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1. Impact of Hydrochar Amendment on the Water Retention Capability of Agricultural Soil

   https://doi.org/10.1061/9780784484258.015  

   Han, Tianyu; Li, Jiangjun; Liu, Lubo (June 2022, World Environmental and Water Resources Congress 2022)

   John Pierson (Ed.)

   The water retention capability of soil significantly impacts plant growth. A scarcity of water in agricultural soil may cause low crop productivity, potentially leading to critical food-deficit problems in arid areas with increasing populations such as central California. New ways to enhance the water retention capability of soil to enable farmers to utilize water more effectively are thus urgently needed. Research has shown that hydrochar, which is produced by hydrothermal carbonization (HTC), can potentially improve soil quality by enabling it to hold water for longer periods. This study therefore explored how the addition of hydrochar affects water retention capacity in the root zone using soil experiments. For the experiments, a column filled with sample sandy soil but without hydrochar, which was used as a control. Meanwhile, 8% weight of hydrochar were mixed with soil at the top of soil columns to investigate how the presence or absence of hydrochar affected: (1) the temporal variation of soil moisture vs depth; (2) the temporal variation in the water’s potential head vs. depth at different times; and (3) the distribution of soil moisture vs the water’s potential head. The results of these experiments can be utilized to show the agricultural benefit gained by soil amendment with a certain amount of hydrochar. 

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2. Within‐field soil moisture variability and time‐invariant spatial structures of agricultural fields in the US Midwest

   https://doi.org/10.1002/vzj2.20337  

   Yang, Yi; Peng, Bin; Guan, Kaiyu; Pan, Ming; Franz, Trenton_E; Cosh, Michael_H; Bernacchi, Carl_J (April 2024, Vadose Zone Journal)

   Abstract Understanding soil moisture variability and estimating high‐resolution soil moisture at subfield to field scales is critical for agricultural research and applications. However, systematic investigation of subfield scale soil moisture variability over cropland is still lacking from both measurement and satellite remote sensing. In this study, we aim to investigate (1) the characteristics of within‐field soil moisture distribution over typical cropland in the US Midwest and (2) the capabilities of satellite remote sensing in capturing the spatiotemporal variabilities of soil moisture at subfield scale. Specifically, we conducted soil moisture field experiments in three typical commercial agricultural fields (∼85 acres per field) in central Illinois, representing typical commercial farmlands in the US Midwest, and compared the soil moisture measurements with satellite remote sensing data from optical and active microwave sensors. In each field, dense soil moisture samples (spaced at 50–60 m) were obtained for two dry down events in May and July 2021, and multiple long‐term soil moisture stations were installed. We found prominent time‐invariant spatial structures of soil moisture at within‐field scales both during the dry down period and over longer time scales, and the stability is minimally affected by plant water use during the growing season. Comparing the field campaign measurements with satellite remote sensing data, we found that surface reflectance of shortwave infrared bands, such as SWIR1 (1610 nm) from Sentinel‐2, can capture relative surface soil moisture patterns at within‐field scales, but their relationships with soil moisture are field specific. These findings and the improved understanding of within‐field soil moisture dynamics could potentially help future research on high‐resolution soil moisture estimation with multi‐source remote sensing data. 

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3. Effect of Irrigation Water Quality and Soil Compost Treatment on Salinity Management to Improve Soil Health and Plant Yield

   https://doi.org/10.3390/w16101391  

   Suvendran, Subanky; Johnson, David; Acevedo, Miguel; Smithers, Breana; Xu, Pei (May 2024, Water)

   Increasing soil salinity and degraded irrigation water quality are major challenges for agriculture. This study investigated the effects of irrigation water quality and incorporating compost (3% dry mass in soil) on minimizing soil salinization and promoting sustainable cropping systems. A greenhouse study used brackish water (electrical conductivity of 2010 µS/cm) and agricultural water (792 µS/cm) to irrigate Dundale pea and clay loam soil. Compost treatment enhanced soil water retention with soil moisture content above 0.280 m3/m3, increased plant carbon assimilation by ~30%, improved plant growth by >50%, and reduced NO3− leaching from the soil by 16% and 23.5% for agricultural and brackish water irrigation, respectively. Compared to no compost treatment, the compost-incorporated soil irrigated with brackish water showed the highest plant growth by increasing plant fresh weight by 64%, dry weight by 50%, root length by 121%, and plant height by 16%. Compost treatment reduced soil sodicity during brackish water irrigation by promoting the leaching of Cl− and Na+ from the soil. Compost treatment provides an environmentally sustainable approach to managing soil salinity, remediating the impact of brackish water irrigation, improving soil organic matter, enhancing the availability of water and nutrients to plants, and increasing plant growth and carbon sequestration potential. 

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4. The Effects of Soil Depth on the Structure of Microbial Communities in Agricultural Soils in Iowa (United States)

   https://doi.org/10.1128/AEM.02673-20  

   Hao, Jingjie; Chai, Yen Ning; Lopes, Lucas Dantas; Ordóñez, Raziel A.; Wright, Emily E.; Archontoulis, Sotirios; Schachtman, Daniel P. (January 2021, Applied and Environmental Microbiology)

   Semrau, Jeremy D. (Ed.)

   ABSTRACT This study investigated the differences in microbial community abundance, composition, and diversity throughout the depth profiles in soils collected from corn and soybean fields in Iowa (United States) using 16S rRNA amplicon sequencing. The results revealed decreased richness and diversity in microbial communities at increasing soil depth. Soil microbial community composition differed due to crop type only in the top 60 cm and due to location only in the top 90 cm. While the relative abundance of most phyla decreased in deep soils, the relative abundance of the phylum Proteobacteria increased and dominated agricultural soils below the depth of 90 cm. Although soil depth was the most important factor shaping microbial communities, edaphic factors, including soil organic matter, soil bulk density, and the length of time that deep soils were saturated with water, were all significant factors explaining the variation in soil microbial community composition. Soil organic matter showed the highest correlation with the exponential decrease in bacterial abundance with depth. A greater understanding of how soil depth influences the diversity and composition of soil microbial communities is vital for guiding sampling approaches in agricultural soils where plant roots extend beyond the upper soil profile. In the long term, a greater knowledge of the influence of depth on microbial communities should contribute to new strategies that enhance the sustainability of soil, which is a precious resource for food security. IMPORTANCE Determining how microbial properties change across different soils and within the soil depth profile will be potentially beneficial to understanding the long-term processes that are involved in the health of agricultural ecosystems. Most literature on soil microbes has been restricted to the easily accessible surface soils. However, deep soils are important in soil formation, carbon sequestration, and providing nutrients and water for plants. In the most productive agricultural systems in the United States where soybean and corn are grown, crop plant roots extend into the deeper regions of soils (>100 cm), but little is known about the taxonomic diversity or the factors that shape deep-soil microbial communities. The findings reported here highlight the importance of soil depth in shaping microbial communities, provide new information about edaphic factors that influence the deep-soil communities, and reveal more detailed information on taxa that exist in deep agricultural soils. 

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5. Recent Progress on Emerging Applications of Hydrochar

   https://doi.org/10.3390/en15249340  

   Islam, Md Tahmid; Sultana, Al Ibtida; Chambers, Cadianne; Saha, Swarna; Saha, Nepu; Kirtania, Kawnish; Reza, M. Toufiq (December 2022, Energies)

   Hydrothermal carbonization (HTC) is a prominent thermochemical technology that can convert high-moisture waste into a valuable product (called hydrochar) at a relatively mild treatment condition (180–260 °C and 2–10 MPa). With rapidly growing research on HTC and hydrochar in recent years, review articles addressing the current and future direction of this research are scarce. Hence, this article aims to review various emerging applications of hydrochars, e.g., from solid fuel to soil amendment, from electron storage to hydrogen storage, from dye adsorption, toxin adsorption, heavy metal adsorption to nutrient recovery, and from carbon capture to carbon sequestration, etc. This article further provides an insight in the hydrochar’s working mechanism for various applications and how the applications can be improved through chemical modification of the hydrochar. Finally, new perspectives with appropriate recommendations have been made to further unveil potential applications and its improvement through hydrochar and its modified version. 

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