Agriculture can be pivotal in mitigating climate change through soil carbon sequestration. Land conversion to pasture has been identified as the most effective method to achieve this. Yet, it creates a perceived trade-off between increasing soil carbon and maintaining arable food crop production. In this on-farm study, we assessed the potential of incorporating a 2-year diverse ley (consisting of 23 species of legumes, herbs, and grasses) within a 7-year arable crop rotation for soil organic matter accumulation. We established upper and lower boundaries of soil organic matter accumulation by comparing this approach to positive (permanent ley, akin to conversion to permanent pasture) and negative (bare soil) references. Our findings in the 2-year diverse ley treatment show greater soil organic matter accumulation in plots with lower baseline levels, suggesting a potential plateau of carbon sequestration under this management practice. In contrast, the positive reference consistently showed a steady rate of organic matter accumulation regardless of baseline levels. Moreover, we observed a concurrent increase in labile carbon content in the 2-year ley treatment and positive reference, indicating improved soil nutrient cycling and ecological processes that facilitate soil carbon sequestration. Our results demonstrate that incorporating a 2-year diverse ley within arable rotations surpasses the COP21 global target of a 0.4% annual increase in soil organic carbon. These findings, derived from a working farm's practical and economic constraints, provide compelling evidence that productive arable agriculture can contribute to climate change mitigation efforts.

Maize is the most important staple food crop in southern Africa with human consumption averaging 91 kg/capita/year. Most smallholder farmers and weaning children depend on maize for much of the daily food requirements and it is the largest contributor of dietary proteins. Despite the development of quality protein maize (QPM) with high tryptophan and lysine content, stunting and kwashiorkor remain high in southern Africa partly due to low adoption of QPM varieties. The objective of this study was to compare the agronomic performance and farmer preferences of new generation of QPM with non-QPM varieties under conservation agriculture on-farm conditions. Eight QPM and four non-QPM varieties were tested on on-farm trials in Zimbabwe during the 2014/15 and 2015/16 cropping seasons at five different locations. Significant differences were detected among the genotypes for the measured traits in the two seasons. Similarly, genotype plus genotype × environment interactions were significant for both seasons for grain yield. Three QPM varieties, SC527, SC535 and SC643, recorded the highest and stable yield. Four QPM varieties, SC643, SC535, SC527 and MQ623, and a non-QPM variety, PAN413, were ranked high among farmers for overall ear characteristics as their most preferred varieties. The high-yielding and stable QPM varieties are likely to be adopted by farmers in southern Africa.

Continuous-cropping conservation tillage systems may provide a viable alternative to the practice of summer fallow; however, concerns have been raised regarding potentially negative changes in weed communities in continuous cropping. Field experiments were established in Saskatchewan at three locations to determine the nature of weed community differences between a crop sequence with and without fallow in zero-, minimum-, and conventional-tillage systems from 1986 to 1990. Weed communities in continuous-cropping treatments tended to have greater total densities and were more similar in composition than crop-fallow treatments. Inclusion or exclusion of fallow within the rotation had a greater impact on weed community composition than did tillage system at Ituna and Waldron, but the reverse was true at Tadmore due to poor crop growth in all tillage systems. Differences in weed community composition were generally characterized by fluctuational changes in species associations. Volunteers of summer-annual crops, such as canola, flax, and barley, were associated with continuous cropping, but other species including perennial weeds, such as Canada thistle, perennial sowthistle, and quackgrass, were not strongly associated with the presence or absence of fallow. The practice of fallowing land to manage weeds may not be necessary.

Field experiments were conducted from 1979 to 1989 to determine the influence of conventional, reduced, and no-tillage systems and different herbicide combinations on weed species and population, weed control, and soybean injury, population, and yield. In no-till (NT) non-treated plots, there was an abrupt shift from horseweed as the dominant early spring emerging weed to gray goldenrod in 1985. Following its initial observation, gray goldenrod became the dominant species within 2 yr, with giant foxtail as the only other species observed in these plots. Giant foxtail was the dominant weed species from 1980 to 1989 in conventional till (CT) and reduced-till (RT) plots. There also was a shift in the frequency of occurrence and in density of several broadleaf weed species during the 11-yr study. Most herbicides provided excellent control of all weeds in all tillage systems, especially those that included POST herbicides. There was little difference between glyphosate and paraquat in controlling weeds present at the time of planting in NT. PRE herbicides caused 2 to 9% soybean injury with slightly greater injury occurring in CT and RT than in NT. The POST broadleaf herbicides did not significantly increase soybean injury. There were no differences in soybean population or yield among the herbicide treatments regardless of tillage. There also was no difference in soybean population or yield in NT compared with CT when averaged over all herbicide treatments.

The establishment and management of nine cover crops in Kentucky production systems were evaluated in field experiments over a 2-yr period. ‘Wheeler’ rye, ‘Barsoy’ barley, and ‘Tyler’ wheat cereal grains produced greater biomass (180 to 260 g/m2) than the pasture species tall fescue, creeping red fescue, and white clover (55 to 110 g/m2). ‘Kentucky 31’ tall fescue, creeping red fescue, and white clover proved most difficult to control, and significant regrowth occurred regardless of herbicide or rate applied. HOE-39866 (1.7 kg ai/ha) was effective in rapidly controlling all cover crops except tall fescue by 30 days after application. Sethoxydim and fluazifop (0.4 and 0.3 kg ai/ha, respectively) effectively controlled the cereals and two ryegrass species. Glyphosate applied at 1.1 and 2.2 kg ai/ha was also effective, while 0.6 kg ai/ha controlled only cereal grain growth adequately. After chemical control, pasture grass plots contained fewest weeds/m2 with some reductions likely due to density and regrowth of the sods. Cover crops were effective in suppressing weed growth at 45 days after chemical control. However, significant weed growth existed in all cover crop plots by 60 days after kill. Row crop establishment increased linearly with increasing glyphosate rate. Cereal grain covers provided the most compatible planting situations for greatest seedling establishment, with rye and wheat providing greatest weed suppression. Generally, increased weed suppression provided by a cover crop was accompanied by reduced row crop establishment, with greatest reductions observed in pasture grass plots. Cucumber was most easily established while snap pea was most difficult.

Adverse changes in weed communities are a limiting factor for the adoption of conservation tillage practices. Predictions of an increased association of annual and perennial grasses, perennial dicot weeds, wind-disseminated species, and volunteer crops as weeds, and decreased association of annual dicot weeds in reduced-tillage systems were tested. Field experiments involving zero-, minimum-, and conventional-tillage systems were conducted in Saskatchewan from 1986 to 1990 at Ituna and Waldron, and from 1986 to 1988 at Tadmore. Weed community composition was analyzed for years 1988 to 1990 by canonical discriminant analysis. An increased association of perennial and annual grasses with zero tillage did not generally occur. Wind-dispersed species and volunteer crops were associated with reduced tillage and summer annual dicots with conventional tillage, but exceptions occurred. Species responded differently among sites or within a site over time. Within the time frame of this research, changes in weed communities were influenced more by location and year than by tillage systems, indicating fluctuational rather than directional or consistent changes in community composition.

Soils from long-term tillage plots at three locations in Ohio were sampled to determine composition and size of weed seed banks following 25 yr of continuous no-tillage, minimum-tillage, or conventional-tillage corn production. The same herbicide was applied across tillage treatments within each year and an untreated permanent grass sod was sampled for comparison. Seed numbers to a 15-cm depth were highest in the no-tillage treatment in the Crosby silt loam (77 800 m–2) and Wooster silt loam (8400 m–2) soils and in the grass sod (7400 m–2) in a Hoytville silty clay loam soil. Lowest seed numbers were found in conventional-tillage plots in the Wooster soil (400 m–2) and in minimum-tillage plots in the Crosby (2200 m–2) and Hoytville (400 m–2) soils. Concentration of seeds decreased with depth but the effect of tillage on seed depth was not consistent among soil types. Number of weed species was highest in permanent grass sod (10 to 18) and decreased as soil disturbance increased; weed populations were lowest in conventional tillage in the Hoytville soil. Common lambsquarters, pigweeds, and fall panicum were the most commonly found seeds in all soils. Diversity indices indicated that increased soil disturbance resulted in a decrease in species diversity. Weed populations the summer following soil sampling included common lambsquarters, pigweeds, fall panicum, and several species not detected in the seed bank.

Experiments were conducted to evaluate the effect of tillage, rye residue levels, and control strategies on weed suppression and potato yield. Reduced tillage (RT) yields in 1989 were lower than in conventional tillage (CT) due to high hairy galinsoga populations. However, in 1990, potato yields were greater in RT when early emerging weeds were suppressed. Increasing residue levels up to 2300 kg ha−1 had no effect on weeds or yields in either year. In a separate study, preemergence herbicides (linuron plus metolachlor, 1.7 kg ai ha−1 each) applied 10 d after planting (DAP) in reduced tillage controlled weeds for 6 wk, but efficacy decreased after hilling. Metribuzin applied postemergence (0.19 kg ai ha−1) 7 d after hilling controlled late germinating weeds. Potato yields were greatest when the preemergence herbicides were applied.

Time of hilling (4, 5, or 6 weeks after planting; WAP) and 0.5x, 1x, and split (0.5x + 0.5x) rates of metolachlor + metribuzin were evaluated in conventional tillage (CT) and rye-stubble, reduced tillage (RT) potato plots. Weed populations 4 to 10 WAP were generally higher in CT than in RT. Weed control was excellent in both tillage systems when 1x rates of metolachlor + metribuzin were applied delayed preemergence, or in a split application where 0.5x was applied delayed PRE and hilled 6 WAP, and followed with a second application of 0.5x metolachlor + metribuzin 7 days after hilling (DAH). Weed control with 0.5x rates of metolachlor + metribuzin applied 7 DAH, when hilled 4 and 5 WAP, was equivalent to the lx and split-rate treatments. Weed control was reduced only when hilling was delayed to 6 WAP and 0.5x of metolachlor + metribuzin applied 7 DAH. Total yields were not influenced by tillage, hilling, or herbicide treatment, however, larger numbers of green and small-sized tubers reduced marketable yields in RT.

Fluchloralin [N-(2-chloroethyl)-2,6-dinitro-N-propyl-4-(trifluoromethyl)benzenamine], pendimethalin [N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine], and trifluralin [2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl)benzenamine] either alone or in combination with fluazifop {(±)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl]oxy]phenoxy] propanoic acid}, haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid}, or sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} were evaluated for johnsongrass [Sorghum halepense (L.) Pers. # SORHA] control in reduced-tillage soybean [Glycine max (L.) Merr.] production systems. Data obtained in 1983 and 1984 near Lexington and Princeton, KY, indicated that johnsongrass could be effectively controlled. A single discing before application of the soil-active herbicides usually had no effect on johnsongrass control. Johnsongrass control was primarily dependent on foliarly applied herbicides. Preplant-incorporated treatments did not provide adequate johnsongrass control when used alone. Johnsongrass panicle numbers recorded in September corresponded to visual evaluations of control recorded earlier in the growing season. Soybean yield with all herbicide treatments was greater than with a nontreated control and was closely associated with the degree of johnsongrass control.

Postemergence applications or a combination of preemergence and postemergence treatments in double cropped soybeans [Glycine max (L.) Merr. ‘Ransom’] resulted in higher soybean yields than preemergence applications. Preemergence-treated plots were 98% weed free early in the growing season; however, weeds emerged later and reduced yields. Weeds had to be controlled in soybeans for 90% of the growing season to avoid yield loss. Soybean yields were higher under no-till than conventionally tilled management in two of three years and tended to be higher during the third year. Distribution and timing of rainfall were more important in determining soybean yield than the total amount received during the growing season.

Field studies were conducted to evaluate weed control with paraquat and glyphosate applied at various rates alone and in combination with residual herbicides. Morningglory, prickly sida, and hemp sesbania control 28 d after treatment was similar regardless of herbicide treatment. In contrast, barnyardgrass control when paraquat was tank mixed with pendimethalin plus imazaquin was equal to that of paraquat alone but less than that for tank mixtures with metolachlor plus metribuzin plus chlorimuron or metolachlor plus metribuzin. Barnyardgrass control and soybean yield when paraquat was applied at 1050 g ai/ha in combination with metolachlor plus metribuzin plus chlorimuron or metolachlor plus metribuzin was greater than when the same residual herbicide treatments were applied with paraquat at 350 g/ha. Yield following glyphosate at 840 and 1120 g ai/ha in combination with residual herbicides was no greater than when glyphosate was applied alone, which was reflective of barnyardgrass control. Tank mixtures of glyphosate at 1680 g/ha with metolachlor plus metribuzin plus chlorimuron or metolachlor plus metribuzin resulted in soybean yield higher than for glyphosate alone. Regardless of the glyphosate and residual herbicide combination, soybean yield was no greater than when paraquat was applied at 350 g/ha in combination with metolachlor plus metribuzin plus chlorimuron.

Field experiments evaluating 11 cereal cover crops were established at two locations in Ontario over a two-year period. Cover crops were interseeded into a ridge-tillage corn crop and evaluated in terms of biomass production and winter annual, biennial, and perennial weed species suppression. Seedling establishment and aboveground biomass production of cover crops were variable between locations and years. At both locations over two years, ‘Danko’ winter rye, ‘OAC Halton’ winter barley and ‘Rodeo’ spring barley were the most consistent cover crops in biomass production. However, cover crop residues had no significant effect on weed biomass or density due to a high degree of spatial variability present in the weed populations. Corn grain yields were not reduced by the presence of inter-seeded cover crops when compared with the bare ground control treatment.

Experiments were conducted to evaluate the effect of tillage, rye residue levels, and control strategies on weed suppression and potato yield. Reduced tillage (RT) yields in 1989 were lower than in conventional tillage (CT) due to high hairy galinsoga populations. However, in 1990, potato yields were greater in RT when early emerging weeds were suppressed. Increasing residue levels up to 2300 kg ha-1 had no effect on weeds or yields in either year. In a separate study, preemergence herbicides (linuron plus metolachlor, 1.7 kg ai ha-1 each) applied 10 d after planting (DAP) in reduced tillage controlled weeds for 6 wk, but efficacy decreased after hilling. Metribuzin applied postemergence (0.19 kg ai ha-1) 7 d after hilling controlled late germinating weeds. Potato yields were greatest when the preemergence herbicides were applied.

Field experiments were conducted from 1985 to 1987 to evaluate herbicide systems for minimum-tillage and conventional-tillage peanut production. While acceptable weed control could be achieved in both tillage systems, minimum-tillage systems generally had to be more herbicide intensive. Preemergence or preplant-incorporated within-the-row applications of either ethalfluralin or pendimethalin plus postemergence applications of paraquat and sethoxydim provided Texas panicum control equivalent to preplant-incorporated applications of ethalfluralin or pendimethalin. Early-postemergence paraquat applications improved Florida beggarweed and pitted morningglory control in conventional-tillage systems at least 15% compared to the same systems without paraquat Control of bristly starbur and sicklepod in conventional-tillage systems did not increase with paraquat application. Broadleaf weed control did not differ between tillage systems, except pitted morningglory control was lower in the minimum-tillage system. Conventional-tillage peanuts produced yields 800 to 1900 kg/ha higher, depending on herbicide system, and also provided greater net returns than minimum-tillage peanuts. The greater yield and net returns in conventional- versus minimum-tillage systems were not attributed to weed control or disease problems.

A sorghum-sudangrass hybrid [Sorghum bicolor (L.) Moench. x Sorghum sudanense (P.) Stapf. ‘DEKALB SX17+’] (SSH) and foxtail millet [Setaria italica (L.) Beauv.] (FM) were evaluated for their effects on weed populations when grown for forage and as land conditioners prior to late-summer, no-till planting of alfalfa (Medicago sativa L. ‘Arc’). Both grasses established well in no-till situations, except for FM when excessive mulch impeded seed placement or seedling summer-annual weeds were not destroyed at planting time. SSH was the better competitor; after both were planted into a dense stand of seedling summer-annual weeds, SSH outyielded the weeds while FM did not. Both grasses suppressed weeds and enhanced subsequent alfalfa establishment. Obtaining adequate alfalfa stands was not a problem in no-till seedings: seedling populations often exceeded 300/m2 3 to 6 weeks after planting. Lack of adequate weed control was associated with stand losses in which disease was also a factor. Biennial and perennial broadleaf species were the predominant weeds. Prior cropping of SSH or FM is a valuable option for growers wishing to establish alfalfa without tillage, particularly when summer forage is useful.

Trifluralin is widely used for control of rigid ryegrass in no-till grain crops in southern Australia. Trifluralin must be incorporated into soil to be effective. Several field studies were conducted to evaluate the effect of different tillage systems on vertical seed distribution and efficacy and rate of loss of bioavailable trifluralin. Experiments were conducted during the growing seasons of 2004 and 2005 at two sites in South Australia: on the Roseworthy Campus farm of the University of Adelaide and near Minlaton on the Yorke Peninsula. The tillage systems at the Roseworthy Campus were minimum tillage (MinTill) and no-till using narrow points, whereas four direct-drill-seeding systems were used at Minlaton. Plastic beads were spread on the soil surface to simulate weed seeds. MinTill sowing buried more plastic beads than no-till, indicating that greater soil disturbance was caused by the MinTill system. Trifluralin efficacy was lower under no-till as compared to MinTill. A bioassay, based on response of oat roots, was used to quantify the concentrations of bioavailable trifluralin under different tillage systems. In both years at the Roseworthy Campus, loss of bioavailable trifluralin was greater under no-till than under MinTill; however, the rate of loss under both systems was much faster in 2004 than in 2005. In 2004, bioavailable trifluralin at 12 d after sowing under MinTill and no-till was 55 and 33% of the initial concentration, respectively. In 2005, bioavailable trifluralin remaining at 23 d after sowing was 86% under MinTill and 54% under no-till. At Minlaton in both years, bioavailable trifluralin was greater under tillage systems that provided the highest level of soil disturbance. These results demonstrate that reduced bioavailability of trifluralin occurs in no-till seeding systems, which could result in reduced weed control.

The influence of four tillage systems, varying from intensive to zero tillage, on weed populations and the vertical distribution of weed seeds in the soil was determined at Alliance, Hairy Hill, and Wainwright in northeastern Alberta. The soil was sampled at two depths (0 to 5 and 5 to 10 cm) in fall. Weed seedling emergence in the greenhouse over the winter was assumed to represent the type and amount of weed seeds present in the soil seedbank. Emerged weed seedlings were also identified and counted in the field in spring. In the zero-tillage system, most of the weed seeds were close to the soil surface (0 to 5 cm) at Alliance and Wainwright but were deeper (5 to 10 cm) at Hairy Hill. The winter annuals, field pennycress, shepherd's-purse, and flixweed, and the summer annuals, wild buckwheat and common lambsquarters, increased in the soil seedbank as tillage was reduced, but the higher populations in the soil seedbank did not always result in higher spring seedling populations under zero tillage. In contrast to the seedbank, spring seedling populations of common lambsquarters at Alliance and field pennycress and ball mustard at Hairy Hill were lowest in the zero-tillage system, suggesting that the requirement for herbicides for controlling these weeds in the crop may be least under zero tillage. Both soil seedbank and spring seedling populations of shepherd's-purse at Wainwright and Alliance and of flixweed at Alliance were highest in the zero-tillage system. At Alliance, wild buckwheat seedling emergence in the spring tended to be highest in the minimum-tillage system (one tillage operation prior to seeding). Both soil seedbank and spring seedling populations of green foxtail decreased as tillage was reduced, indicating that green foxtail should become less of a problem under reduced tillage.

Organic farmers in western Canada rely on tillage to control weeds and incorporate crop residues that could plug mechanical weed-control implements. However, tillage significantly increases the risk of soil erosion. For farmers seeking to reduce or eliminate tillage, potential alternatives include mowing or using a roller crimper for terminating green manure crops (cover crops) or using a minimum tillage (min-till) rotary hoe for mechanically controlling weeds. Although many researchers have studied organic crop production in western Canada, few have studied no-till organic production practices. Two studies were recently conducted in Saskatchewan to determine the efficacy of the following alternatives to tillage: mowing and roller crimping for weed control, and min-till rotary hoeing weed control in field pea (Pisum sativum L.). The first study compared mowing and roller crimping with tillage when terminating faba bean (Vicia faba L.) and field pea green manure crops. Early termination of annual green manure crops with roller crimping or mowing resulted in less weed regrowth compared with tillage. When compared with faba bean, field pea produced greater crop biomass, suppressed weeds better and had less regrowth. Wheat yields following pea were not affected by the method of termination. Thus, this first study indicated that roller crimping and mowing are viable alternatives to tillage to terminate field pea green manure crops. The second study evaluated the tolerance and efficacy of a min-till rotary harrow in no-till field pea production. The min-till rotary hoe was able to operate in no-till cereal residues and multiple passes did not affect the level of residue cover. Field pea exhibited excellent tolerance to the min-till rotary hoe. Good weed control occurred with multiple rotary hoe passes, and pea seed yield was 87% of the yield obtained in the herbicide-treated check. Therefore, this second study demonstrated that min-till rotary hoeing effectively controls many small seeded annual weeds in the presence of crop residue and thus can reduce the need for tillage in organic-cropping systems.

Agricultural soil quality (SQ) research has focused on the influence of individual soil properties, particularly those related to soil organic matter (SOM), on soil processes such as water movement and retention, and nutrient cycling. However, few studies have assessed the influence of these SOM-related properties on crop productivity, particularly under different management systems. Furthermore, agricultural SQ research in tropical regions is limited. The objectives of this study were, for a tropical site, to determine (1) the relationship between selected soil characteristics and resulting soil functional properties such as aggregate stability and porosity, and (2) the relationship between SQ indicators and productivity of corn under three different tillage systems. Twelve plots were randomly demarcated in three adjacent fields under different tillage systems. Profiles were described by augering and the surface soil (0–7.5 cm) was sampled just prior to crop harvest and analyzed for texture, standard soil tests (pH, available P, K, Mg and Ca) and SQ parameters including total N, total and active fraction C, porosity and aggregate stability. Corn dry grain m−2, above-ground crop dry matter m−2, and dry grain per plant was measured in each plot. Soil C parameters were highly predictive of macroaggregate stability and soil porosity across different tillage systems. Macroaggregate stability and soil C (particularly active C oxidizable by 0.025m KMnO4) were highly correlated with crop productivity across tillage systems. These findings suggest that soil C in the surface layer, especially the active C fraction, markedly affected the productivity of this tropical soil through its influence on soil structure.