Change in mechanical properties of wheat straw due to decomposition and moisture

The mechanical properties of straw residues from cereal crops left on the s oil surface are affected by the decomposition rate and moisture during the inter-cropping period. We have examined the relationship between the physic al characteristics and mechanical properties of mature wheat straw as a fun ction of decomposition and moisture. The mechanical properties were determi ned by shearing and bending tests. The ear internode had the lowest mass pe r unit length and the highest density because of its smaller diameter and s tem wall thickness. The difference in maximum force and energy required for failures between internodes is due to their mass per unit length and cross -sectional area. The higher Young's modulus and maximum bending stress of t he ear internode could be due to its higher proportion of hemicelluloses. B ending strength decreased by 70% and shear strength by 80% with decompositi on due to the loss of mas and a change in biochemical composition (mainly l oss of cellulose). Straw moisture had opposite effects on bending and shear ing: the maximum bending stress decreased by 54% and the shear stress incre ased by 83%. As both decomposition and moisture greatly modify the mechanic al properties of straw, these two factors should be taken into account in t he management of straw after harvest.