Abstract
Core Ideas No‐tillage and nitrogen fertilizer may mitigate residue removal impacts on soil microbial biomass. Stover removal decreased soil microbial biomass by 40 to 42%, but did not affect community structure. Residue removal effects on soil microbial biomass were mediated by nutrient limitations. Residue retention and no‐tillage are critical to maintaining microbial populations. Corn stover removal can reduce soil C and N stocks, reduce soil microbial biomass (SMB), and alter soil biogeochemistry. No‐tillage (NT) management may reduce the negative impacts of long‐term stover removal, but how the microbial community mediates N fertilizer and stover removal effects on soil organic carbon (SOC) pools is less clear. We measured the effects of partial stover retention or full stover retention on particulate organic matter carbon (POM‐C), SMB, and community composition under three N fertilization treatments (0, 60, and 202 kg N ha–1) after 7 yr. Residue removal effects on SMB were mediated by nutrient limitations. Stover removal decreased SMB by 40% at low N fertilizer rates, however, at the highest N rate, SMB did not differ between residue treatments, presumably due to the additional C input and bulk SOC content. Interestingly, at deeper depths (>7.5 cm), partial residue retention increased POM‐C by 11% compared with full stover retention, suggesting greater structural root inputs and slower decomposition. Microbial community composition was not influenced by residue removal, but was significantly influenced by N fertilizer. A principal coordinate analysis showed that microbial communities under no or low N were enriched for gram‐negative bacteria, arbuscular mycorrhizal fungi (AMF), and saprotrophic fungal biomarkers reflecting fresh plant‐derived C input, while higher N rates were enriched for actinomycetes and gram‐positive biomarkers. High stover N content promoted rapid decomposition by SMB and incorporation into mineral‐associated C pools rather than POM‐C. Even under NT, residue removal will reduce soil C and SMB, but N fertilizer may mediate this effect by enhancing C input and rhizodeposition.
Highlights
Corn stover removal can reduce soil C and N stocks, reduce soil microbial biomass (SMB), and alter soil biogeochemistry
Treatments with greater residue N may decompose more rapidly, forming particulate organic matter (POM), which is comprised primarily of partially decomposed plant material. These competing drivers of C input and loss may explain why some studies find no significant effect of N fertilizer on particulate organic matter carbon (POM-C) stocks despite predicted increases in POM with N fertilizer based on aboveground production (Brown et al, 2014; Jin et al, 2015; Stewart et al, 2017)
We evaluated residue removal and N rate (0, 67, and 202 kg N ha-1) effects on labile soil C (i.e., POM-C) and microbial biomass and composition in a long-term, NT irrigated corn study after 7 yr of stover removal
Summary
No-tillage and nitrogen fertilizer may mitigate residue removal impacts on soil microbial biomass. The long-term impacts of stover removal may reduce aboveground and root C inputs and reduce SOC storage (Halvorson and Stewart, 2015), particulate organic matter C (POM-C) (Jin et al, 2015; Osborne et al, 2014; Sindelar et al, 2014), and soil microbial biomass (Stewart et al, 2015b, 2016). Treatments with greater residue N may decompose more rapidly, forming particulate organic matter (POM), which is comprised primarily of partially decomposed plant material These competing drivers of C input and loss may explain why some studies find no significant effect of N fertilizer on POM-C stocks despite predicted increases in POM with N fertilizer based on aboveground production (Brown et al, 2014; Jin et al, 2015; Stewart et al, 2017). Nitrogen addition could mediate these effects due to greater root input, and could stimulate residue and SOC decomposition, leading to lower POM-C stocks
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