   of climate change effects.</p></td></tr></tbody></table></div>