Diversified weed management tactics in diversified cropping systems: Foundations for durable crop production and protection

One of the key questions facing Iowa’s agricultural community is how to produce sufficient amounts of food and farm income while improving and protecting environmental quality. Because synthetic fertilizers and pesticides constitute important expenses in Iowa farming systems (Duffy 2011; National Agricultural Statistics Service 2011) and because their use can be linked to environmental damage (U.S. Geological Survey 1999; Dinnes et al. 2002; Gilliom et al. 2006), learning how to reduce reliance on these materials without compromising farm productivity and profitability is a key priority for Iowa and other parts of the U.S. Corn Belt

Long-term Weed Management Using Diverse Crop Rotation Systems

Now that the elevators are filled with grain, farm life is slowing down, and farmers in Iowa can look back at a year with generally good yields, it is important to recognize that our wealth and prosperity are not without a cost. Nationwide, herbicide use has not diminished, despite the use of glyphosate resistant genetically engineered crops (http://www.epa.gov/oppbead1/pestsales/), and intensive row-cropping in combination with the use of high rates of synthetic fertilizer and drainage tiles contributes to high concentrations of nitrate in surface waters (Randall et al., 1997; Schilling and Libra, 2000) and hypoxia in the Gulf of Mexico (Burkart andjames, 1999). Is it possible to run a profitable farm that better promotes human and environmental health? We are conducting an experiment in which three crop management systems are being compared with respect to weed management, crop yield, net return, labor and energy use. Two of the three systems receive reduced rates of herbicide and fertilizer inputs, while the third one is managed with conventional inputs

Crop diversification: Impact on weeds, soybean sudden death syndrome and crop productivity

Crop diversification has diminished in the USA during the past 50 years, and monocultures and short rotation sequences are currently the prevalent cropping systems (Brummer, 1998; Cook, 2006). Simplification of cropping systems has been accompanied by greater reliance on synthetic pesticides and fertilizers to manage weeds, diseases and soil fertility, creating concerns about contamination of underground and surface water by nitrogen, herbicides and soil sediment (Hartwig and Ammon, 2002). Learning how to reduce reliance on synthetic fertilizers and pesticides without compromising farm productivity and profitability is a key priority for Iowa and other parts of the U.S. Corn Belt (Gomez et al., 2012; Cruse et al., 2010). In this report we discuss the impacts of cropping system diversification on weed management, soybean productivity, sudden death syndrome, and root health, based on results from a long-term crop rotation study in Iowa

Does diversifying crop rotations suppress weeds? A meta-analysis

Over the past half-century, crop rotations have become increasingly simplified, with whole regions producing only one or two crops in succession. Simplification is problematic from a weed management perspective, because it results in weeds’ repeated exposure to the same set of ecological and agronomic conditions. This can exacerbate weed infestations and promote the evolution of herbicide resistance. Diversifying crop rotations through addition of crop species and their associated managements may suppress weeds and reduce selection pressure for herbicide resistance by altering stress and mortality factors affecting weed dynamics. Here we report the results of a meta-analysis using 298 paired observations from 54 studies across six continents to compare weed responses due to simple and more diverse crop rotations. We found diversifying from simple rotations reduced weed density (49%), but did not have a significant effect on weed biomass. We investigated the effect of management practices, environmental factors, and rotation design on this effect. Diversification that increased the variance around crop planting dates was more effective in suppressing weeds than increasing crop species richness alone. Increasing rotational diversity reduced weed density more under zero-tillage conditions (65%) than tilled conditions (41%), and did so regardless of environmental context and auxiliary herbicide use. Our findings highlight the value of diversifying crop rotations to control weed populations, and support its efficacy under varied environmental conditions and management scenarios

Switchgrass as a Bioenergy Crop: Biomass Production and Soil Carbon Sequestration in Response to Nitrogen Fertilization [abstract]

Only abstract of poster available.Track II: Transportation and BiofuelsSwitchgrass (Panicum virgatum L.) is a warm-season, perennial grass native to the prairie region of the central U.S. Recent attention has focused on the development of switchgrass as a biomass crop for the production of cellulosic ethanol and other advanced biofuels and bioproducts. Since switchgrass possesses a deep, fibrous root system, it can also offer environmental benefits, including enhanced soil carbon sequestration. Presently, information regarding the management of switchgrass as a low-carbon energy crop is incomplete. Because nitrogen (N) is generally the most limiting resource for crop production, field experiments were conducted to evaluate the effects of N fertilization on biomass production and soil carbon sequestration by switchgrass. In 2006-2007, switchgrass plots were treated with 0, 65, 140, or 220 kg N ha-1 in the spring and harvested following frost in the Fall. Additionally, in Fall 2005 and 2007, soil samples were collected to a depth of 100 cm using a hydraulic probe and soil organic carbon (SOC) content was determined using combustion analysis and pressure calcimetery. Biomass yield demonstrated a quadratic response to N, with optimal yield of 13 ± 0.6 (mean ± se) Mg ha-1 at 140 kg N ha-1. Nitrogen fertilization also had pronounced effects on SOC content. Over the two-year experimental period, significant gains in SOC were detected at input rates of 65 and 140 kg N ha-1, but SOC remained unchanged at rates of 0 and 220 kg N ha-1. Therefore, similar to biomass yield, SOC also exhibited an optimal response to N inputs. These results indicate that both biomass production and carbon sequestration by switchgrass can be managed using N fertilizers, and that over the short-term both are optimized with input rates in the range of 140 kg ha-1

Energy and Economic Returns by Crop Rotation

Energy and economic returns are presented from 2006-2011 comparing three cropping systems at the ISU Marsden Farm: 2-year conventional corn-soybean rotation and 3- and 4-year rotations that add small grain, red clover and alfalfa

TB163: Insect Predation of Seeds and Plant Population Dynamics

This review provides a framework for understanding the mechanisms of insect seed predation, the diversity of insects that prey on seeds, and the ecological and evolutionary consequences of insect seed predation. Insect seed predation can play significant roles in reducing plant population growth, modifying intraspecific and interspecific competition, shifting spatial and temporal distribution, affecting species evolution, and plant community structure, both in natural and agricultural ecosystems.https://digitalcommons.library.umaine.edu/aes_techbulletin/1039/thumbnail.jp