Organic Farming

Managing soil to improve organic matter

By Dr Shahzada Sohail Ijaz

ORGANIC matter in soil affects soil properties and processes and often one effect leads to another resulting in a complex chain of multiple benefits.

For example, adding organic mulch to the soil surface encourages earthworm activity, which in turn produces burrows and biopores increasing infiltration of water and decreasing its loss as runoff which helps reduce pollution of streams and lakes.

The quality of our soil is very poor in organic matter. A soil with 1.29 per cent carbon is considered to be sufficient in organic matter, but here the soil has less than that. The range of carbon in the soil is 0.52 to 1.38 per cent in different soil series, mostly less than one per cent.

Reasons for low organic matter content are stated below.

Climatic conditions: The mean annual temperature influences the processes of decomposition of organic matter. At high temperatures decomposition proceeds quickly. That is why high temperatures prevailing in the country coupled with low rainfall are conducive for a rapid decomposition and loss of organic matter.

Soil orders: The soils have been classified into 12 ‘orders’. The soil order plays key role in determining the potential of a soil to keep a certain level of organic matter. The largest indigenous soil orders are Aridisol and Entisol, which have the lowest organic matter content. Therefore, our soil has lesser capacity to hold higher organic matter content.

Availability of easy to-handle-mineral fertilisers: Before the advent of mineral fertilisers and green revolution, farmers used to replenish their soil by application of organic wastes. With the availability of easy-to-handle mineral fertilisers the farmers were able to get higher yields only with the application of mineral fertilisers. Thereby the use of organic wastes reduced drastically. The increasing prices of mineral fertilisers and soil degradation concerns have forced people to reconsider the organic sources in agriculture.

The poor economic condition of our farmers is another reason for less application of organic wastes. Almost no crop residues are left in the soil after harvest. The straw and other crop residues are used as fodder and animal dung is used as fuel. About 50 per cent 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.

Intensive tillage: Another reason for lower organic matter content of our soil is the practice of intensive soil tillage. Soil tillage aerates soil and breaks up organic residues, making them accessible to microbial decomposition thereby reducing organic matter content of the soil. The slogan “Dab Kay Wah Tay Raj Kay Khah” (Plow more, earn more) is no more valid in modern agriculture.

There is a large contingent of organic sources available in the country to be used for improving organic matter content of our soils. Some of them are as under.

Farmyard manure: Farmyard manure is a decomposed mixture of dung and urine of livestock with straw and litter used as bedding and residues from the fodder. It has been estimated that about 1.5 million tones of nutrients are available from farmyard manure in the country. About 50 per cent of the dung remains uncollected. Out of collected animals dung about 50 per cent is used as fuel. What ever 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 volatilisation 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: Poultry manure has a higher nutrient content than livestock manure. According to estimates the available poultry manure can contribute about 101,000 tones of nitrogen, 58,000 tones of phosphorous and 26,000 tones of potash.

Crop residues: Crop residues include straw, husk, leave, vegetable and fruit waste, grass cuttings, weeds, sawdust etc. Most of the crop residues such as wheat straw, sugarcane tops/trash, cotton sticks, rice husk etc., are used as fodder and as fuel. But other waste materials can be converted into useful compost manures by conserving and subjecting them to a controlled process of decomposition.

Green manure: Green manuring refers to the practice of growing crops, preferably legumes and ploughing them under, when they reach maximum production of green tops. Legumes 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. Sun hemp, guar and dhancha are suitable crops for green manuring.

Filter cake and silage: Sugar industry produces around 1.2 million tones of filter cake every year, which is a rich source of organic matter, micro and macro nutrients. Some sugar mills 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 be a good source of essential plant nutrients for crop growth.

Abattoir waste: Slaughterhouse wastes such as dried blood, meat meal, hoof and horn meal have high nitrogen content and are essentially concentrated organic manures, safe to use and effective on all crops. From slaughterhouse waste about 8,000 tons blood meal could be produced annually for manorial use containing essential nutrients.

Other materials: 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 are used as plant nutrients after proper processing and removal of heavy metals and undesirable materials.

Compost: Composting is the process of decomposing plant residues in a heap or pit with a view to converting the nutrients 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 to produce compost. Municipal/industrial wastes comprising town refuse and human excreta can also be composted.

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 is generally burnt as fuel. Biogas technology reconciles both these objectives: anaerobic decomposition of cattle dung yields both fuel (biogas) and organic fertiliser (sludge). Biogas is composed mainly of methane (CH4), about 60 percent. About 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 which can be generated from the family’s night soil and the dung of three cows.

Strategies for improving organic matter content of soil: Fertilisers, which have all the nutrients in available form, can provide sufficient plant nutrient flow to the corps. Fertilisers 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.

During a survey by the NFDC it was found that 49 per cent farmers use farm yard manure (FYM). Cultivation of sesbania as green manure crop in normal as well as marginally salt effected soils is being practised by some farmers and its worth has been proved in many studies. Among crop residues the practice of ploughing of cotton sticks is picking up among the farmers.

The Pakistan Agriculture Research Council (Parc), the National Institute of Biotechnology and Genetic Engineering (NIBGE) and provincial agricultural research institutes are carrying out work on biological fertilisation. The Parc in collaboration with the Engro Chemical Pakistan Limited commercialised rhizobium specific for chickpea in the name of Biozot. NIBGE is also marketing its bio-fertiliser for rice. Provincial research institutes are also providing inoculums to farmers 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 carbon stored in a soil. 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.

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.