Biochar made from farm waste could help restore soil health and save fertiliser in Bangladesh, agricultural scientists said at a national workshop. Applied with balanced chemical fertiliser in trials, it raised maize yields by 29 per cent, aus rice by 23 per cent and boro rice by 21 per cent. Before it reaches farmers, they said, the costs need working out and national quality standards are needed.
The problem has two sides. Soil fertility is falling and dependence on chemical fertiliser rising, while much of the straw, wood and crop residue is wasted or burnt. Professor G K M Mustafizur Rahman, vice-chancellor of Gazipur Agricultural University, said organic matter in many fields has fallen below 2 per cent and about two-thirds of the country's soils are acidic.
Biochar is made by heating such plant waste at a set temperature with little or no oxygen, a process called pyrolysis. Its porous structure holds water and nutrients in the soil, and part of its stable carbon stays there for a long time. The vice-chancellor called it a 'three in one' technology: it improves soil structure, cuts nutrient losses and can raise the pH of acidic soils.
The keynote at the workshop of the Bangladesh Agricultural Research Council (BARC) in Dhaka on Sunday, 18 October, was given by Professor Mohammad Mofizur Rahman Jahangir of the soil science department at Bangladesh Agricultural University. In the results he presented, maize reached 9.21 tonnes a hectare, aus rice 4.97 tonnes, boro 6.02 tonnes and mustard 1.28 tonnes (17 per cent more). Biochar-coated urea gave the full yield with 75 per cent of the recommended nitrogen, a possible saving of a quarter of the nitrogen.
The data also showed ammonia losses falling by 36 to 37 per cent with biochar and compost, nitrous oxide emissions from soil by about 38 per cent, bulk density down by up to 12 per cent on average, porosity up by 41 per cent and plant-available water up by as much as 130 per cent. These effects depend on soil type, biochar quality and the rate applied.
There was practical advice too. Professor Jahangir said raw biochar should not go straight onto fields but be mixed first with compost, cow dung or another organic manure (co-composting). The trials applied one to three tonnes a hectare in rows or near the roots, though locally tested rates should be used. Dr Mohammad Monjurul Kadir, director general of BARI, suggested maize residue as a raw material.
Noting that Bangladesh uses about 2.7 million tonnes of urea a year, BARC executive chairman Dr Md Abdus Salam said that showing with data how much urea can be saved and what farmers really gain would open the way to subsidies and incentives. He warned against putting anything sold as 'biochar' on fields without testing, because of the risk of heavy metals, and called for national standards. BRRI director general Dr Md Rafiqul Islam spoke of possible income from carbon credits.
Photo: Vbenjou / Wikimedia Commons (CC BY-SA 3.0)
Source: Krishi Shomoy
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