Synergy between compost and cover crops in a Mediterranean row crop system leads to increased subsoil carbon storage

Subsoil carbon (C) stocks are a prime target for efforts to increase soil C storage for climate change mitigation. However, subsoil C dynamics are not well understood, especially in soils under long-term intensive agricultural management. We compared subsoil C storage and soil organic matter (SOM) composition in tomato-corn rotations after 25 years of differing C and nutrient management in the California Central Valley: CONV (mineral fertilizer), CONV+WCC (mineral fertilizer and cover crops), and ORG (composted poultry manure and cover crops). The cover crop mix used in these systems is a mix of oat (Avena sativa L.), faba bean (Vicia faba L.), and hairy vetch (Vicia villosa Roth). Our results showed a ∼19Mgha-1 increase in soil organic C (SOC) stocks down to 1m under ORG systems, no significant SOC increases under CONV+WCC or CONV systems, and an increased abundance of carboxyl-rich C in the subsoil (60-100cm) horizons of ORG and CONV+WCC systems. Our results show the potential for increased subsoil C storage with compost and cover crop amendments in tilled agricultural systems and identify potential pathways for increasing C transport and storage in subsoil layers. Copyright

Effect of cover crop on carbon distribution in size and density separated soil aggregates

Increasing soil organic carbon (SOC) stocks in agricultural soils can contribute to stabilizing or even lowering atmospheric greenhouse gas (GHG) concentrations. Cover crop rotation has been shown to increase SOC and provide productivity benefits for agriculture. Here we used a split field design to evaluate the short-term effect of cover crop on SOC distribution and chemistry using a combination of bulk, isotopic, and spectroscopic analyses of size-and density-separated soil aggregates. Macroaggregates (\u3e250 µm) incorporated additional plant material with cover crop as evidenced by more negative δ13C values (−25.4%∘ with cover crop compared to −25.1%∘without cover crop) and increased phenolic (plant-like) resonance in carbon NEXAFS spectra. Iron EXAFS data showed that the Fe pool was composed of 17–21% Fe oxide with the remainder a mix of primary and secondary minerals. Comparison of oxalate and dithionite extractions suggests that cover crop may also increase Fe oxide crystallinity, especially in the dense (\u3e2.4 g cm−3) soil fraction. Cover crop δ13C values were more negative across density fractions of bulk soil, indicating the presence of less processed organic carbon. Although no significant difference was observed in bulk SOC on a mass per mass basis between cover and no cover crop fields after one season, isotopic and spectroscopic data reveal enhanced carbon movement between aggregates in cover crop soil

Evaluating biochar and its modifications for the removal of ammonium, nitrate, and phosphate in water

Removal of nitrogen (N) and phosphorus (P) from water through the use of various sorbents is often considered an economically viable way for supplementing conventional methods. Biochar has been widely studied for its potential adsorption capabilities for soluble N and P, but the performance of different types of biochars can vary widely. In this review, we summarized the adsorption capacities of biochars in removing N (NH4-N and NO3-N) and P (PO4-P) based on the reported data, and discussed the possible mechanisms and influencing factors. In general, the NH4-N adsorption capacity of unmodified biochars is relatively low, at levels of less than 20 mg/g. This adsorption is mainly via ion exchange and/or interactions with oxygen-containing functional groups on biochar surfaces. The affinity is even lower for NO3-N, because of electrostatic repulsion by negatively charged biochar surfaces. Precipitation of PO4-P by metals/metal oxides in biochar is the primary mechanism for PO4-P removal. Biochars modified by metals have a significantly higher capacity to remove NH4-N, NO3-N, and PO4-P than unmodified biochar, due to the change in surface charge and the increase in metal oxides on the biochar surface. Ambient conditions in the aqueous phase, including temperature, pH, and co-existing ions, can significantly alter the adsorption of N and P by biochars, indicating the importance of optimal processing parameters for N and P removal. However, the release of endogenous N and P from biochar to water can impede its performance, and the presence of competing ions in water poses practical challenges for the use of biochar for nutrient removal. This review demonstrates that progress is needed to improve the performance of biochars and overcome challenges before the widespread field application of biochar for N and P removal is realized

A Spectroscopic Study of Bacterial Polymers Mediating Cell Adhesion and Mineral Transformations

Current understanding of molecular-level interactions is inadequate to explain the initial moments of bacterial adhesion. Such information is required to develop appropriate models for bacteria-surface interactions and predictions of cell transport in subsurface environments. Bacterial adhesion is influenced by bacterial surfaces, substratum physical-chemical characteristics, and solution chemistry. Extracellular polymeric substances (EPS), surface proteins, and lipopolysaccharides (LPS) mediate cell adhesion and conditioning film formation via direct bonding to a substrate. The goal of this dissertation is to probe molecular-scale interactions of cell surface macromolecules at mineral surfaces under environmentally-relevant conditions. Four primary investigations are presented in this dissertation. The first study uses in situ attenuated total reflectance (ATR) Fourier transform infrared (FTIR) spectroscopy to reveal that prior to Mn-oxidation via Pseudomonas putida GB-1, cell adhesion to ZnSe is favorable. Subsequent Mn-oxidation results in increased extracellular proteins expression. Conversely, planktonic cell adhesion is inhibited for Mn-oxide coated cells via blocking of surface proteins. The second investigation reveals the formation of inner-sphere complexes between bacteria surface phosphoryl groups and nanohematite (α-Fe₂O₃). Spectra of bacteria (P. aeruginosa PAO1, Shewanella oneidensis MR-1, and Bacillus subtilis) on α- Fe₂O₃ contain peaks indicative of P-OFe inner-sphere bonding. Spectra collected for oxide-adsorbed model P-containing compounds give spectral signatures similar to those P-OFe bonding interactions observed for whole cell and EPS. The behavior of P. aeruginosa serotype 10 LPS in aqueous solutions was investigated in the third study. Ionic strength, pH, and electrolyte composition were varied during collection of ATR-FTIR and dynamic light scattering (DLS) data. Results reveal stable aggregate Na-LPS aggregates, whereas binding of Ca²⁺ to phosphate groups in the lipid A region leads to aggregate reorientation and increased interaction with ZnSe (hydrophobic). DLS data demonstrate decreasing hydrodynamic radius of LPS aggregates with increasing I and decreasing pH. In the fourth investigation, ATR-FTIR was used to probe the solid-solution interface of LPS on surfaces of ZnSe, Ge, α-Fe₂O₃, and α-Al₂O₃ in solutions of varying ionic composition and pH. Na-LPS aggregates remain stable and spectra are biased towards solution phase LPS. Ca-LPS aggregates are disrupted, leading to enhanced interaction with surfaces via hydrophobic (lipid A- ZnSe) and electrostatic (O-antigenhydrophilic surfaces) interactions

The effect of mineral-ion interactions on soil hydraulic conductivity

The reuse of winery wastewater (WW) could provide an alternative water source for vineyard irrigation.The shift of many wineries and other food processing industries to K+-based cleaners requires studies onthe effects of K+on soil hydraulic conductivity (HC). Depending on clay content and mineral composition,K+additions can affect the HC either positively or negatively. Soil mineralogy was anticipated to exhibita strong influence on HC responses and, therefore, soils of contrasting mineralogy were evaluated forchanges in soil HC resulting from applications of solutions elevated in Na+and K+. To examine the impactof mineral-ion relationships on HC, soils dominant in montmorillonite, vermiculite, or kaolinite from theNapa and Lodi wine regions of California, were packed into soil columns to observe changes in leachatechemistry and HC. Irrigation with Na+- and K+-rich WW was simulated by applying solutions at sodiumabsorption ratio (SAR) values of 3, 6, and 9 and potassium absorption ratio (PAR) values of 1, 2, 4, and 9.While HC was reduced in the 2:1 clay soils (montmorillonite and vermiculite) for all SAR treatments, thevermiculite and the kaolinite rich soils exhibited equal or greater reductions in HC for PAR treatments, ascompared with the SAR treatments. Findings from this evaluation of the interaction of Na+and K+withthree different mineral soils suggest that the reuse of WW with increasing PAR are least problematic formontmorillonite dominated soils and most detrimental to the HC of the vermiculite dominated soil. Thepresence of minerals with a high affinity for K+(e.g., vermiculite, mica) in this soil suggest that the inter-layer binding of K+could lead to greater reductions in HC. Full analysis of soil and WW is recommendedprior to all land applications

Benchmarking Cloud Computing Options Using DEA

This paper covers our exploration into using linear programming to rank the effectiveness of cloud computing options. This paper also serves a culminating group project in a graduate level operations research class at Portland State University. Our primary method was Data Envelopment Analysis using R. We were given a dataset by Dr. Lane Inman, a former student in this class, and head of product development at Krystallize, a startup specializing in assessing cloud computing providers. The data table we were given contains performance metrics obtained by Krystallize while testing available cloud service options offered through Google Cloud, Microsoft Azure, AWS, and SoftLayer. What follows is our process and the significant insights we found

Biological P cycling is influenced by the form of P fertilizer in an Oxisol

Phosphate rock (PR) is an alternative fertilizer to increase the P content of P-deficient weathered soils. We evaluated the effects of fertilizer form on indicators of biological cycling of P using an on-farm trial on a Rhodic Kandiudox in western Kenya. Treatment plots were sampled after 13 cropping seasons of P applications as Minjingu phosphate rock (PR) or as triple super phosphate (TSP) (50 kg P ha−1 season−1), as well as a P-unfertilized control (0 kg P ha−1 season−1). Soils (0–15 and 15–30 cm) were analyzed for microbial biomass P (Pmic), activities of acid phosphomonoesterase, alkaline phosphomonoesterase, and phosphodiesterase, and sequentially extractable P fractions. P additions as Minjingu PR yielded 299% greater Pmic than TSP at 0–15-cm depth despite similar labile P concentrations in the two P fertilization treatments and stimulated activities of acid phosphomonoesterase (+39%). When added in the soluble form of TSP, a greater percentage of total soil P was present in mineral-bound forms (+33% Fe- and Al-associated P). Higher soil pH under Minjingu PR (pH 5.35) versus TSP (pH 5.02) and the P-unfertilized treatment (pH 4.69) at 0–15-cm depth reflected a liming effect of Minjingu PR. The form of P fertilizer can influence biological P cycling in weathered soils, potentially improving P availability under Minjingu PR relative to TSP via enhanced microbial biomass P and enzymatic drivers of P cycling