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Cover cropping has been proposed as an important component of integrated weed management strategies due to its potential effects on multiple demographic processes, including weed seedling emergence from soil, plant survival, seed production, and seed predation. In this article, we report the results of modelling analyses that investigated how a cover crop could affect the population dynamics of Amaranthus tuberculatus (Moq.) J.D. Sauer (waterhemp), an annual dicotyledonous species that is a major problem in maize and soyabean fields in the central USA. We constructed difference equation models for maize–soyabean rotations with and without a rye cover crop and parameterised the models with values drawn from published scientific literature. Results of the analyses indicate that the use of a winter cover crop would have minimal effects on the level of herbicide efficacy required to prevent increases in A. tuberculatus population density in maize and soyabean. However, if a high level of herbicide efficacy was imposed, cover crop‐derived reductions in A. tuberculatus seedling population density, delays in seedling emergence, and increases in seed predation would diminish A. tuberculatus seed population density in soil up to 96% over a 10‐year period. Thus, while cover crops did not replace the need for other control strategies for A. tuberculatus, they could complement them. Relative to cover crops, greater benefits for A. tuberculatus management might be gained using diverse sequences of cash crops. Possible synergies between cover crops and diversified crop rotations should be explored in both field experiments and modelling analyses. [ABSTRACT FROM AUTHOR]

The Agricultural Production Systems sIMulator (APSIM) was used to evaluate two alternative approaches for extending the cover crop growing window into corn (Zea mays L.) and soybean (Glycine max L.) crop rotations in Nebraska, USA. We evaluated how: (i) shifting corn planting dates (mid‐April to early‐June) and (ii) altering comparative relative maturity (CRM) corn hybrids (80 to 115 days) influence cover crop biomass and corn yields over a 30‐year period. The APSIM model was tested using experimental data and was then used to simulate a range of cover crop planting and termination scenarios. Our results showed no significant yield differences within the same corn relative maturity when planted on April 20 and May 13 but that yield declined when planted in June. During a six week fall cover crop planting window (September 15–October 31), every day before October 31 that the cover crop was planted resulted in additional 62 kg ha−1 of biomass. We also simulated a one month spring termination window (April 1–April 30) and, every day delay in cover crop termination resulted in per day additional 35 kg ha−1 of biomass. Cover crop biomass accrual was highly dependent on weather, where for identical fall planting dates, a warm wet season accrued approximately four times more biomass than a cool dry season. Although we found significant yield differences between early, medium and late season CRMs, earlier fall cover crop planting associated with either earlier spring corn planting or planting an early to medium season variety leads to ten‐fold greater cover biomass. Delayed corn planting by mid‐May had no yield penalty relative to April planting, and could facilitate four‐fold greater cover crop biomass (cover crop terminated April 30 instead of April 1). Our results demonstrate that earlier cover crop planting in fall or later cover crop termination in spring can result in significantly more biomass which can be balanced with yield goals. [ABSTRACT FROM AUTHOR]

Identifying agricultural practices that enhance water cycling is critical, particularly with increased rainfall variability and greater risks of droughts and floods. Soil infiltration rates offer useful insights to water cycling in farming systems because they affect both yields (through soil water availability) and other ecosystem outcomes (such as pollution and flooding from runoff). For example, conventional agricultural practices that leave soils bare and vulnerable to degradation are believed to limit the capacity of soils to quickly absorb and retain water needed for crop growth. Further, it is widely assumed that farming methods such as no-till and cover crops can improve infiltration rates. Despite interest in the impacts of agricultural practices on infiltration rates, this effect has not been systematically quantified across a range of practices. To evaluate how conventional practices affect infiltration rates relative to select alternative practices (no-till, cover crops, crop rotation, introducing perennials, crop and livestock systems), we performed a meta-analysis that included 89 studies with field trials comparing at least one such alternative practice to conventional management. We found that introducing perennials (grasses, agroforestry, managed forestry) or cover crops led to the largest increases in infiltration rates (mean responses of 59.2 ± 20.9% and 34.8 ± 7.7%, respectively). Also, although the overall effect of no-till was non-significant (5.7 ± 9.7%), the practice led to increases in wetter climates and when combined with residue retention. The effect of crop rotation on infiltration rate was non-significant (18.5 ± 13.2%), and studies evaluating impacts of grazing on croplands indicated that this practice reduced infiltration rates (-21.3 ± 14.9%). Findings suggest that practices promoting ground cover and continuous roots, both of which improve soil structure, were most effective at increasing infiltration rates. [ABSTRACT FROM AUTHOR]

Land conversion from natural to managed ecosystems, while necessary for food production, continues to occur at high rates with significant water impacts. Further, increased rainfall variability exposes agricultural systems to impacts from flood and drought events. In many regions, water limitations are overcome through technological approaches such as irrigation and tile drainage, which may not be sustainable in the long term. A more sustainable approach to combat episodes of floods and droughts is to increase soil water storage and the overall green water efficiency of agroecosystems. Agricultural practices that promote “continuous living cover,” such as perennial grasses, agroforestry and cover crops, can improve water management relative to annual crop systems. Such practices ensure living roots in agricultural systems throughout the year and offer an approach to agroecosystem design that mimics ecological dynamics of native perennial vegetation. We review how these practices have been shown to improve elements of the water balance in a range of environments, with an emphasis on increased soil hydrologic function. A specific focus on the agriculturally intensive state of Iowa provides insight into how land use centered on agroecological principles affords greater water resilience, for individual farms as well as for broader community and ecosystem health. [ABSTRACT FROM AUTHOR]

The article offers information on use of cover crops by the Iowa farmers to reduce water pollution and improve soil quality. Topics discussed include increase in crop cover acreage from 2011 to 2016 reported by Sustainable Agriculture Research and Education–Conservation Technology Information Center survey; how farmers overcome economic and agronomic challenges to achieve success with cover crops in corn–soybean cropping systems; and negative environmental impacts of bare soil.

The Midwestern United States, a region that produces one-third of maize and one-quarter of soybean grain globally, is projected to experience increasing rainfall variability. One approach to mitigate climate impacts is to utilize crop and soil management practices that enhance soil water storage and reduce the risks of flooding as well as drought-induced crop water stress. While some research indicates that a winter cover crop in maize-soybean rotations increases soil water availability, producers continue to be concerned that water use by cover crops will reduce water for a following cash crop. We analyzed continuous in-field soil water measurements from 2008 to 2014 at a Central Iowa research site that has included a winter rye cover crop in a maize-soybean rotation for thirteen years. This period of study included years in the top third of the wettest on record (2008, 2010, 2014) as well as drier years in the bottom third (2012, 2013). We found the cover crop treatment to have significantly higher soil water storage at the 0–30 cm depth from 2012 to 2014 when compared to the no cover crop treatment and in most years greater soil water content on individual days analyzed during the cash crop growing season. We further found that the cover crop significantly increased the field capacity water content by 10–11% and plant available water by 21–22%. Finally, in 2013 and 2014, we measured maize and soybean biomass every 2–3 weeks and did not see treatment differences in crop growth, leaf area or nitrogen uptake. Final crop yields were not statistically different between the cover and no cover crop treatment in any of the seven years of this analysis. This research indicates that the long-term use of a winter rye cover crop can improve soil water dynamics without sacrificing cash crop growth in maize-soybean crop rotations in the Midwestern United States. [ABSTRACT FROM AUTHOR]

It is critical to evaluate conservation practices that protect soil and water resources from climate change in the Midwestern United States, a region that produces one-quarter of the world’s soybeans and one-third of the world’s maize. An over-winter cover crop in a maize–soybean rotation offers multiple potential benefits that can reduce the impacts of higher temperatures and more variable rainfall; some of the anticipated changes for the Midwest. In this experiment we used the Agricultural Production Systems sIMulator (APSIM) to understand how winter rye cover crops impact crop production and environmental outcomes, given future climate change. We first tested APSIM with data from a long-term maize–soybean rotation with and without winter rye cover crop field site. Our modeling work predicted that the winter rye cover crop has a neutral effect on maize and soybean yields over the 45 year simulation period but increases in minimum and maximum temperatures were associated with reduced yields of 1.6–2.7% by decade. Soil carbon decreased in both the cover crop and no cover crop simulations, although the cover crop is able to significantly offset (3% less loss over 45 years) this decline compared to the no cover crop simulation. Our predictions showed that the cover crop led to an 11–29% reduction in erosion and up to a 34% decrease in nitrous oxide emissions (N 2 O). However, the cover crop is unable to offset future predicted yield declines and does not increase the overall carbon balance relative to current soil conditions. [ABSTRACT FROM AUTHOR]