Sub-surface drip fertigation with conservation agriculture in a rice-wheat system: A breakthrough for addressing water and nitrogen use efficiency

The future of the South Asia's rice-wheat (RW) production system is at stake due to continuously depleting aquifers and increasing pressure on underground water under projected climate change scenario. Conventional management factors such as flood irrigation, intensive tillage and residue burning are threatening sustainability of RW system. With increasing adoption of conservation agriculture (CA), sub-surface drip fertigation (SSDF) provides an exceptional opportunity for complementing irrigation water saving benefits. Presently, there is no research evidence on optimum spacing and depth for drip laterals in a CA (direct drilling and residue mulch) based RW system around the globe. This study was therefore, planned to evaluate effects of residue mulch, different spacing and depths of laterals for SSDF on crop yield, irrigation water productivity (WPi), nitrogen use efficiency (NUE) and net returns for CA based RW system in a silt loam soil in northwestern India. Drip laterals were spaced either at 33.75 cm or 67.5 cm, and installation depths were 0, 15 or 20 cm beneath the soil surface and compared with conventional and zero tillage based flood-irrigated RW systems. Grain yield and irrigation water input in rice and wheat were generally similar under different SSDF treatments. Irrigation water savings were 48-53% in rice and 42-53% in wheat under combination of SSDF and CA compared to flood irrigation system. A similar trend in WPi was recorded in both the crops. Residue mulch contributed to higher irrigation water savings, wheat yield and WPi compared to no mulch. Both rice and wheat needed 20% less N fertilizer under SSDF system to obtain grain yields similar to that under flood irrigated crops. Net returns from SSDF system with 67.5 cm lateral spacing were significantly higher compared to flood irrigation system. In conclusion, SSDF system having laterals spaced at 67.5 cm and installed at 15 cm depth provides tangible benefits for substantial saving in irrigation water and energy and increasing NUE and net income for CA based RW system in South Asia.