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While many studies note the positive effects of soil organic matter (SOM) on crop yields, there is limited quantitative information on the influence of increased SOM on potato (Solanum tuberosum L.) productivity in sandy soil. This study estimated the impact of varying SOM on potato productivity in sandy soils and explored whether nitrogen (N) mineralization served as a primary mediator. Soil from nine fields in Wisconsin (SOM range of 1.1%–3.8%) was collected for a greenhouse study. Both NH4-N and NO3-N extracted from ion strips and potentially mineralizable nitrogen (PMN) were used as the proxies for N mineralization. Linear mixed effect models indicated that fresh matter whole biomass and dry matter vine biomass were 0.45 and 0.54 times greater at 3.8% SOM compared to 1.1% SOM at an optimal soil pH of 5.2, respectively. Similarly, total N uptake in the whole and vine biomass was 0.51 and 1.0 times higher at 3.8% SOM than 1.1% SOM, respectively. While PMN demonstrated a positive correlation with SOM, it only partially mediated the effect of SOM on productivity, specifically in N uptake in the vines. However, for most productivity measures, including PMN with SOM in the models did not substantially reduce the estimated SOM effect on productivity, indicating that SOM affected productivity mostly through mechanisms other than N acquisition by plants available through mineralization of OM. The study underscored the complex interplay between SOM and potato productivity, urging further research into the multifaceted roles of SOM in sandy soils. [ABSTRACT FROM AUTHOR]

Conservation management practices often produced positive but limited desirable outcomes in US Southeast sandy soils, likely due to their intrinsically low clay contents that constrain the soil’s capacity to preserve organic carbon (C) and nutrients. In the field, we tested the effectiveness of a novel approach, that is, clay soil amendment, to improve sandy soils. In October 2017, clay-rich soils (25% clay) were spread at 25 metric tons ha−1 and tilled onto a sandy soil (1.9% clay) in the field, which was further mixed by light tillage at 0- to 15-cm depth, followed by planting winter cover crop mixtures (cereal rye, crimson clover, and winter pea). The crop rotation was cotton and corn with cover crop mixtures planted in the winter fallow season. Soils (0–15 cm) were collected in August 2021 and subjected to physiobiochemical analyses. Clay amendment increased soil clay content to 3.4%, which improved nitrogen (N) availability by 51% but inhibited the activities of C (β-Dcellubiosidase [CB]; β-xylosidase [BX]; N-acetyl-β-glucosaminidase [NAG]) and N (leucine aminopeptidase [LAP]) cycling enzymes, resulting in up to 78% reduction in microbial respiration. A follow-up kinetic study on BG and LAP enzymes suggested that clay addition can have different impacts on enzymes with diverse biological origins through distinct mechanisms. Clay addition can potentially improve sandy soils by stabilizing the organic inputs in soils. However, more research is required to understand its long-term impacts making this approach practical. [ABSTRACT FROM AUTHOR]

Sandy loamy soils are widely distributed in fluvial floodplains and experience flooding events frequently, resulting in a large amount of nitrous oxide (N2O) emissions. This case is more serious when the soil use is changed to paddies. It is of great significance to figure out the N2O consumption and its influencing factors in sandy loamy paddy soils to mitigate N2O emissions. In this study, three sandy loamy paddy soils (0–5 cm) originated from lake deposits were selected (S1, S2, and S3) as objectives. A certain concentration of exogenous N2O was added at the bottom of the flooded soil column to monitor the dynamics of N2O and nitrogen (N2) on the soil surface. Total N2O consumption, N2O uptake, and N2 production were quantified, and the abundance of nitrous oxide reductase genes (nosZI, and nosZII) and other soil properties (ammonium‐nitrogen, nitrate‐nitrogen, and dissolved organic carbon [DOC] content) were analyzed. The results showed that the sandy loamy paddy soil column with a depth of 0–5 cm could intercept more than 95% of the exogenous N2O under the flooded anaerobic condition, indicating that the three sandy loamy paddy soils all had extremely strong N2O consumption capacities. And the increment of N2 accounted for 68.73%–76.09% of the total N2O consumption, which had a stronger relationship with the increase of nosZI gene abundance than nosZII gene. In addition, the total N2O consumption and N2 increment of S1 and S3 soils were significantly higher than those of S2 soil. This difference was mainly related to soil organic matter content, total nitrogen content, DOC consumption, and the increase of nosZI gene abundance (p < 0.05). The strong N2O consumption potential of sandy loamy soils can provide feasible solutions for regulating N2O emissions in a wide range of similar environments in fluvial floodplains. Core Ideas: Over 95% of N2O in 5‐cm‐soil depth was consumed by flooded sandy loamy paddy soils.The microbial reduction of N2O to N2 is the main pathway of N2O consumption.N2O consumption and N2 increment dominated by nosZI‐containing microorganisms. [ABSTRACT FROM AUTHOR]

Organic amendments (OAs) can improve the hydro‐physical properties of a soil and thereby potentially enhance the resilience of agricultural systems to droughts and floods. An OA's contribution to this resilience, however, depends on the timeliness of its impacts, as soil improvements should be achieved when droughts are most frequent or flood risks are greatest. Yet little is known regarding the temporal variability of OA impacts or the influence of OA quantity and quality thereupon. In this research, therefore, we investigated at two agricultural sites the temporal variability of improvements in soil bulk density, aggregate stability, infiltration capacity and water retention after the application of compost, farmyard manure, bokashi, a selection of organic residues from landscape maintenance, and a combination of these residues with manure. Results showed that, depending on management practices and soil type, OAs decrease bulk density by up to 9.8%, increase infiltration capacity by up to 108.1%, aggregate stability by up to 60.0%, and water retention by up to 77.8% relative to unamended controls within 3 years of repeated application. However, the magnitude of these improvements varies up to 96% between seasons, depending on the soil property and OA treatment. On average, for all treatments, impacts relative to the control varied between different seasons by 5% for bulk density, 47.1% for infiltration capacity, 22.6% for aggregate stability, and 26.3% for water retention. When offsetting OA nutrient differences with mineral fertilizers, this variability showed a stronger correlation to differences in OA application quantity than quality (i.e., chemical composition). Results suggest that disregarding temporal variability in OA impacts can result in an inaccurate valuation of OAs as either effective or ineffective in improving soil resilience, given that impacts may, instead of their frequently presumed persistency, actually be highly transient or lagged. Our findings highlight the importance of considering the potential intra‐annual variability of OA impacts on soil hydro‐physical properties when designing OA application strategies to ameliorate the effects of specific seasonal climatic challenges. Core Ideas: Hydro‐physical properties improved within 3 years of repeated organic amendment (OA) application.Improvements were more closely related to OA application rates than to OA composition.The impact of OAs on hydro‐physical properties showed significant temporal variability.Temporal variability in OA impacts was influenced by soil type and land management practices.No single OA quantity or qualitative property could consistently explain the observed temporal variability. [ABSTRACT FROM AUTHOR]

Created wetlands used to mitigate impacts to natural wetlands often have lower organic matter, less microtopography, fewer hydric soil field indicators (HSFIs), and higher bulk density (BD) than natural wetlands. Organic matter amendments may improve soil properties soon after wetland construction, but long-term effects are seldom studied. This study investigated changes with time in soil properties of a sandy freshwater tidal created wetland in the Coastal Plain of Virginia. During construction in 2003/2004, five compost and topsoil treatments were applied, along with pit–mound microtopography. Soil descriptions were made in 2005, 2007, and 2015; samples were taken in 2006 and 2015. Four years after wetland construction, 69% of sandy plots met one or more HSFIs (S5, S6), and 62% of loamy plots met an HSFI (F3). Plots with loamy topsoil additions exhibited greater horizon and structure development, HSFI stability, greater soil mass C (0–30 cm), and higher soil C accumulation. Average soil C accumulation to 30 cm was 2.86 Mg ha−1 yr−1 in topsoil plots. With time, soils became darker (lower value, chroma) and higher in A horizon total C, and grayer (lower chroma) in C horizons, regardless of treatment. In 2015, microtopographic pits had lower color value (2.4), chroma (1.9), BD (0.87 g cm−3), and higher total C (2.39%) than mounds. We recommend adding pit and mound microtopography to created wetlands for increasing diversity of habitat. Further study is needed to see if topsoil and compost amendments improve long-term plant community development in sandy created wetlands and in other wetland types. [ABSTRACT FROM AUTHOR]

Irrigation scheduling based on a real-time and location-specific (RT-LS) model increases irrigation water savings and yield. The RT-LS irrigation scheduling models have been developed as smartphone applications and have been used for crop-specific irrigation requirements. Although many RT-LS irrigation models have been tested and used in several agronomic and horticultural crops in Florida, none of these irrigation-scheduling models has been tested for their impacts on nutrient distribution in Florida’s sandy soils. A two-season (fall 2015 and spring 2016) study was conducted to determine the effects of an RT-LS–based irrigation scheduling on soil water, NO3-–N, and NH4+–N distributions during a tomato cropping season. In both seasons, an RT-LS model for tomato was evaluated at three irrigation application rates (66, 100, and 150% RT-LS–suggested amounts) and compared with a historic evapotranspiration (ET)-based irrigation schedule (Historic ET) currently recommended in Florida. This study suggests that the RT-LS model improves water savings by 20 and 17% for the fall and spring seasons, respectively, compared with the Historic ET irrigation scheduling method. No specific pattern was observed for soil NH4+–N concentration between scheduling methods, but the RT-LS model maintained a higher soil NO3-–N concentration within the crop root zone and hence could reduce NO3-–N leaching potential. In each season, compared with the Historic ET irrigation method, the RT-LS improved both nitrogen recovery and irrigation water use efficiency in the open-field fresh-market tomato production system. Results obtained in this study clearly demonstrate that irrigation applications using the RT-LS irrigation scheduler improved irrigation scheduling accuracy by maintaining nutrients within the tomato root zone and hence could reduce nutrient leaching potential in sandy soil. [ABSTRACT FROM AUTHOR]

Hydraulic conductivity (Ks) and effective porosity (feff) for saturated water flow are essential hydraulic properties for describing fluid and chemical transport in soil and groundwater systems. Typically, Ks is predicted by pedotransfer functions of soil texture and total porosity or ϕeff. This study shows that a more conceptual approach that uses a volume-weighted ratio of coarser (part of the sand fraction) to finer (clay and organic matter) particles alongside total porosity could explain variations in both Ks and ϕeff in intact 100-cm³ samples of 20 sandy surface and subsurface soils with <10% fines (clay + organic matter). The Ks function used was a simple power-law function of the volume-weighted coarse/fine particle ratio with two calibration parameters [A and pore network connectivity (PNC)]. The value of the power-law exponent (PNC) in the calibrated function was 1.8, similar to power-law exponents for gas diffusivity and air permeability in unsaturated soil (1.5-2). The second calibration parameter (A) probably depends on the soil classes under consideration, the Ks measurement method, and the sample scale. A sensitivity analyses showed that both Ks and ϕeff (taken as the volume content of pores larger than 30 µm, that is, drained at -10 kPa of soil water matric potential) are especially sensitive to organic matter content. Besides the water transport parameters, water retention under dry conditions was also closely correlated with the volume-weighted fines content. Therefore, the volume ratio concept seems to be a promising platform for the development of simple, accurate functions for the hydraulic properties of coarse-textured soils. [ABSTRACT FROM AUTHOR]

Temporal changes in the physical and hydraulic properties of pine bark as it degrades above sandy soil likely affect soil water (θv) availability and the efficiency of irrigation in blueberry (Vaccinium corymbosum L.) production. The objectives of this study were to (i) assess the physical and hydraulic properties of commercially available pine bark with large, medium, and fine grades as it aged above well- and poorly-drained sandy soils, and (ii) test the capability of dielectric soil moisture sensors to monitor θv reliably through time. During 3 yr, the depth of the pine bark layer decreased from 26 to 15 cm, and the bulk density of the 0- to 15-cm layer of pine bark increased from 0.33 to 0.62 g cm–3. The water content at field capacity (θfc) of pure pine bark was initially 0.07 cm³ cm–3 and increased to 0.21 cm³ cm–3 during the first 2 yr, but changed little afterward. The measured qfc at two sites with 2-yr-old pine bark remained between 0.19 and 0.21 cm³ cm–3 and agreed well with sensor estimates. The θfc gradually decreased with depth from 0.25 cm³ cm–3 at 7.5-cm depth in the pine bark layer to 0.10 cm³ cm–3 at 60-cm depth. The layer of pine bark mixed with well-drained sandy soil reached the lowest θv (θl of 0.10 cm³ cm–3) after 12 d of drying, but this decrease in moisture required 40 d in poorly-drained sandy soil. The root zone of pine bark in well-drained sandy soil drained to θfc in <2 h compared with 3 h in poorly-drained sandy soil. These data could be used to optimize irrigation efficiency. [ABSTRACT FROM AUTHOR]

Studying the infiltration of water-xanthan solutions into sandy soil to prevent the movements of sand dunes is important for predicting xanthan mobility, understanding xanthan conditioning depth and evaluating the physicochemical effects on the behavior of xanthan in sandy soil. This paper provides insights into laboratory tests conducted to determine the effects of xanthan concentration, temperature, salt and pH on the infiltration of xanthan solutions in sandy soil. The infiltration experiments used a series of batch vertical sand columns. Xanthan solution, which had been treated under different conditions, was poured on the surface of the experimental soil and infiltration of xanthan was measured. Infiltration of xanthan decreased with increasing xanthan concentration. Based on the test results, an optimum concentration of 0.25% (w/v) was selected. The infiltration of xanthan solution in sandy soil increased after an increase of temperature from 25 to 45°C; however, a further increase in temperature to 60°C had no significant effect. The addition of KCl and CaCl2 at concentrations of 100, 500 and 1000 mmol L-1 increased infiltration significantly, but increasing the salt concentration from 100 to 1000 mmol L-1 had no significant effect. Moreover, the type of salt (monovalent or divalent) over the selected concentration range had no significant effect. The results showed that the pH of xanthan solution (5, 7 and 9) had no significant effect on infiltration. The Kostiakov equation fit the experimental infiltration data well for all cumulative infiltration curves. Understanding the effect of xanthan concentration and physicochemical parameters on infiltration of xanthan in sandy soil is helpful in sand dune stabilization. [ABSTRACT FROM AUTHOR]

An accurate evaluation of soil organic C (SOC) stocks is important to C management and to understanding fully the role of soils in the C cycle. However, SOC stocks in deep soils and the factors that affect them have been largely ignored. We measured SOC stocks and other soil properties to a depth of 500 cm (n = 73) under three land uses in the Lao ye Man Qu watershed on the Chinese Loess Plateau. Similar patterns in the vertical distributions of SOC stocks were found under cropland, grassland, and shrubland. However, for the 0- to 200-cm soil layer, SOC stocks were significantly lower under shrubland than under either cropland or grassland. The SOC stocks under cropland, grassland, and shrubland in the 0- to 100-cm layer were 2.64 ± 0.67, 2.50 ± 0.69, and 1.99 ± 0.22 kg m-2, respectively; in the 0- to 500-cm layer they were 8.34 ± 2.26, 8.37 ± 2.01, and 7.26 ± 1.00 kg m-2, respectively. Significantly higher SOC stocks occurred in loamy than sandy soils (P < 0.01), and they were lower at the mid than at the upper and lower slope positions. However, SOC stocks were similar in sunlit and shaded soils. Pearson correlation analysis indicated that land use, soil texture, and soil water content significantly affected SOC stocks in each 100-cm soil layer to a depth of 500 cm. Effects of topographic features and pH varied with increasing depth. A considerable amount of SOC was stored in deep soils, indicating the SOC content dependence on time and depth. This information is essential for evaluating C fluxes, estimating C stocks, and for managing the C cycles in regions around the world with deep soils. [ABSTRACT FROM AUTHOR]

Quantifying evapotranspiration (ET) and partitioning it into its individual components, evaporation (E) and transpiration (T), is essential to understanding eco-hydrological systems and guiding agricultural production practices. Our study tested the possibility of using heat-pulse probes (HPP) to determine E, T, and ET. Values of E and T were determined using the sensible heat balance theory and heat ratio method (HRM), respectively. Field experiments were conducted in a small stand of 10 Salix matsudana trees growing in a sandy soil on the Loess Plateau, China. An arrangement of five three-needle HPP sets determined E throughout the 3-to 33-mm soil layer. sap flux density (vs) was determined by three HPP-sets inserted in the sapwood of three sample trees at breast height; up-scaling was used to determine T at the stand level. summing E and T gave the stand ET. The HPP E, vs, and ET values were compared with those obtained from microlysimeters (MLs), thermal diffusion probes (TDP), and the water budget method, respectively. Daily HPP E had a moderate, but significant (R2 = 0.47; P < 0.001) linear relationship with MLs E. Total HPP E was 13.4% lower than MLs E. Hourly HPP vs had a highly significant linear relationship (R2 = 0.87; P < 0.001) to TDP vs but was consistently underestimated by 49%. Adjusting the original wound-size correction factor removed this bias. summing the HPP E (67.3 mm) and T (89.0 mm) gave the ET (156.3 mm), which was 21.0 mm higher than the water budget ET estimate. we concluded that using HPP to estimate ET, E, and T was a promising approach, suitable for providing long-term, continuous, in situ, and high time-resolution estimations, even though certain issues still need to be resolved. [ABSTRACT FROM AUTHOR]

Advanced citrus production systems (ACPS) are being evaluated in Florida citrus groves for sustainable, profitable citrus production. The ACPS practices provide tight control over water and nutrient-mediated plant growth and development using irrigation to train the root system into a limited area and fertigate with daily nutrient requirements. Thus, a study was undertaken to (i) compare daily water use using the stem heat balance method on ≤5-yr-old citrus trees using two ACPS irrigation methods (using daily drip and microsprinkler irrigation) and conventional irrigation on two Florida sandy soils; (ii) determine relationships between hourly sap flow and time of day, and daily water use vs. total available soil water in the irrigated zone; and (iii) evaluate the effect of Huanglongbing (HLB) disease on water uptake. The sap flow data suggest that intensive drip and microsprinkler irrigation systems resulted in similar or higher water use than conventional irrigation. Water use was greater (P ≤ 0.01) with ACPS than conventional microsprinkler practice irrigation in summer 2010, spring 2011, and late summer 2011 at the Entisol site. Water use was 29 to 38% greater using ACPS than conventional irrigation in June 2011 at the Spodosol site, albeit, not significantly different. All irrigation systems showed water contents close to field capacity at both sites, indicating that water was nonlimiting in each irrigation system despite having different irrigation schedules. The high water uptake using intensive irrigation systems is ascribed to frequent irrigation and improved water distribution in the irrigated zone. [ABSTRACT FROM AUTHOR]

To understand the mechanism of infiltration into fine textured soil with a coarse interlayer and to justify the capability of Richards equation-based models, ponded infiltration experiments were conducted in homogenous (loam and three types of sand) and layered soil (loam with sand interlayer) columns. The HYDRUS-1D numerical software based on the Richards equation was used to simulate the above processes where soil hydraulic parameters of the two kinds of soil were calibrated from infiltration experiments in correspondent homogenous soil columns and were used directly to simulate the infiltration process in layered soil columns. Comparison between the model simulations and the experiments shows that the HYDRUS-1D model was able to predict the infiltration rate and wetting front advancement correctly. Simulation results show abrupt variation of the soil water profile along the interface in layered soil columns. It also demonstrates that the matric suction immediately under the interface was the controlling factor for the stable infiltration rate where a coarse interlayer with higher matric suction tended to facilitate infiltration instead of inhibiting it, contrary to the previous research. [ABSTRACT FROM AUTHOR]

Phosphorus and K are critical nutrients in citrus production whose deficiency or excess can affect yield, fruit quality, and water quality. However, no study has been conducted to understand the nutrient distribution in the root zone using intensive fertigation practices in Florida's sandy soils. Thus, experiments were conducted to: (i) compare the performance of intensively managed drip and microsprinkler fertigation systems with conventional grower practices; and (ii) determine P and K adsorption based on recommended fertilizer application rates on Candler (hyperthermic, uncoated Lamellic Quartzipsamments) and Immokalee (sandy, siliceous, hyperthermic Arenic Alaquods) fine sands. Phosphorus and K were applied and tracked with time and distance from point of application. Soil P on Immokalee soil was 27 to 163% higher in the irrigated zone for drip and restricted microsprinkler fertigation than the unirrigated zone and up to 70% greater in the 0- to 15-cm depth of the irrigated zone than conventional microsprinkler practices. Soil K was 5 to 61% greater in the upper 0- to 15-cm of the irrigated zone with drip and microsprinkler fertigation than conventional microsprinkler practices on Immokalee fine sand. Soil P and K on Candler also differed by fertilization method, depth, and between irrigated and unirrigated zones. The linearized P sorption coefficients for Candler were threeto fourfold greater than the corresponding depths for Immokalee, while sorption coefficients for K were similar for the two soils. It is unlikely that P or K would present a water quality concern as strictly related to irrigation practice. The P application rate for Candler should be lowered for young trees (<3 yr old). [ABSTRACT FROM AUTHOR]

Sandy soils are extensively distributed in semiarid and arid areas in northern china and have low field capacity and water content. Reliable and precise equipment is essential to measure the water content of sandy soils accurately and continuously. The ECH2O EC-5 sensor is a promising soil moisture sensor for sandy soils. Although investigated intensively in laboratories, field-specific calibration of this sensor has not been conducted for sandy soils; therefore, the field performance of the EC-5 sensor remains unknown. This study aimed to: (i) calibrate the EC-5 sensor in the field for sandy soils, (ii) calibrate and evaluate the effects of soil temperature on EC-5 sensor measurements, and (iii) evaluate the performance of the EC-5 sensor for sandy soils. The difference between soil water content predicted by field calibration and gravimetrically derived volumetric soil water content (0.0048-0.1561 m³ m-3) ranged from -0.004 to 0.002 m³ m-3. The EC-5 sensor should be subjected to field-specific calibration because sandy soils have low field capacity and low water content during the growing season. Soil water content was negatively correlated with soil temperature. At the 10-cm depth of fixed and shifting sand dunes, diurnal soil temperature fluctuations of ±10°C underestimated or overestimated soil water content by 0.0021 and 0.0013 m³ m-3, respectively. The EC-5 sensor was used effectively in the Mu Us Sandy Land, Inner Mongolia, and revealed the soil water content dynamics in different soil depths after rainfall events. [ABSTRACT FROM AUTHOR]

Solute transport in unsaturated soil is a scale- and flow rate-dependent process, and high quality experimental studies are needed to introduce scaling relationships in the governing flow and transport models. Within this paper, we present an experimental study to characterize the solute transport for an unsaturated and undisturbed subsoil monolith sampled in a sandy aquifer. Leaching experiments were performed at different flow rates, and solute breakthrough at different positions in the monolith was measured by time domain reflectometry (TDR) probes. At TDR probe scale, the transport is assessed as being a convective-dispersive process with mixing lengths 1 m. At the bottom of the monolith, the meso-scale dispersivity is at least two times larger than the local-scale dispersivity. In addition, this meso-scale dispersivity can be successfully predicted using a stream tube model in combination with a local scale convective-dispersive process. Important scale effects are also observed in the relationship between the square coefficient of variation of the local velocities and the dispersivity. In contrast to previous studies, we do not observe a significant difference in transport properties for different flow rates (from 1.05 to 54.16 cm [d.sup.-1). We attribute this insignificance either to a balance between the decrease of the tortuosity and the increase of the coefficient of variation of the velocity with the flow rate or a non-dependency of both terms on the flow rate.

Decreasing groundwater and surface water quality relative to land use, poorly retentive sandy soils, frequent and intensive rainfalls, and shallow groundwater depths is a major concern in Florida. While the spatial and temporal distributions of N, P, and K in southwest Florida sandy soils cropped with seepage-irrigated tomato (Solarium lycopersicum L.) were previously described, the objective of this study was to calculate seasonal nutrient balances and estimate potential nutrient losses for field conditions. Field experiments were conducted in 2006 spring and 2006/2007 winter growing seasons with 224 or 358, 61, and 553 kg ha-1 of N, P, and K fertilizer, respectively. Total inorganic soil N in the root zone decreased with time, reaching minimum concentrations at the end of growing seasons. Total Mehlich-1 soil P fluctuated widely in the spring but remained relatively constant in the winter season, yet was slightly higher than the preplant values for both seasons. Total Mehlich-1 soil K decreased with time, but large concentrations remained in the soil at the end of both seasons. Potential nutrient loss from the root zone ranged from 35 to 38, 41 to 43, 0 to 2, and 15 to 37% for low N, high N, P, and K, respectively, for both seasons. Phosphorus probably underwent transformation from nonextractable to Mehlich-1 extractable forms during the season. Nutrient use efficiency ranged from 59 to 62, 52 to 55, 10 to 14, and 40 to 52% for low N, high N, P, and K, respectively, for both seasons. Leaching loss during the season was likely for N and K, and there is a post-harvest leaching risk for P and K on removal of the plastic mulch. [ABSTRACT FROM AUTHOR]

Sediments transported from agricultural fields in surface and subsurface waters contain particulate P (PP) that could be partitioned into two pools--one available for aquatic organisms including cyanobacteria, namely bioavailable particulate P (BAPP, determined by 0.1 mol L-1 NaOH extraction), and the remainder not bioavailable (non-BAPP). This study aimed to quantify the PP and BAPP concentrations in surface runoff and tile drain- age water from eight agricultural fields with clay and sandy soils in the Missisquoi Bay region of Quebec, Canada. Particulate P in surface and drainage water varied spatially (among fields) and temporally, with concentrations as high as 3181 µg P L-1 in surface runoff and 1346 µg P L-1 in tile drainage. About 30% of PP was BAPP regardless of the drainage pathway. The PP and BAPP concentrations were related linearly (R² = 0.86) to total suspended solids (TSS) in fine (0.05-1-µm) and coarse (1-100-µm) fractions. About 68% of the PP in clay soils and 50% of the PP in sandy soils were associated with the 0.05- to 1-µm size particles, which had more BAPP, on average 0.46 g P kg-1 than the coarser 1- to 100-µm fraction (0.22 g P kg-1). Soil parameters such as Mehlich-3 extractable (M3) P, M3Fe, and the degree of soil P saturation were related to the PP and BAPP concentrations in TSS and particle size fractions. We concluded that sediments with particle size <1 µm contained more BAPP and their loss from agricultural fields could contribute to the eutrophication downstream. [ABSTRACT FROM AUTHOR]

The variability of the relative soil gas diffusion coefficient (Ds/Do) in space and time is not well known but is important for root respiration, microbial activities, and greenhouse gas emissions. The objectives of this study were to: (i) quantify the spatial variability of (Ds/Do); (ii) decompose this variability into components at small vs. large scales relative to the size of the site; and (iii) analyze temporal changes at each spatial scale during the growing season of 2006 and the spring of 2007 at two depths in two sandy soils under potato (Solanum tuberosum L.)-com (Zea mays L.) rotation. The coefficient of variation of predicted (Ds/Do) varied from 30% at 0.15-m depth to 101 % at 0.30-m depth, possibly because of a change in soil horizons around the 0.30-m depth. The variability in the data on each sampling date was decomposed into small-scale (spatial and nonspatiai) and large-scale (spatial) components using the coregionalization analysis with a drift method. Overall, the small-scale component was predominant at both sites, especially at the 0.15-m depth. Spatial structures were maintained during 2006 and partially carried over to the next year, particularly at the 0.30-m depth, except for the large-scale spatial distribution patterns observed at both depths at Site 1. These results indicate that variability between years may be higher than within a year, probably due to tillage, plant growth, and snowmelt. The studysuggests that spatiotemporal variability of (Ds/Do) should be considered in agricultural research and precision farming approaches. Longer term studies would increase understanding of temporal trends in the spatial distribution. [ABSTRACT FROM AUTHOR]

Cattle-based agriculture on sandy soils has generated concern over P leaching within the basin of Lake Okeechobee, Florida. Elevated P concentrations in surface and groundwater relate to P retention capacity of soils. To evaluate P release and storage capacity of impacted soils with fluctuating water tables, four intact soil cores were analyzed (one upland and three wetland) to determine their maximum sorption capacity (Smax), equilibrium P concentration (EPC0), and soil P storage capacity (SPSC) up to 160-cm depth. Sorption isotherms were measured for samples at 10-cm depth increments and data fitted to a Langmuir model (r2 ≥ 0.88). Both EPC0 and water-soluble P were higher at the surface and decreased with depth. Oxalate-extractable Fe and Al correlated with (i) oxalate- extractable P (r2 = 0.83), and (ii) Smax (r2 = 0.71). In situ pore water concentrations collected using multisamplers were consistently higher than EPC∅ values. This discrepancy was much greater for near-surface horizons for which the difference may partially be due to redox-induced release of P previously scavenged by Fe under anaerobic (flooded) conditions. The SPSC values were positive, however, even when discounting Fe (i.e., assuming in situ chemical reduction) for samples from deeper horizons, suggesting that the small discrepancies for these horizons are not attributable to Fe oxidation. All cores had negative SPSC at the surface and high EPC∅, suggesting that neither wetland nor upland soils safely sequester additional P. High pore water P values in the surface horizons are consistent with the inference of the surface soils potentially being a source for P. [ABSTRACT FROM AUTHOR]

Tillage and cropping sequence may influence C and N sequestration, microbial activities, and N mineralization in dryland soil aggregates. We evaluated the 21-yr effect of rillage and cropping sequence combinations on C and N fractions in aggregates of a Dooley sandy loam (fine-loamy, mixed, superactive, frigid Typic Argiustolls) at the 0- to 20-cm depth in eastern Montana. Tillage and cropping sequences were no-tilled continuous spring wheat (NTCW) (Triticum aestivum L.), spring-tilled continuous spring wheat (STCW), fall- and spring-tilled continuous spring wheat (FSTCW), fall- and spring-tilled spring wheat-barley (Hordeum vulgare L.) (1984-1999) followed by spring wheat-pea (Pisum sativum L.)(2000-2004)(FSTW-B/P), and spring-tilled spring wheat-fallow (STW-F). Carbon and N fractions were soil organic C (SOC), total N (STN), particulate organic C and N (POC and PON), microbial biomass C and N (MBC and MBN), potential C and N mineralization (PCM and PNM), NH4-N, and NO3-N. Aggregate proportion was greater in NTCW than in FSTCW in the 4.75- to 2.00- mm aggregate-size class at 0 to 5 cm but was greater in STW-F than in STCW in the 2.00- to 0.25-mm size class at 5 to 20 cm. After 21 yr, STW-F reduced SOC STN, POC, and PON concentrations in aggregates by 34 to 42% at 0- to 5-cm and by 20 to 32% at 5- to 20-cm compared with NTCW and STCW. The PCM and MBC were greater in NTCW and STCW than in STW-F in the <2.00-mm size class at 0 to 5 cm but MBN varied with treatments, aggregate-size classes, and soil depths. Compared with other treatments, NH4-N concentration was lower in STW-F in the 4.75- to 0.25-mm size class but PNM and NO3-N were greater in FSTW-B/P in the <2.00-mm size class. Long-term reduced tillage with continuous spring wheat increased soil aggregation, C and N sequestration, and microbial biomass and activities in all aggregates but increased tillage intensity with spring wheat-barley/pea rotation increased N mineralization and availability in small aggregates compared with the conventional STW-F. [ABSTRACT FROM AUTHOR]

Rapid population growth and increasing urban demand reduce the availability of water for agriculture in Florida. The water-holding capacity of sandy soils in the Central Florida Ridge area is very poor (<0.10 m³ m-3). Improved soil water monitoring probes can help growers manage irrigation more efficiently and conserve water. This study evaluated a new soil water probe (ECH2O EC-5 sensor, Decagon Devices, Pullman, WA) in terms of probe-to-probe signal variability, response to fertilizer-induced salinity, and changes in soil temperature, soil volume sampled, sensitivity to pockets of air or dry soil, and performance in the field. Results were compared with an earlier version of a Decagon probe, the EC-20. Results indicated that the new probe has several advantages. The EC-5 was not sensitive to salinity or temperature fluctuations. Probe output change was almost zero when the salinity of the soil was increased by adding fertilizer to a soluble solids concentration of 14 g kg-1. When temperature was changed gradually from 3 to ∼38°C, probe output increased by only abbut 1%. Soil volume sampled by the probe was about 15 cm-3. The change in probe response was negligible when soil cores up to 0.95 cm in diameter near the probe surface were removed. Probes responded well to changes in soil water content in the field. The EC-5 probe output increased noticeably when bulk density was increased from 1.1 to 1.6 Mg m-3. Probe-to-probe output signal and response to bulk density variations can affect the estimation of field water consent unless necessary correction factors are utilized. These probes can be useful for monitoring soil water movement, estimating soil water content, and scheduling irrigation. [ABSTRACT FROM AUTHOR]

Soil depth affects plant available soil water storage capacity (PAWC). This storage capacity is important for grain yield, deep drainage, and nitrate leaching in dryland environments but is difficult to measure directly on a broad scale. Measurements of ECa provide a means of estimating soil depth at spatial resolution of <50 m when sufficient contrast in conductivity exists between the surface and the root-impeding subsurface layers. This work was conducted to address the inability of conductivity-based methods to estimate soil depth in commonly occurring sandy soil over lateritic cemented gravels/rock landscapes as both sandy soils and cemented gravels/rock have similar low conductivities. The gravel/rock layer is naturally enriched with radioisotopes of K, Th, and U. We developed the principle to estimate soil depth based on attenuation of radiation due to the thickness of the soil layer. The method was tested using ground and airborne gamma-radiometric surveys coupled with soil depth measurements. Site-specific gamma-emission was used to calculate component emissions from the soil and gravel/rock layers and in turn soil depth from its theoretical relationship with the component emission data. The root mean square error (RMSE) of soil depth estimates from flown and ground data were 7.9 and 4.9 cm, respectively. The maximum measurable soil depth was 45 cm due to attenuation. Plant available soil water storage capacity measured in the <90 cm soil layer was linearly correlated (r² = 0.9) with soil depth. This opens the way to use gamma-radiometry to assess soil depth and PAWC in landscapes with shallow sandy soil over cemented gravels. [ABSTRACT FROM AUTHOR]

Water-based drilling mud (WBM) systems are used by the petroleum industry during drilling of oil and natural gas wells. Provincial regulations in western Canada allow disposal of spent WBM on cropland and sometimes native prairie at low rates. There is concern, however, that application of drilling waste on native prairie in semiarid climates may alter soil properties, which may adversely affect soil biophysical processes and overall ecosystem productivity. This study was initiated to examine the effects of single and multiple applications of differential rates (0, 40, and 80 m³ ha-1) of summer-applied WBM on hydraulic conductivity (Kψ) and macropore indices. Results from unconfined, steady-state infiltration measurements taken at -0.03- and -0.01-m supply pressure potentials (ψ) at the soil surface provide evidence of a significant alteration of these hydraulic parameters with excessive (80 m³ ha-1) drilling mud application. Across the ψ range investigated, Kψ measured 5 to 7 wk after a single mud application and the effective water-transmission macroporosity (θΔψ) calculated using the Kψ decreased by 54 and 61%, respectively, at 80 m³ ha-1 compared with the control (0) and 40 m³ ha-1 rates. Corresponding decreases 5 to 8 wk after a third annual mud application were 62 and 72%. While the rate effect had disappeared 1 yr after the single application, the effect of three annual applications persisted into the following summer. By modifying soil hydrophysical properties, excessive drilling mud applications may adversely affect the soil water balance and alter the plant community structure in this sensitive ecosystem, with important implications on overall biological productivity. [ABSTRACT FROM AUTHOR]

Fertilizer management, particularly of P and K, on sandy soils is crucial to maximize production and minimize environmental impact in agricultural systems. Experiments were conducted at commercial tomato (Lycopersicon esculentum Mill.) farms in southwest Florida during the 2006 spring and winter growing seasons to elucidate P and K distributions in tomato beds and to determine leaching potential under seepage irrigation. Most P was found in the top (0-10 cm) and middle (10-20 cm) soil layers at the centerline (plant row) of the soil bed, and P concentration remained relatively constant. Phosphorus in the bottom layer (20-30 cm) and bed shoulder were similar or less than preplant levels, implying that P did not likely move outside the root zone. However, P fractionation and soil P storage capacity (SPSC) of the root zone samples revealed higher risk of P loss when applied P remained more in soil solution. Most K remained in the top layer of the fertilizer band in an order of magnitude higher concentration compared with the rest of the bed, where low and constant amounts of K were found throughout the season. This result indicated that little or no K leached during this study. Seepage irrigation may have limited downward water movement in the bed, thus nutrient leaching, therefore nutrient loss through surface runoff between growing seasons could be substantial. Current Best Management Practices (BMP) for tomato fertilization should be monitored and evaluated. [ABSTRACT FROM AUTHOR]

Tomato (Lycopersicon esculentum Mill.) in southwest Florida is typically grown on fumigated, raised beds with polyethylene mulch under seepage irrigation. An average grower's N rate currently exceeds the University of Florida's Institute of Food and Agricultural Sciences (UF-IFAS) recommendation (224 kg N ha-1 maximum). Excess nutrients are subject to runoff and leaching, which raises environmental concerns in Florida watersheds. A field study was conducted to elucidate N spatial distribution in tomato beds during the 2006 spring and winter growing seasons with 224 and 358 kg N ha-1 rates. Ammonium N was highest for both seasons during 0 to 1 wk after planting (WAP) at the 0- to 10-cm depth in the fertilizer band, but rarely moved vertically. Lateral movement of NH4+-N was observed through 7 WAP, however, probably due to diffusion' Nitrate N at 0 to 10 cm in the band peaked during 3 to 4 WAP, indicating about 3 wk of nitrification in the spring; however, this process was shortened to 1 to 2 wk in the winter, probably due to greater bacterial activity with warmer temperatures in the beginning of the winter than the spring (average 8°C in the first 3 wk). Both lateral and vertical movements of NO3-N were observed in the spring, even at the 20- to 30-cm depth. A rise and subsequent fall of the water table level during 5 to 8 WAP particularly enhanced NO3-N downward movement, which was attributed 4 greater diffusivity of NO3-N than NH4+-N. Minimizing water table fluctuations and applying a reduced N rate are critical to reduce NO3-N leaching loss. [ABSTRACT FROM AUTHOR]

Polyacrylamide (PAM) is being suggested as a new technology to reduce seepage losses in unlined canals. The goals of this research were to quantify the interactions of PAM and suspended sediment concentrations (SSCs) that reduced the saturated hydraulic conductivity (Ksat) of three sandy-textured soils to the greatest degree, and to better understand the mechanisms contributing to reductions in Ksat. Testing was conducted using a constant-head method in soil columns. Suspended sediment was continuously added to a constant-head water reservoir, into which PAM was added and mixed with an agitator. An unbalanced multifactorial design was used with soil type (line [no. 70 mesh] sand, coarse [ASTM C33] sand, and loamy sand), PAM treatment level (0, 5.6, 11.2, 22.4, and 44.8 kg ha-1), and SSC (0, 150, and 300 mg L-1). Results showed that PAM treatment reduced 40 to 98% in the sands but reductions were much less in the loamy sand (0-56%). Combining suspended sediment and PAM in a 0.005 mol L-1 CaSO4 test solution reduced from 8 to 11 times more than adding PAM without suspended sediment. Mechanisms that reduced included higher viscosity from dissolved PAM and the plugging of larger soil pores near the soil surface. The latter mechanism dominated when the PAM treatment exceeded 5.6 kg ha-1 and when SSC was 150 mg L-1 or higher. Significant Rat reductions were observed when tests were run on filter material (i.e., column experiments without soil), indicating that the creation of a thin soil seal, composed of PAM flocculates, could partially explain the observed Ksat reduction in soil. [ABSTRACT FROM AUTHOR]

Information on the quantitative tillage effects on pore spe and near-saturated hydraulic characteristics is important to improve decision support systems for soil and environmental management. The purpose of this study was to determine the effect of conventional (CT) and reduced tillage (RT) on water retention and infiltration properties of an Agrudalf sandy loam surface soil under long-term winter wheat (Triticum aestivum L.) cropping. Using tension disk inuiltrometry, with supply pressure heads (h) from -15 to -120 mm, the steady-state infiltra- tion rate [i(h)] and hydraulic conductivity [[[Q<(h)] were highest shortly after tillage in October, followed by a steep decrease to minimum values in winter and a recovery to intermediate values during spring and early summer. The range in the temroral variation in saturated Kwas about 65 to 5 and 52 to 8 mm h-1 under CT and RT, respectively. Compared with CT, X(h) under RT was slightly lower shortly after tillage, similar during winter, and considerably higher during early summer. Changes in Kwere accompanied by temporal variations in pore space characteristics, indicating structural collapse during late autumn and early winter followed by structural recovery with aggregation during spring and sumner. The air-entry pressure head was highest under RT. The effective porosities were found to be smaller, by two to three orders of magnitude, than the equivalent fractional pore volumes estimated from the water retention curves determined on soil cores in the laboratory. Wheel traffic was found to obliterate any differences in hydraulic properties between the tillage treatments. Therefore, compared with CT, RT is likely to improve water availability and soil resilience but offers no comparative advantage for controlling wheel-traffic-induced topsoil compaction. [ABSTRACT FROM AUTHOR]

The influence of surfactants on water infiltration in soil is not fully understood. The objective of this study was to propose a model for evaluating effects of an anionic surfactant on upward infiltration under saturated conditions in porous materials with highly contrasting wettability. The simplified equation for upward infiltration based on Darcy's law is equivalent to the widely used Washburn equation. We experimentally determined upward infiltration of sodium dodecyl sulfate (SDS) solution (0-700 mol m-3) into 60-cm-long, 2-cm-diameter columns filled with air-dry materials (glass beads, sand, leaf mold, peat moss, or polyethylene particles). In hydrophilic glass beads and sand, the infiltration rate decreased as the SDS concentration increased due to a decrease in solution surface tension (from 72 to 38 mN m-1). The proposed model could describe the infiltration in all materials and at all concentrations when fitting to the initial parts of the curve of infiltration front vs. time. Contact angles were obtained by fitting the model to the measured height of the infiltration front in the saturated range as a function of time. In columns filled with hydrophobic materials, the infiltration rate increased with SDS concentration, corresponding with a decrease in contact angles from >125 to 69° for polyethylene particles and from 102 to 43° for peat moss. In leaf mold, the infiltration rate decreased as the SDS concentration increased, probably due to swelling. The proposed equation was found useful for calculating saturated hydraulic conductivity and contact angles but limited in the case of swelling porous material. [ABSTRACT FROM AUTHOR]

Most hydrologic studies require knowledge of saturated soil hydraulic conductivity, Ks. This parameter is often measured using saturated soil cores and a constant applied hydraulic head device. A standard approach to reduce uncertainty in the result is to conduct replicate tests at a single hydraulic head gradient. Low-permeability soils are often tested at large hydraulic head gradients to decrease measurement time. Our objective was to test the common assumptions implicit in calculating Ks from constant-head laboratory tests, i.e., the theoretical linear relationship between head gradient and flux density exists in experimental data, and the relationship passes through the origin. In this study, we used linear regression analysis to test these assumptions and determined Ks from a broad range of head gradients for: 4.5-cm (diameter) by 10-cm (height) intact cores of sandy loam soil; 10-cm (diameter) by 10-cm (height) intact cores of clay loam soil; and repacked sand columns of various sizes. We found nonlinear relationships between hydraulic head gradient (i) and flux density (q) for tests conducted on intact cores of both soils, especially for head gradients greater than unity. When we calculated Ks by linear regression of data from intact cores, we found average values approximately one-third greater than the "standard" method of averaging several replicate tests at a single hydraulic head. The difference between the regression and standard analyses was attributed to experimental bias, which is removed by the linear regression. Although no consistent i or q "thresholds" were identified to predict the onset of nonlinearity in i vs. q data, the intact core results imply that i < 1 and q < 5 × 10-3 cm s-1 may be advisable. [ABSTRACT FROM AUTHOR]

The low water-holding capacity of sandy soils, together with spatial and temporal variations of rainfall, require Florida citrus trees to be irrigated for optimal production. Citrus tree root systems are exposed to various hydrologic conditions because of soil temperature and water gradients due to tree canopy shading and under-tree microirrigation. The main goal of this study was to evaluate water balance components in a mature citrus orchard grown on central Florida ridge soils with special interest in quantifying rainfall interception by a citrus canopy and its effect on effective rainfall estimation. Soil water content was monitored every 30 min at 10-, 20-, 40-, and 80-cm depths in the root zone both under and outside of citrus tree canopies. Microirrigation, rainfall, and weather data were used to calculate effective rainfall, plant water uptake, and deep drainage. We found that the tree canopy intercepted 35 and 50% of the incoming high (⩾5-mm) and low (<5-mm) intensity rainfalls, respectively. Effective rainfall calculated without accounting for the canopy interception effect was overestimated by about 30 and 5% for the dry and wet periods, respectively. Citrus crop evapotranspiration was higher under the tree canopy (irrigated area) than outside the tree canopy (unirrigated area) during the dry season because of supplemental irrigation. [ABSTRACT FROM AUTHOR]

Soil P concentrations in agricultural soils have increased over the years, increasing concerns about eutrophication of surface waters. Sandy soils are particularly prone to P leaching due to limited P retention capacity. This study tested the validity of a measure of soil P storage capacity (SPSC) for sandy soils amended with dairy and poultry manure by evaluation of SPSC response to P gain or loss under controlled laboratory conditions. Forty soil samples representing A, E, and Bt horizons were collected from two dairy and two poultry operations within the Suwannee River Basin. Soils were packed into 1.5-cm-diameter columns and 0.05 M KCl solution was passed through the column using unsaturated flow at pore water velocities of approximately 1 cm d-1. Then the soils were leached with known quantities of P. Several P addition and leaching cycles followed and the whole experiment lasted approximately 30 mo. Phosphorus in the leachate was measured after each P addition. The P saturation ratio (PSR) was calculated from oxalate P, Al, and Fe extracts analyzed before and after the study. The SPSC of the soils was calculated based on a threshold PSR of 0.15 for the oxalate solutions. Changes in SPSC due to repeated P additions corresponded to predicted values calculated from P loading amounts, taking into consideration the P concentration before additional P loading. Results support the validity of SPSC as a means of estimating P loading rates that pose low environmental risk for specific sandy soils. [ABSTRACT FROM AUTHOR]

Reduction of diffuse fluxes of sediments from catchments is frequently achieved through the use of vegetative buffers, but the dynamics of this reduction are not fully understood. The physical processes involved in sediment deposition by a stiff grass buffer (hedge) at a low, subcritical flow rate were therefore examined. Flow experiments were performed in the Griffith University tilting-flume simulated rainfall facility using a 0.3-m-width, vetiver (Vetiveria zizaniodes L., sterile cultivar Monto) hedge at a 5% slope. Sediments comprising a sandy soil (Podzol) and red clay (Ferralsol) were introduced into the flow upstream of the buffer and the resultant hydrology, sediment deposition, and outflow characteristics were measured. Flow retardation produced a backwater upstream of the vetiver hedge and sediment deposition varied with soil type in this backwater. The backwater region was greatly extended by the deposition process, increasing overall sediment trapping efficiency. Buffering action reduced mean sediment loads in the out- flow to 3.2 and 6.0% of the inflow concentration for the Podzol and Ferralsol, respectively, with a significant difference (P < 0.01) between the soils. In contrast to other buffer research where deposited sediments were coarsest upstream of the backwater, we found the coarsest particles at the downstream end for the Podzol and Ferralsol, indicating possible bed load movement in addition to the deposition and entrainment processes that dominate supercritical flow. The type of flow therefore affects the size distribution as well as the amount and efficiency of sediment deposition in front of vetiver hedges. [ABSTRACT FROM AUTHOR]

Mixing superabsorbents, such as cross-linked polyacrylamides (PAM), with sandy soils may decrease water percolation rates and increase water availability to crops. Four polymers were evaluated for their effects on water retention and hydraulic conductivity (HC) in the presence of either tap or distilled water and within sand mixtures. Water retained by the absorbents alone (at low suction) ranged between 200 and 500 kg kg-1 of polymer; water retained by the polymers when mixed with sand ranged between 40 and 140 kg kg-1. Water retained per kilogram of polymer increased with an increase in polymer concentration in the sand while undergoing desorption, but absorbed water decreased with polymer concentration during sorption, indicating an effect of hysteresis and absorption kinetics in the water absorption process. Applying a hydraulic head of tap water initially caused a decrease in the HC, explained by the decrease in the volume of the soil-absorbents mixtures, followed by a steady increase in HC ascribed to drainage of water from the swollen polymer granules that led to an increase in the size of pores available for water flow Leaching the soil-absorbent mixtures with distilled water, simulating rainwater, increased the volume of the mixtures (due to polymer swelling) and decreased their HC due to pore blockage by the swollen polymer grains. Better understanding of the interaction among absorbents, soil, and water quality may produce an efficient and economic technology for improving the water management of sandy soils. [ABSTRACT FROM AUTHOR]

Soil phosphate (PO4-P) sorption and release is affected by reactions at the solution-soil surface interface. The objective of this study was to determine how the net negative surface charge and phosphate adsorption/desorption processes in a sandy-loam soil were affected by cattle manure and inorganic fertilizer applications. The soil came from a field experiment where manure and triple superphosphate (TSP) were applied annually on an equivalent plant-available P basis. After 4 yr, manured soils had 37% more negative surface charge in soil suspensions from pH 4 to 7 than TSP-fertilized soils. Phosphate adsorption was 23% lower in soils receiving manure than TSP. The phosphate adsorption data (adsorption of added phosphate + native adsorbed phosphate) was modeled with the Langmuir 2-surface equation, which revealed that the binding strength for phosphate, including native adsorbed phosphate, was about 50% less in the manured soils than the TSP-fertilized soils. These results suggest that manure applications that increase the net negative surface charge also reduce the soil phosphate adsorption capacity. The cumulative desorbed phosphate was twofold greater from manured soils than TSP-fertilized soils. This confirmed the results from phosphate adsorption isotherms showing that phosphate was weakly bound in manured soils, compared with TSP-fertilized soils. We found that manuring not only decreased phosphate retention by the soil but also increased phosphate release into the soil solution, and thus may lead to greater transport of phosphate from agricultural land to waterways. [ABSTRACT FROM AUTHOR]

In agricultural soils, macroporosity and hydraulic properties are influenced by tillage practices. The objective of this study was to characterize macroporosity and surface soil hydraulic properties in two soils of different texture (Lietzen: sandy loam-Humic Dystrudept; Adenstedt: silt loam; Typic Hapludoll) under conventional (CT) and conservational (RT) tillage systems. Soil hydraulic conductivity was assessed in situ by ponded infiltration with single rings (n = 70) and tension infiltration by means of a ‘closed-top’ hood infiltrometer (HIF; n = 48). Macroporosity (pore diameters >1 mm) was estimated from differences in infiltration at saturation and at -3 cm H2O soil matric potential. Mean saturated hydraulic conductivity (Ks) for Lietzen was 3.1 × 10-5 ms-1 and for Adenstedt was 4.3 × 10-5 m s-1. These values are by one order of magnitude higher than values estimated from soil texture. This implies that soil structure has a dominant influence on hydraulic conductivity. Mean values of macroporosity were 0.005% for Lietzen and 0.018% for Adenstedt (using the method of Watson and Luxmoore). The respective values were 0.0008 and 0.0013% when the method of Bodhinayake et al. was used. For Adenstedt, RT showed higher macroporosity than CT (not significant at P < 0.05 for n = 12). Such treatment-induced differences were less developed for Lietzen. The Ks values measured with the ponded ring infiltrometer (RIF) at the sandy Lietzen site were higher than the corresponding values measured with the tension infiltrometer. These differences may be caused by subcritical soil water repellency (i.e., contact angles of the soil-water-air interface below 90°), although further factors could also be important (e.g., air entrapment, differences in water saturation, geometry of infiltration devices). [ABSTRACT FROM AUTHOR]

The fertilized sand-grown cranberry (Vaccinium macrocarpon Aiton cv. Stevens) could be at risk for water contamination by P during seasonal flooding and drainage, especially in high-P soils. The P diagnosis is usually conducted from soil and tissue tests but should also include water-extractable P (PW) as an environmental index. Although the Bray-1P (PBray1) test is the current test for cranberry soils, the Mehlich-III (M-III) test is now commonly used in Quebec and the mid-Atlantic USA as an agri-environmental index with specified thresholds. Our objective was to relate the (P/[Al+Fe])M-III molar ratio to PW and PBray1 and to evaluate this ratio against yield and tissue P responses to added P in high-P sand-grown cranberry crops. Fertilizer trials were conducted during the 2001 to 2004 period at rates of 0, 13,26, and 39 kg P ha-1 yr-1 on permanent plots at five locations in central Quebec. The slope of the relationship between the (P/[Al+ Fe])M-III molar ratio (range: 0.024-0.094) and PBray1(60–235 mg P kg-1) was 0.0004 (R² = 0.92). There were significant site and year effects but no significant effect of added P on berry yield. There were significant linear effects of added P on tissue P concentration in the range of 0.9 to 1.4 g P kg-1 but no critical value could be defined. The simulated (P/[Al+Fe])M-III environmental threshold (9.7 mg PW kg-1) was 0.113. The (P/[AI+Fe])M-III molar ratio could be used interchangeably with PBray1 in Quebec sand-grown cranberry crops but the provisionary environmental threshold must be ascertained from drainage water monitoring. [ABSTRACT FROM AUTHOR]

Transport of phosphorus (P) through surface runoff from agriculture is suspected to contribute to the eutrophication of surface waters in South Florida and elsewhere. There is minimal quantitative information on the concentrations and loads of various P forms in surface runoff water on a field-scale. The objective of this study was to evaluate the annual loads of various P forms in runoff water from citrus and vegetable crop production systems in sandy soil regions in Florida and their relations to soil P status, fertilizer P input, and environmental conditions. Eleven field sites (four on vegetable farms and seven in citrus groves) were selected for this monitoring study over a 2-yr period. The concentrations of total P (TP) in the runoff water samples varied widely from 0.01 to 22.74 mg L-1, with approximately half of the samples having the TP over 1 mg L-1. Eighty-three percent of the samples had orthophosphate (PO4-P) higher than 0.02 mg L-1. The mean proportion of total dissolved P (TDP) in the TP was higher than that of the total particulate P (TPP). The TDP constituted the major proportion of P in runoff water from most of the sites. The PO4-P accounted for approximately 64% of the TDP. The annual median concentrations of various P forms in the runoff water varied spatially and temporally and were correlated with total and labile P in the soils (water-P, Olsen-P, Mehlich 1-P, and Mehlich 3-P) as well as fertilizer P rate. The vegetable farms had higher concentrations of P in the runoff water than citrus groves due to their more severe soil erosion and higher fertilizer P input, which resulted in higher soil P accumulation and availability. The annual loads of TP, TDP, and PO4-P varied among the field sites and between the 2 yr. The TP loads were significantly correlated with soil labile P estimated by the four extraction procedures, but the Olsen-P was best related to runoff P. Runoff P concentrations and the annual discharge rate accounted for 55 to 64% of the variance in the annual P loads. These results indicate that P transport through surface runoff from agriculture is affected by soil P status and water management, and merits attention in the development of best management practices. [ABSTRACT FROM AUTHOR]

Copper (Cu) and zinc (Zn) transport after agricultural applications have accumulated in the sediments and are suspected to affect fish health in the Indian River Lagoon and St. Lucie Estuary, South Florida. Minimal information is available on the release of soil Cu and Zn to water and its relation to their concentrations and physicochemical forms in the soils. Sandy soil samples (n = 13) with a wide range of total Cu and Zn content were collected from forestland and commercial citrus groves in the Indian River area, Florida. The soils were subjected to column leaching and batch extractions to understand the release behavior of Cu and Zn as affected by soil-water contact time, soil/water ratio, pH, and electrolyte concentration and cations. Copper released in batch extractions that simulated long-term leaching was primarily from exchangeable and carbonate-bound fractions, whereas Zn was primarily from the carbonate-bound fraction. The Cu and Zn released from the column represented short-term leaching and were primarily from their exchangeable fractions. Leached Zn decreased linearly as the solution pH was raised froni 3.0 to 9.0. Leached Cu was at a minimum at pH 5 to 7 and increased at higher or lower pH beyond that range. These results indicate that long-term saturated conditions after precipitation enhanced Cu and Zn release to water from the sandy soils. The released Cu decreased with increasing Ca concentration but increased with sodium (Na) concentration in the soil solution because of their differential effects on soil colloids, especially organic matter (flocculated by Ca2+ and dispersed by Na+) because organically bound Cu is the dominant fraction in the soils. Increasing Ca, K, Na, or NH4+ concentration generally increased Zn release through cation exchange. These findings merit attention in the development of best management practices to reduce transport of heavy metals from land to water. [ABSTRACT FROM AUTHOR]

Studying soil hydrological processes requires the determination of soil hydraulic parameters whose assessment using traditional methods is expensive and time-consuming. A specific method, Beerkan estimation of soil transfer parameters referred to as BEST was developed to facilitate the determination of both the water retention curve, θ(h), and the hydraulic conductivity curve, K(θ), defined by their shape and scale parameters. BEST estimates shape parameters from particle-size distribution analysis and scale parameters from infiltration experiments at null pressure head. Saturated water content is measured directly at the end of infiltration. Hydraulic conductivity and water pressure scale parameters are calculated from the steady-state infiltration rate and prior estimation of sorptivity (S). This is provided by fitting transient infiltration data on the classical two-term equations with values from zero to a maximum corresponding to null hydraulic conductivity and using a data subset for which the two-term infiltration equations are verified as valid. BEST was compared with other fitting methods to estimate sorptivity and hydraulic conductivity from infiltration modeling data on the basis of the same infiltration equations for three contrasting soils: agricultural soil, sandy soil, and a coarser fluvioglacial deposit. The other methods failed sometimes to model accurately experimental data and to provide values in agreement with physical principles of water infiltration (negative values for hydraulic conductivity, too high steady-state infiltration rate). None of these anomalies was encountered when modeling cumulative infiltration with BEST. BEST appears to be a promising, easy, robust, and inexpensive way of characterizing the hydraulic behavior of soil. [ABSTRACT FROM AUTHOR]

Nitrogen fertilizer inputs for intensive, irrigated crop production on sandy soils can contribute to elevated NO3 concentrations in groundwater. This study was conducted from 1995 to 1998 to determine the potential of a winter rye (Secale cereale L.) cover crop to recover fertilizer N from soil and crop residues and the availability of this N to corn (Zea mays L.). Nitrogen fertilizer treatments included no N and N-labeled (15N-depleted) fertilizer (NLF) applied to sweet corn at 190 kg ha-1 and to potato (Solanum tuberosum L.) at 224 kg ha-1. Cover crop treatments (fallow and winter rye) were established following harvest, plowed the following spring, and corn was grown with unlabeled fertilizer N at 112 kg ha-1. Whole plant fertilizer N recovery averaged 54% for sweet corn and 34% for potato using the NLF (15N isotope) method, and was significantly lower than N recovery determined by the difference method. Total NLF recovery decreased between harvest and the following spring (from 66 to 43% following sweet corn and from 47 to 37% following potato), presumably due to mineralization and leaching of crop residue N. Winter rye NLF uptake averaged 2 kg ha-1 and had no effect on total NLF recovery. Corn grain yields were significantly higher following potato than following sweet corn and following a winter rye cover crop compared with fallow in 2 of 3 yr. Corn NLF uptake averaged 3 kg ha-1 indicating the yield benefit following potato or winter rye was due to a rotation effect rather than a direct N contribution. These results indicate that on irrigated sandy soils in this region most of the N fertilizer not removed in the harvested portion of crops will be lost by leaching during the growing season or by the following spring. [ABSTRACT FROM AUTHOR]

To identify the most suitable technique for measuring solute leaching in a sandy soil, we compared three methods in an irrigation experiment (irrigation rates: 5 and 2.4 mm h-1) using Cl- as a tracer. We tested tensiometer-controlled suction plates, wick samplers, and ionexchange resin boxes installed between fiberglass pads. Ten samplers of each type were installed at a 52-cm depth (suction plates) or a 60-cm depth (wick and resin box samplers) into soil monoliths. The recovery of water and Cl- by the suction plates varied little with irrigation rate (107-118%). The wick samplers performed well during 5 mm h-1 irrigation (Cl- recovery: 111%; water recovery: 103%). However, at the irrigation rate of 2.4 mm h-1, the water recovery was significantly lower (70%), probably because the soil suction exceeded the maximum capillary force of the wicks. The wicks did not induce a retardation or additional dispersion of Cl- compared with suction plates. The recovery of Cl- by the resin boxes was only 6%. Tensiometer-controlled suction plates allowed an overall satisfactory estimation of water and solute fluxes in the sandy soil. [ABSTRACT FROM AUTHOR]

Investigates the differences of ion and gas diffusion coefficients in an unsaturated sandy soil. Obstruction in measuring tortuosity parameters; Comparison of gas diffusion coefficient and bulk soil electrical conductivity; Use of lattice-Boltzmann simulation models to examine the transport properties of unsaturated soils.

Investigates the soils and hydrology of a wet-sandy catena in east-central Minnesota. Description and history of the Cedar Creek Natural History Area in Anoka; Climate; Saturation, redox potential and redoximorphic features.

Predicts temperature and heat flow in a sandy soil by electrical modeling. Soil temperature in different water contents; Role of the soil column in determining soil temperature; Influence of rain on soil temperature; Influence of water content on heat transmission.

Compares the effectiveness of techniques for direct extraction of fatty acids from soils, ester-linked method and the method developed by Microbial ID, Inc., in characterizing soil microbial communities of silt loams and sandy soils. Analysis of fatty acid methyl ester profiles changes; Types of fatty acids obtained from each of the technique.

Examines the ability of microbes and plants to assimilate nitrogen (N) from cover crop residue in sandy soils in Salinas Valley, California. Description of changes in soil responses and N fates under field management conditions; Addition of fresh residues to miniplots; Importance of proper water and fertilizer input management for preventing N loss.

Describes a method for the installation of minirhizotron tubes in sandy, rocky soils while keeping soil disturbance to a minimum. Use of a pneumatic rock-drill alternately to drill and drive drill casing into the soil; Finding of less soil compaction and disturbance than traditional installation techniques entail.

Assesses the morphology, chemistry and mineralogy of isotropic coatings in indurated sandy soil horizons. Field observations; Optical microscope data; Chemical analyses; Scanning electron microscopy; Mechanisms of horizon induration.

Investigates the air-water interfacial areas and water contents in an unsaturated sandy soil column. Use of chloroform as the water-partitioning gaseous tracers; Estimation of the velocity of air-water interface.