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1.
Soil surface crusting and sealing are frequent but unfavorable processes in Mediterranean areas. Soil crust and seals form on bare soil subject to high-intensity rainfall, resulting in a hard, impenetrable layer that impedes infiltration and hampers the germination and establishment of plants. The adverse consequences of overland flow and reduced fertility can lead to erosion and ongoing degradation. Therefore, information on the distribution of surface crusts and their physical properties is essential to combat the undesired effects of crust formation in e.g. soil erosion and soil compaction. We studied the occurrence of crusts in a study area in Mediterranean southern France. Our objectives were to compare the physical and hydrological properties of the crusts and underlying soil, to identify the spectral characteristics (400 to 2500 nm) of the crusted and non-crusted soil surfaces using high-resolution field spectra, and to investigate the potential of mapping crust occurrence using airborne, hyperspectral HyMap images. The differences in some physical properties between crusted and non-crusted surfaces are significant while others are only marginal. Crusting markedly reduces the infiltration capacity and crust strength varies between the different soil types. Spectral differences are small, mainly in albedo values (overall reflectance) and in absorption band depth and shape. Albedo differences range from 8 to 40%. Differences in absorption band features in the spectra of crusts and non-crusted surfaces are small. Sixty percent of the crusted soil surfaces showed stronger absorption features in the clay mineral absorption bands at 2200 nm than non-crusted soils. Increased absorption is due to a relative enrichment in fines. Spectral feature fitting and linear spectral unmixing algorithms were applied to airborne HyMap images to evaluate the possibilities of mapping surface crusts. Crusts could be mapped in fallow, agricultural fields, but the spectral response of natural badlands was too fragmented for crust mapping.  相似文献   

2.
Rapid wetting of irrigated soils often leads to slaking and slumping, and on drying a surface crust and hard-set conditions may occur. This results in reduced crop emergence unless the surface is kept moist. The effect of aggregate size and water content on the emergence of soybean and maize from an Entic chromustert (heavy cracking clay) was determined using pots of sieved aggregates with size ranges less than 1, 1–2, 2–5 and 5–15 mm at soil water contents of 15, 20 and 25 g (100 g)−1. Unsieved soil was used as a control. Greatest emergence tended to occur from fine (1–2 mm) seedbeds compared with coarse (5–15 mm) seedbeds for both crops. A covered treatment, simulating a stubble mulch, resulted in greater emergence than an uncovered treatment for all water contents and aggregate sizes. Earlier emergence occurred from finer (less than 1 mm and 1–2 mm) seedbeds than from coarse (5–15 mm) seedbeds, and at the greatest water content used. Soil strength, measured with a shear vane, decreased with increasing water content and tended to be less on fine (1–2 mm) seedbeds compared with very fine (less than 1 mm) or coarse (5–15 mm) seedbeds. It is recommended that, for good emergence from this Entic chromustert, seedbeds be brought to a water content of 25 g (100 g)−1 by capillary wetting to prevent hardsetting and consist of 1–2 or 2–5 mm aggregates for soybean and maize, respectively, and have a stubble mulch on the surface. This corresponds to an equivalent depth of water of 15 mm and 9 mm for soybean and maize, respectively, in the top 50 mm of the profile.  相似文献   

3.
《Soil & Tillage Research》1988,11(2):133-145
The effect of aggregate size, a low level of stress (load of 2.7 kPa) and a surface crust on emergence and yield of wheat was determined, using field micro-plots of sieved aggregates with size ranges of <1, 1–2, 2–4 and >4 mm. The time to emergence was less with smaller aggregates, but in a wetter year the <1-mm aggregates caused a slight delay in emergence. Percentage emergence was greatest with the 2–4-mm aggregate-size range. Dry-matter production and grain yield both decreased with increasing aggregate-size range in the drier year, but the 1–2 mm aggregates gave maximum values in the wetter year. The presence of a crust increased the time to emergence and reduced the percentage emergence, but had no significant effect on yield. The low-level stress had no significant effect on any measured parameter.Crust strength at the completion of emergence was less on medium-sized aggregates (1–2 and 2–4 mm) than on the fine or large sizes, and these differences persisted until the end of the season. The erodibility and crust formation on aggregated seedbeds was assessed using simulated rainfall. Surface crusting was delayed, and total run-off volume was less from large aggregates (>4 mm) than from fine aggregates (<1 mm).  相似文献   

4.
Two field experiments were conducted on small plots in the Philippines to determine the effects of tillage, seeding method and time of sowing on the establishment of mungbean (Vigna radiata (L.) Wilczek cv. IPB-M79-17-79) in seedbeds created in drying soil that had been puddled as for an immediately preceding wetland rice crop.

Conditions following rice were simulated by flooding, puddling and then draining the plots. Mungbean was sown at 2–14 days after draining (DAD) as the soil dried. In one experiment, seeds were sown manually into plots that were either non-tilled or for which the surface 10 cm had been ploughed and harrowed. In a second experiment, manual sowing into non-tilled plots was compared with prototype machine seeding. Soil matric potential and temperature were monitored throughout the experiments, and germination and seedling emergence recorded.

Surface cultivation slowed the rate of water loss from depths below 5 cm and resulted in lower thermal diffusivity than in non-tilled soil. Germination results indicated that following drainage of a seedbed in previously puddled soil, manual sowing at a depth of 5 cm could be delayed until 8 DAD (while soil matric potentials remained > − 0.1 MPa) without a significant reduction in seed germination. The seeding machine was quicker and easier to use, but its constraint of shallow sowing (maximum depth 2 cm) meant that sowing could be delayed only to 5 DAD before germination and emergence were inhibited. Predictions of germination from measured values of temperature and water potential were made using equations derived from controlled-environment studies. Differences from germination observed could probably be accounted for by seed/soil/water contact effects, which appeared to be especially important in dry soil (< − 0.7 MPa). Subsequent seedling emergence was, however, often severely restricted in non-tilled soil by soil mechanical constraints in the drying, strengthening seedbed. In the first experiment, these conditions were alleviated by the cultivation treatment; in the second, disturbance of surface soil before drainage resulted in greater emergence and faster seedling growth.  相似文献   


5.
This study was carried out to observe the dynamics of crust formation on the soil surface under field conditions and analyse the effects of seedbed structure and water content on soil surface crusting. Seedbed sensitivity to crusting was also estimated in the laboratory by stability tests on aggregates. We observed 57 plots during the sowings of spring and autumn crops in fields in Northern France (Estrees-Mons, 50°N latitude, 3°E longitude). The soil is an Orthic Luvisol according to the FAO classification (0.17–0.25 g g−1 clay and 0.02 g g−1 organic matter on average). Visual assessments in situ were performed and photographs taken of crust stages on delimited areas, each 5 mm of cumulated rainfall since sowing. In 2004–2005, the seedbeds were characterised by their distribution of aggregate sizes and tests of aggregate stabilities of surface samples kept with their water content at sowing. A penetrometer was used to measure crust resistance and estimate its thickness. These data were analysed to detect the cumulative rainfall values needed for the initiation and development of the successive stages of crusts. A fully developed structural crust (stage F1) required 13, 22, 27 mm cumulated rainfall respectively for seedbeds with proportions of clods over 2 cm ranging from 0 to 0.15 (fine seedbed), 0.15 to 0.30 (medium seedbed), >0.30 g g−1 (coarse seedbed). Aggregate stability measured on samples kept at sowing water content was low for soil with low water content (<0.17 g g−1) but increased sharply for water contents over 0.17 g g−1. Stage F1 was reached more rapidly (only 11 mm versus 19 mm cumulated rainfall) only for fine seedbeds with less than 0.15 g g−1 of clods over 2 cm and with a low water content at sowing, The stage of 50% of soil surface covered with sedimentary crusts was reached for 85 mm for fine seedbed versus 120 mm for medium seedbed. The mean penetrometer resistance of dry crusts was 0.55 ± 0.43 MPa for stage F1 and 3.54 ± 0.83 MPa for a sedimentary stage; mean penetrometer resistance increased continuously with cumulated rainfall and was much lower for wet crusts. These quantitative data gathered under field conditions constitute the first step towards the prediction of soil surface crusting. The cumulative rainfalls were used in order to estimate the risk of occurrence of structural and sedimentary crusts forming during crop emergence with several types of seedbeds.  相似文献   

6.
Field experiments were conducted at Harran Plain on a clay silt soil (Xerosol in FAO/UNESCO soil classification) in Southeast of Turkey in 1996 and 1997 to study the effects of cotton planting system, tillage method, and row spacing on the performances of cotton (Gossypium hirsutum L.), such as seedling emergence and yield. The tillage methods evaluated were: traditional (inversion) with a mouldboard plough (M) and conservation (non-inversion) with chisel tine (C). The seedbeds studied were: normal planting system (NS) with no-ridging, and ridge planting system (RS). Results showed that mouldboard plough had slightly greater yield than chisel in each year but the difference was not significance in 1997. Non-ridging had the second best emergence rate and yield according to 2 years mean. Ridging with chisel in 70 cm row spacing produced the highest seedling emergence for both years, but the difference was not significance in 1997. The yields obtained for ridging with mouldboard plough from 70 cm row spacing in 1996, and for ridging with mouldboard plough from 76 cm in 1997 were superior to the other applications. Finally 70 cm row spacing produced the highest seedling emergence and yield in both years regardless of the treatment. Row spacing of 90 cm resulted in the lowest seedling emergence and yield in both years regardless of the treatment. The results indicate that ridging can be used instead of non-ridging with 76 cm row spacing (suitable for mechanical harvesting) which gave similar yield to the ridging with 70 cm row spacing in 1997, and both of the planting systems with 76 cm seem to be suitable to mechanical harvesting.  相似文献   

7.
A range of soils from Pleistocene deposits with sandy to sandy loam textures, and a group of loess-derived soils with predominantly silty textures were subjected to 60 mm of simulated rainfall to form structural seals. After drying, samples of the surface crusts were collected to determine their bulk: densities at a high resolution of depth (0–15 mm) using an immersion method. The bulk density data obtained for each soil sample were plotted as a function of depth beneath the soil surface. Two models were fitted to these plots. The first was an exponential decay type function as proposed by Mualem et al. (1990), and the second was a sigmoidal type of function assuming that maximum compaction had already progressed to some depth below the soil crust surface.All of the results indicated a gradual decrease in the bulk density with depth below the surface, until convergence with the initial bulk density of the undisturbed soil was attained. The maximum bulk densities recorded for crust segments representing the uppermost 2 mm of the crusts ranged from 1.713 to 1.91 g cm−3 for soils with silty sand, loamy sand or sandy loam textures. Crusts of loess-derived soils showed lower values, ranging from 1.44 to 1.65 g cm−3. The maximum surface bulk density was shown to be highly significantly correlated with the log of geometric mean diameter of the primary grain size distribution. In most cases, both models showed good to very good fits to the measured data; the exponential decay function appeared to better represent the initial stages of surface compaction, and the sigmoidal function the later stages of structural crust formation.  相似文献   

8.
Thirty soils differing widely in origin, texture and organic carbon content were used to study crust properties and development under laboratory conditions. Crust strength was measured as penetration resistance to an upward moving probe both with and without artificial rain treatment. The patterns of penetration resistance with time of drying under infra-red lamps varied considerably, the time taken to reach maximum and steady values for penetration resistance varying from 4 to 10 days. Maximum penetration resistance values ranged from approximately 50 to 500 kPa with one Iraqi soil recording a value of 800 kPa. The soils separated into 3 fairly distinct groups when penetration resistance was plotted against moisture content: Group I showed a sudden and sharp increase, Group II a gradual increase, whereas Group III did not show a definite relationship. A positive linear relationship was found between maximum penetration-resistance values of soils with and without artificial rain treatment. There was also a high positive correlation between small (2?0.53 mm) water-stable aggregates and penetration resistance and a negative correlation between penetration resistance and percentage water-stable aggregates of > 2 mm in size.In seedling emergence trials with spring barley (Hordeum vulgare L.), maximum emergence (90–98%) was recorded at penetration resistance (no rain treatment) of 75–110 kPa and zero emergence at approximately 300 kPa, with a good negative relationship between these values. There was a positive relationship between seedling emergence and penetration resistance values < 75 kPa, failure to emerge being due to a lack of anchorage and radial support for the shoot. Simulated rain treatment, which led to additional crust strength, reduced seedling emergence further for the limited number of soils tested.  相似文献   

9.
针对北方地区春季玉米播种期干旱、出苗困难、苗情差等问题,筛选低聚糖、甲壳素、腐植酸盐等含量适宜的抗旱物质及多种助剂,制成玉米专用抗旱种衣剂,进行种子包衣,同时结合起垄栽培技术,进行大田实验,以探究其对玉米出苗率、生长状况和产量的影响。实验设4个处理：起垄+抗旱种衣剂（RD）、起垄（R）、抗旱种衣剂（D）,以平地种植为对照（CK）。结果表明,施用抗旱种衣剂对玉米种子进行包衣处理,出苗期提早1～2d,生育期缩短1周左右。RD、R、D处理的玉米出苗率与CK相比,分别提高18.3%、7.2%、12.1%,产量与CK相比,分别增加17%、6%、3%,其中RD处理与CK间的差异显著（P＜0.05）,说明抗旱种衣剂结合起垄栽培技术,对提高玉米出苗率、促进生长、提高产量有积极作用。  相似文献   

10.
Abstract. . A soil crust, produced by applying 44 mm of distilled water at an intensity of 290 mm/h using a rainfall simulator, was sufficiently rigid to significantly decrease emergence of barley from 76 to 40% and of oil seed rape from 82 to 61%. If the crust was kept wet by regular application of water as a fine mist, its strength was significantly decreased, but emergence remained poor because of prolonged soil wetness. After mist-spraying the crusted surface just before emergence, per cent emergence was greater than uncrusted controls.
Application to the soil of a static pressure after sowing but without crusting either had no effect or increased emergence, probably because of improved seed-soil contact. However, crusting of the compacted soil decreased emergence severely. If the crust was allowed to dry it became very strong (> 300 kPa). Mist-spraying at the time of emergence only also improved seed emergence almost to that in the uncrusted controls. Repeated mist spraying after crusting decreased the strength of the crust, but the resulting waterlogging decreased emergence to less than half those of the controls and of the treatments sprayed just before emergence only. Compared with other management techniques available for amelioration of crusted seedbeds, carefully timed fine spray watering seems to offer the best opportunity for ensuring rapid seed emergence comparable to that in uncrusted soils.  相似文献   

11.
The River Estate Loam in Trinidad is micaceous. It is weakly structured and prone to surface crusting which results in decreased gaseous diffusion, infiltration- percolation, and seedling emergence. Mulching with ‘Encap’ (a liquid petroleum product) increased infiltration but not seedling emergence whereas ‘Krilium’ (sodium polyacrilonitrile) was more effective in improving seedling emergence. Bagasse mulch had a beneficial effect on infiltration but in common with pen manure was not very effective in aiding seedling emergence. Thin section examination showed that the uncrusted soil had an open structure with a large volume of pores, but, on crusting, the particles became densely packed with negligible air-spaces. Soil particles on die surface of the crust showed some degree of orientation but below the surface there was no such tendency, although particles coalesced with negligible air-spaces. The liquid petroleum mulch prevented crust formation and maintained a stable soil structure.  相似文献   

12.
Soil crust formation can be affected by soil tillage. Alternative soil conservation practices consisting of reduced tillage were tested against traditional tillage, which involves mechanical weeding by frequent ploughing in rainfed vineyard soils in Catalonia, Spain. After 2 years of the experiment (1994–1996), thin sections of the surface crusts were studied to evaluate the effects of the soil management treatments on crust morphology and genesis, using micromorphological observations and pore characterisation with image analysis. Reduced tillage caused thicker and more complex crusts consisting of layers with different degrees of sorting and pore types, compared to traditional tillage. Total porosity of crusts did not differ from that of non-crusted areas, but pores in crusts were less interconnected, more horizontally distributed and more elongated than in the underlying non-crusted material. The soil type, especially structure and texture, affected crust morphology and played an important role in the process of crusting. The results show that reduced tillage may be limited as an alternative management practice when used to reduce crust formation in Mediterranean conditions, due to the difficulty to establish an effective groundcover.  相似文献   

13.
Stand establishment and subsequent autumn development and growth are important determinants of winter wheat (Triticum aestivum L.) yield. Soil management practices change soil properties and conditions, which alter seedling emergence, crop development and growth. Pre-plant soil management practices were studied for 6 years in a wheat–fallow rotation in eastern Colorado, USA, to isolate the impacts of pre-plant tillage (PT) and residue level on winter wheat seedling emergence and autumn development and growth. A split plot design was used with PT, using a moldboard plow that incorporated surface residue, and with no-tillage (NT). The tillage systems represented the main plots and three residue levels within each tillage treatment as subplots: no residue (0R), normal residue (1R) and twice-normal residue (2R). Residue amount had little effect on emergence or autumn growth and development. PT resulted in soil water loss from the plow zone. NT plots had more favorable soil water levels in the seeding zone which resulted in faster, more uniform and greater seedling emergence in 4 out of the 6 years. This is especially critical for stand establishment in years with low rainfall after planting. Soil or air temperature did not account for differences among treatments. Earlier and greater seedling emergence in NT treatments resulted in greater autumn development and growth. Shoot biomass, tiller density and leaf numbers were greater in NT, and again residue amount had little effect. At spring green-up, NT treatments had greater soil water in the profile. Grain yield was always equal or greater in NT than in PT, and positively correlated with earlier/greater seedling emergence and autumn growth. NT will enhance soil protection and likely increase snow catch, reduce evaporation and benefit yield in semiarid eastern Colorado.  相似文献   

14.
蒋剑敏  仓东卿 《土壤学报》1964,12(3):320-329
“瓦碱”是一种碱化的浅色草甸土,零星分布于我国黄淮海平原的盐碱土地区。瓦碱的土表板平,呈灰白色,没有盐霜或很少盐霜。早春干旱时,土表易于板结,抑制幼苗生长,常引起缺苗现象,土壤板结严重时,甚至全部死亡,形成光板地。瓦碱上难以出苗,卽使出苗,苗也弱,分蘖少,但是出苗以后植株的生长此在附近盐土上好得多,因此羣众说:“瓦碱发老苗,不发小苗”。黄淮海平原内瓦碱的情况已有报导[1-6],但少有详细的理化研究。本文拟就瓦碱苗弱和不出苗的原因及其改良原则进行初步研究。  相似文献   

15.
Total porosity and width, length and irregularity of elongated pores from thin sections, prepared from undisturbed Ap horizon samples taken from a zero versus conventional-tillage field experiment, were analysed by means of a Quantimet 720 System 23 image analysing computer. Both total porosity and elongated pore area were significantly higher in conventionally-tilled plots. On the contrary, both the total number of pores and the proportion of elongated pores were significantly higher in no-tilled plots. Thus, zero tillage reduced the size of pores. Conventional tillage caused an increase in the length of a few large, elongated pores which also showed very strong irregularity. In samples from no-tilled plots the total length of elongated pores was smaller, but these pores were more numerous and more regular than in samples from conventionally-tilled plots. Consequently, soil conditions for root growth were better.  相似文献   

16.
Emergence of cotton (Gossypium hirsutum L.) under flatland mechanized planting system with crust-forming soil and saline soil and irrigation water can be suboptimal in central Iran. A field experiment was conducted to determine furrow opener type and crust-breaking method effects on cotton emergence on a silty clay soil (Calcic Cambisols). The effects of five planters (equipped with runner, single- and double-disk type openers) and five crust-breaking methods (using rolling cultivator, rolling-type crust breaker, spike-tooth, chain-type harrows and no crust-breaking) on the seedling emergence were studied. The results showed that planter type significantly affected cotton seedling emergence. In non-crust-breaking method, the best emergence was produced with the double-disk opener planter that created crack lines along the seed rows. This phenomenon was not observed with the runner-type opener planter. However, some crack lines were observed on the outside edges of its smooth-crown zero-pressure press wheels tires, which resulted in large clod formation after crust-breaking and had therefore negative effect on seedling emergence. Crust-breaking had negative effect on final emergence for double-disk planter due to filling the crack lines with loosened soil. Crust-breaking improved emergence percentages for runner opener planters, when the depth of penetration of the crust breaker teeth was shallow. The conclusion is that irrigated cotton emergence on crust-forming soils in a flatland planting system might significantly be improved by selecting a double-disk planter with zero-pressure press wheel tires without any crust-breaking operation under the soil and climate of central Iran.  相似文献   

17.
A research program concerning the seedbed preparation problems in Swedish agriculture included a series of pot experiments in shallow plastic boxes. Seedbeds of well-defined characteristics were arranged, and seedling emergence was determined by daily plant countings. In the experiments reported, the main subject of study was the efficiency of the seedbed in controlling evaporation. Clay or clay loam soils were used, and the crops were mainly small grain cereals.Seven experiments with unstratified seedbeds showed that for small grains in a dry weather situation, the seed should be placed directly onto the moist bottom of a harrowed layer, which should be 4–5 cm deep and mainly consist of aggregates smaller than 4 mm. If the bottom layer contains less than 5% plant available water, or if a fine enough seedbed structure cannot be produced, the depth of both harrowing and sowing should be increased. In four experiments with stratified seedbeds, no reasons were found for sorting the coarse aggregates to the soil surface, provided the initial moisture content increased with depth.Effects of seed quality were studied in two experiments. Seed lots with equal germinability under optimum moisture conditions gave large differences in emergence in a moisture stress situation. Within a rather wide seed size range, the size as such had only minor influence on the emergence rate.  相似文献   

18.
《Soil & Tillage Research》1988,11(2):167-181
Six techniques of sowing seed in an untilled seedbed, which subsequently became wet, were compared in the presence and absence of earthworms and surface residue. In the absence of earthworms, surface broadcasting produced the highest seedling emergence (89%), followed by a 100-mm-wide power-till opener (42%). All other openers produced poor seedling emergence (mean 20%). Where earthworms were present, however, a winged opener under residue produced high seedling counts equivalent to surface broadcasting (mean 82%). Power-till and hoe openers also performed reasonably well (63%), but triple-disc and corer openers failed (19%). Surface broadcasting was not considered practical because of its reliance on regular rain for a long period.Surface residues in the presence of earthworms had beneficial effects on most of the openers which performed well and which separated the seed from the residue, but little effect on the other treatments, including the power-till opener. High seedling-emergence counts were associated with high numbers and activity of earthworms close to the sown groove, high soil oxygen diffusion rate regimes, low soil bulk densities and high root and shoot weights.  相似文献   

19.
为了明确在单粒播种条件下田间出苗率对玉米产量的影响,以蒙特卡罗二项分布作缺苗模拟,以Voronoi图分配缺苗土地,通过对产量-密度方程进行数学恒等变换计算产量补偿,模拟了2种单粒播策略的玉米产量随出苗率(75%~95%)的变化。结果表明,缺苗斑数目与出苗率呈单峰曲线关系,缺苗斑大小随出苗率呈负指数下降;单粒播造成0.06%~16.78%的减产,且减产率随出苗率下降而增加;两种单粒播策略的产量大小和产量稳定性均有差异,且差异随出苗率下降而扩大。该研究推荐的玉米单粒播策略是:在千方百计提高出苗率基础上,播种的种子数目应当等于目标种植密度除以出苗率、保证出苗的植株数目达到推荐种植密度。该结论对于在玉米生产上广泛采用单粒精量播种具有重要参考价值。  相似文献   

20.
侵蚀坡地草被快速恢复与控制水土流失技术研究   总被引：2，自引：0，他引：2       下载免费PDF全文
研究了在侵蚀坡地采用条沟—草块的特殊建植草地方法。在治理后的3个月内,用条沟—草块建植草地的小区其土壤侵蚀量仅为140 kg,比整地但无种植、原坡面和全垦等高种草的小区分别减少了823,249和670 kg。用条沟—草块建植草地的小区当年的土壤侵蚀为1 500 t/km2,比整地但无种植、原坡面和全垦等高种草分别减少了10 591,3 514和7 760 t/km2;第2 a以后,条沟—草块草地的土壤侵蚀量均在700t/km2以下。治理3 a后侵蚀坡地的草被物种由6种发展到16种。在侵蚀坡地治理当年,坡地的植被覆盖率就可达85%,能在短期内控制水土流失。  相似文献   

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