Root growth conditions in the topsoil as affected by tillage intensity

Many studies have reported impeded root growth in topsoil under reduced tillage or direct drilling, but few have quantified the effects on the least limiting water range for root growth. This study explored the effects of tillage intensity on critical soil physical conditions for root growth in the topsoil. Samples were taken from a 7-year tillage experiment on a Danish sandy loam at Foulum, Denmark (56°30′ N, 9°35′ E) in 2008. The main crop was spring barley followed by either dyer's woad (Isatis tinctoria L.) or fodder radish (Raphanus sativus L.) cover crops as subtreatment. The tillage treatments were direct drilling (D), harrowing 8-10 cm (H), and ploughing (P) to 20 cm depth. A chisel coulter drill was used in the H and D treatments and a traditional seed drill in the P treatment. Undisturbed soil cores were collected in November 2008 at soil field moisture capacity from the 4-8 and 12-16 cm depths.We estimated the critical aeration limit from either 10% air-filled porosity (ε_a) or relative gas diffusivity (D/D₀) of 0.005 or 0.02 and found a difference between the two methods. The critical limit of soil aeration was best assessed by measuring gas diffusivity directly. Root growth was limited by a high penetration resistance in the D and H soils (below tillage depth). Poor soil aeration did not appear to be a significant limiting factor for root growth for this sandy loam soil, irrespective of tillage treatment. The soil had a high macroporosity and D/D₀ exceeded 0.02 at field capacity. Fodder radish resulted in more macropores, higher gas diffusivity and lower pore tortuosity compared to dyer's woad. This was especially important for the H treatment where compaction was a significant problem at the lower depths of the arable layer (10-20 cm depth). Our results suggest that fodder radish could be a promising tool in the amelioration of soil compaction.     

A long-term comparison of ploughing, tine cultivation and direct drilling on the growth and yield of winter cereals and oilseed rape on clayey and silty soils

The effects of mouldboard ploughing, shallow tined cultivation and direct drilling on yields of winter wheat, barley, oats and oilseed rape were compared over 10 years. Three field experiments were conducted on two non-calcareous clays (stagnogleys) and a weakly structured silty soil (argillic brown earth). Two spring N levels were applied to the winter wheat plots on the clay soil in three years and to the winter barley plots on the silty soil in one year. This paper reports the soil bulk density and water content at sowing and the crop growth, yield components and yields obtained during the later years of the study: 1979–1984 on the clayey soils and 1981–1984 on the silty soil.

In the years when cereals were grown, differences in yield between cultivation treatments were small and inconsistent. Oilseed rape yielded significantly more after direct drilling than ploughing because of better establishment and uniformity of growth.

The success of continuous reduced tillage depended on both burning crop residues and good weed control.     

A study of mole drainage with simplified cultivation for autumn-sown crops on a clay soil. 4. A comparison of direct drilling and mouldboard ploughing on drained and undrained land on root and shoot growth,nutrient uptake and yield

Cereal crops were grown after direct drilling or ploughing on an undrained or drained clay soil over 4 years to examine whether crop growth after different methods of tillage is influenced by the intesiity of drainage. Winter cereals were grown in each year, wheat for 3 years and oats in the remaining year. In 3 of the years (years 1–3) the total annual precipitation was close to the long-term mean, and the mean depths of the water table during the winter in the undrained and drained land were about 20 and 40 cm, respectively. In the 3rd year, an unusually wet autumn also caused very wet topsoil at sowing time, which persisted throughout the winter. The 4th year was much drier than average, and the water tables remained below drain depth.An interaction between the intensity of drainage and the method of tillage occurred only in the 3rd year, with the wet autumn, when completion of ploughing, seed-bed preparation and sowing of the oats were delayed. This disadvantaged the direct-drilled crop on the undrained land, where seedlings experienced pre-emergence waterlogging so that the plant population was 20 m⁻² and yield was only 55% of the crop grown after ploughing; on drained land, there was little difference in establishment or yield between the tillage treatments.Drainage did not affect yield in the 2 drier years, the 1st and 4th, and in the latter year the grain yield of winter wheat was 11.5 t ha⁻¹. In the 2nd year, drainage increased yield by about a quarter, when root growth and nutrient uptake were restricted on the undrained treatment. Averaged over the whole duration of this experiment, 4 years reported here and 2 years already published, the mean increase in grain yield of winter cereals due to drainage was 13% (0.9 t ha⁻¹).On average, the 3 direct-drilled winter wheat crops yielded 4% more grain than crops grown on ploughed land due to an advantage in one year. Root extension in winter was slightly faster after direct drilling than after ploughing, but the difference subsequently diminished or disappeared.     

Effects of tillage on productivity of a winter wheat-vetch rotation under dryland Mediterranean conditions

An experiment was conducted to determine the effects of three tillage systems on crop yield in a winter wheat-vetch (Vicia sativa L.) rotation during 3-year growing seasons on a clay-loam soil in the northwest region of Turkey. The three tillage treatments were: (1) conventional tillage (CT); (2) shallow tillage (ST); (3) double disk tillage (DD).The wheat grain yield was significantly affected by tillage when averaged across years. The highest wheat grain yield was obtained with shallow tillage treatment. The year affected wheat grain yield significantly, mainly due to the distribution of rainfall through the growing season and probably due to the wheat-vetch rotation. Heads density and head length increased significantly with shallow tillage when compared with conventional tillage. Tillage practices had no significant influence on thousand kernel weight. Results from this study indicated that for a dryland wheat-vetch rotation cropping system, shallow tillage had higher wheat grain yields than that obtained from conventional tillage. Furthermore, mouldboard ploughing tillage in this crop rotation could be replaced by shallow tillage that would increase yield and would be likely to improve soil properties in the long-term. On the other hand, double disk tillage proved to be a promising soil management practice to improve vetch grain yield when compared with conventional tillage.     

Soil fertility in a long‐term fertilizer trial with different tillage systems

The presented results originate from a field experiment established in 1972 on an Eutric cambisol with two main factors: soil tillage (conventional‐, reduced‐, and no‐tillage) and NPK fertilization. The test plants were maize and winter wheat in two years rotation.

The long‐term soil fertility without and with optimum fertilization, the influence of fertilization, tillage and crop sequence on grain yields, the organic carbon content (C_org) and the nitrate infiltration are discussed.

In the course of years without any NPK fertilization grain yields of maize and winter wheat decreased significantly and reached a minimum level which was modified however by the actual climatic conditions. The analogous yield level of optimum NPK fertilization at maize showed a growing tendence while at wheat it remained mostly constant.

The method of soil tillage influenced grain yield of winter wheat to a lesser extent than the yield of maize. Grain yields of maize and winter wheat were consistently lower with no‐till as compared to reduced or conventional tillage, however the differences with w. wheat were much smaller. The effect of tillage was especially high at N₀ P₀ K₀. Crop rotation had a positive effect on the yields of maize. For winter wheat at N₀ P₀ K₀ oneself was the better forecrop, while at optimum N and PK maize performed a little better. C_orgcontent of soil slightly increased in the course of 25 years not only on the fertilized plots but on the nil plots too. Increasing N‐doses showed only a little effect on the C_org. There was a little positive effect of no‐till on C_org content of soil as well as compared fall ploughing. Soil tillage did not much influence the total amount of nitrate in the soil profile. The distribution of nitrate‐N in the soil profile was more affected by the actual climatical circumstances than by the system of tillage. However big nitrate accumulations were found in the subsoil according to different soil tillage systems at some other times, as well as lack of it, which suppose the possibility of a relative quick nitrate infiltration.     

Nitrous oxide emissions, cereal growth, N recovery and soil nitrogen status after ploughing organically managed grass/clover swards

The period after ploughing of grass–clover leys within a ley‐arable rotation is when nitrogen accumulated during the ley phase is most vulnerable to loss. We investigated how ploughing date and timing of cessation of grazing before ploughing affected nitrous oxide (N₂O) losses of the first cereal crop. Ploughing dates were July and October for a winter wheat pilot study and January and March for spring barley in the main experiment. Timings of cessation of grazing (main experiment only) were October, January and March. Spring barley yield, nitrogen uptake and soil mineral nitrogen were also assessed. A separate large‐scale laboratory incubation was made to assess the effect of temperature and rainfall on nitrous oxide emissions and nitrate leaching under controlled conditions. Nitrous oxide emissions in the 1‐ to 2‐month period after autumn or spring ploughing, or sowing were typically between 20 and 150 g N ha^?1 day^?1 and increased with temperature and rainfall. Tillage for crop establishment stimulated N₂O emissions with up to 2.1 kg N ha^?1 released in the month after spring tillage. Cumulative nitrous oxide emissions were greatest (～8 kg ha^?1 over 17 months) after cessation of grazing in March before March ploughing, and lowest (～5.5 kg ha^?1) after cessation of grazing in January before January ploughing. These losses were 1.2–3.9% of the N inputs. In the laboratory study, winter ploughing stimulated nitrate leaching more than nitrous oxide emissions. The optimum time of ploughing appears to be early spring when the cold restricts nitrogen mineralization initially, but sufficient nitrogen becomes available for early crop growth and satisfactory N offtake as temperature increases. Early cessation of grazing is advantageous in leaving an adequate supply of residues of good quality (narrow C:N ratio) for ploughing‐in. Restricting tillage operations to cool, dry conditions, being aware of possible compaction and increasing the use of undersown grass–clover should improve the sustainability of organic farming.     

耕作方式和秸秆还田对砂姜黑土碳库及玉米小麦产量的影响

长期秸秆还田免耕覆盖措施导致沿淮区域砂姜黑土耕层变浅、下表层(10～30 cm)容重增加、土壤养分不均衡等问题凸显,限制了小麦-玉米周年生产力的提高。耕作和秸秆还田措施合理的搭配组合是解决这一问题的有效方法。通过8年的小麦-玉米一年两熟田间试验,设置4个处理:1)玉米季免耕-小麦季免耕秸秆不还田(N);2)玉米季深耕-小麦季深耕秸秆不还田(D);3)玉米季秸秆免耕覆盖还田+小麦秸秆免耕覆盖还田(NS);4)玉米季秸秆免耕覆盖还田+小麦季秸秆深耕还田(DS)。通过分析作物收获后不同土壤深度(0～60 cm)总有机碳(TOC)、颗粒态碳(POC)、微生物生物量碳(MBC)、易氧化态碳(KMnO4-C)、可溶性有机碳(DOC)和土壤碳库管理指数(CPMI),并结合小麦-玉米的周年产量变化,以期获得培肥砂姜黑土的最佳模式。研究结果表明:1)相对于长期免耕措施(N),DS处理能够提高0～30 cm土层TOC、POC、MBC、KMnO4-C等组分含量和CPMI;而NS措施仅提高土壤表层(0～10 cm)TOC、活性有机碳组分含量和CPMI;2)DS处理显著提升了小麦-玉米的周年生产力,其麦玉的周年产量均值分别比N、D和NS处理高出14.7%、12.9%和8.5%;3)MBC和KMnO4-C对于耕作和秸秆还田措施都是较为敏感指示因子。总的来说,玉米季小麦秸秆覆盖还田+小麦季玉米秸秆深耕还田(DS)是改善沿淮地区砂姜黑土土壤碳库、提高小麦-玉米周年产量的一种有效农田管理模式。     

黄土旱塬区平衡施肥下不同土壤耕作模式的蓄水纳墒及作物增产增收效应研究

【目的】黄土旱塬半湿润易旱区是典型的雨养农业区,多数一年一熟或两年一熟制,冬小麦和春玉米是该区主要的粮食作物,平衡施肥是主要的施肥方式。多年研究和生产实践证明,建立与不同作物轮作方式相配套的土壤轮耕技术体系,可以为作物生长发育创造良好的土、 肥、 水、 气、 热的土壤环境条件,保持农田生态健康发展,促进作物增产增收。本文在当地平衡施肥条件下,通过多年耕作模式定位试验,研究在平衡施肥条件下,不同土壤耕作模式对休闲期和作物生育期0200 cm土层蓄水纳墒状况、 作物产量及其经济效益的影响,为黄土旱塬半湿润易旱区建立在一定肥力水平下与作物轮作体系相配套的土壤轮耕模式提供理论依据。【方法】选择位于黄土旱塬半湿润易旱区腹地的陕西省合阳县甘井镇一年一熟旱作冬小麦春玉米轮作田为试验区,采用免耕、 深松和翻耕3种土壤耕作方法组成4种土壤轮耕模式,即: 翻耕免耕翻耕免耕(RT1); 深松翻耕深松翻耕(RT2); 免耕深松免耕深松(RT3); 免耕翻耕深松免耕(RT4); 以连年翻耕(CK1)、 连年深松(CK2)和连年免耕(CK3)为对照,通过连续4年(2007~2011年)定位试验,研究平衡施肥条件下的7种土壤耕作模式对冬小麦春玉米轮作田0200 cm土层土壤贮水量、 土壤水分含量、 作物籽粒产量、 水分利用效率(WUE)和经济效益的影响。【结果】 1)在土壤休闲期,RT3模式下0200 cm土层土壤贮水量最高,其次是RT2。与对照组相比,4种轮耕模式0200 cm土层土壤贮水量均高于CK1; RT3显著高于CK3,但与CK2差异不显著。0200 cm土层土壤剖面含水量,亦以RT3模式最高。2)在冬小麦生育期,0200 cm土层土壤贮水量和土壤含水量,RT3和CK2模式的较高。3)在春玉米生育期,0200 cm土层土壤贮水量和土壤含水量RT3和CK3较高。4)不同耕作模式的作物籽粒产量、 水分利用效率(WUE)和经济效益,以RT2和CK2模式最高。四年平均结果RT2处理较CK1、 CK2和CK3处理增产10.2%、 3.6%和17.1%,增收23.6%(P0.05)、 6.8%(P0.05)和28.3%(P0.05),提高WUE 9.7%(P0.05)、 4.3%和18.6%(P0.05)。【结论】年际间轮流进行深松和翻耕(RT2)处理,虽然其在土壤蓄水保墒效应方面略低于年际间轮流进行免耕和深松(RT3)和连年深松(CK2)处理,但可获得最佳增产增收效果和最高水分利用效率; 连年深松能够增加水分入渗,保护土壤,增加蓄水能力,但产量和经济效益不如RT2处理,也是该区比较适宜的耕作方法。根据实际状况,在平衡施肥条件下的一年一熟作物轮作区,应推荐深松翻耕的轮耕或连年深松的耕作模式。     

Managing traffic-induced soil compaction by using conservation tillage

The term ‘Konservierende Bodenbearbeitung’ has a somewhat different meaning than conservation tillage as used worldwide. In Germany the term is used not only in relation to the retention of surface residues to reduce erosion but in association with compaction control by carefully timed loosening operations.Field experiments were conducted from 1985 to 1990 on a loamy sand (Dystric-Luvisol) in north-central Germany. The effect of crop rotation-specific soil loosening on some soil physical properties and crop yields was studied in the presence and absence of wheel-induced soil compaction when growing sugar beet, winter wheat, winter barley and a cover crop. Five tillage treatments were studied in a 3-year crop rotation: sugar beet; winter wheat; winter barley; cover crop. These included conventional mouldboard ploughing, conservation tillage with no loosening and conservation tillage where loosening was carried out with a wide blade chisel plough, (1) before winter barley, (2) before the cover crop (mustard or California bluebell) and (3) before winter barley and the cover crop.Wheel-induced compaction decreased the pore space and in most cases eliminated differences due to tillage practice. Pore space on the wheel-tracked plots of the conventional treatment was considerably lower than on the non-wheel-tracked plots. Similar results were obtained for the conservation tillage plots but only where loosening had been carried out within the last 18 months.In summary of the 6 years experiment, there was in general no evidence that conventional tillage was superior to conservation tillage with respect to the yields of sugar beet, winter wheat, or, within certain limits, winter barley on loamy sand.Accordingly, conservation tillage with crop rotation-specific non-inverting soil loosening, promises to be a potential strategy not only with regard to reducing soil erosion, but a programme for reducing costs and alleviating traffic-induced soil compaction.     

Traffic and tillage effects on soil conditions and crop growth on a swelling clay soil

Abstract. Trafficked and non-trafficked (12 m gantry) crop production systems, which had been maintained on an Evesham series 60% clay soil since 1986, were used again in 1993 during the cultivation and sowing of winter wheat. After a one year set-aside break, mouldboard ploughing, tine cultivation and rotary digging were compared. Measurements were made of tillage energy, soil tilth, cone penetration resistance, biological activity and crop performance, and on specific plots, soil density, seedbed tilth and water release characteristics. Despite the one year's set-aside break, the effect of the previously applied traffic treatments remained and resulted in a smaller specific plough resistance and tillage energy on the non-trafficked soil. Tine cultivator draught however was greater on the non-trafficked compared with the trafficked plots. The specific energy required for rotary digging on non-trafficked soil was similar to that required during the ploughing of similar plots. A measure of indefinite biotic activity indicated that this was apparently greater on the non-traffficked soil, while soil density was decreased by up to 18% in these conditions compared with the trafficked land. Average cone resistance over the depth range 0 to 0.5 m was 1.51 MPa on the trafficked, compared with 1.24 MPa on the non-trafficked soil. Cone resistance also tended to be greater after tine cultivation compared with that after ploughing. Water release curves were interpreted as showing more macropores within the topsoil of the non-trafficked compared with the trafficked plots. Tine cultivation on trafficked soil had more smaller pores than mouldboard plough cultivation. Winter wheat yield was increased by 25% (from 8 to 10 t/ha) on non-trafficked compared with trafficked soil.     

The role of tillage and crops on a soil loss of an arable Stagnic Luvisol

The poor physical, chemical and biological properties make Stagnic Luvisol highly susceptible to water erosion on sloping terrains. The objective of this paper is to estimate the effect of different tillage treatments and crops (maize, soybean, winter wheat, spring barley, oilseed rape) on water erosion. The highest erosion in investigation period (1995–2014) was recorded in the control treatment with fallow, followed by the treatment that involved ploughing and sowing up and down the slope. Significantly, lower soil losses were recorded in no-tillage and treatments with ploughing and sowing across the slope. Regarding the crops significantly higher soil losses were recorded in spring row crops (maize and soybean) compared to high-density winter crops (wheat and oilseed rape) and double crop (spring barley with soybean). In the studied period, an average loss of 46 mm of the plough layer was recorded in the control treatment, while in treatment with ploughing and sowing up and down the slope average annual soil loss was 10 mm. According to the results of this study no-tillage and tillage across the slope are recommended as tillage which preserves soil for the next generations in agro-ecological conditions of continental Croatia.     

Nitrogen uptake,nitrate leaching and root development in winter‐grown wheat and fodder radish

Early seeding of winter wheat (Triticum aestivum L.) has been proposed as a means to reduce N leaching as an alternative to growing cover crops like fodder radish (Raphanus sativus L.). The objective of this study was to quantify the effect of winter wheat, seeded early and normally, and of fodder radish on N dynamics and root growth. Field experiments were carried out on a humid temperate sandy loam soil. Aboveground biomass and soil inorganic N were determined in late autumn; N uptake and grain yield of winter wheat were measured at harvest. Nitrate leaching was estimated from soil water samples taken at 1 m depth. Root growth was measured late autumn using the core break and root washing methods. Winter wheat root growth dynamics were followed during the growing season using the minirhizotron method. The 2013–2014 results showed that early seeding of wheat improved autumn growth and N uptake and reduced N leaching during the winter compared with the normal seeding time. Early‐seeded wheat (WW_early) was, however, not as efficient as fodder radish at reducing N leaching. Proper establishment of WW_early was a prerequisite for benefiting from early seeding, as indicated by the 2012–2013 results. Early seeding improved root growth throughout the 2013–2014 growing season compared with normal seeding time, but had no significant effect on crop grain yield. Our results indicate the potential of using early seeding as a tool to limit drought susceptibility and increase nutrient uptake from the subsoil.     

Tillage and water conservation: experience in the Pacific Northwest

Abstract. Tillage practices for water conservation in the Pacific Northwest, USA, wheat region emphasize the infiltration and retention of winter rain and snow and suppression of evaporation and transpiration by weeds. The wheat-fallow system dominates in the semi-arid areas and winter wheat-spring crop rotations are most common in the sub-humid areas. The main features of water conservation during the fallow season include chisel ploughing in the autumn to reduce winter runoff, and spring and summer tillage to kill weeds, minimize evaporation, and conserve seed-zone water. Water in the seed zone is conserved by establishing a soil mulch having properties that thermally insulate the seed zone while at the same time restricting upward liquid and water vapour flow. Water conservation in the more humid zones involves chisel ploughing in autumn, uphill ploughing, and stubble retention to reduce winter runoff. New practices include minimum tillage and no-till planting methods which maintain surface residues. However, heavy equipment associated with current trends in no-till is causing soil compaction which may decrease infiltration rates. Methods under experimentation to improve infiltration with conservation tillage systems include slot mulching, paraplowing, and the use of basin pitters.     

耕作方式对麦–玉轮作农田固碳、保水性能及产量的影响

【目的】 农田固碳保水性能是影响作物产量的关键因素,研究耕作方式对耕层 (0—20 cm) 土壤碳、水含量和产量的影响,为选择适宜该地区的最佳耕作措施提供参考。 【方法】 保护性耕作长期定位试验始于2002年,种植制度为冬小麦–夏玉米一年两熟,两季秸秆全量粉碎 (3～5 cm) 还田,试验设传统翻耕、深松、旋耕和免耕4种耕作方式。对2015—2016年作物生长各时期土壤有机碳含量、土壤含水量、碳水储量、产量和等价产量等进行了测定。 【结果】 不同处理麦–玉轮作农田0—20 cm土层有机碳含量有所不同。耕作措施对土壤有机碳含量有显著 (P < 0.05) 影响,表现为深松和免耕能显著增加0—10 cm土层有机碳含量,且以深松效果最为显著 ( P < 0.05)。与传统翻耕相比,免耕和旋耕降低了10—20 cm土层土壤有机碳含量;深松比传统翻耕显著 ( P < 0.05) 增加了小麦季土壤有机碳含量,玉米季没有显著性差异 ( P < 0.05)。0—10 cm土层,玉米季旋耕和免耕处理的土壤含水量高于深松和传统翻耕;在10—20 cm土层小麦季免耕处理土壤含水量高于其他三种耕作方式。产量结果表明,深松能有效增加作物的有效穗数、穗粒数和千粒重,进而增加籽粒产量和周年等价产量;免耕显著 ( P < 0.05) 降低了亚表层 (10—20 cm) 有机碳含量,降低穗粒数和千粒重,不利于作物增产。两年小麦玉米单作产量和周年等价产量均表现为深松 > 传统翻耕 > 旋耕 > 免耕。 【结论】 深松能有效促进耕层土壤有机碳积累和保水性能提高,增加作物的有效穗数、穗粒数和千粒重,从而增加产量;免耕显著 (P < 0.05) 提高了表土层 (0—10 cm) 碳储量,有助于增强耕层土壤的保水性能。      

Early season nitrogen accumulation in winter wheat

Cereal rye (Secale cereale L.) is widely used as a winter cover crop to conserve soil residual nitrogen (N) in the mid‐Atlantic region of the United States. Cereal rye, however, has agronomic drawbacks that may make other winter small grain crops more desirable alternatives. Winter wheat (Triticum aestivum L.) is a small grain that could substitute for cereal rye as a cover crop because it would give growers the flexibility of using it as a cover crop or growing it to maturity. There is currently little information on early season N accumulation of winter wheat cultivars, which is critical for the success of a small grain cover crop. To determine the degree of variation in early season N accumulation and early season biomass yield in soft red winter wheat in the mid‐Atlantic region, twenty‐five commercially available cultivars were evaluated at Beltsville, MD in the 1996/1997 and 1997/1998 growing seasons. Acereal rye cultivar ("Wheeler") was included as a cover crop control. Samples of plant tissue were taken at Feekes growth stage 5 and at physiological maturity each year. There were significant differences among cultivars for early season N accumulation and biomass yield. A large group of wheat cultivars had similar early season N accumulation and biomass yield as the cereal rye cover crop control. This suggests that some cultivars of winter wheat may be as effective as cereal rye as a winter cover crop. Early season N accumulation was highly correlated (r=0.90***) with early season biomass yield rather than with plant N content. These results indicate that soft red winter wheat has potential as a dual grain and cover crop and could be considered an alternative to cereal rye as a winter cover crop for conserving residual soil nitrogen in the mid‐Atlantic region of the United States.     

Subsoil loosening in a crop rotation for organic farming eliminated plough pan with mixed effects on crop yield

Compacted subsoil may reduce plant root growth with resulting effects on plant uptake of water and nutrients. In organic farming systems subsoil loosening may therefore be considered an option to increase nutrient use. We investigated the effect of subsoil loosening with a paraplow to ca. 35 cm depth within a four-crop rotation in an organic farming experiment at Foulum (loamy sand) and Flakkebjerg (sandy loam) in Denmark. In each of the years 2000–2003, half of four plots per site were loosened in the autumn bearing a young grass-clover crop (mixture of Lolium perenne L., Trifolium repens L. and Trifolium pratense L.) established by undersowing in spring barley (Hordeum vulgare L.). The grass-clover was grown for another year as a green manure crop and was followed by winter wheat (Triticum aestivum L.), lupin (Lupinus angustifolius L.):barley and spring barley in the following 3 years. On-land ploughing was used for all cereal and pulse crops. Penetration resistance was recorded in all crops, and the results clearly showed that subsoil loosening had effectively reduced the plough pan and that the effect lasted at least for 3.5 years. Measurements of wheat root growth using minirhizotrons at Foulum in 2002/2003 did not show marked effects of subsoil loosening on root frequency in the subsoil. Subsoil loosening resulted in reduced growth and less N uptake of the grass-clover crop in which the subsoil loosening was carried out, probably due to a reduced biological nitrogen (N) fixation resulting from a smaller clover proportion. This had a marked effect on the growth of the succeeding winter wheat. Negative effect of subsoil loosening on yield of winter wheat and spring barley was observed without manure application, whereas small positive yield effect of subsoil loosening was observed in crops with a higher N supply from manure. Yield decrease in winter wheat was observed in years with high winter rainfall. There was no significant effect of subsoiling on grain yield of the lupin:barley crops, although subsoiling had a tendency to increase crop growth and yield during dry summers. Our results suggest that subsoil loosening should not be recommended in general under Danish conditions as a measure to ameliorate subsoil compaction.     

Residue cover,soil structure,weed infestation and spring cereal yields as affected by tillage and straw management on three soils in Norway

Four field trials (spring wheat and oats) were conducted (one on clay soil, one on loam soil and two on silt soil) for three years in important cereal growing districts, to investigate the influence of tillage regimes (ploughing versus reduced tillage in either autumn or spring) and straw management (removed and retained) on plant residue amounts, weed populations, soil structural parameters and cereal yields. The effect of tillage on soil structure varied, mainly due to the short trial period. In general, the amount of small soil aggregates increased with tillage intensity. Reduced soil tillage, and in some cases spring ploughing, gave significantly higher aggregate stability than autumn ploughing, thus providing protection against erosion. However, decreasing tillage intensity increased the amounts of weeds, particularly of Poa annua on silt soil. Straw treatment only slightly affected yields, while effects of tillage varied between both year and location. Reduced tillage, compared to ploughing, gave only small yield differences on loam soil, while it was superior on clay soil and inferior on silt soil. Our results suggest that shallow spring ploughing is a good alternative to autumn ploughing, since it gave comparable yields, better protection against erosion and was nearly as effective against weeds.     

耕深对土壤物理性质及小麦-玉米产量的影响

为了解不同犁底层破除程度对黄淮海平原农田土壤蓄水保墒、穿透阻力动态变化及作物产量的影响,在山东德州试验基地以冬小麦-夏玉米轮作农田为研究对象,设置4个犁底层厚度处理,分别为犁底层不破除(RT15)、犁底层破除1/3(DL20)、犁底层破除2/3(DL25)和犁底层完全破除(DL40)。结果表明:1)完全或者部分破除犁底层均能够显著降低10~30 cm土层容重和穿透阻力,各处理降低幅度具体表现为DL40DL25DL20RT15。2)DL20、DL25和DL40处理有利于增加降水或灌溉后水分入渗,冬小麦苗期20~70 cm土壤平均含水率分别较RT15处理提高5.3%、15.9%和23.6%,且冬小麦季耗水量分别较RT15处理提高4.9%、10.2%和11.6%;DL20、DL25和DL40处理夏玉米苗期20~70 cm土壤平均含水率分别较RT15处理提高7.7%、14.2%和15.8%,但夏玉米季耗水量分别较RT15处理降低5.8%、7.6%和10.5%。3)冬小麦季0~15和15~30 cm土层穿透阻力均表现为双峰型,且2土层受冻融作用影响各处理在越冬期达到穿透阻力峰值1 489.2~2 128.1和1 925.4~4 423.7 kPa;30~45 cm土层各处理穿透阻力变化规律在两季作物生长后期差异较大,冬小麦生长后期表现为DL40DL25DL20RT155,而夏玉米后期表现为DL40DL25DL20RT15。4)相对完全打破犁底层,部分打破犁底层更有利于提高水分利用效率,显著增加作物产量,DL25处理冬小麦和夏玉米产量分别较DL40处理增加4.2%和2.4%。综合考虑,DL25是目前相对较好的犁底层改良方式,此时犁底层厚度适当,既可节省农机能耗,又可兼有透水、增产效能。     

Residue Decomposition and Fate of Nitrogen‐15 in a Wheat Crop under Different Previous Crops and Tillage Systems

Abstract

Nitrogen (N) management may be improved by a thorough understanding of the nutrient dynamics during previous‐crop residue decomposition and its impact on fertilizer N fate in the soil–plant system. An experiment was conducted in the Argentine Pampas to evaluate the effect of maize and soybean as previouscrops and plow‐till and no‐till methods on N dynamics and ¹⁵N‐labeled fertilizer uptake during a wheat growing season. Maize and soybean residues released N under both tillage treatments, but N release was faster from soybean residues and when residues were buried by tillage. Net immobilization of N on decomposing residues was not detected. A regression model that accounted for 92% of remaining N variability included time, previous crop, and tillage treatment as independent variables. The rapid residue decomposition with N release was attributed to the high temperatures of the agroecosystem. The recovery of ¹⁵N‐labeled fertilizer in the wheat crop, soil organic matter, and decomposing residues was not statistically different between previous crop treatments or tillage systems. Crop uptake of fertilizer N averaged 52% across treatments. Forty percent of fertilizer N was removed in grains. Immobilization of labeled N on soil organic matter was substantial, averaging 34% of the ¹⁵N‐labeled fertilizer retained, but was very small on decomposing residues, averaging 0.2–3.0%. Fertilizer N not accounted for at harvest in the soil–plant system was 12% and was ascribed to losses. Previous crop or tillage system had no impact on wheat yield, but when soybean was the previous crop, N content of grain and straw+roots increased. Discussion is presented on the potential availability of N retained in wheat straw, roots, and soil organic matter for future crops.     

Effects of tillage systems and rotations on crop production for a thin Black Chernozem in the Canadian Prairies

Soil degradation is the single most important threat to global food production and security. Wind and water erosion are the main forms of this degradation, and conservation tillage represents an effective method for controlling this problem. The objective of this study was to quantify the effects of three tillage methods [zero (ZT), minimum (MT) and conventional (CT)] and three four-year crop sequences [spring wheat (Triticum aestivum L.)–spring wheat–winter wheat–fallow; spring wheat–spring wheat–flax (Linum usitatissimum L.)–winter wheat; spring wheat–flax–winter wheat–field pea (Pisum sativum L.] on crop establishment, plant height, seed weight, soil water storage, crop water use, crop water use efficiency and grain yield over a 12-year period under Canadian growing conditions. Plant establishment was not adversely affected by tillage systems or crop sequences except for flax, where a small reduction was observed with ZT and MT. Conservation tillage showed a yield benefit over CT of 7%, 12.5% and 7.4% for field pea, flax and spring wheat grown on cereal stubble, respectively over the 12 years of the study. Much of the yield increase was due to an increase in soil water in the 0–30 cm soil layer with ZT and MT. However, tillage systems had no effect on grain yield for spring wheat grown on fallow and field pea stubble due to a lack of differences in spring soil water content. Flax grown in sequence with cereals only yielded higher than when it was grown in the sequence which included field pea, even though flax was seeded on spring wheat stubble in both cases. Winter wheat yielded higher when grown on flax stubble than on spring wheat stubble. The results indicate that a one-year non-cereal break crop was enough to alleviate the negative effects of consecutive cereal crops on winter wheat. Spring wheat grown on field pea stubble always yielded more than when grown on cereal stubble. A 10% increase in water use efficiency was observed with flax grown with ZT and MT management. Crop sequence improved water use efficiency in flax and spring wheat. Growing spring wheat on field pea stubble as opposed to growing it on cereal stubble resulted in a 10% increase in water use efficiency. Overall, rainfall accounted for 73%, 72%, 67% and 65% of total water used by field pea, flax, winter wheat and spring wheat, respectively. This explains the large year effect as a result of variation in growing (May–August) season precipitation. The non-significant tillage system by year interaction implies that the positive benefits of ZT and MT occur over a wide range of growing conditions, while the absence of a tillage system by crop sequence interaction suggests that knowledge developed under CT management also applies to ZT and MT. The results of this study support the large shifts towards in conservation tillage being observed in the Canadian prairies.