Excessive heat due to climate change shrinks cotton boll size

MULTAN: The cash crop is extremely sensitive and cannot tolerate frost or temperatures exceeding 35°C. However, climate change and the resulting scarcity of green clusters are the primary threats to this single-crop economy.

The climate change, excessive temperatures and heat have badly affected the cash crop cotton and variations have appeared in cotton boll size in the current crop season, agriculture experts said. Yield and quality are adversely affected by periods of extreme heat (daily maximum temperatures greater than about 35°C).

High temperatures during the day or night reduced yield by limiting the availability of assimilates to support fruit growth causing shedding of squares and young bolls and lowering the number of seeds set per boll. At high temperatures, many biological processes no longer have the same responses to changes in temperature as they do at moderate temperatures. When air temperature and sunlight heat cotton plants they attempt to maintain optimum growing temperatures by opening stomata in the leaves, allowing water to pass out and evaporate and cool leaves. If leaf temperatures rise above 32ºC during the day, this slows the function of plant enzymes for photosynthesis and growth. Night temperature is also important for optimum cotton growth. Warm nights (above 26ºC minimum) mean that leaf temperature remains high, and respiration remains high, consuming stored assimilates that would have been used for additional growth. Small bolls with uneven seed numbers between the locks caused by poor pollination /seed set particularly in one lock. High temperatures reduce the viability of the pollen at flowering. This reduces boll size and can reduce yield. There are no known studies to show if the plant compensates for parrot beak bolls by having other normal bolls grow bigger.

Talking to The News, Punjab Agriculture Directorate of Information Director General Naveed Asmat Kahloon said that production increased due to strategy and collective efforts but excessive heat has badly damaged cotton boll size across Punjab. The Crop Reporting Service Wing of the Punjab Agriculture Department has estimated the cotton production data till July 31.