Carbon and Nitrogen Pools in Deep Soil Horizons at Different Landscape Positions

Abstract

Core Ideas Total C and total N were greater at shoulder position for alfalfa than in the other two land uses. No observed differences for total C among land uses at backslope and footslope positions. Labile pools of C and N showed differences with land use and topographic positions. In general, labile C and N pools followed alfalfa > black walnut plantation > corn–soybean. Labile and bulk pools of carbon and nitrogen (C and N) play different functional roles in soil organic matter dynamics and nutrient cycling. The objectives of this study were to evaluate the (i) effects of land use [corn (Zea mays L.)–soybean [Glycine max (L.) Merr.], alfalfa (Medicago sativa L.), and black walnut (Juglans nigra L.) plantation] and (ii) vertical distribution of labile [potassium permanganate oxidizable carbon (POXC), water extractable organic carbon (WEOC), water extractable nitrogen (WEN)] and bulk [total carbon (TC), total nitrogen (TN)] pools of C and N in soil to a depth of 105 cm at different topographic positions within a watershed. Alfalfa had 10.02 to 14.86 Mg ha−1 greater TC than corn–soybean and black walnut plantation on the shoulder position in the surface horizon (0–15 cm), whereas the subsurface horizon (15–105 cm) showed no significant differences for TC measured at all topographic positions. Soil POXC was significantly higher in alfalfa than corn–soybean in the surface layer of 0 to 15 cm by 1748.6, 1904.03, and 2878.67 kg ha−1 at the shoulder, backslope, and footslope positions, respectively. However, no differences were observed for POXC at the shoulder position when all subsurface layers were combined at 15‐ to 105‐cm depth. In general, the labile pools of C and N showed differences with land use and topographic positions and followed alfalfa > black walnut plantation > corn–soybean. The study results suggest that for accurate assessment of land use on C and N gains and/or losses both bulk and labile pools should be measured including the entire root zone depth. Topographic differences should be accounted for assessing C and N pools at the watershed scale.

Relating four‐day soil respiration to corn nitrogen fertilizer needs across 49 U.S. Midwest fields

“…Additional tests estimate N requirements by measuring soil organic C fractions. Soil organic C can be divided into labile and recalcitrant portions, with the latter being relatively stable in soils (Singh, Schoonover, Williard, Kaur, & Crim, 2018; Weil, Islam, Stine, Gruver, & Samson‐Liebig, 2003). Labile substances are thought to be water soluble and quickly decomposed by the soil microbial community (Ghani, Dexter, & Perrott, 2003; Singh et al., 2018).…”

“…Soil organic C can be divided into labile and recalcitrant portions, with the latter being relatively stable in soils (Singh, Schoonover, Williard, Kaur, & Crim, 2018; Weil, Islam, Stine, Gruver, & Samson‐Liebig, 2003). Labile substances are thought to be water soluble and quickly decomposed by the soil microbial community (Ghani, Dexter, & Perrott, 2003; Singh et al., 2018). These substances are composed of plant amino acids, microbial enzymes, and other plant residues which are decomposed easily by soil microorganisms with the mineral constituents made available for plant uptake and growth (Lehmann & Kleber, 2015; Soil Science Society of America, 1997; Weil & Brady, 2015).…”

Kura Clover Living Mulch Reduces Fertilizer N Requirements and Increases Profitability of Maize

“…Forage legumes increase the soil labile N pool relative to fertilized maize systems [37,38]. Forage stands ≥3 yr. old at termination often accumulate enough labile organic N to eliminate the need for fertilizer N in first-year maize [35] and in many cases second-year maize [36,39].…”

Cover crops and topography differentially influence weeds at a watershed scale

“…Weed densities could be expected to be greater on lower topographic positions as a result of relatively greater water availability on these positions compared to side slopes (Forster 2005;Manning et al, 2001). Soil water and nutrient dynamics are affected by the topographic positions in a watershed, which results in differences in CC biomass, crop yields, soil properties, and water quality (Singh 2018;Singh et al 2016Singh et al , 2018aSingh et al , 2018bSingh et al , 2019. It is possible that weed suppression by CCs could vary by topographic positions within a watershed.…”