The biological decomposition of plant materials

Abstract

An investigation waa made of the relations between composition of materials and effects of various modifying extractions on the amount of supplemental N as (NH4)2CO3 required in decomposition. The "N factor" was lowered by water extraction of oat straw, and further by 4% NaOH extraction. Boiling with 2% HC1 further decreased the loss by decomposition, but not the "N factor," which appeared to depend somewhat on the amount of readily soluble and fermentable material present. The lower availability of N in certain substances, as willow peelings, increased the amount of supplemental N used, although the quantity originally present was theoretically ample for decomposition. Additional N retarded decomposition of materials relatively high in N, such as corn stalks or bean hulls. The "N factor" changed at different stages of decomposition because of composition changes affecting the equilibrium between biological utilization and ammonification. The factor "N equivalent" was introduced to admit the calculation of supplemental N used, based on amount of decomposition accomplished, indicating variations of availability among different materials. It is concluded that struc-tual differences in materials affect biological availability of the tissue and that the N of natural proteins and microbial tissues may enter into the composite reaction, making "N factor" and "N equivalent" both measures of net immobilization rather than of total utilization.