Proximate controls on semiarid soil greenhouse gas fluxes across 3 million years of soil development

Soils are important sources and sinks of three greenhouse gases (GHGs): carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). However, it is unknown whether semiarid landscapes are important contributors to global fluxes of these gases, partly because our mechanistic understanding of soil GHG fluxes is largely derived from more humid ecosystems. We designed this study with the objective of identifying the important soil physical and biogeochemical controls on soil GHG fluxes in semiarid soils by observing seasonal changes in soil GHG fluxes across a three million year substrate age gradient in northern Arizona. We also manipulated soil nitrogen (N) and phosphorus availability with 7 years of fertilization and used regression tree analysis to identify drivers of unfertilized and fertilized soil GHG fluxes. Similar to humid ecosystems, soil N2O flux was correlated with changes in N and water availability and soil CO2 efflux was correlated with changes in water availability and temperature. Soil CH4 uptake was greatest in relatively colder and wetter soils. While fertilization had few direct effects on soil CH4 flux, soil nitrate was an important predictor of soil CH4 uptake in unfertilized soils and soil ammonium was an important predictor of soil CH4 uptake in fertilized soil. Like in humid ecosystems, N gas loss via nitrification or denitrification appears to increase with increases in N and water availability during ecosystem development. Our results suggest that, with some exceptions, the drivers of soil GHG fluxes in semiarid ecosystems are often similar to those observed in more humid ecosystems

Source-tracking cadmium in New Zealand agricultural soils: a stable isotope approach

Cadmium (Cd) is a toxic heavy metal, which is accumulated by plants and animals and therefore enters the human food chain. In New Zealand (NZ), where Cd mainly originates from the application of phosphate fertilisers, stable isotopes can be used to trace the fate of Cd in soils and potentially the wider environment due to the limited number of sources in this setting. Prior to 1997, extraneous Cd added to soils in P fertilisers was essentially limited to a single source, the small pacific island of Nauru. Analysis of Cd isotope ratios (ɛ114/110Cd) in Nauru rock phosphate, pre-1997 superphosphate fertilisers, and Canterbury (Lismore Stony Silt Loam) topsoils (Winchmore Research Farm) has demonstrated their close similarity with respect to ɛ114/110Cd. We report a consistent ɛ114/110Cd signature in fertiliser-derived Cd throughout the latter twentieth century. This finding is useful because it allows the application of mixing models to determine the proportions of fertiliser-derived Cd in the wider environment. We believe this approach has good potential because we also found the ɛ114/110Cd in fertilisers to be distinct from unfertilised Canterbury subsoils. In our analysis of the Winchmore topsoil series (1949-2015), the ɛ114/110Cd remained quite constant following the change from Nauru to other rock phosphate sources in 1997, despite a corresponding shift in fertiliser ɛ114/110Cd at this time. We can conclude that to the present day, the Cd in topsoil at Winchmore still mainly originates from historical phosphate fertilisers. One implication of this finding is that the current applications of P fertiliser are not resulting in further Cd accumulation. We aim to continue our research into Cd fate, mobility and transformations in the NZ environment by applying Cd isotopes in soils and aquatic environments across the country

Sphagnum physiology in the context of changing climate: emergent influences of genomics, modelling and host-microbiome interactions on understanding ecosystem function.

Peatlands harbour more than one-third of terrestrial carbon leading to the argument that the bryophytes, as major components of peatland ecosystems, store more organic carbon in soils than any other collective plant taxa. Plants of the genus Sphagnum are important components of peatland ecosystems and are potentially vulnerable to changing climatic conditions. However, the response of Sphagnum to rising temperatures, elevated CO2 and shifts in local hydrology have yet to be fully characterized. In this review, we examine Sphagnum biology and ecology and explore the role of this group of keystone species and its associated microbiome in carbon and nitrogen cycling using literature review and model simulations. Several issues are highlighted including the consequences of a variable environment on plant-microbiome interactions, uncertainty associated with CO2 diffusion resistances and the relationship between fixed N and that partitioned to the photosynthetic apparatus. We note that the Sphagnum fallax genome is currently being sequenced and outline potential applications of population-level genomics and corresponding plant photosynthesis and microbial metabolic modelling techniques. We highlight Sphagnum as a model organism to explore ecosystem response to a changing climate and to define the role that Sphagnum can play at the intersection of physiology, genetics and functional genomics

Specific interactions leading to transgressive overyielding in cover crop mixtures

Growing mixtures of species instead of sole crops is expected to increase the ecosystem services provided by cover crops. This study aimed at understanding the interactions between species and investigating how they affect the performance of the mixture. Four species were combined in six bispecific mixtures in a field experiment. The performance of each species when grown in a mixture was compared to its performance as a sole crop at different sowing densities, to characterise the influence of intra- and interspecific competition for each species. Intra- and interspecific competition coefficients were quantified using a response surface design and the hyperbolic yield-density equation. Interactions between the four species ranged from facilitation to competition. Most of the mixtures exhibited transgressive overyielding. Without nitrogen (N) fertilisation, high complementarity between species allowed to achieve the highest biomass. With N fertilisation, high dominance of one mixture component should be avoided to achieve good performance. A revised approach in the use of the land equivalent ratio for the evaluation of cover crop mixtures is also proposed in this study. It allows to better identify transgressive overyielding in mixtures and to better characterise the effect of one species on the other within the mixture

Selenate-enriched urea granules are a highly effective fertilizer for selenium biofortification of paddy rice grain

Citation: Premarathna, Lakmalie, Mike J. McLaughlin, Jason K. Kirby, Ganga M. Hettiarachchi, Samuel Stacey, and David J. Chittleborough. “Selenate-Enriched Urea Granules Are a Highly Effective Fertilizer for Selenium Biofortification of Paddy Rice Grain.” Journal of Agricultural and Food Chemistry 60, no. 23 (June 13, 2012): 6037–44. https://doi.org/10.1021/jf3005788.We examined the effects of applied selenium (Se) species, time of application, method of application and soil water management regime on accumulation of Se in rice plants. Plants were grown to maturity in a temperature- and humidity-controlled growth chamber using three water management methods: field capacity (FC), submerged until harvest, and submerged and drained two weeks before harvest; two Se species: selenate (SeO[subscript 4] ˉ²) and selenite (SeO[subscript 3]ˉ²) applied at a rate equivalent to 30 g haˉ¹; and four application methods: i) Se applied at soil preparation, ii) Se-enriched urea granules applied to floodwater at heading iii) foliar Se applied at heading and iv) fluid fertilizer Se applied to soil or floodwater at heading. Total Se concentrations in rice grains, husks, leaves, culms and roots were measured, as well as Se speciation in grains from the Se-enriched urea granule treatment. Highest Se concentrations in the grain occurred with SeO[subscript 4] ˉ² and with fertilizer applied at heading stage; SeO[subscript 4]ˉ²-enriched urea granules applied at heading increased grain Se concentrations 5 to 6 fold (by 450-600 μg kgˉ¹) compared to the control (no fertilizer Se applied) in all water treatments. Under paddy conditions other Se fertilization strategies were much less effective. Drainage before harvesting caused Se to accumulate in/on rice roots, possibly through adsorption onto iron plaque on roots. Rice grains contained Se mainly in the organic form as selenomethionine (SeM) which comprised over 90 % of the total grain Se in treatments fertilized with SeO[subscript 4]ˉ² -enriched urea granules. The results of this study clearly show of the fertilizer strategies tested that biofortification of Se in rice grains can best be achieved in lowland rice by broadcast application of SeO[subscript 4]ˉ² -enriched urea granules to floodwater at heading stage

Role of fish in enhancing ricefield ecology and in integrated pest management: summary report

Summary report of the Third Asian Regional Rice-Fish Farming Research and Development Workshop, Indonesia, 1993. Includes sessions on ricefield ecology and fish; integrated pest management (IPM); research methodology; and IPM adoption.Rice-fish aquaculture, Culture effects, Pest control, Integrated farming

The HPx software for multicomponent reactive transport during variably-saturated flow: Recent developments and applications

Abstract HPx is a multicomponent reactive transport model which uses HYDRUS as the flow and transport solver and PHREEQC-3 as the biogeochemical solver. Some recent adaptations have significantly increased the flexibility of the software for different environmental and engineering applications. This paper gives an overview of the most significant changes of HPx, such as coupling transport properties to geochemical state variables, gas diffusion, and transport in two and three dimensions. OpenMP allows for parallel computing using shared memory. Enhancements for scripting may eventually simplify input definitions and create possibilities for defining templates for generic (sub)problems. We included a discussion of root solute uptake and colloid-affected solute transport to show that most or all of the comprehensive features of HYDRUS can be extended with geochemical information. Finally, an example is used to demonstrate how HPx, and similar reactive transport models, can be helpful in implementing different factors relevant for soil organic matter dynamics in soils. HPx offers a unique framework to couple spatial-temporal variations in water contents, temperatures, and water fluxes, with dissolved organic matter and CO2 transport, as well as bioturbation processes