A 1200 m‐long river segment of Carmel River (California) was constructed to bypass trapped reservoir sediment when San Clemente Dam was removed from the Carmel River in 2015. Hundreds of large boulders were used to construct 53 steps in an 800 m‐long reach of the project. Nearly all the boulders were scattered to new locations in high flows of 2017, and have been relatively stable since that time. We analysed the causes of incipient motion and distance travelled for 226 randomly selected large boulders (0.5–1.8 m) impacted by a flood event in winter of 2019. Channel width, water depth, and isolation from neighbouring boulders were the main variables controlling individual large boulder incipient motion during a 10‐year peak flow event in the ‘auto‐naturalized’ constructed step‐pool river in 2019. There is weak statistical evidence that a combination of shear stress and the presence of boulders located laterally downstream of the subject boulder controlled the distance the boulder moved. Frequentist statistics and Akaike information criterion model comparison determined that boulder size, boulder shape, boulder roundness, and local thalweg slope were not good predictors of large boulder incipient motion or distance transported. Average dimensionless critical shear value for the four largest mobilized boulders (1.5–1.6 m) was 0.014. We describe the geomorphic history of the site and use our results to discuss potential causes of unanticipated large boulder transport at the site that occurred in a <2‐year peak flow of winter 2016 soon after step construction. © 2020 John Wiley & Sons, Ltd.

Anaerobic soil disinfestation (ASD) is emerging globally as an alternative to fumigant pesticides. To investigate ASD mechanisms, we monitored microbially produced volatile organic compounds (VOCs) and other volatile gases in situ using Fourier Transform Infrared Spectroscopy. Study plots infested with Fusarium oxysporum, Macrophomina phaseolina, and/or Verticillium dahliae included: organic flat ground (fASD, 6.7 + 13.5 megagrams per hectare, Mg/ha, rice bran/broccoli) and uncovered soil treated with mustard seed meal (MSM, 3.4 Mg/ha) at one site performed in fall of 2018; formed bed (bASD, 20 Mg/harice bran), control (UTC) and fumigant (FUM) at a second field site in fall of 2019 and 2021. Here, we present VOC diversity and temporal distribution. fASD generated 39 VOCs and GHGS, including known pathogen suppressors: dimethyl sulfide, dimethyl disulfide, and n-butylamine. bASD produced 17 VOCs and greenhouses gases (GHGs), 12 of which were also detected in fASD but in greater concentrations. Plant mortality and wilt score (fASD: 3.75% ± 4.79%, 2.8 ± 0.8; MSM: 6.25% ± 12.50%, 2.7 ± 0.3; bASD: 61.27% ± 11.26%, 4.1 ± 0.5; FUM: 13.89% ± 7.17%, 2.3 ± 0.2; UTC: 76.63% ± 25.11%, 4.3 ± 1.0) were significantly lower for fASD and MSM versus bASD and UTC (p < 0.05). Only FUM was not statistically different from fASD and MSM, and was significantly lower than UTC and bASD (bASD-FUM, p < 0.05; UTC-FUM, p < 0.05). The cumulative strawberry yield from bASD-treated plots was not different from FUM or UTC (bASD: 60.3 ± 13.6; FUM: 79.4 ± 9.19; UTC: 42.9 ± 12.4 Mg/ha). FUM yield was significantly greater than UTC (p = 0.005). These results, and to a far greater extent, additional challenges faced during both bASD trials, suggest that bASD is not as effective or as feasible at maintaining overall plant health as fASD or traditional fumigants. However, differences in management practices and environmental conditions at both sites across years cannot be fully excluded from consideration and many of our observations remain qualitative in nature.

CAL-CORE is a network of researchers, farmers, extension professionals, industry and non-profit organizations dedicated to furthering research into organic strawberry and vegetable production in coastal California. Formed 9 years ago, we have worked on a variety of fertility, pest and disease management issues facing organic growers. Currently, our main effort centers on vegetable/strawberry rotations and different options for fertility and disease management. In a replicated field trial we compare treatments across a range of sustainability criteria: crop yield, nitrogen cycling and losses, greenhouse gas emissions, disease incidence, biocontrol of insect pests, soil carbon pools, and economics. Main treatments are 2 versus 4 year rotations with different crop combinations believed to be either suppressive of a major soil borne disease (Verticillium wilt), or more profitable but more conducive to disease. Superimposed on the rotations are fertility treatments (legume/cereal cover crop only, legume/cereal cover crop + compost + additional fertility amendments, cereal cover crop + mustard seed meal, or untreated control) and in the two legume/cereal cover cropped treatments anaerobic soil disinfestation (ASD, a promising option for controlling a range of soil borne diseases) is used for disease management prior to planting strawberries. Six network farmers also chose a sub-set of these treatments to test on their farms and compare to their own management practices. The study is in year 4 and all treatments at all locations are now planted to strawberries. Preliminary data show Verticillium wilt to be the major cause of yield loss in strawberry, and that ASD provided partial control, but mustard seed meal did not. Soil inorganic N pools are very dynamic with rapid release of nitrate from crop residues observed. Soil carbon is already declining in the bare fallow (no winter cover crop) treatment and in the 2 year rotation as compared to the 4 year rotation. This project will provide farmers with tools to improve their production systems, meet water quality regulations, and quantify climate-related impacts of these intensive organic systems.