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NITROGEN MANAGEMENT

Corn Root Effects on the Nitrogen-Supplying Capacity of a Conditioned Soil

^a Dep. of Crop and Soil Sci., Michigan State Univ., East Lansing, MI 48824
^b Nat. Resour. Ecol. Lab., Colorado State Univ., Fort Collins, CO 80523
^c Southwest Kansas Res. and Ext. Cent., Kansas State Univ., Garden City, KS 67846

* Corresponding author (sanche22{at}msu.edu)

Received for publication April 18, 2000. The design of sustainable N management strategies requires a better understanding of the processes influencing the ability of soils to supply N to a growing crop. Although commonly ignored, the release of C by plant roots may have a tremendous impact on soil organic matter turnover under certain soil conditions. The main objective of this study was to determine if living corn (Zea mays L.) roots would increase the N-supplying capacity of a soil with an enhanced mineralizable N pool. A rotation of corn–corn–soybean [Glycine max (L.) Merr.]–wheat (Triticum aestivum L.) in combination with cover crops and the application of composted manure were used to increase the mineralizable N pool. The N-supplying capacity of bare soil and soils planted with corn and wheat was calculated, and changes in N and C pool sizes were determined by laboratory incubations. Living corn roots increased the inorganic N–supplying capacity of the conditioned soil by >50%. We suggest that this increase is caused by an increase in net N mineralization. This is supported by the considerable size reduction of the 70-d N pool in the soil planted with corn. No significant increase in the soil N-supplying capacity was observed when wheat was planted, indicating the possibility that this effect may vary dramatically among plant species. The contribution of corn and wheat root rhizodeposition to the active C pool and as energy source to enhance microbial activity and organic matter turnover is discussed.

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