Investigation of Rice Yields and Critical N Losses from Paddy Soil under Different N Fertilization Rates with Iron Application

Abstract

The application of iron powder stimulated the growth of iron-reducing bacteria as a respiratory substrate and enhanced their nitrogen (N)-fixing activity in flooded paddy soils. High N fertilization (urea) in the flooded paddy soils has caused adverse environmental impacts such as ammonia (NH3) volatilization, nitrous oxide (N2O) emissions, and nitrate (NO3−) leaching. This study aims to investigate the effects of N fertilization rates in combination with an iron amendment on rice yields and N losses from flooded paddy fields. We performed a 2-year field plot experiment with traditional rice–wheat rotation in China’s Yangtze River Delta. The investigation consisted of seven treatments, including 100%, 80%, 60%, and 0% of the conventional N (urea and commercial organic manure) fertilization rate, and 80%, 60%, and 0% of the conventional N with the iron powder (≥99% purity) amendment. The rice yields decreased with a reduction in the conventional N fertilization rate, whereas they were comparable after the iron application under the 80% and 60% conventional N rate. The critical N losses, including NH3 volatilization, N2O emissions, and NO3− and NH4+ leaching, generally decreased with a reduction in the conventional N fertilization rate. These N losses were significantly greater after the iron amendment compared with the non-amended treatments under the 80% and 60% conventional N fertilization rate in the first rice-growing season. However, it was comparable between the iron-amended and the non-amended treatments in the second season. Furthermore, NO3− leaching was the most significant N loss throughout the two rice seasons, followed by NH3 volatilization. The iron amendment significantly increased soil Fe2+ content compared with the non-amended treatments irrespective of N fertilization, suggesting the reduction of amended iron by iron-reducing bacteria and their simultaneous N fixation. A combination of the iron application with 60–80% of the conventional N fertilization rate could maintain rice yields similar to the conventional N fertilization rate while reducing the critical N losses in the flooded paddy field tested in this study. Our study leads to the establishment of novel and practical rice cultivation, which is a step towards the development of green agriculture.

Active Nitrogen Fixation by Iron-Reducing Bacteria in Rice Paddy Soil and Its Further Enhancement by Iron Application

“…In our field experiment, a significant increase in soil nitrogen-fixing activity was also observed after the application of iron powder to straw-returned paddy field soil [25]. Another field experiment in China demonstrated that a combination of iron application with 60-80% of the conventional nitrogen fertilization rate could maintain rice yields similar to those of the conventional nitrogen fertilization rate while reducing critical nitrogen losses in flooded paddy fields [26]. These studies strongly suggested that iron application to paddy soil increased the amount of nitrogen fixed in the soil by enhancing nitrogen fixation by iron-reducing bacteria.…”

Global soil metagenomics reveals distribution and predominance of Deltaproteobacteria in nitrogen-fixing microbiome

“…Moreover, nitrogen-fixing bacteria have long been considered useful microorganisms for improving soil nitrogen fertility, and methods to promote their activity have been developed for sustainable agriculture [64]. For example, in paddy soils, recent studies showed that application of iron-bearing materials could enhance the nitrogen-fixing activities of indigenous iron-reducing bacteria within the families Anaeromyxobacteraceae and Geobacteraceae and maintain rice yields under reduced nitrogen-fertilizer application [65,66]. Given the ubiquity of iron-reducing diazotrophs (Fig.…”

Enhancing Resiliency and Productivity of Flood Prone Coastal Rice Farming through Integrated Organic-Biofertilizers and Crop Management for Climate Change Adaptation

“…This damages the rice plant throughout their growth cycle. Flooding constrains the nutrient availability and limits the effective use of organic and chemical fertilizers resulting in decreased N use efficiency and N losses through NH3 volatilization, N2O emissions, and NO3 leaching causing environmental pollution [5,6]. Salinity increases transpiration demands through higher concentration of Na + and Clions and disturbs the…”