In a perennial plant such as coffee, consistent crop yield depends on the balance between vegetative and reproductive growth. Various external and internal factors influence the growth and performance of the coffee plant. External factors may be climate and edaphic such as light, temperature, rainfall, humidity, soil fertility, soil moisture and soil temperature whereas internal factors may be genetic. The coffee plants take nearly three years to develop from seed to first flowering to and fruit production. Arabica coffee plants can be economically productive for over 30 years while Robusta can be productive up to 60 years. However, they can be trained and maintained further with proper cultural operations and improved cultivation methods.
The pattern of shoot growth in coffee under south-west monsoon conditions is typically sigmoid with a slow growth from March/April to July and a period of rapid growth slows down with the onset of the dry periods from November and it will be minimal during December-February (winter period) and once again growth resumes in March after the receipt of summer showers.
Coffee leaves grow on a petiole in opposite pairs on the sides of the main stem and braches. The leaf shape is elliptical and veins are conspicuous. Arabica leaves are slender, succulent and delicate, whereas Robusta leaves are broad and thin. Leaf growth of coffee shows a periodicity with the maximum temperature range of 23 to 27C, a minimum temperature of 11 to 12C, high soil moisture and humidity, and optimal hours of sunshine however, a high temperature(above 27C) inhibits leaf expansion and causes formation of smaller leaves. Defoliation is generally observed observed during summer months, under water logging conditions, and also during fruit ripening stage.
Under South Indian conditions, flower bud initiation takes place from September onwards. The factors which influence the floral initiation are short day (less hours of day light), carbon/nitrogen (C/N) ratio, intermediate temperature and endogenous hormonal balance. High concentration of gibberllic acid during July/August tends to produce more vegetative growth and less induction of flower buds. Such a problem is observed in certain plant materials at high altitudes as well as in the areas which receive continuous precipitation. To improve the flower bud induction and the cropping nodes under excessive vegetative growth condition foliar application of mepiquat chloride at 1000 ppm concentration (4 l of chamatkar in 200 l of water) or 0.75% single super phosphate (SSP) at 1.5 kg per 200 l of water twice at monthly intervals, during August and September could be given. These treatments improve the crop yield significantly by enhancing flower bud production. After elongation (up to 7 to 8 mm), there will be cessation of growth for a few weeks till the receipt of blossom showers. A little bit at a faster rate, change colour and open in about 8 to 10 days after the blossom showers.
Floral abnormalities like ‘star flowering’ in Arabica and ‘pink flowering’ in Robusta can occur when the coffee plant is under stress. Stress conditions occur due to low humidity after flowing, prolonged high temperature and low rainfall. The conservation of soil moisture and its efficient use during the dry period will certainly avoid floral abnormalities like star flower, snake mouthed flower, pinking and paddying. Arabica is a self-pollinating plant which uses the pollen of the flowers from the same plant while Robusta plants use pollen from another plant (cross pollination). In both cases, successful fertilization depends on the meteorological conditions prevailing during the time of blossom. Strong rais or winds hinder pollination which results in a larger proportion of non-fertilized flowers.
Normally, a minimum of 3 to 4 months dry spell has been observed in the coffee tracts of south India. This affects the yield especially in the susceptible cultivars of Robusta coffee. improper and inadequate rainfall results in floral abnormalities in these cultivars. Irrigation is an important management practice to overcome the adverse effects of dry spells although excessive irrigation can adversely affect the yield. Early irrigation (before the full maturity of flower buds) can lead to floral abnormalities and running blossom which results in poor fruit set. Irrigation is an expensive operation and water resources are limited in many of the coffee estates, hence irrigating the plants at the correct time based on the needs of the plant in essential to increase the yield.
Growth of Arabica coffee fruits under South Indian conditions shows a bi-sigmoidal curve with two grand periods of growth during 120 to 150 and 180 to 210 days after blossom. The growth pattern in Robusta coffee is linear. Robusta coffee takes 6 to 8 weeks more than Arabica coffee for fruit maturity and ripening.
Premature Fruit Drop and Crop Yield
During the development stage of berries, premature fruit drop occurs between 90 to 120 days after blossom. The percentage of fruit drop varies depending upon the environment conditions (water logging or ‘wet feet’) as well as internal factors such as reduction in cytokinins coupled with high content of abscissic acid (ABA), reduction in carbohydrate content and nutrient deficiency. ‘wet feet’ observed in plantations is due to continuous heavy rainfall with cool ambient temperature, high relative humidity, cloudy weather and improper drainage leading to soil saturation and water logging. Multiple blossoms (running blossom) results in formation of different size berries, which increase premature fruit drop. Overbearing plants also show high percentage of fruit drop due to competition among the developing fruits.
Improving the root aeration by providing good drainage and cradle pits can help to maintain the normal physiology of plant to some extent. In addition, premonsoon application of plants growth regulators (PGRs) is useful in controlling the premature fruit drop and increasing crop yield by enhancing the internal concentration of growth promoters.
Foliar Application of PGRs
Among the formulations tried planofix agronna, Hormonol, Ascorbic Acid, Miraculan, ProtoZyme, Cytozyme crop plus Atonik (green magic) and vrudhi have shown significant mean yield increase of 130 to 212 kg cc ha-1 (11.9 to 19.4% yield increase over control) of Arabica coffee for four seasons when these growth regulators were given in two foliar application as post blossom .
(15 days after blossom) and pre-monsoon. The following concentrations of these formulations were found useful in increasing the crop yield.
The improvement in crop yield due to foliar application of these growth regulators was mainly on account of increased fruit set by 3 to 9%. Control of defolidation to the extent of 7% promotion of vegetative growth (which could be the cropping wood for the following year) and control of premature fruit drop by 8 to 12%. Further, treated plants showed less variation in yield for consecutive years. The application of these hormones did not affect the cup quality of coffee. Any one of these nine formulations could be used on coffee, since there were no significant differences in yield among the formulations. However, the cost of these formulations varies.
Compatibility of PGRs
Out of various PGRs formulations tested, planofix was found to be compatible. 50 ml of planofix can be mixed in 200 l of Bordeax mixture during pre-monsoon application.
Soil application of PGRs
For controlling premature fruit drop and defoliation ‘Biozyme’ at 10 g plant-1 along with NPK fertilizer could be applied during pre and post-monsoon period.
Suggestions for Minimizing Fruit Drop
· Improve the drainage by cleaning the cradle pits and trenches in the plantations.
· Apply of any one of the recommended growth regulators as per the schedule below:
First spray: 15 days after blossom
Second spray: pre-monsoon
· Carry out thinning of shade.
· Carry out desuckering and centering before May-June.
· Apply application of fungicides to diseases prior to monsoon.
· Remove of mulch to expose the soil around the plants.
During berry development, the bean disorders such as normal jollu (floats) during early endosperm filling stage, black jollu during mid-endosperm filling stage and black bean during endosperm hardening stage are observed in Arabica coffee. Normally, black bean disorder is reported to an extent of 2 to 10%.
The following factors could be responsible for the higher incidence of the bean disorders:
· Short supply or depletion of carbohydrate reserves during grand period of growth. Analysis of beans has shown less content of total sugars and starch in black bean compared to normal beans. Such depletion of reserves may be due to defoliation and consecutive high crop yield.
· High incidence of leaf rust due to skipping of Bordeaux mixture application or delayed application. This also causes leaf fall.
· Low light intensity due to overcast/hanging mist.
· Damage to the cropping wood due to hail storm.
· Soil saturation during 14 to 16 weeks after flowering.
· Skipping/reducing the fertilizer dosage based on the existing crop rather than anticipated next year crop.
· Lack of cultural operations like handling, centering, de-sucking and pruning.
· Maintenance of high shade.
Remedial Measures for Bean Disorders
· Two rounds of Bordeaux mixture as pre-monsoon and post-monsoon applications have to be given during May and September.
· The post-monsoon application of Bordeaux could be given along with urea 0.5% and muriate of potash 0.375% (1 kg urea and 750 g of MOP 200 l of water).
· The soil application of NPK at recommended doses should be given in 3 split doses during pre-monsoon, mis-monsoon, and post-monsoon application of phosphate or di-ammonium phosphate is beneficial.
· Proper pruning/desuckering /centering/handling and other routine cultural operations have to be carried out at appropriate time.
· Periodic shade regulation has to be carried out to maintain optimal day light of 40 to 50% (photosynthetically active radiations 900 to 1000 micro einstin).
· Regular weeding and plant protection operation have to be carried out.
These measure help in increased vegetative growth, leaf retention and maximizes the synthesis of carbohydrates and their transaction from leaves and wood to developing fruits which is turn decreases bean disorder.
Leaf to Fruit Ratio
Carbohydrates are necessary to produce vegetative growth (bearing wood for the next season) and also for the growth and development of the crop. The leaf to fruit ratio on coffea Arabica cv. S.795 and coffee canephara cv. S.274 was found to be 1:3 and 1:6 respectively. This ratio may vary from season to season depending on berry drop and defoliation. Studies further revealed that 17 cm2 and 27 cm2 of foliar areas were required to produce one fruit in Arabica and robusta respectively.
There should be proper balance between number of leaves and fruits in a plant. If the number of leaves and fruits are more than what the plant can sustain on plants and die-back in the next season. Therefore, there is a need for maintaining proper leaf to fruit ratio which will sustain the crop over a number of seasons without producing adverse effect on the health of the bush. Balance between vegetative and reproducing growth can be achieved through handling/pruning. However, nodes without leaves may sustain fruits, since carbohydrates are easily translocated from one region to another depending upon the quantum stored in the wood.
A simple method of measuring carbohydrate status
To know the status of carbohydrate reserves in plants, a simple method of visual scoring of starch has been evolved. The assessment has to be carried out either in pre-blossom periods or during monsoon.
The method to assess the starch index of the wood is as follows:
- Collect secondary or tertiary branches at random from the plants in the field. For an accurate assessment at least 10 branches should be collected from different plants in the same plot.
- After stripping off all the leaves, make a cut exactly in the middle of each inter node. Make a thin cross section from the cut end of the inter node with a sharp razor blade. Take cross sections from each internodes starting from any one end (top or bottom) of the branch and accordingly proceed one inter node after another.
- Take 5 ml solution of iodine reagent in a watch glass or petridish or any glass dish. Keep the wood section in this solution for 2 min. A blue colour as a percentage of the entire area with the help of starch index in the similar manner in all the internodes of the 10 branches.
- Calculate the approximate starch index of a branches as follows:
Total starch index of all the internodes
Number of internodes
- Preparation of iodine reagent: Dissolve 2 kg potassium iodide in 50 ml water and add to this solution 0.2 g iodine crystal. Finally make up the solution to 100 ml.
Inadequate and uneven distribution of rainfall causes drought conditions in coffee, which affects vegetative growth, induces floral abnormalities; results in poor fruit set and prolonged drought after fruit set increases production of more pea berries and ‘B’ grade beans and ultimately loss in crop yield. Plants vary in their capacity to constitution. High ‘osmotic adjustments’ occur in the drought depending on their genetic constitution. High ‘osmotic adjustments’ occur in the drought-tolerant cultivars through accumulation of solutes such as free proline, nitrogen, phosphorus, potassium, calcium etc. these compounds increase the bound water capacity, regulate stomatal movements, trigger water uptake, induce heat stability and maintain the integrity of the membrane.
Among coffee species, Arabica is more tolerant to drought than Robusta. The comparative decreasing order of tolerance among twelve selections of Arabica is as follows:
Among these Sln.7.3, Sln.9, Sln.10, Sln.4 and Sln.5B are highly tolerant and can be cultivated in drought prone areas.
Robusta coffee was found to be drought susceptible than Arabica coffee. Among Robusta, S.4040 (BR.9xBR.10) shows higher tolerance followed by Sln.3R (CxR), Sln.IR (S.275)and S.4042 (BR.9xBR.11).
Drought ameliorative measures
The coffee being perennial crop experiences depletion of soil moisture during dry period every year. Hence to mange growth, development and crop yield drought ameliorative measures play very important role. The following drought ameliorative measures enrolled at CCRI are found usefull for coffee.
- Nutrient mixture spray
Attempts have been made to overcome the effect of drought in Robusta coffee through osmotic adjustment. Field trials conducted for 7 years nutrient mixture in the following combination could result in overcoming the adverse effects of drought and also increase crop yield to an extent of 22%. Suggested concentration and schedule of spray are:
Nutrients mixture in 200 l of water
Urea (0.5%) :1 kg
Super phosphate (0.5%) : 1 kg
Muriate of potash (0.375%) :750 g
Zin sulphate (0.5%) 1 kg
- 1st spray:45 days after the last rainfall (2nd fornight of January)
- 2nd spray: 30 to 45 days after the first spray
- Spray solution: one litre per plant
- Lantana camera leaf extract’s spray
Foliar application of Lantana camera leaf extract at 1% twice at monthly intervals during second fortnight of January and February could be taken up. As studies on Robusta coffee in replicated multi-locational field trails for 4 years, increase crop yield significantly (p=0.05) by 252 kg ccha-1.
Preparation of Leaf Extract
Collect 2 kg fresh leaves of Lantana camera, chop them into small pieces and immerse in 10 l of boiled water and keep overnight (24h). Filter using a cloth and mix the filtrate with 200 l of water. The extract spray is applied to the plants concentrating on the lower surface of the leaves.
- 1st spray :45 days after the first rainfall
- 2nd spray :30 days after the first spray
(If the rainfall is not more than 15 mm)
Alternatively a foliar spray of 10% spray lime (Ca(OH)2) in combination with 0.5% starch (20 kg spray lime along with 1 kg starch in 200 l of water) could be given to the upper surface of the leaves, once after 40 to 45 days of last rainfall. The lime spray reflects the direct solar radiation thus, reducing leaf temperature and acts as a contact shade protection the leaves from chlorosis and scorching.
Preparation of Spray Solution
Finley powdered lime powder (Ca(OH)2) is sieved through a 0.3 mm mesh. 20 kg of this sieved lime powder along with 1 kg of starch is mixed in 200 l of water. This ensures the spray nozzles do not get blocked and that the solution adheres to the upper surface of the leaves.
Die-back refers to death of young tertiary branches which is a physiological disorder occurring during the dry period. The various aspects of the problem have been studied for more than a decade. These studies indicated that it occurs due to adverse environmental factors such as high temperature, high light intensity, low soil moisture and low relative humidity. Under controlled conditions of the glass house die-back symptoms were induced successfully, confirming thatth
Symptoms were induced successfully, confirming that these factors are responsible. Depletion of carbohydrate reserve was also found to be associated with the disorder.
Interveinal chlorosis and narrow start drying from the 3rd and 4th node progressing downwards as well as forward and also from apex and progressing downwards. Premature yellowing of leaves is the initial symptom.
Interveinal chlorosis and narrow crinkled small leaf formation (rosette type) usually occurs with abnormal branching after the onset of first summer showers.
The following remedial/control measures are suggested
- Removal of dead and whippy wood.
- Providing judicious shade of 50 to 60%.
- Pre-blossom and pre-monsoon spray of 0.5% boredeaux mixture.
- Conserving soil timely fertilizer application.
- Foliar application of nutrients.
- Lime application to correct the soil pH.