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 (CO 2 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 14 C‐ and 82 P‐labelled white clover ( Trifolium repens L.) were assessed for 10 weeks in the controlled environment chambers (26°C/16°C, 12‐hour 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, about 55 and 70% of the C was lost from the roots and tops, respectively, of the added plant material. The half‐lives, t 1/2 , of 82 P utilization from the roots and tops were 10.8 and 12.4 weeks, respectively. The corresponding t 1/2 of 14 C mineralization were 15.3 and 8.1 weeks in the presence of plants and 15.2 and 9.7 weeks 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.
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Ram C. Dalal (1979) studied this question.