# Journal Paper Digests

## Journal Paper Digests 2023 #1

• Variability of phosphorus sorption properties in hydromorphic soils: Consequences for P losses in agricultural landscapes
• Fraser Island (K’gari) and initiation of the Great Barrier Reef linked by Middle Pleistocene sea-level change
• Stable Carbon Isotopic Composition (delta C-13) as a Proxy of Organic Matter Dynamics in Soils on the Western Shore of Lake Baikal
• Methods for downhole soil water sensor calibration-Complications of bulk density and water content variations
• Feasibility assessment on use of proximal geophysical sensors to support precision management
• Soil acidity amelioration improves N and C cycles in the short term in a system with soybean followed by maize-guinea grass intercropping

### Soil acidity amelioration improves N and C cycles in the short term in a system with soybean followed by maize-guinea grass intercropping

Lime application has been associated with N and C losses from agricultural systems through NO3- leaching, N2O and CO2 emissions. However, we hypothesized that in an intensive crop system where soybean is grown in rotation with maize intercropped with a forage grass, liming associated with the application of gypsum to ameliorate the subsoil, and N fertilization increase soil N and C by improving root and crop growth. To evaluate the interaction of lime, gypsum and N fertilizer on soil and N and C partial balances, an experiment was carried out under no-till, where soybean was grown in rotation with maize intercropped with Guinea grass (Megathyrsus maximus cv Tanzania) as relay crop. Lime and gypsum were applied before soybean planting in October 2016 and October 2017. Two N rates (0 and 160 kg ha(-1) yr(-1) of N as ammonium sulphate) were applied to maize annually. Outputs through N-NO3- leaching, N-N2O emission and N-NH3 volatilization did not exceed 30 kg ha(-1) of N in two years. The N exported in grains consisted in 96% of the N output and was greater with fertilizer and lime. Soil acidity amelioration and N-fertilization favoured soil C fixation with high plant biomass production (C in plant residue, roots, and grains), while soil C-CO2 emission was not affected, and soil C increased. Although the partial N balance was negative, there was an increase in soil N, probably due to biological N fixation by soybean, which was not considered in the partial balance. We concluded that lime and gypsum application, along with an adequate N fertilization, to a tropical highly-weathered soil with soybean cropped in rotation with maize-guinea grass intercropping benefit N and C cycles and the environment in the short-term, increasing soil N and C stocks and reducing GHG emitted to the atmosphere.

### Feasibility assessment on use of proximal geophysical sensors to support precision management

A study was conducted at three sites in North Dakota to strengthen understanding of the usefulness of different proximal geophysical data types in agricultural contexts of varying pedology. This study hypothesizes that electromagnetic induction (EMI), gamma-ray sensor (GRS), cosmic-ray neutron sensor (CRNS), and elevation data layers are all useful in multiple linear regression (MLR) predictions of soil properties that meet expert criteria at three agricultural sites. In addition to geophysical data collection with vehicle-mounted sensors, 15 soil samples were collected at each site and analyzed for nine soil properties of interest. A set of model training data was compiled by pairing the sampled soil property measurements with the nearest geophysical data. Eleven models passed expert-defined uncertainty criteria at Site 1, 16 passed at Site 2, and 14 passed at Site 3. Electrical conductivity (EC), organic matter (OM), available water holding capacity, silt, and clay were predicted at Site 1 with an R-squared of prediction (Rpred2)$(R_{pred}<^>2)$ > .50 and acceptable root mean square error of prediction (RMSEP). Bulk density (BD), OM, available water capacity, silt, and clay were predicted with Rpred2$R_{pred}<^>2$ > .50 and acceptable RMSEP at Site 2. At Site 3, no soil properties were predicted with acceptable RMSEP and an Rpred2$R_{pred}<^>2$ > .50. These results confirm feasibility of our method, and the authors recommend the prioritization of EMI data collection if geophysical data collection is limited to a single mapping effort and calibration soil samples are few.

### Methods for downhole soil water sensor calibration-Complications of bulk density and water content variations

Downhole soil volumetric water content (VWC) sensors are used in access tubes to assess the soil water content at multiple depths. If sensor readings are spaced closely enough vertically and are accurate enough, then accurate soil profile water content storage and change in storage can be determined over the depth range of readings, leading to accurate estimates of evapotranspiration (ET) if readings extend to well below the root zone. Even if sensing only covers the active root zone, soil water depletion may be determined well enough to inform irrigation scheduling. While sensor accuracy is dependent on many factors, including the sensor’s physical principle of operation, soil-specific calibration is typically required for good accuracy. In soils with multiple horizons (layers) of different texture, bulk density (BD), or chemical composition, horizon-specific calibrations may be necessary. We describe methods and equipment used for downhole sensor calibration to typical accuracy of <0.01 m(3) m(-3) with specific reference to calibration of 10 neutron scattering meters in a soil that required three different horizon-specific calibrations. Our results contrast with the factory calibration, which would result in a 38-mm error in water stored in a 1.5-m deep profile of our soil. We describe variability of measured VWC and BD with depth, distance, and water content and the errors that result from using BD to convert mass basis (g g(-1)) water content data to VWC data, which can be as much as 35 mm (7.26% underestimation) for soil water storage in a 1.5-m deep profile of our soil.

### Stable Carbon Isotopic Composition (delta C-13) as a Proxy of Organic Matter Dynamics in Soils on the Western Shore of Lake Baikal

Assessing the main factors that control carbon dynamics in soils is an urgent problem in the context of modern climate change. The analysis of stable carbon isotope (delta C-13) composition is one of the approaches to understanding this dynamics. The study was carried out in the landscapes of the southeastern slope and foothills of the Primorskii Range, characterized by contrasting physico-geographical conditions. Climatic parameters, spatial variations in the composition of stable carbon isotopes and their distribution in soil profiles, and soil physicochemical properties controlling carbon dynamics have been analyzed. The soil humus horizons formed in mountainous tundra and steppe landscapes manifest the highest delta C-13 values (-24.72 and -23.97 … -24.75 parts per thousand ); whereas the lowest (-25.61 … -27.18 parts per thousand ) values are registered in the mountainous taiga soils. Based on the calculation of linear dependence between delta C-13 values and the total carbon content in soil, which varies with the depth, the carbon turnover intensity was determined using the slope of linear regression. It was revealed that under the contrasting conditions of mountainous tundra and steppe landscapes, the climate (deficiency of heat and moisture) has a significant impact on the intensity of organic matter transformation, blocking the effect of edaphic (soil profile) factors. Under more favorable climatic conditions of mountainous taiga landscapes, the dynamics of organic matter in soils is controlled mainly by edaphic factors.

### Fraser Island (K’gari) and initiation of the Great Barrier Reef linked by Middle Pleistocene sea-level change

The eastern Australia coastline is characterized by impressive coastal landforms and an extensive northward-moving longshore drift system that have been influenced by a stable, long-term tectonic history over the Quaternary period. However, the timing and drivers of the formation of two conspicuous landscape features-Fraser Island (K’gari) and the Great Barrier Reef-remain poorly understood. Here we use optically stimulated luminescence and palaeomagnetic dating to constrain the formation of the extensive dunes that make up Fraser Island, the world’s largest sand island, and adjacent Cooloola Sand Mass in southeastern Queensland. We find that both formed between 1.2 Ma and 0.7 Ma, during a global climate reconfiguration across the Middle Pleistocene transition. They formed as a direct result of increased amplitude of sea-level fluctuations associated with increasing global ice volume that redistributed previously stored sediment across the continental shelf. The development of Fraser Island dramatically reduced sediment supply to the continental shelf north of the island. This facilitated widespread coral reef formation in the southern and central Great Barrier Reef and was a necessary precondition for its development. This major reorganization of the coastal sedimentary system is probably not unique to eastern Australia and should be investigated in other passive-margin coastlines.

Disruption of sediment flows along the eastern Australia coast due to the Middle Pleistocene formation of Fraser Island set the stage for Great Barrier Reef initiation, according to optically stimulated luminescence and palaeomagnetic dating of sand dunes.

### Variability of phosphorus sorption properties in hydromorphic soils: Consequences for P losses in agricultural landscapes

Increasing concerns over water eutrophication due to agricultural phosphorus (P) loss have led to the development of indicators to assess the risk of P release from agricultural soils. Recently, a logarithmic equation linking the degree of phosphorus saturation (DPS) to the simple water-soluble P (WSP) content of soils has been proposed as a universal method to assess this risk based, however, mainly on the analysis of well-drained soils. Here, we studied the P sorption properties and DPS values of 69 hydromorphic soils from cultivated and uncultivated wetland zones located in Brittany, Western France, to test whether the method could also apply to poorly-drained soils. The bulk soil analysis showed that P contents of the studied hydromorphic soils were 30% to 80% higher than P contents normally found in Brittany soils, evidencing a possible P enrichment process. Adsorption isotherms revealed a surprisingly high variability in the P sorption properties as a function of the location of the soil (maximum P adsorption capacity ranging from 500 to 1850 mg kg(-1)), which is caused by variations in the phases controlling P sorption in soil (from clay to organic matter and/or iron and aluminium oxides, depending on the soil location). Distinct relationships between DPS and WSP values were also obtained depending on the location of the soils. The obtained DPS versus WSP relationships showed that the P saturation threshold above which the risk of dissolved P release increases markedly is 30% lower on average for hydromorphic soils than for well-drained soils. Hydromorphic soils appear to be more at risk of releasing dissolved P at the same DPS values than well-drained soils. The present study indicates an underestimation of the P release risk from hydromorphic soils by the existing method developed for well-drained soils and calls for the development of specific risk assessment tools for hydromorphic soils, especially given on the strong spatial heterogeneity of their P sorption properties.

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