10th Annual conference & Exhibition
"Peak of Perfection"

Denver, Colorado
April 17-21, 1998

Presentation Handouts

Name of Presenter: Richard Hornack and Samuel Olivieri, PhD
Title of Presentation:  Unique Agricultural Formulas and Their Benefits; Test Methods and Preliminary Results

Unique Agricultural Formulas and Their Benefits:
Test Methods and Preliminary Results


By Richard S. Hornack

Why Should We Change From Our Present Practices?

Arabica coffee can be grown where the dry seasons are not too long and the soil has a high water retention capacity, arabica coffee could, theoretically, be grown without irrigation where the average total rainfall is at least 1100 mm. In practice, poor rainfall distribution or adverse soil conditions create a high risk where the annual rainfall is less than 1300 mm.

Similar conditions apply to robusta coffee, but it is more suited to lower altitudes where temperatures are higher, however, the total water requirement will be higher.

The most important requirement for coffee growing is good drainage from your soil. Poor drainage will reduce your yield by a substantial amount and also kill trees if it is prolonged. The soil structure should be such that water from peak rains will drain away quickly from the root zone and yet in close enough proximity that roots can retrieve water through capillary action. Roots will be able to grow freely in such soil. Heavy clay soils are undesirable because of slow drainage, and root growth will be restricted. In very heavy clay soils you will get almost no root penetration.

A high water capacity is necessary so that sufficient available water can be stored to maintain proper transpiration rates throughout the dry season. Rocks in a soil of otherwise suitable texture, reduces water capacity and root growth.

A deep porus soil provides a greater root proliferation which brings more water and nutrients within range of the tree. In areas of lower rainfall and long dry season a deep soil is essential. A depth of 3 meters is ideal. Nutman (1933) reported that roots explored the profile extensively down to 3.05 meters. Wallis (1963) reported that in Kenya, on some occasions the soil was at its wilting-point (i.e. no more water could be extracted by plants down to 3.05 meters at the end of the dry season.)

Soil Chemistry: When rock breaks down to the particles that form soil, the rupture of the crystal structure leaves free electrical charges on the surface of the particles. Negatively charged ions (anions) absorb the positive charges (cations), because opposites attract. Each charge must be neutralized by an ion of the opposite charge. Ions can exchange one with another, which allows them to move within the solution surrounding the particles so they can be absorbed by the plants or lost by leaching in the drainage water. Almost all the plant nutrients are bases (cations). The capacity of the soil to absorb these bases is known as the Cation Exchange Capacity (CEC); this is a measure of the number of negative charges at the soil particle surfaces.

When an exchange site is not occupied by a base it will be occupied by a hydrogen ion. The higher the proportion of sites occupied by hydrogen, the more acidic the soil or the water system. One of the important measures of fertility in a soil is the quantity of nutrients available to plants. Organic material has a high capacity for adsorption of ions, which varies with the source of the material. The proportion of exchange sites which are occupied, will be increased by the elements that have entered the system, decomposition of organic matter and fertilizer applications.

Coffee Soils

Coffee is growing on soils varying from extremely acid (pH below 4.0) to slightly alkaline (pH up to 8.0). Neither one of these extremes are suitable for economic high production. A slightly acid soil is preferred; most written work suggest a pH of 5.2 to 6.2 for arabica. Robusta is more tolerant of neutral and slightly alkaline soils. Robusta planted in the high pH soil gave a crop yield, when averaged over the first five harvests, yielded 47.2% greater than the yield from coffee planted in the lower pH soil.

Remember that pH is not the only requirement. The necessary nutrients must be available at a reasonable level and in appropriate relative proportions. For optimum yields it is imperative that you adhere to the "law of the minimum". If only one nutrient is lacking for the plant it will react as though all nutrients are lacking and greatly effects the yield of the crop.

In non-equatorial coffee-growing regions, coffee follows a single annual cycle of growth and fruiting. This is so even though there may be no marked dry season.   i.e. in Costa Rica, Cannell, 1972; Maestri and Barros, 1977 reported "In general, rates of floral initiation are fastest, and rates of shoot growth are slowest, during the dry and/or cool winter months, and blossoming and rapid shoot growth are triggered by spring rains. Low internal water potentials during the dry season seems to increase the unusually low hydraulic conductivity of coffee roots, thereby predisposing the trees to rapid rehydration following the first rains (Browning and Fisher, 1975). This rapid rehydration triggers both blossoming and flushes of new shoot growth.

The fruits develop during the hot summer rainy season and ripen at the start of the next dry and/or cool season. The further shoot growth during the rains provides more branch nodes where the flower buds initiate for the next season. Shoot growth is not continuous however, and you will often see a mid-summer depression in shoot elongation. This may be due to high tissue temperatures and daytime water stress due to the high evaporative demand and/or nutrient leaching from the soil. See the Figure on seasonal phenology.

Nutrient Requirements

The coffee crop (green beans) includes many mineral nutrients which are removed from the plantation system. Catani and Moraes (1958) estimated that the major nutrients removed in 1 ton of arabica green beans amounted to 34.0 kg N, 5.2 kg P2O5 and 47.8 kg K2O. However the crop is harvested as cherry which includes pulp and parchment in addition to the beans. In many cases these are not returned to the field so that the nutrients are lost to the system. Using data published by Ripperton, Goto and Pahau (1935:55) the nutrients removed in the bean, pulp and parchment equal to 1 ton of arabica green beans are as follows:

in beans 45.50  kg N 7.67  kg P2O5   37.90 kg K2O
in parchment 2.27 kg N 0.30  kg P2O5 1.87  kg K2O
in pulp 15.33  kg N 3.67  kg P2O5   27.40 kg K2O
Totals 63.10  kg N 11.64  kg P2O5 67.17  kg K2O

 These results of course vary with the type of soil and the amount of fertilizer that is used. Even the pruned stems which are often used as firewood causes heavy loss of nutrients. There are similar losses for robusta without returning the pulp and parchment.

The root system of coffee explores the soil extensively to a depth of at least 3 meters in suitable soil (Nutman, 1933). DeCastro (1960) reported that the proportion of roots in all sizes below 30 cm depth in the soil, increased with the age of the tree. Of the roots of seven-year-old trees, 61% were at depths below 30 cm. Cuenca, Aranguren and Herrera (1983) investigated root systems of arabica coffee variety mundo novo planted 25 years earlier under shade and managed without fertilizers. Of the fine roots which are mainly responsible for absorption of nutrients, 33% were found in the top 10 cm of soil, which consisted largely of litter. Of the fine roots, 73% were in the upper 30 cm of the soil. The main purpose of the deeper roots is to absorb water. It is therefore extremely important that your soil structure is porous and has good tilth.

In the absence of fertilizer applications the nutrient reserves in the soil will be quickly used up. Coffee is a long-lived crop and a significant reduction in the amounts of nutrients available in the soil occurs over every ten years. Arabica coffee is prone to overbearing as it tries to survive, causing the plants to deplete the nutrient supply within the tree which restricts vegetative growth, thereby reducing the number of buds available to flower the following year. Vegetative shoots often die back when the nutrients from the leaves and stems have been transferred to the fruit.

When you add an application of fertilizer and improve the nutrient supply you can reverse this overbearing of the arabica plants. Pereira and Jones (1954) reported a significant reduction in die-back following an application of fertilizer.

The degree of shading interacts with nutrition. Beside the actual effect of different light intensities on the coffee trees. Shade trees supply nutrients in leaf fall and leguminous trees will make a contribution by fixation of atmospheric nitrogen. Shading affects soil conditions because the organic material decomposes more slowly at lower temperatures. The net effect of shade, is that unfertilized shaded trees will yield at a higher level than unfertilized unshaded trees. However, unshaded trees have a higher rate of response to fertilizer so that the highest yields are produced by heavily fertilized unshaded coffee.

The unique new product that has been designed specifically to meet these problems of soil and nutrient absorption that are so prevalent in the coffee growing industry. We have used similar technology in the agriculture industry since 1992 with great success and feel confident that we can prove to be just as successful in the coffee industry. We understand the importance of being able to increase production while still preserving the health of the trees and the plantation at an affordable cost.

R. S. (Dick) Hornack,


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