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Mixed cropping in plantations will boost productivity

by Dr. N. Yogaratnam, Consultant/National Institute of Plantation Management

Mixed cropping in plantations is a type of agroforestry system where two or more crops are grown simultaneously on the same land. When properly planned and managed, it has certain favourable economic, social and environmental effects and will boost productivity.

Types and combinations of mixed crops



Mixed cropping of Tea and Rubber

Intercrops in plantations can be classified into two types on the basis of their adaptability to the different plantation development stages.

For example, in rubber, the first type includes those fit for immature rubber plantations where there is an adequate solar radiation, e.g. pineapple, passionfruit, banana etc. The second type includes those tolerant to limited or higher degrees of shade and can therefore be grown during both the immature and mature phase of the rubber plantations.

Essentially, these are tea, coffee, cocoa, pepper, cinnamon etc. (See box).

Economic returns of mixed cropping

Economic returns include those from intercrops via harvesting and from increased output from a main crop as well as cost savings due to intercropping.

The economic return of the intercrops depends on market demand. It can be as high as 1 to 7 times that of the value of the main crop output when the market is high or negligible or even a deficit when the market is low.

Ecological benefits



Mixed cropping of Tea and Rubber

Correct mixed cropping has been found to increase the growth rate and yield whilst also reducing the upkeep cost and fertilizer applications. Generally, a saving of 45 - 60 labour days/ha/year can be expected during the immature period of properly intercropped rubber stands.

Mixed cropping can be considered as an integrated system for the use of agricultural resources. Correct cropping pattern can help to establish a stable artificial ecological community in plantations to form a favourable recycling system and improve the ecological environment.

This makes possible satisfactory sustained growth and production from both the main crop and the intercrops.

Higher biomass production is demonstrated by higher total yield from the main crops and the intercrops due to normal growth of both crops.

In addition, a larger amount of litter is a common phenomenon in some intercropping combinations such as rubber/pepper (creeping), which contribute litter of 7545 - 9205 kg/ha/year which is higher than that of rubber/legume cover (Pueraria, 5352 kg/ha/year).

Higher rate of output

The commodity output rate per unit area in properly intercropped plantations is higher than that of the monoculture system, generally 0.5 - 1 time higher.

This is due to faster growth and higher yield of trees, assisted by certain produce from the intercrops.

Ecologically, this is due to the favourable environment of the new ecosystem formed.

Higher land use capacity

Generally, intercrops do not require the planting density to be changed drastically when planted between the trees or in the interrows.

This facilities a higher land use capacity per unit area. Land use capacity can be increased by 30-50% with a maximum of 75%.

Increased soil nutrient content

An analysis of soil nutrient contents of some intercropping combinations indicates higher soils organic matter content, N,P and K with Rubber/Tea, Rubber/pepper and Rubber/sugarcane combinations.

Steady micro-environment

The thicker canopy intercropped plantations reduces the airflow rate while increasing the solar absorption and reflection rates. Therefore, less sunlight reaches the ground and there is weaker air turbulence at ground level and a lower wind velocity.

Hence, evaporation is decreased but the relative humidity and the soil moisture content is increased. This is especially marked during high temperature periods when the under-canopy temperature is lower to form a favourable microclimate for growth and yield. This is also true of the soil to maintain a steady micro-environment.

Reduced soil erosion

It has been shown that properly intercropped plantations can reduce surface runoff and soil erosion due to the better raindrop interception capacity of the thicker canopy, thicker litter coverage and better soil structure.

However, it should be noted that not all intercropped plantations can reduce soil erosion. Soil erosion can occur in plantations on steeper slopes where soil tillage is required or downslope planting is practised. This is true even in those plantations with good intercropping combinations if no mulching or cover crop establishment is made in the early stage of the plantation establishment.

It is therefore emphasized here that only system that are properly intercropped can result in desirable ecological effects.

Social implications

Intercropping can produce more products and goods for the market and increase the income of growers. Plantations are sometimes in peril of natural calamities such as wind damage, drought stress etc. Intercropping can help to reduce the damage in terms of economic returns.

More job opportunities are created. For example a field worker can take care of about 1.67-2.0 ha. in conventional immature rubber plantations, but in intercropped plantations each field worker can take care of only about 0.27-0.67 ha. thus increasing job opportunities by 3-6 times.

In mature monoculture rubber plantations, each field worker can be responsible for about 1.0 ha. on the conventional tapping system but each field worker can take care of only about 0.32 - 1.33 ha. in intercropped stands thus increasing job opportunities by 1-2 times.

Objectives of Mixed Cropping

The prime objectives of mixed cropping in plantations should be therefore,

* To utilize the inter-row space in plantations to generate an early income from the land during the unproductive period.

* To generate an income even during unfavourable weather conditions when harvesting may not be possible from the main crop and thereby to provide a steady stream of income for the grower.

* To generate an income during adverse trading conditions for the main crop.

* To increase the productivity per unit area of land.

* To convert marginal/uneconomical areas into better use with a view to make such units more profitable and economically viable.

* To generate or reduce employment (depending on the type of previous crop) which would enable estates to utilize the available labour resources more efficiently and effectively.

Selection of Crops

Crops selected for mixed cropping should posses the following qualities:-

* Should not complete with each other.

* The soil and climatic conditions of the area should be acceptable.

* Less labour intensive.

* Free from diseases that effect the crops.

* Readily marketable.

Mixed Cropping of Tea and Rubber

Mixed cropping of Tea and Rubber is considered feasible in agro-climate regions where conditions are favourable for the cultivation of both these crops.

In summary, the area under mixed cropping in Sri Lanka is still rather small. Constrained by available resources and knowledge, researches into mixed cropping in plantations are also very limited and superficial.

Nevertheless, the market mechanism will play more and more important role in regulating and maintaining the sustainability of mixed cropping.

The recommendation of annual or perennial crops for the use as mixed crops in plantations must take market demands into consideration quite apart from the technical availability based on research findings.

Some traditional intercrops can be continued with but some new intercrops with high market potentials must be introduced into the cropping scheme, eg. animal feed intercrops.

Environmental concern must be a further factor for consideration in the mixed crop decision-making process. Another, and final aspect for concern is that of rural social development.

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