Diminishing water resources to irrigation is a major global challenge in sustainable food production. Terrapon-Pfaff et al. (2018), analysed the linkages between small-scale energy projects in developing countries and the food and water aspects of development. Successful cultivation in semi-arid tropics region mostly depends on irrigation and small-scale water resources but the ecosystem is highly vulnerable. Therefore, development of efficient and environment-friendly water management system to deal with the water-energy-food nexus assumes utmost importance.

Indian agriculture in the region of semi-arid tropics, characterized by smallholders, small water harvesting and recycling system assumes a significant potential to sustain agricultural productivity by providing supplemental as well as lifesaving irrigation and mitigating mid-season drought. In Indian agriculture, major energy consuming activities include on-farm water management. Efficient and cost-effective irrigation system matching the small-scale water harvesting and storage, are not available in this region.

India has 58% of its geographical area falling under solar hotspots and it has a 4–7 kWh m−2day−1 of solar radiation incident over the country with 1200–2300 kWhm−2 of annual radiation range. Several studies suggested that this solar energy received every single year is significantly higher than the energy output from all fossil fuel reserves put together.

In recent years, considerable amount of research has been carried out on various aspect of solar energy and its application. The photovoltaic cells are most important components in solar energy application and it has been investigated intensively. The recent paper ‘Development of green energy based micro-sprinkler irrigation system for small holdings of semi-arid tropics region’ published in the journal ‘Cleaner Engineering and Technology’ deals with the need to develop solar powered micro-sprinkler system considering the techno-socio-economic situation of the small holders of the dryland region.

The system was developed considering two hypotheses - (1) can such system operate on low pressure utilizing water from small scale water harvesting pond and (2) can such system provide the balance between economy and efficiency for available water and land resources to enable extensive small-scale vegetable production.

As a part of the study, the selected experimental site is located at Central Research Institute for Dryland Agriculture, Hyderabad. Location typically represents the dryland farming situation of semi-arid tropical region with hot summer and mild winter.

Hyderabad receives good amount of solar radiation during summer months (March to June) ranging between 6.54 KW-h/m2/day to 7.11 KW-h/m2/day followed by winter months (October to February) ranging between 4.94 KW-h/m2/day to 6.10 KW-h/m2/day. During rainy season (monsoon months of July to September), the solar radiation received in the range of 3.31 KW-h/m2/day to 3.4 KW-h/m2/day.

The location receives mean annual rainfall of 750 mm which accounts for nearly 42% of annual potential evapotranspiration of 1754 mm. Nearly 80% of the annual rainfall are received during southwest monsoon season which is sufficient to practice one crop in a year. However, second and third crops can be practiced in this region where intensive irrigation facility exists. The soil in the site typically has sandy surface layer and increasing clay content in the sub soil.

In view of this, a carry-and-irrigate type micro-sprinkler irrigation system was designed and developed in order to achieve the holistic utilization of water resources and niche-potential of solar energy and gravity. The performance was measured on various parameters of application rate, Christiansen uniformity coefficient and pattern efficiency and were quantified as 14.2 mm/h, 91.3% and 89.01% respectively.

The developed irrigation system qualified the performance criteria as standardized by ASAE, 1996. Given the characteristics of low cost and portability, it can considerably substantiate the vegetable production at household scale. Though, this system is developed exclusively for the location representing typical dryland agriculture of India, it can be easily and effectively replicated in other part of the world having similar agro-ecosystem. This simple water management technique utilizing the niche potential of gravity and solar energy can significantly contribute to the various objectives of sustainable development goal.

Discussion

Most of the small and marginal farmers in semi-arid tropics regions of India are practicing subsistence farming due to over dependency on rainfall. Due to this. there is a limited scope to adopt intensive agriculture in such region. However, in this region, one or two supplemental irrigations can increase the farm yield substantially.

Small scale water harvesting ponds are popularized intensively through many national and international development programs, a paradigm shift from earlier development program for groundwater recharge. Such intervention could substantially intensify cropping system and has the potential to enhance the food and nutritional as well as livelihood security to the small and marginal farmers.

Given the small size of water harvesting and storage ponds (usually of capacity up to 1000 m3), most of the time, the existing means of water lifting pumps turns to be grossly over designed. This mismatch not only adversely affects the functional and economic efficiency of the irrigation system but also leads to higher carbon footprint. Additionally, given the high cost involved in establishing such conventional pumping system for water lifting, most of the time, small and marginal farmers can't afford these systems.

As a result, they go for hand watering by fetching water as head load which cause drudgery and consumes significant time. The developed irrigation system can prove to be the economical and efficient alternative to the water lifting and high-pressure requiring irrigation system. Additionally, the present system addresses the issue of carbon footprint which is estimated as 1.47 t/ha/month (Reddy et al., 2015). The proposed irrigation system, has the potential to substantially mitigate the carbon footprint arise due to the pumping system.

The develop system could provide irrigation in 7.5 m × 7.5 m area at a time. It is suggested to run the system during 11 a.m. to 4 p.m. (5 h in a day) in order to achieve the full potential of solar energy. Thus, for 1-h irrigation at weekly interval, 0.5-acre area can be brought under irrigation from one such system.

These provisions are best suited for small scale vegetable cultivation as urban agriculture which surrounds the metropolitan areas for regular supply of farm fresh vegetable. This system has the potential to bring nutritional security among the resource poor farmers by optimally utilizing the water resources.

The various specifications and quantity prescribed in the development of present irrigation system are not the mandatory requirement but indicative. The basic principle of utilization of energy from source of solar and gravity remain same, there can be changes in these specifications based on local conditions and farming practices.

Conclusion

In the semi-arid tropic region, water is harvested from rain and stored in small ponds. There is always a need for economical and cost-effective measures to lift water from these ponds and efficiently distribute it to the field. This region however, has the rich niche-potential of solar energy that could be harvested and utilized in various farm practices. The small scale solar powered micro-sprinkler irrigation system was developed considering niche-potential and socio-economic conditions and limitations of small holders in the semi-arid tropics region.

The developed irrigation system is sufficient to provide irrigation in up to 0.5 acre of land, typical of average land size in this region. The system's functional parameters such as application depth, Christensen Uniformity Coefficient and pattern efficiency respectively and qualifies the standard criteria as suggested by the American Society of Agricultural Engineers, 1985 and 1996. However, the irrigation system developed exclusively for the location representing typical dryland agriculture of India can be easily and effectively replicated in other part of the world having similar ecosystem.

The system will address the most important issue of water management and enhance water productivity. Additionally, this system has the potential to mitigate carbon footprint and contribute towards the sustainable development goal. Moreover, given the low cost and functionality, such a system can be included in the nutrition kits which is envisioned by FAO to achieve food and nutrition security in resource poor countries.

The full paper can be viewed here