Weed seed bank composition under three long-term tillage regimes on a fine sandy loam in Atlantic Canada

Tillage systems can influence weed seed viability and the distribution with depth of weed seeds in soil. To investigate this ‘tillage effect’, weed seed bank composition was determined at two soil depths (0–10 and 10–20 cm) in three tillage systems [mouldboard plough (MP), shallow tillage (ST), and direct drilling (DD)] established for 14 years on a sandy loam (Podzol) in Prince Edward Island, Atlantic Canada. The cropping system was a cool-season soybean (Glycine max L. Merr.) in rotation with barley (Hordeum vulgare L.). The objectives were to evaluate the size and composition of the viable soil seed bank, using the seedling germination method, and to determine if the adoption of non-inversion tillage practices (DD and ST) influence seed bank parameters relative to the conventional full inversion MP. The diversity of weed species was slightly lower for MP (17 species) compared to the ST (21 species) and DD treatments (22 species). The population for most weed species was relatively low with only three common species [low cudweed (Gnaphalium uliginosum L.), creeping buttercup (Ranunculus repens L.), common lambsquarters (Chenopodium album L.)] above 5 m⁻². For the total soil depth sampled (0–20 cm), weed seed population was significantly greater under DD (56 weeds m⁻²) and ST (66 weeds m⁻²), compared to MP (25 weeds m⁻²), and mainly related to changes in the number of annual broadleaf weeds, compared to perennial broadleaf and grasses. Comparison of the 0–10 with the 10–20 cm soil depth showed a relatively uniform weed seed distribution for the MP treatment, while a greater proportion of weed seeds was found at the lower soil depth for DD and ST. This distribution tended to be weed species dependent. Soil texture and weed seed characteristics were considered to have a critical impact on the total weed seed bank size, specifically for the 10–20 cm soil depth. Overall, the weed bank size was relatively small indicating that adoption of conservation tillage practices for sandy loams in Atlantic Canada should not cause a major change in weed community and weed populations, or present a need for significant changes in weed control management.     

Weed seed bank affected by tillage intensity for barley in Alaska

The weed seed bank of a long-term tillage study in subarctic Alaska was studied at the end of 10 years of continuous spring barley (Hordeum vulgare L.). Tillage treatments were: no-till, disked once (spring), disked twice (spring and fall), and chisel plow (fall). Soil cores were obtained from each tillage treatment and seeds were manually separated from soil after washing through sieves. Tillage treatment had a significant effect on seed density of shepherds purse (Capsella bursa-pastoris (L.) Medic.), cinquefoil (Potentilla norvegica L.), foxtail barley (Hordeum jubatum L.), and on total seed density. Seed density was higher for these species and total seed density was greater under no-till than under other tillage treatments. Seed density was higher near the soil surface under no-till and chisel plow treatments than under disked treatments, which helps explain the greater difficulty of controlling weeds under reduced tillage.     

Tillage and crop management effects on soil erosion in central Croatia

Soil erosion continues to be a primary cause for soil degradation and the loss of soil quality throughout the world. Our objectives were to quantify soil erosion (referred to as erosional drift) and to assign erosion risk to six tillage and crop management treatments evaluated from 1995 to 1999 for a 5-year maize (Zea mays L.), soybean (Glycine hyspida L.), winter wheat (Triticum aestivum L.), oil-seed rape (Brassica napus var. oleifera L.), and spring barley (Hordeum vulgare L.) plus double-crop soybean rotation on Stagnic Luvisols in central Croatia. Standard black fallow (tilled, unsown, and without any vegetative cover) Universal Soil Loss Equation (USLE) plots were used to establish the erosion potential associated with the rainfall pattern for each year. Soil loss from the check plots was several times greater than the T value, which is estimated to be 10 t ha⁻¹ per year. During the 2 years when spring seeded maize or soybean were grown (1995 and 1996) erosion risk was extremely high, especially for treatments where tillage and planting (row direction) were up and down the slope. When autumn seeded winter wheat or oil-seed rape were grown (1996/1997 or 1997/1998), soil erosion was insignificant. Also, except when plowing and sowing were up and down slope, erosion loss for the spring barley plus double-crop soybean crops in 1999 was insignificant. With no-tillage, soil erosion from the maize and soybean crops was reduced 40 and 65% compared to plowing up and down slope, even though the planting direction was still up and down the slope. With the exception of maize in 1995, erosion losses were moderate to insignificant when plowing and planting were performed across the slope. We conclude that erosion risk can be used as a reliable indicator of sustainable land management and that using no-tillage or plowing and planting perpendicular to the predominant slope are effective soil conservation practices for this region.     

土壤杂草种子库与杂草综合管理

土壤杂草种子库是农田杂草发生危害的主要根源,种子库的动态变化规律对于杂草的综合管理具有非常重要的意义。目前研究表明,杂草种子库的密度和组成变化很大,与田间杂草群落具有密切的联系。杂草种子库时刻处于输入和输出的动态变化之中。耕作方式影响杂草种子在土壤中的垂直分布,从而间接影响种子库的密度和种类组成;作物轮作使杂草的生存环境趋于多样化,能够限制某些对单一种植系统有着良好适应性的杂草种类的生长,作物轮作对杂草种子库种类组成和丰富度的影响要大于耕作方式;杂草管理措施能够大大降低田间杂草的结实,从而减小杂草种子库的规模。随着人们对除草剂使用和环境安全问题的日益关注,发展基于生态规律的杂草管理措施越来越受到人们重视,结合近几年国内外的研究进展,作者提出了杂草种子库今后的一些新的研究发展方向。     

Tillage effects on water storage during fallow, and on barley root growth and yield in two contrasting soils of the semi-arid Segarra region in Spain

In semi-arid areas under rainfed agriculture water is the most limiting factor of crop production. To investigate the best way to perform fallow and its effect on soil water content (SWC) and root growth in a barley (Hordeum vulgare L.) crop after fallow, an experiment was conducted on two soils in La Segarra, a semi-arid area in the Ebro Valley (Spain). Fallow was a traditional system used in these areas to capture out-of-season rainfall to supplement that of the growing period, usually lasting 16 months, from July to October of the next year. Soil A was a loamy fine Fluventic Xerochrept (Haplic Calcisol, FAO) of 120 cm depth and Soil B was a loamy Lithic Xeric Torriorthent (Calcaric Regosol, FAO) of only 30 cm depth. The experiment was continued for four fallow-crop cycles in Soil A and for two in Soil B. In Soil A, three tillage systems were compared: subsoil tillage (ST), minimum tillage (MT) and no-tillage (NT). In Soil B, only MT and NT were compared. In the fields cropped to barley, SWC and root length density (LV) were measured at important developmental stages during the season, lasting from October to June. In the fallow fields SWC was also monitored. Here, evaporation (EV), water storage (WS) and water storage efficiency (WSE) were calculated using a simplified balance approach. The fallow period was split in two 8-month sub-periods: July–February (infiltration) and March–October evaporation (EV). In Soil A, values of WSE were in the range 10–18% in 1992–1993, 1993–1994 and 1994–1995 fallow, but fell to 3% in 1995–1996. Among tillage systems, NT showed significantly greater WSE in the July–February sub-period of 1992–1993 and 1993–1994 fallow, but significantly lower WSE in the March–October sub-period, due to greater EV under NT. Consequently, no differences in total WSE were found between tillage systems. In Soil B, WSE was low, about 3–7%, and there were no difference between tillage systems. During the crop period, the differences in SWC and LV between tillage systems were small. Regarding yields, the best tillage system depended on the year. NT is potentially the best system for executing fallow, but residues of the preceding crop must be left spread over the soil.     

Soil organic matter and related physical properties in a Mediterranean wheat-based rotation trial

Under semi-arid Mediterranean conditions, limited moisture is the main constraint to rainfed cropping with wheat (Triticum aestivum), barley (Hordeum vulgare), and food and forage legumes. With increasing land-use pressure, moisture-conserving fallowing is being replaced by continuous cropping, which is considered an unsustainable practice. Thus, a long-term trial with durum wheat (T. turgidum var. durum) was established in 1983 at Tel Hadya, Aleppo, Syria (mean annual rainfall 330 mm) to assess alternative rotation options to fallow and continuous cropping. Nitrogen (N) and grazing/residue management were secondary factors. Soil aggregation, infiltration, hydraulic conductivity, and total soil organic matter and component fractions (fulvic and humic acids and polysaccharides) were determined at the end of 12 years. Some rotations, e.g., medic (Medicago sativa) and vetch (Vicia faba), significantly increased soil organic matter (12.5–13.8 g kg⁻¹ versus 10.9–11 g kg⁻¹ for continuous wheat and wheat/fallow). All measurements, or indices, indicated parallel trends with increasing organic matter, e.g., coefficients of macro-structure, micro-aggregation, and water-stable aggregates, and decreasing dispersion. Similarly, legume rotations had higher infiltration rates (16.2–21.8 cm h⁻¹ versus 13.9–14.4 cm h⁻¹ with continuous wheat and wheat/fallow) and hydraulic conductivity rates (8.7–12.4 cm h⁻¹ versus 6.2–7.4 cm h⁻¹ with continuous wheat and wheat/fallow). We conclude that cereal/legume rotations, in addition to being biologically and economically attractive, also enhance soil quality and thus promote soil use sustainability in fragile semi-arid areas as in the Mediterranean zone.     

Effects of mouldboard ploughing and direct planting on yield and nutrient uptake of potatoes in Norway

The use of conservation tillage systems is now widespread for cereals in erosion-prone areas of Norway. However, few growers are willing to adopt such practices for other crops. An experiment was conducted in southern Norway (60°46′N, 10°49′E) from 1987 to 1993 to compare the effects of two different tillage treatments on potato (Solanum tuberosum L.) yield and quality. The conventional labour-intensive treatment, with autumn mouldboard ploughing, levelling and two passes with a spring-tine harrow in spring was compared with planting directly into untilled barley (Hordeum vulgare L.) stubble, with straw removed. The soil type in the experiment was a morainic, stony loam (Typic Cryoboroll, Orthic Melanic Brunisol). Prior to the start of the experiment direct-planted plots had not been ploughed for 9 years. During the trial years (1987–1993) a pattern of two different yield curves emerged as functions of the date of harvesting. The yield curve for direct planting was steeper, crossing that of conventional tillage on approximately 10 September, thus predicting higher tuber yield for direct planting when harvesting occurred after this date, but lower tuber yield than with conventional tillage in the case of early harvesting. The reason for this is thought to be cooler soil and delayed growth and maturation with direct planting. Furthermore, direct planted potatoes gave higher haulm yield, and also had higher contents of N, P and K in both haulm and tubers. No significant differences in tuber quality were found between the two treatments. A strong negative correlation was found between the yield increase caused by direct planting and mean air temperature in August. The trial indicated that direct planting of potatoes in cereal stubble is a viable alternative to conventional plough tillage on loam soil in Norway, provided that the growing season is adequately long.     

Long-term continuous cropping in the Pacific Northwest: Tillage and fertilizer effects on winter wheat, spring wheat, and spring barley production

Conventional tillage winter wheat (Triticum aestivum) (WW)–summer fallow reduces soil productivity and increases soil erosion. Conservation tillage management, together with intensive cropping may have the potential to reverse these sustainability concerns. The objective of this study was to determine the effects of conventional tillage (CT) and no-tillage (NT) systems on grain yield of long-term annual cropping of monoculture WW, spring wheat (SW), and spring barley (Hordeum vulgare) (SB) grown with or without fertilizer, in the Pacific Northwest region of the USA. In unfertilized crops, grain yield of WW, SW, and SB was 15%, 25%, and 50% higher, respectively, in CT than in NT plots, an indication of the involvement of yield limiting factors under the NT cropping system. When fertilized, there were no significant differences in grain yield of WW. Yields of SW and SB, however, remained 21% and 15% higher, respectively, in CT than in NT, an indication that factors other than fertility were involved. These results suggest that in order for NT management to be widely adopted by area growers, the yield-limiting factors need to be addressed.     

Effect of reduced tillage on weeds and soil organisms in winter wheat and summer maize cropping on Humic Andosols in Central Japan

Although reduced tillage (RT) may preserve soil biota and improve the productivity and sustainability of arable lands in temperate regions, the extension of RT is limited by difficulties in controlling weeds. We studied the effect of RT without herbicide application on weed communities and soil biota in a 1-year 2-crop rotation system with winter wheat (Triticum aestivum L.) and maize (Zea mays L.) on Andosols in Japan. RT of the surface 3 cm and conventional moldboard plowing (CT) were conducted before seeding twice per year. For the first 3 years, from autumn 1997 to spring 2000, one field was managed with RT and another with CT. For the second 3 years, from autumn 2000 to spring 2003, RT and CT were conducted in two replicated plots in each field. Weed communities and soil biota were studied in the last 2 years. Dominant weed species in winter wheat cropping were Italian ryegrass (Lolium multiflorum Lam.) in 2002 and common vetch (Vicia angustifolia L.) in 2003, and their biomass was high where RT or CT was continuously conducted. Switching of tillage methods, from RT to CT or vice versa, reduced the biomass of winter weeds. In summer maize cropping, several annual and perennial weed species tended to increase under RT in the second 3 years. However, redroot pigweed (Amaranthus retroflexus L.), the most dominant weed in 2002 and 2003, responded to tillage inconsistently and its biomass was not always increased by RT. Species diversity of winter weeds was decreased by CT conducted in the first 3 years, and that of summer weeds was decreased by CT conducted in the second 3 years. The seedbank in the 0–10-cm soil layer under recent RT was large (7200–16 300 seeds m⁻²) compared with that under CT (2900–7300 seeds m⁻²). The microbial substrate-induced respiration (SIR) and the population densities of nematodes and mites were higher under RT in the second 3 years and were not affected by previous tillage practices. Both were highly correlated with soil total nitrogen. The positive effect of RT on these soil organisms was primarily attributable to the accumulation of organic matter in soil, but not to plant cover as a result of incomplete weed control by RT. Occasional adoption of RT in current CT systems may be effective at enriching soil organisms with little risk of weed infestation.     

Conservation tillage in the subarctic

Three tillage practices were compared on a subarctic silt-loam soil to evaluate whether conservation tillage could be used effectively to reduce soil losses from wind erosion without delaying crop maturity or reducing yield. Urea and ammonium nitrate were also compared as sources of fertilizer nitrogen. Plots were cropped to rapeseed (Brassica campestris L.) and barley (Hordeum vulgare L.) in a rapeseed-barley-fallow rotation and in continuous barley. Zero-tillage did not delay maturity nor did it result in reduced yields except where there was excessive competition from perennial grassy weeds. Neither placement appeared to be less than optimum in zero-tilled plots. With proper fertilizer placement and grassy-weed control, conservation tillage appears to be a viable method of reducing the potential for wind erosion in the subarctic.     

Conservation tillage systems, fungal complexes and disease development in soybean and barley rhizospheres in Prince Edward Island

A potential for reduced soil macroporosity (below 12% soil volume) under direct drilling, with a concomitant increase in soil relative saturation, is associated with an increase in crown and root rots in Prince Edward Island field crops. Four long-term tillage systems (moldboard plowing, paraplowing-direct drilling, rotary cultivation and direct drilling) were compared in relation to the pathogenic fungal complexes formed in a two crop rotation in spring barley (Hordeum vulgare L.) and soybean (Glycine max L. Merrill) over a 3 year period in a cool humid region of eastern Canada. The principal phytopathogenic fungal complex of Rhizoctonia solani Kühn, Fusarium avenaceum (Fr.) Sacc. and F. oxysporum Schl. remained constant over the treatments. Tillage practice did not affect the number of colony forming units of R. solani in the rhizosphere. The recovery of R. solani from root tissues tended to be lower following conservation tillage and was attributed to antagonism associated with elevated numbers of saprophytic trash microflora concentrated at the soil surface. Disease levels in potato (Solanum tuberosum L.) plantlet bioassays were not influenced significantly by soil source or tillage regime. However, plantlet growth tended to be depressed following transplantation into soil from soybean plots in 1993. Under optimum soil physical conditions conservation tillage did not appear to influence disease levels in barley and soybean rotations.     

Twenty years of tillage research in subarctic Alaska: I. Impact on soil strength, aggregation, roughness, and residue cover

Soil properties and surface characteristics affecting wind erosion can be manipulated through tillage and crop residue management. Little information exists, however, that describes the impact of long term tillage and residue management on soil properties in the subarctic region of the United States. This study examines the impact of 20 years of tillage and residue management on a broad range of physical properties that govern wind erosion processes on a silt loam in interior Alaska. A strip plot experimental design was established in 1983 and included intensive tillage (autumn and spring disk), spring disk, autumn chisel plow, and no tillage with straw either retained on or removed from the soil surface. Soil and residue properties measured after sowing barley (Hordeum vulgare L.) in May 2004 included penetration resistance, soil water content, shear stress, bulk density, random roughness, aggregate size distribution, and residue cover and biomass. No tillage was characterized by larger aggregates, greater soil strength (penetration resistance and shear stress), wetter soil, and greater residue cover compared to all other tillage treatments. Despite crop failures the previous 2 years, crop residue management influenced residue biomass and cover, but not soil properties. Autumn chisel and spring disk appeared to be viable minimum tillage options to intensive tillage in controlling erosion. Autumn chisel and spring disk promoted greater roughness, aggregation, and residue cover as compared with intensive tillage. Although no tillage appeared to be the most effective management strategy for mitigating wind erosion, no tillage was not a sustainable practice due to lack of weed control. No tillage also resulted in the formation of an organic layer on the soil surface over the past 20 years, which has important ramifications for long term crop production in the subarctic where the mean annual temperature is <0 °C.     

Soil biotic and biochemical factors in a long-term tillage and stubble management experiment on a vertisol. 1. Seedling inhibition by stubble

In a long-term experiment on a vertisol in southern Queensland, depression of vegetative growth of barley (Hordeum vulgare L.) by stubble retention was far greater with zero tillage than with mechanical tillage of the fallow. The possible phytotoxic effects of stubble on barley and wheat (Triticum aestivum L.) were investigated in seedling bioassays. Stubble collected from field plots just prior to planting did not reduce germination of wheat or barley seed but markedly reduced coleoptile length at 4 days. This effect of stubble became less apparent after 6 and 8 days, and was overcome by increasing water volume in the bioassay dish. Stubble absorbed 4.5–6 times its own weight of water and thereby competed with the germinating seed. Filtrates of stubble macerates in water, collected either before or after incubation of the saturated stubble, had no effect on coleoptile length indicating the absence of a water-soluble phytotoxin.

Brown lesions on wheat coleoptiles (most apparent at 8 days) and roots were decreased by stubble but increased by more water in the bioassay dish. Alternaria sp. and two types of bacteria were associated with the coleoptile lesions, and Fusarium sp. and several types of bacteria were associated with root lesions. Surface sterilisation of seed reduced root lesions but not coleoptile lesions. Filtrates of both incubated and unincubated stubble macerates reduced coleoptile lesions.

Poor early growth of barley in the field on zero-till, stubble-retained plots was not associated with incorporation of stubble into the drill slit in contact with the seed. Poor early growth was not overcome by nitrogen fertilizer drilled into the soil 2 months before planting. The quantities of air-dried stubble on the soil surface were capable of absorbing of the order of 4 mm rainfall. It is concluded that neither phytotoxins nor water absorption by the stubble were likely causes of the problem of poor early growth.     

Rotation and tillage effects on available soil water for winter wheat in a semi-arid environment

The recent adoption of conservation farming systems in the semi-arid Canadian prairies opens up the possibility of replacing the traditional fallow period with non-cereal crops (oilseeds, legumes). However, information on changes to soil water regimes by inclusion of these crops, especially in combination with zero tillage, is sparse. A study was initiated in 1984 on a sandy clay loam soil at Lethbridge, Alberta, to investigate the performance of winter wheat (Triticum aestivum L.) under conventional, minimum and zero tillage in monoculture and in 2-year rotations with fallow, canola (Brassica campestris L.) or lentils (Lens culinaris Medic.)/flax (Linum usitatissimum L.). Conventional tillage in the Lethbridge region is shallow cultivation (10 cm) with a wide-blade (sweep) cultivator. Continuous cropping greatly depleted soil water reserves, resulting in some crop failures. Averaged over 10 years, available water for establishment of winter wheat in fall was least after canola (45 mm), followed by continuous winter wheat (59 mm), lentils/flax (74 mm) and fallow (137 mm). In this semi-arid region, the effect of rotation on soil water was much greater than that of tillage. Zero tillage had relatively little impact on available water to 1.5 m depth. However, once the experiment had been established for 6–7 years, available water in the 0–15 cm depth under winter wheat in spring was greatest under zero tillage. Precipitation storage efficiency during the fallow year was generally unaffected by tillage system.     

Tillage and crop straw methods affect energy use efficiency,economics and greenhouse gas emissions in rainfed winter wheat field of Loess Plateau in China

Data from a field experiment conducted in China's Loess Plateau (2013–2015) were used to determine the energy balance of winter wheat (Triticum aestivum L.) as affected by tillage and straw treatments. Tillage treatments included chisel plow, no tillage, and mouldboard plow. Crop straw levels included straw returning and straw removed. The energy balance was evaluated by comparing the following parameters: net energy, energy profitability, energy use efficiency, and energy intensity. The yield parameters were significantly influenced by the tillage treatments and revealed that the chisel plow entailed fewer field operations and lower energy requirements with a higher yield than mouldboard plowing tillage. The highest proportion of energy input came from a nitrogen fertiliser, followed by diesel fuel. The total energy input applied per hectare increased with an increase in the tillage intensity, and the lowest energy input was required for the no tillage case with the straw returning treatment, and the highest for the case of mouldboard plow with the straw returning treatment. The lowest average energy intensity was recorded for the no tillage case, followed by the case of chisel plow tillage in both cropping seasons. Moreover, in the case of mouldboard plough tillage, the maximum energy intensity was recorded in both cropping seasons. In the cases of the chisel plow tillage and the no tillage, we observed the maximum energy gain, while in the no tillage case, we observed the maximum energy use efficiency. The net return and the benefit/cost ratio were higher in the case of straw returning than those in the case of no straw treatment. We concluded that no tillage and chisel plow tillage with straw returning could improve the energy use efficiency and the benefit/cost ratio of winter wheat production systems.     

Effect of tillage intensity on weed infestation in organic farming

Conservation tillage is not yet widely accepted by organic farmers because inversion tillage is considered to be necessary for weed control. Three long-term experiments were established with combinations of reduced and conventional plough tillage and stubble tillage to determine weed infestation levels in organic farming, i.e. herbicide application being excluded. Experiment 1 (with very low stocking density of perennial weeds) showed that in presence of primary tillage by mouldboard ploughing the number of annual weeds was nearly unaffected by the mode of stubble tillage. In experiment 2, however, with Canada thistle (Cirsium arvense) being artificially established, thistle density was significantly affected by stubble tillage and by a perennial grass–clover forage crop. Experiment 3 combined two levels of stubble tillage (skimmer plough, no stubble tillage = control) with four implements of primary tillage in the order of decreasing operation depth (deep mouldboard plough, double-layer plough, shallow mouldboard plough or chisel plough). Primary tillage by chisel plough resulted in significantly highest annual weed density compared to all other treatments. The natural C. arvense infestation in experiment 3 showed highest shoot density in the “skimmer plough/chisel plough” treatment compared to the lowest infestation in the “skimmer plough/double-layer plough” treatment. The poor capacity of the chisel plough for weed control was also reflected by the soil seed bank (5500 m⁻² C. arvense seeds for chisel plough, <300 seeds for all other primary tillage). A reduced operation depth of the mouldboard plough (“shallow mouldboard plough”) seemed to have an insufficient effect in controlling C. arvense infestation as well. Stubble tillage by the skimmer plough in addition to nearly any primary tillage operation largely reduced both annual weeds and thistle shoots. Most effective in controlling C. arvense was also a biennial grass–clover mixture as part of the crop rotation.Double-layer ploughing is a compromise between soil inversion and soil loosening/cutting and can be regarded as a step towards conservation tillage. In terms of controlling annual weeds and C. arvense, the double-layer plough was not inferior to a deep mouldboard plough and seems to be suitable for weed control in organic farming. Tilling the stubble shallowly after harvest can support weed control in organic farming remarkably, particularly in reducing C. arvense. If no noxious, perennial weeds occur and primary tillage is done by soil inversion, an omission of stubble tillage can be taken into consideration.     

Changes in soil chemical properties following a 12-year fallow: A 2-year comparison of conventional tillage and no-tillage agroecosystems

Soil chemical parameters including total N, exchangeable ammonium, soluble nitrate, and extractable phosphate, potassium, calcium and magnesium, were compared between conventional and no-tillage treatments on land which had been left fallow in old-field vegetation for 12 years. Tillage treatments were also compared to an adjacent old-field which was not cropped. The study was carried out on the Georgia Piedmont for 2 years following the fallow period. Soil nutrient availability was related to chemical concentrations in the soil solution, plant nutrient uptake and litter decomposition. During 1978–1979, soil nitrate concentrations were highest in plowed systems and lowest in the old field. Extractable cation concentrations were generally higher in conventional tillage than in no-tillage soil during the 1st year after fallow (1978). However, during the 2nd year, higher cation concentrations in no-tillage soil prevailed. Nitrate concentrations in the soil solution at 60 cm depth were generally highest in conventional tillage, followed by no-tillage and lowest in old-field systems. During 1978–1979, total nutrient uptake by crops (grain sorghum and rye) and weeds was higher in conventional than in no-tillage systems. From 1978–1979 to 1979–1980, uptake decreased in both cropping systems, but proportionately more in conventional tillage systems so that uptake in 1979–1980 was similar in the two cropping treatments. Higher nitrate concentrations in leachate of conventional than in no-tillage and old-field systems suggested that plowing stimulated nitrification processes.     

旱作麦田保护性耕作蓄水保墒和增产增收效应

为了揭示渭北旱塬连作麦田不同保护性耕作措施下土壤蓄水保墒效果和冬小麦增产增收效应。于2007－2009年通过田间试验研究了渭北旱塬夏闲期免耕、深松和翻耕等3种耕作方式对麦田夏闲期蓄水保墒效果,以及3种耕作处理与平衡施肥、常规施肥和低肥等3种施肥处理组合对冬小麦生育期土壤水分动态、产量和经济效益的影响。免耕和深松较翻耕保墒作用好,夏闲期免耕、深松较翻耕0～300 cm土层3 a平均土壤含水率分别增加了0.6和0.5个百分点,平均贮水量分别增加了24.2和21.5 mm;生育期内平衡施肥免耕、深松较翻耕处理0～200 cm土层2 a平均土壤贮水量分别增加了17.7和14.4 mm;以平衡施肥深松处理产量最高,2 a平均产量高达5033.1 kg/hm2,较平衡施肥翻耕和平衡施肥免耕分别增产5.5%和6.3%;以平衡施肥免耕经济效益最高,2 a平均纯收益高达5 553.7元/hm2,较平衡施肥深松和平衡施肥翻耕分别增收3.3%和9.2%。综合考虑各处理土壤蓄水保墒效果和小麦增产增收效应,平衡施肥深松处理是渭北旱塬连作麦田较佳的耕作和施肥处理组合。     

Wheat yield and weed population as influenced by three tillage systems on a clay soil in temperate continental climate

The potential benefits of conservation tillage practices depend mainly on the soil and climatic conditions of the site. A study was conducted to determine the effects of three tillage systems (conventional, CT; reduced, RT; zero, ZT) on spring wheat (Triticum aestivum L.) and weed growth on a clay soil in temperate continental climate, northern Alberta (55°43′N, 118°41′W), Canada. A medium duty cultivator with 25 cm sweeps spaced 22 cm apart and a working depth of 8–10 cm was used for tillage in the CT (once in fall and twice in spring) and RT (once in spring) plots. The ZT plots received a harrowing to spread straw and a preseeding application of Roundup (glyphosate) to control weeds. Experimental design was a randomized complete block with four replications and the tillage systems were fixed in space for the 1989, 1990 and 1991 seasons. The RT treatment resulted in higher yields than the CT or ZT treatments. However, the differences were not always significant. The ZT treatment produced higher yields than CT in 1989 and 1991, whereas its yields were lower than CT in 1990. The 3 year means of total dry matter (TDM) were 3899 kg ha⁻¹, 3640 kg ha⁻¹ and 3331 kg ha⁻¹ for the RT, ZT and CT treatments, respectively. The corresponding grain yields were 1728 kg ha⁻¹, 1573 kg ha⁻¹ and 1530 kg ha⁻¹. The concentration of total N in plants and grains of wheat, amounts of extractable NO₃-N, NH₄-N and P in soil and soil moisture and bulk density were not significantly affected by tillage. The mean weight diameter of aggregates in surface soil was significantly greater under ZT than under the other systems. Wild buckwheat (Polygonum convolvulus L.) was more abundant under CT, but common groundsel (Senecio vulgaris L.), dandelion (Taraxacum officinale Weber), hemp nettle (Galeopsis tetrahit L.), field horsetail (Equisetum arvense L.) and smartweed (Polygonum scabrum Moench) tended to have higher populations under the ZT system. The populations of foxtail barley (Hordeum jubatum L.) wild rose (Rosa sp.), stinkweed (Thlaspi arvense L.) and wild oats (Avena fatua L.) showed no consistent effect of tillage. Tillage or preseeding application of glyphosate did not provide an effective control of all weed species. The spring tillage of the RT system improved crop yields and weed control relative to ZT, whereas the fall tillage of the CT system (in addition to spring tillage) reduced crop yields and had no significant effect on weed population relative to RT. The overall results showed that tillage intensity could be reduced to the level of RT without any adverse influence on crop yields, soil properties or weed populations. The RT system is also economical and environmentally desirable owing to lower tillage and herbicide requirements.     

Effect of mouldboard and chisel ploughing and their timing on seedbed quality

The effects of tillage on weed growth are supposed to depend largely on the type of implement, the timing of the operation and the type of soil. Experiments on the effect of mouldboard and chisel ploughing with duckfeet, used for the main tillage operation and the timing of the main tillage operation on seedbed quality and weed development in sugar-beet were carried out from 1981–1983 on silty clay, silty loam and two sands. Seedbed quality was only slightly influenced by type and timing of the main tillage operation. Soil texture affected seedbed quality significantly: seedbeds on light soils compared with silty soils had a finer tilth, were deeper and were scarcely sorted (stratified according to particle size). Chisel ploughing with duckfeet to the full depth of the arable layer required much tractor power and during the late autumn on silty loam and in spring on sand, chiselling was impossible because the soil was too wet; the mouldboard plough did not cause problems of this kind. Moreover, soil inversion by the mouldboard plough was attended by a surface free of crop residues and weeds after the main tillage operation and a strong suppression of weeds during winter, sowing time and in the young crop.