Chapter 4
Plant nutrition & fertiliser management

Nutrients are recycled within the environment. A 'closed' environment such as a rainforest, recycles its own nutrients and is more or less self-sufficient. However, where plants are grown in a commercial situation, it is necessary to replenish the nutrients that are removed from the system. Without additional nutrients in some form of fertiliser, coffee yields will remain very low as nutrients are removed with the coffee beans. Unshaded plants of dwarf, high-yielding varieties such as Catimor, will quickly develop dieback and die if adequate nutrients and water are not added to the soil. Plants with mild to moderate dieback will recover with timely good fertilising, watering and weed management.

In India, it was found that for every 6,000 kg of ripe coffee cherry (1 tonne of green bean) removed from the plants, approximately 40 kg nitrogen (N), 2.2 kg phosphorus (P) and 53 kg potassium (K) must be replaced yearly.

There are 16 natural elements (nutrients), that are essential for plant growth (see table below). Three elements (carbon, hydrogen and oxygen) make up 94% of the plant tissues and are obtained from air and water. The other 13 elements are obtained from the soil and are divided into two broad categories - 'macro' and 'micro'. These terms do not refer to the importance of the elements; macronutrients are required in greater amounts than micronutrients for normal plant growth.

Essential minerals and their role in the coffee plant

Soil and leaf analysis

To help determine the best nutrition practices, soil and leaf analyses are recommended. While Lao currently does not have access to these services, in nearby Thailand the Mae Jo University in Chiang Mai and Department of Land Development (DLD) can offer fee-for-service analyses. The FAO project used Mae Jo University for the soil and leaf analysis survey of Arabica coffee farms in the Bolovens in 2005.

In order to standardize procedures between farms, years and personnel involved, the following practices are suggested for soil and leaf analysis.

Soil sampling

Figure 23. Remove surface litter and old fertiliser etc., from area to be sampled but do not remove soil. Take samples to a depth of 150 mm

• Remove surface litter (leaves, etc.) before sampling. Do not scrape away soil (Figure 23).

• Take samples to a depth of 150 mm with soil auger or spade.

• Place soil in a CLEAN bucket.

• Sample from a minimum of 20 sites across a block of two to four hectares.

• Thoroughly mix each soil sample collected and then sub-sample to reduce volume for sample bags.

• Properly label all samples and laboratory sheets.

• Clean the auger or spade after sampling each of the sites.

• DO NOT sample after fertilizer application. Scrape away any fertilizer/lime residue from previous applications before taking a sample.

• Do not sample next to shade trees.

• Areas of different tree size, age, soil types, fertilizer or other major differences should be treated as separate samples.

• Samples need to be dried before sending for analysis. If laboratory ovens are unavailable, spread out each sample on a paper bag or plain paper and dry slowly on raised benches under shade and protected from rain. Samples are usually air dry in four to five days.

If possible, soil samples should be taken once per year before flowering.

Leaf sampling

Figure 24. Leaf sampling

• Sample the third or fourth pair of leaves from the tip of an actively growing branch. Do not count new leaves if they are not fully expanded (Figure 24).

• Sample at the same time/growth stage each year, before flowering.

• Sample a minimum of 40 trees per block across a block size of two to four hectares.

• Sample diagonally across the block.

• Sample average trees only. Do not sample obviously sick, excessively healthy or odd/unusual coffee trees.

• Sample in the morning where possible when leaves are the most turgid (full of water).

• Use CLEAN HANDS. Do not smoke while sampling and make sure hands are free of fertilizer, soil etc.

• Do not sample when leaves are wet as the paper sample bags will break!

• Do not sample after any application of foliar fertilizer sprays.

• Areas of different tree size, age, soil types, fertilizer or other major differences should be treated as separate samples.

• Properly label all samples and laboratory sheets.

• Samples are to be stored in paper (not plastic) bags. Keep leaves cool but do not freeze!

• Samples need to be dried if they are not sent for analysis within one to two days. This is normally done at the laboratory at 60 to 65°C until dry and brittle.

Pre-flowering is preferred sampling time if only one sample is taken each year. More frequent sampling (every four months) is highly desirable for large plantations, especially if nutritional problems occur.

A soil and leaf sampling survey on 15 properties has recently been conducted on the Bolovens Plateaux; results were not available at the time of publication.

Optimum leaf and soil nutrient levels

Once the soil and leaf samples have been taken, it is important to analyse the results and compare them to levels that have been determined as optimum in coffee plantations around the world in order to devise a nutrition programme for the coffee.

Optimum leaf nutrient levels

Optimum soil nutrient levels

* Different extraction methods would give different results and different optimum levels.

Fertiliser programme

Coffee soils in Lao PDR are low in a number of essential plant nutrients; therefore these must be supplied to promote high yielding, high quality coffee. Manure, bio-fertiliser, cover crops, compost, legume tree leaves and shoots and chemical fertilisers all supply nutrients.

Manure and compost such as coffee pulp and husks have a low nutrient content. When utilised as a source of nutrients, they must be used in large quantities to supply sufficient nutrients for coffee plants. Manure and compost help improve soil structure and organic matter.

Chemical fertilisers are higher in nutrient content than organic fertilisers and are a more effective method of applying nutrients. For optimal results, it is best to apply a combination of manure and compost and chemical fertilisers.

At present, there has been little or no soil and leaf analysis services available for Lao coffee growers. When such services are available, a detailed coffee fertiliser programme can be devised. Meanwhile the following fertiliser programme is suggested for Arabica coffee in Lao.

Note: NPK is nitrogen, phosphorus, and potassium

Explanation

Higher yielding coffee plots may require 25% more fertiliser.

Use lime or preferably, dolomite (Ca + Mg) at 500 g per plant every two years and apply before the end of the rainy season. Use the last rains to wash the lime into the soil or water in well by hand or irrigation. The following table shows the nutrient uptake and consumption by different parts of coffee tree (expected yields / ha: 1000 kg green beans).

Nutrient uptake of a coffee tree

It is obvious from this table that leaves need the major part of the uptake - more than the flowers or fruits. However, nutrients are returned to the soil when the leaves drop. The early years of root development are very important as branches and roots store nutrients for a long time.

Nutrients accumulated in the fruits will be removed when cherries are harvested. This loss needs to be compensated by the addition of fertilizers, organic manures, leaf fall or prunings and leaves from shade trees. Recycling of pulp to the soil after composting can help to reduce the additional (chemical) fertiliser needed.

Fertiliser placement

Figure 25. Place a band of fertiliser around the drip line

Spread fertiliser evenly on the soil around the drip line (the outside edge of the canopy) of the coffee tree, as this is where most feeder/hair roots are found (Figure 25). Keep fertiliser at least 100 mm from the stem of the plant; fertiliser applied closer than this can damage the coffee tree.

Manure (if not using fertiliser). The minimum amounts to apply are:

Legume shade trees, ground covers and suitable intercrops supply nutrients and organic matter through litter and leaf fall and through prunings added as mulch to the surface of the soil.

Nutrient deficiency symptoms

The overall rate of coffee growth and production depends on the least available plant nutrient. Plants will grow and produce only as much as the least available nutrient will allow them to. It does not matter how much of the other nutrients are available to the plant because it is the least available nutrient that limits growth and development. This is well illustrated in the following 'Barrel Analogy', where the barrel can hold only as much water as the shortest plank will allow (Figure 26). This is known as the 'Law of the Minimum' and is explained thus:

Figure 26. 'Barrel Analogy' using nitrogen as the least available nutrient

The level of water in the barrel represents the level of crop yield that is restricted by the most limiting nutrient, nitrogen. When nitrogen is added, the level of crop production is controlled by the next most limiting factor (in this example, potassium).

Poor nutrition is a major cause of coffee dieback. Plants lacking sufficient N (nitrogen) and K (potassium) suffer from dieback, especially where there is poor shade cover and insufficient water. Low soil calcium and phosphorus will hinder root development and contribute to dieback. Dieback causes loss of yield and when severe, plants can die, especially high yielding, dwarf Catimor varieties.

Each nutrient has unique deficiency symptoms. These are briefly described below and can be seen in the photographs.

Coffee nutrient deficiency symptoms