Ground Surface Area Research Articles

Root distribution and water uptake by irrigated soybeans on a duplex soil

Water uptake by plants is described in relation to the root system configuration for an irrigated soybean crop on a duplex soil in northern Victoria. Measurements are described for three irrigation cycles as the crop grew to maximum ground cover and advanced physiological development. Few roots penetrated below 0.7 m, and the total root length beneath unit area of ground surface was lower than soybean root systems measured elsewhere. Water uptake patterns reflected this as uptake took place mainly from the depth interval 0.15-0.5 m. 'Crop water use' decreased below maximum values, even though water was placed in the profile at potentials higher than c. -90 kPa. In this situation, it is suggested that low root numbers at depth and low hydraulic conductivity in the subsoil were limiting water uptake. Practical consequences for irrigation management of soybeans are discussed.

Die Aussagekraft von Gefäßversuchen im Vergleich zu Feldversuchen

The worth of pot experiments for use in comparison with field trialsIn pot experiments most growth factors are at an optimal level. As a result, plant yields often approach the maximum that is genetically possible. The application of pot experiment results to field conditions using pot surface area as a basis of conversion calculations is therefore questionable.In this paper, data of pot experiments are presented in which competition, as occurs as crop stands in the field, has been simulated by close placement of pots in a special revolving frame structure. Using this set‐up, yields were obtained that corresponded to field grown crops provided that the total area within the frame was used in the conversion calculation and not the pot surface area.Using the area within the frame as a basis of conversion it was found that the amount of fertilizer applied, nutrient uptake, the number of ear bearing tillers and the thousand‐grain weights were all similar to values obtained in field practice. The ground surface area is thus a suitable conversion factor for the comparison of pot and field experiments.

正面研削に関する研究

An analytical consideration on the face grinding mechanism is made by statistical method. As the result, the theoretical equations for the rate of effective cutting edges and the distribution of grain depth of cut, grain cutting area and roughness of ground surface in the perpendicular section to grinding direction are obtained.Furthermore, in order to estimate the influence of elastic displacement of grain cutting edges on them, Monte-Carlo simulation is performed. As the result, it is found that the existence of elastic displacement of grain cutting edges increases the number of effective cutting edges but has a little effect on the roughness of ground surface.

Estimating Truncation Error in Image Well Theory

Assume that groundwater production from wells located beyond a distance, say r1, that is large relative to the spacing between adjacent image wells may be treated as an equivalent, continuous, constant production rate per unit of ground surface area. By means of the Theis [1935] equation and the usual symbol nomenclature, the result is s (r1, ∞) = QNw (t/S) [e−u1 − u1 W(u1)[, where s(r1, ∞) is the drawdown at the observation point due to all image wells beyond distance r1, and Nw is the density of wells per unit area. This equation is useful for calculating the minimum radius r1 min of the image well model in which image wells must be included for a given pumping time t to keep the truncation error due to omitted image wells less than some predesignated value s(r1, ∞)max. On the other hand, if an image well model exists and is composed of a fixed number of image wells for approximating an areally infinite system, then the equation will give the maximum allowable pumping time for a given allowable truncation error s(r1, ∞)max.

NET PHOTOSYNTHESIS AND LEAF AREA INDEX RELATIONSHIPS IN SWARDS OF DACTYLIS GLOMERATA UNDER CONTRASTING DEFOLIATION REGIMES

ABSTRACTNet photosynthesis per unit area of ground surface was determined at saturating light energy levels in Dactylis glonwrata swards over a wide range of leaf area indices (LAI). The relationship between net photosynthesis and LAI was influenced by the particular defoliation regime to which the sward was subjected. In most instances net photosynthesis and LAI were linearly related, with defoliation regime influencing both the slope and intercept of the regression. However, a defoliation regime which left leaves below 3 inches (7.5 cm) resulted in a curvilinear relation. The net photosynthesis‐LAI relationships were compared with the DM production of the swards on which they were obtained. Differences in these relationships did not entirely explain the differences in sward yield. The significance of these findings is discussed with reference to the theories of light interception and pasture growth.