Crop Stubble or Paddy Straw - Utilities and Constraints

Instead of burning and discarding stubble, put it for better use!!

India is second largest producer of rice in Asia, after China. Every year India produces 120 million tons of paddy, out of which 24 million tons of rice husk is generated. Punjab produces 23 million tonnes of paddy straw and 17 million tonnes of wheat straw. On an average 2 tonnes of rice straw or stubble is produced per acre(0.4 hectares).

Rice husk is the outermost layer of the paddy grain that is separated from the rice grain during milling process. It is formed from hard materials, including silica and lignin, to protect the seed in the growing season. Rice husk was largely considered waste product and was burned or dumped until its prolific value and utility was realized.

Rice husk is commonly used in three forms as solid fuel, carbonized rice husk produced after burning and remaining husk ash after combustion.  

Rice husk in its loose form is mostly used for energy production, such as combustion and gassification. Combustion is the process of burning carbon in the rice husk, which emits CO2 and generates heat energy for further use. One of the most efficient uses of this by-product is its direct combustion without the need for a heat exchanger with a proper furnace to generate heat for drying paddy. Gassification is the process of converting rice husk to synthesis gas (syngas) in a gasifier reactor with a controlled amount of air. Syngas can be used as fuel for drying and cooking or in a cogeneration system to produce electricity.

Rice husk briquettes and pellets are produced using densification to increase the density of materials and their combustion performance. These densified rice husks are mainly used in industrial boilers as a substitute for fossil fuel. 

Rice husk ash is the remaining by-product after combustion is done. The amount of carbon remaining in ash depends on the combustion performance (i.e., complete or incomplete combustion). Rice husk ash can be used as a soil amendment and as additive in cement and steel, among others. However, only small amounts compared to the total rice husk production are used for such purposes.

Carbonized rice husk is produced by thermal decomposition of the rice husk under a limited supply of oxygen (O2) and at relatively low temperatures (less than 700°C). Biochar produced from carbonization can be used as soil amendment, for processing fertilizer, and as activated carbon, etc.

UTILITIES:

Few common uses of husks are:

1) Fuel: 1 ton of rice paddy produces 290 kg rice straw. Its calorific value is 2400 Kcal/Kg and 290 kg can produce 100 KWh of power. Rice straw or stubble can be used alone or mixed with other bio mass material in direct combustion, whereby combustion boilers are used in combination with stream turbines to produce electricity and heat. The energy content of rice straw is around 14MJ per Kg at 10 percent moisture content. The by product is rice husk ash, which has an economic value and can be used in cement and brick manufacturing, construction of roads and embankments, etc. 

2) Fodder: Rice straw is mainly used as a source of fodder for the livestock. With the biological treatments and use of certain organic chemicals, its digestibility and nutrient value can be increased. A  difficult for fodder cutter to cut the straws as they get easily blunt while cutting the thick and sharp paddy straws. 

3) Used as husk ash in cement industry: When husk is burned under control temperature, it forms husk ash. Rice husk ash is used as partial replacement of ordinary Portland cement in concrete(Small quantity), saving on cost.

4) Fertilizers and Substrate Manure: Rice stubble or straw is rich in nitrogen, potassium and silicon. The potassium in the straw can get leached by rain water. On burning rice straw large losses of nitrogen and small losses of potassium occurs. Rice straw can be added to field as straw itself, or as compost or as straw ash depending on the local field itself. Rice straw and rice husk is a very valuable fertilizer and should not be wasted.   

5) Maintaining the moisture content in the soil: Rice stubble or straws and husk spread on the farm fields control the moisture levels in the soil helping it to stay fertile and productive. Optimum levels of moisture maintain right levels of nutrients and microbes in the soil, that enhances soil's fertility.  

6) As Packaging goods and Paper/board making: Paddy stubble or rice straws are used in paper making. It is also recycled into products such as boxes, chopsticks, boards, pellets, etc without using trees. There are environmental friendly and don't adversely affect the environment like new packing.e.g thermocole, plastic, etc

7) Insulating material as filling and spreads: Rice straws have high surface area and light weight. They posses insulation quality and are frequently use as spreads while transporting delicate and fragile objects.e.g fruits, glass, ceramic etc.

8) Mulching in Crop production: Mulching is the process of weed management by reducing the weed seed germination, blocking weed growth and holding soil moisture for better crop growth. Rice Husk straw suppresses weed seedlings and help retaining moisture in the soil. Later it break downs to form substrate manure. In this process husk straws are spread underneath the vegetables. Mulching was a successful technique in turmeric crop and is usually used in creepers. Mulching basically does:

• Reduce weed seed germination
• Shade and physically hinder emerging weeds
• Enhance crop growth by soil moisture conservation and sometimes by modifying soil temperature.

CONSTRAINTS:

1) Lack of awareness of its potential to farmers and industry persons: Farmers and agriculture industry person are not much aware of the use of rice stubble. They usually consider it as a waste and discard it in farm grounds.

2) Insufficient information about its proper use: Farmers usually use rice stubble for livestock fodder. Or as burning fuel in households. Not much of its use is known to people.  

3) Economic problems: Farmers usually have economic troubles. For them it gets difficult to put money in machines and other technologies for the collection and processing of stubble.

4) Penetration of technology: Processing of rice stubble for better use requires technological inputs. But farmers due to lack of finances lack technologies to fully utilise by products. 

5) Lack of interest: Burning stubble is easy for farmers instead of putting it to some other use. Processing and utilising it in other forms require stringent inputs.

6) Lack of environmental concerns: Those who burn stubble are less concerned about its adverse effects on the environment. 

8) Stubble difficult to be used as fuel: Rice straws are difficult to burn in most combustion furnaces, especially those designed for power generation. The primary issue concerning the use of the rice straws and other bio mass material for power generation is fouling, slagging and corrosion of the boiler due to the alkaline and chlorine components of the ash. 

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