Cover crops are used to scavenge residual soil nitrate, with the goal of reducing N losses from agricultural fields and increasing subsequent N availability. Two experiments were conducted to determine fall‐planted brassica cover crops’ effect on N availability for rotational crops. The first evaluated five species—brown mustard [Brassica juncea (L.) Czern], hybrid turnip (Brassica rapa L. × B. napus L.), radish (Raphanus sativus L.), rapeseed (Brassica napus L.), and white mustard (Sinapis alba L.)—in rotation with oat (Avena sativa L.). The second evaluated radish in rotation with corn (Zea mays L.). End of season cover crop biomass averaged 1160 to 6170 kg ha−1 across experiments, locations, and years. Biomass did not differ by species. Nitrogen accumulation was generally greater than 70 kg ha−1 (range 31–136 kg ha−1). In the subsequent spring and summer, brassica cover crops reduced soil nitrate N levels relative to a no‐cover control by 0 to 132 kg ha−1. In Exp. 1, all brassicas reduced oat N accumulation by ≥77 kg ha−1 and oat biomass by ≥1255 kg ha−1 in June 2012, relative to the control. Mustards reduced oat grain yield by 505 kg ha−1 in 2011, while radish increased oat yield by ≥578 kg ha−1 in each year. In Exp. 2, radish did not affect corn V8 biomass N concentration, grain yield, or response to N fertilizer. Nitrogen taken up by brassica cover crops often is not available when the subsequent crop needs it.

Cover cropping is a common practice in U.S. Midwest carrot production for soil conservation, and may affect soil ecology and plant-parasitic nematodes-to which carrots are very susceptible. This study assessed the impact of cover crops-oats (Avena sativa), radish (Raphanus sativus) cv. Defender, rape (Brassica napus) cv. Dwarf Essex, and a mixture of oats and radish-on plantparasitic nematodes and soil ecology based on the nematode community in Michigan carrot production systems. Research was conducted at two field sites where cover crops were grown in Fall 2014 preceding Summer 2015 carrot production. At Site 1, rootlesion (Pratylenchus penetrans) and stunt (Tylenchorhynchus sp.) nematodes were present at low population densities (less than 25 nematodes/100 cm 3 soil), but were not significantly affected (P . 0.05) by cover crops. At Site 2, P. penetrans population densities were increased (P # 0.05) by 'Defender' radish compared to other cover crops or fallow control during cover crop growth and midseason carrot production. At both sites, there were few short-term impacts of cover cropping on soil ecology based on the nematode community. At Site 1, only at carrot harvest, radish-oats mixture and 'Dwarf Essex' rape alone enriched the soil food web based on the enrichment index (P # 0.05) while rape and radish increased structure index values. At Site 2, bacterivore abundance was increased by oats or radish cover crops compared to control, but only during carrot production. In general, cover crops did not affect the nematode community until nearly a year after cover crop growth suggesting that changes in the soil community following cover cropping may be gradual.

PREMISE Nucleic acid integrity can be compromised under many abiotic stresses. To date, however, few studies have considered whether nucleic acid damage and damage repair play a role in cold‐stress adaptation. A further insufficiently explored question concerns how age affects cold stress adaptation among mature perennials. As a plant ages, the optimal trade‐off between growth and stress tolerance may shift. METHODS Oxidative damage to RNA and expression of genes involved in DNA repair were compared in multiple mature cohorts of Thinopyrum intermedium (an emerging perennial cereal) and in wheat and barley under intermittent freezing stress and under nonfreezing conditions. Activity of glutathione peroxidase (GPX) and four other antioxidative enzymes was also measured under these conditions. DNA repair genes included photolyases involved in repairing ultraviolet‐induced damage and two genes involved in repairing oxidatively induced damage (ERCC1, RAD23). RESULTS Freezing stress was accompanied by large increases in photolyase expression and ERCC1 expression (in wheat and Thinopyrum) and in GPX and GR activity (particularly in Thinopyrum). This is the first report of DNA photolyases being overexpressed under freezing stress. Older Thinopyrum had lower photolyase expression and less freezing‐induced overexpression of ERCC1. Younger Thinopyrum plants sustained more oxidative damage to RNA. CONCLUSIONS Overexpression of DNA repair genes is an important aspect of cold acclimation. When comparing adult cohorts, aging was associated with changes in the freezing stress response, but not with overall increases or decreases in stress tolerance.

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Several brassica cover crops have recently gained popularity in the U.S. Midwest as nitrogen scavengers that are believed to reduce N losses and increase the amount of residual N available to the next cash crop. Field studies were conducted at three sites in Minnesota to determine the effect of fall‐planted brassica cover crops on (i) N availability to the subsequent year's crop of oat or corn, (ii) oat and corn grain yield, and (iii) corn yield response to applied N fertilizer. Earn 0.5 CEUs in Crop Management by reading this article and completing the quiz at http://www.certifiedcropadviser.org/certifications/self-study/755.