Capillary-Diffusion and Self-Diffusion of Liquid Water in Unsaturated Soils

Capillary-diffusion coefficients were measured by use of inflow and outflow methods. With both methods the capillary-diffusion coefficients decreased very rapidly with decreasing water content. The lighter textured soils were found to have the higher diffusion coefficients over the entire moisture content range studied, 0 to 1 bar tension. Self-diffusion coefficients were measured over a moisture content range from air dryness to saturation using 3H as a tracer of water. Each of the soils gave the same diffusion characteristics when the self-diffusion coefficients were expressed as a function of either water content or average number of water layers on the external surface of each mineral. As the water content decreased from saturation to near field capacity, the self-diffusion coefficients decreased very rapidly. An attempt was made to separate the self-diffusion coefficients into a liquid and a vapor component by use of 36Cl as a tracer of liquid water. The results showed 36Cl not to be a good tracer of liquid water movement in soil. The results suggest that a functional relationship exists between capillary-diffusion and self-diffusion; however, before this relationship can be firmly established, the liquid and vapor components of water movement must be separated

Solute Transport as Related to Soil Structure in Unsaturated Intact Soil Blocks

Concern about soil and groundwater pollution has resulted in numerous studies focused on solute transport. The objectives of our study were to investigate the effect of soil type and land-use management on solute movement. Transport of water and Cl− were measured through intact blocks of Maury (fine, mixed, semiactive, mesic Typic Paleudalf) and Cecil (fine, kaolinitic, thermic Typic Kanhapludult) soils, under steady-state, unsaturated flow conditions. Three replicate blocks for the Maury soil and two replicate blocks for the Cecil soil were studied per land-use treatment. The land-use treatments were conventional-till corn (Zea mays L.) production and long-term grass pasture. Individual blocks were instrumented with time domain reflectometry (TDR) probes at the 5-, 15-, and 25-cm depths. The effluent Cl− and TDR breakthrough curves were fitted using the convection dispersion equation (CDE); the estimated parameters were pore water velocity (v), dispersion coefficient (D), and, for the TDR breakthrough curves, maximum bulk electrical conductivity (BECmax). The CDE fitted the data very well, with model R 2 values ranging from 0.971 to 0.999. Volumetric water content (θ), total porosity, the soil water retention curve, and saturated hydraulic conductivity were determined on the same blocks. Volumetric water content increased (R2 = 0.25) as the slope of the water retention curve decreased. Increasing θ resulted in decreasing v (R2 =0.20) and thus, because of the linear relationship between D and v(R2 = 0.26), decreasing D Structural controls on solute dispersion in this study were mainly indirect, and related to variations in water content produced by differences in pore-size distribution

Overexpression of the aphid-induced serine protease inhibitor <i>CI2c </i>gene in barley affects the generalist green peach aphid, not the specialist bird cherry-oat aphid

<div><p>Aphids are serious pests in crop plants. In an effort to identify plant genes controlling resistance against aphids, we have here studied a protease inhibitor, CI2c in barley (<i>Hordeum vulgare</i> L.). The <i>CI2c</i> gene was earlier shown to be upregulated by herbivory of the bird cherry-oat aphid <i>(Rhopalosiphum padi</i> L.<i>)</i> in barley genotypes with moderate resistance against this aphid, but not in susceptible lines. We hypothesized that CI2c contributes to the resistance. To test this idea, cDNA encoding <i>CI2c</i> was overexpressed in barley and bioassays were carried out with <i>R</i>. <i>padi</i>. For comparison, tests were carried out with the green peach aphid (<i>Myzus persicae</i> Sulzer), for which barley is a poor host. The performance of <i>R</i>. <i>padi</i> was not different on the <i>CI2c</i>-overexpressing lines in comparison to controls in test monitoring behavior and fecundity. <i>M</i>. <i>persicae</i> preference was affected as shown in the choice test, this species moved away from control plants, but remained on the <i>CI2c</i>-overexpressing lines. <i>R</i>. <i>padi</i>-induced responses related to defense were repressed in the overexpressing lines as compared to in control plants or the moderately resistant genotypes. A putative susceptibility gene, coding for a β-1,3-glucanase was more strongly induced by aphids in one of the <i>CI2c</i>-overexpressing lines. The results indicate that the CI2c inhibitor in overexpressing lines affects aphid-induced responses by suppressing defense. This is of little consequence to the specialist <i>R</i>.<i>padi</i>, but causes lower non-host resistance towards the generalist <i>M</i>. <i>persicae</i> in barley.</p></div

Soil Physical Responses of a Compacted Sports Field Following Various Core Aerification Techniques

Aims:&nbsp;Soil compaction is detrimental to turfgrass health and potentially hazardous to users of sports field participants. Previous research has evaluated numerous core aeration programs and their effects on water infiltration and thatch levels in a myriad of soil series under various management programs. The goal of this study was to identify detailed soil responses of a highly compacted, multi-purpose sports field to different soil aerification techniques while minimizing the negative impact of core removal on turfgrass quality.&nbsp; Study Design:&nbsp;The study was designed as a randomized complete block with 4 replications and a 2 × 2 factorial treatment arrangement. Place and Duration of Study:&nbsp;The study was conducted over two years on Clemson University’s band practice field, Clemson, SC, USA. Methodology:&nbsp;The study evaluated deep (17.8 cm) and shallow (7.6 cm) tine core aerification and number of yearly aerification events on several soil and turf parameters. Extracted cores were either removed or incorporated back into the plots.&nbsp; Results:&nbsp;Little effect on turfgrass quality was observed due to mowing height (2.65 cm) masking any reduction in turfgrass density. Deep tine aerification lowered bulk density 5% in the first year compared to shallow tine aerification. In year one, infiltration was increased 29% after deep tine core aeration and 34% when cores were removed after aerification. Conclusion:&nbsp;Treatment effects were not as drastic as studies conducted in sand based soils, reflecting the necessity of a perpetual soil aerification program in clay-based soils