MINERALIZATION OF CARBON AND PHOSPHORUS FROM C-14 AND P-32 LABELED PLANT-MATERIAL ADDED TO SOIL

Soil receives a large amount of P annually through above and below ground plant materials and animal excretions. This P in these materials becomes available to the growing plants through microbial decomposition. Since P mineralization follows C mineralization (CO2 loss), both C loss and P mineralization, measured by the amount of P utilized by oats (Avena sativa L.) from the added roots and tops of 14C- and 32P-labeled white clover (Trifolium repens L.), were assessed for 10 wk in the controlled environment chambers (26.degree. C/16.degree. C, 12 h day/night temperature). By 10 weeks, 42 and 38% of applied P was utilized by oats from the roots and tops, respectively. During the same period, .apprx. 55 and 70% of the C was lost from the roots and tops, respectively, of the added plant material. The half-lives, t1/2, of 32P utilization from the roots and tops were 10.8 and 12.4 wk, respectively. The corresponding t1/2 of 14C mineralization were 15.3 and 8.1 wk in the presence of plants and 15.2 and 9.7 wk in the absence of plants. After the initial rapid loss of C, P mineralization followed C mineralization (or loss) of the added plant material closely. Since the decaying of roots and tops of crop plants and pastures in the field release P upon mineralization, this factor should be considered in soil P management practices.