The agriculture sector topped the list among sectors in the Greenhouse gases (GHG) emissions in the 2009 report of the National Environment Commission (NEC). Emission of methane from manure and nitro oxides from the application of inorganic fertilizers appeared to be the main sources of GHG. These emission figures have not changed significantly as reported in the Third National Communication Report to the UNFCCC by NEC in 2020, except an additional emission contribution from urea fertilizer applications.
Perhaps it is time to engage relevant national research institutes to study and update these emission figures including small farmers contribution in carbon sequestration or GHG emissions.
Farmers in many parts of the country remove weeds manually and leave it in between growing crops or on the bunds of cultivated fields. These weeds compete with the crops for plant nutrients, soil moisture and sunlight during the growing season. The dried weeds are either burnt or ploughed back into the soil in the coming season. For instance, the dryland farmers of Shingkhar-Lauri gewog of Samdrupjongkhar plough dried weeds into soil to increase soil organic matter. The farmers of Lumang gewog of Trashigang burn these weeds and maize stubbles to eradicate sources of pests and diseases. Farmers along the southern foothills mostly keep their farmlands fallow after the harvest of paddy crop. They allow cattle to tether and the remaining paddy stubbles are either burnt or ploughed back into soil before the rainy season. Farmers in west Bhutan use farmyard manure (FYM) as the main source of plant nutrients. After the harvest of the main crop, they keep land fallow or grow a second crop depending on the soil fertility status. Soil organic matter reduces erosion risks, improves water-holding capacity/fertility, and a strong carbon sink.
Cattle manures are mixed with forest litter and crop residues to produce FYM. When FYM matures, it is applied to the cultivated fields at the rate ranging from 3 to 7 tons per hectare. The methane emission from such traditional manure management system is unlikely since manures are not in a slurry form like in the developed countries. In some farming communities, farmers produce slurries by collecting manure and urine in a chamber. The methane generated from this chamber is used for cooking and heating as a substitute for fuel energy derived either from burning wood or fossil fuels.
Emission of methane from the paddy fields is also unlikely or minimal in these mountainous farming landscapes. The paddy crops remain submerged on irrigated fields for a period of 2 to 3.5 months in a year, and the water temperature during the growing period remains below 20 C on average while optimum temperature for microbes to produce methane is reported to be around 27 C.
The country introduced inorganic fertilizers to supplement traditional soil fertility management practices in the early 1960s. These fertilizers were first demonstrated on government farms and research stations by integrating with locally available organic resources like FYM and other crop residues. Since the release of plant nutrients from organic residues is slow, it is essential to supplement crops with the inorganic fertilizers that are known to release nutrients immediately in presence of soil moisture.
Inorganic fertilizers recommendation guidelines for rice, maize, potato and wheat crops were made available by early 1990s based on 600 farm-fertilizer trials conducted across the country. The uptake of inorganic fertilizers reached 2,833 tons/year, equivalent to 9 kg of plant nutrients per hectare by 2004 compared to the World average of 90 kg of plant nutrients per hectare. The record of fertilizer distribution in 2020-2021 reported by the Agriculture department was around 2,390 tons, suggesting that the farmers are still depending more on organic inputs to produce crops than on inorganic fertilizers.
The application of inorganic fertilizers beyond the requirements of growing crops is likely to pollute local water bodies and air through surface soil erosion/leaching and emission of GHG nitrous oxide respectively. For these reasons, it is always recommended to test soils after the harvest of crops to avoid excess application of fertilizers for the next crop. Excess application of nitrogen containing fertilizers also causes emission of GHG nitrous oxide if conditions are right. Soil microbes can produce nitrous oxide from nitrogenous fertilizers when temperature is right in the absence or limited oxygen that is anaerobic condition. Records in Bhutan indicate that potato, maize and other horticulture crops grown on dry land take the biggest share of imported inorganic fertilizers where conditions are not favorable for the emission of GHG nitrous oxide.
The local climate is changing and small farmers are the ones most affected. For instance, local farmers are not in a position to follow their routine farm work as scheduled – planting or harvesting because of localized windstorms, droughts, and outbreak of pests caused by extreme weather conditions. For a dry land farmer, rill or sheet erosion, a form of surface erosion is increasing ever year. These surface erosions are the main causes of increased sediment loads in the rivers, decrease in crop yield and loss of biological productivity of land. If unchecked, rill erosions could lead to the formation of ravines and gullies like those in Wamrong Dungkha of Trashigang after continuous rainfall for 4 to 5 days in 2004.
One of the approaches adopted to combat climate change at local site is the promotion of Sustainable Land Management (SLM) technology. In consultation with the affected farmers, SLM technologies to improve crop yield and local ecosystem services were promoted from 2004-2006. One experimental study showed that the results from SLM soil erosion plots established in 2009, the highest soil loss rate of 24.6 t/ha was observed on the bare reference plot and the lowest soil loss was observed at the rate 3.36 t/ha from SLM introduced plots.
Cultivated soils capture carbon dioxide from atmosphere via organic material inputs provided by crop residues, dried weeds and forest litters. Small farmers for generations have been using these organic residues as the main source of plant nutrients to produce their food requirements. These farming practices combined with improved soil and land management technologies is a strong adaptation measures against extreme weather events, and also a good mitigation mechanism of capturing and storing of carbon dioxide from the atmosphere. It is time to measure these unaccounted local and regional environment benefits and reward where it is due!
Contributed by
Chencho Norbu
cndofps@gmail.com