Yazar "Smucker, AJM" seçeneğine göre listele

Listeleniyor 1 - 2 / 2
  • [ X ]
    Öğe
    Soil aggregate sequestration of cover crop root and shoot-derived nitrogen
    (Springer, 2005) Kavdir, Y; Smucker, AJM
    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 ((NH4)-N-15)(2)SO4. Isotopic 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 15 N 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 N-derived from roots in July 1999, which was three times more than their interior regions. This was slightly greater than the % N-derived (from shoot). One month later, as the maize root absorption of N increased rapidly, % Nderived front 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 in greater leaching losses.
  • [ X ]
    Öğe
    Specific contributions of decaying alfalfa roots to nitrate leaching in a Kalamazoo loam soil
    (Elsevier, 2005) Kavdir, Y; Rasse, DP; Smucker, AJM
    Alfalfa (Medicago sativa L.) contributes 430 million kg N year(-1) to the US Corn-Belt soils, according to a 1991 survey. Minimizing leaching losses from these very large N inputs requires a better understanding of the specific root dynamics that relate to the shoot-borne nitrates which have been reported to develop throughout many soil profiles. The objective of the present study was to determine the impact of decaying alfalfa roots on nitrate inputs to soils and on soil hydraulic conductivity properties which affect nitrate leaching. An experiment was initiated in 1994 and data for this report were taken from research on a Kalamazoo loam soil (fine-loamy, mixed, mesic Typic Hapludalf) at the KBS/LTER (long-term ecological research) site in southwestern Michigan, during the period from 1996 through 1997. Soil extractable nitrate (NO3-N) and ammonium (NH4-N) were monitored to soil depths of 150 cm and soil soluble NO3-N and NH4-N were monitored by suction lysimeters to the depth of 65 cm. Saturated hydraulic conductivity (K-sat) of soil was measured by the double-ring infiltrometer method. Following glyphosate termination of the alfalfa stands, nitrate-N released from mineralized alfalfa roots plus shoots totaled 75 kg ha(-1). Alfalfa roots generated 36 kg ha(-1) and alfalfa shoots generated 39 kg ha(-1) which accumulated in the Ap horizons from April to July in 1997. The presence of decaying alfalfa roots in the profile quadrupled Ksat values as compared to bare fallow soils. Nitrates released from decomposing alfalfa roots combined with root-enhanced hydraulic conductivities dramatically increased NO3-N leaching following the termination of alfalfa stands. NO3-N leaching to deeper horizons approached 83 kg ha(-1) in root treatments and 144 kg ha(-1) in the root plus shoot treatments during the period from April to December, following alfalfa termination. Our data suggest that under temperate climate such as that of Michigan, groundwater contamination by nitrates can be reduced by terminating alfalfa stands immediately before spring-planting of the subsequent row crop, which can absorb the large quantities of N leaking from decomposing shoots and roots of the legume. (c) 2005 Elsevier B.V. All rights reserved.