Nitrous oxide and nitric oxide emissions from lowland rice cultivation with urea deep placement and alternate wetting and drying irrigation

S M Mofijul Islam,Upendra Singh,M A Saleque,Yam Kanta Gaihre,Joaquin Sanabria,Jatish Chandra Biswas,Md Nayeem Ahmed

doi:10.1038/s41598-018-35939-7

Abstract

Urea deep placement (UDP) and the alternate wetting and drying (AWD) irrigation method are two promising rice production technologies. However, studies on the impact of UDP under AWD irrigation on nitrous oxide (N2O) and nitric oxide (NO) emissions are limited. In this study, the effects of UDP with AWD irrigation on these emissions, nitrogen use efficiency (NUE), and rice yields are investigated, compared to conventional broadcast application. N2O and NO emissions from three fertilizer treatments – no nitrogen, UDP, and broadcast application of prilled urea (PU) – were measured. Measurements were taken using an automated gas sampling and analysis system continuously for two consecutive Boro (dry) rice seasons. N2O emission peaks were observed after broadcast application of PU but not after UDP. In contrast, large spikes in N2O emission were observed after UDP, compared to broadcast application, during dry periods. Despite differences in emission peaks, seasonal cumulative N2O emissions from UDP and broadcast treatments were similar. However, NO emissions were minimal and unaffected by UDP or AWD. UDP increased rice yields by 28% and N recovery efficiency by 167%, compared to broadcast urea. This study demonstrates that UDP with AWD irrigation can increase yields and NUE without increasing N2O and NO emissions.

Highlights

Agriculture is a significant anthropogenic source of nitrous oxide (N2O) and nitric oxide (NO), contributing up to 60% of total anthropogenic N2O emissions[1,2]
N2O emission from the Urea deep placement (UDP) treatment tended to be higher than broadcast prilled urea (PU), but this difference was below statistical significance (p > 0.05) (Table 1)
In contrast to these observations, Gaihre et al.[37] reported that UDP reduced cumulative N2O emissions significantly, compared to broadcast PU; in that study, experiments were conducted under a continuous standing water (CSW) irrigation regime in which emissions from UDP were very low, relative to the present study in which experimental plots were maintained under AWD conditions

Summary

Introduction

Agriculture is a significant anthropogenic source of nitrous oxide (N2O) and nitric oxide (NO), contributing up to 60% of total anthropogenic N2O emissions[1,2]. N2O alone contributed 6% to total anthropogenic GHG emissions in 20104 Since both N2O and NO gases are produced in the soil through the biochemical process of nitrification and denitrification[6,7], their emissions are highly variable with soil properties, climate, crops, irrigation regimes, and fertilizer sources and methods of application[8–10]. The intermittent soil drying and wetting often produces cracks, in clayey soil, in addition to changes in soil physicochemical properties[30] These cracks increase the oxygen content in the deeper soil layer, which in turn increases the rate of nitrification and, N2O emissions[30,31]. The addition of N fertilizer, either as broadcast or deep placement, under AWD irrigation may increase the conversion rate of soil NH4+ to NO3− as well as the rate of subsequent denitrification of the NO3−, leading to more N2O emissions[12,27,34]

Methods

Results

Discussion

Conclusion