Soil security is the foundation of green agriculture and strategic component of eco-friendly economic development. It harmonizes the ecosystem of earth. Commonly called ''OM'' organic matter is very imperative element for soil health as it maintain the stability of profile, texture, fertility and structure of soil ecosystem. As the Sustainable Development Goals no. 15 is ''Life on Land'', context demands organic matter oriented soil health for sustainable food chain. Organic matter influences the physical conditions of a soil in several ways. Plant residues that cover the soil surface protect the soil from sealing and crusting by raindrop impact, thereby enhancing rainwater infiltration and reducing runoff. Surface infiltration depends on a number of factors including aggregation and stability, pore continuity and stability, the existence of cracks, and the soil surface condition. Increased organic matter contributes indirectly to soil porosity (via increased soil faunal activity). Fresh organic matter stimulates the activity of macro-fauna such as earthworms, which create burrows lined with the glue-like secretion from their bodies and are intermittently filled with worm cast material.

Setting the Scene

Soil is a complex growing habitat that remains productive only if it is cared for and nurtured. Combating and addressing soil pollution is the only way to minimize the risks for food security, human health and the environment. The major part of Bangladesh is on the delta formed by the three major rivers like Brahmaputra, Ganges and Meghna. The Ganges, Brahmaputra, Meghna river system drains a basin of some 1.76 million sq.km. Over millennia the sediments have built a broad delta forming most of the area of Bangladesh and the submerged delta-plain in the Bay of Bengal. These huge sediments are the major sources of formation of 80% soils of the country. The remaining 20% of soils have been formed in tertiary and quaternary sediments of hills (12%) and in uplifted Pleistocene terrace (8%).

Heavy Metals Contamination in Soil

Heavy metals, one of such toxic contaminants, are not bio- and thermo-degradable, hence accumulate in the environment up to hazardous levels. For some years, reports have told of its alarming degradation by several means. If the current rates of loss are continuing then the topsoil reserves would disappear in about 150 years. Trace elements can be mobilized from arid soils through plant uptake and erosion/leaching processes, but these soils usually contain higher contents of trace elements than other soils.

Soil Cadmium is derived from weathering of rocks and minerals or from numerous anthropogenic sources. Two primary sources of heavy metals in the soil are (i) the natural back¬ground i.e. metals derived from parent rocks; and (ii) the anthropogenic contamination i.e. those orig¬inated from human activities. Most of the soil metals today have originated from anthropogenic sources than natural ones. Meanwhile, irrigation of agricultural soil with polluted municipal and indus¬trial wastewater is another vital source of pollution.

Heavy metal content is one of the deciding factors for the quality of phosphate fertilizers, which does not have any standard permissible limit because the maximum allowable content depends on soil characteristics, irrigation water quality, crop type, etc. Fertilizers are one of the key factors for agricultural development to promote food security and maintain the agricultural productivity of soils. It also causes serious environmental contamination notably in the agricultural soils. Day by day the fertilizer unfortunately now becomes a 'necessary evil'. Excessive and continuous uses of nitrogen and phosphorous fertilizers for decades have converted the agricultural soils into virtual chemical time bombs. However, soils are polluted with pesticides and organic and mineral fertilizers.

Arsenic is widely distributed in soils, mostly combined with iron, nickel, gold and sulphur. Arsenic in soil may originate from the parent materials that form the soil and from industrial waste discharges or agricultural use of arsenical pesticides. Soil is an important natural resource for mankind, but it also serves as an important medium for the accumulation, transformation and migration of toxicants. The total amount of arsenic in soil and its chemical forms has an important influence on plant growth and animal and human health. Accumulation of arsenic in soil may be caused by irrigation water from sources such as mines. About 40% of the net cultivable area of Bangladesh is irrigated, where 60% of irrigation water comes from ground water. This leaves a risk of soil accumulation of the toxic element and eventual exposure of the food chain to Arsenic contamination through plant uptake and animal consumption. In some highly affected areas, the concentration of Arsenic has been found to about as high as 84 mg/kg. In a study, the maximum Arsenic concentration in irrigation water was found to be 0.55 mg / l; irrigating a rice field with this water when the requirement is 1000 mm of water, it has been calculated that the As load will come to 5 kg As/ha/yr.

To ensure food quality assurance, the heavy metal contamination of food is one of the most important assessment parameters. In agricultural field heavy metal contamination is an important problem that directly posing a serious health risk for human beings and others. In Latin America, the East, and South Asia, the Middle East and the West Indies rice is one of the most important staple foods which are the staff of life for 3 billion people. It also provides about 30% of the dietary energy and 20% of the dietary protein in Asia. But rice may contain significant amounts of contaminants such as arsenic (As), cadmium (Cd) and lead (Pb).

Agro-chemicals and Organic Matter in Soil

In our country, farmers employ different inimical pesticides and fertilizers in agricultural soil without considering water and land pollution. They employ potash, sulphate, calcium carbonate, triple super phosphate in land without the adequate knowledge on agrochemicals. Specifically, for potato, egg-plant they use − carbendajin, wantap-50, wansilva 10, quinfis-25%, denitol, festaq 2.5, melathion, corden, methoxicore, bydrin, dibrone, diajinon 10, lebasid and dimecron. Fenom, theovit, nexin, sevin 10%, diplerox, monotuf 40, thiojen are applying in agro field for sponse gourd, ribbed gourd, teasle gourd, sweet gourd, cucumber, cabbage, cauliflower and Hyacinth bean. For Aush, Amon and Boro − polivit-500, kiridan-5, crijol-5, basudin-10, topsin mithyle, ripcord, dursburn 20 and sebin-60. As more chemical fertilizer and pesticide are used in crop production, more methane gas is produced, thus commercial cultivation contributes to the climate change, globally and particularly in Bangladesh. Consequently, application of inimical fertilizers and pesticides lessen water holding capacity and nutritional content of soil which are raising a concern about toxicants free food.

According to Soil Resources Development Institute (SRDI), our soil health has been loosed 40% organic matter for last 1 decade. Men made disasters and climate change affects the content of organic matter (Sulfur, Phosphorus, Potassium, Boron, Calcium and Magnesium) of soil in Bangladesh. 52 lacs hectares of soil has been loosed micro-organisms which affects natural soil ecology. Research mentions, 10 lacs 56 thousands hectares of agricultural is polluted through salinity mostly in coastal region (93 sub-distrcits of 18 districts).

Fundamental Causes and Consequences

Lose of organic matter in soil is very harmful for our civilization. In general, brick field, construction of new ponds and lakes; cultivation of AKASMONI AND EUKALYPTUS tree, Jhum cultivation, contract farming, plastic pollution and crop rotation pattern changes our organic matter content in soil. Soil Resources Development Institute mentions, 25% organic matter lose in 1973 and 40% in 2008. Now the rate is 53%. Diverse study clarifies individually potassium (K) is 50%, Boron (B) is 15% and Phosphorus (P) is lose for last 10 years. If this figure is continue, 6 core people can be refugee and natural food chain would be damaged.

Concluding Remarks

Every year, world soil day celebrates to aware the mass people on soil pollution, soil biodiversity, soil health and related climatic insurgencies. As the global context of bioterrorism, contract farming between famers and international companies, micro-organisms business affects ecological health of soil, time needs inducement of green or bio-fertilizers to escalate organic matter.

The components of bio-fertilizers can be green wastes, coconut cake, oil cakes, farm yard manures, sludge, coal ash, wood ash, paddy husk, castor cake, mustard cake, groundnut cake, linseed cake, fish meal, water hyacinths, cow dung, vegetable materials, stool of livestock's, weeds of big tree make soil more (Boron, Magnesium, Calcium, Phosphorus and Potassium) enriched and healthy for sustainable agricultural production as well as environmental sustainability.

Shishir Reza, The Writer is an Environmental Analyst and associate member, Bangladesh Economic Association