Drought and coffee culture: what plant physiology has to explain - by Jose Alves Donizeti*
In view of this catastrophe that Brazilian coffee is going through, I would like to add some points that have not been discussed or if they have been that was made in a hypothetical manner.
Much has been said about the effects of drought in coffee growing. And I, sorry for the pun, do not want to "flog a dead horse". The fact that no one disputes is that this meteorological anomaly had not manifested itself in decades. At least in terms of strength and durability. Unfortunately this time it was accompanied by temperature and luminosity extremely high and occurred/occurs in phenological phases which are most demanding in terms of water temperature and adequate luminosity.
The practical consequences of all this have also been shown and discussed in this place. In terms of producing what you see is the leaf shriveling; small dehydrated fruits with detachment of parchment (hardened) from the seed, mummified malformed grains, high percentage of void grains. All these physiological abnormalities should be seen as QUITE HIGH. This is the fundamental difference of this drought with the ones in past years. In other words: without any intention of being alarmist or supporter of "the worse the better", the situation of Brazilian coffee culture this time is extremely serious. Obvious conclusion: 2014 season is strongly committed both in terms of quantity as quality. In my opinion, after visiting several coffee growing regions, I deduct that the loss will vary between 20-45% depending on the region.
In terms of vegetative growth, the drought and heat came at a time of full growth of leaves and branches. Therefore, that was also damaged. This is to say that the 2016 season will also suffer negative consequences of this drought. As the blooming phase (not flowering) will start in the coming weeks, we will probably have problems of induction of reproductive buds which will also reflect negatively on the 2015 harvest. But these are subject of further analysis.
Concerned about the current moment, my team went to the field (before the drizzle last week) to do a mapping of the coffee canopy measuring various physiological parameters in a horizontal gradient (the tip of the branches to the inner canopy, near the trunk) and vertical (the apex of the plants to the base of the leaves). Data is being compiled because they are objects of a dissertation, but preliminarily revealed interesting aspects and yet unpublished literature on coffee culture.
The leaves at 5am had an average temperature of 21° C (see that the night was hot) at 3pm this figure rose to 38° C. The temperature of the trunk at this same time on the base of the leaves was 33° C. These high temperatures will seriously compromise the photosynthesis, as will be seen later.
The hydroelectric potential which shows the degree of hydration of the plant, in other words, the water that can maintain work, measured at 5am was -1.1 MPa. That is to say the coffee tree did not recover during the night, the water lost during the day. This is because the amount of water stored in the soil was not sufficient for this. And to make matters worse, we detected intense death of rootlets. From noon until 3pm, the hydroelectric potential had become extremely low reaching values of -2.3 MPa . This value for certain crops mean "permanently wilting" or death of the plant. For coffee, according to numerous researches, it is a value that causes serious damage, such as, declining photosynthesis and translocation of carbohydrates, wilt and leaves falling, drought of the tips of the branches, roots death, decrease in the number and crop yield, amongst others. Most importantly, the coffee tree does not die, and with the return of the rains it regains its turgor. But the damage caused by the loss of dry matter (leaf falling, fruits and dried tips of the branches) are irreversible.
At 9am, photosynthesis, as expected, was the highest, but their value in the leaves from the base, was on average 64% lower when compared with those of the apex. Likewise, the innermost leaf canopy had photosynthesis 54% lower than those exposed to the sun. From that time, photosynthesis declined substantially and at 3pm, the region of the crown with maximum photosynthesis showed a 75% lower rate when compared to the same region photosynthesis at 9am. The inner leaves of the canopy as well as the lowest leaves showed photosynthetic rates near zero.
In summary, considering all the canopy of coffee culture, photosynthesis in most of the time operated in extremely unsatisfactory rates and certain moments even negatively. That means that the contribution of carbon for plant growth, which is equivalent to the bricks of a wall under construction, was minimal and in some cases were broken. And for those who understand at least a little of plants biochemistry will see that the carbon gain is enough just to maintain the plant alive. Very little or nothing will be left for plant growth, ie, if it was a new building site, it would not have walls and in some areas we would have demolished walls.
Based on these data now, responding to numerous inquiries that had been made to me, I think that even if the rains return, there will not be enough time (until the dry and cold season arrives) for the "fruit filling" and this equals to saying that this empty space, that many are observing when they cut the fruit crosswise, will no longer be filled, or if it is, will be very little. In conclusion, the yield loss at harvest, as many are empirically assuming will happen, for sure.
These placements of mine come in order to give satisfaction to people who ask me why I did not speak out until now. I did not, because it was collecting field data to be able to make the statement I made in the previous paragraph. To not prolong myself any further, in the coming days I will pursue the matter.
*Professor at the Federal University of Lavras. Degree in Agricultural Engineering from the Lavras Superior Degree of Agriculture, today Federal University of Lavras (UFLA), Masters in Plant Physiology from Federal University of Viçosa, PhD in Soils and Plant Nutrition from Federal University of Viçosa and Post-Doctorate from The Ohio State University and University of Missouri. In UFLA was Head of the Department of Biology, Coordinator and Sub - Coordinator of the program of Graduate Studies in Plant Physiology. In the Brazilian Society of Plant Physiology held the positions of Vice President, Treasurer, Chief Editor of the Brazilian Journal of Plant Physiology where he currently serves as Associate Editor. He was the President of the XIV Brazilian Congress of Plant Physiology held in Poços de Caldas from 09 to 12 September 2013. He has experience in the areas of Botany with emphasis on Plant Physiology, working mainly in the areas of nutrition and metabolism and physiology from the yield of coffee culture and plants under conditions of anaerobic stress. He is the current Coordinator of the Post-graduate program of Plant Physiology at UFLA.
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