CHAPTER VI: LAND PREPARATION, PLANTING OPERATION AND FERTILISATION REQUIREMENTS

by P. Klein and A. Zaid Date
Production Support Programme

I. Land preparation

When establishing a new date plantation, certain actions need to be implemented to ensure the long term success of the plantation. One of these actions involve the initial land preparation which should be done prior to transplanting of the plant material (offshoots or tissue culture-derived plants).

The purpose of land preparation is to provide the necessary soil conditions which will enhance the successful establishment of the young offshoots or the tissue culture plants received from the nursery. Considering the nature of the date palm, one can not "save" on this operation and hope for long term sustainability of the plantation.

The aim is to enable the date grower to plan and structure the implementation process in advance, ensuring the successful establishment of the date plantation. Planning forms part of the initial preparation and will help to limiting unnecessary stoppages during the implementation phase.

Critical factors to consider during this planning exercise are summarised as follows:

- Availability and quality of irrigation water;
- Field selection;
- Mechanical actions to be implemented;
- Chemical needs for pre-plant soil improvement;
- Tools and equipment needed for date cultivation;
- Labour needs;
- Irrigation design and installation;
- Leaching schedule;
- Hole preparation;
- Financial requirements and
- Time schedule.

1. Field selection

The area selected for the establishment of the date plantation can infl uence the cost of land preparation to the extent that it may not be viable to proceed with the development at all. The authors' aim is to highlight the critical areas to be considered when selecting the land for the establishment of a new date plantation.

1.1 Availability of water

Although not always realised, the date palm requires a rather large quantity of water for sustainable growth. Critical factors regarding water for irrigation purposes are:

(i) the sustainability of the water source,
(ii) the quantity of water available for irrigation,
(iii) the distance to the fi eld, and
(iv) the quality of the water.

1.2 Soil depth

In time date palms grow very tall and become top heavy especially during the fruit bearing stage. They therefore need sufficient room for proper root development to support the palms. Besides the importance of root development, soil depth also infl uences drainage and leaching possibilities. Any obstructive layers must be evaluated to determine whether they will infl uence root development and whether they can be corrected.

1.3 Soil quality

Date palms can grow and produce in different types of soil in both hot arid and semi-arid regions. Adaptation could go from a very sandy to a heavy clay soil. The soil quality is related to its drainage capacity mainly when soils are salty or the irrigation water is characterised with a high salt content. Sandy soils are common in most date plantations of the old world. Rare cases of clay soils (i.e. Basra-Iraq) with drainage systems are found allowing the culture of date palms. The optimum soil conditions are found where water can penetrate to at least 2 m deep.

When evaluating the soil quality, attention must be given to:

(i) the soil texture which will infl uence the water retention capacity, and
(ii) the nutrient content to determine the corrective measures necessary for soil improvement.

1.4 Soil salinity or acidity

Plant growth is influenced by either saline or acid soil conditions which, in the end, will result in a loss of potential yield.

Saline and alcaline soils are common in date plantations and are characterised by a high concentration of soluble salts, and exchangeable sodium, respectively. Soluble salts present in these soils belong to cations: sodium, calcium and magnesium and to chloride and sulphate anions.

Saline soils have an electric conductivity (EC) of their saturated extract higher than 4 mmhos/cm at 25°C, with a sodium absorption rate less than 15 and a pH generally less than 8.5. Saline soils can be recognised by the presence of a white layer on the surface of the soil resulting from the high salt concentration which may harm the growth and development of date palm.

Alcaline soils are characterised by an EC of their saturated extract less than 4 mmhos/cm at 25°C with a sodium absorption rate higher than 15, and a pH higher than 8.5. Alcaline soils do contain harmful quantities of alkalis with the hydroxyl group - OH, especially NaOH. These types of soil are usually diffi cult to correct coupled with a low production resulting from low content of calcium and nitrogen. However, it is recommended to eliminate the excess of sodium by the addition of acidifying agents (gypsum, sulphate of iron or sulphur).

Saline and alkaline soils are usually the result of:

(i) an increase of the underground level caused by excessive drought situations (high evaporation);

(ii) the use of high salt content water, and

(iii) very poor drainage system.

Where date palm grows in climates of little rain, but great heat and much evaporation, irrigation or flood water evaporates quickly, and its salts are left on the surface of the soil.

The negative infl uence of saline conditions are:

(i) high concentration of soluble salts;
(ii) high soil pH;
(iii) poor drainage and aeration; and
(iv) the negative effect of sodium on the plant metabolism.

Table 37 shows the relationship between crop responses and soil salinity expressed in terms of the conductivity of the saturation extract (Richards et al (1954)).

TABLE 37
Relationship between crop response and soil salinity

Source: Richards et al., 1954.

* The electrical conductivity values of the saturation extract in millimhos per cm at 25°C associated with a 50 % decrease in yield.

Compared to other fruit crops, the date palm is considered to have a high tolerance for salts. Table 38 illustrates this high tolerance.

TABLE 38
Relative salt tolerance of fruit crops ⁽¹⁾

⁽¹⁾ (Source: Richard et. al., 1954).

⁽²⁾ The numbers following EC_e × 10³ are the electrical conductivity values of the saturation extracts in millimhos per cm at 25°C associated with a 50 % decrease in yield.

According to Arar (1975), the date palm is more salt tolerant than any other fruit crop. It will survive in soils containing 3 % soluble salts; when this content goes above 6 %, the date palm will not grow. This author also studied the crop tolerance and leaching requirements of some important crops, including date palms (Table 39). It is clear from these results, that it is possible to irrigate date palms with water of a salinity of up to 3.5 mmhos/cm with no reduction in yield, provided that a leaching requirement of 7 % is provided for. A ten (10) % reduction in yield is obtained when irrigation water is of 5.3 mmhos/cm salt content and with a leaching requirement of 11 %.

TABLE 39
Crop tolerance and leaching requirements

Yield Decrement to be Expected for Certain Crops due to Salinity of Irrigation Water when Common Surface Irrigation Methods are Used.

1 ECe - Electrical Conductivity of soil saturation extract in milliohms per centimeter (mmohs/cm)

2 ECw - Electrical Conductivity of irrigation water in mmhos/cm

3 LR - Leaching Requirement

4 ECdw - maximum concentration of salts that can occur in drainage water under crops due to ET

N.B. For conversion to TDS as PPM multiply mmhos/cm by 640.
(Source: Arar, 1975).

Soil acidity contributes towards negative plant growth and is mainly due to:

(i) the toxic levels of certain elements (aluminium, manganese);
(ii) the defi ciency of certain elements (calcium, magnesium, molybdenum);
(iii) the low availability of phosphorous; and
(iv) a drop in the efficiency of fertiliser and water usage because of poor root development.

2. Physical land preparation

Once a suitable area for establishing the plantation is selected and the planning operation is fi nalised, the actual preparation can be activated. These activities are divided to structure and pace the implementation process in order to be ready for planting at the most suitable time, according to the specifi c regional climatic conditions.

2.1 Mechanical fi eld preparation

The mechanical or initial soil preparation concerns mainly the preparation of a fi eld for further detailed preparation such as irrigation system installation, hole preparation, etc. Actions, if applicable to the area, include:

(i) debushing/bush clearing;
(ii) removal of stones and rocks;
(iii) ripping; and
(iv) levelling of the soil.

2.2 Irrigation system installation

The type of irrigation system to be used will be determined by the availability of water, topographical and soil conditions. When the initial soil preparation is completed, the installation of the required irrigation system will be implemented according to the prescribed design (Figure 55).

2.3 Soil improvement

The scheduling of the soil improvement programme will depend on the date grower, as certain applications could be combined with the initial actions of soil preparation. Due to the long waiting period, planting to first production, it is a trend to establish date plantations on new soils, with the exception of areas where date palm is used for intercropping.

If new soils are considered, the soil improvement programme will mostly deal with:

(i) the application of organic matter; and/or
(ii) the elimination of soil salinity.

2.3.1 Organic material

In general, most soils are poor in organic matter content and the improvement of this situation plays an important role in soil fertility. Some of the advantages of a higher humus content in the soil are summarised as follows:

- Enhances crumb formation which improves the respiration of the roots;
- Increases the water infi ltration rate;
- Increases the water holding capacity;
- Lowers soil compaction and crust formation; and
- Limits the harmful effects of alkalinity and improves the leaching of salts.

2.3.2 Salinity

In an attempt to reclaim salt affected soil, consideration should be given to:

(i) the type of salinity/alkalinity,
(ii) the drainage possibilities of the soil profi le,
(iii) the origin or the source of salts,
(iv) the quality of irrigation water and
(v) the leaching of salts from the soil.

If the source of salts is identifi ed as drainage water from higher lying areas, a cut-off canal may be suffi cient to eliminate this source of "salt" supply.

Poor drainage normally goes hand in hand with soil salinity problems and therefore the improvement of the drainage potential should be addressed before any leaching programme is implemented. A soil cover (mulching) and the application of organic material will improve the water infiltration resulting in improved drainage (excluding soils with obstructive layers).

In saline soils (soluble salts present as chlorides, sulphates and/or carbonates of calcium, sodium or magnesium), only leaching will be necessary to drain the excess salts. In the case of alkaline and/or saline-alkaline soils, sodium can be replaced through the application of gypsum or acidifying agents like sulphur. Once the sodium has been replaced, a programme should be followed to leach it out.

When the irrigation water is of poor quality, proper drainage and over irrigation, without the development of a water table, is very important.

2.4 Hole preparation

The actual digging of the hole is one of the last actions before planting takes place, but it must be emphasised that this is not the fi nal preparation for the planting operation itself. This is the point where the required inputs such as gypsum and organic materials are worked into the soil and a start is made with the leaching programme. The reason why the leaching is only applied at this stage is because of the relatively small area that is occupied by the date palm. If the total area had to be leached, it would become very costly with little or no benefi t in the long run.

It is recommended that a hole of 1 m³ be prepared and that the soil from the hole be mixed with the organic material and gypsum (Figures 56 and 57). The soil mix is then put back into the hole, whereafter the site is clearly marked for positioning of the small date palm plants.

At this stage, once the hole has been prepared and closed, it is irrigated and a leaching programme implemented. The water supply will then enhance the leaching of excessive salts and contribute to the fermentation process of the organic material. Subsequent irrigation, several times (2 to 3) before planting, will also allow the mixed soil to settle in the hole.

In most soils, the early and rapid growth of the date plant is better when the holes are prepared one to two months before planting. Well-rotted manure can also be used in holes prepared and irrigated shortly before planting, but extreme care must be taken to put the manure (and fertilisers) deep enough to allow a layer of soil at least 15 to 20 cm thick to be placed between the manure and the roots of the date plant.

II. Planting operation

This is probably the most critical phase in the establishment of a new date plantation. Mistakes at this point may lead to a poor survival rate of offshoots or tissue culture-derived plants, regardless of the efforts put in during the preparation phases. The aim is to assist the date grower to execute the planting operation in a way that will ensure a high transplanting survival rate in the newly established plantation. The planting operation is divided into different activities which will be discussed separately.

1. Plant spacing

It is diffi cult to prescribe a defi nite plant spacing but there are specifi c factors infl uencing the spacing such as:

- to allow for suffi cient sunlight when palms are tall;
- to allow for suffi cient working space within the plantation; and
- to provide suffi cient space for root development.

Previously, the general assumption for a commercial date plantation was to use a plant spacing of 10 m × 10 m (100 palms/ha). It has, however, changed over time and a plant spacing of 9 m × 9 m (121 palms/ha; Israel) or 10 m × 8 m (125 palms/ha; Namibia), is used in modern plantations.

As an example of different spacing used with date palm, Table 40 illustrates the distance apart, the square unit to each palm and the number of palms in each spacing.

TABLE 40
Comparative table of spacing distances (Palms planted at the corners of squares)

Source: Dowson, 1982.

The planting density also depends on ecological factors (mainly humidity) and on varieties. In general, commercial plantations use 10 m × 10 m, 9 m × 9 m or 10 m × 8 m, for all varieties except for Khadrawy (dwarf variety with a small canopy) which could be planted at a higher density. The tendency to plant more closely is found when the prevailing wind is dry and extremely hot and strong. The 10 × 10 is desired in areas where humidity during the date ripening period (Coachella valley-USA, Elche-Spain and Coast of Libya (Zliten)) is high (Dowson, 1982); This wider spacing is to allow sun and wind to counteract the humidity's infl uence. According to Nixon (1933), wide spacing is also recommended whenever there is considerable danger of rain damage to dates during the ripening season.

2. Time of planting

The critical factor is to transplant the young tissue culture date palms or offshoots at that time of the year that will ensure a good survival rate and proper establishment before the beginning of a "hard" season.

In most of the date regions in the northern hemisphere, spring and autumn are preferred for the planting out of tissue culture-derived date plants or offshoots. Spring avoids the cold of winter and takes advantage of the warm weather that encourages rapid growth, while autumn gives the young shoot a longer time to establish itself before the heat of summer. Each of the two seasons, however, has its corresponding disadvantage; spring, the early approach of the great heat, and autumn, the early approach of the cold.

In the southern hemisphere the best time of establishment is during autumn (February/March) because of the following reasons:

- Winters are relatively frost free,
- Very high summer temperatures,
- Strong, dry winds during August-January, and
- Sand storms during the summer.

In areas without extreme dry, hot summers and with severe frost during winter it is recommended to plant during August/September or at a time safe from the occurrence of frost.

3. Transplanting stage

Research has shown that the best fi eld survival rate, as well as early plant development, is obtained when the date tissue culture plantlets are transplanted at the four (4) plus pinnae leaf stage. Plants received from a tissue culture laboratory normally only have juvenile leaves or one pinnae leaf at the most. These plants are thus too small to be transplanted into the field. It is therefore necessary to include a hardening-off phase for plant development which also allows some time for plants to adapt to local climatic conditions. This results in the young plants being kept in the farm nursery for a period (approximately 8-12 months), until the suffi cient number of pinnae leaves have developed before transplanting takes place.

In a fi eld test at the Eersbegin project (Namibia), tissue culture plants with 4-6 pinnae leaves were transplanted and the results indicated that the initial plant development, after transplanting, was better when the plants were transplanted at the 4-pinnae leaf stage than at the 5-6 pinnae leaf stage. Regarding offshoots, it is highly recommended to ensure their rooting in the nursery after separation from the plant mother (at least 10 to 12 months). It is not recommended to plant an offshoot directly after its separation.

4. Planting time and depth

Planting should always be initiated early in the morning to limit stress on the date plantlets and also to allow suffi cient time for adaptation (from the plastic bag to the soil). Bags are to be removed with care and the plant, with most of its surrounding substrate, to be planted carefully.

Planting is probably the area where most people make the vital mistake of planting the plant too deep. The planting depth is critical because the "heart" of the plant should never be covered with water. Once the plant is covered with water the growing point rots and the plant dies off. If a date plant is planted too shallow, its roots will desiccate and die.

The golden rule is to ensure that the greater diameter of the bulb of the plant is at the same level as the soil surface after transplanting and to ensure that water does not go over the top of the date plant.

5. Basin preparation

Immediately after transplanting, a basin is prepared around the palm to prevent run-off and to ensure a suffi cient supply of water to the plant. When using a micro irrigation system, it is recommended to have a basin of approximately 3 m in diameter and 20 to 30 cm deep. The basin should have a slight downward slope towards the plant to allow the water to reach the root system of the young plant.

6. Mulching

The benefi ts of organic material were highlighted when land preparation, as part of the plantation development, was discussed. The mulching is done by putting a layer of organic material (e.g. wheat straw) around the base of the palm. Mulching of the basin has the following advantages:

- Limits water loss from the soil through evaporation;
- Prevents crust formation;
- Allows better water penetration into the soil:
- Limits weed growth around the plant; and
- Improves the humus content of the soil.

7. Irrigation

Immediately after transplanting, the palm should be irrigated to limit transplant stress. Once the plantation is established, a frequent irrigation schedule is to be followed to allow suffi cient water supply to the young date palm.

The irrigation frequency, is soil type dependant, but on very sandy soils it requires daily irrigation during the first summer. Heavy soils will require irrigation once a week, while in most soils, irrigation is required every second or third day. During the first six weeks, the date growers should inspect their planted date palms to verify that the surface soil does not dry and shrink away from the plant.

8. Protection

Tissue culture-derived plants and young offshoots should be protected from harsh climatic conditions (sun and wind during the first summer and cold the following winter) and against some animals (rabbits, etc.). The use of a hessian wrapping, a shade net cover, or a tent of date leaves is recommended. The top is to be left open so that new growth may push out.

9. Aftercare

Beside irrigation applications, the annual fertilisation schedule, weeding and mulching, the date grower should, for at least the first 10 to 12 months, keep an eye on the plantation in order to detect and consequently correct any adverse situations.

III. Fertilisation requirements

1. Introduction

The initial land and orchard preparation aims at preparing the soil for establishment of the young tissue culture date palm or offshoots, but does not ensure proper establishment and growth after transplanting. A fertilisation programme should be included in the date plantation establishment phase for optimum growth.

In general, farmers do not realise the importance of following a date palm fertilisation programme. This behaviour is normally caused by one or more of the following factors:

- Information, regarding date palm fertilisation requirements, is not readily available.

- Information may confuse farmers, because of the differences between literature/studies conducted by various scientists. This example will be discussed later in the document.

- Farmers tend to assume that date palms do not require any nutrients, because of the general view that date palms can survive the toughest conditions.

The importance of a fertilisation programme at and after transplanting is to provide in the nutrient needs of the young tissue culture plants or the offshoots, to ensure rapid growth in preparation for the first production season. An under-developed plant will not have the capacity to reach its production potential at an early stage.

The purpose of this chapter is to serve as a basic reference guide for fertilisation planning in date plantations.

2. Functions of nutrient elements and their availability in relation to soil conditions

Date palm has similar fertiliser requirements to other cultivated crops. Nutrient elements necessary for plant growth and production (but not absorbed from the air), i.e.: boron, calcium, chlorine, cobalt, copper, iron, magnesium, manganese, molybdenum, nitrogen, phosphorus, potassium, sodium, sulphur and zinc, are all needed at different rates by the date palm culture.

2.1 Soil pH

Nitrogen

Nitrogen plays a major role in plant life processes such as photosynthesis, vegetative growth and the maintenance of genetic identity. This ensures high yield at the end of the season.

Nitrogen is freely available to plants within the pH range of 5.5 to 8.5. When the soil pH is below 5.5 or above 8.5, the availability decreases to the extent that plants are not able to take up any nitrogen from the soil profile.

Phosphorus

Phosphorus also plays a role in processes such as photosynthesis, respiration, vegetative growth, reproduction and maintenance of the genetic identity. It is also associated with cell division, root development and flowering.

Phosphorus is freely available to plants within the pH range of 6.0 to 8.0 and above 8.5. When the soil pH is below 5.0, phosphorus is, for all purposes, not available to plants. At a pH of around 8.0 to 8.5, phosphorus is relatively unavailable to plants, but from approximately 8.5 and above it becomes freely available again.

Potassium

Potassium is found in cell sap and plays a role in the transport of nitrogen in the plant and the promotion of photosynthesis. This nutrient helps to strengthen fi bre and has an infl uence on the opening and closing of the stomata. Potassium is also associated with resistance to drought, cold and the improvement of fruit quality.

Potassium is freely available to plants within the pH range of 5.5 to 7.5 and above 8.5. When the soil pH is below 5.0, potassium, is for all purposes, not available to plants. At a pH of around 7.5 to 8.5, potassium is relatively unavailable to plants but from approximately 8.5 and above it becomes freely available again.

Hence, measures are needed to adjust the soil pH to ensure the availability of nitrogen, phosphorus and potassium for plant utilisation.

Boron

Boron is an essential nutrient in pollination and the subsequent reproduction processes, i.e. the formation and growth of flowers and fruits. It also plays a role in the uptake of calcium, magnesium and potassium.

2.2 Soil texture

Nitrogen and potassium are easily leached from the soil profile when excess water is applied. Therefore, it is important to control the irrigation schedule on sandy soils to avoid any unnecessary leaching. When working with sandy soils, it is also recommended to divide the amount of fertilisers over two or more applications to decrease nutrient losses.

3. Nutrients lost through date palm plants

The amount of nutrients lost through fruits and pruned leaves as well as the world-wide application of fertilisers were considered as a basis for the calculation of the amount of fertilisers required by an adult date palm. Our study was based on related literature, experiments and fi ndings in various countries (Algeria, Iraq, Morocco and USA). Hass and Bliss (1935) showed that one hectare (120 palms), exports 29 kg of nitrogen, 5 kg of phosphate and 70 kg of potassium. Embleton and Cook (1947) estimated that leaf pruning of one hectare caused the loss of 25 kg of nitrogen, 2 kg of phosphate and 74 kg of potassium.

Nixon and Carpenter (1978) recommended for most Coachella Valley soils, the use of 1.81 to 2.72 kg of actual nitrogen per palm, divided into two to three applications on sandy soils to reduce leaching. While other authors (Furr and Barber, 1950) estimated the nitrogen export per hectare of Deglet Nour variety at about 78 kg.

For the above, it is estimated that in order to produce 50 kg of date fruits per palm, the fertilisation needs are about 45 kg of nitrogen, 13.5 kg of phosphate and 81 kg of potassium, of which most of it could be covered by irrigation water (Djerbi, 1995).

Unfortunately, there are variations amongst the results of different scientists and, it was therefore decided to calculate the average between the different sources in order to recommend a fertilisation programme at three levels: nursery, young plants (less than 4 years old) and adult palms. It must also be indicated that, in most cases, the relationship between the nutrients lost through fruits and leaves is roughly constant. Tables 41 and 42 illustrate the average nutrient loss and the average world-wide fertilisers application, respectively.

TABLE 41
Average nutrient loss

TABLE 42
Average world-wide application

* For both Tables 41 and 42, it is assumed that 121 palms are planted per hectare.

4. Micronutrients

Rare are the cases where defi ciency of micro-elements were studied as most of them are found in the irrigation water. However, boron defi ciency was probably responsible for the death of some date palms; both the terminal bud and the root system were affected (Djerbi, 1995). Boron has an effect on the activity of some enzymes, increases cell membrane permeability and enhances the transport of carbon hydrates; it also participates in the lignin's synthesis. Boron controls the ratio between potassium and calcium contents and plays an important role in the synthesis of proteins and cell division.

According to Djerbi (1995), lack of manganese was also found in several Tunisian date plantations, causing the death of palms within a period of five to seven years (called disease of broken leaves). Manganese is a catalyst of several enzymatic and physiological reactions. It is involved in respiration and activates enzymes that are active in the metabolism of nitrogen and the synthesis of chlorophyl. Iron could also be defi cient in some soils and symptoms are usually characterised by a sound yellowing of the older (outer) leaves (Figures 58 and 59).

In conclusion, measures to correct defi ciencies of micro nutrients are to be taken, early enough, through a simulation study based on leaf/soil analysis and date palm requirements.

5. Fertilisation programme recommended for the nursery

In order to ensure strong, healthy plants for transplanting and to shorten the period in the nursery, (approximately six to eight months instead of eight to ten months), a fertilisation programme is recommended (Table 43).

TABLE 43
Fertilisation recommendation for date palm nursery plants

6. Fertilisation at fi eld planting

Part of the fertilisation programme starts at the time prior to transplanting, during the land preparation phase. At that stage, attention is to be given to the improvement of the soil which may have a direct infl uence on the utilisation of certain nutrients which are necessary for plant growth.

Actions that precede this phase include the initial hole preparation, application of lime/gypsum/organic material, and a leaching programme in the case of saline soils.

Instead of opening the original hole again to apply the required fertilisers, only a smaller planting hole (± 60x60x60 cm) is prepared and the fertilisers are mixed with the soil from this hole before it is put back at transplanting.

The application rates for nitrogen and phosphorus are calculated by adding 50 % to the average loss of nutrients through fruits and pruned leaves. The amount of potassium is not increased due to the fact that most soils normally yield a relatively high natural potassium content. If soil analysis shows a decrease in potassium content over a period of time, this fi gure should be increased.

TABLE 44
Application rate for date palms younger than 4 years

* It is assumed that 121 palms are planted per hectare.

Table 45 shows the necessary nitrogen quantities for a date palm of four (4) years and older. For newly transplanted palms up to and including the age of three years, only 50 % of the amount of nitrogen is recommended as shown in Table 44.

TABLE 45
Application rate for date palms 4 years and older

* It is assumed that 121 palms are planted per hectare.

7. Annual fertilisation programme

7.1 Time of application

In an effort to obtain the best results from any fertiliser application, it is important to link the stages of application to critical times over the growing period, i.e. vegetative phase, reproduction phase. The same principle applies to date palm fertilisation and therefore the time of application is co-ordinated with certain growth phases during the year.

The date season is divided into two growth phases: vegetative and reproductive. The latter is also divided into two stages namely the fl ower formation stage (February - April in the northern hemisphere and June - August in the southern hemisphere), and the fruit development stage (July - October in the northern hemisphere and November - February in the southern hemisphere). Scheduling the application of fertilisers according to these phases ensures an increase in the amount of properly developed flowers and a potential increase in yield. The best results will be realised when the fertiliser applications are done as soon as possible after the initiation of the two stages (fl ower and fruit formation). Therefore, it is recommended that these applications take place during February and July for northern hemisphere, and June and November for southern hemisphere.

To prevent root burn, not all the required fertilisers should be applied at the planting stage, and therefore the following is recommended as a follow-up programme:

- Apply 300 g potassium sulphate four weeks after transplanting and repeat four weeks later,
- Apply 250 g sulphate of ammonia six weeks after transplanting and repeat six weeks later.

Although no major problems are noticed with the above technique (twice per year), some commercial plantations, mostly in Israel, apply the fertilisation throughout the year monitored with irrigation (fertigation). This programme is aimed at applying the required nitrogen during 8 months (November till August in northern hemisphere and April till November in southern hemisphere); while for phosphorus and potassium the application is at a three months interval (4 times per year).

The following table (Table 46) summarises this fertilisation programme:

TABLE 46
Date palm annual fertilisation programme

(*) Amount to be applied per palm and per month for a period of 8 months.
(**) Amount to be applied per palm every 3 months.

(1) A total of 4.8 kg per palm for the eight months.
(2) A total of 3.65 kg per palm for eight months.
(3) A total of 2.4 kg per palm for eight months.
(4) A total of 1.374 kg per palm to be distributed in 4 applications (every 3 months).
(5) A total of 1.030 kg per palm to be distributed in 4 applications (every 3 months).
(6) A total of 0.692 kg per palm to be distributed in 4 applications (every 3 months).
(7) A total of 6.5 kg per palm distributed in 4 applications (every 3 months).
(8) A total of 4 kg per palm distributed in 4 applications (every 3 months).
(9) A total of 2 kg per palm distributed in 4 applications (every 3 months).

The three months frequency for both potassium and phosphate could be: 1 November, 1 February, 1 May and 1 August for northern hemisphere and 1 April, 1 July, 1 October and 1 January for southern hemisphere.

Once the young palms have been planted and the follow-up fertilisation programme completed, an annual fertilisation programme should be introduced to ensure sufficient supply of nutrients to the young palms.

7.2 Transplanting

Before transplanting can take place, and as stated above, a planting hole must be prepared to ensure that the nutrient needs of the small plant are satisfi ed once it has been planted into the fi eld. In addition to this, a fertiliser application at this stage also serves as a measure of soil improvement by adding nutrients to a possibly poor soil.

The exact amounts and types of fertilisers to be applied will be determined by soil analysis. The aim of this section is to make a general recommendation with regard to the fertilisers included in the process of plant hole preparation.

The recommendation presented in this chapter is to be used as an example as well as a general recommendation, for sandy/sandyloam soil types. When digging the hole, ensure that the top and bottom soil are separated, because the fertilisers are mixed with the top soil.

General recommendation:

The sulphate of ammonia and potassium chloride can either be mixed into the top soil together with the rest of the products or it can be applied through the irrigation system after transplanting. It is important to note that nitrogen and potassium should be applied separately with two or three irrigation cycles in-between.

7.3 Method of application

7.3.1 Manual

This method is used when applying fertilisers to a plantation where the fertiliser can not be supplied through the irrigation system. Fertilisers are then measured in small quantities and applied by hand to individual palms. The most important precaution when applying through this method is to ensure an even distribution of the fertilisers within the palm drip area and not too close to the base of the palm (Figure 60). However, the disadvantages are:

- time consuming;
- labour intensive;
- root burn may occur if not evenly distributed; and
- the correct amount of fertiliser is not always applied.

A product like phosphorus, which does not move well in the soil profi le, should be applied though holes within the drip area to ensure contact with the roots.

7.3.2 Through irrigation system (Figure 61)

This method called fertigation, is used when the irrigation system is designed for fertiliser application. All top dressing of soluble fertilisers are applied through the irrigation system. Nonsoluble fertilisers, however, still have to be applied by hand. The main advantage of this system is that the correct amount of fertiliser is evenly distributed within the drip area.

8. Soil, water and leaf analysis

The importance of fertilisation can be summarised as follows:

- Overcome nutrient defi ciencies in the soil;
- Ensure proper establishment, growth, and development; and
- Increase the yield potential.

This chapter serves merely as a fertilisation guideline, since there are many potential variables among different locations. The aim is to supply a reference document to serve as a framework in fertilisation planning, and it is highly recommended that the date grower consults the local extension offi cer regarding the exact application of nutrients for his/her specifi c conditions, based on leaf, soil and water analyses.

Van Zyl (1983) summarised the optimum age of leaf and time of the year for leaf analyses of dates in the southern hemisphere plantations (Table 47).

Source: Van Zyl, 1983.

(*) The optimum month indicates the period when the element concerned remains most constant. However, and for a commercial plantation, only two periods are recommended:

(i) Just after harvesting and before the emergence of new leaves (April for southern hemisphere and November for northern hemisphere), and

(ii) After flowering and before final fruit set (August for southern hemisphere and April for northern hemisphere).

In the literature, data on leaf analysis of dates vary from one place to another and results depend strongly on edaphoclimatic conditions. The authors advise to set own-standards, based on the performance of the date palms in the local plantations, rather than taking over data from other areas. For setting standards for soil and leaf sampling, the authors are proposing the following:

- 12 palms/ha will be randomly and representatively selected over each ha of date plantation (10 %).

- 1 kg of soil/profile sample will be used.

- For leaf: At least one kg of fresh leaf material is needed/palm.

- Leaflets and rachis of approximately 10 photosynthetic leaves are the parts to take.

- The 12 palms and their soil profiles will be followed up for at least 4 years (with two samplings per year).

- Metal markers must be used to identify the site of soil profile and will also be reported on the site map).

- Soil information to request for the laboratory: pH, EC (ms/m); SAR; Exchangeable Sodium percentage, with textural class. All micro and macro elements (N, P, Ca, Mg, Boron, Molybdenum, Sulphate, Iron, Mn, Zinc, etc.).

- For leaf analysis: Request in percentage the content of the following: N, P, K, Ca, Mg, S, Na, and Cl. While we need the content in mg/kg of Fe, Cu, Mn, B, Zn and Mo.

- For water analysis: pH, EC (ms/m), TDS (mg/L), SAR (meg.) with content of all micro and macro elements.

Figure 55. Irrigation design and lay-out of a date plantation with 10 m × 8 m spacing (Eersbegin, Namibia).

Figure 56. A m³ planting hole; note that the top 1/3 and the bottom 2/3 soils are separated.

Figure 57. A device to make sure that workers do respect the required 1 m³ volume.

Figure 58. Iron defi ciency symptoms on a Barhee variety at Naute (Namibia).

Figure 59. Potassium defi ciency symptoms on a Barhee variety at Naute (Namibia).

Figure 60. Fertilisation damage on one year old Medjool tissue culture palm at Eersbegin, (Namibia).

Figure 61. Fertigation system at Eden Research Station (Israel).