Evaluation of Continuous In Situ Monitoring of Soil Changes with Varying Flooding Regimes

Abstract

To support investigations of flood tolerance occurring at a field‐based research facility, changes in soil volumetric water content, temperature, redox potential, dissolved oxygen content, and pH over the course of flood events were monitored. Electronic sensors connected to dataloggers for continuous monitoring of these parameters were installed, and soil redox potential and pH were also monitored manually for comparison. Soil volumetric water content showed that soils became saturated quickly following inundation. Soil redox potentials revealed a reduction of the soil with inundation; however, stagnant water treatments did not result in lower redox potentials than flowing water treatments. Similarly, dissolved oxygen content was not lower in the stagnant water treatment. The automated and manual systems detected similar trends in redox potential response to flooding; however, redox potentials measured manually were generally higher and significantly different from those obtained with the automated system. Anomalous readings were detected with the automated measurement of soil pH, indicating further need for improvement of this system.     

Soil Phosphorus Extracted by Three Anion Exchange Membranes Compared to Water-Soluble and Truog-Extractable Phosphorus

Effects of different kinds of anion exchange membrane (AEM) on soil P extracted by AEM (AEM P) were investigated in three soils (Cumulic Andosol, Yellow soil, and Gray Lowland soil). There was no significant difference in AEM P among the AEMs tested (BDH-Prolabo 551642S, AGC Engineering Selemion AMT, and AGC Engineering Selemion AMV). The AEM P was greater than water-soluble P in all soils. Although AEM P was greater than Truog-extractable P in Cumulic Andosol, the reverse was true in the Yellow soil and Gray Lowland soil.     

Ultrasound Method for Extraction of Phosphorus in Soil

In the present work, an ultrasoundic procedure for the extraction of phosphorus (P) available in soil is described. The proposed method is based on extraction by 0.5 M sodium bicarbonate (NaHCO₃), following with sonication under different conditions. Phosphorus was determined by the Murphy and Riley method. Sonication time and soil–extractant relative quantities were optimized. A statistical analysis approach was used to find suitable conditions for the ultrasoundic extraction. The main advantages of the sonication method are the reduced times of extractions, which take 10 min in contrast to the 30 min required by a shaking method, and the possibility to reduce soil and extractant quantities from 5 g–100 mL to 2 g–40 mL. Performance of the method was evaluated, and the procedure was utilized to analyze soils from Santiago del Estero, Argentina.     

土壤磷向地表径流迁移的提取系数研究

农田土壤磷随降雨径流进入地表水体是水环境富营养化的主要污染源。通过天然降雨径流小区,动态监测溶解态磷在降雨径流-土壤系统中的迁移,研究坡耕地表层土壤水浸提磷(WEP)和降雨径流溶解态磷(DTP)之间的关系。应用SPSS统计软件线性回归土壤WEP和径流DTP关系,拟合方程,y=0.281x-0.179(R=0.943)。方程斜率表示降雨径流溶解态总磷浓度对土壤不稳定磷浓度的提取系数。经最小二乘法线性回归检验,该模型拟合优度较高,整体性显著。土壤磷提取系数方程可实现磷素从农业营养元素向水环境污染因子内涵的转换,为农业非点源污染防治和水环境保护规划提供了一种估算农业非点源磷素污染潜在负荷的简单有效工具。     

Phosphorus Amendment of a Lead-Spiked Soil with Low Phosphorus Availability: Roles of Phosphorus on Soil and Plant Lead

Phosphorus (P) is both a macronutrient for plants and an effective amendment to reduce lead (Pb) toxicity in soil. Thus, in Pb-polluted soil with low P availability, P will act as a nutrient as well as a Pb-immobilizing agent. However, this has not been fully investigated. A soil with 2.50 mg kg^?1 Olsen P was spiked with soluble Pb and then amended with superphosphate to examine the effect of P on soil Pb availability and ryegrass (Lolium perenne L. cv. Aubisque) growth. It was found that P/Pb = 2 increased ryegrass yield by 804% and decreased root Pb concentration and soil diethylenetriaminepentaacetic acid (DTPA)–extractable Pb concentration by 25.6% and 1.0%, respectively. As P amendment increased to P/Pb = 4, both plant yield and root Pb concentration declined compared with P/Pb = 2. Results of the sequential extraction indicated that the proportion of carbonate phase Pb decreased, while that of the manganese oxide phase increased as P was added. The proportion of residual Pb was little affected by the amendment. The results suggest that in soils with low P availability and high Pb availability, availability of soil Pb and root concentration of Pb are less affected, whereas the toxicity of Pb is greatly depressed by the P amendment; P/Pb = 2 is high enough to alleviate the stresses of low P availability.     

Polyethersulfone Membrane Filters for Sampling Soil Water from In Situ Soils and Intact Soil Columns for Phosphate Analysis

Abstract

Porous plates or cups are commonly used to collect soil solution samples in field studies or from intact soil columns. Some commonly used materials for porous plates may adsorb soil solution constituents such as phosphorus (P). An alternative to using a porous plate is to use a membrane filter with a known pore size and bubble point. The objective of this study was to evaluate the utility of polyethersulfone membranes (pore size 0.45 µm and bubble point >200 kPa) to extract soil solution from in situ soils and intact soil columns for phosphate analysis. In situ soil solution samplers were constructed from modified reusable polysulfone membrane filter holders equipped with polyethersulfone membranes (47 mm diameter). A ?10 kPa vacuum was maintained in the samplers, which enabled soil solution collection at soil water potentials of 0 to ?4 kPa in loamy sand, 0 to ?10 kPa in sandy loam, and 0 to ?12 kPa in sandy clay loam soils. In a laboratory study, soil solution samplers continued to hold a vacuum to ?77 kPa soil water potential. Soil solution samplers were further evaluated in a field study at 45‐, 90‐, and 135‐cm depths in two soils. Samplers operated with relatively few difficulties for the first 12 months of field evaluation. Membranes apparently dried during periods of low soil water potential but increases in soil moisture were sufficient to rewet the membrane. Sampler failures in the field increased during 13–18 months because aged vacuum tubing and root interferences with samplers at 45 cm. Improvements in sampler design may improve the durability for implementation in long‐term field experiments. Membrane filters worked near flawlessly to maintain unsaturated conditions in intact soil columns. The filter units facilitated easy collection of soil water from the intact soil columns without altering the chemical composition of the percolate.     

Characterization of Soil Phosphorus in Differently Managed Clay Soil by Chemical Extraction Methods and 31P NMR Spectroscopy

Changes in land use alter the natural cycling of phosphorus (P) in soil. Understanding the chemical nature of these changes is important when developing sustainable management practices for cultivated soils. In this study, we evaluated the ability of commonly used laboratory methods to characterize land use–induced changes in various P pools. Also, the characteristics of soil P revealed by different methods are discussed. Soil samples were taken from three differently managed field plots of the same clay soil: uncultivated grassland and organic and conventional crop rotations. Soil P reserves were characterized using Chang and Jackson and Hedley sequential fractionation procedures and by sodium hydroxide (NaOH)–ethylenediaminetetraacetic acid (EDTA) extraction followed by ³¹P NMR spectroscopy. Both of the tested fractionation methods identified differences in the P pools and provided evidence regarding land use–induced changes. However, the ³¹P NMR analysis suggests that the quality of organic P in this soil was not affected by the change in land use.     

云南坡耕地红壤地表径流氮磷流失特征定位监测

选取南方典型坡耕地红壤为试验区,采用田间小区试验方法,在自然降雨条件下,于2008—2010年连续3 a对不同农业管理方式下地表径流及氮磷流失特征进行田间实地监测。结果表明,试验区域干湿季极其分明,3 a平均降雨量为838.6 mm,主要集中在5月到10月,坡耕地红壤地表径流、养分流失时间、流失量与降雨量之间具有显著的相关性,在常规施肥处理下径流量和氮磷流失量之间呈极其显著的指数相关性,相关系数分别为R=0.897 4＊＊和R=0.529 7＊＊。坡耕地红壤地表径流量、径流系数及氮磷流失量变化规律一致,不施肥条件下,总氮、总磷流失量最大,优化施肥、揭膜、横坡垄作及秸秆覆盖等农艺措施能降低氮、磷流失量,尤其是横坡垄作种植,相对于顺坡垄作氮、磷流失总量降低了2/3左右。不同处理之间径流中各种形态氮磷含量无显著差异,说明不同农业措施主要通过地表径流流失量而影响坡耕地地表径流氮磷流失量的多少。坡耕地红壤地表径流氮磷流失以颗粒态为主,TDN占TN比例年均为24.58%,TDP占TP的比例年均为7%,TN流失量是TP的3倍左右;优化施肥和揭膜条件下可溶性氮磷所占比例增加,横坡垄作和秸秆覆盖条件下降低。在可溶性氮素中,NO3-N、NH3-N占TN的比例年均分别为8.41%、12.65%,但是2009、2010年NH3-N均小于NO3-N。因此,关于坡耕地地表径流不同流失氮素形态的影响因素较多,目前研究结果不确定,且年际之间差异较大,尚需要进一步研究。     

Phosphorus Determination after Mehlich 3 Extraction and Anion Exchange Resin in an Agricultural Soil of Northwestern Spain

Differences in soil phosphorus (P) contents measured by various techniques may have implications for agronomic and environmental testing. Reduced-tillage systems combined with surface manure application increase the potential risk of nutrient losses by surface runoff. A field trial was conducted to evaluate the effect of livestock slurry on nutrient accumulation at the surface layer of an acidic soil rich in organic matter with excess P levels and loamy texture. Two reduced-tillage systems, no tillage (NT) and minimum tillage (MT), and four different fertilizer treatments were assessed. The amounts of P extracted by anion-exchange resin (AER) and by Mehlich 3 (M3) were compared; in addition, differences between two determination methods of P contents extracted by Mehlich 3, namely molybdic acid colorimetric standard procedure (M3-COL) and inductively coupled plasma–mass spectroscopy (M3-ICP), were evaluated. Ninety-six soil samples were taken from the 0- to 5-cm surface layer in three successive dates after increasing manure addition. Colorimetric Mehlich 3 P ranged from 49 to 431 mg dm^–3. The ranks of mean extractable soil P concentrations were AER < M3-COL < M3-ICP. The linear correlation coefficient between M3-COL and M3-ICP was highly significant (R² = 0.89; P < 0.01), but a two-straight-lines model or a quadratic relationship were more adequate for describing the dependence between the two determination procedures after M3 extraction. Relative and absolute differences between M3-COL and M3-ICP showed a tendency to increase as organic carbon content increased. Phosphorus content extracted by AER and M3-COL or M3-ICP reported a significant but much less predictable relationship with R² values of 0.27 and 0.21 (n = 96), respectively. The P in the surface layer accumulated more under NT than under MT.     

Organic and Inorganic Forms of Phosphorus in a Calcareous Soil Planted with Four Species of Eucalyptus in Southern Iran

The objectives of the present study were to evaluate the effect of four eucalyptus species on (i) selected surface soil properties and (ii) the distribution of inorganic and organic phosphorus (P_i and P_o) fractions. Soil samples were collected from soil 0–20 cm deep beneath and between trees. The P_i forms were determined by sequential extraction with sodium bicarbonate (NaHCO₃‐P), ammonium acetate (NH₄OAc) (OAc‐P), ammonium fluoride (NH₄F‐P), sodium hydroxide (NaOH)–sodium carbonate (Na₂CO₃) (HC‐P), citrate dithionite (CD‐P), and sulfuric acid (H₂SO₄) (H₂SO₄‐P). The P_o forms were sequentially extracted with NaHCO₃ (NaHCO₃‐P_o), NaOH (NaOH‐P_o), and H₂SO₄ (H₂SO4‐P_o). The NaOH‐P_o was subdivided into moderately stable (NaOH‐P_om) and highly stable P_o (NaOH‐P_os). Organic matter, clay and silt contents, total nitrogen, and available potassium of the soil beneath the trees increased. The OAc‐P and HC‐P forms beneath the trees were less than of that between them, which shows that these fractions probably are labile inorganic P pools. The NaHCO₃‐P_o and NaOH‐P_os forms were greater beneath the trees than those of interspaces, whereas NaOH‐P_om and H₂SO₄‐P_o were not affected by plantation.     

In Situ Method for Measuring Water Fluxes,Sediment, and Phosphorus at High Drip Infiltrometer Intensities in the Upper Half Meter of a Tilled Clay Soil

The first step in evaluating phosphorus (P) loss risks should be to investigate the topsoil, which is generally considered a source of P transport via macropore flow. A procedure is presented for in situ measurement of hydraulic response times, critical water outflow rates, as well as turbidity (T), sediment (SC), and total phosphorus (Ptot) concentrations in outflowing soil water solution from the upper half meter of a clay soil. The method applies to a range of controlled experimental rainfall intensities from a drip infiltrometer, and a zero-tension collection tray located at 0.5 m depth through which percolating water/sediment solution is sampled. Reasonable positive relationships were observed between T, SC, and Ptot versus steady output flow rates (qs). Dependencies were strong between Ptot and each of qs and T, and weaker between Ptot and SC. The methods require further validation and will be further developed in upcoming studies.     

灌水对不同次生盐渍化水平设施土壤氮、磷迁移特征的影响

通过野外调查与室内土柱模拟试验相结合的方法,对灌水条件下不同次生盐渍化水平设施土壤氮、磷含量的变化及迁移特征进行研究.结果表明:(1)灌水后土壤水分变化主要集中于20 cm以上土层,灌水后13～15 d,不同次生盐渍化程度的土壤水分都表现出向下迁移的特征.(2)设施土壤硝态氮含量最高值均出现在土层20 cm处,且次生盐渍化程度越严重,硝态氮表聚现象越为突出.灌水15d后,各处理铵态氮集中分布于20-40 cm土层,灌水后土壤铵态氮含量变化不明显,环境风险较小.(3)设施土壤速效磷含量高于露地土壤,且表层土壤速效磷含量介于40～60 mg/kg之间,灌水后各时期不同次生盐渍化程度土壤剖面中速效磷的分布趋势基本一致,虽受灌水的影响较小,但存在潜在的环境风险.     

Evaluating Nutrient Availability in Semi-arid Soils with Resin Capsules and Conventional Soil Tests,I: Native Plant Bioavailability under Glasshouse Conditions

Resin capsule technology developed for nutrient analysis in agriculture soils recently has been expanded to semi-arid soils without knowledge of effectiveness. This study determined if resin nutrient adsorption is correlated to plant uptake and yield in semi-arid soils. Two soils were treated with five rates of nitrogen (N) and four rates of phosphorus (P), placed in pots with resin capsules, seeded with squirreltail grass (Elymus elymoides), and grown in a glasshouse for 120 d followed by biomass determination and nutrient analysis of capsules, soils, and tissues. Yield and total nutrient uptake were highly correlated to fertilizer application rates, resin ammonium (NH₄)-N, and sodium bicarbonate (NaHCO₃)–extracted P; marginally correlated to resin and potassium chloride (KCl)–extracted nitrate (NO₃)-N, and unrelated to KCl-extracted NH₄-N and resin P. Use of resin capsules to estimate N bioavailability is promising, but P bioavailability is not effectively estimated with resin capsules; instead traditional NaHCO₃ extraction is recommended.     

一套GPS两种功能的结合在水土保持监测中的应用研究

通过试验与分析,利用一套双频GPS进行单点定位与快速RTK技术的结合来快速测量水土流失面积,即:先用GPS单点适时定位完成控制测量,再利用RTK技术测量水土流失的边界,当超出RTK测量的有效范围时,再采用单点定位法进行控制点的加密,以便于继续RTK测量工作,直至测区边界的测量工作全部完成为止。这种方法简单、准确、经济,解决了水土保持监测中的面积度量问题,克服了由于国家三角点被破坏而受数量与分布的限制的缺点。