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.     

Effect of tillage and residue management on hydrol-thermal regimen, nutrient uptake and yield of wheat in a river deposit

Field experiments were conducted on a river deposit during 1983–1984 and 1984–1985 in order to study the effect of different soil management practices, such as zero tillage with surface-applied crop residue mulch at a rate of 10 t ha⁻¹ (ZT+M), conventional tillage (CT), CT+ surface-applied crop residue mulch at a rate of 10 t ha⁻¹ (CT + M), CT+crop residue incorporation at a rate of 10 t ha⁻¹ (CT + SI), CT + farmyard manure incorporation at a rate of 10 t ha⁻¹ (CT + FYM), on soil hydro-thermal regime root growth, nutrient uptake and dry matter yield of winter wheat (Triticum aestivum L.). The soils of the site are classified as Entisol, Typic Psammaquent with pH 6.0, cation exchange capacity 10 c mol (p⁺) per kg in the surface (0–0.3 m) depth. In the CT + M and CT + FYM treatments, higher water retention was observed compared to CI. The minimum soil temperature was also raised by 3°C under CT + M to CT at 0.1-m depth. CT + M and CT + FYM had significantly higher root mass density compared with other treatments at all stages of crop growth. The nitrogen (N) uptake under these two treatments was also significantly higher compared to CT. Under CT+M, plants did not suffer from N stress compared to other treatments. Phosphorus (P) uptake (except at tillering) and potassium (K) uptake under CT+M and CT + FYM were significantly higher than for all the other treatments. Treatments ZT+M and CT+SI behave simply to CT in terms of hydro-thermal regime, root growth, nutrient uptake and dry matter yield. The grain yield under CT+M and CT+FYM during 1983–1984 and 1984–1985 was significantly higher than that under all the other treatments.     

Wheel traffic and tillage effects on runoff and crop yield

Traffic and tillage effects on runoff, soil water and crop production under rainfall were investigated over a period of 6 years on a heavy clay vertosols (vertisols) in Queensland, Australia. A split plot design was used to isolate traffic effects, while the cropping program and treatments were broadly representative of extensive grain production practice in the northern grain region of Australia. Treatments subject to zero tillage and stubble mulch tillage each comprised pairs of 90 m² plots, from which runoff was recorded. A 3 m wide controlled traffic system allowed one of each pair to be maintained as a non-wheeled plot, while the complete surface area of the other received a single annual wheeling treatment from a working 100 kW tractor.

Mean annual runoff from controlled traffic plots was 81 mm (36.3%) smaller than that from wheeled plots, while runoff from zero tillage was reduced by 31 mm (15.7%). Traffic and tillage effects appeared to be cumulative, so the mean annual runoff from controlled traffic and zero tillage plots, representing best practice, was 112 mm (47.2%) less than that from wheeled stubble mulch plots, representing conventional cropping practice. Rainfall infiltration into controlled traffic zero tillage soil was thus 12.0% greater than into wheeled stubble mulched soil. Rainfall/runoff hydrographs show that wheeling produced a large and consistent increase in runoff, whereas tillage produced a smaller increase. Treatment effects were greater on dry soil, but were still present in large and intense rainfall events on wet soil.

Plant available water capacity (PAWC) in the 0–500 mm zone increased by 10 mm (11.5%) and mean grain yields increased by 337 kg/ha (9.4%) in controlled traffic plots, compared with wheeled plots. Mean grain yield of zero tillage was 2–8% greater than that of stubble mulch plots for all crops except for winter wheat in 1994 and 1998. Increased infiltration and plant available water were probably responsible for increased mean grain yields of 497 kg/ha (14.5%) in controlled traffic zero tillage, compared with wheeled stubble mulch treatments. Dissipation of tractive and tillage energy in the soil is the apparent mechanism of deleterious effects on the soils ability to support productive cropping in this environment. Controlled traffic and conservation tillage farming systems appear to be a practicable solution.     

宁南山区保护性农业措施对冬小麦农田休闲期土壤水分的影响

[目的]研究宁南山区冬小麦农田休闲期保护性农业措施对土壤水分的影响,为该区降雨资源的高效利用以及保护性农业的可持续发展提供理论依据。[方法]基于不同时期多个保护性农业试验土壤水分数据比较分析。[结果](1)在干旱的情况下,免耕留茬处理能够显著增加土壤表层(0—20cm)含水量。(2)在免耕的情况下,随着秸秆留茬高度的增加,土壤水分呈现增加趋势。(3)在降雨量较大且降雨量具有连续性的情况下,常规耕作处理在土壤表层保蓄了较多的土壤水分(0—20cm),免耕秸秆覆盖处理能够增加土壤20—80cm土壤水分含量。(4)冬小麦休闲期种植豆科作物,降低了土壤水分,其降低幅度与降雨量以及种植密度有关,种植密度越大,对土壤水分的影响越大。[结论]免耕+留茬耕作措施能够提高冬小麦农田休闲期土壤水分含量,覆盖作物降低了休闲期土壤水分含量。     

Crown rot and common root rot in wheat grown under different tillage and stubble treatments in southern Queensland, Australia

In southern Queensland, crown rot caused by Fusarium graminearum Group 1 and common root rot caused by Bipolaris sorokiniana are common soilborne diseases of wheat and barley. The incidence of these diseases was measured in the susceptible wheat (Triticum aestivum L.) cultivar, Hartog which was grown under no tillage, reduced tillage (two tillage operations plus herbicides) and where stubble was retained or removed by burning (1984–1986) or physically removed (1987–1993). Primary tillage was with blade, disc or chisel implements. The level of crown rot and common root rot was higher where stubble was retained than where it was removed. There was a significant interaction in incidence of crown rot between stubble management and some types of tillage. Where there was no tillage, incidence of crown rot was significantly higher where stubble was retained (32.2%) than where it was removed (4.7%) whereas under disc tillage, there was no significant difference in disease level between stubble treatments (12–17%). Incidence of crown rot was not affected by the type of tillage employed. The incidence of deadheads (heads without grain) caused by crown rot was lowest in the no tillage plots (4.3%) and highest in the reduced (19.3%) and conventional (12.2%) disc tillage stubble retained treatments. Available soil water (depth of 1.2 m) at sowing and anthesis was lowest in the conventional disc stubble retained plots and highest in the no tillage stubble retained plots. It is hypothesised that the high levels of deadheads were due to moderate to high levels of disease and low available soil water at planting and anthesis. Although incidence of crown rot was high under no tillage, incidence of deadheads was lower than in other treatments due to the higher availability of soil water. Severity of common root rot was lower in stubble removed, than in stubble retained, treatments and also lower in no tillage than in any of the other tillage treatments.     

轮作、耕作及行距对麦田土壤温度动态的影响

研究了加拿大南部冬小麦田在轮作、耕作和行距共同作用下的土壤温度动态。田间裂区试验主区为3个轮作(冬小麦连作、冬小麦/油菜轮作和冬小麦/夏休闲),副区包括两种耕作技术(免耕和常规耕作),小裂区包括两种种植行距(等行距和大小行)。结果表明,免耕处理下秸秆覆盖有效地降低了冬季土壤的冻结深度。在1993～1994年度,连作小麦免耕土壤的-5℃等温线要比常规耕作浅22cm。免耕秸秆覆盖的温度效应在冬小麦连作和冬小麦/油菜两种轮作上比在冬小麦/夏休闲上更为明显。在冬小麦连作和冬小麦/油菜轮作下,免耕土壤2.5cm的春季温度连续4个月显著低于常规耕作土壤。1994年4月8日,免耕和常规耕作农田2.5cm处的温差在冬小麦连作处理上达到4.1℃。对于冬小麦/夏休闲处理,由于秸秆覆盖量较少,耕作措施对土壤温度的影响不太明显。在1994年春季,大小行种植的土壤温度显著高于等行距种植的土壤温度。因此,免耕主要通过秸秆覆盖来改变土壤的温度状况。通过轮作、耕作和行距等措施,可以在一定程度上实现土壤温度的人为调节     

Long-term effect of ploughing, and organic matter input on soil moisture characteristics of a Ferric Lixisol in Burkina Faso

Soil moisture characteristic curves were determined in long-term trials at the agronomic research center of Saria (latitude 12°16′ N, longitude 2°09′ W) in West-central Burkina Faso. The agronomic treatments combined soil tillage with organic and chemical fertilizers. The twin values for soil moisture and water potential showed that on ploughed plots, moisture content was higher at low suction and lower at high suction than the hand hoed plots. Moisture contents were higher for extreme suctions (pF < 1.5 and >3) on plots that received high dose of animal manure. The bush fallow plots behaved as a ploughed plot at low suction and like a hand hoed plot at the high suction. Field capacities were around 9.50% (g/g) and 8% (g/g), respectively, for hand hoed and ploughed plots, while the wilting points for both were of 5–6% (g/g). Organic matter input improved field capacity and soil water content at wilting point but not the useful available water (UAW). The UAW ≥10 mm on the fallow and the control, while it was <9 mm on the other treatments in 0–20 cm soil layer. Soil structural modifications induced by tillage and organic matter input explained these differences in soil hydrologic regime.     

科学耕作与留茬改良小麦-玉米两熟农田土壤物理性状及增产效果

为了探讨不同覆盖耕作方式对农田土壤物理性状及作物产量的影响,该试验研究了免耕、常规2种耕作方式和4种留茬高度的玉米秸秆还田处理,对麦-玉两熟农田土壤含水率、容重、孔隙度以及作物产量的影响。结果表明:在0～40cm土层内,秸秆还田的集雨和保水效果显著,免耕留茬0.5m还田处理的含水率比免耕无覆盖处理增加了15.95%。秸秆还田量对0～40cm内土壤贮水量的影响不同。耕作措施显著影响了土壤容重,小麦播种前常规留茬1m还田、常规全量还田处理容重低至1.0g/cm3左右。秸秆还田能增加土壤总孔隙度、降低毛管与非毛管孔隙度的比值。单一免耕处理降低了作物产量,而免耕覆盖能增产,其留茬1m还田处理比无还田处理增产22.44%,比常规留茬0.5m还田处理高3.64%。因此,免耕留茬1m还田处理在改善农田土壤物理性状和增加作物产量方面显著,该研究可为农田管理过程中耕作措施和秸秆还田量的选择提供参考依据。     

Effects of three soil tillage systems on some biological activities in an Ultisol from southern Chile

Intensive tillage for annual crop production may be affecting soil health and quality. However, tillage intensity effects on biological activities of volcanic-derived soils have not been systematically investigated. We evaluated the effects of three different tillage practices on some biological activities of an Ultisol from southern Chile during the third year of a wheat–lupin–wheat crop sequence. Treatments were: no tillage with stubble burning (NTB), no tillage without stubble burning (NT) and conventional tillage with disk-harrowing and stubble burning (CT). Biological activities were evaluated in winter and summer at 0–200 mm and at three soil depths (0–50, 50–100 and 100–200 mm) in winter. Total organic C and N were significantly higher under no-tillage systems than CT. In general, NT increased C and N of microbial biomass in comparison with CT, especially in winter. Microbial biomass C was closely associated with microbial biomass N (r = 0.986, P < 0.05); acid phosphomonoesterase (r = 0.999, P < 0.05); β-glucosidase (r = 0.978, P < 0.05), and others. Changes in biological activities occurred mainly in the upper soil layer (0–50 mm depth) in spite of the short duration of the experiment. Biological activities could be used as practical biological indicators to apply the more appropriate management systems for increasing soil sustainability or productivity.     

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.     

Long-term effects of tillage systems and rotations on soil structural stability and organic carbon stratification in semiarid central Spain

Under semiarid Mediterranean climatic conditions, soils typically have low organic matter content and weak structure resulting in low infiltration rates. Aggregate stability is a quality indicator directly related to soil organic matter, which can be redistributed within soil by tillage. Long-term effects (1983–1996) of tillage systems on water stability of pre-wetted and air dried aggregates, soil organic carbon (SOC) stratification and crop production were studied in a Vertic Luvisol with a loam texture. Tillage treatments included conventional tillage (CT), minimum tillage (MT) and zero tillage (ZT) under winter wheat (Triticum aestivum L.) and vetch (Vicia sativa L.) rotation (W–V), and under continuous monoculture of winter wheat or winter barley (Hordeum vulgare L.) (CM). Aggregate stability of soil at a depth of 0–5 cm was much greater when 1–2 mm aggregates were vacuum wetted prior to sieving (83%) than when slaked (6%). However, slaking resulted in tillage effects that were consistent with changes in SOC. Aggregate stability of slaked aggregates was greater under ZT than under CT or MT in both crop rotations (i.e., 11% vs. 3%, respectively).

SOC under ZT tended to accumulate in the surface soil layer (0–5 and 5–10 cm) at the expense of deeper ones. At depths of 10–20 and 20–30 cm no differences in SOC were encountered among tillage systems, but CT exhibited the highest concentration at 30–40 cm depth. Nevertheless, when comparisons were made on mass basis (Mg ha⁻¹), significant differences in stocked SOC were observed at depths of 0–10 and 0–20 cm, where ZT had the highest SOC content in both rotations. The stock of SOC to a depth of 40 cm, averaged across crop rotations, was greater under ZT (43 Mg ha⁻¹) than under CT (41 Mg ha⁻¹) and MT (40 Mg ha⁻¹) although these figures were not significantly different. Likewise, no significant differences were encountered in the stock of SOC to a depth of 40 cm among crop rotations (i.e., 42 Mg ha⁻¹ for W–V vs. 40 Mg ha⁻¹ for CM).

Crop production with wheat–vetch and continuous cereal showed no differences among tillage systems. Yields were strongly limited by the environmental conditions, particularly the amount of rainfall received in the crop growth season and its distribution. Similar yield and improved soil properties under ZT suggests that it is a more sustainable system for the semiarid Mediterranean region of Spain.     

Wheel traffic impact on soil conditions as influenced by tillage system in Central Anatolia

The increased limiting effects of soil compaction on Central Anatolian soils in the recent years demonstrate the need for a detailed analysis of tillage system impacts. This study was undertaken to ascertain the effects of seven different tillage systems and subsequent wheel traffic on the physical and mechanical properties of typical Central Anatolian medium textured clay loam soil (Cambisol), south of Ankara, Turkey. Both tillage and field traffic influenced soil bulk density, porosity, air voids and strength significantly except the insignificant effect of traffic on moisture content. Traffic affected the soil properties mostly down to 20 cm. However, no excessive compaction was detected in 0–20 cm soil depth. The increases of bulk density following wheel traffic varied between 10–20% at 0–5 cm and 6–12% at 10–15 cm depth. In additions, traffic increased the penetration resistance by 30–74% at 0–10 cm and 7–33% at 10–20 cm. Less wheel traffic-induced effects were found on chisel tilled plots, compared to ploughed plots. Soil stress during wheel passage was highly correlated with soil strength. Also, both tillage and traffic-induced differences were observed in mean soil aggregate sizes, especially for mouldboard ploughed plots. The obtained data imply that chisel+cultivator-tooth harrow combination provides more desirable soil conditions for resisting further soil compaction.     

Corn stubble height and residue placement in the northern US Corn Belt Part I. Soil physical environment during winter

Management of crop residue is important for sustaining biological activity in soils during winter and promoting soil water recharge and early spring thaw in cold regions. This study assessed the impact of stubble height and residue placement in a corn (Zea mays L.) production system on the soil microclimate during winter in the northern Corn Belt of the USA. Residue treatments were established in a randomized block design after corn harvest in the autumn of 1993–1995 near Morris, MN. Corn was harvested using a combine that cut stalks at 60, 30 and approximately 0 cm above the soil surface and uniformly spread harvested residue over the soil. Treatments included: (1) 60 cm stubble, (2) 30 cm stubble, (3) 30 cm stubble with alternating bare and residue covered inter-rows, (4) 0 cm stubble, and (5) 0 cm stubble with all residue removed from the soil surface. Snow cover, depth of soil freezing and thawing, soil temperature and water content at various depths in the soil profile, and reflected global and net radiation were monitored during winter from November to March each year. Taller (60 cm) stubble trapped more snow, reduced the depth of frost penetration by at least 0.5 m, and hastened thawing of the soil profile by at least 25 days during winter as compared with short (0 cm) stubble and 0 cm stubble without residue treatments. Near surface, winter soil temperatures were moderated by at least 2 °C in the 60 cm stubble versus 0 cm stubble without residue treatments. Linear regression analysis suggested that 52, 93 and 40% of the variability in soil water recharge caused by residue treatments during successive winters, respectively, could be explained by differences in snow cover, soil water content and thaw depth among treatments. On clear days in autumn and spring, albedo was highest for the 0 cm stubble and lowest for the 0 cm stubble without residue treatments. Net radiation, however, was lowest for the 0 cm stubble and highest for the 0 cm stubble without residue treatments as compared with other residue treatments. Results from this study suggest that corn production systems in the northern Corn Belt which retain tall stubble on the soil surface will promote warmer soils during winter and earlier spring thaw as compared with those which retain short or no stubble on the soil surface.     

Tillage and crop residue management affect Vertisol properties and grain sorghum growth over seven years in the semi-arid sub-tropics. 2. Changes in soil properties

Six treatments, disc (D), blade (B) or zero (Z) tillage, each with stubble (crop residue) retained (+) or removed (−), were imposed during fallow periods between annual grain sorghum crops from June 1978 to June 1985 on a grey Vertisol in the semi-arid sub-tropics of central Queensland. Plots were neither irrigated nor fertilized. Soil profiles for chemical analysis were sampled post-harvest and pre-plant after fallow. For surface soil (0–0.1 m and sometimes also 0.1–0.2 m) during the 7 years, net decreases were measured for organic and total carbon, total nitrogen, total bicarbonate extractable and calcium chloride extractable phosphorus, total sulphur, total and exchangeable potassium. Net increases were measured for exchangeable sodium, calcium and magnesium. No net changes were found for dispersion ratios and cation exchange capacity. A net decrease in nitrate at 0.6–1.6 m began after 3 years. At 0–1.6 m, changes in pH, electrical conductivity, chloride and ammonium were negligible.

General means at 0–0.1 m decreased annually from June 1978 by 3.9% for organic carbon, 3.1% for total nitrogen, 7.5% for bicarbonate extractable phosphorus and 10.0% for calcium chloride extractable phosphorus. Decreases in organic carbon and total nitrogen had similar trends for each tillage treatment, being greater with stubble removed than with stubble retained. Decreases were least for Z+. After five years the increase in exchangeable sodium was highest for Z−. The pattern for each tillage treatment was for higher exchangeable calcium and magnesium at 0−0.1 m and higer exchangeable potassium at 0–0.02 m with stubble retained than with stubble removed. After 7 years the silt + clay dispersion ratio was lower for Z+ and Z− than for the other treatments.

There was an average net gain of 30 kg ha⁻¹ of nitrate-N at 0–0.6 m during fallow periods followed by a similar loss during cropping periods. Nitrate at the end of the fallow was equally distributed at three depths: 0–0.1, 0.1–0.2 and 0.2–0.6 m. On two occasions after a crop, the pattern was less nitrate (0–0.6 m) with stubble retained than with stubble removed, the difference for each tillage treatment increasing in the order D−1) ranged from 62 kg N ha⁻¹ for Z− to 128 kg N ha⁻¹ for Z+. The decrease for all tillage treatments was greater where stubble was retained than where it was removed. Decreases where stubble was retained were in the order D相似文献   

Effects of Tillage Methods on Soil Carbon and Wind Erosion

Current interest in soil‐conserving tillage in China has developed from the concern that Chinese agricultural land loses 73·8 Mg C annually. Previous research has shown that changing from conventional tillage to conservation tillage field management increases soil C sequestration. The aim of this study is to determine if no tillage with stubble retention can reduce soil carbon loss and erosion compared with conventional tillage for a cornfield in northern China. We found that soil organic C storage (kg m⁻²) under conservation tillage in the form of no post‐harvest tillage with stubble retention increased from 28% to 62% in the soil depths of 0–30 cm (p < 0·01) compared with the conventional tillage. Retaining post‐harvest stubble with a height of 30 cm and incorporating the stubble into the soil before seeding the next spring increased soil organic carbon the most. Carbon storage (kg ha⁻¹) in aboveground and belowground biomass of the corn plants in seedling and harvest stages was significantly greater (p < 0·01) with stubble retention treatments than with conventional tillage. Carbon content in root biomass in all treatments with stubble retention was significantly greater than that with conventional tillage. Soil erosion estimates in the study area under conservation tillage with stubble retention was significantly lower than that under conventional tillage during the monitoring period. Given the complexities of agricultural systems, it is unlikely that one ideal farming practice is suitable to all soils or different climate conditions, but stubble retention during harvesting and incorporation of the stubble into soil in the next spring appears to be the best choice in the dry northern China where farmlands suffer serious wind erosion. Copyright © 2015 John Wiley & Sons, Ltd.     

Effects of tillage and straw management on Alaskan weed vegetation: a study on newly cleared land

The effects of tillage and straw management in a continuous spring barley system were studied during 1983–1985 on land near Delta Junction, Alaska, that had just been cleared for agricultural production. This research was a part of a multidisciplinary approach to design agricultural systems to minimize soil erosion on interior Alaskan agricultural land. Total weed ground cover and cover of native grasses such as bluejoint reedgrass (Calamagrostis canadensis (Michx) Nutt.) and native broadleaves was highest in no-till plots and was lowest in plots that were disked twice each year. Total weed ground cover increased during 1983–1985. Ground cover of native grasses was greater when stubble and straw residues were left on the soil surface than when the residues and stubble were removed. Greater snow cover where stubble is left may help to prevent freezing injury to the native grasses.     

Soil erosion estimation in conservation tillage systems with poultry litter application using RUSLE 2.0 model

Soil erosion is a major threat to global economic and environmental sustainability. This study evaluated long-term effects of conservation tillage with poultry litter application on soil erosion estimates in cotton (Gossypium hirsutum L.) plots using RUSLE 2.0 computer model. Treatments consisting of no-till, mulch-till, and conventional tillage systems, winter rye (Secale cereale L.) cover cropping and poultry litter, and ammonium nitrate sources of nitrogen were established at the Alabama Agricultural Experiment Station, Belle Mina, AL (34°41′N, 86°52′W), beginning fall 1996. Soil erosion estimates in cotton plots under conventional tillage system with winter rye cover cropping declined by 36% from 8.0 Mg ha⁻¹ year⁻¹ in 1997 to 5.1 Mg ha⁻¹ year⁻¹ in 2004. This result was largely attributed to cumulative effect of surface residue cover which increased by 17%, from 20% in 1997 to 37% in 2004. In conventional tillage without winter rye cover cropping, soil erosion estimates were 11.0 Mg ha⁻¹ year⁻¹ in 1997 and increased to 12.0 Mg ha⁻¹ year⁻¹ in 2004. In no-till system, soil erosion estimates generally remained stable over the study period, averaging 0.5 and 1.3 Mg ha⁻¹ year⁻¹with and without winter rye cover cropping, respectively. This study shows that cover cropping is critical to reduce soil erosion and to increase the sustainability of cotton production in the southeast U.S. Application of N in the form of ammonium nitrate or poultry litter significantly increased cotton canopy cover and surface root biomass, which are desirable attributes for soil erosion reduction in cotton plots.     

Ploughless tillage in Sweden. Results and experiences from 15 years of field trials

Results and experience from 140 field trials carried out during the period 1974–1988 are presented. The whole of Sweden was represented in the investigation, but the majority of sites were in the central and southern areas of the country. In the unploughed experimental plots, conventional autumn ploughing to 20–25 cm was compared with two or three stubble cultivations to approximately 10–12 cm depth. on average, use of ploughless tillage reduced yields of winter wheat, spring barley, winter and spring oilseed rape and sugarbeet and somewhat improved yields of oats and potatoes. The results from ploughless tillage were generally improved by the use of dual rear tractor wheels instead of single wheels, by the placement of artificial fertilizer instead of broadcasting and by the removal of straw. The incidence of annual weeds increased on average by 25% and stoloniferous weeds by 100%. The most suitable soils were peats, sandy loamy tills, silty loams or silty clay loams and heavy clays.     

Soil biotic and biochemical factors in a long-term tillage and stubble management experiment on a vertisol. 2. Nitrogen deficiency with zero tillage and stubble retention

The aim of this investigation was to find the cause of poor growth of barley that occurred with zero tillage and stubble retention in a long-term fallow management experiment on a vertisol in southern Queensland. The experiment compares 12 treatments comprising three factors of tillage (zero, mechanical), stubble (burnt, retained) and nitrogen fertilizer (0, 23 and 46 kg ha⁻¹ year⁻¹) in four randomised blocks. Dry matter yield of barley at anthesis showed a highly significant Mitscherlich relationship with tissue nitrogen (N) concentration. Cate-Nelson analysis indicated a critical N concentration of 1.58%N. The barley responded to fertilizer N although 9 of 12 zero-till, stubble-retained plots and 5 of 12 mechanical-till, stubble-retained plots still lay below the critical N concentration. Zero-till, stubble-retained treatment had least nitrate-N in the soil profile to 120 cm indicating a problem in N supply rather than in N recovery by the roots.

The effects of the long-term treatments on properties related to the N supplying capacity of the soil were investigated by determinations on topsoil samples from which undecomposed stubble was removed. Soil from zero-till, stubble-retained treatment had more organic carbon (C) and Kjeldahl N than mechanical-till, stubble-retained treatment which had more than stubble-burnt treatments. The C:N ratio of the soil was lower in stubble retained treatments. Kjeldahl N was higher with annual N fertilization only where stubble was retained. Organic C increased and Kjeldahl N decreased over a 3 year period in all treatments. Respiration of CO₂, mineralizable N, and microbial biomass C and N in the soil were all greater with long-term stubble retention than with stubble burning irrespective of tillage treatment.

Numbers of root-lesion nematodes (Pratylenchus thornei Sher and Allen) and stunt nematode (Merlinius brevidens (Allen) Siddiqi) following a wheat crop were substantially greater with zero-till than with mechanical-till. Root-lesion nematode were increased by N fertilization of previous crops while stunt nematodes were increased by stubble-retention. Earthworm numbers were increased by stubble retention particularly when combined with zero tillage.

Factors responsible for observed differences in soil nitrate and crop response to N in this field experiment appear to be: (a) N immobilization by recently retained stubble, (b) lower rates of mineralization of soil N under surface-retained stubble, and (c) higher rates of leaching in zero-till treatment.     

Impact of tillage, stubble management and crop rotation on nematode populations in a long-term field experiment

The population abundance of free-living and plant-parasitic nematodes was investigated in a long-term rotation/tillage/stubble management experiment at Wagga Wagga Agricultural Institute, New South Wales (NSW), Australia. The treatments were a combination of two crop rotations: wheat (Triticum aestivum)–wheat and wheat–lupin (Lupinus angustifolius); two tillage systems: conventional cultivation (CC) and direct drill (DD); and two stubble management practices: stubble retention (SR) and stubble burnt (SB). Plots of one of the wheat–wheat treatments received urea at 100 kg N ha⁻¹ during the cropping season. Soil samples from 0–5 and 5–10 cm depths were collected in September (maximum tillering), October (flowering) and December (after harvest), 2001, to analyse nematode abundance. Soil collected in September was also analysed for concentrations of total and labile C, and pH levels.Three nematode trophic groups, namely bacteria-feeders (primarily Rhabditidae), omnivores (primarily Dorylaimidae excluding plant-parasites and predators) and plant-parasites (Pratylenchus spp. and Paratylenchus spp.) were recorded in each soil sample. Of them, bacteria-feeders (53–99%, population range 933–2750 kg⁻¹ soil) dominated in all soil samples. There was no difference in nematode abundance and community composition between the 0–5 cm and 5–10 cm layers of soil. The mean population of free-living and plant-parasitic nematodes varied significantly between the treatments in all sampling months. In most cases, total free-living nematode densities (Rhabditidae and Dorylaimidae) were significantly (P < 0.001) greater in wheat–lupin rotation than the wheat–wheat rotation irrespective of tillage and stubble management practices. In contrast, a greater population of plant-parasitic nematodes was recorded from plots with wheat–wheat than the wheat–lupin rotation. For treatments with wheat–wheat, total plant-parasitic nematode (Pratylenchus spp. and Paratylenchus spp.) densities were greater in plots without N-fertiliser (295–741 kg⁻¹ soil) than the plots with N-fertiliser (14–158 kg⁻¹ soil).Tillage practices had significant (P < 0.05) effects mostly on the population densities of plant-parasitic nematodes while stubble management had significant effects (P < 0.05) on free-living nematodes. However, interaction effects of tillage and stubble were significant (P < 0.01) for the population densities of free-living nematodes only. Population of Rhabditidae was significantly higher in conventional cultivated plots (7244 kg⁻¹ soil) than the direct drilled (3981 kg⁻¹ soil) plots under stubble retention. In contrast, plots with direct drill and stubble burnt had significantly higher populations of Dorylaimidae than the conventional cultivation with similar stubble management practice. No correlations between abundance of free-living nematodes, and concentration of total C and labile C in soil were observed in this study. These results showed that stubble retention contributed for enormous population density of free-living (beneficial) nematodes while conventional cultivation, irrespective of stubble management, contributed for suppressing plant-parasitic nematodes.