Nutrient Cycling in Agroecosystems

, Volume 79, Issue 1, pp 45–58

Soil aggregates control N cycling efficiency in long-term conventional and alternative cropping systems

  • Angela Y. Y. Kong
  • Steven J. Fonte
  • Chris van Kessel
  • Johan Six
Research Article

DOI: 10.1007/s10705-007-9094-6

Cite this article as:
Kong, A.Y.Y., Fonte, S.J., van Kessel, C. et al. Nutr Cycl Agroecosyst (2007) 79: 45. doi:10.1007/s10705-007-9094-6

Abstract

This paper presents novel data illustrating how soil aggregates control nitrogen (N) dynamics within conventional and alternative Mediterranean cropping systems. An experiment with 15N-labeled cover crop residue and synthetic fertilizer was conducted in long-term (11 years) maize–tomato rotations: conventional (synthetic N only), low-input (reduced synthetic and cover crop-N), and organic (composted manure- and cover crop-N). Soil and nitrous oxide (N2O) samples were collected throughout the maize growing season. Soil samples were separated into three aggregate size classes. We observed a trend of shorter mean residence times in the silt-and-clay fraction than macro- (>250 μm) and microaggregate fractions (53–250 μm). The majority of synthetic fertilizer-derived 15N in the conventional system was associated with the silt-and-clay fraction (<53 μm), which showed shorter mean residence times (2.6 months) than cover crop-derived 15N in the silt-and-clay fractions in the low-input (14.5 months) and organic systems (18.3 months). This, combined with greater N2O fluxes and low fertilizer-N recoveries in both the soil and the crop, suggest that rapid aggregate-N turnover induced greater N losses and reduced the retention of synthetic fertilizer-N in the conventional system. The organic system, which received 11 years of organic amendments, sequestered soil organic carbon (SOC) and soil N, whereas the conventional and low-input systems merely maintained SOC and soil N levels. Nevertheless, the low-input system showed the highest yield per unit of N applied. Our data suggests that the alternating application of cover crop-N and synthetic fertilizer-N in the low-input system accelerates aggregate-N turnover in comparison to the organic system, thereby, leading to tradeoffs among N loss, benefits of organic amendments to SOC and soil N sequestration, and N availability for plant uptake.

Keywords

Aggregate dynamicsLong-term cropping systemMean residence timePlant nutrient uptakeSoil organic matter sequestrationSoil nitrogen cycling

Copyright information

© Springer Science+Business Media B.V. 2007

Authors and Affiliations

  • Angela Y. Y. Kong
    • 1
  • Steven J. Fonte
    • 1
  • Chris van Kessel
    • 1
  • Johan Six
    • 1
  1. 1.Department of Plant SciencesUniversity of California, DavisDavisUSA