Alternative Wet & Dry Irrigation (AWD) Technology

Paddy is a water-sensitive crop that produces optimum yield at saturation of soil water conditions. As a result, the consumptive use (CU) of rice is calculated as a combination of evapotranspiration as an energy loss and soil percolation as a soil loss. This value is generally calculated as 10mm per day in rice fields under the Low Humic Gley (LHG) soil type in the dry zone of Sri Lanka. It is understood that the percolation from paddy fields are consistent throughout the base period of rice plant in Sri Lanka's practice of flood irrigation.

According to the experimental results obtained in Sri Lanka, rice plants can produce an optimum yield at a variation of water levels in rice fields from 5cm standing water and 20% depletion of soil saturation during the period of seven to ten days. Irrigation frequency is decided by the consumptive use (CU) and the water level depletion in rice fields.

Even though the optimum harvest can be reached at a variation of water level in rice fields from standing water to depletion of saturation, farmers used to continue with standing water conditions to control weeds in paddy plots and continue without any water stress for the rice crop. This practice is dominant under diversion systems and partly in the storage system in wet and intermediate climatic zones.

Soil fertility is commonly misinterpreted as the amount of nitrogen, potassium, phosphorous and microelements quantity in the root zone depth of soil. But in reality, it is defined as the ability to mobilise nutrients quickly, scientifically known as soil's cation exchange capacity (CEC). CEC of the topsoil that can be used to feed food crops like rice can be considerably increased by adding organic fertiliser and increasing the organic matter content (OMC) that will facilitate the plant to absorb available nutrients from the soil straight away without any obstruction or fixation and finally resulted in fairly high rice yield production while minimising the yield gap.

Aeration of soil in the root zone, especially the oxygen (O2) content, is very much essential to improvements;

• The growth of roots
• Nutrient absorption
• Maintain a variety of microorganisms

Finally, resulting in achieving desired rice yield with higher quality. However, irrigation techniques with complete flooding of paddy plots will replace soil air with water, release O2 into the atmosphere, and maintain anaerobic soil conditions that adversely affect crop growth.

It is identified that paddy cultivation under flooded conditions contributes nearly 10% to 12% of global greenhouse gases, and methane and nitrous oxide are identified as dominant GHG emissions that will act as climate pollutants. Methane is a dangerous, potent GHG that can expedite global warming and is a chronic hazard for human and animal health. It also can act as a climate pollutant much more powerful than carbon dioxide (CO₂), experimentally determined as ten times more potent for global warming of the atmosphere. Therefore it is essential to control methane emissions from paddy under flooded conditions all over the world, especially in Sri Lanka. This critical aspect can be achieved by appropriate water management techniques such as AWD for rice cultivation scientifically without affecting crop yield.

Alternative wet and dry irrigation technology is implemented in rice lands as follows.

• Standing water in paddy fields during the land preparation at the inception.
• Soil saturation before tillage and transplanting.
• Maintain dry paddy field for 10 to 14 days after transplanting
• Apply irrigated water initially for saturation and then 5cm standing water in paddy fields. (rice).
• Wait till the water level drops to 20% to 50% depletion of soil saturation in the root zone. This value can be changed depending on the basic infiltration rate of each soil type.
• This value can be monitored by using equipment at the field level and by measuring Potential Evapotranspiration (PET) with the help of a Class A Evaporation Pan and standard rain gauge at the system level.
• This intermittent irrigation method is demand-oriented and saves more water while producing better rice yield.

The persistent flood condition of the rice fields will result in the generation and emission of methane as a result of the decomposition of organic matter by bacteria under anaerobic conditions, and the effect of methane emission is considerably increased when trying to adapt ecological farming techniques by adding more organic matters into rice fields.

Under the AWD irrigation technique, the drainage of paddy fields will be considerably improved after 3 to 4 days from irrigation, and oxygen will penetrate the soil improving the soil aeration while suppressing methane production and this technique can be used to reduce methane emission from paddy by more than 50% and can be measured by using remote sensing technique.

Different criteria should be adopted for different soil types, mainly by considering the drainage capacity and ease of operation in well-drained sandy soils compared to poorly drained clay soils.

It is necessary to undertake and develop datasets for different soils, climates, and crop varieties before implementing AWD to ensure all possible outcomes without compromising crop yield as well as ecological services inherited by Sri Lanka.

The following Statistics can be used to design a national-level approach for AWD

(Source: Details of Irrigation Systems in Sri Lanka, DAD, 2020)

(Source: Details of Irrigation Systems in Sri Lanka, DAD, 2020)

Geo-info mapping private limited is a well-established company initiated in 2014 and well-equipped with high-level professionals, researchers, measuring equipment, innovative techniques and field-level experiences in implementing this type of project. The commitment and contribution of our organisation and staff look forward to the successful implementation of this global intervention in the Sri Lankan context of rice farming at different levels from Village Level to National Level

.Our intervention and contribution can be utilised for formulating new projects, problem identification and project design, project implementation, monitoring and evaluation and assuring community participation. Training of farmers and officers and risk assessment approaches, and we're capable of undertaking consultancy as well as turnkey options in this regard for the betterment of the country and Global Environmental Conservation.