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To improve understanding of relationships between crop diversity, weed management practices, and weed population dynamics, we used data from a field experiment and matrix models to examine how contrasting crop rotations affect velvetleaf. We compared a 2-yr rotation system (corn–soybean) managed with conventional rates of herbicides with a 4-yr rotation (corn–soybean–triticale + alfalfa–alfalfa) that received 82% less herbicide. In November 2002, a pulse of velvetleaf seeds (500 seeds m−2) was added to 7- by 7-m areas within replicate plots of each crop phase–rotation system combination. Velvetleaf seed, seedling, and reproductive adult population densities, seed production, and seed losses to predators were measured during the next year. Velvetleaf seed production was greater in the 4-yr rotation than in the 2-yr rotation (460 vs. 16 seeds m−2). Averaged over 12 sampling periods from late May to mid-November 2003, loss of velvetleaf seeds to predators also was greater in the 4-yr rotation than in the 2-yr rotation (32 vs. 17% per 2 d). Modeling analyses indicated that velvetleaf density in the 4-yr rotation should decline if cumulative losses of seeds produced in the soybean phase exceeded 40%. Achieving such a level of predation appears possible, given the observed rates of velvetleaf seed predation. In addition, no tillage occurs in the 4-yr rotation for 26 mo after soybean harvest, thus favoring seed exposure on the soil surface to predators. Models that included estimates of seed predation indicated that to prevent increases in velvetleaf density, weed control efficacy in soybean must be ≥ 93% in the 2-yr rotation, but could drop to 86% in the 4-yr rotation. These results support the hypothesis that diverse rotations that exploit multiple stress and mortality factors, including weed seed predation, can contribute to effective weed suppression with less reliance on herbicides.

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We conducted a 9-ha field experiment near Boone, IA, to test the hypothesis that yield, weed suppression, and profit characteristics of low-external-input (LEI) cropping systems can match or exceed those of conventional systems. Over a 4-yr period, we compared a conventionally managed 2-yr rotation system {corn (Zea mays L.)/soybean [Glycine max (L.) Merr.]} with two LEI systems: a 3-yr corn/soybean/small grain + red clover (Trifolium pratense L.) rotation, and a 4-yr corn/soybean/small grain + alfalfa (Medicago sativa L.)/alfalfa rotation. Synthetic N fertilizer use was 59 and 74% lower in the 3-and 4-yr systems, respectively, than in the 2-yr system; similarly, herbicide use was reduced 76 and 82% in the 3-and 4-yr systems. Corn and soybean yields were as high or higher in the LEI systems as in the conventional system, and weed biomass in corn and soybean was low (≤4.2 g m −2 ) in all systems. Experimentally supplemented giant foxtail (Setaria faberi Herrm.) seed densities in the surface 20 cm of soil declined in all systems; supplemented velvetleaf (Abutilon theophrasti Medik.) seed densities declined in the 2-and 4-yr systems and remained unchanged in the 3-yr system. Without subsidy payments, net returns were highest for the 4-yr system ($540 ha −1 yr −1 ), lowest for the 3-yr system ($475 ha −1 yr −1 ), and intermediate for the 2-yr system ($504 ha −1 yr −1 ). With subsidies, differences among systems in net returns were smaller, as subsidies favored the 2-yr system, but rank order of the systems was maintained. Disciplines Agronomy and Crop Sciences | Statistics and Probability CommentsThis is an article from Agronomy Journal 100 (2008): 600, doi:10.2134/agronj2007.0222. Posted with permission. RightsWorks produced by employees of the U.S. Government as part of their official duties are not copyrighted within the U.S. The content of this document is not copyrighted. O ne of the key questions facing agriculturalists in the 21st century is how to produce adequate amounts of food, feed, and farm income while protecting and improving environmental quality (Robertson and Swinton, 2005). Th e need to answer this question is particularly acute in the midwestern United States, one of the largest regions of intensive, rain-fed agriculture in the world. Crop production in this region currently relies heavily on synthetic N fertilizer and herbicides to manage soil fertility and weeds (National Agricultural Statistics Service, 2003, 2007a. Concomitantly, N and herbicides emitted from midwestern cropland are detected regularly in ground and surface waters, and are viewed by many analysts as important environmental contaminants that require improved management approaches (Goolsby et al., 1999;Dinnes et al., 2002;Gilliom et al., 2006). Th e midwestern United States has also been a major recipient of agricultural subsidy payments from the federal government (Environmental Working Group, 2007), and there are persistent questions concerning farm economic viability if these subsidies were removed due to global tra...

Summary1. Post-dispersal seed predation is an important source of mortality for arable weed populations that can potentially contribute to ecologically based management strategies. The extent to which cropping practices influence rates of seed predation is not well established. 2. Removal of Abutilon theophrasti and Setaria faberi seeds by predators was measured in 2-year (maize/soyabean), 3-year (maize/soyabean/triticale + red clover) and 4-year (maize/soyabean/triticale + lucerne/lucerne) crop rotations in Iowa, USA, during 27 48-h sampling periods conducted during the 2003 and 2004 cropping seasons. 3. Predation of S. faberi seeds was equal (eight sampling periods) or greater (19 sampling periods) than predation of A. theophrasti seeds, but the influence of crops on seasonal predation patterns was generally similar for the two weeds. 4. Seasonal patterns in seed predation were crop-specific and complementary. In maize and soyabean, seed predation was low in spring, high in summer and low in autumn. In triticale-legume intercrops, seed predation was high in spring, low in summer and moderate in autumn. In lucerne, seed predation fluctuated from high to low, matching the periodic harvest and regrowth cycle of the crop. 5. Measurements of crop canopy light interception taken in 2004 were positively correlated with rates of seed removal for both A. theophrasti ( r = 0·54, P < 0·001) and S. faberi ( r = 0·25, P < 0·001), suggesting that vegetative cover promotes weed seed predation. 6. Synthesis and applications. The results indicate that crop vegetation can be managed to promote weed seed predation. Diversified farming systems that include a range of phenologically dissimilar crop species are likely to provide the greatest opportunities for weed seed destruction by predators.

We determined feeding preferences of invertebrate seed predators and the effect of seed predation on weed emergence. Feeding choice studies were completed with three species of common ground beetles: (Amara aeneaDeGeer,Anisodactylus sanctaecrucisF., andHarpalus pensylvanicusDeGeer) (Coleoptera: Carabidae) and the northern field cricket (Gryllus pennsylvanicusDeGeer) (Orthoptera: Gryllidae).Anisodactylus sanctaecrucis,H. pensylvanicus, and the female and maleG. pennsylvanicusconsumed more redroot pigweed seeds compared with giant foxtail seeds;A. aeneaseed consumption did not differ between these two weed species. All invertebrates consumed fewer velvetleaf seeds compared with redroot pigweed and giant foxtail seeds; however, when seed biomass was compared,A. aeneaconsumed similar biomass of velvetleaf, giant foxtail, and redroot pigweed, whereasA. sanctaecrucisandH. pensylvanicusconsumed greater biomass of velvetleaf compared with giant foxtail seed. Seed burial depths of 0.5 or 1.0 cm reduced redroot pigweed and giant foxtail seed consumption byA. aeneaandA. sanctaecrucisbut not by the larger carabid beetle,H. pensylvanicus. In a greenhouse study,A. sanctaecrucisdecreased total weed emergence by 15%, andG. pennsylvanicusfemales and males decreased weed emergence by 16 and 5%, respectively. Emergence of redroot pigweed, but not velvetleaf or giant foxtail, decreased whenA. sanctaecrucisand the maleG. pennsylvanicuswere present, whereas the emergence of all three weed species decreased in the presence of the femaleG. pennsylvanicus. In field experiments, vertebrate access to velvetleaf seeds reduced emergence from 4 to 9% across field sites; invertebrate access reduced emergence 4 to 6%. Vertebrate access to giant foxtail seeds reduced emergence 3 to 7%, and invertebrate access reduced emergence 4 to 13%. These results suggest that predation of weed seeds by both vertebrates and invertebrates may reduce weed emergence and influence the weed community.

Summary 1.Carabid beetles are polyphagous predators that can act as biological control agents of insect pests and weeds. While current agricultural practices often create a harsh environment, habitat management such as the establishment of within-field refuges has been proposed to enhance carabid beetle abundance and impact. We examined the joint effects of refuge habitats and insecticide application on carabid activity density ( parameter of population density and relative activity) and species composition in a cornfield. 2. Our 2-year study comprised four treatments: (i) -refuge/-insecticide; (ii) + refuge/ -insecticide; (iii) -refuge/+insecticide; (iv) + refuge/ + insecticide. Refuge strips consisted of grasses, legumes and perennial flowering plants. '-Refuge' strips were planted with corn and not treated with insecticide. 3. Before planting and insecticide application, carabid activity density in the crop areas was similar across all treatments. Insecticide application immediately reduced carabid activity density and altered community composition in the crop area. 4. Refuge strips had significantly higher activity density of beetles than -refuge strips before planting and during the summer. 5. During summer, as new carabids emerged and insecticide toxicity declined, the presence of refuge strips influenced carabids in the adjacent crop area. Carabid activity density within crop areas previously treated with insecticide was significantly higher when adjacent to refuge strips. Also, carabid communities within insecticide-treated crop areas were affected by the presence or absence of a refuge strip. 6. The presence of refuge strips did not consistently augment carabid numbers in crop areas where insecticide was not applied. One explanation may be that insecticides decreased the quality of crop habitat to carabids by depletion of prey and direct mortality. However, subsequent rebounds in prey density and the absence of competing predators may make these areas relatively more attractive than unperturbed crop habitats to carabid colonization from refuges. 7. This study demonstrates that refuges may buffer the negative consequences of insecticide application on carabids in adjacent fields. Diversifying agro-ecosystems with refuge habitats may be a viable strategy for maintaining carabid populations in disturbed agricultural landscapes to keep pests below outbreak levels.