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Use of chemical and organic fertiliser

By Prof. Saman K. Herath – sundayobserver.lk

It is apparent that world agriculture has significantly changed during the last six to seven decades.

This change is basically due to the ‘green revolution’ which is experienced since the late 1950s. The main purpose of the green revolution was to increase productivity in agricultural lands (production capacity) in order to feed the increasing population of the world.

Many strategies and practices were adopted accordingly to achieve set targets facing various challenges. High yielding crop varieties (hybrid varieties) were introduced using plant breeding technology.

The expected yield could be obtained by providing greater amount of chemical fertilisers (nutrient sources) and by improved irrigation practices due to the fact that these hybrid varieties were highly sensitive for chemical fertilisers and irrigation.

As a result, hybrid seeds became abundant in the market; correspondingly, other traditional varieties disappeared gradually from the use. Except high yield, some quality aspects were also improved in hybrid varieties. In order to produce same food in large quantities over and over, same crops were cultivated in the same land (mono cropping) and as a consequence, certain pests multiplied exponentially becoming dominant.

Having effective control mechanisms was thus needed and subsequently pesticides (agrochemicals) were introduced. Within a short time period, these chemical pesticides were popularized all over the world giving promising results causing detrimental effect to the pests.

Since then, farmers apply both chemical fertilisers and pesticides as major inputs of crop production in agriculture. Overall, green revolution has resulted both positive and negative impacts in agriculture sector, and on the environment and human health.

Parallel to the evolution of world agriculture, similar changes can be seen in local agriculture sector. Accordingly, use of hybrid seeds for cultivation, application of chemical fertilisers and pesticides, and application of irrigation techniques can be seen.

However, compared to other developed countries, certain areas of agriculture have not yet been improved with technology; for example, farm mechanization, application of information technology etc. On the other hand, agriculture has not developed to a business in many regions of the country. So far, around 7 percent contribution of agriculture to the GDP can be seen during the last couple of years. Nevertheless, value added agriculture sector is taken under industry and therefore, the exact contribution of whole agriculture sector to the GDP is not well reflected.

Plant nutrition and nutrient requirement

Use of plant nutrients is important for a better plant growth and reproduction. In crop cultivation, 18 essential plant nutrients have been recognised and their supply is mandatory for optimum plant growth and development. Among the essential plant nutrients, carbon, hydrogen and oxygen are naturally taken from water and air; they are known to be framework elements. All other fifteen nutrients are provided from the soil as inorganic ions (mainly) and depending on requirement, they are categorised into two groups as ‘macro nutrients’ and ‘micro nutrients’.

Nitrogen, phosphorous, potassium, calcium, magnesium and sulphur are considered as macro nutrients while chlorine, iron, zinc, manganese, boron, copper, molybdenum, nickel and cobalt are considered as the micro nutrients. However, there are arguments on nickel and cobalt to be considered as micro nutrients.

All these plant nutrients are essential for plant growth and development. Under shortage of each, plants do not perform well and therefore, they show deficiency symptoms.

When the concentration of micro nutrients is greater in the soil they become toxic for the plants. Therefore, these nutrients should be maintained in the soil at optimum level.

Requirement of such plant nutrients can be determined by conducting soil analysis and plant tissue analysis. Under Sri Lankan context, mostly farmers think of supplying only primary macro nutrients (nitrogen, phosphorous, and potassium) to the crops. They do mostly this just as a practice even when there is no shortage of these nutrients in the soil. Then, either accumulation of those nutrients or washing off can be seen in the soil.

There are some other farmers who are technically sound about fertilizer application and hence, apply fertilisers only after soil testing. Therefore, they earn more profits by cutting down the amount of fertilisers. It is important to emphasise that, in certain soils, some nutrients are naturally available up to the required level, in particular some micro nutrients. Hence, external supply of such nutrients is not needed. Determination of soil pH is also equally important here as it affects the availability of nutrients in the soil.

Soil fertility management and fertiliser usage

Simply, soil fertility management means maintaining the basic soil physical, chemical and biological properties at optimum level for plant production.

Soil structure, soil texture, bulk density, soil water content and drainage property are considered as specific soil physical properties whereas pH, nutrient content, cation exchange capacity and organic matter content are considered as specific soil chemical properties. Soil organisms, both macro and micro, and their related aspects are the soil biological properties.

Except all these properties, there are many more other soil physical and chemical properties that are important in terms of soil fertility management and in turn the crop production.

In order to maintain soil properties, soils of the agricultural land should be frequently amended with organic and inorganic fertilisers.

Nutrient requirement of the plants can be correctly achieved by chemical fertiliser application whereas all other soil properties can be improved by organic fertiliser application (except inherent properties like soil texture).

However, the nutrient requirement cannot be sufficiently achieved by organic fertilisers especially in the present scenario given the hybrid varieties are concerned.

For example, urea contains 46% nitrogen but the commercial compost contains only one percent or little higher amount of nitrogen. Therefore, to supply the nutrient requirement of a particular crop, organic fertilisers should be applied in large quantity. If urea is applied with a rate of 100 kg per hectare, to obtain the same nitrogen requirement, organic fertilisers (compost) should be applied in metric tons.

In present agriculture, what is observed is most of the farmers think that supply of chemical fertilisers is the only practice that they should compulsorily follow to improve soil fertility.

Therefore, they keep adding chemical fertilisers regularly even with over dosages. Given this overdose use and also fertilizer application without soil analysis, cost of production has increased unwantedly. Although, over dosages are used plants uptake only the amount that they can uptake and really want for their needs.

Therefore, rest of the chemical fertilisers is released to the environment causing many adverse effects. For example, unused fertilisers (phosphates, nitrates etc.) are washed off on the surface of the soil into lowland water bodies and their concentration is then increased.

This leads to eutrophication facilitating algae like plants to freely grow in water bodies. Thus, the whole water system is disturbed causing environmental imbalance.

As reported, there is a high risk that blue babies can be born due to the consumption of high nitrate concentrated water.

On the other hand, continuous use of chemical fertilisers does not improve soil properties, except the precious supplement of nutrients. But, it can lead to soil degradation over the time likely due to misuse and overuse.

Chemical fertiliser use and crop yield

According to present discussions going on, there is a question whether chemical fertilizer application is essential for crop production in agriculture. It is noteworthy to mention here that irrespective of the source of supplement (organic or chemical), plants uptake nutrients in the same forms of inorganic ions. For example, plants absorb nitrogen into the plants either as nitrates (NO3˗) or ammonium (NH4+) ions.

The most important thing in relation to chemical fertilisers is that its overuse and misuse have to be evaluated and overcome.

As mentioned above, given the high sensitiveness of hybrid seeds to nutrient supplement and water use, high yields can be resulted only when nutrients and water are provided sufficiently.

Therefore, the need of hybrid seeds for their growth and development can be easily addressed by chemical fertilisers. But, it is questionable whether the same requirement of these cultivating varieties (high yielding) can be achieved by the organic fertilisers.

If the required nutrient quantity is not supplied by the organic fertilisers the yield will reduce drastically. Depending on the crop type and its duration, reduction of yield can be expected in different degrees.

For example, as per the available research findings, yield of paddy can be reduced at least by 20 percent. In tea cultivation, it could be 30 percent or more. Compared to organic fertilisers, chemical fertilisers are needed in small quantities and the most needed practice is the use of chemical fertilisers at the optimum dose.

Organic fertiliser usage and commercial agriculture

Compared to the time before 1950s, population of the country has increased from 6 million to 21 million over the time. Parallel to this population growth, demand for basic requirements was also increased and food requirement is prominent.

Among different crops, the country has reached to self-sufficiency in paddy due to application of technology over the past few decades. For example, the new varieties released by the Department of Agriculture have significantly contributed to such achievement. There is a reasonable question whether this achievement (yield) is realistic under organic fertilizer application only. This applies to all crops; however, we also have lost some traditional crop varieties from present agriculture.

This is experienced mostly due to the low yield of such varieties compared to hybrid varieties although they had some considerable qualitative considerations.

Given certain limitations, organic agriculture can be applied either as a subsistence farming system or as a system which produces food for a limited number of people.

However, soil quality improvement can be expected over the time. In commercial agriculture, supply of organic inputs (fertilisers) is a challenge as large quantities are needed to supply the nutrient requirements.

Thus, there should be some strategies to produce the required amount of organic fertilisers even though it definitely takes a considerable time period. There is a possibility that both organic and inorganic fertilisers can contain heavy metals depending on the original source of their raw materials. For example, the compost that is produced from municipal waste can contain heavy metals abundantly. When converting traditional agriculture into organic agriculture, around 8 million tons of organic fertilisers will be needed in total, as calculated.

The practical issue is whether we can produce this amount under local conditions with the available resources. If a certain portion of the organic fertilisers or their raw materials is to be imported in future to meet the local requirement we cannot assure about their quality in particular the availability of heavy metals and other toxic compounds.

Some exogenous weed seeds and microbial species that can make some detrimental effects can enter into the country. Given the amount needed, transportation problems can also be experienced with organic fertilisers as tons of inputs are needed to compensate the nutrient requirement which is supplied by only a number of kilograms of chemical fertilisers.

Therefore, production of organic fertilisers within farm site will be advisable. However, there should be a preparation for this need beforehand.

Under a fully converted organic fertilizer application system, there will be some specific challenges. For example, the falling of crop yield will have to be compensated by importing some food products.

Thus, a considerable amount of foreign exchange will be needed for this purpose. Another portion of foreign exchange will be needed for importing organic fertilisers if the required amount cannot be produced locally.

The next challenge is that the country is not in a position to produce at least a half of the total requirement of organic fertilisers for the moment and therefore, some practical strategies and solutions are needed in this regard. Similar efforts are recorded in some other countries like Australia for more than a decade but they have not yet been able to reach the target due to many difficulties. Therefore, understanding the realistic background is essential in this regards.

Integrated approach and soil fertility improvement

Given all above matters, it is clear that there should be a practical and holistic approach for addressing these issues. It is certain that a considerable time period is needed for converting a traditional agriculture system into a pure organic agriculture. That may be at least 10 years but can vary up to 20 years or more. Considering need of the country, an approach should be developed to maximise the positive impacts without affecting the food security of the country while minimising the negative impacts.

Here, one important aspect is that the application of fertilisers should be practiced only after conducting a soil analysis or a plant tissue analysis. If doing so, the fertiliser application rate can be reduced by a considerable fraction it may be a half for some soils and crops concerned and also may be less than that for some other soils and crops.

This will definitely reduce the cost of production as only the actual amount of fertilisers needed is recommended for a given site (site-specific fertiliser recommendation). Application of correct dose will prevent environmental exposure of unused fertilisers and in turn the contamination of water bodies.

However, the facilities should be developed all over the country for analysing soil samples and plant tissues. If we can do it in such a way undoubtedly, this will be a long term investment in terms of reducing the cost of production in agriculture as well as to receive great environmental and health benefits.

Overall, integrated plant nutrient management approach is suggested to obtain more benefits while preserving the soil.

This implies the sustainable use of soil as a resource for future use. Both organic and chemical fertilisers should be applied simultaneously in the field in order to increase the productivity. It helps develop soil and provide greater yield for a long time.

Also, it will prevent soil degradation and promote sustainable utilisation of the soil. Meanwhile, fertiliser subsidy should also be re-evaluated in order to avoid misuse of chemical fertilisers. Taking examples about practical application of chemical and organic fertilisers under both local and international conditions will provide more information on the reality of plant nutrients management in the soil.

Accordingly, new technologies and recommendations should be applied. In particular, local entrepreneurs should be promoted to produce technological tools and equipment for the use in national agriculture.

In conclusion, use of both chemical and organic fertilisers at fifty percent (50:50) basis or in another applicable ratio will provide greater benefits without collapsing the present status of the agriculture production. Here, some regulations are needed in implementing such practices.

Preventing misuse and overuse of chemical fertilisers in agriculture is the actual need of the day while encouraging application of quality-assured fertilisers in order to develop optimum conditions in soils for plant growth and development.

Finally, it is believed that all above matters will be helpful for the betterment of agriculture sector in the country. The experience we had on agriculture for thousands of years should be integrated with new technologies for a sustainable existence of agriculture assuring food security of all Sri Lankans.

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Chandana Sesath Jayakody

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