In the conventional cropping systems, increased costs and resource pollution are attributed to the intensive use of chemical inputs. The adoption of cover crops could be a part of a suitable strategy for improving the sustainability of the agro-ecosystems due to their ability to affect nutrient and weed management. A 2-yr field experiments were conducted in Gorgan, North of Iran, with the aim of assessing the effect of cover crop residue management and herbicide rates on weed management and the yield of tomato crop. The treatments consisted in: (a) three winter soil management: two cover crops [annual medic (Medicago scutellata L.) and barley (Hordeum vulgare L.)] and no covered soil; (b) two soil tillage (no-tillage, where cover crop residues were left in strips on the soil surface, and conventional tillage, where cover crop residues were green manured at 30 cm of soil depth); and (c) three pre-emergence herbicide rates (no-herbicide application, half rate recommended or full rate recommended ). Cover crops were sown in early September and mechanically suppressed in March about 2 weeks before tomato transplanting. At cover crop suppression, annual medic showed the highest aboveground biomass [569 g m−2 of dry matter (DM)], while barley showed the lowest weed content (32 g m−2 of DM). At tomato harvesting, weed density and aboveground biomass ranged from 6.9 to 61.5 plants m−2 and from 33.6 and 1157.0 g m−2 of DM, respectively. Cover crop residues placed on soil surface suppressed weeds more effectively than incorporated residues, especially in barley, mainly due to the physical barrier of residues which reduced the stimulation of weed germination and establishment. As expected, herbicide rate decreased both weed density and biomass, even if the adoption of annual medic and barley cover crops before the tomato cultivation could allow a possible reduction of herbicide rate while maintaining similar fruit yield. Tomato yield was higher in annual medic than barley and no cover regardless of tillage management (on average 62.3, 51.8 and 50.1 t ha−1 of fresh matter, respectively) probably due to an abundant availability of soil nitrogen throughout the tomato cultivation. This was confirmed by high and constant values of tomato N status grown in annual medic and evaluated using SPAD chlorophyll meter. Although further research of cover crop residue management is required to obtain a better understanding on herbicide rate reduction, these preliminary results could be extended to other vegetable crops which have similar requirements of tomato.

Linuron, metribuzin, oryzalin, and dinoseb were evaluated for weed control in conventional (CT) and rye-stubble reduced-tillage (RT) systems for potatoes. Early season control of weeds was equivalent for all herbicides in both tillage systems. In 1985, redroot pigweed populations were significantly greater in RT than in CT control plots. Populations of common lambsquarters were equivalent, regardless of the tillage system. In 1986, the rye mulch reduced early emergence of both species in untreated RT plots when compared to the untreated CT controls. During both seasons, potato stands decreased 16% with RT. In 1985, total yields did not differ between tillage systems; however, in 1986, total potato yields in RT plots decreased an average of 22% compared to yields in CT plots.

Amaranthus control in cotton can be difficult with the loss of glyphosate efficacy, especially in conservation-tillage cropping systems. Research was conduction from 2006 to 2008 at EV Smith Research Center, Shorter, AL, to determine the level of glyphosate-susceptible Amaranthus control provided by four initial tillage and herbicide treatments, including 1) moldboard plowing followed by a single-pass disking and field cultivation plus pendimethalin at 1.2 kg ai ha−1 preplant incorporation (PPI), 2) two-pass disking followed by field cultivation plus pendimethalin at 1.2 kg ha−1 PPI, 3) no tillage including an application of pendimethalin at 1.2 kg ha−1 PRE, or 4) no tillage without pendimethalin in 2006. No further tillage practices or pendimethalin applications were utilized after study initiation. Initial tillage operations, including inversion with disking or disking twice, resulted in Amaranthus density of ≤ 4 plants m−2 and 47 to 82% control, whereas no-tillage treatments had ≥ 4 plants m−2 and 14 to 62% control. Subsequent applications of PRE herbicides included fluometuron at 1.68 kg ai ha−1 or prometryn at 1.12 kg ai ha−1 and provided 53 to 98% and 55 to 93% control, respectively, and reduced Amaranthus density compared to no PRE herbicide to < 2 plants m−2, regardless of tillage treatment. A POST application of glyphosate at 1.0 kg ae ha−1 improved control in conjunction with almost all treatments in each year. Results indicate that a one-time tillage operation followed by a return to reduced tillage may aid in the reduction of Amaranthus density when used with PRE-applied herbicides; however, this system will likely not provide adequate control when high population densities of glyphosate-resistant Amaranthus are present, thus highlighting the need for a highly efficacious POST herbicide system.

A field study was conducted during 1997 to 2001 on a Dundee silt loam soil at Stoneville, MS, to examine the effects of rye and crimson clover residues on weeds, soil properties, soil microbial populations, and soybean yield in conventional tillage (CT) and no-tillage (NT) systems with preemergence (PRE)-only, postemergence (POST)-only, and PRE plus POST herbicide programs. Rye and crimson clover were planted in October, desiccated in April, and tilled (CT plots only) before planting soybean. Both cover-crop residues reduced density of barnyardgrass, broadleaf signalgrass, browntop millet, entireleaf morningglory, and hyssop spurge but did not affect yellow nutsedge at 7 wk after soybean planting (WAP) in the absence of herbicides. Densities of these weed species were generally lower with PRE-only, POST-only, and PRE plus POST applications than with no-herbicide treatment. Total weed dry biomass was lower when comparing CT (1,570 kg ha−1) with NT (1,970 kg ha−1), rye (1,520 kg ha−1) with crimson clover (2,050 kg ha−1), and PRE plus POST (640 kg ha−1) with PRE-only (1,870 kg ha−1) or POST-only (1,130 kg ha−1) treatments at 7 WAP. Soils with crimson clover had higher organic matter, NO3–N, SO4–S, and Mn, and lower pH compared with rye and no–cover crop soils. Total fungi and bacterial populations and fluorescein diacetate hydrolytic activity were higher in soil with crimson clover, followed by rye and no cover crop. Soybean yields were similar between CT (1,830 kg ha−1) and NT (1,960 kg ha−1), no cover crop (2,010 kg ha−1) and rye (1,900 kg ha−1), and rye and crimson clover (1,790 kg ha−1), but they were higher in PRE plus POST (2,260 kg ha−1) than in PRE-only (1,890 kg ha−1) or POST-only (1,970 kg ha−1) treatments.

Field experiments were conducted to evaluate the potential of hyperspectral reflectance data collected with a hand-held spectroradiometer to discriminate soybean intermixed with pitted morningglory and weed-free soybean in conventional till and no-till plots containing rye, hairy vetch, or no cover crop residue. Pitted morningglory was in the cotyledon to six-leaf growth stage. Seven 50-nm spectral bands (one ultraviolet, two visible, four near-infrared) derived from each hyperspectral reflectance measurement were used as discrimination variables. Pitted morningglory plant size had more influence on discriminant capabilities than tillage or cover crop residue systems. Across all tillage and residue systems, discrimination accuracy was 71 to 95%, depending on the size of pitted morningglory plants at the time of data acquisition. The versatility of the seven 50-nm bands was tested by using a discriminant model developed for one experiment location to test discriminant capabilities for the other experiment, with discrimination accuracy across all tillage and residue systems of 55 to 73%, depending on pitted morningglory plant size.

During the summer fallow period of the sugarcane production cycle, glyphosate in conjunction with frequent tillage is used to destroy sugarcane regrowth and reduce perennial weed infestations. For tillage to be reduced or eliminated in fallowed fields, weed control must be maintained and sugarcane must be completely destroyed so as not to interfere with the subsequent planting operation. Field studies were conducted to evaluate glyphosate rates and formulations for control of sugarcane, bermudagrass, and johnsongrass. Glyphosate (isopropylamine salt) applied in April at 1.68, 2.24, and 2.80 kg ai/ha controlled 15-cm sugarcane at least 95% 42 d after treatment (DAT). Control of 25- and 40-cm sugarcane was maximized at 1.68 kg/ha (91 and 86% control, respectively). In another study, 25-cm sugarcane was controlled equally with isopropyl amine and potassium salt glyphosate formulations. Bermudagrass control 40 d after glyphosate was applied at 1.12 kg/ha was 86% and increased to 98% when the same rate was applied sequentially. In fallowed sugarcane fields, conventional-tillage, reduced-tillage, and no-tillage programs were implemented from mid-April through mid-August to evaluate weed control and economics. When a glyphosate application was substituted for a tillage operation, bermudagrass and johnsongrass control was increased compared with the conventional tillage alone program, but differences in sugarcane and sugar yield among the various programs the following year were not observed. Based on 2006 costs, elimination of a single tillage operation reduced cost $18.49/ha and addition of glyphosate (2.8 kg/ha plus application cost) increased cost $43.47/ha. Total cost for the conventional tillage–alone fallow program was $110.94/ha; where herbicide was used in the reduced-tillage and no-tillage programs, total cost was $19.47 to $77.38/ha more.

In a 6-yr study on four farms (36 fields) in Ontario, Canada, we tested the effects of tillage (moldboard, chisel plow, no tillage) and crop rotations (continuous corn, corn-soybean, corn-soybean-winter wheat) on emerged and seedbank weed species diversity and density. Aside from the imposed experimental treatments, all other management was generally consistent among farms. Tillage had the largest effect on weed diversity and density. No tillage promoted the highest weed species diversity, chisel plow was intermediate, and moldboard plow resulted in the lowest species diversity. These results are consistent with ecological succession theory. The increase in weed species diversity resulted from 20 species being associated with no tillage systems, 15 of which were winter annuals, biennials, or perennials. Emerged weed density was affected only by tillage. Over 6 yr, seedbank declined in no-tillage systems from 41,000 to 8,000 seeds m−3. Crop yields were not affected by tillage or crop rotation. In practical terms, reduced tillage in combination with a good crop rotation may reduce weed density and expenditures on weed management.

Field research was conducted to determine the potential of hyperspectral remote sensing for discriminating plots of soybean intermixed with pitted morningglory and weed-free soybean with similar and different proportions of vegetation ground cover. Hyperspectral data were collected using a handheld spectroradiometer when pitted morningglory was in the cotyledon to two-leaf, two- to four-leaf, and four- to six-leaf growth stages. Synthesized reflectance measurements containing equal and unequal proportions of reflectance from vegetation were obtained, and seven 50-nm spectral bands (one ultraviolet, two visible, and four near-infrared) derived from each hyperspectral reflectance measurement were used as discrimination variables to differentiate weed-free soybean and soybean intermixed with pitted morningglory. Discrimination accuracy was 93 to 100% regardless of pitted morningglory growth stage and whether equal or unequal proportions of reflectance from vegetation existed in weed-free soybean and soybean intermixed with pitted morningglory. Discrimination accuracy was 88 to 98% when using the discriminant model developed for one experiment to discriminate soybean intermixed with pitted morningglory and weed-free soybean plots of the other experiment. Reflectance in the near-infrared spectrum was higher for weed-free soybean compared with soybean intermixed with pitted morningglory, and this difference affected the ability to discriminate weed-free soybean from soybean intermixed with pitted morningglory.

Buckwheat is a broadleaved annual species that is often used as a summer cover crop for its quick growth, weed suppressive ability, and ease of management. Tartary buckwheat is a species related to buckwheat, with many of the same traits valued in buckwheat as a cover crop. However, Tartary buckwheat has been reported to grow more vigorously than buckwheat, especially in cool conditions, which might fill a unique niche for vegetable farmers in Wisconsin and other northcentral states. Our research objectives were to determine the effectiveness of Tartary buckwheat relative to buckwheat for weed suppression, both during the cover-cropping phase and after cover-crop termination during cabbage production, and quantify weed suppression, soil compaction, soil nitrogen availability, and cabbage yield in no-tillage (roller-crimped or sickle-bar mowed) and conventional-tillage (rototilled) systems. Across three site-years, we found that buckwheat emerged earlier and produced 64% more shoot dry biomass than Tartary buckwheat. Pretermination weed shoot biomass (predominantly Amaranthus and Setaria spp.) in Tartary buckwheat treatments was approximately twice that of buckwheat, and did not differ from weed shoot biomass in a control fallow treatment. Cabbage yield did not differ between cover crop species nor did yield differ between conventional-tillage cover cropped and control fallow treatments. However, weed biomass was greater, and cabbage yield was reduced, in no-tillage compared to conventional-tillage treatments. We also found evidence of greater soil compaction and less nitrate–nitrogen (NO3–N) availability in no-tillage than conventional-tillage treatments. These results suggest that Tartary buckwheat is not a suitable summer cover crop alternative to buckwheat for weed suppression prior to cabbage production.

Crop rotations, particularly those that include legumes, often result in improved soil quality and crop yields. A study was conducted to confirm the presence and persistence of the residual effects of crop rotation and weed management on a test crop and weeds in three tillage systems (moldboard plow [MP]; chisel plow [CP]; no tillage [NT]). Rotation (spring barley monoculture and spring barley–red clover rotation) and weed management (intensive, moderate, minimum) treatments, initiated in 1987, were terminated, and a test crop of spring wheat was grown in 1995 and 1996. Tillage treatments were maintained throughout. Multivariate analysis showed that weed communities were more affected by treatment termination in the rotation NT treatment with minimum weed management than in all other treatments. The former treatment was dominated by perennial broadleaf weeds but sustained adequate wheat yields (3.3 Mg ha−1) compared with the monoculture (1.0 Mg ha−1) one year after termination. Weed communities in CP and MP plots were less affected by treatment termination. Yet, changes in herbicide use at termination caused the virtual elimination of quackgrass from tilled plots and allowed field pennycress to become ubiquitous across treatments. Residual effects from crop rotation were more important than those from weed management in increasing wheat yields in tilled systems. Differences in wheat yield in NT systems 2 yr after treatment termination were attributed to residual effects from previous weed management rather than from crop rotation. Beneficial effects of crop rotation and weed management may persist for 2 yr but will vary according to tillage system.

Management practices and cropping systems that serve as integrated weed management practices, and at the same time can contribute to improved soil quality, will be important for the sustainability of agricultural production systems. The objective of this study was to assess weed species population density under contrasting tillage (conventional tillage [CT] and no tillage [NT]), residue burning (burn and no burn), and residue level (low and high) treatments after 5 and 6 yr of consistent management in a wheat–soybean double-crop production system. A field experiment was conducted from fall 2001 to fall 2007 in the Mississippi River Delta region of eastern Arkansas on a Calloway silt–loam. Weed assessments were conducted twice during the soybean growing season, before (early season) and after herbicide application (late season) in 2006 and 2007. Total weed density was greater under CT (513 plants m−2) than under NT (340 plants m−2) early in the growing season in 2006, but was greater under NT than CT late in the season in 2007, suggesting that the effectiveness of glyphosate on total weeds differs between CT and NT. Averaged across residue levels, grass species density was greatest in the NT–burn (68 to 167 plants m−2) combination and lowest in the NT–no-burn (41 to 63 plants m−2) early in the growing season in both years. Broadleaf density was greater early (200 to 349 plants m−2) than late (18 to 20 plants m−2) in the growing season under both CT and NT in 2006, but in 2007 broadleaf density did not differ by tillage treatment between seasons. Perennial weed density was greater in the burn (99 plants m−2) than in the no-burn (59 plants m−2) treatment in 2006. No tillage, no burning, and a high residue level appeared to contribute to the suppression of most weed species without reducing herbicide efficiency.

The fertility and soil health of organic agroecosystems are determined in part by the size and turnover rate of soil carbon (C) and nitrogen (N) pools. Our research contrasts the effects of best management practices (BMP) (reduction in soil disturbance, addition of organic amendments) on C and N cycling in soils from two field sites representing five organic agroecosystems. Total soil organic C (SOC), a standard measure of soil health, contains equal amounts of biologically and non-biologically active C that is not associated with release of mineral N. A three-pool first-order model can be used to estimate the size and turnover rates of C pools but requires data from a long-term incubation. Our research highlights the use of two rapid C fractions, hydrolysable and permanganate (0.02 M) oxidizable C, to assess shifts in biologically active C. Adoption of BMP in organic management systems reduced the partitioning of C to the active pool while augmenting the slow pool C. These pools are associated with potentially mineralizable N supplied by residues, amendments and soil organic matter affecting the concentration and release of mineral N to crops. Our data show that minimizing disturbance (no tillage, pasture) and mixed compost additions have the potential to reduce carbon dioxide emissions while enhancing slow pool C and or its turnover, a reservoir of nutrients available to the soil biota. Use of these rapid, sensitive indicators of biological C activity will aid growers in determining whether a BMP fosters nutrient loss or retention prior to shifts in total SOC.

Soil quality has been proposed as a prime indicator for characterizing and defining management factors contributing to soil degradation. In this study, biological (soil respiration, fluorescent Pseudomonas bacteria and entomopathogenic nematode populations), chemical (pH, inorganic N, and total C & N), and physical (bulk density and infiltration) indicators were used to determine soil quality. The specific research objective was to determine the capacity of this specific set of indicators to assess soil quality and determine its ability to detect short-term changes in soil conditions and processes. The assessment was comparative because of the lack of specific criteria or guidelines available in the literature for interpretation of most soil property indices measured. The following treatments were chosen from an ongoing farming systems study to achieve a preplanned set of comparisons that would make this type of assessment possible: (1) best management practices/conventional tillage (BMP/CT), (2) BMP/no-tillage (BMP/NT), (3) an organic system, and (4) a successional fallow system. Assessments were made multiple times between 1999 and 2000. Statistical differences between systems were found for all soil quality indicators except for entomopathogenic nematodes. Differences between systems varied across dates, a result that supports other research stating the need to consider the temporal variability of these indices for an unbiased overall soil quality assessment. Differences in total carbon and total nitrogen between systems were most evident in the 2000 sampling dates with BMP/NT showing greater contents on the last sampling date. The soil pH and inorganic N results did not suggest a possible difference in soil function status between any of the three agricultural systems studied. All three agricultural systems, BMP/NT, BMP/CT and organic, had similar pH values and overall low soil inorganic N levels. The non-agricultural successional system had a slightly more acidic soil condition than the three agricultural systems. Soil bulk density increased with time in the untilled BMP/NT and successional systems but the resulting values were not considered detrimental to either productivity or environmental quality. Infiltration was lower in the BMP/NT and successional systems than in the BMP/CT and organic systems. In conclusion, all soil quality indicators except for entomopathogenic nematodes proved to be sensitive to the detection of rapid changes in soil conditions that occur by the influence of soil management. The importance of using soil bulk density to express soil results on a volume basis, as the soil exists in the field before sampling, prevented an average interpretation error of 7–14% as compared to treatment comparisons on a soil weight basis only. This also demonstrates the need to carefully consider field sampling locations (row, between row, or wheel traffic areas) which dramatically influence soil density, physical characteristics, organic matter concentrations, and biological activity. Failure to consider these factors can invalidate even the most careful approaches to establishing baseline soil quality levels in the field as affected by various tillage and residue management practices and associated comparisons in time.