◊ By Dr Karthik Nagendra

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The increasing prevalence of ecologically sustainable products in consumer markets is generally assumed to curtail anthropogenic impacts on the environment.

One of the most sustainable approaches to food production is organic agriculture. A 1% increase in its acreage could reduce emissions by 0.049%.

The solution revolves around recycling techniques and low external input with high harvest strategies. The main principle is based on enhancing soil fertility and diversity at all levels, making soil less susceptible to erosion.

These practices generally have a positive impact on the environment per unit of area, but not necessarily per product unit. Our food system has substantial impact on climate change and organic agriculture helps to mitigate the burning issues at a social and environmental front as well.

According to the Intergovernmental Panel on Climate Change (IPPC), the annual amount of greenhouse gases emitted by the agricultural sector was estimated at between 5.1 and 6.1 giga tonnes of CO2 equivalents in 2005.

This accounts for approximately 10–12% of total greenhouse gas emissions. Of these emissions, methane emission is the highest, with nitrous oxide in second position, while net emissions of CO2 are relatively minute.

Agriculture is the main emitter of nitrous oxides and methane according to current practice and knowledge. This could be due to our narrow approach to achieving high production and productivity without giving importance to environmental and social issues.

It is high time we harvest natural resources like sunlight and rainwater including recycling of biomass produced in the farm itself. Every blade of grass helps to sink atmospheric carbon, in addition to harvesting sunlight to produce food/feed for the living beings in the ecosystem.

Compared to conventional or integrated systems, the global warming potential of organic farming systems is considerably small when calculated per land area.

However, when the same is calculated for per product unit, the difference declines as conventional yields are higher initially than organic yields.

Under stress conditions like dry conditions or water constraints, organic agriculture may outperform conventional agriculture, both per crop area and per harvested crop unit.

The use of synthetic nitrogen fertilisers increases the global warming potential of conventional agriculture. Global nitrogen fertiliser usage (produced by fossil energy) in 2005 was 90.86 million tonnes. This is about 1% of global fossil energy consumption.

On the other hand, organic agriculture is self-sufficient in nitrogen.

Mixed organic farms practise highly efficient recycling of manures from livestock and of crop residues by composting.

Leguminous crops deliver additional nitrogen in enough quantities (this is the main source on stockless organic farms). Legumes help to fix atmospheric nitrogen in the soil.

Potential nitrogen production by leguminous plants through intercropping and off-season cropping is approximately 154 million tonnes, a potential which exceeds nitrogen production from fossil fuel by far, which is not fully exploited by conventional farming techniques.

Diversified crop rotation with green manure improves soil structure and diminishes emissions of nitrous oxide.

Soils treated organically are more aerated and tend to have much lower mobile nitrogen concentrations.

Both factors reduce emissions of nitrous oxides.

To further reduce any environmental impacts, it is advised to improve crop varieties, feature perennials in crop rotations, use cover crops (between successive crops or between rows of plantations) to avoid bare fallows, enhance plant and animal productivity and efficiency, and reduce unnecessary tillage using minimum to no-till strategies.

The on-farm use of farmyard manure – a practice increasingly ignored in conventional production – needs to be reconsidered in the light of climate change.

Conventional stockless arable farms using synthetic nitrogen fertilisers, manure and slurry from livestock production, or from non-ruminant farms, have become an environmental problem.

In livestock operations, nutrients are in excess due to which, over fertilisation occurs.

However, only 17% of the 100 Mt N produced in 2005 was taken up by crops. The remainder was somehow lost to the environment.

Between 1960 and 2000, the efficiency of nitrogen uses for cereal production decreased from 80 to 30%. High levels of reactive nitrogen (NH4, NO3) in soils may contribute to the emission of nitrous oxides and are the main drivers of agricultural emissions.

The efficiency of fertiliser use decreases with increasing fertilisation, because a great part of the fertiliser is not taken up by the plant but instead emitted into the water bodies and the atmosphere.

The emission of GHG in CO2 equivalents from the production and application of nitrogen fertilisers from fossil fuel amounted to 750 to 1,080 million tonnes (1 to 2% of total global GHG or Greenhouse Gas emissions) in 2007. In 1960, 47 years earlier, it was less than 100 million tonnes.

Recycling nitrogen on the farm by using manure and nitrogen fixing plants enhances soil quality and provides nutrients. This is the most prominent technique of organic and low external input agriculture.

However, timing and management of its use are essential. Soil mineralisation should deliver the elements to the plant at times of peak demand.

Organic and green manures, as well as, nitrogen from legumes can be managed very precisely owing to crop rotations including cover and catch crops.

In addition, improved distribution systems, such as decomposed desi cattle manure (dung and urine) application into soils, reduce nutrients losses considerably.

All these techniques are knowledge-intensive and require site-specific adaptations. As nitrogen on organic farms is far more costly than industrial nitrogen, there is a strong incentive to avoid losses and to learn and implement recycling techniques.

Methane accounts for about 14% of the greenhouse gas emissions. Two-thirds of this is of anthropogenic origin and mainly from agriculture.

Methane emissions stem to a large extent from enteric fermentation and manure management and are directly proportional to livestock numbers. A reduction of the Global Warming Potential (GWP) has also been found in organic dairies as compared to conventional dairies.

Organic cattle husbandry helps in reducing methane emissions by aiming towards animal longevity.

Cattle naturally prefer to graze and move freely under open atmospheric conditions. By doing so, they help to improve soil water-holding capacity. While moving, cattle nibble, mob, mow, mulch, and excrete, which helps to improve soil fertility.

It is important to manage cattle movement to avoid over-grazing of grasses so that regeneration of soil surface vegetation is not affected.

If we consider milk as only the economic product, the ratio between the unproductive phase of young cattle and the productive phase of dairy cows is favourable in organic systems because, calculated on the basis of the total lifespan of organic dairy cows, less methane is emitted.

On the other hand, lower milk yields of organic cows caused by a higher proportion of roughage in the diet, might increase methane emissions per yield unit. A model calculation of the best yield-methane emission rate at different diets (roughage versus concentrates) is missing.

The slightly reduced yields of organic farms might be nearer the optimum than conventional dairy production.

Composting and biogas production are often suggested as measures for mitigating climate change. Storage and composting of manure and organic waste have been strongly improved on organic farms in recent years.

Using modern techniques such as covering, processing compost and steering, the composting process prevents leaching and reduces N2O emissions.

Composting manure may reduce CH4 but enhances N2O emission. Compost use can greatly increase carbon sequestration in the soil compared to raw manure use.

The benefits of aerobic fermentation of manure by means of composting are ambiguous, as a shift from anaerobic to aerobic storage of manure can reduce methane emissions.

A very promising option, however, is controlled anaerobic digestion of manure and waste combined with biogas production. Biogas production from liquid slurry makes use of the evolving CH4 for energy and is applied by many sustainable farmers.

While this option is not restricted to organic production methods, organic agriculture has been at the forefront of biogas production systems for decades.

In the Rodale Farming Systems Trial in USA, the manure-based organic system sequestered 1,218 kg carbon per ha and year; the legume-based stockless organic system sequestered 857 kg per ha; and the conventional system sequestered 217 kg per ha.

18 organic and 10 conventional farms in Bavaria, Germany, were compared to calculate the organic farms’ annual sequestration at 402 kg carbon, while the conventional farms had losses of 202 kg. It was estimated that compost application and cover crops in rotation were particularly adept at increasing soil organic matter.

Agriculture can help mitigate climate change by either reducing GHG emissions or by sequestering CO2 from the atmosphere in the soil.

The application of improved agricultural techniques (ex, organic agriculture, conservation tillage, agroforestry with native tree species) reduces or stops soil erosion and converts carbon losses into gains.

Consequently, large amounts of CO2 are removed from the atmosphere. Organic agriculture possesses effective methods to reach both of these goals.

If agricultural practices remain unchanged, the loss of organic carbon in typical arable soils will continue and eventually reach a new steady state at a low level.

The author is COO, Aditi Organic Certifications