The agriculture sector topped the list among sectors in greenhouse gas (GHG) emissions in the 2009 National Environment Commission (NEC) report. The emission of methane from manure and nitrogen oxides from the application of inorganic fertilizers appeared to be the main sources of greenhouse gases. These emission figures have not changed significantly as reported in NEC’s Third National Communications Report to the UNFCCC in 2020, with the exception of an additional emission contribution from urea fertilizer applications.
Perhaps it is time to commission relevant national research institutes to examine and update these emissions figures, including smallholder farmers’ contribution to carbon sequestration or greenhouse gas emissions.
Farmers in many parts of the country manually remove weeds and leave them between crops or at the edges of cultivated fields. These weeds compete with plants for plant nutrients, soil moisture and sunlight during the growing season. The dried weeds are either burned or plowed back into the ground in the coming season. For example, the dryland farmers of Shingkhar-Lauri weighed by Samdrupjongkhar plow dried weeds into the soil to increase soil organic matter. Lumang gewog of Trashigang farmers burn these weeds and corn stubble to eradicate sources of pests and diseases. Farmers along the southern foothills mostly leave their farmland fallow after harvesting the rice paddies. They allow cattle to be tied and the remaining rice stubble is either burned or plowed back into the ground before the rainy season. Farmers in western Bhutan use farmyard manure (FYM) as the main source of plant nutrients. After harvesting the main crop, depending on soil fertility, they keep land fallow or grow a secondary crop. Soil organic matter reduces erosion risks, improves water holding capacity/fertility and is a powerful carbon sink.
Cattle manure is mixed with forest waste and crop residues to make FYM. As FYM matures, it is applied to cultivated fields at a rate of 3 to 7 tons per hectare. Methane emission from such a traditional manure management system is unlikely because manure does not exist in the form of a slurry as in developed countries. In some farming communities, farmers produce manure by collecting manure and urine in a chamber. The methane produced from this chamber is used for cooking and heating, replacing fuel energy that comes from either burning wood or fossil fuels.
Also, the emission of methane from the paddy fields is unlikely or minimal in these mountainous agricultural landscapes. The paddy fields remain submerged in irrigated fields for a period of 2 to 3.5 months a year and the water temperature remains below 20°C on average during the growing season, while the optimum temperature for methane-producing microbes is said to be around 27°C.
The country introduced inorganic fertilizers in the early 1960s to complement traditional soil fertility management practices. These fertilizers were first demonstrated on state farms and research stations by combining them with locally available organic resources such as FYM and other crop residues. Because the release of plant nutrients from organic residues is slow, it is important to supplement plants with inorganic fertilizers, which are known to release nutrients immediately in the presence of soil moisture.
Recommendation guidelines for inorganic fertilizers for rice, corn, potato and wheat crops were provided in the early 1990s based on 600 agricultural fertilizer trials conducted across the country. The uptake of inorganic fertilizers reached 2,833 tons/year, equivalent to 9 kg of phytonutrients per hectare by 2004, compared to the world average of 90 kg of phytonutrients per hectare. The record fertilizer distribution in 2020-2021 reported by the Ministry of Agriculture was around 2,390 tons, suggesting that farmers are still more dependent on organic inputs for the production of crops than on inorganic fertilizers.
The application of inorganic fertilizers in excess of crop needs is likely to pollute local waters and air through soil erosion/surface leaching and GHG nitrous oxide emissions respectively. For these reasons, it is always recommended to test soils after crops have been harvested to avoid over-application of fertilizers for the next crop. Excessive application of nitrogenous fertilizers also causes emissions of GHG nitrous oxide when conditions are right. Soil microbes can produce nitrous oxide from nitrogenous fertilizers if the temperature is right in the absence or limited oxygen, i.e. anaerobic conditions. Records in Bhutan show that potatoes, maize and other horticultural crops grown on dry land account for the largest proportion of imported inorganic fertilizers when conditions are not favorable for GHG nitrous oxide emissions.
The local climate is changing and small farmers are hardest hit. For example, local farmers are unable to carry out their routine agricultural work as planned – planting or harvesting – due to local storms, droughts and pest infestations caused by extreme weather conditions. For a dryland farmer, rill or leaf erosion, a form of surface erosion, increases every 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 left unchecked, creek erosion could lead to the formation of ravines and ravines like those seen in Trashigang’s Wamrong Dungkha after 4 to 5 days of continuous rains in 2004.
One of the approaches to combating climate change at the site is the promotion of Sustainable Land Management (SLM) technology. In consultation with the affected farmers, SLM technologies were promoted from 2004 to 2006 to improve crop yields and local ecosystem services. An experimental study showed that results from SLM soil erosion plots established in 2009 observed the highest soil loss rate of 24.6 t/ha on the bare reference plot and the lowest soil loss rate of 3.36 t/ha by introduced SLM became land.
Cultivated soils absorb carbon dioxide from the atmosphere via inputs of organic matter provided by crop residues, dried weeds and forest residues. For generations, small farmers have used these organic residues as a primary source of plant nutrients to meet their food needs. These agricultural practices combined with improved soil and land management technologies are strong adaptation measures against extreme weather events and also a good mitigation mechanism for capturing and storing carbon dioxide from the atmosphere. It is time to measure and reward these unaccounted for local and regional environmental benefits where appropriate!