Technical Manual for mitigating soil salinization with Preferential shallow sub-surface drainage and Sub-surface irrigation

Irrigated agriculture with high productivity played an important role in global food security, especially in arid and/or semi-arid regions, irrigation is essential for stable agricultural production. However, salinization due to irrigated agriculture has become a serious problem. Until now, the global area of salt affected soil was estimated at 1 billion ha, but the latest FAO report (2024) estimated that it has increased to 1.4 billion ha. This kind of salinization is remarkable in Indo-Gangetic plains (IGP) located in North part of India, the area of salt affected extends to approximately 6.7 million ha. Of these, 3.78 million hectares are sodic soils. The main causes of salt accumulation due to irrigated agriculture are using high saline water, excessive irrigation under surface irrigation like border irrigation, poor and/or lack of drainage. Therefore, water saving like sprinkler and/or drip system and improve drainage function like constructing open drainage and sub-surface drainage network are effective to mitigate salinization. However, these technologies require a lot of investment and maintenance costs. In other word, once salt accumulation has been progressed, a huge manpower and funds are required to reclaim. Considering these situations, to realize sustainable management of salt affected soil, it is necessary to establish low-cost and practical countermeasures for farmers. Japan International Research Center for Agricultural Sciences (JIRCAS) and ICAR Central Soil Salinity Research Institute (ICAR-CSSRI) initiated collaborative research to develop low-cost technologies for the management of salt affected soils in India for sustainable agricultural production from 2018. In this research, we focused on Shallow Sub-surface drainage with “Cut-soiler” which is tractor attachment developed in Japan and Sub-surface irrigation with “Water drop tube” made by porous tubes with microscopic holes (60 to 80 microns). These technologies are relatively inexpensive and easy to implement compared to conventional methods, and it could be expected to sustainable countermeasures. In this Technical manual explain the construction and/or application method of “Cut-soiler” and “Water drop tube”, and their effectiveness. Further, characteristics of Sodic Soils which cause serious reduction of drainage function, and fluctuations of groundwater level which is closely related to salt accumulation are explained. Permanent Skip Furrow Irrigation (PSFI) and Simplified Surge Flow Irrigation (SSF) which based on furrow irrigation is also explained as option of water-saving.