Key Role of Humic acid in Growth and Development of Arabica Coffee in South India.

Humatesis the purest form of natural organic matter formed as a result of decomposed prehistoric plant and animal matter. Humates contain fulvic, humic, Ulmicacid and lignin. Leonnoditeis the most commonly occurring humateore which is yellow to dark brown in color.

Benefits of humates

Humate is one of the most powerful natural antioxidants and free radical scavengers. Residual pesticides, herbicides and fertilizers are bound to compounds like lignin. This is then broken down by the beneficial microbes present in the rhizosphere to be taken up by the plants.

Major portion of humic acid is in carboxylic acid functional groups which endows these molecules with the ability to chelate (bind) positively charged multivalent ions like Ca++,Mg++,Fe++ and other trace elements. Thereby making the nutrients available in the soil to the plant roots by breaking down into absorbable forms

Humate is a complex energy source of acids and oxygen vital for stimulating microbial activity.

Positive Role of Humic Acid

Increased leaf chlorophyll index and luster of the leaves.

Increased leaf area compared to the preceding leaf.

Increased feeder roots at the root zone which help in better absorption of nutrients.

All the above factors help in increased food production which in turn helps in better health condition of the plants.

Field Experiments At Melkodige Plantations

A field trial was conducted at Melkodige group of Estates , located in South India, to observe the benefits of humic acid on coffee Arabica. Humic acid was applied twice a year. The first application of 12% humic acid solution was sprayed on to the urea and DAP granules and raked to ensure uniform coating and applied at the rate of one litre per acre.

The second application of 12% humic acid was done post monsoon (sept-oct) along with foliar, micronutrients and fungicide spray at the rate of 200 ml per barrel.

A control plot was also maintained with regular two rounds of basal dose of fertilizers and two rounds of fungicide sprays without the application of humic acid.


To illustrate the potential of humic acid, best yielding plants were randomly selected in the experimental as well as control blocks and observed for the following parameters leaf area, leaf lustre, number of bearing nodes in a primary, number of berries in a bunch and weight of berries.

A fortnight after the application of humic acid there was a marked increase in leaf chlorophyll index, the leaves turned dark lustrous green. There was a significant increase in the leaf area of emerging leaves in all varieties compared to the previous leaves in treated plants as well as control plants.

Table-1 Leaf Area in humic acid treated blocks

157.25 180 198 105
157.5 136 236.5 90
185.25 161.5 199.5 105
170 144 241.5 91
190 152 264 122.5
153 180.5 264 94.25
170 153 280.5 104
AVERAGE 169 158.1428571 240.5714286 101.6785714

Table 2 Leaf Area in Control Blocks

79.25 142.5 144.5 82.5
81 128 171 74.25
112.5 136 189 71.5
94.25 112 144 100.5
105 127.5 160 91
AVERAGE 94.4 129.2 161.7 83.95

The highest mean leaf area of 240.57 Sq. cms was recorded in humic acid applied sachimore variety. The lowest mean leaf area of 83.95 was recorded in control block of cattimore variety. Sachimore variety also had the highest mean leaf area difference of 201.13Sqcms compared to the control plants. The difference between control and humic acid treated blocks was 50.03 Sqcms across all varieties.

The number of nodes on a randomly selected primary was also recorded. The highest number of nodes on a primary was observed in humic acid applied blocks of sachimore variety 11.6 closely followed by cattimore 11.4.

Table-3 Number of Nodes in Primaries treated with Humic Acid

9 8 12 11
11 10 11 12
11 10 11 10
8 7 10 9
9 14 14 15
TOTAL 9.6 9.8 11.6 11.4

Table-4 Number of Nodes in Primary in Control Blocks

9 10 6 7
8 6 9 6
7 8 7 8
8 6 9 8
9 8 10 10
AVERAGE 8.2 7.6 8.2 7.8

The highest mean difference between treated and control block was found in sachimore variety 9.9 nodes. The mean difference between treated and control block was 2.65.

The third bunch from the apical end was used to record the number of berries. The highest number of berries 18.4 was observed in SLN 9 in the treated Block closely followed by sachimore variety.

Table-5 Number of berries in a Node/Bunch in Humic Acid treated Blocks.

15 30 23 20
15 20 15 18
21 28 21 20
20 18 24 22
17 15 18 23
AVERAGE 17.6 22.2 20.2 20.6

Table-6 Number of berries in a Node/Bunch in Control Blocks.

12 13 16 13
10 15 17 16
16 16 15 11
10 16 12 13
11 13 16 16
AVERAGE 11.8 14.6 15.2 13.8

The lowest number of berries 11.8 were observed in Un treated Block of S 795. The lowest mean average of 14.7 between the treatments was also recorded in S795 were a high of 18.4 was recorded in SLN9. The mean difference6.3 berries per bunch was observed across all varieties between the treatments.

Hundred berries of each variety from both treated as well as control blocks was harvested and weighed. The berry weight was highest in Sachimore variety closely followed by SLN 9 in treated blocks. However the lowest berry weight was observed in cultivar SLN 795

Root growth and development

Visual observations of root growth and development among and between cultivars was also looked into though not analysed statistically. Humic acid application had a strong desired effect in terms of root hair growth and development in the surface feeder root zone of all the cultivars treated with humic acid compared to control.


Humic acid treatment among all the five cultivars chosen for the study showed significant difference in terms of leaf enhancement when compared to the control.

Table-11 Data Analysis pertaining to Leaf Analysis.

Varieties Treatments
Control Humic Acid Mean
SLN 795 94.40 169.00 131.70
SLN 9 129.20 158.14 143.67
SACHIMORE 161.70 240.57 201.14
CATTIMORE 83.95 101.67 92.81
Mean 117.31 167.35

The study revealed that variety Sachimore responded the best and the significant difference in enhancement of leaf area was 42.6%. Review of literature indicates that humic acid application has increased left area in vegetable crops like bell pepper and tomato but there are no studies to indicate the effect of humic acid on coffee. Perhaps this is the first systematic study were the authors have tried to probe the role of humic acid application and its effect on coffee as a Plantation crop. (Erlanger yildirim, 2002;FabrizioAdani,  1998) .

Sachimore variety showed significant promise and the percentage increase in terms of increase in number of nodes was to the extent of 33.3%.

Table-8 Number of Nodes

SLN 795 8.2 9.6 8.9
SLN 9 7.6 9.8 8.7
SACHIMORE 8.2 11.6 9.9
CATTIMORE 7.8 11.4 9.6
MEAN 7.95 10.6

The other cultivars showed promise with SLN 9 coming very close to Sachimore. (J. A. Fagbenro and A. A. Agboola, 2008; these authors observed increased plant height growth and nutrient uptake in humus rich and non humus Soils in teak plants. However no review is available for coffee arabica).

Another important parameter With respect to number of berries in a bunch was also evaluated towards to the varietal response of humic acid application.

Table-9 Number of Berries in a Bunch

SLN 795 11.8 17.6 14.7
SLN 9 14.6 22.2 18.4
SACHIMORE 15.2 20.2 17.7
CATTIMORE 13.8 20.6 17.2
MEAN 13.85 20.15

The study revealed that a significant increase to the extent of 45.4% was observed in variety Sachimore with respect to control. All other varieties also showed a remarkable incremental value when compare to the control.

Response of humic acid application on weight of berries among the five different arabica varieties involved in this study,  revealed that variety SLN 9  showed a significant increase to the extent of 16.33% followed by the variety Sachimore.

Table-10 Weight of Coffee Berries

SLN 795 174.49 155.71 165.1
SLN 9 210.86 181.26 196.06
SACHIMORE 216.99 202.92 209.955
CATTIMORE 183.68 163.33 173.505
MEAN 196.505 175.805 186.155

Our observations point out to the fact that apart from humic acid application, the genotype may also play a role in the inherent weight of a particular cultivar. However it was clearly evident in our study that humic acid application increased the weight of the berries uproar to 11.7% in comparison to control. (YasarKarakurt.  Et. AL, 22.  The authors observed an increased chlorophyll and mean fruit weight in bell pepper due to the influence of foliar and soil fertilization of humic acid).

Our study also indicated that there was an increase in root development and stimulation of root hairs in feeder roots of coffee which is essentially restricted to the top two inches layer of soil even though this aspect of the study was not qualitatively assessed, humic acid has a important role to play in root stimulation and development. (Fabrizioadani, et;al 1998. These authors also observed an increased root growth and nutrient uptake due to the effect of commercial humic acid on tomato plant growth).


Melkodige estate has to its credit a number of eco-certifications in terms of sustainability. The present study, perhaps the first of its kind in relation to coffee has shown tremendous response in significantly bringing about a positive change in all the parameters studied. Humic acid application will not only contribute in maintaining the humus content but in the long run will significantly bring about a qualitative and quantitative change in the coffee eco – system.


Anand T Pereira and Geeta N Pereira. 2009. Shade Grown Ecofriendly Indian Coffee. Volume-1.

Humic Acid

What are some agricultural uses of humic acid?

Humic acid From Wikipedia




Physiological Role of Potassium in Eco-friendly Shade Coffee

Coffee production requires a well-balanced and adequate supply of nutrition in the form of major elements such as Nitrogen, Phosphorus and Potash and other minor and trace elements. Among all the essential elements, potassium is the third most likely, to limit coffee growth and productivity. In Plantation crops like coffee, potassium is commonly considered as the quality nutrient for increased fruit set and dry weight and volume. Coffee is known to harvest large amounts of potassium throughout its life cycle because of the high amount of energy required in terms of building of productive woods and berries. Hence, it is classified as a macro-nutrient.

Availability of potassium at the right time leads to higher yields and better quality. Application of potassium fertilizers stimulates early growth, increases leaf area and influences both Arabica and Robusta bean size. Since potassium plays a vital role in the synthesis of various organic compounds, it plays a significant role in the cupping quality.

Understanding, the nature of potassium is very important, which in turn helps the coffee farmer in making the right choice in the application of fertilizers. Many soil scientists have clearly elucidated the role of potassium and are of the view that potassium is present in the soil solution as a positively charged cat ion, K+. Vegetative growth, stem size, productive woods, flower setting. Fruit setting, fruit development, ripening of berries and other biological processes are catalyzed by enzymes which in turn are primarily influenced by the presence of potassium. Potassium enhances the activity of various enzymes and keeps them active over a longer period of time, thus extending the ripening period of fruits and improving fruit quality.


Like phosphorus, potassium does not form any gases that could be lost to the atmosphere. Its behaviour in the soil is influenced primarily by soil cat ion exchange properties and mineral weathering and not mediated by microbial processes. The advantage of potassium is that it does not contaminate the soil or water systems by way of leaching or residual toxicity.

Role of Potassium

It is very important to understand that potassium promotes photosynthesis and increases leaf chlorophyll content.

K regulates the opening and closing of stomata and therefore regulates carbon dioxide uptake.

It activates those enzymes which are involved in the energy transfer, in the build-up of adenosine tri phosphate (ATP) which stores the energy needed for carbon dioxide assimilation and the synthesis of sugar, starch, proteins.

ATP is the major carrier of energy in plant metabolism.

Potassium plays a pivotal role in osmo regulation. Recent findings suggest that potassium improves the tolerance of the plant to various stress situations like drought, low temperatures or salinity.

Potassium favors the production of proteins.

Potassium speeds up the flow of assimilates in the plant system.

Potassium intensifies the storage of assimilates.

Potassium improves the effect of nitrogen fertilizers. In simple terms high rates of nitrogen can be utilized by the plant and transformed into high yields only in the presence of high potassium levels.

Since coffee forests are associated with a large population of heterogeneous trees, herbs, shrubs, many of them nitrogen fixing, potassium is known to play a positive role in enhancing the fixation of atmospheric nitrogen fixation through a process called biological nitrogen fixation (BNF).

Adequate application of potassium helps in efficient utilization of soil moisture in comparison to plots deficient in potassium.

A balanced availability of potassium helps in improving the beverage quality.

Coffee blocks with good amounts of potassium availability improves the coffee foliage and helps in maintaining the regular size of the bean which in turn helps in the post-harvest operations.

Potassium plays an important role in building up resistance against fungal diseases and other insects.

Potassium improves the plants tolerance to the impact of climate change.

Role of Potassium in Water Use Efficiency

Review of literature clearly shows that potassium improves water use efficiency by increasing the osmotic pressure of the plant cells. This in turn plays a key role in the opening and closing of the stomata, which regulates the transpiration of water.

In plants which are water stressed, application of adequate amounts of potassium, help in the closing of stomata, thus preventing excessive water loss.

Plants having an optimum water regime, in such cases the stomata open wide and carbon dioxide assimilation is high.

Deficiency of Potassium

Potassium affects the plant shape, size, and color of fruit, leaves, and other biological measurements attributed to healthy produce. Fruits which are half filled and empty and those smaller in size is to the deficiency of potassium. Beginning of necrosis on the leaf tip, with a yellow halo limiting it, is a typical symptom of potassium deficiency in plants. Other symptoms associated with deficiency include brown scorching and curling of leaf tips as well as chlorosis (yellowing) between leaf veins. Purple spots may also appear on the leaf undersides. Plant growth, root development, and seed and fruit development are usually reduced in potassium-deficient plants. Often, potassium deficiency symptoms first appear on older (lower) leaves because potassium is a mobile nutrient, meaning that a plant can allocate potassium to younger leaves when it is K deficient.

Potassium Fertilizers

The most widely used potassium fertilizer is potassium chloride (muriate of potash). Other inorganic potassium fertilizers include potassium nitrate, potassium sulphate, and monopotassium phosphate.


Coffee production continues to be constrained by a number of factors that can reduce crop yield and influence both the quantitative as well as qualitative aspect of coffee. This is the second article that we have written on potassium to highlight the role of potassium as an essential macro-nutrient that affects most of the biochemical and physiological processes that influence plant growth and metabolism.

Although potassium is not assimilated into organic matter, potassium deficiency has a strong impact on the entire coffee physiology, especially stress. Although plant responses to potassium deficiencies are well documented at the physiological and transcriptional levels, the regulatory mechanisms underlying these changes are still obscure.

We hope that the Coffee Board Scientists will undertake further research to understand and evaluate the potential for improving plant stress resistance by modifying potassium fertilizer applications in the package of practices for coffee cultivation.


Anand T Pereira and Geeta N Pereira. 2009. Shade Grown Ecofriendly Indian Coffee. Volume-1.

Bopanna, P.T. 2011.The Romance of Indian Coffee. Prism Books ltd.

Dr. G. Kemmler and H.Hobot, Ing.agr.,Buntehof Agricultural Research Station, Hannover, Fed. Rep. of Germany. Potassium in Plant Production.

Dr. G. Kemmler and H.Hobot, Ing.agr.,Buntehof Agricultural Research Station, Hannover, Fed. Rep. of Germany. Potassium dynamics in the soil.

CCRI (2003) Coffee Guide, Central Coffee Research Institute, Chikmagalur

Potassium deficiency (plants)

Potassium for crop production

Potassium Deficiency Disorder in Coffee

Nutrient Management