Water yield values are given for 35‐cm columns of two soil types, Ramona and Yolo loam. Three to four surface cm of water were withdrawn from the columns in periods of about a week, using 900 cm of water tension. Simultaneous tension values are given for four locations along the column during wetting and drying periods. Some effects of preparing the disturbed soil samples and of length of soil column are indicated. A method is suggested for calculating capillary conductivity by the use of data obtained during transient changes of moisture content and tension in a soil column. Values for Ramona loam are calculated for a tension range of 76 to 627 cm of water. Although the method is not precise, conductivity values are obtained with less complicated equipment and in a shorter time than is possible by the use of previously described methods. Capillary conductivity values seem to vary with tension independent of tension gradients.

The O.D.R. values under tensiometer guided irrigation were found to be high at the time measurements were made. Under the set irrigation program, the O.D.R. were lowest for unamended soil, next lowest for peat amended soil, and highest for soil amended with lignified redwood and calcined clay. Root growth in containers receiving water on a set schedule was associated with the measured O.D.R. A value of about 0.15 µg cm−2min−1 appeared to be the lower limit for root growth. Each amendment promoted the development of a root system of unique characteristics.

No abstract

Soil suction (soil moisture tension) from zero to 0.8 bar is explicitly indicated by tensiometers. Higher values can be measured by suitably calibrated soil moisture resistance units. An irrigation program, both as to timing and duration of applications, can be carried out based on day‐to‐day records of soil suction at two or more depths in the root zone of the crop involved. Available moisture depletion is a commonly used basis for recommending irrigation practices. Curves are presented which show that, when irrigation timing is based on a given value of available moisture depletion, irrigations may be applied at widely differing values of soil suction if soil texture varies. A layered soil experiment shows the usefulness of soil suction measurements for evaluating relative moisture conditions in soils of varying texture. Examples are given of irrigation practices by avocado growers which are based on tensiometer readings. When related to soil suction measurements, an irrigation program is adapted to soil, climate, and plant variables.

The decomposition rate and binding effect in soil of a polysaccharide from Chromobacterium violaceum was compared with that of a variety of bacterial and plant polysaccharides and more complex organic residues. MIost of the polysaccharides tested decomposed more readily than mature plant residues and fungus mycelium. The ease of decomposition varied, however, and polysaccharide from C. violaceum over a period of 1 month was more resistant than corn stalks, Rhodes grass, bean straw, and orange leaves. During the first week, it was as resistant to decay as pine needles. The C. violaceum polysaccharide was more effective in binding or aggregating the soil than all others tested. It also reduced the bulk density of Greenfield sandy loam and increased hydraulic conductivity in neutral soil. indicating that some may be relatively resistant to decomposition or may become less resistant to attack by combining with other soil con