Differential response from nitrogen sources with and without residue management under conservation agriculture on crop yields, water-use and economics in maize-based rotations

Under the present scenario of resource degradation, shortage of water & labour, growing production cost, falling water tables as well as farm profitability and climate-change; the sustainability of traditional rice-wheat (RW) system became a major challenge in Indo-Gangetic Plains (IGP). Therefore, to address these issues in India's, north-western IGP, RW system need to be diversified with conservation agriculture (CA) based profitable and sustainable systems. Full CA based crop production technologies may furnish more yield, reduce water need and enhance farm profitability, without hampering the sustainability of natural resources. So in an established on-going long term study (since 2012), we assessed the medium term-impact of four different nitrogen management practices [Unfertilized, N through Prilled urea (PU), N through Sulphur coated urea (SCU) and N through Neem coated urea (NCU)j in residue retained permanent bed (PB + R) vs. residue removed permanent bed (PB-R) plots under maizemustard-mungbean (MMuMb) and maize-wheat-mungbean (MWMb) crop rotations. Results showed that, the maize, wheat and mustard yields were statistically similar in first year of study irrespective of residue retention or removal, whereas during subsequent years, yields of maize, wheat and mustard were significantly (P < 0.05) higher by 10.1-16.7%, 9.3-23.6% and 13.6-21.9% under residue retained plots (full CA) than residue removed plots (partial CA), respectively. However, the mungbean yield was significantly (P < 0.05) greater by 12.4-24.3% in residue retained plots right from first year onwards. In permanent bed plots, residue retention reduced the water requirement by 50-55 ha-mm, and improved water productivity by 9.4-27.6%, 17.7-30.4%, 21.7-42.6% and 33-57.2% in maize, wheat, mustard and mungbean, respectively compared to no residue plots. Economic profit for MMuMb (from 2nd year onward) and MWMb rotations (in all the 5-years) was significantly (P < 0.05) higher by 220-464 and 165-474 US$/ha/year, respectively in residue retained plots compared to residue removed plots. Among N management practices, application of neem and sulphur coated urea significantly improved the individual crops yield, water productivity and system profitability compared to un-fertilized both under residue retained and removed plots. However, across the cropping systems the effectiveness of different N sources varied with residue management, as the annual increment in system productivity of SCU treated and residue retained plots under MMuMb system was about thrice than the residue removed plots. Whereas, in MWMb system the annual increment in system productivity was double in NCU treated and residue retained plots as compared to residue removed plots. Effectiveness of PU was not increased with residue retention in maize and mustard, whereas in wheat both the coated and uncoated urea application increased the annual yield by manifolds. Findings of this study support differential opportunity of residue management and suggest that a combination of full CA-based MMuMb/MWMb system with use of proper N sources [like slow release coated fertilizers (NCU/SCU)] could augment the system productivity, resource-use efficiency, farm profitability, while sustaining the natural resources in Western IGP in India and other similar agro-ecologies.