Sawdust composts in soil improvement
As indicated in a previous paper 2) the use of wood wastes in soil improvement has received considerable attention lately. Composting seems to offer large possibilities for avoiding the adverse effects of fresh sawdust and to utilize the potentialities of sawdust as a soil builder in the best fashion. The literature on composting of various waste products has been listed and reviewed very comprehensively i n t w 0 recent publications 1). The investigations rePorted here are preliminary tests of methods of composting sawdust and tests of the resulting materials on plant growth in greenhouse pot cultures.
LIMITATIONS OF AUTO-IRRIGATORS FOR CONTROLLING SOIL MOISTURE UNDER GROWING PLANTS.
An accurate, convenient method for controlling soil moisture under growing planits would be of obvious advantage to the experimenter attempting to grow plants under uniform conditions, as well as to the physiologist who may wish to study the effect of varyiing soil moisture on plant development. Since the time of the original suggestioin by LIVINGSTON in 1908 (3), various forms of auto-irrigators have been proposed for this purpose. Porous clay cones were later developed by LIVINGSTON (4) to overcome difficulties ascribed to poor contact between the soil and the porous water-supplying surface of the early cylindrical cups. LIVINGSTON, HEMMI and WnSON (5) used tenisions up to 40 cm. of mercury and state, "The moisture conditions of the soil are now among the environmental conditions most susceptible of control and satisfactory measurement." Tensions of 60 to 65 cm. of mercury, equivalent to 8 or 9 meters of water, were considered to be maximum for satisfactory irrigator performance. HENDRICKSON an1d VEIHMEYER (1), with an unstated water supply tensionl, were unable to mainitain uniform moisture distribution with irrigator cones, but found a layer of moist soil near the irrigator surface filled with absorbiing roots. Uinder such conditions growth of plants might easily give indications of controlled low soil moisture which actually were only responses to a restricted rooting zone. A substantial imiprovement in apparatus design was made with the development of double-walled irrigator pots by KORNEFF (2), RICHARDS (6), WILSON (14) and RICHARDS and BLOOD (7). Compared with porous irrigator cylinders or cones, these units maintain a larger fraction of the soil mass in proximity to and in good contact with the irrigator surface. WIGGIN (11, 12) has published results from a study of double-walled irrigators from the samiie source as those described by WISON (14). He states that, "Soils can be held at an approximately constant percentage of soil moisture anywhere within a range from below the wilting point for plants to a condition of soil saturation." His data, however, hardly justify this conclusion for he reports, " The greatest difference found between the water content of the soil in the outside layer and the center of the pot was 4.2 per cent.; the greatest difference between the top and bottom layers of soil, 5.1 per cent. The variation in the water content of the soil . . . is therefore
GROWTH OF YOUNG WHEAT PLANTS IN AUTO-IRRIGATED SOILS, AS RELATED TO THE WATER-SUPPLYING POWER OF THE SOIL AND TO THE ADJUSTMENT OF THE AUTO-IRRIGATOR.
The auto-irrigator (4, 5) furnishes a convenient means for maintaining approximately constant moisture contents in the soil masses of pot cultures, the maintained moisture content being dependent on the kind of soil used (indicated by its water-holding power, moisture equivalent, etc.), on the packing of the soil, and on the hydrostatic head against which water moves from the irrigator reservoir into the soil mass. The experiments briefly described below were planned as a preliminary study of the relations between the growth of young wheat plants in autoirrigated pot cultures and the water-supplying power of the soil about their roots, this dynamic soil feature being itself controlled, for each kind of soil used, by the water content of the soil, controlled in turn by the height of the mercury column introduced between the irrigator reservoir and the water-supplying, porous-porcelain cone. The experiment here reported was carried out by Hemmi in the greenhouse of the Laboratory of Plant Physiology of the Johns Hopkins University, in the winter of 1922-23, and he left his notes with the other authors of this paper when he returned to Japan. The results seem worthy of publication because of the great fundamental importance of the water-supplying power of the soil in plant physiology and plant culture, and because they add considerably to our knowledge of the manner in which the auto-irrigator operates in practice. It seems to be becoming more generally appreciated that the influential conditions of plant environments must be controlled or quantitatively recorded for effective experimentation in plant physiology, and the moisture conditions of the soil are now among the environmental conditions most susceptible of control and satisfactory measurement.