Methane oxidation in an intensively cropped tropical rice field soil under long-term application of organic and mineral fertilizers

Multi-criteria assessment to screen climate smart rice establishment techniques in coastal rice production system of India

Introduction

Conventional rice production techniques are less economical and more vulnerable to sustainable utilization of farm resources as well as significantly contributed GHGs to atmosphere.

Methods

In order to assess the best rice production system for coastal areas, six rice production techniques were evaluated, including SRI-AWD (system of rice intensification with alternate wetting and drying (AWD)), DSR-CF (direct seeded rice with continuous flooding (CF)), DSR-AWD (direct seeded rice with AWD), TPR-CF (transplanted rice with CF), TPR-AWD (transplanted rice with AWD), and FPR-CF (farmer practice with CF). The performance of these technologies was assessed using indicators such as rice productivity, energy balance, GWP (global warming potential), soil health indicators, and profitability. Finally, using these indicators, a climate smartness index (CSI) was calculated.

Results and discussion

Rice grown with SRI-AWD method had 54.8 % higher CSI over FPR-CF, and also give 24.5 to 28.3% higher CSI for DSR and TPR as well. There evaluations based on the climate smartness index can provide cleaner and more sustainable rice production and can be used as guiding principle for policy makers.

To shake or not to shake: Silicone tube approach for incubation studies on CH4 oxidation in submerged soils

Incubation experiments are the most common approach to measure methane (CH₄) oxidation potential in soils from various ecosystems and land-use practices. However, the commonly used headspace CH₄ injection into microcosms and the shaking of the soil slurry during incubation fully removes CH₄ (soil-born) and O₂ (air-born) gradients common in situ, and may also induce various errors and disturbances. As an alternative, we propose CH₄ input into microcosm soils via a silicone tube located within the slurry. We hypothesized that (i) poor CH₄ diffusion in slurry will be compensated by direct CH₄ delivery into the slurry via a silicone tube and, consequently, (ii) shaking of microcosms can be substituted with the soil silicone tube CH₄ injection. During a 29-day submerged paddy soil incubation, the highest net CH₄ oxidation rate was 1.6 μg C g^-1 dry soil h^-1, measured between the 3rd and 7th day after injecting ¹³CH₄ into the slurry via a silicone tube without shaking. This rate was 1.5-2.5 times faster than the respective CH₄ oxidation after headspace injection without shaking (1st hypothesis supported). As expected, shaking accelerated CH₄ oxidation regardless of injection methods by 3.2-3.7 times (most intensively on days 3-7) compared to headspace injection without shaking. Nonetheless, the rates were similar between silicone tube injection without shaking and headspace injection with shaking. This supports the hypothesized potential of silicone tubes to substitute the common shaking method (2nd hypothesis). Furthermore, shaking increased the incorporation of ¹³C from CH₄ into soil organic matter and microbial biomass by 1.8-2.7 times compared with CH₄ injection into tubes and the static control without tubes. This reflects an overestimation of CH₄ oxidation due to shaking. We conclude that direct soil CH₄ injection via silicone tubes is advantageous in incubation experiments because gas concentration gradients are maintained and thereby more realistically reflect natural soil conditions.

Cyanobacteria as potential options for environmental sustainability - promises and challenges

Cyanobacteria represent an ancient group of photosynthetic prokaryotes, whose ubiquity, metabolic flexibility and adaptive abilities have made them a subject of research worldwide. These structurally simple organisms combine in themselves interesting facets of plant and bacterial metabolism, which is amenable to genetic exploitation. Despite their globally recognized significance in the sustenance of fertility in rice based cropping systems, they have not been tapped for their extraordinary repertoire of activities, especially their beneficial role as biological agents in remediation and amelioration of soil and water environment and as sinks for greenhouse gases. The information available on these aspects and future lines of research for more efficient utilization of these microorganisms is presented.