Nitrate (NO3
−) leaching from agriculturalproduction systems is blamed for the rising concentrations ofNO3
− in ground- and surface-waters around the world.This paper reviews the evidence of NO3
− leachinglosses from various land use systems, including cut grassland, grazed pastures,arable cropping, mixed cropping with pasture leys, organic farming,horticultural systems, and forest ecosystems. Soil, climatic and managementfactors which affect NO3
− leaching are discussed.Nitrate leaching occurs when there is an accumulation ofNO3
− in the soil profile that coincides with or isfollowed by a period of high drainage. Therefore, excessive nitrogen (N)fertilizer or waste effluent application rates or N applications at the wrongtime (e.g. late autumn) of the year, ploughing pasture leys early in the autumn,or long periods of fallow ground, can all potentially lead to highNO3
− leaching losses. N returns in animal urine havea major impact on NO3
− leaching in grazed pastures.Of the land use systems considered in this paper, the potential for causingNO3
− leaching typically follow the order: forest< cut grassland < grazed pastures, arable cropping < ploughing ofpasture < market gardens. A range ofmanagement options to mitigate NO3
− leaching isdescribed, including reducing N application rates, synchronizing N supply toplant demand, use of cover crops, better timing of ploughing pasture leys,improved stock management, precision farming, and regulatory measures. This isfollowed by a discussion of future research needs to improve our ability topredict and mitigate NO3
− leaching.

Nitrate leaching in temperate agroecosystems: sources, factors and mitigating strategies

Keywords: Mecanique des sols ; Drainage ; Ecoulement souterrain Reference Record created on 2004-09-07, modified on 2016-08-08

Applications of soil physics.

Soil tillage practices can affect soil hydraulic properties and processes dynamically in space and time with consequent and coupled effects on chemical movement and plant growth. This literature review addresses the quantitative effects of soil tillage and associated management (e.g., crop residues) on the temporal and spatial variability of soil hydraulic properties. Our review includes incidental management effects, such as soil compaction, and natural sources of variability, such as topography. Despite limited research on space-time predictions, many studies have addressed management effects on soil hydraulic properties and processes relevant to improved understanding of the sources of variability and their interactions in space and time. Whether examined explicitly or implicitly, the literature includes studies of interactions between treatments, such as tillage and residue management. No-tillage (NT) treatments have been compared with various tillage practices under a range of conditions with mixed results. The trend, if any, is for NT to increase macropore connectivity while generating inconsistent responses in total porosity and soil bulk density compared with conventional tillage practices. This corresponds to a general increase in ponded or near-zero tension infiltration rates and saturated hydraulic conductivities. Similarly, controlled equipment traffic may have significant effects on soil compaction and related hydraulic properties on some soils, but on others, landscape and temporal variability overwhelm wheel-track effects. Spatial and temporal variability often overshadows specific management effects, and several authors have recognized this in their analyses and interpretations. Differences in temporal variability depend on spatial locations between rows, within fields at different landscape positions, and between sites with different climates and dominant soil types. Most tillage practices have pronounced effects on soil hydraulic properties immediately following tillage application, but these effects can diminish rapidly. Long-term effects on the order of a decade or more can appear less pronounced and are sometimes impossible to distinguish from natural and unaccounted management-induced variability. New standards for experimental classification are essential for isolating and subsequently generalizing space-time responses. Accordingly, enhanced methods of field measurement and data collection combined with explicit spatio-temporal modeling and parameter estimation should provide quantitative predictions of soil hydraulic behavior due to tillage and related agricultural management.

Tillage effects on soil hydraulic properties in space and time: State of the science

Irrigation and drainage systems are disclosed, including a saturated zone and at least one pipe in communication with the saturated zone. The pipe(s) can be configured to comprise a tubarc porous microstructure for conducting water from the saturated zone to an unsaturated zone in order to drain the water from the saturated zone. The water can be delivered from the saturated zone to the unsaturated zone through the tubarc porous microstructure, thereby permitting the water to be harnessed for irrigation or drainage through the hydrodynamic movement of the water from one zone of saturation or unsaturation to another.

Irrigation and drainage based on hydrodynamic unsaturated fluid flow

Grazing animals exert pressure on the ground comparable to that of agricultural machinery. As a result, soil under pasture can be compacted. In grazing systems based on permanent pastures or rangelands, there is little opportunity to ameliorate poor soil physical conditions through tillage. Hence, it is important to understand the effects of grazing on soil physical properties and the consequent effects of these properties on pasture growth and composition. Most soils under grazed pasture, even those managed to minimise soil physical degradation, will be compacted to some extent. However, the magnitude of this compaction is usually small, and limited to the upper 50–150 mm of the soil. Compaction to greater depth, and other changes in soil physical properties, are more likely in recently tilled or wet soils. The response of pasture to the poorer soil conditions caused by grazing is difficult to determine, but it is likely to be small compared with the defoliation effects of grazing. Maintenance of a vigorous pasture should be a major aim of grazing management and would also achieve the secondary aim of maintaining acceptable soil physical conditions.

Grazing effects on soil physical properties and the consequences for pastures: a review

A new method is proposed for determining in situ unsaturated hydraulic conductivities from unsaturated infiltration measurements made at several tensions on the same infiltration surface. Wooding's equation for steady-state unconfined infiltration rates is used in calculating hydraulic conductivities. Hydraulic conductivities calculated with the new method are consistent with unit gradient laboratory measurements of saturated and unsaturated hydraulic conductivity. This simple field method is potentially valuable because it is faster than unit gradient laboratory methods, and it is less disruptive of pore continuity than other field infiltration techniques. R OF SOIL WATER INFILTRATION and SUbSUrface water movement are important to researchers developing soil management practices to minimize potential groundwater contamination from land applied chemicals. A simple and rapid field technique of determining field unsaturated hydraulic conductivity would be useful in achieving this objective. Field and laboratory techniques for measurement of unsaturated hydraulic properties of soil were described by Green et al. (1986) and by Klute and Dirksen (1986), respectively. Solution of unsaturated flow problems generally requires experimental determination of the relationship between hydraulic conductivity and water potential or water content. Field methods used to obtain these relationships include the instantaneous profile method, steady-flux methods (with sprinkler irrigation or artificial crusts), sorptivity measurements, and use of tension infiltrometers (Clothier and White, 1981; Ankeny et al., 1988, 1989; Elrick et al., 1988a; White and Perroux, 1987, 1989; Smettem and Clothier, 1989). Because instantaneous profile and steady-flux techniques require laborious installation of tensiometers or neutron probe access tubes, sample numbers and the extensiveness of a site characterization can be limited. Sorptivity is an unsaturated soil parameter sometimes measured in the field (Green et al., 1986). Although sorptivity measurements are fast and simple, these measurements usually require that initial water content be known. White and Perroux (1989) have proposed a laboratory method for calculating unsaturated hydraulic conductivity from sorptivity measurements. Their method, however, requires air drying the sample between measurements at different tensions, which increases experimental time and may cause wetting/drying effects on soil structure. The Guelph infiltrometer (Soilmoisture Equipment Corp., Santa Barbara, CA) compares infiltration rates for difM.D. Ankeny, Daniel B. Stephens & Assoc., 4415 Hawkins NE, Albuquerque, NM 87109; M. Ahmed, Bangladesh Univ. of Engineering and Technology, Dhaka-1000, Bangladesh; T.C. Kaspar, National Soil Tilth Lab., Ames, IA 50011; and R. Horton, Dep. of Agronomy, Iowa State Univ., Ames, IA 50011. Joint contribution from USDA-ARS and Iowa State Univ. Journal Paper no. J-13716 of the Iowa Agric. and Home Economics Exp. Stn. Projects no. 2659 and 2715. Received 6 Nov. 1989. *Corresponding author. Published in Soil Sci. Soc. Am. J. 55:467-470 (1991). ferent radii surface disks and does not require driving a ring. Different soil surface areas, however, are being compared, which may introduce spatial variability associated with the different soil surfaces. A field method to measure in situ hydraulic conductivity at low water tensions is needed for studies of macroporosity and water flow in agricultural soils. The desired criteria for such a method are: 1. Only steady-state infiltration rate measurements are needed. Knowledge of the initial water potential or content should not be required. 2. Soil pore structure should not be disturbed by driving a ring into soil to obtain one-dimensional flow. This way, larger pores are not truncated or collapsed and infiltration through larger pores is less likely to be underestimated. 3. Measurements should be taken on the same soil surface. Measurements taken by using different radii (e.g., Elrick et al. 1988a) are more dependent on the assumption of soil homogeneity. 4. Calculation of hydraulic conductivities should be straightforward. We present a simple scheme for determination of in situ hydraulic conductivity that meets these criteria.

Simple field method for determining unsaturated hydraulic conductivity

Design for an Automated Tension Infiltrometer

Tillage and wheel-traffic compaction alter pore structure and hydraulic properties of agricultural soils. These alterations will affect root growth and movement of water and solutes. This study was conducted to develop new methods needed to characterize the effects of wheel traffic and tillage on pore structure as measured by water flow through macropores. Unconfined (three-dimensional) saturated and unsaturated infiltration measurements (0-, 30-, 60-, and 150mm water tension) at the soil surface were taken sequentially at field sites to determine the steady-state rate of water flow through different pore-size classes on a Tama silty clay loam (fine-silty, mixed, mesic Typic Argiudoll). A tension infiltrometer was used to obtain the unsaturated infiltration rates. Sites were selected on trafficked and untrafficked interrow positions in two tillage systems (chisel plow and no-till). Steady-state infiltration rates from 2 to 300 ion s" were measured. Increasing the tension of applied water resulted in decreasing infiltration rates for both tillages and traffic treatments because, as tensions increased, larger pores emptied. Wheel traffic reduced infiltration rates in both tillages, but caused a greater decrease in infiltration rates in the chisel-plow system than in no-till. Increasing tension caused proportionately smaller decreases in infiltration rates for wheel-trafficked positions. This suggests that larger macropores were transporting a greater proportion of the total water flow in untrafficked soil than in trafficked soil and reinforces the concept that larger, as opposed to smaller, pores are more easily destroyed by wheel traffic. Unconfined infiltration measurements were shown to be useful in quantifying the effects of tillage and compaction on soil macropores. I OF WATER INTO SOIL is directly related to soil macroporosity. Macropores are also important for root growth (Wang et al., 1986) and for solute movement (Beven and Germann, 1982). Tillage and compaction, however, can alter soil macroporosity. Thus, to elucidate the effects of tillage and compaction on soil macroporosity, we measured the rate of water infiltration into macropores for different tillage and wheel-traffic treatments. Macropores have been denned in several ways (Luxmoore, 1981). In this study, we define macropores as pores than empty at 0.2 mm nominal diameter or larger will drain at 150 mm tension. This pore-size range was selected because it includes the pore sizes important for (i) root growth and (ii) preferential solute flow. Secondary laterals of cereal root tips have an average diameter of ~0.2 mm (Hackett, 1969). A root tip growing into a pore smaller than its own diameter undergoes mechanical stress (Russell, 1977). Therefore, an estimate of pores with diameter of >0.2 mm should be correlated with unrestricted root extension, in a soil of moderate Joint contribution from the Natl. Soil Tilth Lab., USDA-ARS, and Dep. of Agronomy, Iowa State Univ., Ames, IA 50011. Journal Paper no. J-13513 of the Iowa Agric. and Home Economics Exp. Stn., Ames, IA; Project no. 2878. Received 8 June 1989. •Corresponding author. Published in Soil Sci. Soc. Am. J. 54:837-840 (1990). strength. Preferential solute flow also occurs in large soil pores. Scotter (1978) calculated that significant preferential flow of both strongly and weakly absorbed solutes could occur in continuous macropores with diameters >0.2 mm. Tension infiltrometers have been used to estimate soil pore and hydraulic properties. Clothier and White (1981) and Walker and Chong (1986) used tension infiltrometer measurements to estimate sorptivity. Moore et al. (1986) and Wilson and Luxmoore (1988) measured one-dimensional infiltration rates on forest soils to estimate macroporosity and unsaturated hydraulic conductivity. Control of tension at the soil surface by a tension infiltrometer limits the size of pores that are conducting water (Clothier and White, 1981) and allows measurement of unsaturated infiltration. Imposition of sequentially greater tensions leads to the incremental draining of smaller and smaller pores. Infiltration rates decrease as more of the water-conducting pores empty. Therefore, by comparing infiltration rates at increasing tensions, the relative contributions to water flow by various pore sizes can be evaluated. Greater relative water-flow rates are assumed to indicate more and/or better-connected pores within a pore-size class. This study was conducted to determine the effects of wheel traffic and tillage on pore structure as measured by water flow through macropores. MATERIALS AND METHODS Unconfined infiltration rates at selected tensions were measured, using a tension infiltrometer. Measurement at multiple tensions allowed evaluation of treatment effects on different pore sizes. Three-dimensional flow measurement avoids two problems inherent in one-dimensional measurement: (i) truncation or destruction of pores caused by driving a ring or isolating a soil monolith and (ii) wall flow along the edge of the soil sample. Field plots were established in the fall of 1984 on a Tama soil 12 km west of Marshalltown, I A. Corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] were grown in rotation on the site beginning in 1985. Corn was grown in 1988 on the areas where infiltration measurements were taken. Three tillage systems (no-till, ridge, and chisel plow) with controlled wheel traffic and four replications had been established on the site. Infiltration measurements were taken only on the no-till (NT) and chisel-plow (CP) tillage systems. The NT plots received no primary tillage and were cultivated once a year; CP plots were chiseled in the fall, disked shortly before planting, and cultivated. Plots were arranged in a five-row configuration, with 76-cm rows. Foot traffic was confined to trafficked interrows throughout the year. Infiltration measurements were made in mid-June, shortly before the 1988 cultivation. Infiltration measurements were taken in the center of trafficked and untrafficked interrows at two sites within each tillage replication. Thus, eight sites were measured in each tillage/traffic combination, for a total of 32 sites. At each of the 32 sites, steady-state (unconfined) infiltration rates were measured at four tensions: 0-, 30-, 60-, and 150-mm water tension. At each infiltration site, an area approximately 25 to 30

https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1316&context=agron_pubs

Characterization of Tillage and Traffic Effects on Unconfined Infiltration Measurements

Spatial variability of surface hydraulic properties and the extrinsic (e.g., traffic, cropping, etc.) and intrinsic (e.g., soil type, pore size distribution, etc.) factors associated with these properties are important for infiltration and runoff processes in agricultural fields. Disc infiltrometers measured infiltration at 296 sites arranged on two parallel transects. To examine and differentiate the factors contributing to spatial structure under different field conditions these measurements were made in the corn rows, no-track interrows, and wheel track interrows of the field using four different soil water tensions * (0, 30, 60, and 150 mm). Unsaturated hydraulic conductivity (K) and saturated hydraulic conductivity (K,) were maximum in the corn rows and minimum in wheel track inter-rows, with no-track interrows intermediate. Exponents (CZ parameters) of K, and K relationships (K = K, exp -aV) for corn rows and no-track interrows were not significantly different from each other but were significantly different from Q for the wheel track interrows a t P = 0.01 level. Spatial variability o f K and K, values showed some pseudoproportional effect in nugget variance for all three field conditions. No-track interrows clearly showed an inverse trend for semivariogram o f K with changing tension (q) values, whereas differences were found for corn rows and wheel traffic interrows. The spatial structure of (Y for all three field conditions were mostly white noise. Under corn rows, in addition to random variation, a small five-row periodic variation at th e P = 0.20 level, matching the five-row traffic configuration, was discovered. The spatial structure of a was influenced by soil type for the no-track interrows. Spatial structure was absent in wheel track interrows, indicating the destruction of pore structure due to compaction.

https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1973&context=abe_eng_pubs

Spatial analysis of hydraulic conductivity measured using disc infiltrometers

Summary Compactive processes affect soil hydraulic properties and associated soil water flow. Soil water retention and transport properties are altered in response to changes in pore space geometry. Soil water flow is affected not only by soil hydraulic properties but additionally by the distribution of sources and sinks of water in the soil system. Compaction can alter soil pore geometry, and can also affect sources and sinks of water by changing surface configuration, and crop rooting distribution. This paper reviews the literature and presents data and relationships showing the effects of compaction on soil hydraulic properties and water flow, presents numerically modeled water flow for some management systems, and identifies future directions for research.

https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1312&context=agron_pubs

Mark D. Ankeny

Papers

Simple field method for determining unsaturated hydraulic conductivity

Design for an Automated Tension Infiltrometer

Characterization of Tillage and Traffic Effects on Unconfined Infiltration Measurements

Spatial analysis of hydraulic conductivity measured using disc infiltrometers

Effects of Compaction on Soil Hydraulic Properties