ing spatial variations of soil water content using noncontacting electromagnetic inductive methods. Can. J. Soil Sci. 68:715-722.The relationships among the spatial variations of soil water content, soil texture, soil solution electrical conductivity, and bulk soil electrical conductivity were examined for a field characterized by net drainage and low concentrations of dissolved electrolytes. Bulk soil electrical conductivity was measured over various depths at 52loca-tions within a 1.8-ha field using noncontacting electromagnetic inductive meters. Soil water content (0-0.5 m depth) was measured at the same locations using the time domain reflectometry method. Measurements of soil texture and soil solution conductivity were obtained from core samples from-37 of the sampling locations. Soil water content at the site ranged from 0.06 to 0.36 m j m '. Clay content ranged from 2.5 to 44% percent and bulk soil electrical conductivity ranged from 0.0 to 0.21 S m-1. Significant correlation existed among almost all ofthe measured variables. Regression analysis indicated soil solution conductivity had no effect on measured bulk soil electrical conductivity for soil water contents less than 0.25 m3 m-t. Bulk selected to obtain the maximum variation in 0" and texture across the site (Fig. l). RESULTS AND DISCUSSIONSand content in the 0-to 0.5-m depth of the study area varied from 5 to70% and clay content from 2.5 to 44.0% (Table 1)

Conservation tillage has become an attractive form of agricultural management practices for corn and soybean production on heavy textured soil in southern Ontario because of the potential for improving soil quality. A controlled drainage system combined with conservation tillage practices has also been reported to improve water quality. In Southwestern Ontario, field scale on farm demonstration sites were established in a paired watershed (no-tillage vs. conventional tillage) on clay loam soil to study the effect of tillage system on soil structure and water quality. The sites included controlled drainage and free drainage systems to monitor their effect on nitrate loss in the tile drainage water. Soil structure, organic matter content and water storage in the soil profile were improved with no-tillage (NT) compared to conventional tillage (CT). No-tillage also increased earthworm populations. No-tillage was found to have higher tile drainage volume and nitrate loss which were attributed to an increase in soil macropores from earthworm activity. The controlled drainage system (CD) reduced nitrate loss in tile drainage water by 14% on CT site and 25.5% on NT site compared to the corresponding free drainage system (DR) from May, 1995 to April 30, 1997. No-tillage farming practices are definitely enhanced by using a controlled drainage system for preventing excessive nitrate leaching through tile drainage. Average soybean yields for CT site were about 12 to 14% greater than the NT site in 1995 and 1996. However, drainage systems had very little effect on soybean yields in 1995 and 1996 due to extremely dry growing seasons.

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soil water storage (0-1.7 m) was measured every l0 m in a 660-m-long transect using a neutron probe and compared to bulk electrical conductivity, ECa, measurements obtained using noncontacting electomagnetic induction meters. Coherency analysis indicated a lack of correlation at scales less than 40 m. At scales greater than 40 m, ECo explained more than 8O7o of the variation of soil water storage. Measurement of ECo should be a simple and fast method of determining general field pafterns of soil water storage.

Atrazine (6-chloro-N2-ethyl-N4-isopropyl-1,3,5-triazine-2,4-diamine) and metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] have been found with increasing occurrence in rivers and streams. Their continued use will require changes in agricultural practices. We compared water quality from four crop-tillage treatments: (i) conventional moldboard plow (MB), (ii) MB with ryegrass (Lolium multiflorum Lam.) intercrop (IC), (iii) soil saver (SS), and (iv) SS + IC; and two drainage control treatments, drained (D) and controlled drainage-subirrigation (CDS). Atrazine (1.1 kg a.i. ha-1), metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazine-5(4H)-one] (0.5 kg a.i. ha-1), and metolachlor (1.68 kg a.i. ha-1) were applied preemergence in a band over seeded corn (Zea mays L.) rows. Herbicide concentration and losses were monitored from 1992 to spring 1995. Annual herbicide losses ranged from < 0.3 to 2.7% of application. Crop-tillage treatment influenced herbicide loss in 1992 but not in 1993 or 1994, whereas CDS affected partitioning of losses in most years. In 1992, SS + IC reduced herbicide loss in tile drains and surface runoff by 46 to 49% compared with MB. The intercrop reduced surface runoff, which reduced herbicide transport. Controlled drainage-subirrigation increased herbicide loss in surface runoff but decreased loss through tile drainage so that total herbicide loss did not differ between drainage treatments. Desethyl atrazine [6-chloro-N-(1-methylethyl)-1,3,5-triazine-2,4-diamine] comprised 7 to 39% of the total triazine loss.

No abstract

Methods for measuring and estimating flux density of soil fumigants under field conditions are important for the purpose of providing inputs to air dispersion models and for comparing the effects of management practices on emission reduction. The objective of this study was to measure the flux of 1,3-dichloropropene (1,3-D) and chloropicrin at a site in Georgia (GA) using the aerodynamic method and the dynamic flux chamber (FC) method. A secondary objective was to compare the effects of high density polyethylene (HDPE), and virtually impermeable film (VIF) tarps on fumigant flux at a site in Florida (FL). Chloropicrin and 1,3-D were applied by surface drip application of In-Line soil fumigant on vegetable beds covered by low density polyethylene (LDPE), HDPE, or VIF. The surface drip fumigation using In-Line and LDPE tarp employed in this study resulted in volatilization of 26.5% of applied 1,3-D and 11.2% of the applied chloropicrin at the GA site, as determined using the aerodynamic method. Estimates of mass loss obtained from dynamic FCs were 23.6% for 1,3-D and 18.0% for chloropicrin at the GA site. Flux chamber trials at the FL site indicate significant additional reduction in flux density, and cumulative mass loss when VIF tarp is used. This study supports the use of dynamic FCs as a valuable tool for estimating gas flux density from agricultural soils, and evaluating best management practices for reducing fumigant emissions to the atmosphere.

In field solute‐transport experiments, two spatial scales of the continuum of the dispersion process have been measured: local scale and field scale. The objective of this experiment was to develop a method for measuring in situ the transition from the local scale to the field scale during unsaturated flow conditions. The spatial variability of in situ solute dispersion was examined in two field sites. Soil‐solution samplers were installed in a transect at a 0.4‐m depth and 0.2‐m spacing in both a cultivated and never‐cultivated (forested) site. A pulse of KCl was applied to both sites under conditions of constant surface flux density of water, which was applied using a trickle irrigation system. The variance of solute travel time, V2(t), at different spatial scales was calculated from moment analysis of breakthrough curves (BTC) obtained by averaging local BTC across different spatial scales. The scale dependence of V2(t) indicated scales of at least 2.8 and 3.8 m were needed to reach an effective far field variance for the forested and cultivated sites, respectively. The larger scale in the cultivated site was due to an increase in horizontal correlation length scales of soil properties caused by tillage mixing. The scale dependence of V2(t) can be used to determine the minimum plot size necessary to include all major horizontal variations in solute travel time, which can then be compared with spatial distributions of soil properties affecting transport.