保水剂底施对沙子剖面水分和硝态氮运移的影响研究

【目的】解决沙土地区漏水漏肥的核心问题,建立保水防渗漏新技术体系,促进沙土地区农业可持续发展。【方法】基于保水剂的吸水保肥等物理化学特点,以保水剂和土壤混合物底施为技术方法,选用聚丙烯酸钠和壤土为材料,采用沙柱模拟试验,研究了不同施用厚度的保水剂-土壤混合物对剖面水分运移及硝态氮淋洗的影响。【结果】聚丙烯酸钠在壤土中的质量分数为1%时,可以对水分有效截流;混合物底施,以0.9～1.5 cm厚度为最佳;淋溶试验表明硝态氮主要集中在表层和保水剂层,占比为87.2%,有效防止了硝态氮的下移。【结论】保水剂壤土混合物底施,可以起到显著的水分养分截流作用,本试验中聚丙烯酸钠质量分数1%及1 cm厚度时,可获得较好效果。     

Leaf Phosphorus Diagnosis of Sugarcane on Organic Soils

ABSTRACT

Most of the sugarcane (interspecific hybrids of Saccharum sp.) production in Florida is on organic soils. Supplemental phosphorus (P) fertilizer is often applied for optimum yields, but producers are required to reduce P levels in farm drainage waters. The objectives of this study were to relate optimum leaf P tissue concentration with yield in organic soil, and to determine optimum leaf sampling dates during the summer. Eight genotypes were planted at two locations, eight additional genotypes were planted at a third location, and eight more genotypes were planted at a fourth location. Crops were grown for three years. Measurements of leaf P concentration were repeated during growth seasons and over crop years for a total of six sampling dates at each location. Three fertilizer P treatments (0, 24, and 48 kg ha^?1 yr?1) were applied to all genotypes at each location. Leaf samples were partitioned into early-, mid-, and late-summer dates. Early-leaf samples had the widest range in leaf P concentrations compared with mid- and late-season leaf samples. Correlation analyses of yield vs. leaf P concentration across all treatments in early- and mid-summer were statistically significant (P < 0.05), but coefficients were low (r = 0.14 and 0.26, respectively). No consistent relationship across locations described the effect of leaf P tissue concentration on yield. Leaf P concentrations could not provide accurate P fertilization rates that will give maximum sugarcane yields and prevent over-fertilization of P. The highest potential for relating leaf P concentrations with yield appears to be from early leaf samples.     

Delineating the zone of topsoil disturbance around buried utilities on agricultural land

Installation of pipeline utilities (oil, natural gas, water) in central Canada prior to the 1970s often resulted in extensive mixing of topsoil with subsoil materials within the easements due to largely unregulated construction practices. The main objectives of this study were (1) to develop a simple field protocol for the rapid delineation of the zone of topsoil disturbance (or topsoil–subsoil mixing) around buried utilities on agricultural land in southern Ontario, and (2) to characterize the zone of topsoil disturbance in the vicinity of an existing pre-1970s pipeline in terms of agronomically important soil properties. The study was carried out at six farm sites chosen along a pipeline easement (30+ years old) in southern Ontario. Soil organic carbon content, CaCO₃ content and pH were found to be useful in delineating the zone of topsoil disturbance around the buried utility. Standardized laboratory techniques for determination of these three soil attributes were used to analyse surface soil samples (Ap horizons) taken at 1·5 m intervals along 45·7 m long transects oriented perpendicular to the easement. In addition, rapid field tests for these same three variables were adopted/developed and tested, and two portable instruments were evaluated for their usefulness for in situ soil property measurements. In particular, a Minolta^™ CR-310 Chroma Meter was successfully used to relate moist soil colour to the organic carbon content of the surface soil. The chromaticity coordinate a* (CIE L*a*b* colour space notation) was shown to provide good estimates of organic carbon content for soils of medium to fine texture in this region of Ontario. The zone of topsoil disturbance was most often characterized by an appreciable increase in per cent CaCO₃ equivalent and pH, and a decrease in organic carbon content (dilution), over the pipeline trench when compared to off-easement areas. The zone of topsoil disturbance was usually a minimum of 15 m wide (i.e. the approximate width of the original trench and workspace areas during construction), and frequently much wider due most likely to wet soil conditions at the time of construction, agricultural tillage translocation of topsoil over time, and other factors. It is recommended that rapid on-site determinations of the zone of topsoil disturbance should be based primarily on field estimates of CaCO₃ content (10 per cent HCl) and organic carbon content (a* chromaticity coordinate using a portable colorimeter). Copyright © 1999 John Wiley & Sons, Ltd.     

Investigations on the Behaviour of Fenpropimorph and its Metabolite Fenpropimorphic Acid in Soils

The fate of fenpropimorph and its metabolite fenpropimorphic acid was investigated in a silty sand soil and in a clayey silt soil. In laboratory and field experiments fenpropimorph disappeared without a lag phase. A few days after application fenpropimorphic acid was detected. Additional laboratory experiments with [¹⁴C]fenpropimorph emphasized the significance of mineralization and the formation of non-extractable residues. The determination of soil/water distribution coefficients of parent compound and metabolite yielded a higher leaching potential for fenpropimorphic acid due to its higher polarity. This was confirmed by performing a laboratory column test under worst-case conditions. Under field conditions, however, fenpropimorphic acid was detected only in the superficial soil layers (0–5 cm) of both investigation sites at very low concentrations.     

梯田基线设计与简易放线法

梯田基线设计,多采用经验法,等高等宽不好兼顾,“大弯就势,小弯取直”往往只能定性,不能量化,由此设计出的梯田埂线,难以得出最佳梯田断面。如根据地形图等高线走向趋势,选择代表地面走向的等高线,通过概化分析,以数学函数式表达等高线,使其横贯坡面切割等高线为最少,以此作为梯田地埂基线,由其函数对应值,在实地进行坐标放线,即可做到等高布设、等宽兼顾和“大弯就势,小弯取直”定量化,既满足机械作业对曲率半径的要求,也避免了施工时的大切大垫。     

Potential carbon stock in Japanese forest soils – simulated impact of forest management and climate change using the CENTURY model

Forest management and climate change may have a substantial impact on future soil organic carbon (SOC) stocks at the country scale. Potential SOC in Japanese forest soils was regionally estimated under nine forest managements and a climate change scenario using the CENTURY ecosystem model. Three rotations (30, 50, 100 yr) and three thinning regimes were tested: no‐thinning; 30% of the trees cut in the middle of the rotation (e.g. 15 year in a 30‐yr rotation) and thinned trees all left as litter or slash (ThinLef) and the trees from thinning removed from the forest (ThinRem). A climate change scenario was tested (ca. 3 °C increase in air temperature and 9% increase in precipitation). The model was run at 1 km resolution using climate, vegetation and soil databases. The estimated SOC stock ranged from 1600 to 1830 TgC (from 6800 to 7800 gC/m²), and the SOC stock was largest with the longest rotation and was largest under ThinLef with all three rotations. Despite an increase in net primary production, the SOC stock decreased by 5% under the climate change scenario.