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Available Carbon Released from Crop Roots During Growth as Determined by Carbon-13 Natural Abundance

USDA-ARS, 119 Keim Hall, Univ. of Nebraska, Lincoln, NE 68583-0915

*Corresponding author (jdoran{at}unlinfo.unl.edu)

ABSTRACT

Quantifying plant contributions to root-zone available C during the growing season is important for better understanding of microbial processes regulating N cycling. However, it is difficult to determine root-derived available C under conditions that better reflect plant growth in the field. We proposed an approach using ¹³C natural abundance in soil with a history of C₃ vegetation, which is planted to a C₄ plant, to estimate the contribution of C₄ root-derived C to soil microbial biomass by measuring the ¹³C change in microbial biomass C during crop growth. In a pilot greenhouse study using this approach with large-diameter (30.5 cm) repacked soil cores, we estimated that 48 and 121 kg C ha^–1 of root-derived available C was produced, which accounted for 16 and 13% of total C₄-C entering the soil during 5 and 10 wk growth of corn (Zea mays L.), respectively. Similarly, 88, 283, and 402 kg C ha^–1 of root-derived available C from corn were estimated at 4, 8, and 16 wk, respectively, in a repeated experiment. Thus, the ¹³C natural abundance signals in microbial biomass can provide a practical and reliable way to assess available C released from plant roots during growth.

Journal series No. 11301.

Received for publication February 15, 1995.

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