The global concern has heightened in the recent past over the need for sustainable agricultural production and environmental protection with the Asian region being especially vulnerable due to the twin problems of population pressure and land scarcity. The question that is very often being asked is whether the growth in agricultural production required to feed, clothe and shelter the ever growing population and even the land resource base itself can be maintained in a sustainable and environmentally sound manner.

Developing countries are expected to produce more and more from less and less to meet the global demand; thus presenting the biggest challenge to agronomist to boost crop production and productivity. In countries like Sri Lanka, which heavily depends on agricultural production, the problem is aggravated by degradation of agricultural soils due to mismanagement of soil resources and monocultureal cropping systems adopted in plantation areas. Thus, science and technology are under strong pressure to improve the agricultural productivity of the land that is currently under production, reclaim degraded and unproductive agricultural soils and conversion of marginally productive soils to significantly higher level of productivity. Future environmental sustainability will however need gradual and careful shift to lower external input. Plantation agriculture is known to heavily dependent on relatively intensive use of purchased inputs such as chemical fertizers and other agrochemicals.

To meet these targets, usage of inorganic / Organic manures, organic wastes and biofertilizers will have a major and important roll to play. Yet, even in the developing countries handling and using inorganic fertilizers, organic manures and composting procedures are all being considered as labour intensive and expensive. In these circumstances, agronomic technology packages with biofertilizers & byproducts in combination with the conventional inorganic and organic nutrient management systems relevant to the identified needs may offer an effective answer. Over the years, the technology of inoculants production, quality control and simple procedures for implementation at growers level have drastically progressed towards a global movement.

The advantages of cyanobacteria ( blue-green algae) and rhizobia have been clearly established in several countries all over the world. The critical role of Symbiotic Biological Nitrogen Fixation systems ( SBNF) in the nitrogen economy of the soils is no longer arguable. The usage of Azotobacter for Tea, Rubber, Coconut, Plantation crops and most of the horticultural crops was established way back in 1960’s.

The relatively newly recognized "broderline" SBNF systems such as Azospirillum and asymbionts like Acetobacter, Alcaligenes etc., has also opened up the concept of microbial nitrogen fixation. There is abundant testimony to the existence and successful application of this technology at the farm level. Presently the technology is well accepted and practiced in Australia, Brazil, Argentina, USA, Italy, India, China, Philippines etc. By using genetically engineered strains, it is now possible to fix about 250kg/ha and even more atmospheric nitrogen at the field level. Specific nitrogen fixing strains have been isolated by scientists which are compatible with specific agro-climatic conditions, soil, nitrogen status, root exudates and nutrient availability.

According to published information on phosphate status of soils 4% of the Asian soils are reported to be low in phosphate. A group of heterotrophic microorganisms are known to have the ability to solubize inorganic phosphorous derived from insoluble sources. The solubilization of P is found practically feasible in the on-farm trials and the useful organisms available are : Bacillus megatherium, B. circulans, B. subtitles, Pseudomonas striata, Penicillium solitum, Aspergillus awarmori, Trichorderma sps. etc. The solubiluzation of P by these microorganisms is attributed to excertion of organic acids like Citric, Glutamic, Succinic, Lactic, Oxalic, Gly-oxalic, Maleic, Fumaric, Tartaric and Alfa-keto butyric. These microbes whither the rock Phosphate and tricalcium phosphate by decreasing the particle size to amorphous.

The action of organic acids has been attributed to their ability to form stable complexes with Al++, Ca++; Fe++ and Mg++. In addition to ‘P’ Solubilization, these microorganisms can mineralize organic P into soluble form. These reaction take place in the rhizophere. The microorganisms render more P than is required for their growth and metabolism. The surplus is more than 50%, which is generally absorbed by the host plant. ‘P’ solubilizers also produce fungistatic and growth promoting substances which influence plant growth. Mycorrohizas are very useful in making the bound and rock phosphate available to plants. Methodologies have been worked out to make the application of mycorrhiza successful at field level. Research on this subject in rubber plantings had been done way back in 1970s

A consortium of decomposers are responsible for solubilization of the unavailable potassium into easily assimilable form by the plants. The package of potassium solubilizers was first produced in China and now being produced in India and other Asian countries.

In the last decade, microbial products were success-fully demonstrated by the scientists around the world for N fixation and P & K solubilization in non-legume plants. They include tea, coconut, rubber, tropical cereals, vegetables, plantations etc. & commercial crops like cotton, sugarcane, tubers etc. Infestation of beneficial microflora in cereals and commercial plants by paranodulation is also in progress at research centers.

Research is continuing on effective mineralization of soil by Agrobacterium sps. and on the pollution control by bacteria & fungi and other related subjects. The products for controlling Hydrogen Sulphide, Mercaptans, Ammonia and Nitrite levels are already being marketed in other countries and they have wide range of applications.

The process of decomposition or breakdown of organic matter under aerobic conditions ( oxygen rich conditions) into a soil like material called compost is termed composting. This transformation of material into compost is aided by invertebrates( insects and earth worms) and microorganism ( bacteria and fungi). Different species of earth worms and aerobic bacteria are used to produce " Vermi Casting" – a biofertilizer. The gut of earth worms is an effective tubular bioreactor with raw materials entering from month and product ( castings) coming out from the other end. Castings produced have balanced plant nutrients, rich in vitamins, enzymes, antibiotic and growth hormones. Experiments with different earth worm species have shown that some have been able to reduce the C:N ratio of waste by about 60 – 75%. The available P has been increased by some to about 160% and the available K by about 200%.

Plantations are well aware of the many advantages of applying organic manures to the soil. But their knowledge of the various types and techniques of recycling organic waste is still limited. The scientific methods of composting in particular are still lacking or not being followed in practice by growers as it is believed to be labour intensive and materials for composting are not available in large quantities. But this is not tree. The main organic resources available in agricultural areas such as cattle dung, poultry litter manure, urine and litter, crop waste/residues like rice straw, poultry droppings sheep and goat droppings, waste from fruit and vegetables, coir dust and rice husk and bran, can easily be used effectively for such purposes.

In Sri Lanka, farm yard manure is the most important organic manure. It is a decomposed mixture of dung and urine of cattle, poultry or other livestock together with residues from the fodder, and the straw used as bedding, Generally, because of improper storage and composting conditions, loss of nutrients takes place by leaching or volatilization. The quantities of FYM produced would depend upon animal population and efficiency with which the animal excreta is collected and preserved. The droppings of different animals have different contents of NPK. It is imperative that the collection and preservation of farm year manure should be done properly. In addition to farm yard manure, poultry manure is also important because of its higher nitrogen content. Storage of farm yard manure in heaps, exposed to sun, air and rainfall accounts for substantial nutrient losses. Appropriate technology is available for rapid composting and growers can reduce nutrient loss and instead recycle in crop productivity.

The most common crop residues are prunings from tea bushes, litter of leguminous cover crops, stubble, fallen leaves, rice straw etc. But, most of it is not used for composting or recycling because large portions are either used as dead mulch and are not collected, and left in the field for natural recycling ( Stubble, fallen leaves etc.) except rice straw which has to be transported from paddy fields.

A leguminous manure crop may contribute about 30 – 40 kg/ha/year of nitrogen. Green manuring can very effectively contribute to economize on nitrogen fertilizers. Factors like cost and availability of seeds at the right time of sowing green manure crops, availability of moisture for its growth etc., may however, hamper its adoption under different agro-ecological conditions.Green manures, when allowed to decompose certainly add the nutrients present in their biomass. This includes bulk of the N they have captured ( fixed) from the air but other nutrients that have been absorbed from the soil. Green manuring, apart from making net nitrogen addition, basically recycles other nutrients back to the soil.

In the past, and even currently emphasis has been and is being placed on increased use of chemical fertilizers, possibly due to misleading yet, effective sales promotion campaign adopted by large fertilizer dealers and sales promotion agencies and the conservative approach adopted by research, although indiscriminate use of chemicals fertilizers have long been known to increase cost of production, create imbalances and cause environmental penalties.

The cost escalation of chemical fertilizers resulting from galloping price increases of crude oil, shifts in governments fertilizer policies through reduction or removal of subsidies, widely fluctuating produce prices and growing concern of environmental degradation, demand that approach should shift to eco-friendly and cost effective agro-technologies to increase crop production / productivity from steadily decreasing and degrading land resource base that places considerable strain on the fragile ecosystem. For example in Rubber, the drainage of nutrients via the latex does not adversely affect the overall nutrient status. The mature rubber ecosystem does not respond continually, in terms of increased latex flow, to fertilizer application. The rubber boom in the past may have provided an opportunity to conceptualize that with additional chemical fertilizer, for which the necessary financial resources could have been found then, latex production could be boosted. This is a very misleading thinking. With application of fertilizers at the required rate during the unproductive immature phase, fertilizer application during the early production phase could be easily discontinued. The benefits in terms savings in fertilizer bills and less environmental penalties would be considerable. Several years of experience in rubber fertilizer use provides support for this concept.

In any case, indiscriminate use of chemical fertilizers cannot find a place in the current socio-economic scenario in plantations. The recent wage increase demand by plantation workers is of deep concern and is an indication that the plantation workers have been driven in to poverty with escalating cost of living. Plantation workers are among the lowest paid and the most oppressed sections of the Sri Lanka working class. National data on poverty indicates that 30% of the estate population live below the poverty line. Inputs such as chemical fertilizers and other agrochemicals are no doubt required to boost productivity, but indiscriminate use of such inputs is definitely not warranted. Millions could be saved. Benefits of galloping price increases in produces were also unknown to this community that has provided strength for the sustainability of the industry they serve. Several avenues other than worker wages are still available to keep the COP at reasonable levels.

The hallmark of sustainability of plantation agriculture will depend heavily on the strategies adopted for reducing the agro-chemical load by skillful manipulation and deployment of motivated, skilled, trained, well managed, well looked-after and contented work force.