No abstract

We consider the appropriateness of institutionalizing soil quality as a defined parameter in soil science. The soil management research of land grant universities and the Agricultural Research Service (ARS) and the mission and goals of state, federal, and private conservation agencies stand to be significantly affected. We feel that a non-advocalive examination of this concept could provide a positive contribution.

To understand the development of a crop, information is needed concerning the dynamics of root growth and water uptake. An extendible, 13 mm diam borescope, a low light, monochrome video camera, and a video tape recorder were combined into a system for in situ root observation through 51 mm inside diam clear acrylic tubes installed at an angle 30° from vertical. The viewing area was illuminated by two fiber optic light guides and a variable intensity light source. The observation tubes could also be used as access for a neutron probe to measure water uptake and root growth at the same point. Sector intersections rather than line intersections were counted and used to convert observations from the mini‐rhizotrons to root length densities. A comparison of root length densities determined through mini‐rhizotrons, installed in four orientations with respect to plant rows, with those determined by soil sampling indicates there was a linear relationship between the two techniques. When only depths greater than 20 cm were used the correlation was higher than when all depths were included. Results indicated that no installation orientation was clearly the best when only the depths greater than 20 cm were included. Because of the variability of the results from individual mini‐rhizotrons the results from several tubes had to be averaged before there was a satisfactory correlation with the bulk soil root length density.

Dryland crops grown in semiarid environments often do not completely cover the soil, leaving a portion of the soil surface exposed to a condition of rapid soil‐water evaporation. Quantitative separation of soil evaporation and crop transpiration is important if cultural practices or cultivars are to be evaluated. This study was designed to evaluate a combined energy and water balance model, ENWATBAL, to describe the concurrent heat and water fluxes in a row crop. Inputs to the model include soil and plant variables and daily weather data. Measurements were made for a period of 74 d over a cotton (Gossypium hirsutum L.) canopy during 1985 on an Olton soil (fine, mixed, thermic Aridic Paleustolls) at Lubbock, TX. Data collected included soil‐water content, soil temperature, root distribution, soil evaporation with microlysimeters, and leaf area index, for both an irrigated and a dryland plot. The values for daily evaporation and evapotranspiration calculated with the model were within 1 standard deviation of the measured values. Cumulative evaporation and evapotranspiration from the model agreed with measured values within 7% for the dryland and 8% for the irrigated plot. Estimated soil‐water and temperature profiles also agreed closely to measured values. Soil evaporation was found to be 30% of evapotranspiration, for both the irrigated and the dryland plot. The ENWATBAL model provides a reliable method of evaluating the effects of management practices and crop selection on the water‐use efficiency of crop production in a semiarid area.