Influence of Sample Pretreatment on Soil Moisture Retention

Abstract The effect of sample pretreatment on soil‐moisture retention was measured on eight Wisconsin soils to find the moisture tension range in which undisrupted soil samples are necessary to represent the moisture relations of field soils. The moisture retention of samples with pretreatments either of 2‐mm. sieving or puddling was compared with the retention of undisrupted cores over the moisture tension range of 0.01 to 15 atm. In general, the moisture retention of sieved samples of the medium textured soils studied was increased over core samples at tensions less than 0.4 atm. There was no general relationship in the tension range of 0.4 to 1.0 atm. because of the irregular nature of the release curves of individual soils. Sieving decreased moisture retention about 1 part in 10 at tensions greater than 1.0 atm. Thus sieved samples of the medium textured soils studied can be used to approximate undisrupted soils in the high tension range with a relative error of 10%. Core samples should be used at tensions less than 1.0 atm. to avoid relative errors greater than 10% (up to 30%). Puddled samples retained considerably more water than cores in the tension range from 0.1 to 2.0 atm. although they differed little from core samples at tensions less than 0.05 to 0.1 atm. and greater than 5.0 atm. Puddled soils give a better approximation of undisrupted soils than sieved soils at tensions between 5 and 15 atm.