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1. Effect of nitrogen fertilization on central tendency and spatial heterogeneity of soil moisture, pH and dissolved organic carbon and nitrogen in two bioenergy croplands#

   https://doi.org/10.1002/jpln.202100311  

   Wang, Xuehan; Jian, Siyang; Gamage, Lahiru; Li, Jianwei (March 2022, Journal of Plant Nutrition and Soil Science)

   Abstract BackgroundSoil moisture, pH, dissolved organic carbon and nitrogen (DOC, DON) are important soil biogeochemical properties in switchgrass (SG) and gamagrass (GG) croplands. Yet their spatiotemporal patterns under nitrogen (N) fertilization have not been studied. AimsThe objective of this study is to investigate the main and interactive effects of N fertilization and bioenergy crop type on central tendencies and spatial heterogeneity of soil moisture, pH, DOC and DON. MethodsBased on a 3‐year long fertilization experiment in Middle Tennessee, USA, 288 samples of top horizon soils (0–15 cm) under three fertilization treatments in SG and GG croplands were collected. The fertilization treatments were no N input (NN), low N input (LN: 84 kg N ha⁻¹in urea) and high N input (HN: 168 kg N ha⁻¹in urea). Soil moisture, pH, DOC and DON were quantified. And their within‐plot variations and spatial distributions were achieved via descriptive and geostatistical methods. ResultsRelative to NN, LN significantly increased DOC content in SG cropland. LN also elevated within‐plot spatial heterogeneity of soil moisture, pH, DOC and DON in both croplands though GG showed more evident spatial heterogeneity than SG. Despite the pronounced patterns described above, great plot to plot variations were also revealed in each treatment. ConclusionThis study informs the generally low sensitivity of spatiotemporal responses in soil biogeochemical features to fertilizer amendments in bioenergy croplands. However, the significantly positive responses of DOC under low fertilizer input informed the best practice of optimizing agricultural nutrient amendment. 

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2. Soil extracellular oxidases mediated nitrogen fertilization effects on soil organic carbon sequestration in bioenergy croplands

   https://doi.org/10.1111/gcbb.12860  

   Duan, Jianjun; Yuan, Min; Jian, Siyang; Gamage, Lahiru; Parajuli, Madhav; Dzantor, Kudjo E.; Hui, Dafeng; Fay, Philip A.; Li, Jianwei (June 2021, GCB Bioenergy)

   Abstract Nitrogen (N) fertilization significantly affects soil extracellular oxidases, agents responsible for decomposition of slow turnover and recalcitrant soil organic carbon (SOC; e.g., lignin), and consequently influences soil carbon sequestration capacity. However, it remains unclear how soil oxidases mediate SOC sequestration under N fertilization, and whether these effects co‐vary with plant type (e.g., bioenergy crop species). Using a spatially explicit design and intensive soil sampling strategy under three fertilization treatments in switchgrass (SG:Panicum virgatumL.) and gamagrass (GG:Tripsacum dactyloidesL.) croplands, we quantified the activities of polyphenolic oxidase (PHO), peroxidase (PER), and their sum associated with recalcitrant C acquisition (OX). The fertilization treatments included no N fertilizer input (NN), low N input (LN: 84 kg N ha⁻¹ year⁻¹in urea), and high N input (HN: 168 kg N ha⁻¹ year⁻¹in urea). Besides correlations between soil oxidases and SOC (formerly published), both descriptive and geostatistical approaches were applied to evaluate the effects of N fertilization and crop type on soil oxidases activities and their spatial distributions. Results showed significantly negative correlations between soil oxidase activities and SOC across all treatments. The negative relationship of soil oxidases and SOC was also evident under N fertilization. First, LN significantly depressed oxidases in both mean activities and spatial heterogeneity, which corresponded to increased SOC in SG (though by 5.4%). LN slightly influenced oxidases activities and their spatial heterogeneity, consistent with insignificant changes of SOC in GG. Second, HN showed trends of decrease in soil oxidase activities, which aligned with the significantly enhanced SOC in both croplands. Overall, this study demonstrated that soil oxidase activities acted as sensitive and negative mediators of SOC sequestration in bioenergy croplands and optimizing fertilizer use particularly in switchgrass cropland can improve for both carbon sequestration and environmental benefit. 

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3. Evaluation of eastern gamagrass as dual‐purpose complementary bioenergy and forage feedstock to switchgrass

   https://doi.org/10.1111/gcbb.13054  

   Kieffer, Christina; Hui, Dafeng; Matamala, Roser; Li, Jianwei; Tyler, Donald; Dzantor, E. Kudjo (April 2023, GCB Bioenergy)

   Switchgrass (SG) is considered a model bioenergy crop and a warm- season peren-nial grass (WSPG) that traditionally served as forage feedstock in the United States. To avoid the sole dependence on SG for bioenergy production, evaluation of other crops to diversify the pool of feedstock is needed. We conducted a 3- year field ex-periment evaluating eastern gamagrass (GG), another WSPG, as complementary feedstock to SG in one- and two- cut systems, with or without intercropping with crimson clover or hairy vetch, and under different nitrogen (N) application rates. Our results showed that GG generally produced lower biomass (by 29.5%), theoreti-cal ethanol potential (TEP, by 2.8%), and theoretical ethanol yield (TEY, by 32.9%) than corresponding SG under the same conditions. However, forage quality meas-ures, namely acid detergent fiber (ADF), crude protein (CP), and elements P, K, Ca, and Mg were significantly higher in GG than those in SG. Nitrogen fertilizer signifi-cantly enhanced biomass (by 1.54 Mg ha−1), lignin content (by 2.10 g kg−1), and TEY (787.12 L ha−1) in the WSPGs compared to unfertilized treatments. Intercropping with crimson clover or hairy vetch did not significantly increase biomass of the WSPGs, or TEP and TEY in unfertilized plots. This study demonstrated that GG can serve as a complementary crop to SG and could be used as a dual- purpose crop for bioenergy and forage feedstock in farmers' rotations. 

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4. Fertilization (NPK) alter dryland biogeochemical processes

   https://doi.org/10.6073/pasta/3b66861166da7a9f5311ffef86a6b147  

   Yogi, Purbendra N (January 2022, Environmental Data Initiative)

   Nutrient augmentation is one major global change disturbance that could have cascading effects on local plant and microbial communities thus altering biogeochemical properties (Peñuelas et al. 2012). While many studies have investigated fertilization effects on community change and ecosystem processes, less work has been done in dryland ecosystems (Schimel 2010), where nutrient availability often comes as pulses correlated with rain events (Collins et al. 2008). We leveraged an ongoing fertilization experiment (NutNet) at the Sevilleta to answer the question: How does fertilization alter dryland biogeochemical processes, and how does this effect change seasonally? To explore this topic, we specifically measure three important soil hydrolase enzymes, N-acetyl- glycosaminidase (NAG), phosphatase (AP), and β- glucosidase (BG), microbial biomass, and soil nitrogen levels at 5 points along a seasonal gradient within the NutNet plots. 

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5. Clay soil amendment suppressed microbial enzymatic activities while increasing nitrogen availability in sandy soils

   https://doi.org/10.1002/saj2.20731  

   Poudel, Pratima; Ye, Rongzhong; Parajuli, Binaya (July 2024, Soil Science Society of America Journal)

   Abstract Conservation management practices often produced positive but limited desirable outcomes in US Southeast sandy soils, likely due to their intrinsically low clay contents that constrain the soil's capacity to preserve organic carbon (C) and nutrients. In the field, we tested the effectiveness of a novel approach, that is, clay soil amendment, to improve sandy soils. In October 2017, clay‐rich soils (25% clay) were spread at 25 metric tons ha⁻¹ and tilled onto a sandy soil (1.9% clay) in the field, which was further mixed by light tillage at 0‐ to 15‐cm depth, followed by planting winter cover crop mixtures (cereal rye, crimson clover, and winter pea). The crop rotation was cotton and corn with cover crop mixtures planted in the winter fallow season. Soils (0–15 cm) were collected in August 2021 and subjected to physio‐biochemical analyses. Clay amendment increased soil clay content to 3.4%, which improved nitrogen (N) availability by 51% but inhibited the activities of C (β‐d‐cellubiosidase [CB]; β‐xylosidase [BX];N‐acetyl‐β‐glucosaminidase [NAG]) and N (leucine aminopeptidase [LAP]) cycling enzymes, resulting in up to 78% reduction in microbial respiration. A follow‐up kinetic study on BG and LAP enzymes suggested that clay addition can have different impacts on enzymes with diverse biological origins through distinct mechanisms. Clay addition can potentially improve sandy soils by stabilizing the organic inputs in soils. However, more research is required to understand its long‐term impacts making this approach practical. 

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