Another option to manage rice straw for enhanced crop productivity

By Punjab Agricultural University on 03 Oct 2018 | read
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Prali char: Another option to manage rice straw for enhanced crop productivity

R.K. Gupta, O.S.Sandhu and Vicky Singh

Department of Soil Science

In Punjab state, rice is cultivated on 30 lakh hectares with annual production of 225 lakh tons of rice straw. This huge quantity of rice straw has to be mopped up in about 15-20 days to plant succeeding wheat crop. Therefore, majority of farmers’ burn rice residue after combine harvesting of rice.Besides human/animal health and environmental hazards, substantial loss of plant nutrients (especially Nitrogen and Sulphur) and organic carbon occurs during burning of crop residues, which has important implications for soil health. Dear farmers keeping in view the decision taken by the National Green Tribunal to ban the burning of rice residues, now it is high time to give up burningand follow various methods and techniques developed by the scientists of the Punjab Agricultural University, Ludhiana to manage crop residues effectively and efficiently. We wish to apprise you with the latest techniques to utilize the hidden nutrients in the rice straw and contribute to the cause of soil and environment and serve the mankind.

Dear farmers, Punjab Agricultural University has recommended another technology which converts rice straw in to prali char and its subsequent use in crop production results in enhanced productivity from first year itself. In this section, procedure for the preparation of pralichar and the results of its application in the rice wheat system from demonstrations carried out at KVKs will be discussed.

Procedure for the preparation of prali char from rice straw

Prali char/biochar is carbon rich porous product obtained after thermo-chemical conversion of rice straw at low temperatures in the presence of little or no oxygen. It is prepared by heap method. In this traditional method, a heap or pyramid like structure (brick kiln) is raised to a height of 14 ft with 10 ft diameter. Then it is filled with rice straw. To start the combustion, rice straw is ignited from the top of the dome, covered with an iron lid and then immediately sealed with mud. To allow the combustion products to escape, vents are kept open. The paddy straw is subjected to partial combustion until the fire became clear and a very thin blue smoke starts coming out from the vents located in the upper portion of the dome. It indicates that biochar has been formed in this zone. Now seal the vents located in the upper portion of the dome with clay. Now the combustion advances to the middle portion of the dome and in the same way smoke starts coming out of these vents. Wait till the very thin blue smoke starts coming out from these vents. The moment it starts, seal the vents located in the middle portion of the dome immediately with clay. It shows that biochar is also ready in this portion also. Now finally combustion reaches the lower portion of the dome and again seal the vents located in the lower portion of the dome with clay as soon as the thin blue smoke starts coming out from these vents. Now biochar is formed in this portion also. This whole process usually takes 10-12 hours. After that cooling process is started by pouring diluted clay in water.  After two days, the biochar is taken out. It can also be removed on the same day by cooling it with water. By this process 12 quintals of rice straw can be converted in to approximately 6.5-7.0 quintals of prali char.

Change in different nutrients

To understand the advantages of this technology, let us know some facts that what happens to nutrients when rice straw collected from one hectare is subjected to burning in the open fields.

Table 1.Nutrient lost from the crop fields due to paddy straw burning


Sr No

Nutrient

Nutrient (kg) per ton of rice straw

Nutrient lost (kg) during burning of one ton of rice straw

Nutrient lost (kg) /acre

Equivalent to fertilizer

(kg/acre)

Equivalent cost of fertilizers /

acre (Rs)

1

Nitrogen

5.5

4.95

11.9

25.8 (Urea)

146.7

2

Phosphorus (P2O5)

2.3

0.575

1.4

8.6

(SSP)

77.6

3

Potash

(K2O)

25.0

5.0

12.0

20

(MOP)

240.0

4

Sulphur

1.2

1.08

2.6

2.9

(Bentonitesulphur)

311.0

5

Carbon

400

400

960



Total

775.3


In NW India cultivation of paddy produces 23 million tons of rice straw. Burning of this huge amount of rice straw will result in loss of 2.67 lakh tons(N, P, K&S) of nutrients worth Rs743 crores. Loss of carbon during burning of rice straw has not been accounted so far which is very essential for microbial activities in the soil to make the nutrients available to crop plants as well as health of the soil. Beside this monetary loss, approximately 46 million tons of CO2 (carbon dioxide) will be released to the atmosphere, in addition to CH4 (methane), N2O (nitrous oxide) and air pollutants. About 75% of greenhouse gases (GHG) emissions from agro-residues burning are CH4 and the remaining one-fourth was N2O. Burning has to be discouraged in view of its harmful effects on environment and soil productivity.

On the other hand, the prali char prepared from rice straw on an average contains 30-36% carbon, 0.5-0.6 % N, 0.16-0.22 % phosphorus and 2.0- 2.5 % potassium.

Table 2.Effect of prali char on the grain yield (q/acre) of rice during 2016 at USF, Ladhowal

Use of prali char

Grain yield of rice

% increase in rice yield

110 kg urea + 25 kg DAP

22.0

-

prali char-2t + 75 kg urea + 25 kg DAP

24.3

10.4

The data given in table 2 shows that application of 2 t/acre prali char along with 75 kg urea and 25 kg DAP resulted 10.4 per cent more grain yield over the yield obtained with the recommended fertilizers. Also it helped in saving 35 kg urea.The results of demonstrations carried out at different KVKs are given in Table 3.

Table3.Effect of prali char on the grain yield (q/acre) of wheat at different KVKs during 2017-18.

Use of prali char

Wheat Grain yield


Pathankot

Amritsar

Gurdaspur

Ferozepur

Mean

(90 kg urea + 55 kg DAP)

19.1

20.4

15.9

21.5

19.24

(55 kg urea + 55 kg DAP) +prali char- 2 t

22.2

23.2

17.5

22.5

21.47

(90 kg urea + 55 kg DAP) + prali char- 2 t

19.2

21.4

16.8

21.7

19.78


The data given in Table 3 shows that application of 2 tons of prali char along with recommended fertilizers resulted in 8.8, 10.1, 13.7 and 16.2 per cent increase in grain yield of wheat over the recommended fertilizers at KVK Ferozepur, KVK Gurdaspur, KVK Amritsar and Pathankot, respectively. It was observed that on an average 11.5 per cent increase in grain yield of wheat was recorded at the four sites with the application of prali char over recommended fertilizers. The increase in grain yield of wheat with the application of 75% of the recommended fertilizers along with 2 tons of prali char over recommended fertilizers varied from 0.5 to 5.6 per cent with an overall increase of 2.8 per cent. The results clearly shows that either you can save 25 per cent of the nitrogen with little increase in yield or can obtain 11.6% higher yields by applying prai char over recommended doses of fertilizers right from the first year.




Effect of prali char on soil health

Table 4. Effect of Prali char on different soil properties


Treatments

pH

EC(dsm-1)

O.C (%)

P

(kg/ha)

K

(kg/ha)

Amendments

No amendment

6.70

0.17

0.41

14.60

99.6

RSB -5 t/ha

6.70

0.22

0.52

22.93

299.7

CD(0.05)

NS

0.051

0.064

1.86

21.7

Initial values

6.73

0.10

0.41

13.2

138.0

Addition of prali char after two years resulted in increase of 26.8 % organic carbon, 57 % phosphorus and 200 % potassium (Table 4).Besides these properties, physical properties of the soil also increased significantly.

Dear farmers, at the end I will suggest you to stop burning rice straw and follow the aforesaid methods of straw management. It will help to increase crop yields, improve soil and human health, reduce the consumption of chemical fertilizers and in keeping the environment clean.

Kiln for the preparation of Prali Char










 

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