Soil aggregate sequestration of cover crop root and shoot-derived nitrogen

• Published in: Plant and soil 2005-05, Vol.272 (1-2), p.263-276
• Main Authors: Kavdir, Y, Smucker, A.J.M
• Format: Article
• Language: English
• Subjects: Agricultural soils; Agronomy. Soil science and plant productions; Biological and medical sciences; carbon nitrogen ratio; carbon sequestration; Cell aggregates; Clay soils; Cover crops; eutrophication; Fundamental and applied biological sciences. Psychology; General agronomy. Plant production; leaching; Loam soils; losses from soil; nitrogen; nitrogen sequestration; Organic soils; Physical properties; Physics, chemistry, biochemistry and biology of agricultural and forest soils; Plant roots; roots; Rye; Secale cereale; shoots; Soil aggregates; soil nutrients; Soil organic matter; Soil science; soil-plant interactions; Soil-plant relationships. Soil fertility; Soil-plant relationships. Soil fertility. Fertilization. Amendments; Structure, texture, density, mechanical behavior. Heat and gas exchanges; Water and solute dynamics
• ISSN: 0032-079X; 1573-5036
• DOI: 10.1007/s11104-004-5294-x

Cover crop roots and shoots release carbon (C) and nitrogen (N) compounds in situ during their decomposition. Depending upon the season, these C and N compounds may be sequestered, the C may be respired or the N may be leached below the root zone. A field study was established to identify the contributions of cover crop root and shoot N to different regions within aggregates in the A p horizon of a Kalamazoo loam soil. Fall-planted rye plants (Secale cereale L.) were labeled the next May with foliar applications of solutions containing 99% atom (^{15}NH_4^ + $)₂SO₄. Isotopie enrichment of soil aggregates ranging from 2.0 to 4.0, 4.0-6.3 and 6.3-9.5 mm across was determined following plant residue applications. Concentric layers of aggregates were removed from each aggregate by newly designed meso soil aggregate erosion (SAE) chambers. Non-uniform distributions of total N and recently derived rye N in soil macroaggregates, across time, suggested that the formations and functions of macroaggregates are very dynamics processes and soil aggregates influence where N is deposited. Early in the season, more ¹⁵N migrated to the interior regions of the smallest aggregates, 2-4 mm across, but it was limited to only surfaces and transitional regions of the larger aggregates, 6.3-9.3 mm across. Exterior layers of aggregates between 6.0 and 9.5 mm retained 1.6% of the Nderived from roots in July 1999, which was three times more than their interior regions. This was slightly greater than the % Nderived from shoot· One month later, as the maize root absorption of N increased rapidly, % Nderived from roots and % Nderived from shoot were nearly equal in exterior layers and interior regions of soil aggregates. This equilibrium distribution may have been from either greater diffusion of N within the aggregates and/or maize root removal form aggregate exteriors. Results supported that most of roots grew preferentially around surfaces of soil aggregates rather than through aggregates. Cover crop roots contributed as much N as cover crop shoots to the total soil N pool. Subsequent crops use N from the most easily accessible zones of soil structure, which are surfaces of larger soil aggregates. Therefore maintaining active plant roots and aggregated soil structure in the soil enhances N sequestration and maximize soil N availability. These studies suggest that the rapid and perhaps bulk flow of soil N solutions may bypass many of the central regions of soil aggregates, resulting