In view of unstable price structure, higher cost of cultivation, coconut based cropping systems and economic status, farmers are looking for some alternate cropping in oil palm gardens. Often, inter cropping is chosen as an insurance against the risk of main crop failure/ low price or at least to ensure the stability of crop yields in variable environments. Inter cropping enhances productivity and employment potential considerably.

Cultivation of banana, cocoa, black pepper, coffee, pine apple etc as inter crops in mature phase is practiced to some extent in oil palm gardens of India. The major constraint in oil palm gardens as compared to coconut gardens is presence of more density of shade. Even then, there is a scope for utilizing both horizontal as well as vertical space in oil palm gardens by growing suitable inter crops.

Criteria for selection of suitable inter crops for oil Palm gardens 

• Crops should have complementary effects rather than competitive effects on the base crop.
• The component crops should have different root systems so that they do not compete with the base crop for water and nutrients.
• A standard plant population of the base crop should be maintained.
• Component crops of similar pest infestation should not be chosen.
• The management should be simple, economical and profitable so that it may have wider adoptability.
• The selected crop should be a local choice with good market demand.
• If possible, inter crops should enrich the soil and create positive allelopathic effects on oil palm.
• Only the shade loving and shade tolerant crops should be selected due to less availability of sun light in mature oil palm gardens.

Advantages of inter cropping in oil palm gardens

• Better utilization of resources like land, light, water, nutrients and man power.  
• Improvement in soil fertility, health and productivity.  
• Reduction in soil and water erosion.
• Control of weeds due to more shade.
• Effective utilization of nutrients from different layers of soil.
• Increased crop productivity or total biomass production/unit area/unit time due to effective utilization of space and light which otherwise would have been utilized for weed growth.
• Provides crop yields in installments and security during the period of fluctuating market prices and main crop failure.
• Offers better employment to family and others round the year.
• Increased carbon sequestration.
• No adverse effect on the main crop/improved oil palm yield and
• The net profit /unit area is very high due to higher productivity.

Disadvantages of inter cropping in oil palm gardens

• There may be a risk of pest incidence with certain crop combinations and quick spread of pests owing to more density of cropping. Ex. Incidence of psychids (bag worm) and leaf web worm in oil palm – cocoa cropping system.
• There is always a possibility of one component of the system acting as a trap crop, which in turn may damage another component subsequently.
• It restricts the free movement of workers in the garden and makes FFB harvesting and cultural operations laborious.
• Running of tractor/bullock cart which are commonly used for collecting FFB in inter space cannot be possible.
• And also, mechanization of cultural operations may not be feasible in inter cropped oil palm gardens.

Scope for inter cropping in oil palm gardens

Being perennial in nature, it remains in farmers’ gardens for 25-30 years. Normally, it is planted in an equilateral triangular system having 9x 9x 9m spacing. Such a wide spacing is required for canopy development at peak vegetative growth which comes after 10 years of planting.

Based on growth, the life span of oil palm is divided into three distinct phases i.e., first phase called juvenile/pre bearing is spread over 3 years, second phase (yield stabilizing) 4- 10 years and third phase (mature) starts from 11^th year on wards.

The optimum time for incorporating various inter crops in oil palm gardens is during II ( 7 - 10 yr) and III phases. Complete covering of inter space, crisscrossing of leaves and short trunk (<1 m height) will make inter cropping difficult during the first 3 years (4, 5 & 6 yr) of II phase. After 10 years, there is a gradual increase in trunk height and reduction in crown size which facilitates more penetration of sun light to reach the ground

Being monocot, oil palm has an adventitious root system which is fairly close to the surface while few roots penetrating below 90 cm particularly in deep soils. The active root system of adult palms under good management is mainly concentrated within a radius of 50- 300 cm laterally from the bole and 10-60 cm depth vertically. Even then, about 60-65 per cent of land area can be available for inter cropping in grown-up oil palm gardens.  

The sun light reaching the ground through canopy of mature oil palm trees of different age groups (6-20 yrs) is ranged from 14 to 28 per cent. But the availability of solar radiation is almost the double in coconut garden when compared to oil palm gardens of same age and therefore, the same cropping system may not be possible in oil palm gardens.

Status of inter cropping in oil palm growing states of India

Considering the well established coconut based cropping systems, farmers have taken up many crops in mature oil palm gardens but the performance of crops was not satisfactory. Large canopy size and equilateral triangular system of planting restrict choice of crops to be grown in oil palm. The following is the list of inter crops grown on a small scale in different oil palm growing states:

Table1. Inter crops grown in mature oil palm gardens.

Suitable inter crops for Oil palm garden

The availability of space and light during bearing stage are the major factors to be considered for growing inter crops in oil palm gardens. Low light penetration or more shade level restricts the list of crops grown in oil palm. 

In fact, the choice of crops is varied with geographical location and local preference. Reports say that cocoa has been found as an ideal companion crop without affecting oil palm yield. In Africa and Far East, cocoa and coffee are recommended to grow in 7-8 year old oil palm plantations. The performance of coco-yam and tapioca in oil palm was found better up to 12 years age in Nigeria.

A trial conducted at Directorate of Oil Palm Research (DOPR) Regional Station, Palode, Kerala, revealed that combination of cocoa and cinnamon in alternate inter rows, pepper trailed on palms and anthurium planted in the intra row space was found ideal for getting maximum net returns. Crops tried were cocoa, cinnamon, pepper, guinea grass, anthurium and kacholam.

Among medicinal plants viz., Adhatoda beddomei, Alpinia calcarata, Kaempferia galanga, Nilirianthes haenianus and Asparagus recemosus tried in different age group oil palm gardens in Kerala, Kaempferia galanga emerged as the most remunerative crop due to the highest cost benefit ratio.

Based on the results obtained so far at DOPR, Pedavegi, heliconia, red ginger, bush pepper, betel vine have been found as most successful and profitable inter crops in mature oil palm garden.

It may be possible to grow only the shade loving and shade tolerant crops in oil palm since the availability of light is less than 30 per cent. Hence, it is advised to take up only shade tolerant crops like cocoa, banana, elephant foot yam, black pepper, bush pepper, long pepper, heliconia, red ginger, ginger, colocasia, guinea grass,  some medicinal and aromatic and cut foliage plants/greens and shade loving crops like anthurium, orchids, vanilla and some medicinal and aromatic plants in mature oil palm gardens.           

Effect of inter cropping on oil palm 

When crops are grown together, they compete with each other for nutrients, water and space when they are limiting. It is to be ensured that there is no serious overlapping of active root zones of base crop and inter crops. So, it is recommended that the nutrient requirement of all the crops should be met separately.         

The crop combination in the multi-tier system viz: oil palm+cocoa or cinnamon or glyricidia with balck pepper+ pepper trailed on oil palm+ anthurium or kacholam has enhanced the out put of the system. Leaf nutrient values of N, P, K, Ca and Mg were found within optimum range irrespective of the treatments. This showed that the system does not have adverse effect on the nutritional health and performance of oil palm.

The study also revealed that the multi-tier system helped in reducing the run off of water and soil erosion. Thus, experiments conducted both in abroad and India revealed that inter cropping in mature phase of oil palm did not affect the yield of oil palm. Crops like cocoa, coco-yam and banana add lot of organic matter to the system.

Steps for successful intercropping in oil palm

Many farmers have been cultivating inter crops indiscriminately in oil palm gardens. Ploughing of inter space, pruning of leaves for providing more light to inter crops, planting in oil palm basins and more density of cropping are the major mistakes noticed in farmers gardens. As a result, oil palm growth and yield are severely hampered. The following are the suggestions for the betterment of inter cropping in oil palm gardens:

• Ploughing of palm basin or close to the stem should be avoided as it destroys the root system of oil palm and affects absorption of water and nutrients.
• Inter cropping should be practiced only under assured water supply conditions with separate irrigation systems for the base crop and inter crops.
• Utilize only the inter space by leaving at least 3 m radius free around each palm to avoid competition for nutrients and water in the system.
• Adjust the pruning of oil palm leaves in such a manner that it should be coincided with peak requirement of component crops. At the same time, heavy and unnecessary pruning will severely affect the growth and yield of the base crop.
• There should not be overcrowding of component crops in the system which results in air tightness, spread of pests, poor soil health and inconvenience for movement of workers. Leave intra space of oil palm empty which is required for carrying out various cultural operations of crops.
• There should be proper ventilation and solar radiation at the ground level of the system to provide the energy for micro flora and fauna in the system.
• Proper recycling of biomass of the system to maintain the soil fertility, health and productivity which are basics in intensive cropping systems.
• Finally, proper planning and judicious management of system with their recommended package of practices will make the system highly successful.

Conclusions   

Barring early years of canopy development, light availability is the major limiting factor in mature oil palm gardens. Considering the nature of growth of oil palm and the light infiltration pattern through its canopy, inter cropping in mature oil palm gardens appears to be feasible from the II phase onwards.  Only the shade loving and shade tolerant crops may be chosen in mature oil palm gardens. Therefore, the success of inter/mixed cropping in oil palm depends on the selection of suitable crops as per the light availability and efficient management.

Authors:

K. Ramachandrudu, S. Arulraj and B.N.Rao

Directorate of Oil Palm Research, Pedavegi-534 450, Andhra Pradesh.

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