Methods for assessing coconut fertilization requirements

By Jean Ollivier and R. Bourdeix, 2018.

Leaf analysis

Leaf analysis (LA) is a basic tool used in coconut palm mineral nutrition management. Leaf sampling instructions are presented below for use by growers. LA is used in three cases:
  • Regular sampling in a plantation, structured into leaf sampling units (LSU), with a view to drawing up annual fertilizer schedules (generally conducted annually).
  • Monitoring palm response to fertilization in field trials, based on a statistical trial design.
  • Special sampling to deal with a particular problem (suspected mineral deficiency, etc...). In each case, a sampling design should be adopted for the choice of palms.

A small holder, having a one hectare coconut plantation, can sample about 20 palms taken at random in the plantation and harvest about 4 leaflets per palm. Their is an interest for farmers to group together in cooperatives or NGOs in order to facilitate the procedure and obtain better prices.

The cost of analysis varies among  countries. In Cirad (France) a high quality analysis (nitrogen, phosphorus, potassium, magnesium, chlore and boron together) costs is about 80 USD plus sending cost; in Indonesia, it is about 30 USS plus sending; Oil palm plantation in the Solomon presently conducts these analysis in New Zealand. It is probably possible to make such analysis in the Pacific Region (Fiji?).

Date and frequency of leaf sampling
In large and well managed plantations, the LA frequency is usually annual. In this case, as a seasonal effect is always possible on leaf contents, it is essential to fix the same sampling period that will be respected. Smallholders and.or their cooperatives can also use this technique, especially if  mineral deficiency is suspected. Sampling can be conducted less often to reduce the cost of analysis.
Sampling should not take place in a wet period (it is necessary to wait 36 hours after rainfall of more than 20 mm), samples are usually taken in the dry season at sites with marked seasons. Ideally, samples should not be taken at the end of the dry season: spears do not open and accumulate at the top of the crown, and determination of fronds 1, 9 and 17 becomes increasingly difficult and less precise. The optimum period is therefore right at the beginning of the dry season. This is not a strict obligation, as other requirements may play a role: for example, the need to obtain results before the end of the budgetary year in order to include fertilizer orders. There is therefore a degree of flexibility in the choice of LA period provided very wet periods are avoided.

Sampling method
Kraft paper envelopes or labels are prepared the day before to identify the samples to be taken; each team receives its work program and its itinerary on which the groups of palms are indicated. There will be two symmetrical envelopes per group of palms to be sampled (given that one of the samples will be sent to a dedicated Laboratory and the other kept in reserve at the plantation). Samples are usually taken early, from 6-7 am to 11 am. A standard team comprises an experienced leader with good knowledge of phyllotaxis, a cutter with a pole adapted to the height of the palms to be sampled, and one or two assistants. For each palm in the sample, it is necessary to:
  • identify, without mistakes, the frond to be sampled (rank 14 for coconut palm),
  • Cut off a given number of leaflets (4 to 6) from the central section of the frond, divided equally either side of the rachis. Damaged leaflets should be discarded,
  • do not allow leaflets to fall to the ground where they may be contaminated by soil or fertilizers, Place the leaflets together in envelopes or labelled boxes and carefully check the information marked on them. Important comments:
  • The envelopes must be kept open at all times to allow leaf tissue transpiration to escape, and they should be large enough for the leaflets not to stick out, even when open.
  • Avoid cutting the entire frond, though a few more leaflets than needed can be cut to facilitate identification of the frond when checking sampling rank.
  • In the event of light rainfall, continue sampling to finish the current sampling operation, but stop if the rain becomes heavier. Between 11 am and midday, sampling should be completed and the samples transported for packaging.
Between 11 am and midday, sampling should be completed and the samples transported to the laboratory for packaging. 

Sample preparation 
Ideally, fresh samples brought from the field should be processed the same day: the samples taken in the morning are therefore prepared in the afternoon. The purpose of preparation is to obtain samples in duplicate. One will be sent to the laboratory for analysis, the other will be kept as back-up until the laboratory results are received. Some plantations prefer to make up their duplicate samples when sampling in the field. Other teams make up their duplicate samples when cleaning, using each half-leaflet. The essential thing is that each palm is equally represented in each sample. 

The preparation area must be clean, ventilated and dry. The central section of the leaflet is cut off (sample length: 10 to 15 cm) and the outer edges and veins, along with the midrib, are discarded (they come away in strips very easily). The lamina is then wiped with cotton wool soaked with distilled water, to remove dust and any impurities that would falsify the results. 

Distilled or demineralized water is used so as not to pollute the leaf tissue with any minerals contained in ordinary water. It merely involves wiping each side of the lamina without soaking. The pieces of cotton wool should be changed frequently as they become dirty. The pieces of lamina are then spread on trays and placed in the oven: one tray per sample, checking that it is strictly identified with a perfectly legible provisional label. 

The samples are left in the oven overnight. The ideal thing is to have an oven with a thermostat and with stacked wire shelves inside to optimize the volume of tissues to be dried. The more the pieces of lamina are spread out on the trays the quicker and more uniform the drying will be. The ideal temperature is between 70 to 80°C for 8 to 10 hours, i.e., in practice, a complete night in the oven: trays placed in the oven late afternoon are removed the following morning. When they leave the oven the samples should be beige in color and brittle. If they are too green, drying is incomplete; too brown or black and drying has been excessive. Lastly, the uniformity of color and consistency reflect drying uniformity. 

25 to 30 grams of dry matter are easily enough for the complete analysis of a sample. Drying time and shipment costs (by air) are thus reduced. Failing a calibrated laboratory oven, domestic ovens or hotplates can be used, provided the temperature is controlled at a constant value. It is also worth mentioning the possibility of easily making a home-made electric oven heated by infrared rays (e.g. 250 Watt infrared lamps) or incandescent light bulbs. 

However, use of a microwave oven is not recommended. From experience, we recommend growers who regularly prepare a large number of leaf samples to invest in enough laboratory ovens of the right size to meet their requirements. Such equipment guarantees good results. 

On leaving the oven the following morning, the samples are packed in hermetically sealed plastic or paper bags bearing the ultimate identification on a standard format label. Before closing the plastic bags it should be carefully checked that the samples have been properly dried (otherwise there is a risk of mould development, which would make the sample unusable). The labels must be clearly visible from the outside without having to open the bag. The information to be marked on the labels differs depending on whether it concerns. If it is a commercial plantation, it must contains: Company name; Estate; Division; Plot; leaf sampling units (LSU) number; Leaf sampling date; number of palms and rank of the sampled fronds. 

Shipment takes place if the following two conditions are satisfied: - you have received a cost estimate from CIRAD and you have returned it to us signed by your company, - The green light is given by a CIRAD agronomist (contact person for your dossier) to send the samples. At the time of shipment, a copy of the dossier is faxed or e-mailed to the Cirad contact person: shipment date, name of transporter, AWB number, list of samples and elements to be analyzed. The plastic bags should be grouped by category, and packed in a parcel. The full list of samples contained should be marked on the parcel (a copy of that list should be sent separately to CIRAD) and the list of nutrients to be analyzed should be indicated again (list drawn up beforehand, in principle with a CIRAD agronomist). The parcel should be sent to the following address: Mrs Elisabeth Villarem CIRAD-UPR Tree Crop Based Systems-Bât. 1 TA B-34/01 Avenue Agropolis 34398 Montpellier CEDEX 5 FRANCE. The full address with the name of the consignee must be indicated to avoid wasting time when the parcel arrives at CIRAD. In terms of Customs and Excise, no permits are required for importing dry plant material into the European Union. Consequently "Contents: Dried coconut palm leaves, of no commercial value" should be written on the parcel. 

When the parcel arrives, the Cirad Agronomist checks that the contents are right and sends an acknowledgement of receipt to the sender. The analysis process is then set in motion. The duplicate of each sample is kept at the plantation until the final results of the originals have been received. This is a security measure: duplicates exist in case any originals are lost or checks need to be made. Some properly dried and packaged leaf samples can be stored as they are for several months, or even several years. 

Service restricted to analysis. 
The services provided by Cirad include analyzing samples and checking the quality of the results obtained. Such control consists in replicating the analysis of a few samples detected by cross-checking information on two levels: ➢ compared to the results in previous years, in cases where the same samples are regularly analyzed, ➢ In accordance with known balances between nutrients (N and P, K and Ca ...) when only its results are available. Such checking does not usually provide any agronomic information. 

Agronomic assessment of results.
This involves judging analysis results or their annual trends, depending on other variables provided by the client: age of the plantations, planting material origin, fertilization, etc. This service gives rise to a report commenting on the distribution of the results and an assessment of the levels reached on an agronomic scale. Contact the CIRAD agronomist to receive a detailed cost estimate : Jean Ollivier Tel: +33 4 67 61 56 34 jean.ollivier@cirad.fr

Agronomic interpretation and recommendations.
This service is usually covered by an agreement including a visit to the plantation by the expert. The results are compared to ground truth, and the intrinsic characteristics of the plantation (soil type, topography, etc...) are taken into account for an in-depth interpretation of the results and for making fertilizer recommendations. Contact the CIRAD agronomist to receive a detailed cost estimate : Jean Ollivier Tel: +33 4 67 61 56 34 jean.ollivier@cirad.fr

Soil analysis and management
(Brazilian way)

This text is partly traduced and adapted by R. Bourdeix from the document "Tecnologias para produção intensiva de coco anão / José Simplicio de Holanda, Marcos Tomaz de Oliveira, Ernesto Espínola Sobrinho, & Tarcísio Batista Dantas. – Natal : EMPARN, 2007. 40 p.: (Boletim de Pesquisa, n. 34)."

The nutritional condition of the coconut is crucial for the production of fruits. The amount of nutrients extracted by the crop can reach high values, considering that the productivity can be between 150 and 250 fruits per plant per year (50 years of cultivation). The plant under nutritional deficiency reduces the number of female flowers per spathe and has difficulties in keeping fertilization and fruits formed, occurring prematurely dropping them. For a program of intensive production of coconut, it is necessary that the essential nutrients to the crop be supplied during the periods of demand, in adequate quantities. Aiming for balanced orchard nutrition, soil fertility assessment is the initial basis of knowledge for the planning and use of correctives and fertilizers. Correction of soil acidity benefits the crop under three aspects: it neutralizes the toxicity of aluminum and manganese, increases the supply of calcium and magnesium in the soil and raises the pH by providing nutrients. The most used method for limestone recommendation in soil acidity correction is that of saturation of bases, which, in the case of coconut, the desired value corresponds to 60%. For sandy soils, the doses of limestone as a corrective of acidity are usually between 2.0 t.ha-1 and 3.0 t.ha-1. Once the corrective recommendation has been established, the next step is to verify the equilibrium between cations in the soil in order to reinforce the fertilization of the nutrient found in an unfavorable proportion, preventing problems of competitive interaction that may interfere with the absorption by the plants. For potassium, calcium and magnesium the suitability range in the soil is between 1: 9: 3 to 1: 25: 5 (PPI, cited by Malavolta et al., 1993).