WATER POTENTIAL WATER-CONTENT CHARACTERISTICS OF WHEAT STRAW

Water is an important environmental factor affecting microbial decomposition of crop residues. To study the influence of water on residue decomposition, knowledge of the water potential-water content relationship of crop residue would be very useful. The concept of soil-water potential is well established, but limited data are available relating water potential to crop residue water content. Thermocouple psychrometry and hydraulic press methods were used to measure the water potential (.psi.) characteristics of chopped and ground wheat straw (T. aestivum L.). The data fit the empirical relationship .psi. = a.theta.-b (where .theta. = water content and a and b are empirical constants), with large coefficients of determination likely, because the osmotic component of wheat straw can be significant depending on leaching history. There was no difference between the matric potential curves of ground and chopped straw over the range -50 to -1 bar. The hydraulic press did not appear to measure the true matric potential characteristics of wheat straw as determined by thermocouple psychrometry. The water potential-water content relationships of wheat straw were quite different from those of a Palouse silt loam (fine-silty, mixed, mesic pachic Ultic Haploxerolls) used as an example. The data presented show the importance of using water potential to adjust water when, e.g., comparative residue-soil incubation studies are conducted, otherwise differences in water relationships can result when these studies are conducted on the basis of water content.