心土不同间隔混拌对白浆土物理性状及大豆产量的影响

为了探讨机械作业改良白浆土,以常规机械作业为对照,设6个处理,研究心土不同间隔混拌对白浆土物理性质及大豆产量的影响。结果表明：与对照相比,改土2年后不同处理20~60 cm混拌层都能提高土壤含水量,增幅1.02%~4.90%,降低土壤容重,降幅4.93%~10.56%,降低土壤硬度,降幅3.05%~28.15%,以单向条沟改良(T2)效果最好。6个处理中,隔垄交错条沟改良(T5)和单向条沟改良(T2)大豆产量最好,分别达到1991.92 kg/hm2和1969.57 kg/hm2,比常规机械作业提高7.92%和6.71%,差异达到显著水平。     

Rules of thumb for minimizing subsoil compaction

Subsoil compaction is persistent and can affect important soil functions including soil productivity. The aim of this study was to develop recommendations on how to avoid subsoil compaction for soils exposed to traffic by machinery at field capacity. We measured the vertical stress in the tyre–soil contact area for two traction tyres at ca. 30‐ and 60‐kN wheel loads on a loamy sand at field capacity. Data on resulting stress distributions were combined with those from the literature for five implement tyres tested at a range of inflation pressures and wheel loads. The vertical stress in the soil profile was then predicted using the Söhne model for all tests in the combined data set. The predicted stress at 20 cm depth correlated with the maximum stress in the contact area, tyre inflation pressure, tyre–soil contact area and mean ground pressure. At 100 cm depth, the predicted vertical stress was primarily determined by wheel load, but an effect of the other factors was also detected. Based on published recommendations for allowable stresses in the soil profile, we propose the ‘50‐50 rule’: At water contents around field capacity, traffic on agricultural soil should not exert vertical stresses in excess of 50 kPa at depths >50 cm. Our combined data provide the basis for the ‘8‐8 rule’: The depth of the 50‐kPa stress isobar increases by 8 cm for each additional tonne increase in wheel load and by 8 cm for each doubling of the tyre inflation pressure. We suggest that farmers use this simple rule for evaluating the sustainability of any planned traffic over moist soil.     

心土培肥改良白浆土的研究Ⅱ心土对作物产量的贡献及磷、钙培肥心土的效果

为明确心土对作物产量的贡献和P、Ca培肥心土的效果,采用盆栽试验与室内模拟试验相结合的方法,研究心土层对作物产量贡献和白浆土心土培肥的机理。结果表明:良好的心土层对作物产量影响十分明显。黑土厚度从20 cm增加到60cm,大豆增产40.4%;不同土层位置对大豆产量的贡献率分别为:20～40 cm土层10%以上,40～50 cm土层为4.57%;50 cm以下土层为1%。磷培肥后心土层吸附磷的能力降低、解吸率增加,土壤中有效磷含量提高;钙培肥后心土层土壤电导率和pH提高,但使土壤中磷的有效性降低;磷培肥后磷在土壤中主要转化为Ca2-P、Ca8-P、Al-P和Ca10-P。     

Nitrate-N dynamics following improved fallows and maize root development in a Zimbabwean sandy clay loam

Improved or planted fallows using fast-growing leguminous trees are capable of accumulating large amounts of N through biological N₂-fixation and subsoil N capture. During the fallow phase, the cycling of nutrients is largely efficient. However, there are few estimates of the fate of added N during the cropping phase, after the 'safety net' of fallow-tree roots is removed. Nitrate-N at the end of the fallow phase, which is pre-season to the subsequent crop, was monitored in seven land use systems in successive 20-cm soil layers to 120 cm depth at Domboshawa, Zimbabwe in October 2000. Thereafter, nitrate-N dynamics was monitored during cropping phase until April 2001 at 2-week intervals in plots that had previously 2-year planted fallows of Acacia angustissima and Sesbania sesban, and in a continuous maize control. Pre-season nitrate concentrations below 60 cm soil depth were <3 kg N ha⁻¹ layer⁻¹ for S. sesban, A. angustissima, Cajanus cajan and natural woodland compared with the maize (Zea mays L.) control, which had >10 kg N ha⁻¹ layer⁻¹. There was a flush of nitrate in the S. sesbania and A. angustissima plots with the first rains. Topsoil nitrate had increased to >29 kg N ha⁻¹ by the time of establishing the maize crop. This increase in nitrate in the topsoil was not sustained as concentrations decreased rapidly due to leaching. Nitrate then accumulated below 40 cm, early in the season when maize root length density was still low (<0.1 cm cm⁻³) and inadequate to effectively intercept the nitrate. It is concluded that under light soil and high rainfall conditions, there is an inherent problem in managing nitrate originating from mineralization of organic materials as it accumulates at the beginning of the season, well ahead of peak demand by crops, and is susceptible to leaching before the crop root system develops. This revised version was published online in June 2006 with corrections to the Cover Date.     

Responses of wheat and barley to liming on a sandy soil with subsoil acidity

A 3 years field trial examined the effect of newly and previously applied lime on the growth and yield of two near-isogenic wheat genotypes differing only in aluminium (Al) tolerance (Triticum aestivum L. Al-sensitive line ES8 and Al-tolerant line ET8), and barley (Hordeum vulgare cv. Mundak) on an acid soil (pH_CaCl2 4.6 in 0–10 cm and pH 4.1–4.3 in 10–40 cm) in the medium rainfall region of Western Australia. The trial consisted of four lime treatments: (i) no lime control; (ii) surface liming at 1.5 t ha⁻¹ in 1999; (iii) surface liming at 2.5 t ha⁻¹ in 1984; (iv) liming in 1984 and re-liming in 1999. Wheat crops were grown in 1999 and 2001, and barley was grown in 2000.

Liming in 1984 increased the pH in both topsoil and subsoil and decreased toxic Al in the subsoil. Liming in 1999 largely increased soil pH in the 0–10 cm in previously unlimed and limed plots, but only slightly increased the pH in 10–20 cm 2 years after application. In 1999, there was an overall 14% grain yield increase by growing ET8, mostly due to much better performance (41%) of ET8 over ES8 in the treatment with surface liming in 1999. In 2001, ET8 had yield 24% higher in the no lime control and 14% higher in the treatment with liming in 1999 compared with ES8. While both genotypes had similar root length density in the topsoil, root length density in acid subsoil was 22–160% higher for ET8 than for ES8. Wheat genotypes produced 23–24% higher yield due to the liming in 1984 compared to the no lime control. In 2000 season, shoot biomass of barley increased by 45–70% in the limed treatments compared with the no lime control. Liming at 2.5 t ha⁻¹ in 1984 or liming at 1.5 t ha⁻¹ in 1999 increased yield by 25%. Liming in 1984 and re-liming in 1999 increased the yield by over 50%. The results suggest that surface liming can ameliorate subsoil acidity as measured 15–17 years after application, and that growing an Al-tolerant crop in combination with surface liming provides a good strategy to combat subsoil acidity. The genotypic variation in response to liming appears to result from the difference in the sensitivity of root proliferation to low pH and high Al.     

Changes in soil physical properties and crop root growth in dense sodic subsoil following incorporation of organic amendments

Measurements of soil physical properties, root growth and the water content in the subsurface layers of a clay Sodosol soil were carried out to determine why the incorporation of organic amendment (20 t/ha) resulted in marked increases in wheat yield in an earlier paper. The incorporation of lucerne or dynamic lifter^® pellets at a depth of 30–40 cm resulted in an almost doubling of the macroporosity from <10% to >18%, together with reductions in bulk density and the volumetric water content (θv$\theta v$) at −1500 kPa, and a 50-fold increase on saturated hydraulic conductivity in this subsurface layer. These changes in physical properties in the 30–40 cm deep layer were highly correlated (r values 0.69–0.93, P < 0.01) with increased root growth in this layer, and increases in crop yield. The practice of incorporating an organic amendment in the top clay layer of the B horizon in soils where the high density restricts root growth, which is termed ‘subsoil manuring’, shows promise for increasing crop productivity on these soils in the high rainfall zone of southern Australia.     

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.     

Simulation of the impact of subsoil compaction on soil water balance and crop yield of irrigated maize on a loamy sand soil in SW Spain

Irrigation of crops in Mediterranean countries can produce some conditions that favour soil compaction processes. The SIMWASER model takes into account the effects of subsoil compaction on water balance and crop yield. The objectives of this paper were: (i) to test the mentioned model using the data set collected, during three years (1991–1993), from irrigation experiments with maize (Zea mays L., cv. Prisma) on a sandy soil (Cambisols (FAO, 1990) or Xerocrepts (USDA, 1998)) in SW Spain and (ii) to estimate the influence of subsoil compaction on soil water balance and crop yield assuming long lasting heavy subsoil compaction that may be developed under irrigation for the SW Spain conditions. The model was run to simulate soil water content, evapotranspiration, drainage below the root zone, and crop yield for the same period in which the experiment was carried out. Results of simulation were compared with the experimental results in order to know the agreement between them. The results obtained show a fairly good agreement between simulated and measured values for most of the parameters considered. For the scenario in which subsoil compaction is developed under irrigation, the results simulated by the model indicate a reduction of the rooting depth. However, the effects on water balance and crop yield in this sandy soil were not relevant under the SW Spain conditions.     

Organic compounds that reach subsoil may threaten groundwater quality; effect of benzotriazole on degradation kinetics and microbial community composition

Toxic compounds in soils threaten groundwater quality in two ways: as potential contaminants themselves, and by retarding the microbial degradation of other organic compounds, thus enhancing their deep penetration. Benzotriazole (BTA) is a chemical with versatile industrial applications, used in large quantities worldwide, and represents a potential threat to the environment due to its apparent toxicity and recalcitrance. When used as an additive in aircraft deicing/antiicing fluid on airports, substantial spills of these mixtures and jet fuel will inevitably reach the soil. We have investigated the subsoil (1-2 m depth) microbial degradation and growth on four relevant organic substrates found in airport run-off (acetate, formate, glycol and toluene) in the presence of concentrations of BTA which can be found in airport run-off. Monitoring CO₂ evolution showed growth-dependent degradation rates for all substrates (sigmoid CO₂ accumulation curves), which were significantly affected by BTA. The mineralization of acetate was only moderately retarded and only by the highest BTA concentration used (400 mg l⁻¹ in soil solution); formate and glycol mineralization was substantially retarded at 200 mg l⁻¹, and toluene mineralization already at 10 mg l⁻¹ BTA. Mass balances (fraction of added C recovered as CO₂) suggested that the microbial growth yield (g biomass-C formed per g substrate C) was severely reduced with increasing concentrations of BTA. The analysis of phospholipid fatty acids (PLFA) demonstrated that Gram-negative bacteria were dominating among the organisms growing on all four substrates. The total amount of PLFA increased with approximately 1000 pmol PLFA g⁻¹ soil in response to a dose of 0.93 μmol glycol-C g⁻¹ soil, but this increase was gradually reduced with increasing BTA concentrations. This was in agreement with C mass balances based on CO₂ measurements, verifying that BTA severely reduced the growth yields. The response of individual PLFA's to BTA and substrates demonstrated that non-growing organisms were largely unaffected (i.e. the PLFA's of which the absolute amounts did not increase in response to substrates were not affected by BTA), whereas those which were growing on the added substrates were uniformly reduced by BTA (all the PLFA's which increased in response to the substrates were negatively affected by BTA). The results suggest that BTA functions as an uncoupler, i.e. a substance that reduces the yield of ATP per mole of substrate used, or that the defence mechanisms represent a large energy burden to all microbial cells.     

土壤溶解性有机碳四种测定方法的对比和转换

针对土壤溶解性有机碳(DOC)不同测定方法之间可比性较差的问题,应用TOC仪法、容量法、紫外分光光度法和比色法分别测定了中亚热带丘陵山地6个土属共46个新鲜土壤样品的DOC含量。结果表明:参照TOC仪法测得的DOC数据,容量法一致性地低估20%~67%;比色法测定DOC含量较低的底土时(200 mg/kg)仅低估7%~27%,但在分析DOC含量较高的表土(600 mg/kg)时最不敏感,低估达53%~93%;紫外分光光度法在DOC含量较高时也存在一定的低估,但在DOC含量较低时高估65%~189%。4种方法测得的DOC数据均呈极显著正相关关系(P0.01)。统计分析获得的线性或指数方程可应用于将容量法、紫外分光光度法和比色法的测定结果向TOC仪法的数据转换,而且有必要针对表土和底土使用不同的转换方程或参数,这些经验转换方程的建立有助于增强不同研究结果之间DOC数据的可比性,也有利于推动土壤DOC测定标准的完善。