Soil organic matter influences many soil properties and processes, so a complete discussion is beyond this article’s scope. One effect often triggers another, creating a chain of multiple benefits. For example, adding organic mulch to the soil surface encourages earthworm activity. Earthworms produce burrows and other bio-pores, which increase water infiltration and reduce runoff. This process ultimately decreases pollution in streams and lakes.

In Pakistan, farmers struggle with soils low in organic matter. Soils need at least 1.29% carbon to be sufficient, but most Pakistani soils fall below this level. A survey by Farooq-e-Azam reported that soil carbon in different Pakistani soil series ranges from 0.52% to 1.38%. Most of them have less than 1%.

Reasons for Low Organic Matter Content of Pakistan’s Soils

The low organic matter content in Pakistani soils results from several key factors:

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 differ in organic matter content, which affects their potential to maintain adequate soil organic matter levels. Aridisol and Entisol, the largest soil orders in Pakistan, contain the lowest organic matter levels among all 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 cheap and easy-to-use mineral fertilizers, farmers achieved higher yields by applying only mineral fertilizers. As a result, farmers drastically reduced the use of organic waste. 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. After harvest, farmers leave almost no crop residue in the soil. Farmers usually heap the remaining dung for manuring on the ground with fodder residues and household sweepings. Some dung is burned as fuel, while only a small portion is applied to the fields.

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 organic residues, making them available for microbial decomposition. This process reduces the soil’s organic matter content. The slogan “Dab Kay Wah Tay Raj Kay Khah” (Plough more, earn more) has significantly contributed to these organic matter losses.

Different organic sources are available for improving soil organic matter in Pakistan.

Pakistan has a large supply of organic sources that farmers can use to improve soil organic matter. Farmers can use these organic sources, which we describe below.

Farmyard manure

Farmyard manure consists of decomposed cattle and livestock dung and urine, bedding straw and litter, and leftover fodder residues. Experts estimate that farmyard manure provides about 1.5 million tonnes of nutrients in Pakistan. About 50 percent of the dung in Pakistan remains uncollected. Farmers use about 50% of collected animal dung as fuel in the dried cakes, locally called “Pathi.” Farmers usually heap the remaining dung for manuring on the ground along with fodder residues and household sweepings. Nitrogen in the manure can volatilize or leach, so the material farmers apply to the fields often has low nitrogen content. Using well-decomposed manure is more effective than applying 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, farmers use most crop residues, such as wheat straw, sugarcane tops, cotton sticks, and rice husk, as animal fodder and fuel. Farmers can convert other organic waste into valuable compost by conserving it and using a controlled decomposition process.

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.Farmers prefer legumes because they can 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 farmers recycle all these materials through composting, they provide essential nutrients for crop growth.

Slaughterhouse wastes, such as dried blood, meat meal, and hoof and horn meal, contain high nitrogen and act as concentrated organic manures that work quickly, are safe, and benefit all crops. Slaughterhouses exist throughout Pakistan, but farmers leave most by-products unused. One study estimated that farmers could produce about 8,000 tonnes of blood meal annually, providing essential nutrients for manuring.

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. Farmers cannot use these materials 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, farmers can collect crop residues, stubble, weeds, fallen leaves, fodder remnants, and green manure and store them in heaps or pits. As the last pit fills, the compost in the first pit becomes ready for field application. Farmers can also compost municipal and industrial wastes, including town refuse and human excreta. Many countries produce urban compost on a large scale, and Pakistan has installed some composting plants. Producing urban compost may require sophisticated machinery.

Biogas compost

In this process, microorganisms biologically decompose organic materials to produce energy in the form of combustible gases. The residual material provides valuable manure. Farmers should use cattle dung to improve soil productivity, but they generally burn it as fuel. Biogas technology reconciles both of these objectives: anaerobic decomposition of the cattle dung yields both fuel (biogas) and organic fertilizer (sludge). Biogas, commonly called “gobar gas,” contains about 60% methane (CH₄). One thousand cubic feet of biogas equals 600 cubic feet of natural gas, 5.2 gallons of gasoline, or 4.6 gallons of diesel oil. A family of four can generate 150 cubic feet of biogas per day for cooking and lighting using their night soil and the dung from 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 need a rapid supply of nutrients at specific growth stages to achieve higher yields, which natural weathering of minerals and organic materials cannot provide. 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. Farmers often overcome the limitations of individual nutrient sources by using them in balanced combinations, creating a mixture that is both complementary and synergistic in the long term.

A survey by the NFDC found that 49% of farmers in Pakistan use farmyard manure (FYM). Some farmers also cultivate sesbania as a green manure crop in both normal and slightly salt-affected soils, and numerous studies have confirmed its benefits. 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 farming system where farmers leave the soil undisturbed. The only disturbance occurs in a narrow band created by the soil-engaging parts 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. Farmers cultivate the soil only when necessary, such as during seedbed preparation or when weed levels exceed the threshold. This would also help reduce the use of chemicals for the control of weeds and insects. Thereby reducing input costs and environmental concerns.