Soil organic matter affects so many soil properties and processes that a complete discussion of the topic is beyond the scope of this article. Often, one effect leads to another, so 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 bio pores, 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.
Soil organic matter affects so many soil properties and processes that a complete discussion of the topic is beyond the scope of this article. Often one effect leads to another, so that a complex chain of multiple benefits results from the addition of organic matter to Often,s. For example, adding organic muto the soil surface encourages earthworm activity, which in turn leads to the production of burrows and other bio pores, which in turn increase the infiltration of water and decrease 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 compared to the desired level. A soil having 1.29 % C is considered to be sufficient in organic matter, but Pakistani soils have less than that. In a survey conducted by Farooq-e-Azam, it was reported that the range of soil carbon in Pakistani 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’s Soils
The low organic matter content of Pakistani soils can be attributed to the following reasons:
Climatic Conditions
The mean annual temperature influences the processes of decomposition of organic matter. At high temperatures, the decomposition proceeds very quickly. That is why the high temperatures prevailing in Pakistan are conducive to rapid decomposition and the loss of organic matter.
Soil Orders: The differences in organic matter content among soil orders also play a key role in determining the potential of soil to maintain a certain level of organic matter. The largest soil orders in Pakistan are aridisol and entisol, which are known to have the lowest organic matter content among all the soil orders. So our soils naturally have a lower capacity to hold higher organic matter content.
Use of Mineral Fertilisers
Before the advent of mineral fertilizers and the green revolution, farmers used to replenish their soils by applying organic waste. With the availability of cheap and easy-to-handle mineral fertilizers, farmers were able to get higher yields only with the application of mineral fertilizers. As a result, the use of organic waste was drastically reduced. The increasing price of mineral fertilizers and soil degradation concerns have forced people to reconsider organic sources in agriculture.
Poor Economic Conditions of Farmers
The miserable economic condition of our farmers is another reason for less application of organic waste back to the soil. Almost no crop residue is 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 material is burned as fuel, and only one-fourth is available for field application. Green manure is not adopted by our farmers because it does not give short-term economic returns.
Intensive Tillage
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 and thereby reducing the organic matter content of the soil. The slogan “Dab Kay Wah Tay Raj Kay Khah” (Plough more, earn more) has played a considerable role in the organic matter losses.
Different organic sources are 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
Farmyard manure is a decomposed mixture of the dung and urine of cattle and other livestock, the straw and litter used as bedding, and residues from the fodder fed to them. It has been estimated that about 1.5 million tonnes of nutrients are available from farmyard manure in Pakistan. About 50 percent of the dung in Pakistan remains uncollected. Out of the collected animal dung, about 50 percent is used as fuel in the 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 is finally spread on the field may have a 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 estimates, the poultry manure available in the country can contribute about 101 thousand tonnes of nitrogen, 58 thousand tonnes of phosphorous, and 26 thousand tonnes of potash.
Crop residues include straw, husk, leaves, 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 fuel. But other waste materials can be converted into useful compost manures by conserving them and subjecting them to a controlled process of decomposition.
Green manure
Green manuring refers to the practice of growing crops, preferably legumes, and plowing 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, the Pakistan sugar industry produces about 1.2 million tonnes of filter cake every year, which is a rich source of organic matter and micro- and macronutrients. Some sugar mills have molasses-based distillery plants, which produce silage-containing nutrients, especially potassium. If all these materials are recycled by composting back into the soil, they will also be a good source of essential plant nutrients for crop growth.
Slaughterhouse wastes, such as dried blood, meat meal, and hoof and horn meal, have a high N content and are essentially concentrated organic manures that are fairly quick-acting, safe to use, and effective on all crops. Slaughterhouses are widely spread throughout Pakistan, and largely their by-products are left outside. In one appraisal, it was shown that about 8000 tonnes of 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 from food processing industries. All these materials cannot be used directly as sources of plant nutrients. However, after proper processing and removal of heavy metals and undesirable materials, these can prove to be good sources of plant nutrients.
Compost
Composting is the process of decomposing (through the action of microorganisms in the soil) plant residues in a heap or pit with a view to converting the nutrients contained in the residue into a more readily available form.
In rural areas, crop residues, stubble, weeds, fallen leaves, remnants of fodder and green manure, etc. can be collected and stored in a heap or pit. In this way, as the last pit is filled, the compost in the first pit is ready for application. Municipal and 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.
Biogas compost
This is a process by which organic materials are biologically decomposed to yield energy in the form of combustible gases. The residual material provides valuable manure. Cattle dung, which should be used to improve soil productivity, is generally burned as fuel. Biogas technology reconciles both of these objectives: anaerobic decomposition of the cattle dung yields both fuel (biogas) and organic fertilizer (sludge). Biogas, popularly known as “gobar gas”, is composed mainly of methane (CH4), about 60 percent; thus, 1000 cubic feet of 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 that can be generated from the family’s night soil and the dung of three cows.
Strategies for Improving the Organic Matter Content of Pakistan Soils
Integrated Plant Nutrition Management System
Organic sources (farmyard 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 the natural weathering of minerals and organic materials. Biological sources have their own limitations because they are crop-specific. Fertilizers, which have all the nutrients in their available form, can provide sufficient plant nutrient flow to the crop. 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 associated with either source of plant nutrients are often overcome when they are used in judicious combinations, providing a mixture that, in the long term, is not only complementary but also synergistic.
At present, in Pakistan, during a survey by the NFDC, it was found that 49 percent of farmers use the FYM. The cultivation of sesbania as a green manure crop in normal as well as marginally salt-effected soils is being practiced by some farmers, and its worth has been proven in many studies. Among the crop residues, the practice of plowing cotton sticks is picking up among the farmers. Pakistan Agriculture Research Council (PARC), the National Institute of Biotechnology and Genetic Engineering (NIBGE), and the Provincial Agricultural Research Institute are carrying out work on biological fertilization. The Pakistan Agriculture Research Council, in collaboration with Engro Chemical Pakistan Limited, commercialized rhizobium specific for chickpeas under the name Biozot. NIBGE is also marketing its bio-fertilizer for rice under the brand name Biopower. Provincial Research Institutes are also providing inoculums to farmers for leguminous and non-leguminous crops.
Zero or Minimum Tillage System
Zero tillage is a system in which the soil is left undisturbed. The only soil disturbance is a narrow band caused by soil-engaging components of the planter or drill. Reducing soil disturbance from conventional, highly disturbed tillage methods to a minimum or zero tillage produces slower carbon losses and may even increase the amount of carbon stored in the soil. Long-term experiments conducted in developed countries support this conclusion. Other benefits of zero tillage for farmers include less labor, reduced machinery wear and tear, high soil moisture, improved soil tilth, reduced soil erosion, and reduced production costs.
In Pakistan, zero tillage has proven excellent for the rice-wheat cropping system. It allows utilization and conservation of antecedent soil moisture, time savings due to early planting, and minimizes yield losses attributed to soil structural breakdown under continuous cropping practices. The adoption of a zero-tillage system for all the agroecological 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 they are costly and environmentally hazardous, it is desirable to use cheaper and more 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 remove them when they exceed the threshold level. Increasing the cropping intensity is an excellent way to reduce weeds.
However, under our conditions, a minimum tillage system seems more promising than zero tillage. Cultivation can be done only when it is inevitable, for example, during seedbed preparation or when weeds exceed the threshold level. This would also help reduce the use of chemicals for the control of weeds and insects. Thereby reducing input costs and environmental concerns.