Post-harvest Tillage Research Articles

Effect of Some Tillage Systems on Surface Runoff and Soil Erosion in Northern Gedarif Area, Sudan

A study was carried out for three consecutive seasons (2005/06, 2006/07 and 2007/08) under rain- fed condition, to investigate the effectof some tillage systems on surface runoff and soil erosion in northernGedarif. The study was conducted at the pilot farm of the Faculty ofAgricultural Sciences and Environment, University of Gedarif ,in thenorthern area of Gedarif State ( Latitude 12° 45′ N, Longitude 35° 15′ Eand 540 m above sea level ). The experimental design was randomizedcomplete block with three replications. Treatment were three tillagesystems: No tillage or zero tillage (ZT), offset disc as post harvest tillage(PHT) and wide level disc, farmers practices as control ( WLD ). Raingauge was used to measure the rainfall, whilst the surface runoff and soillosses were measured using runoff plot technique. Total recorded annualrainfall was 368.1mm (2005), 463.6 mm (2006) and 495.2 mm (2007)which was spread over 32, 30 and 32 rainy days during the first , secondand third growing seasons, respectively. The results showed that thesecond season had the best distribution and satisfaction pattern. Itrecorded 15 %, 36 %, 26 % and 5 % for July, August, September andOctober, respectively, compared to 24 % ,53 % 13 % and 2 % ; and 29% ,41 % , 21 % and 1 % for first and third seasons in the same months.Zero tillage treatment showed more runoff and soil loss than PHT andWLD. In terms of accumulation, ZT produced more runoff by 28 % and 9% and soil loss by 53 % and 28 % over PHT and WLD respectively forfirst season ,30 % and 13 % runoff and 28 % and 13 % soil loss for thesecond season and 55 % and 23 % runoff and 105 % and 24 % soil lossfor third season . The post harvest tillage reduced average annual runoffand soil loss to the lowest values compared to the Wide level disk andZ T.

Modeling dynamic soil carbon attributes among common southern New England land uses

Tracking changes in the quantity and variability of soil organic carbon (SOC) stocks associated with different land uses over time is a critical step in understanding decadal-scale impacts of soils on climate change, and can be an important reality check for more complex modeling efforts. In this study, we used a Bayesian statistical framework to quantify and compare SOC stocks among common southern New England land use types (sod farms, silage corn, forest, and turfgrass), including sod fields in continuous production for different periods of time (approximately 10, 20, and 30 years). Further, we modeled the export of SOC associated with sod harvesting, propagating uncertainty from observations to export estimates. Despite unsustainable annual rates of soil removal (74 to 114 Mg ha−1), SOC stocks for sod fields in production for different time periods were not credibly lower than those of the other land uses examined. Mean exported SOC from sod harvest ranged from 1.67 to 3.23 Mg ha−1, which was enough to entirely deplete the 0–30 cm SOC stock in approximately 30 years. These results suggest that organic C inputs to the upper 30 cm of sod farm soils, from subsoil incorporation during post-harvest tillage and belowground net primary production, may have been maintaining SOC by offsetting loses over several decades. This is unlikely to continue, however, if the eolian mantle that characterizes these soils is depleted due to the cumulative impact of sod harvest on soil removal.

Three decades of field surveys reveal a decline of arable bryophytes in the Swiss lowlands despite agri-environment schemes

Agricultural intensification represents one of the major drivers for the dramatic loss of biodiversity worldwide. To halt the decline of farmland biodiversity, Switzerland adopted agri-environment schemes (AES) in 1998. Here, we monitored the occurrence, abundance and habitats of two species of arable bryophyte specialists, the Field hornwort (Anthoceros agrestis) and the Carolina hornwort (Phaeoceros carolinianus), in 28 crop fields in the intensively cultivated Swiss Plateau from 1991–2018, to investigate the effects of arable management, AES directives, and weather conditions on their performance. The target species are characteristic of the specialized short-lived arable bryophyte flora of Central Europe that depend on bare substrate in low-intensively cultivated and regularly ploughed fields. Trends in their occurrence thus reflect in many respects the status of the arable bryophytes in cultivated fields. Hornwort occurrence significantly declined between 1991 and 2018. A strong decrease in stubble fields that remain unmanaged after harvest, the favourite habitat for many arable specialists in the study area, largely accounted for the decline. Stubble fields nearly disappeared in the study area because of a gradual reduction in the cultivation area of cereals and the increasing practice of immediate post-harvest tillage. The latter is common in intensive arable farming and was accentuated by AES directives amended in 2005. Hornwort occurrences were positively affected by high air humidity during summer, but weather effects were subordinate to management effects. We propose tailored amendments of AES regulations, that are implemented at selected sites, to maintain the characteristic arable specialist bryophytes in the Swiss Plateau: crop rotation with adequate proportions of cereals that are regularly ploughed but not before the end of October, no post-harvest processing of stubble fields, and optimization of the existing instrument ‘Biodiversity Promoting Areas’, e.g., short-term fallows in crop fields. Late-autumn or overwintering stubbles and short-term fallows will benefit many other organisms that depend on extensively managed open habitats, for example arable wildflowers, farmland breeding birds and specialized arthropods.

Efficiency of disc harrow adjustment for stubble tillage quality and fuel consumption

The compact disc harrow due to post-harvest tillage is used to incorporate the stubble and plant residues into soil, to induce their decomposition and to increase mineralization. The high-cut winter rape stubble is often main challenge of clear disc harrowing, especially in clay loam soil at minimum expenditure of fuel consumption. The aim of this study was to find optimal tillage performances and determine the fuel consumption what required to achieve the preferred level of stubble tillage in loam and clay loam soil after winter oilseed rape harvest. The tillage quality and fuel consumption were investigated in dependence on harrow disc angle (10°, 15° and 20°), tillage depth (5 and 8 cm) and working speed (1.4; 1.9; 2.5; 3.1; 3.6 m∙s−1). The tractor “CASE 135″ was instrumented with data acquisition system and was used to measure fuel consumption, actual working speed and implement draft. Research developed the efficient adjustment of aggregate regime mode to the best soil structure and plant residue incorporation. The beneficial relationship was established by obtaining tillage quality level to fuel consumption, which varied from 2.6 to 5.9 L·ha−1 in depending of soil type (loam and clay loam). Based on research results, the optimal fuel consumption (2.85 L·ha−1) was identified at disk harrow adjustment: disc angle 10°, working speed 3.5 m∙s-1 on both soils, but in different tillage depth 8 cm on loam and 5 cm on clay loam soil.

Weed Seedbank and Weed Biomass Dynamics in a Long-Term Organic Vegetable Cropping Systems Experiment

AbstractMost previous research on changes in weed abundance and community composition in cropping systems has focused on field crops. The study presented here examined changes in the weed seedbank and aboveground biomass in four organic vegetable cropping systems over a 10-yr period. The systems included an Intensive system with six crops per 4-yr rotation, an Intermediate system with one cash crop per year, a Bio-extensive system with alternating cash crop and tilled fallow years plus prevention of seed rain, and a Ridge-tillage system with one cash crop per year. Systems also differed in the types and number of cover crops between cash crops. During the course of the experiment, the weed community shifted from one dominated by summer annual broadleaf species that reproduce at the end of their lives to a community dominated by summer and winter annuals that mature rapidly. This shift in community composition can be attributed to the change in land use from conventionally managed corn (Zea maysL.) and alfalfa (Medicago sativaL.) to organic vegetable production. In particular, crop rotations with diverse preplantings and postharvest tillage dates interrupted the life cycle of common lambsquarters (Chenopodium albumL.) and pigweed species (Amaranthusspp.: mostly Powell amaranth [Amaranthus powelliiS. Watson], with small numbers of redroot pigweed [Amaranthus retroflexusL.] and smooth pigweed [Amaranthus hybridusL.]), while favoring a diverse assemblage of quickly maturing species. The study thus demonstrates that an appropriate crop rotation can control the seedbank of weeds likeC. albumthat potentially persist well in the soil. The Ridge-tillage system greatly reduced the frequency and depth of tillage relative to other systems while effectively suppressing perennial weeds. The early-reproducing annuals, however, became more abundant in the Ridge-tillage system than in the other systems, primarily due to escapes along the edge of the scraped ridges. The tilled fallow periods coupled with prevention of seed rain in the Bio-extensive system substantially reduced weed abundance through time and relative to the other systems.

Timing and depth of post-harvest soil disturbance can reduce seedbank and volunteers of oilseed rape

Appropriate timing of post-harvest tillage to oilseed rape (OSR, Brassica napus L.) is crucial for the creation of a soil seed bank and unwanted OSR volunteers. Existing recommendations, however, can contrast with needs for early post-harvest tillage e.g. for pest control. To specify and to systematically further improve preventive volunteer management through post-harvest tillage of imidazolinone-tolerant oilseed rape (Clearfield®; CL OSR), field experiments were set up at two locations in two separate trial periods at each location (2013–2014 and 2014–2015) in south-west Germany. After OSR harvest, and average harvest losses of 1500 m−2 seeds, or artificially broadcasting of 20000 OSR seeds m−2, stubble tillage was performed at weekly intervals (immediate (0), 1, 2, 3, and 4 weeks) at each of three depths (1–2, 6–8, and 15–17cm). To depict a worst case scenario in which herbicides were ineffective, no herbicides were applied. There were significantly smaller soil seed banks found in spring the longer the period lasted between seed rain and stubble tillage; 265 vs 145 seeds m−2 referred to 0 week vs. 4 weeks on average. Depth of stubble tillage had no significant effects on the seed number in the soil. In the first spring after seed loss, 0–2.6 CL OSR volunteers m−2 were found in the winter wheat, and the number decreased with delayed timing depth of stubble tillage. These volunteers mainly emerged in the treatment of shallow stubble tillage (1–2cm), with 0.7-0.9 flowering volunteer m−2, while volunteers averaged less than 0.04 plants m−2 in the treatment “15–17cm”. OSR volunteers in winter wheat got ripened only in one out of the four fields, and produced 1.0 seed m−2 on average. The delay between harvest and stubble tillage can be limited to approximately three weeks if stubble tillage is performed at a depth of about 6–8cm; further delay did not bring additional advantage. We recommend to retain the stubble for three weeks as further delay does not bring additional advantage, and then to apply stubble tillage deeper than 6cm. Very superficial or shallow stubble tillage should be avoided. This procedure seems appropriate for avoiding oilseed rape volunteers without use of herbicides.

Weed Seed Fate during Summer Fallow: The Importance of Seed Predation and Seed Burial

Maximizing weed seed exposure to seed predators by delaying post-harvest tillage has been suggested as a way to increase weed seed loss to predation in arable fields. However, in some areas of northeastern Spain, fields are still tilled promptly after cereal harvest. Tillage usually places seeds in a safer environment compared to the soil surface, but it can also increase seed mortality through seed decay and fatal germination. By burying the seeds, tillage also prevents weed seed predation. Weed seed fate in a tilled vs. a no-till environment was investigated during the summer fallow months in three cereal fields in semi-arid northeastern Spain. Rigid ryegrass and catchweed bedstraw seeds were used. Predation rates were measured in a no-till area within each field in 48-h periods every 3 wk, and long-term predation rates were estimated. Fate of buried seeds was measured by burying 20 nylon bags with 30 seeds of each weed species from July to September at a depth of 6 cm in a tilled area contiguous to the no-till area. Predation rates over the entire summer were 62% and 49% for rigid ryegrass and catchweed bedstraw, respectively. High availability of crop seeds (preferred by ants) on the soil surface may have decreased predation of weed seeds early in the season. Seed loss due to burial was 54% and 33% for rigid ryegrass and catchweed bedstraw, respectively. Unusual above-average precipitation probably prompted higher than normal weed germination rates (fatal germination) in some fields, and thus led to higher seed mortality rates compared with an average year. These results suggest that leaving the fields untilled after harvest may be the optimum strategy to reduce inputs to the weed seedbank during the summer fallow period in semi-arid systems.

Flat-cutting loosening in the system of fallow cultivation of chernozem soil and weediness of crops

The article presents the results of field experiments, where on the basis of podsolized heavy loamy chernozem the influence of replacement of mouldboard ploughing with nonmouldboard cultivation over top soil weediness, weediness at the beginning and end of spring crop vegetation and weed species composition before harve sting were studied. Investigation methods of main fall ploughing under spring crops of five-course rotation: soybeans–rape–wheat–flax–barley at the depths of 15-17, 20-22, 25-27 cm were conducted after post-harvest field tillage.
 Analysis of data on contamination of the top soil with weed seeds have shown that with the replacement of fall main mouldboard ploughing gwith nonmouldboard cultivation the figure before sowing of all crops withdifferent tillage depthat crop rotation average increased by 131-132%. It caused the increase of actual weed infestation of all crops and at the beginning and end of spring crop vegetationafter different depths of fall nonmouldboard cultivation compared with ploughing at crop rotation average it was 120–132 and 123-138%respectively.
 Species composition of weeds afterthe replacement of main fall mouldboard ploughing with nonmouldboard cultivation remained mainlyunchanged; although in rape plantings the proportion of white campion and early spring weed sincreased, in wheat plantings– wild mustard andscentless mayweed, insoybean plantings– late spring weeds, in flax plantings– white campion, and in barley plantings– scarlet pimpernel.

Cereal stem borer management practices in subsistence farms of eastern Ethiopia

ABSTRACTIn eastern Ethiopia, empirical information regarding farmers’ perceptions and implementation of research results about stem borer management is either scarce or unavailable. A survey of 120 farmers from four maize- and sorghum-growing districts of eastern Ethiopia was carried out in 2014 to study common management practices of cereal stem borers. Drought, pests, and land shortage were reported as the main constraints to maize and sorghum production in the area. Stem borers were perceived as the most important pests in these crops. The estimated yield losses from stem borers ranged from 10% to 50%. The majority of the farmers reported not using chemical insecticides to control these pests due to lack of capital, unavailability, and lack of knowledge. Moreover, most farmers were not using improved maize varieties. Cultural practices were found to be the most promising control method of cereal stem borers. Despite differences among districts, farmers practiced crop rotation, intercropping, manipulation of planting dates, crop residue disposal, and post-harvest tillage as common control strategies, even though a considerable proportion of the farmers was not implementing these practices sufficiently. The design of appropriate strategies for stem borer management based on farmers’ needs and priorities should be promoted.

Post-harvest summer tillage to control wind erosion in the Khanasser Valley, Syria

Abstract Northern Syria is an arid and semi-arid region prone to land degradation by wind erosion. In this region lies the Khanasser Valley, where intensive grazing of cumin and barley stubble during the hot, dry and long summers leaves insufficient residues to protect the soil surface against wind erosion. The sheep’s hooves pulverize the soil crust, further enhancing wind erosion. The objective of this research was to assess the effect of post-harvest tillage and sheep grazing on soil transport rate during the dry summer months. The grazing treatments were heavy grazing, light grazing, and no-grazing. The tillage treatments were post-harvest tillage (one or two passes) and no-tillage. Eroding soil transport rate (horizontal movement of wind-blown sediment) was measured using Big Spring Number Eight (BSNE) sediment samplers during the summers of 2003–2005. Wind-blown sediment movement was 24% higher in grazed, tilled treatments than in non-grazed, non-tilled treatments. Under both heavy and light grazing, post-harvest one-pass tillage resulted in approximately 20% less sediment movement than not tilling. This reduction in sediment movement was probably related to the rougher surface created by tillage. Sediment movement in grazed fields was 42% higher after two tillage passes compared to grazed fields that were not tilled at all. This was likely caused by pulverization of the dry soil by the two tillage passes destroying the roughness created with just one tillage pass. Calculated soil surface random factor K′ showed lower values in the tilled treatments and higher values in the untilled treatments and the highest value associated with the 2 tillage passes. This study shows that sheep grazing is an important factor causing wind erosion, while excessive tillage renders the soil surface even more susceptible to wind erosion. Transport rate for all treatments, measured at all sites, was positively related to the wind factor (Wf) based on threshold wind speeds of 5 and 7 m/s, although the Wf was relatively low. Although further comparisons of tillage effects are necessary, the results suggest that one pass of a shallow duck-foot cultivator may be considered as a short-term, emergency tillage practice to aid in wind erosion control during the dry summer months in arid and semi-arid areas.

Postharvest Tillage Reduces Downy Brome (Bromus tectorumL.) Infestations in Winter Wheat

In the Pacific Northwest, downy brome continues to infest winter wheat, especially in low-rainfall areas where the winter wheat–summer fallow rotation is the dominant production system. In Washington, a study was conducted for 2 yr at two locations in the winter wheat–summer fallow region to determine the influence of four postharvest tillage treatments on vertical seed movement, seedbank depletion, and plant densities of downy brome. The four tillage implements included a disk, sweep plow, harrow, and skew treader. The study also included a no-till treatment for comparison. The sweep plow and disk led to the most vertical movement of downy brome seed compared with the no-till treatment. Approximately 75% of the fall postharvest seed in the no-till treatment was located either on the soil surface or in the 0- to 3-cm depth at both locations. In contrast, 75% of the seed in the disked treatment was located from 0 to 6 cm deep at both locations. The disk and sweep plow both decreased downy brome seed in the soil at the 0- to 3-cm depth compared with the harrow and no-till treatments. There was no difference in downy brome plant densities following postharvest tillage in the summer fallow due to any of the treatments. However, plant densities in the subsequent winter wheat crop were reduced by the disk and sweep plow compared with the no-till and skew-treader treatments. In general, seed densities as affected by the skew treader fell between the disk and the no-till treatments. The use of the sweep plow and the disk should be integrated into a weed management strategy for downy brome in the wheat–fallow region of the Pacific Northwest.

Evaluating the Cloude–Pottier and Freeman–Durden scattering decompositions for distinguishing between unharvested and post-harvest agricultural fields

This study evaluates the utility of the Cloude–Pottier and Freeman–Durden scattering decompositions for providing agricultural land surface information during autumn months using C-band polarimetric RADARSAT-2 data. We applied these decompositions over 94 agricultural fields in Southern Ontario, Canada, to characterize scattering mechanisms from unharvested senesced crops and harvested fields with three generalized soil tillage practices. The decompositions were applied to RADARSAT-2 images over six dates during October and November 2010 at high (49°) and low (23°) incidence angles. Agreement was found between the decompositions for the identification of primary (volume and rough surface scatter) scattering mechanisms for the senesced unharvested crops and the harvested fields. Significant statistical separability was observed between the strengths of decomposition parameters when comparing (i) senesced unharvested crops to post-harvest conventional tillage fields and (ii) post-harvest no tillage fields to post-harvest conventional tillage fields. These results suggest that high accuracy classifications may be possible with these data; however, weak separability was observed when comparing fields with conservation tillage. The strongest separability was observed with Entropy and α-angle of the Cloude–Pottier decomposition and the rough surface scattering component of the Freeman–Durden decomposition, suggesting sensitivity of these parameters to surface roughness and crop residue. Results also demonstrated that superior separability was found with the data at the higher 49° incidence angle in contrast to data acquired at the lower 23° incidence angle imagery.

Molecular marker-based identification of oilseed rape volunteers with different secondary dormancy levels in oilseed rape fields

Pod dehiscence of oilseed rape (OSR) occurs before and during harvest, resulting in seed losses and in seed persistence in the soil for several years. Persisting seeds can emerge as volunteers in subsequent crops. Volunteers with deviating traits and especially genetically modified (GM) oilseed rape volunteers can impair the product quality of an oilseed rape crop. Under experimental field conditions seed persistence and volunteer abundance were found to be efficiently controlled by delayed post-harvest tillage and selection of cultivars with low secondary seed dormancy.To investigate the long-term factors affecting volunteer abundance in farmer-managed fields, an on-farm survey was carried out in winter oilseed rape fields at different locations in Germany, using artificial sowing gaps as one method to detect putative volunteers. Molecular marker analysis (ISSR-PCR), which was performed for 11 out of 31 fields, confirmed that most of the plants identified within sowing gaps were indeed volunteers. In fields with low OSR cropping frequency high percentages of volunteers could be assigned to previously cultivated varieties. Results indicate that seeds of varieties with high secondary dormancy (HD) persist in the fields for longer times and in larger numbers than seeds of varieties with low secondary dormancy. However, cultivation of HD varieties did not necessarily result in high volunteer abundance, as location and management factors have further impact on long-term seed survival. Nevertheless, with respect to GM oilseed rape cultivation proper variety selection will be an important means to assure co-existence with conventional oilseed rape.

Potencjał techniczny gospodarstw specjalizujących się w produkcji buraków cukrowych

The survey investigates into equipment of sugar beet farms of the Lublin region, Poland, with machinery – with reference to plantation size and yields. To assess the production potential of the farms, the authors determined the age structure of the machinery owned by the farmers and established the scale of investment in new equipment. The machinery most important for sugar beet production are pre-sowing and post-harvest tillage units, sprayers, seed drills, combine harvesters and self-unloading trailers. In most cases, the surveyed farmers own most of these machines, but they are often obsolete: 37% of them is in operation for more than 15 years. As for the machines dedicated solely to sugar beet growing (harvesters and seeders), their age structure is most unfavourable – 70% of them have been used for over 15 years. A trend towards increasing plantation sizes provides incentives for introducing innovation to cultivation methods. However, the scale of investment in new machinery is small, especially in the case of small and medium-sized farms that dominate in the region. The authors surveyed also the scale of using professional services in the field of tillage processes to determine changes in farming practices.

Effects of Harvest Residue and Tillage on Lesser Cornstalk Borer (Lepidoptera: Pyralidae) Damage to Sugarcane

Lesser cornstalk borer, Elasmopalpus lignosellus (Zeller) (Lepidoptera: Pyralidae) is an important pest of sugarcane (a complex hybrid of Saccharum spp.) in southern Florida. Cultural controls for E. lignosellus were evaluated in preparation for the potential loss of effective insecticides. Field studies conducted in 2006 compared the effects of harvest residues from green-harvested sugarcane (no preharvest burning to remove leaf matter) on E. lignosellus stalk damage and yield. Damage by E. lignosellus was significantly lower in plant cane plots that were covered with harvest residues collected from a green-harvested field before shoot emergence compared with plots without harvest residue. There were no yield differences between plots with and without harvest residues in plant or ratoon sugarcane fields in the 2006 study. The effects of three postharvest tillage levels (conventional, intermediate, and no tillage) were evaluated in preharvest burned and green-harvested fields in 2008 and 2009. Significantly less E. lignosellus damage was observed in the green- versus preharvest burned fields in both years. Intermediate and no-tillage plots had very little damage in green-harvested field. Conventional tillage plots had the greatest damage in the green-harvested field and the lowest damage in the preharvest burned field. In 2008, biomass yield was greater in the intermediate than conventional tillage in the green-harvested field, but it was greater in the conventional than in other tillage levels in the preharvest burned field. These studies demonstrated that cultural controls could greatly reduce E. lignosellus damage in sugarcane without the use of insecticides.

Earthworm populations in relation to soil organic matter dynamics and management in California tomato cropping systems

Earthworms are key regulators of soil structure and soil organic matter (SOM) dynamics in many agroecosystems. They are greatly impacted by agricultural management, yet little is known about how these factors interact to control SOM dynamics. This study sought to explore linkages between agricultural management, earthworms and aggregate associated SOM dynamics through a survey of tomato ( Solanum lycopersicum L.) cropping systems in northern California. Earthworms and soil samples were collected between February and April of 2005 from 16 fields under one of three types of residue management: (1) tomato mulch – no postharvest tillage and tomato residues left on the soil surface, (2) cover crop – tomato residues tilled in and leguminous cover crop planted, and (3) bare fallow – tomato residues tilled in and soil surface left exposed throughout the winter. Earthworms were collected via hand-sorting and identified to species, while soils were wet sieved to yield four aggregate size classes: large macroaggregates (>2000 μm), small macroaggregates (250–2000 μm), microaggregates (53–250 μm) and the silt and clay fraction (<53 μm). The combined large and small macroaggregate fraction was then fractionated into coarse particulate organic matter (cPOM; 250 μm), microaggregates within macroaggregates (mM; 53–250 μm) and macroaggregate occluded silt and clay (Msc; <53 μm). The earthworms identified in this survey were composed entirely of exotic species and were dominated by Aporrectodea caliginosa. Earthworm abundance was related to residue management, with the tomato mulch systems averaging 4.5 times greater fresh earthworm biomass than bare fallow ( P = 0.024). Aggregate stability and total soil C and N also appeared to be influenced by residue management, such that the tomato mulch system displayed significantly greater mean weight diameters than the bare fallow system ( P = 0.049), as well as more than 50% greater total soil C and N ( P = 0.049 and P = 0.036; respectively). Earthworm biomass was also found to be positively correlated with total soil C ( P = 0.009, R 2 = 0.39) and N ( P = 0.010, R 2 = 0.039) as well as the proportion of macroaggregate C in the cPOM fraction ( P = 0.028, R 2 = 0.30). Our findings suggest that residue handling and the associated management practices (e.g., tillage, organic vs. conventional agriculture) are important for both earthworm populations and SOM storage. Although earthworms are known to influence SOM in many ways, other factors appear to play a more prominent role in governing aggregate associated SOM dynamics.

Post-harvest gene escape and approaches for minimizing it.

Abstract Data about gene escape by seeds and volunteers were compiled for the first time in one study for several crops, i.e. wheat ( Triticum aestivum ), sugar beet ( Beta vulgaris ), oilseed rape/canola ( Brassica napus ) and maize ( Zea mays ). These species represent important genetically modified (GM) crops with herbicide tolerance (HT) or insect resistance (Bt), show different levels of autogamy and allogamy and are grown in different climatic zones of the world. Post-harvest measures and strategies were identified for minimizing gene escape from these crops. All species were found to cause problems in terms of gene escape by seed and volunteers though there are important differences between species and climatic zones. Post-harvest tillage was identified as a key factor for reducing the soil seed bank and volunteers. Timing and intensity of tillage has to be specifically adapted to the dormancy characteristics of each species. Furthermore, there is a close interaction between gene escape and the cropping system. Rotations should avoid the same crop or other critical crops in temporal vicinity to the GM crop in order to keep volunteer populations below a critical density. In no-till systems with use of HT varieties, HT volunteers can reduce the efficiency of the whole system if additional herbicides have to be applied. Seed impurities and admixtures during seed production are another major source of gene escape. Since seed lots of certified growers present less adventitious presence of other varieties, these should be preferred to farm-saved seeds. Education of farmers, cleaning of equipment, control measures and separate production and supply chains are additionally important to minimize gene escape.

Ecology and Control of Russian Thistle (Salsola iberica) After Spring Wheat Harvest

Russian thistle is the most problematic broadleaf weed for spring-sown crops in the low-precipitation (&lt; 340 mm yr−1) region of the inland Pacific Northwest of the United States. A 6-yr field experiment was conducted at Lind, WA, to evaluate three postharvest control strategies for Russian thistle in continuous annual spring wheat. Postharvest treatments were (1) tillage with low-disturbance overlapping undercutter V-blade sweeps; (2) paraquat + diuron at the labeled rate, which is widely used by farmers; and (3) an untreated check (letting Russian thistle grow unhindered). The undercutter V-sweep consistently killed all Russian thistle with essentially no residue burial, and no seed was produced. In contrast, the paraquat + diuron treatment halted Russian thistle dry biomass production, but plants continued to extract soil water and produce an average of 310 seeds m−2on the lower branches. In the check, Russian thistle produced an average of 700 kg ha−1postharvest dry biomass and 5,670 seeds m−2. The undercutter V-sweep treatment had significantly more water in the 180-cm soil profile at time of wheat harvest, after a killing frost in October, and in mid March as well as greater spring wheat grain yield compared with the herbicide and check treatments. Results show that postharvest tillage with an undercutter V-sweep consistently achieved 100% control, retained ample wheat residue on the surface to control erosion, and was by far the most effective treatment in this experiment.

Fecundity of volunteer oilseed rape and estimation of potential gene dispersal by a practice-related model

Abstract Oilseed rape volunteers were able to flower and to set seed in winter wheat and winter barley. The flowering period of the volunteers coincided with the flowering of related wild species which are potential crossing partners, but there was only a short period of synchrony with the flowering period of the sown oilseed rape. Consequently, cross-pollination of volunteers with wild species and sown oilseed rape can potentially occur, even if the number of fertile hybrid offspring is predicted to be small. The number of seeds/volunteer in cereal crops was about 10% of the usual seed number of sown oilseed rape. There were several factors causing this loss, particularly hares which heavily damaged volunteer oilseed rape in cereals. A maximum of 1 GM seed/m2 returned to the soil seed bank from oilseed rape volunteers in winter cereals. The seed productivity of oilseed rape volunteers in sown oilseed rape reached 45% of the sown oilseed rape crop. In a low-risk scenario (low volunteer density, low seed persistence), less than 0.1 GM seed/m2 returned to the soil seed bank. In a high-risk scenario (high volunteer density, high seed persistence), 519 GM seeds set by volunteers would replenish the soil seed bank. As a result of outcrossing an additional 0.4 GM seeds (low-risk: low outcrossing rate, low seed persistence) or 339 GM seeds (high-risk: high outcrossing rate, high seed persistence) set by conventionally bred oilseed rape would also enter the soil seed bank. The EU legislation limit for defining crop seeds as non-GM of 0.9% GM content, would be exceeded in both scenarios, but the low-risk scenario was only shortly beyond the threshold. The number of seeds entering the soil seed bank in high risk-situations can be reduced by measures to reduce seed persistence, such as delayed post-harvest tillage.

Reducing potential gene escape in time by appropriate post-harvest tillage—Evidence from field experiments with oilseed rape at 10 sites in Europe

Persistence of oilseed rapeseed in soil can result in weed problems but also reduce oil quality of following rape crops or result in unwanted gene escape which is particularly relevant in the context of genetically modified oilseed rape. In this paper data from 13 field experiments at sites in England, Austria and Germany are presented where tillage operations were tested that potentially reduce the build-up of a seed bank. In the majority of experiments seed losses were artificially simulated by broadcasting ca. 10,000 freshly ripened rapeseed m −2 onto cereal stubbles. Oilseed rapeseedlings in autumn, the seed bank in winter–spring and yields of the following crop winter wheat were assessed as a function of tillage regime. During summer and autumn 19–70% of the seeds germinated and emerged. This part of the population was killed by following tillage operations or herbicide applications. However, 0–29%, in moist years 0–5%, of the initially broadcasted seeds developed dormancy and remained ungerminated in the soil until the following winter–spring. Delaying incorporation of the seeds by leaving the stubble untouched for up to 4 weeks resulted in a reduced seed bank in almost every case. Also, repeated stubble tillage compared to an early single stubble tillage operation resulted in a smaller seed bank. The type of primary tillage (ploughing versus non-inversion cultivation) had no clear effect. No relation was found between the number of seedlings in autumn and the size of the seed bank the following winter–spring. Grain yield of the following crop winter wheat was not adversely affected by delayed stubble tillage. The results indicate that stubble tillage aiming at a reduced seed bank of oilseed rape should focus on conditions avoiding induction of secondary dormancy rather than improving germination conditions. This means that, under the climatic conditions of central and western Europe, the stubble should be left untouched for several weeks after harvest before starting the usual tillage sequence with stubble tillage and ploughing or a non-inversion tillage sequence.