PARENT SESSION
Friday, August 11, 8:00-10:30 am
Poster Session 26 - Latebreaking and newsworthy posters
Exhibit Hall, Ballroom Level, Cook Convention Center

Interactions between soil texture, organic residue quality, and mineral fertilizer affect the rate of carbon and nitrogen cycling.

Grote, Kristin^*,1, Gentile, Roberta ¹, Vanlauwe, Bernard¹, Six, Johan¹, ¹ University of California, Davis, Davis, CA

ABSTRACT- Managing organic residues for optimum long-term carbon stabilization and short- and long-term nitrogen use efficiency is a critical challenge for small-scale farmers in sub-Saharan Africa. The combined use of organic residues with mineral fertilizers is promoted as a practice to enhance yields and reduce nutrient losses within the Integrated Soil Fertility Management approach. The rate of the build-up and break-down of aggregates influences the rate at which carbon and nitrogen are sequestered within and released from aggregates. The combined application of organic residues and mineral fertilizer is expected to result in an intermediate rate of aggregate turnover; namely, a slower rate than when mineral fertilizer is applied alone and more rapid than when organic residue is applied alone. An incubation study was undertaken to assess the interactive effects between soil texture, organic residue quality and mineral fertilizer on the rate of soil aggregate dynamics in two African soils. A loamy sand and a sandy clay loam were incubated for 6 months at 25°C with two different quality ¹³C and ¹⁵N labeled residues with and without mineral fertilizer. Gas (N₂O and CO₂) sampling and soil fractionation were undertaken to assess carbon and nitrogen dynamics in the different treatments. Results indicate significant residue quality and combined application effects on the decomposition of residue, but no significant texture affect was observed. For example, in the loamy sand, residue derived CO₂ fluxes were significantly less in the combined applications than in the sole organic residue applications. In the sandy clay loam, significantly less residue derived carbon was lost from the combined treatment of low quality residue and mineral nitrogen. These results indicate the potential of carbon stabilization when organic and mineral resources are combined.

Key words: agroecosystem, soil aggregate turnover, agroecology