Incorporation of compost into soil can significantly alter soil physical properties, nutrient dynamics, and vegetation establishment. Strategic compost application to disturbed, degraded urban soil may provide benefits to soil properties. This review compared twenty-five peer-reviewed studies that evaluated changes in soil bulk density, infiltration rate, hydraulic conductivity, and water retention where compost was incorporated into urban soils. A wide range of compost rates and incorporation depths were evaluated in these studies across many soil types. Compost incorporation generally reduced bulk density, enhanced infiltration and hydraulic conductivity, and increased water content and plant available water, compared to unamended controls. In the four studies on runoff water quality, compost incorporation often resulted in higher initial nutrient content in runoff water, but also enhanced grass growth and reduced sediment loss. Few studies evaluated multiple compost application rates or incorporation depths, and the ways in which compost application rates were reported varied widely between studies making it difficult to directly compare them. Four studies investigated the long-term effects of compost incorporation, and there was no clear pattern of why some soils display enhanced physical properties over time and others do not. Compost was largely reported to have a positive effect on degraded urban soils. Little research has focused on the longevity of compost in urban soils after one application, and thus, this would be a valuable topic of further investigation.

Anammox and denitrification mediated by bacteria are known to be the major microbial processes converting fixed N to N ₂ gas in various ecosystems. Codenitrification and denitrification by fungi are additional pathways producing N ₂ in soils. However, fungal codenitrification and denitrification have not been well investigated in agricultural soils. To evaluate bacterial and fungal processes contributing to N ₂ production, molecular and ¹⁵ N isotope analyses were conducted with soil samples collected at six different agricultural fields in the United States. Denitrifying and anammox bacterial abundances were measured based on quantitative PCR (qPCR) of nitrous oxide reductase ( nosZ ) and hydrazine oxidase ( hzo ) genes, respectively, while the internal transcribed spacer (ITS) of Fusarium oxysporum was quantified to estimate the abundance of codenitrifying and denitrifying fungi. ¹⁵ N tracer incubation experiments with ¹⁵ NO ₃ ⁻ or ¹⁵ NH ₄ ⁺ addition were conducted to measure the N ₂ production rates from anammox, denitrification, and codenitrification. Soil incubation experiments with antibiotic treatments were also used to differentiate between fungal and bacterial N ₂ production rates in soil samples. Denitrifying bacteria were found to be the most abundant, followed by F. oxysporum based on the qPCR assays. The potential denitrification rates by bacteria and fungi ranged from 4.118 to 42.121 nmol N ₂ -N g ⁻¹ day ⁻¹ , while the combined potential rates of anammox and codenitrification ranged from 2.796 to 147.711 nmol N ₂ -N g ⁻¹ day ⁻¹ . Soil incubation experiments with antibiotics indicated that fungal codenitrification was the primary process contributing to N ₂ production in the North Carolina soil. This study clearly demonstrates the importance of fungal processes in the agricultural N cycle.

Core Ideas: Results of agronomic management effects on SOM are inconsistent among methods. Correlations among methods of measuring SOM differ depending on soil. Soil organic matter content should be compared using similar procedures. Soil organic matter (SOM) provides many beneficial soil ecosystem services for sustainable soil management, but it is unclear how results from different methods of measuring SOM should be compared when making soil management decisions. To compare different methods, we used 84 soil samples from long‐term agronomic trials in the coastal plain, piedmont, and mountain regions of North Carolina. Coastal plain and mountain trials included combinations of tillage and management (conventional vs. organic), whereas piedmont trials were configured to evaluate tillage intensity. The methods used to measure SOM were Walkley‐Black (WB), mass loss on ignition (LOI), automated dry combustion (ADC), and humic matter (HM) colorimetry. Correlations among LOI, WB, and ADC were significant ( p < 0.0001) for SOM measured from the total population of soils, but variability due to location implied that HM had no correlation to other methods. For measures of soil organic carbon compared to SOM, the WB results were biased high compared to ADC, and ADC was more strongly correlated to LOI than WB. When using the methods to evaluate the effects of agronomic management on SOM, results varied for different methods and locations. Conservation management did not consistently accumulate more SOM than other soil management practices, and no method consistently differentiated soils based on management. Variation in the composition of SOM measured using conventional methods may be causing discrepancies in reported changes in SOM content over time. To avoid confusion about how agronomic management affects SOM, assessments should limit comparisons to methodologies with similar measurement protocols.

Recent soil tests evaluating “soil health” on a broad scale may not properly consider the intrinsic limitations of soil properties, and have not been assessed in regionally unique soil conditions. To evaluate three soil tests in North Carolina, we used long-term agronomic management trials from three distinct physiographic regions: mountain (22 yr), piedmont (32 yr), and coastal plain (17 yr). Mountain and coastal plain trials included combinations of organic or chemical management with or without tillage; the piedmont trial included nine different tillage treatments. Soil samples were collected and submitted for analysis as recommended by the North Carolina Department of Agriculture and Consumer Services, Haney soil health test (HSHT), and Cornell comprehensive assessment of soil health (CASH). Plant nutrient concentrations varied but were still sufficient for crops. The CASH physical soil indicators, such as surface hardness and aggregate stability, were not statistically different, regardless of tillage intensity or management. Biological soil indicators (e.g., CO₂ respiration) responded differently to management, but this differentiation was inconsistent among locations and tests. Despite many years of conservation management, the CASH results described mountain soils as “low” or “very low” soil health for all but no-till organic management, which received a “medium” score. The HSHT results considered soil from all but moldboard plowing (piedmont) to be in good health. Finally, there was no correlation between soil health tests and crop yields from North Carolina soils. Soil health tests should be calibrated to better differentiate among soil management effects that vary depending on intrinsic soil limitations. Copyright © 2017. . Copyright © by the Soil Science Society of America, Inc.

Particularly in light of California’s recent multiyear drought, there is a critical need for accurate and timely evapotranspiration (ET) and crop stress information to ensure long-term sustainability of high-value crops. Providing this information requires the development of tools applicable across the continuum from subfield scales to improve water management within individual fields up to watershed and regional scales to assess water resources at county and state levels. High-value perennial crops (vineyards and orchards) are major water users, and growers will need better tools to improve water-use efficiency to remain economically viable and sustainable during periods of prolonged drought. To develop these tools, government, university, and industry partners are evaluating a multiscale remote sensing–based modeling system for application over vineyards. During the 2013–17 growing seasons, the Grape Remote Sensing Atmospheric Profile and Evapotranspiration eXperiment (GRAPEX) project has collected micrometeorological and biophysical data within adjacent pinot noir vineyards in the Central Valley of California. Additionally, each year ground, airborne, and satellite remote sensing data were collected during intensive observation periods (IOPs) representing different vine phenological stages. An overview of the measurements and some initial results regarding the impact of vine canopy architecture on modeling ET and plant stress are presented here. Refinements to the ET modeling system based on GRAPEX are being implemented initially at the field scale for validation and then will be integrated into the regional modeling toolkit for large area assessment.