Shahzada Sohail Ijaz
Soil organic matter affects so many soil properties and processes that a complete discussion of the topic is beyond the scope. Often one effect leads to another, so that a complex chain of multiple benefits results from the addition of organic matter to soils. For example, adding organic mulch to the soil surface encourages earthworm activity, which in turn leads to the production of burrows and other biopores, which in turn increases the infiltration of water and decreases its loss as runoff, a result that finally leads to less pollution of streams and lakes.
In Pakistan, the soils are very poor in organic matter than the desirable level. A soil having 1.29 % C is considered to be sufficient in organic matter, but Pakistan soils are having less than that. In a survey conducted by Farooq-e-Azam it is reported that the range of soil carbon in Pakistan soils is 0.52 to 1.38% in different soil series. Most of them have less than 1%.
Reasons For Low Organic Matter Content of Pakistan Soils
The low organic matter content of Pakistan soils can be attributed to the following reasons.
The mean annual temperature influences the processes of decomposition of organic matter. At high temperatures the decomposition proceeds very quickly. That is why high temperatures prevailing in Pakistan are conducive for a rapid decomposition and loss of organic matter.
The differences of organic matter content among soil orders also play key role in determining the potential of a soil to keep a certain level of organic matter. The largest soil orders in Pakistan are Aridisol and Entisol, which are known to have lowest organic matter content among all the soil orders. So our soils naturally have lesser capacity to hold higher organic matter content.
Use of Mineral Fertilizers
Before the advent of mineral fertilizers and green revolution the farmers used to replenish their soils by the application of organic wastes. With the availability of cheap and easy to handle mineral fertilizers the farmers were able to get higher yields only with the application of mineral fertilizers. Thereby the use of organic wastes reduced drastically. The increasing price of mineral fertilizers and soil degradation concerns have forced people to reconsider the organic sources in agriculture.
Poor Economic Conditions of Farmers
The miserable economic condition of our farmers is another reason for less application of the organic wastes back to soils. Almost no crop residues are left in the soil after harvest. The straw and other crop residues are used as fodder for the farm animals and the animal dung is used as fuel. About 50% of animal droppings are not collected, about half of the collected is burnt as fuel and only one fourth is available for field application. Green manuring is not adopted by our farmers because it does not give short term economic returns.
Another culprit for the lower organic matter content of our soils is the practice of intensive soil tillage. Soil tillage aerates the soil and breaks up the organic residues, making them accessible to microbial decomposition thereby reducing the organic matter content of the soil. The slogan “Dab Kay Wah Tay Raj Kay Khah” (Plow more, earn more) has played a considerable role in the organic matter losses.
Different Organic Sources Available for Improving Soil Organic Matter in Pakistan
There is a large contingent of organic sources available in the country to be used for improving the organic matter content of our soils. Some of them are discussed here under.
Farmyard manure is decomposed mixture of the dung and urine of cattle of other livestock with the straw and litter used as bedding and residues from the fodder fed to them. It has been estimated that about 1.5 million tones of nutrients are available from farmyard manure in Pakistan. About 50 per cent of the dung in Pakistan remains uncollected. Out of collected animals dung about 50 per cent is used as fuel in the from dried cake, locally called “Pathi”. Whatever is collected for manuring is usually heaped on the ground surface with residues from fodder and other house sweepings. The nitrogen in the manure is subject to volatilization and leaching losses and the material that finally will be spread on the field may have low nitrogen content. The application of well-decomposed manure is more desirable than using fresh materials.
Poultry manure has a higher nutrient content than livestock manure. According to the estimates the poultry manure available in the country can contribute about 101 thousand tones of nitrogen, 58 thousand tones of phosphorous and 26 thousand tones of potash.
Crop residues include straw, husk, leave, vegetable and fruit waste, grass cuttings, weeds, sawdust etc. In Pakistan, most of the crop residues such as wheat straw, sugarcane tops/trash, cotton sticks, rice husk etc are used as fodder for animals and as a fuel. But other waste materials can be converted into useful compost manures by conserving and subjecting them to a controlled process of decomposition.
Green manuring refers to the practice of growing crops, preferably legumes and ploughing them under, when they reach maximum production of green tops. Legumes are preferred as they have the ability to fix atmospheric nitrogen. The amount of N fixed varies from crop to crop and may be about 20-40 kg/ha. In Pakistan Dhancha, Guar and Sunhemp are suitable crops for green manuring.
Filter cake and silage
According to an estimate Pakistan sugar industry is producing about 1.2 million tones of filter cake every year, which is a rich source of organic matter, micro and macronutrients. Some sugar mils have molasses based distillery plants, which produce silage containing nutrients specially potassium. In case, all these materials are recycled by composting back to soil, it will also be a good source of essential plant nutrients for crop growth.
Slaughter house waste
Slaughter house wastes such as dried blood, meat meal, hoof and horn meal; have a high N content and are essentially concentrated organic manures, fairly quick acting, safe to use and effective on all crops. Slaughter houses are wide spread throughout Pakistan and largely their by-products are left outside, in one appraisal, it was shown that about 8000 tons blood meal could be produced annually for manorial use containing essential nutrients.
Other solid and liquid based materials
The other solid and liquid based materials available include sewage and sludge, fishpond effluent, city refuse and some waste of food processing industries. All these materials cannot be used directly as source of plant nutrients. However, after proper processing and removal of heavy metals and undesirable materials, these can prove good source of plant nutrients.
Composting is the process of decomposing (through the action of micro-organisms in the soil) plant residues in a heap or pit with a view to converting the nutrients contained in the residue in more readily available form.
In rural areas crop residues, stubbles, weeds, fallen leaves, remnants of fodder and green manure, etc. can be collected and stored in heap or pit. In this way, as the last pit is filled, the compost in the first pit is ready for application. Municipal/industrial wastes comprising mainly town refuse and human excreta can also be composted. The preparation of urban compost on a large scale is being done in many countries. Some plants are also installed in Pakistan. Quite sophisticated machinery may be required for this purpose.
This is a process by which organic material are biologically decomposed to yield energy in the form of combustible gases. The residual material provides valuable manure. Cattle dung which should be used for improving soil productivity is generally burnt as fuel. Biogas technology reconciles both these objectives: anaerobic decomposition of the cattle dung yield both fuel (biogas) and organic fertilizer (sludge). Biogas, popularly known as “gobargas”, is composed mainly of methane (CH4), about 60 percent; thus 1000 cubic feet biogas is equivalent to 600 cubic feet of natural gas, 5.2 gallons of gasoline and 4.6 gallons of diesel oil. A small family of four would require 150 cubic feet of biogas per day, for cooking and lighting an amount which can be generated from the family’s night soil and the dung of three cows.
Strategies For Improving Organic Matter Content of Pakistan Soils
Integrated Plant Nutrition Management System
Organic source (farm yard manure, crop residues), in addition to providing nutrients, improve the physical condition of the soil. Nevertheless, organic materials release plant nutrients slowly. Crops require an instant flow of nutrients at special growth stages to ensure higher yield, which cannot be supplied by natural weathering of minerals and organic materials. Biological sources have their own limitations of being crop specific. Fertilizers, which have all the nutrients in available form, can provide sufficient plant nutrient flow to the corps. Fertilizers are the quickest and surest way of boosting crop production but their cost and constraints frequently deter farmers from using them in the recommended quantities and balanced proportions. The limitations associates with either source of plant nutrients are often overcome when they are used in judicious combinations providing a mixture, which in the long-term, is not only complementary but also synergistic.
At present in Pakistan during a survey by NFDC it was found out that 49 per cent farmers use the FYM. The cultivation of sesbania as green manure crop in normal as well as marginally salt effected soils is being practiced by some farmers and its worth has been proved in many studies. Among the crop residues the practice of ploughing of cotton sticks is picking up among the farmers. Pakistan Agriculture Research Council (PARC), National Institute of Biotechnology and Genetic Engineering (NIBGE) and Provincial Agricultural Research Institute are carrying out work on biological fertilization. Pakistan Agriculture Research Council in collaboration with Engro Chemical Pakistan Limited commercialized rhizobium specific for chickpea in the name of Biozot. NIBGE is also marketing its bio-fertilizer for rice in the brand name as Biopower. Provincial Research Institutes are also providing inoculums to the farmers formers for leguminous and non leguminous crops.
Zero/ Minimum Tillage System
Zero tillage is a system in which the soil is left undisturbed. The only soil disturbance is of a narrow band by soil engaging components of the planter or drill. Reduction in soil disturbance from conventional, highly disturbed tillage methods to minimum or zero tillage produces slower carbon losses and may even increase the amount of C stored in a soil. Long-term experiments conducted in developed countries support this conclusion. Other benefits of zero tillage to farmers include: Less labour, reduced machinery wear and tear, high soil moisture, improved soil tilth, reduced soil erosion and reduced production cost.
In Pakistan, the zero tillage has proved excellent for rice-wheat cropping system. It allows utilization and conservation of antecedent soil moisture, time saving due to early planting, and minimize yield losses attributed to soil structural break down under continuous cropping practices. Adoption of zero tillage system for all the agro ecological zones of Pakistan still needs a lot of experimentation and research work.
Weed control through chemicals is one of the drawbacks of this system. Because of being costly and environmentally hazardous it is desirable to use some cheaper and environmentally safe chemicals. It is also possible that instead of keeping the field completely free of weeds, we can keep them to a safe threshold level and only till when weeds exceed threshold level. Increasing the cropping intensity is excellent way-out to reduce weeds.
However, under our conditions, minimum tillage system seems to be more promising than zero tillage. Cultivation can be done only when ever it is inevitable, for example at seedbed preparation or when weeds exceed the threshold level. This would also help reduce the use of chemicals for control of weeds and insects. Thereby reducing the input costs and environmental concerns.
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