Minimal soil disturbance combined with spring cropping can halt soil seedbank accumulation of Alopecurus myosuroides

The basic mechanism of soil inversion tillage for control of annual weeds is based on the vertical translocation of weed seeds from the soil surface to deeper soil layers. Buried weed seeds either remain dormant in the soil seedbank and are exposed to biological and chemical decay mechanisms, or they germinate but the seedlings cannot reach the soil surface (fatal germination). However, depending on the seed biology of the respective target species, frequent inversion tillage can lead to a build-up of the soil seedbank. For soil seedbank depletion based on available knowledge of the biology of Alopecurus myosuroides seeds, soil inversion tillage is suggested to be reduced to every third or fourth year with reduced or even no-tillage (direct seeding) in between (rotational inversion tillage systems). Including spring crops in the crop rotation could further help dampening the population growth and hence the seed return into the seedbank. This study investigated the effect of rotational inversion tillage in combination with reduced tillage or direct seeding on the soil seedbank and population development of A. myosuroides. In a long-term field trial, set up in 2012, these tillage strategies were compared with continuous inversion tillage in a 3-year crop rotation with two consecutive years of winter wheat (Triticum aestivum) followed by spring barley (Hordeum vulgare). The results showed a significant decline in the soil seedbank following the spring crop, irrespective of the tillage system. The continuous inversion tillage system and inversion tillage before spring cropping with reduced tillage (shallow tillage with a disc harrow) before winter wheat both led to accumulation of seeds in the soil seedbank. In contrast, inversion tillage before spring cropping with direct seeding of winter wheat depleted the soil seedbank significantly after only one crop rotation. Although only covering one intensively studied field site, these findings highlight the need for diversified cropping systems and indicate potential avenues for reducing soil tillage while controlling economically important weeds.     

Strategic tillage in Australian conservation agricultural systems to address soil constraints: How does it impact weed management?

In the conservation agricultural systems practised in Australia, cultivation is not commonly utilised for the purpose of weed control. However, occasional use of tillage (strategic tillage) is implemented every few years for soil amelioration, to address constraints such as acidity, water repellence or soil compaction. Depending on the tillage method, the soil amelioration process buries or disturbs the topsoil. The act of amelioration also changes the soil physical and chemical properties and affects crop growth. While these strategic tillage practices are not usually applied for weed control, they are likely to have an impact on weed seedbank burial, which will in turn affect seed dormancy and seedbank depletion. Strategic tillage impacts on seed burial and soil characteristics will also affect weed emergence, plant survival, competitive ability of weeds against the crop and efficiency of soil applied pre-emergent herbicides. If growers understand the impacts of soil amelioration on weed demography, they can more effectively plan management strategies to apply following the strategic tillage practice. Weed seed burial resulting from a full soil inversion is understood, but for many soil tillage implements, more data is needed on the extent of soil mixing, burial of topsoil and the weed seedbank, physical control of existing weeds and stimulation of emergence following the tillage event. Within the agronomic system, there is no research on optimal timing for a tillage event within the year. There are multiple studies to indicate that strategic tillage can reduce weed density, but in most studies, the weed density increases in subsequent years. This indicates that more research is required on the interaction of amelioration and weed ecology, and optimal weed management strategies following a strategic tillage event to maintain weeds at low densities. However, this review also highlights that, where the impacts of soil amelioration are understood, existing data on weed ecology can be applied to potentially determine impacts of amelioration on weed growth.     

Which model species for weed seedbank and emergence studies? A review

Models predicting the effects of cropping systems on weed demography are important tools for testing new rules for integrated weed management that may reduce the use of herbicides and preserve the biodiversity of agro-ecosystems. Such models already exist for a few species and should now be extended to a larger flora, in order to predict and understand the effects of agricultural practices on the evolution of weed communities. This review analysed the literature from 1973 to 2006, focusing on 45 species, to identify past reasons for choosing particular species when modelling the effects of cropping systems on the processes leading to seedling emergence. The frequency or harmfulness of the species were the main reason for studying them. It appears that the studied species were mainly autumn-emerging in north-western Europe cropping systems and summer-emerging in North America; the effects of deep soil tillage were studied mainly in Europe, as simplified sowing techniques are more often practised in North America. A voluminous literature exists on seed persistence in the soil, dormancy, germination and emergence, but rarely with the attempt of establishing generic relationships between species characteristics and model parameters. Until now, such an approach has been mostly developed in ecological studies. Taxa, as well as ecological preferences, seed size and the relationships of these characteristics with weed emergence model parameters should be considered when selecting a range of species for multi-specific modelling purposes.     

Germination,emergence, and persistence of Sonchus oleraceus,a major crop weed in subtropical Australia

Sonchus oleraceus (common sowthistle) is a dominant weed and has increased in prevalence in conservation cropping systems of the subtropical grain region of Australia. Four experiments were undertaken to define the environmental factors that favor its germination, emergence, and seed persistence. Seeds were germinated at constant temperatures between 5 and 35°C and water potentials between 0 and ?1.4 MPa. The maximum germination rate of 86–100% occurred at 0 and ?0.2 MPa, irrespective of the temperature when exposed to light (12 h photoperiod light/dark), but the germination rate was reduced by 72% without light. At water potentials of ?0.6 to ?0.8 MPa, the germination rate was reduced substantially by higher temperatures; no seed germinated at a water potential >?1.0 MPa. Emergence and seed persistence were measured over 30 months following seed burial at 0 (surface), 1, 2, 5, and 10 cm depths in large pots that were buried in a south‐eastern Queensland field. Seedlings emerged readily from the surface and 1 cm depth, with no emergence from below the 2 cm depth. The seedlings emerged during any season following rain but, predominantly, within 6 months of planting. Seed persistence was short‐term on the soil surface, with 2% of seeds remaining after 6 months, but it increased with the burial depth, with 12% remaining after 30 months at 10 cm. Thus, a minimal seed burial depth with reduced tillage and increased surface soil water with stubble retention has favored the proliferation of this weed in any season in a subtropical environment. However, diligent management without seed replenishment will greatly reduce this weed problem within a short period.     

Night‐time tillage revisited: the delayed soil desiccation process in night‐time tilled plots may promote unexpected weed germination

Night‐time tillage and sowing (photocontrol of weeds, soil cultivation in darkness) can reduce the germination and subsequent density of light‐sensitive weeds by excluding the short light flash during soil disturbance. In most experiments conducted from 1990 to 2004 worldwide, total weed density was reduced in night‐time tilled plots as expected. However, in a few field experiments, total weed density was significantly increased in night‐time compared with daytime tilled plots. We hypothesise that the desiccation process of the upper soil layer (roughly about 0–30 mm), from where most small seeded weeds emerge, may have been delayed in night‐time compared with daytime tilled plots, with significant effects on early seed germination processes. Daytime tillage was usually performed around noon, to capture high light intensities during soil tillage. However, around noon soil desiccation can be much higher than during the night. A few hours of relatively higher water availability for seeds in the upper soil layer during the night, before the next morning when soil desiccation usually increases again, may have favoured seed germination and subsequent weed emergence compared with daytime tillage, finally resulting in higher weed density in night‐time tilled plots. On the other hand, crop germination and emergence may also be higher under such conditions.     

Effects of drought on weed emergence and growth vary with the seed burial depth and presence of a cover crop

In conservation agriculture, weed seed germination could decrease with the presence of a cover crop, surface weed seed location and temporal drought in summer just after seed shedding. This study simultaneously examined the effects of a cover crop, burial depth (seed location) and hydric stress on weed emergence and early growth. It was hypothesized that drought would reduce weed emergence and the initial growth of weed seeds and that this effect would be greater when the seeds were on the soil surface and in the presence of a cover crop. Four annual weed species were chosen that are frequently found (Anisantha sterilis, Vulpia myuros, Sonchus asper, Veronica persica) and not frequently found (Alopecurus myosuroides, Poa annua, Cyanus segetum, Capsella bursa‐pastoris) in fields that implement conservation agriculture. The unburied seeds had 26% lower emergence, on average, than the buried seeds (significant for six of the eight species), hydric stress reduced emergence by 20% (for seven of the eight species) and the presence of a cover crop reduced the level of emergence by 17% (for all species). The unburied seeds with hydric stress were emerging under the “most stressful” set of factors, with a 45% decrease in emergence, compared with the seeds emerging under the “least stressful” set of factors (buried seeds without hydric stress). All the weed growth measurements (height, dry matter content and number of leaves) decreased with the presence of a cover crop. The species that are found frequently in the fields that implement conservation agriculture, compared with the species that are not frequently found in conservation agriculture fields, had higher rates of germination and a higher tolerance of hydric stress when their seeds were unburied.     

Size and composition of the weed seedbank after 7 years of different cover-crop-maize management systems

The objective of this study was to obtain detailed information on the long‐term weed suppression potential of four winter soil cover types included in an arable crop system managed at various input levels. We used weed seedbank size and composition to assess weed suppression potential. A field experiment was established in 1993 as a split‐split‐plot design with four replications, including two tillage systems [a conventional system (CS) including ploughing in the cover crops and a low‐input system (LIS) including no tillage with surface mulching of the cover crops] in the main plots, three mineral nitrogen fertilization rates for the main crop in the sub‐plots and four soil cover types (main crop residue, rye, crimson clover and subterranean clover) in the sub‐sub‐plots. Seedbank sampling took place in winter 2000/01. The weed seedbank was analysed with the seedling emergence method. Data were analysed using anova and multivariate techniques. Results indicated that the seedbank density in the LIS was about five times higher than in the conventional input system. In the CS, use of a rye cover crop resulted in a lower seedbank density with respect to the crop residue treatment (?25%), whereas in the LIS the subterranean clover cover crop decreased weed seedbank density as compared with the other cover crops and the crop residue treatment (?22% on average). Differences in species composition were mainly related to tillage system. Implications for cover crop management and the development of sustainable cropping systems are discussed.     

Germination, persistence, and emergence of flaxleaf fleabane (Conyza bonariensis [L.] Cronquist)

Flaxleaf fleabane ( Conyza bonariensis [L.] Cronquist) is a difficult-to-control weed in dryland minimum tillage farming systems in the northern grains region of Australia. Experiments under field and controlled environments were conducted to study the seed germination, emergence, and persistence of C. bonariensis . The base, optimum, and maximum temperatures for seedling germination were estimated at 4.2, 20, and 35°C, respectively, with light stimulating germination. The soil types and burial depths had significant effects on seed persistence and emergence. The persistence pattern showed an initial rapid drop, followed by a slow but steady decline over time. After 3 years of burial, there were ≈ 7.5%, 9.7%, and 1.3% viable seeds at 10, 5, and 0–2 cm soil depths, respectively. Conyza bonariensis predominantly emerged from the soil surface or from the burial depth of 0.5 cm. Very few seeds emerged from a depth of 1 cm and none emerged from ≥ 2 cm. The emergence was greater in lighter soils. On-farm monitoring of the field emergence over time in a light sandy loam soil showed that 99% emergence occurred in late autumn, early and late winter, and a small fraction of 1% emerged in mid-spring. The predominant emergence from the soil surface suggests that the fleabane problem is a result of weed species shift toward the minimum tillage systems that provide moist conditions for better emergence compared to conventional tillage systems. The seed longevity of at least 3 years in the soil and the prolonged emergence patterns between autumn and spring have posed great difficulties for the long-term management of C. bonariensis .     

Correlation between the soil seed bank and weed populations in maize fields

Annual weed populations establish every year from persistent seed banks in the soil. This 3 year study investigated the relationship between the number of weed seeds in the soil seed bank and the resultant populations of major broadleaf and grass weeds in 30 maize fields. After planting the crop, 1 m² areas were protected from the pre-emergence herbicide application. Soil samples were collected soon after spraying to a depth of 100 mm and the weed seeds therein were enumerated. The emerged weed seedlings in the field sampling areas were counted over the following 8 weeks. Up to 67 broadleaf species and five grass weeds were identified, although not all were found at every site and some were specific to a region or soil type. For the most abundant weeds in the field plots, on average 2.1–8.2% of the seeds of the broadleaf species and 6.2–11.9% of the seeds of the grass weeds in the soil seed bank emerged in any one year, depending on the species. Overall, the results showed a strong linear relationship between the seed numbers in the soil and the seedling numbers in the field for all the grasses and for most broadleaf weeds. For some species, like Trifolium repens , only a weak relationship was observed. In the case of Chenopodium album , which had the largest seed bank, there was evidence of asymptotic behavior, with seedling emergence leveling off at high seed numbers. An estimate of the soil seed bank combined with knowledge of the germination and behavior of specific weed species would thus have good potential for predicting future weed infestations in maize fields.     

The effect of maize residues and tillage on emergence of Setaria faberi, Abutilon theophrasti, Amaranthus retroflexus and Chenopodium album

Tillage and maize (Zea mays L.) residues at up to four times the base level had variable effects on the emergence of four annual weed species in the field. Environmental conditions varied during the three years of the research and interacted with residue and tillage to govern seedling emergence. When tillage affected Setaria faberi Herrm., emergence was greater in untillcd than tilled plots. The effect of residues varied among years. Abutilon theophrasti Medik, emergence from tilled soil was greater than from untilled soil in two of three years. Maize residue at two or four times the base levei reduced emergence. Amaranthus retroflexus L. emergence was often greater from untilled than tilled soil. The effect of maize residues on this species was dependent on tillage and precipitation. Chenopodium album L. emergence was affected by tillage and residues but differences over the three years were inconsistent. Results of this research indicate that tillage and residues interact with weed species, precipitation and other factors to regulate seedling emergence. The reduced soil disturbance and minimal weed seed burial associated with the elimination of tillage appear to have a greater impact on weed population dynamics than surface residues in non-tillage maize production systems.     

Effect of burial depth and soil water regime on the fate of Lithospermum arvense seeds in relation to burial time

Lithospermum arvense is an increasing annual weed in winter crops of the semiarid region of southern Argentina under low impact tillage systems, an agricultural practice that has become popular in recent years. Seed distribution in the soil profile under conventional tillage will change when reduced tillage is implemented, thus affecting the germination microenvironment. The effect of seed burial depth and soil water regime on field germination, enforced dormancy, innate dormancy and seed decay was studied in relation to burial time in a field experiment. In addition, the effect of burial depth on seed germination and seedling emergence was examined under laboratory controlled conditions. Field germination of buried seed ranged from 55% to 65% for shallow (2 cm) and from 5% to 30% for greater depths (20 cm). Enforced dormancy levels were significantly higher among deeper seeds. The amount of innate dormant seeds was reduced to <10% after a year of burial. Lithospermum arvense seedbanks can be classified as short-term persistent. Germination in the laboratory was unaffected by burial depth, while seedling emergence reduction was adequately described by a sigmoidal model. Results indicate that agricultural practices that accumulate L. arvense seeds near the soil surface enhance seedling recruitment.     

Factors affecting seed germination and emergence of button grass (Dactyloctenium radulans) (R.Br.) P.Beauv.

Button grass (Dactyloctenium radulans) is a native, widely spread summer grass weed species in Australia. However, limited information is available on the seed germination biology of this species. Experiments were conducted to evaluate the effect of environmental factors on the germination and emergence of two populations of D. radulans. The seeds of these populations were collected separately from Dalby, Queensland and Coleambally, NSW. Seeds were germinated at a range of constant and alternating temperatures (25/15, 30/20, 35/25 and 40/30°C day/night). The greatest seed germination was at a constant temperature of 30°C. Seed germination was reduced at the lowest alternating temperature (25/15°C). Germination of both populations was strongly stimulated by light, suggesting a great amount of emergence of D. radulans on bare ground, such as crop seedbeds. Germination of the D. radulans population collected from a northern cotton farming system (Dalby) was more tolerant to a greater range of salt stress than the population sourced from the south (Coleambally). Seeds of both populations germinated over a wide range of pH, between 4 and 10. However, germination was the greatest in a high pH buffer solution, indicating that the species prefers to germinate in alkaline soil. These results showed that D. radulans seeds possess a wide range of tolerance mechanisms to different environmental stresses. Information obtained in this study will help in developing more sustainable and effective integrated weed management strategies for the control of this weed and weeds with similar responses in summer cropping systems, such as cotton.     

Seed survival and patterns of seedling emergence studies of Rottboellia cochinchinensis (Lour.) W.D. Clayton in cultivated soils

The longevity of buried Rottboellia cochinchinensis (Lour.) W.D. Clayton seed represents a major survival mechanism for the weed, enabling the persistence of a continuing source of weed seeds in crop land. The pattern of seed persistence and depletion of R. cochinchinensis in cultivated maize soils was investigated by means of (1) studies on the effect of depth and duration of burial on the viability of the weed seeds, (2) quantitative estimation of the seed population and viability in cultivated fields, and (3) the periodicity of emergence and effects of cultivation on seed germination both in the field and in the greenhouse. The results indicated that the mode of persistence was innate (8.5%) and enforced (35%) dormancy after 1 year of burial, and that the persistency component of the seed population on cultivated soils ranged from 40.60%. The weed was able to remain viable at depths of 45 cm, indicating an excellent mechanism of escaping the effects of most soil-applied herbicides, and it was shown that tillage increases the depletion rate of the weed seed reserve by 32% per year.     

Fates of Setaria faberi and Abutilon theophrasti seeds in three crop rotation systems

Weed seeds in and on the soil are the primary cause of weed infestations in arable fields. Previous studies have documented reductions in weed seedbanks due to cropping system diversification through extended rotation sequences, but the impacts of different rotation systems on additions to and losses from weed seedbanks remain poorly understood. We conducted an experiment in Iowa, USA, to determine the fates of Setaria faberi and Abutilon theophrasti seeds in 2‐, 3‐ and 4‐year crop rotation systems when seed additions to the soil seedbank were restricted to a single pulse at the initiation of the study. Over the course of the experiment, seedlings were removed as they emerged and prevented from producing new seeds. After 41 months, seed population densities dropped >85% for S. faberi and >65% for A. theophrasti, but differences between rotation systems in the magnitude of seedbank reductions were not detected. Most of the reductions in seedbank densities took place from autumn through early spring in the first 5 months following seed deposition, before seedling emergence occurred, suggesting that seed predation and/or seed decay was important. For S. faberi, total cumulative seedling emergence and total seed mortality did not differ between rotation systems. In contrast, for A. theophrasti, seedling emergence was 71% lower and seed mortality was 83% greater in the 3‐ and 4‐year rotation systems than in the 2‐year system. Results of this study indicate that for certain weed species, such as A. theophrasti, crop rotation systems can strongly affect life‐history processes associated with soil seedbanks.     

The demography of Datura ferox (L.) in soybean crops

The emergence, survival, seed production and seed dispersal of Datura ferox was studied in soybean fields in 1982–1983 and 1984–1985. Most seedling emergence occurred within one month of crop sowing. Later germination, associated with inter-row cultivation, represented 4–26% of the total seedlings, and none survived to seed production. Only 5% of the first cohort in 1982–1983, and 7% in 1984–1985, survived to seed production; it was independent of initial density. Although weed density was greatly reduced by control measures, negative relationships were observed between peak seedling density and plant height, stem diameter, number of ramifications, number of reproductive structures and seed production per plant. Only a small proportion of seeds (about 1%) were shed prior to soybean harvest. Combine harvesters collected more than 90% of capsules, but between 7% and 40% of the seeds were returned to the field. Seed viability was unaffected by passing through the machine. The patterns of seed dispersal varied depending on the design of the combine harvester. Two models shed seeds between 0 m and 21 m from their source, but another shed seeds between 0 m and 98 m. Calculations, based in life history parameters, showed that weed seed production would increase more rapidly if the seeds were dispersed during crop harvesting than if they arc not, even when the return of seeds to the soil by the combine is not large.     

Seed germination and seedling emergence of Iberian starthistle (Centaurea iberica)

Centaurea iberica has become a problematic weed in some regions of western Iran. Little published data are available in the literature regarding its seed germination and seedling emergence. Therefore, this study was conducted in order to evaluate the effects of different factors on C. iberica seed germination. The highest level of germination of C. iberica was achieved at fluctuating temperatures of 15/25°C (night/day). The seed germination of C. iberica was stimulated by light and little germination occurred under continuous darkness. The pH solution did not have any effect on its seed germination. Centaurea iberica was tolerant to both salt and water stress. The level of seedling emergence was greatest for the seeds that were located on the soil surface, declining with depth, and no seedling emerged from a soil depth of 4 cm. These results indicated that C. iberica has the potential to infest more fields in the western parts of Iran, particularly rainfed areas. Based on the results of this study, crops with a dense canopy and/or planted in narrow‐row intervals could be used to diminish the seed germination of C iberica. In addition, the adoption of tillage systems that bury the seeds of C. iberica under the 4 cm depth would effective in its management.     

Influence of after-ripening environments on the germination characteristics and seed fate of Italian ryegrass (Lolium multiflorum)

Italian ryegrass ( Lolium multiflorum Lam.) is an exotic winter annual weed that recently has seriously infested wheat fields in central Japan. To understand the influence of tillage systems on the germination ecology and seedbank dynamics of naturalized Italian ryegrass, we compared the fate of the seeds that were after-ripened in the soil with that of the seeds on the soil surface, and then examined the germination characteristics of the seeds retrieved from both treatments by germination tests in both a light/dark (12 h photoperiod) condition and in constant darkness. The seedling emergence was greater initially for the seeds after-ripened on the soil surface than for the seeds in the soil. The component of emergent seeds after-ripened on the soil surface increased as time passed during the summer, whereas that of emergent seeds in the soil scarcely increased. This contrasting emergence was, in part, attributable to the ability of the seeds to germinate at higher temperatures in the light/dark condition than in constant darkness. These results suggest that untilled systems, which leave many seeds on the soil surface, might promote the rapid depletion of Italian ryegrass seeds through germination before wheat sowing in early winter. In contrast, seed burial by tillage might inhibit the germination of the seeds and form a large transient seed bank available to germinate during the wheat-growing season.     

Effect of environmental conditions on Alopecurus myosuroides germination. II. Effect of moisture conditions and storage length

Summary More effective control of Alopecurus myosuroides with a minimum amount of herbicide may be achievable by using models describing the impact of cropping system effects on the weed's demography. In order to develop the submodel relating the weed seedbank to the emerged seedlings, a series of laboratory experiments was set up to analyse and quangify the effects on A. myosuroides germination of length of seed storage in dry conditions, soil water potential and dryness during imbibition. The base soil water potential for germination was estimated at −1.5 MPa. A four-parameter non-linear equation depending on accumulated day–degrees was fitted to the observed germination data, resulting in the estimation of parameters illustrating germination proportion and rate. Germination proportion and rate increased with seed storage length, and were increased by short and decreased by long dry periods occurring after imbibition. These results showed that, in contrast to crop species, A. myosuroides germination cannot be expressed simply as a function of hydrothermal time, but also requires the determination of the proportion of non-dormant seeds as a function of seed age and environmental conditions.     

Cropping systems modify soil biota effects on wheat (Triticum aestivum) growth and competitive ability

Plants alter soil biota which subsequently modifies plant growth, plant–plant interactions and plant community dynamics. While much research has been conducted on the magnitude and importance of soil biota effects (SBEs) in natural systems, little is known in agro‐ecosystems. We investigated whether agricultural management systems could affect SBEs impacts on crop growth and crop–weed competition. Utilising soil collected from eight paired farms, we evaluated the extent to which SBEs differed between conventional and organic farming systems. Soils were conditioned by growing two common annual weeds: Amaranthus retroflexus (redroot pigweed) or Avena fatua (wild oat). Soil biota effects were measured in wheat (Triticum aestivum) growth and crop–weed competition, with SBEs calculated as the natural log of plant biomass in pots inoculated with living soil divided by the plant biomass in pots inoculated with sterilised soil. SBEs were generally more positive when soil inoculum was collected from organic farms compared with conventional farms, suggesting that cropping systems modify the relative abundance of mutualistic and pathogenic organisms responsible for the observed SBEs. Also, as feedbacks became more positive, crop–weed competition decreased and facilitation increased. In annual cropping systems, SBEs can alter plant growth and crop–weed competition. By identifying the management practices that promote positive SBEs, producers can minimise the impacts of crop–weed competition and decrease their reliance on off‐farm chemical and mechanical inputs to control weeds, enhancing agroecosystem sustainability.     

Seed survival and predation of Anoda cristata in soyabean crops

Anoda cristata is a troublesome annual broad-leaved weed in summer crops in the rolling Pampa in Argentina; seeds are the only source of regeneration of this species. Seed persistence or depletion is the result of survival and loss processes, including predation. The objective of this study was to determine survival at two burial depths in undisturbed soil and predation rates of A. cristata seeds in soyabean crops in different rotations and tillage systems. Survival was discontinuous and decreased to 25% after 35 months, after which no further reduction in survival was observed to the end of the experiment at 96 months. No differences in seed survival between seeds placed on the soil surface and buried 5 cm below the soil surface were found at 80 months, but at later times survival was lower for seeds placed on the soil surface. Predation rates ranged between 0.3% day⁻¹ and 6.7% day⁻¹. Of the models tested, a polynomial regression of the rate of predation with time gave the best representation of seed predation. From January to July, predation was higher in non-tillage plots in the wheat/soyabean rotation. There was no significant difference in predation rates between tillage systems in the soyabean monoculture and no difference between planting densities. Higher crop residue levels in non-tillage plots in the wheat/soyabean rotation was the dominant factor influencing seed predation, probably because such habitat favours the presence of seed predators.