Cover crops (CCs) can provide multiple soil, agricultural production, and environmental benefits. However, a better understanding of such potential ecosystem services is needed. We summarized the current state of knowledge of CC effects on soil C stocks, soil erosion, physical properties, soil water, nutrients, microbial properties, weed control, crop yields, expanded uses, and economics and highlighted research needs. Our review indicates that CCs are multifunctional. Cover crops increase soil organic C stocks (0.1–1 Mg ha−1 yr−1) with the magnitude depending on biomass amount, years in CCs, and initial soil C level. Runoff loss can decrease by up to 80% and sediment loss from 40 to 96% with CCs. Wind erosion potential also decreases with CCs, but studies are few. Cover crops alleviate soil compaction, improve soil structural and hydraulic properties, moderate soil temperature, improve microbial properties, recycle nutrients, and suppress weeds. Cover crops increase or have no effect on crop yields but reduce yields in water‐limited regions by reducing available water for the subsequent crops. The few available studies indicate that grazing and haying of CCs do not adversely affect soil and crop production, which suggests that CC biomass removal for livestock or biofuel production can be another benefit from CCs. Overall, CCs provide numerous ecosystem services (i.e., soil, crop–livestock systems, and environment), although the magnitude of benefits is highly site specific. More research data are needed on the (i) multi‐functionality of CCs for different climates and management scenarios and (ii) short‐ and long‐term economic return from CCs.

The sensitivity of soybean [Glycine max (L.) Merr.] main stem node accrual to ambient temperature has been documented in greenhouse‐grown plants but not with field‐grown plants in the north‐central United States. Biweekly V‐node and R‐stage, stem node number, internode length, and other traits were quantified in an irrigated split‐plot, four‐replicate, randomized complete block experiment conducted in Lincoln, NE, in 2003–2004. Main plots were early‐, mid‐, late‐May, and mid‐June sowing dates. Subplots were 14 cultivars of maturity groups 3.0 to 3.9. Node appearance was surprisingly linear from V1 to R5, despite the large increase in daily temperature from early May (10–15°C) to July (20–25°C). The 2003 and 2004 May planting date regressions exhibited near‐identical slopes of 0.27 node d−1 (i.e., one node every 3.7 d). Cold‐induced delays in germination and emergence did delay the V1 date (relative to planting date), so the primary effect of temperature was the V1 start date of linearity in node appearance. With one exception, earlier sowings led to more nodes (earlier V1 start dates) but also resulted in shorter internodes at nodes 3 to 9 (cooler coincident temperatures), thereby generating a curved response of plant height to delayed plantings. Delaying planting after 1 May led to significant linear seed yield declines of 17 kg ha−1 d−1 in 2003 and 43 kg ha−1 d−1 in 2004, denoting the importance of early planting for capturing the yield potential available in soybean production, when moisture supply is not limiting.

Herbicide‐resistant crops like glyphosate resistant (GR) soybean [Glycine max (L.) Merr.] are gaining acceptance in U.S. cropping systems. Comparisons from cultivar performance trials suggest a yield suppression may exist with GR soybean. Yield suppressions may result from either cultivar genetic differentials, the GR gene/gene insertion process, or glyphosate. Grain yield of GR is probably not affected by glyphosate. Yield suppression due to the GR gene or its insertion process (GR effect) has not been reported. We conducted a field experiment at four Nebraska locations in 2 yr to evaluate the GR effect on soybean yield. Five backcross‐derived pairs of GR and non‐GR soybean sister lines were compared along with three high‐yield, nonherbicide‐resistant cultivars and five other herbicide‐resistant cultivars. Glyphosate resistant sister lines yielded 5% (200 kg ha−1) less than the non‐GR sisters (GR effect). Seed weight of the non‐GR sisters was greater than that of the GR sisters (in 1999) and the non‐GR sister lines were 20 mm shorter than the GR sisters. Other variables monitored were similar between the two cultivar groups. The high‐yield, nonherbicide‐resistant cultivars included for comparison yielded 5% more than the non‐GR sisters and 10% more than the GR sisters.

Cover crop (CC) biomass production dictates agricultural and environmental services that CCs deliver, but finding a review on this topic is difficult. We synthesized published data on CC biomass production for 20 common CC species in temperate regions and discussed factors affecting CC biomass production. Review of 389 papers indicated CC biomass production was 3.37 ± 2.96 Mg ha-1 (mean ± SD). Cover crop biomass production for the top five biomass-producing species was: sorghum (Sorghum sp.) (5.99 Mg ha-1) > sunn hemp (Crotalaria juncea L.) (5.77 Mg ha-1) > millet (Pennisetum glaucum L.) (4.95 Mg ha-1) > rye (Secale cereale L.) (4.93 Mg ha-1) > two-species mix (4.18 Mg ha-1). In humid regions (>750 mm precipitation), CC biomass production ranged from 1.67 to 6.30 Mg ha-1 depending on species. In regions with <750 mm precipitation, CC biomass production ranged from 0.87 to 6.03 Mg ha-1. Cover crop biomass production was in this order by cropping system: vegetables > other systems [soybean (Glycine max L.), cotton (Gossypium hirsutum L.), and others] > maize (Zea mays L.) > small grains. Rye was among the most common and highest biomass producing species in most regions and cropping systems. Drill-planting and maximizing CC growing season, such as early planting or late termination, can increase CC biomass production. Irrigation at establishment increased CC biomass production for legumes and mixes in humid regions, and all CC groups in semiarid regions. Overall, CCs can produce significant amount of biomass, but this can be highly dependent on climate, CC species, cropping system, and management.