Bhutanese farmers have been cultivating native rice varieties that are tall, and low-yielding, but well adapted to their local environment for many centuries. Some farmers have switched to growing high-yielding varieties in the irrigated paddy fields in the past few decades. The cultivation of both irrigated and upland rice is found from the wet subtropical in the south to the warm temperate landscapes in the north.

Rice as the preferred food grain consumed, drew the attention of Bhutanese scientists to study both local and introduced rice varieties with the aim to increase rice yields from the early 1980s. The paddy production in the country has been dwindling over the years and has not been able to meet the domestic demands. The production dropped from 63,890 MT in 2018 to 41,049 MT in 2022 according to the agriculture census report of 2022.

The conversions of rice fields to other land uses, farm labor shortage, impacts of climate change, and crop depredations by wildlife were some of the frequently cited reasons for the decline. The current domestic rice production is estimated to be around 47.08% of the total required.

There is a big opportunity to increase the cultivation and yield of irrigated paddy in the country through the adoption of improved rice production technologies according to some agriculture experts and progressive farmers. The Agriculture Research Centers in collaboration with the farmers and the extension services developed a number of improved rice production technologies in the past four decades. There are 27 improved rice varieties available in the country, of which 15 varieties were introduced, and 12 were locally-bred for specific climatic zones of the country. It takes about 8 to 14 years to breed a high-yielding local rice variety. The introduced and locally-bred rice varieties are high-yielding, early-maturing, and climate-resilient (disease resistant, resistant to lodging, drought and cold tolerant). One of the papers in 2013 reported around 52% HYV adoption rate an increase from 35% in 2004. The rice yield increased due to HYV was 33% higher compared to native varieties.

The rice and wheat productions in the South Asian Region increased substantially in the 1960s through the 1980s with the adoption of the Green Revolution Technology- the use of HYV seeds, increased use of chemicals (fertilizers, pesticides), and improved irrigation facilities. The wheat yields increased from 850 kg/ha to 2281 kg /ha in India with the adoption of the Green Revolution technologies in the 1960s. In one of the International Food Policy Research Institute papers (1985), the land area irrigated using modern technology went from 0.9 million to 5 million acres in Bangladesh. By early 1980s, the cultivation of modern rice varieties in the region was estimated at 22% of rice area in Bangladesh, 26% in Nepal, 47% in India, and 71% in Sri Lanka.

One of the essential inputs of the Green Revolution is the application of right amount of inorganic fertilizers to meet the nutrients requirement of the high-yielding crop varieties. The inorganic fertilizers that supply primary nutrients like Nitrogen (N), Phosphorus (P) and Potassium (K) were first introduced in Bhutan around mid 1960s to supplement existing traditional fertility management practices. The traditional soil fertility management still practiced widely includes the routine application of farmyard manure, burning of crop residues, tethering of cattle, keeping land fallow, crop-rotation, and seasonal incorporation of organic residues (dried weeds, crop residues and forest litter). The nutrients from these traditional inputs remain unavailable to the plants until these organic materials are decomposed. This is one of the reasons why the release of nutrients are slow from organic residues compared to the application of inorganic fertilizers. The nutrient like nitrogen (N) is absorbed by plants in the form of ammonium or nitrates ions regardless of organic or inorganic fertilizer sources.

The inorganic fertilizer applications were promoted widely among farming communities, notably through the Yield increase through the use of Fertilizer and other Inputs’ project supported by FAO. The project studied the response of cereals, potato, and oilseeds to the application of inorganic fertilizer (N, P and K) and farmyard manure from 1986-1989. The analysis of crop yields and soils of 600 on farm fertilizer trails confirmed that N was the major limiting nutrient, and response to P was moderate followed by response to K positive only in the south where loose- textured sandy loam soils with high monsoon rain were prevalent. The proposed inorganic fertilizer rates recommendation in the 1990s for all HYV rice growing areas of the country was 70-90 kg N/ha, 40-60 kg P2O5/ha and 20-40 kg K2O/ha.

One of the risks associated with inorganic fertilizer application is the pollution of local environment through leaching of nitrates, surface runoff of phosphates, and possible release of some greenhouse gases like methane and nitrous oxide into the atmosphere. The paddy fields of southern foothill are highly prone to leaching of nitrates because of loose-textured soils, and likewise the potato and maize fields that are on the steep slopes are prone to surface runoff of phosphate.

Good soil fertility management practices like continuous application of organic resources, and applying the right amount and type of fertilizers at the right growth stage of a crop are some of the guidance needed. It is indeed imperative that the right fertilizers are supplied in the right season. There are no empirical data in the country that confirms local environment pollution by the application of fertilizers. This is primarily because the application of inorganic fertilizers per cultivated land is minimal compared to any other country in the region. Bhutan was the lowest with 14.3kg/ha followed by Nepal (102 kg/ha), Pakistan (155.2kg/ha), India (209kg/ha), Sri Lanka (297.8kg/ha), and Bangladesh (320.9kg/ha), the inorganic fertilizer applied/ha of arable land in 2020   (https://www.theglobaleconomy.com/rankings/fertilizer_use/Asia/).

The wet and humid sub-tropical paddy fields of Samtse, Sarpang, Dagana, and Tsirang are in the ideal climate zones to produce high paddy yields. However, the paddy fields are mostly dominated by loose-textured soils that are poor in water and nutrient retention. It is therefore, not surprising that the lowest-harvested rice yield was in Samtse (2.8 t/ha) followed by Tsirang (2.9 t/ha) and Dagana (3.4 t/ha) among rice-growing areas in the country in 2022. Cultivation of cover crops including the reintroduction of Sesbania aculeta (Dhaincha, a green legume introduced in 1990s to improve soil fertility), and the application of both organic and inorganic fertilizers are some of the solutions to improve soil fertility and its physical properties such as water-holding capacity.

The adoption of HYV rice coupled with improved soil-fertility, weed-management and assured irrigation water are required to produce higher yield than the warm temperate zones of Paro valley. In the late 1980s, one of the options proposed for alternative irrigation water was tapping of ground water in the areas of high rainfall, and frequent problems of blockages and collapses of irrigation channel. This proposal is more relevant now than before given the areas are highly prone to extreme weather events like flashflood, landslides and heavy erratic rainfall caused by global warming.

Paro valley stands at the highest elevation among the prominent rice-growing areas in the country. The farmers have consistently harvested the highest irrigated paddy yield  (on average 5.9 t/ha) in the last five years (2018-2022), higher than the global average yield of 4.25 t/ha. The farmers are cultivating HYV rice in place of native rice varieties. Some experts estimate that the adoption rate of HYV in Paro could be as high as 85%. The inorganic fertilizer Urea, a rich source of N, is widely applied to paddy fields at the rate of 37 to 62 kg/ha to supplement the farmyard manures (estimated around 6-7t/ha). Butachlor, a popular pre-emergency herbicide is applied at the rate of 40-50kg/ha within 5 to 7 days after rice transplantation. This herbicides usage is much higher than the recommended doses of 25-30 kg/ha and should be monitored. Indeed, the adoption of locally-developed modern rice-production technologies is one of the best solutions for the rice farmers to adjust to extreme weather events and increase productivity of their small land-holdings.

Contributed by

Chencho Norbu

Former Secretary

National Environment Commission Secretariat