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Determining the preferential flow characteristics of a soil is important because agrichemicals can contaminate groundwater via preferential flow pathways. A model that predicts solute transport due to preferential flow is the mobile-immobile solute transport model, which partitions the total water content ([Theta], [m.sup.3] [m.sup.-3]) into a mobile fraction ([[Theta].sub.m]) and an immobile fraction ([[Theta].sub.im]). Recently, an in situ method was proposed for determining the mobile-immobile model parameters of [[Theta].sub.im], and mass exchange coefficient ([Alpha]) between the fractions by using a tension infiltrometer to apply a series of four fluorobenzoate tracers. The objective of this study was to test the in situ technique at 47 sites along a transect in a ridge-till corn (Zea mays L.) field of Nicollet soil (fine-loamy, mixed, mesic Aquic Hapludoll). The immobile fraction ([[Theta].sub.im]/[Theta]) ranged from 0.394 to 0.952 with a median of 0.622. The mass exchange coefficient ranged from 0.000237 to 0.00481 [min.sup.-1] with a median of 0.00123 [min.sup.-1]. These values are similar in magnitude and range to values reported by other investigators, and they follow the same relationships. The values of [[Theta].sub.im]/[Theta] and [Alpha] along the transect indicated no obvious spatial trends or spatial Correlations. Significant linear correlations did exist between [Alpha] and soil water flux, [Alpha] and [[Theta].sub.im], and [Theta] and [[Theta].sub.im].

Subsurface water-flow barriers have the potential for reducing N[O.sub.3]-N leaching and may improve fertilizer-use efficiency in cropping systems. This concept was investigated in field lysimeters near Ames, IA, filled with Sparta loamy fine sand (sandy, mixed mesic Entic Hapludoll) in 1989 and 1990. Our objectives were to determine (i) the effects of subsurface water-flow barriers on leaching losses of N[O.sub.3]-N and [Cl.sup.-] and on N uptake by corn plants, and (ii) the effects of an absorbent (vermiculite) on the leaching of N[O.sub.3]-N and [Cl.sup.-]. Subsurface water-flow barrier treatments were: no barrier (NB), a polyethylene sheet placed above the banded chemicals (PA), a polyethylene sheet placed below the band (PB), and a compacted soil layer formed in situ above the chemicals (CL). In 1989 with corn (Zea mays L.) plants growing in the lysimeters, subsurface barriers delayed and reduced leaching and increased plant N uptake compared with NB. The PA treatment was the most effective, reducing [Cl.sup.-] and N[O.sub.3]-N leaching by 24 and 21%, respectively, and doubling total N in corn shoots compared with NB. The CL treatment reduced anion leaching by 12%, but did not affect total plant N. In 1990, the subsurface barrier treatments were combined with two application methods, solution banding (S) and solution-vermiculite mixture banding (V). Averaged across barrier types, V banding delayed initial breakthrough of [Cl.sup.-] and N[O.sub.3]-N by 1.5 and 2.5 mm, respectively, and reduced the peak anion concentrations by an average of 25% compared with the S banding.

There have been few studies on rational or lateral spacing between soil temperature sensors that are used to obtain spatially independent field measurements under various tillage systems. This makes it difficult for sensors in tillage plots to be properly positioned since data on the spatial dependence of the measurements are virtually non-existent. The spatial variability and daily fluctuation of soil temperature in three different tillage systems is studied.

Use of more nitrogen than the required amount helps maximize crop yields but causes deficiency of soil organic matter (SOM). This factor was analysed when an excess amount of stover and NO(sub 3)(super -1) in Galva silty clay loam suppressed the mineralization of carbon from SOM. This observation has meticulously been discussed.

A simple technique has been developed to measure the immobile water fraction; theta(sub im)/theta, and the solute exchange coefficient, alpha; between the mobile and immobile zones of an unsaturated soil. With this method theta(sub im) in moderately slow mobile/immobile transfer rate, assumes the two-domain model for field soils, simultaneous measurement of both hydraulic conductivity, and the solute transport parameter theta(sub im). From this data alpha can be determined.

Chloride (Cl-) breakthrough experiments were conducted on three repacked soil columns under saturated steady-flow conditions to examine the effects of the types and sizes of subsurface barriers on anion leaching. Small subsurface barriers showed the ability to reduce or postpone the leaching of anions. A 5-centimeter-diameter barrier postponed early breakthrough of Cl-, restricted peak concentration by 40%, and delayed peak formation by 0.6 pore volumes.

Transforming growth factor (TGF-betas) is a highly homologous polypeptide family of which TGF-beta1 and -beta2 are dimer members. Biological metabolic features such as cellular development and differentiation are seen in both dimers. Steroid cells which generate hormones are widely influenced by TGF-beta in different ways. Release of renin is also controlled by TGF-beta. Release of basal renal renin is induced by the two highly concentrated TGF dimers. Lower levels of concentration do not influence the release of renin. Smooth muscle cells, fibroblasts, osteoblasts and chondrocytes are stimulated by TGF-beta to reveal a proliferative reaction.

Soil water flux (J) can be estimated from the velocity (V) of a pulse of heat introduced into the soil. Here we consider a method in which V is measured with a three-probe sensor. The center probe heats the soil and the outer probes measure temperature increases downstream ([T.sub.d]) and upstream ([T.sub.u]) from the heater. An equation was recently proposed for approximating J from the ratio [T.sub.d]/ [T.sub.u]. In this note we show that the accuracy of this equation can be improved by adding a term to correct for the time dependence of [T.sub.d]/[T.sub.u]. This term is simple to evaluate mad requires no additional measurements. Example calculations (three cases) are used in evaluate improvement in accuracy: When [T.sub.d]/[T.sub.u] is measured at a time of 45 s, relative errors in flux estimates are reduced from 10.5, 2.6, and -10.5% to 0.23, 0.06, and -0.23%, respectively; by using the correction term.