Nitrogen Fertilization Restructured Spatial Patterns of Soil Organic Carbon and Total Nitrogen in Switchgrass and Gamagrass Croplands in Tennessee USA

Abstract

Nitrogen (N) fertilizers can potentially alter spatial distribution of soil organic carbon (SOC) and total nitrogen (TN) concentrations in croplands such as switchgrass (SG: Panicum virgatum L.) and gamagrass (GG: Tripsacum dactyloides L.), but it remains unclear whether these effects are the same between crops and under different rates of fertilization. 13C and 15N are two important proxy measures of soil biogeochemistry, but they were rarely examined as to their spatial distributions in soil. Based on a three-year long fertilization experiment in Middle Tennessee, USA, the top mineral horizon soils (0–15 cm) were collected using a spatially explicit design within two 15-m2 plots under three fertilization treatments in SG and GG croplands. A total of 288 samples were collected based on 12 plots and 24 samples in each plot. The fertilization treatments were no N input (NN), low N input (LN: 84 kg N ha−1 in urea) and high N input (HN: 168 kg N ha−1 in urea). The SOC, TN, SOC/TN (C: N), δ13C and δ15N were quantified and their within-plot variations and spatial distributions were achieved via descriptive and geostatistical methods. Results showed that SG generally displayed 10~120% higher plot-level variations in all variables than GG, and the plot-level variations were 20~77% higher in NN plots than LN and HN plots in SG but they were comparable in unfertilized and fertilized plots in GG. Relative to NN, LN and HN showed more significant surface trends and spatial structures in SOC and TN in both croplands, and the fertilization effect appeared more pronounced in SG. Spatial patterns in C: N, δ13C and δ15N were comparable among different fertilization treatments in both croplands. The descending within-plot variations were also identified among variables (SOC > TN > δ15N > C: N > δ13C). This study demonstrated that N fertilizations generally reduced the plot-level variance and simultaneously re-established spatial structures of SOC and TN in bioenergy croplands, which little varied with fertilization rate but was more responsive in switchgrass cropland.

Effects of nitrogen fertilization and bioenergy crop type on topsoil organic carbon and total Nitrogen contents in middle Tennessee USA

“…Within each plot, 24 cores were randomly collected using a spatially explicit sampling design [39] and a total of 288 soil cores were obtained in 12 plots. This soil sampling design has been used to quantify the spatial heterogeneity of soil microbial biomass, SOC and TN in the same experiment [36,40], and in a former study [41]. The soil samples were transported to the TSU lab in a cooler filled with ice packs and were then subsequently stored at 4˚C until analysis.…”

Effects of nitrogen fertilization and bioenergy crop species on central tendency and spatial heterogeneity of soil glycosidase activities

“…This may lie in several different mechanisms. First, relative to SG, the percentage increases of SOC under N fertilization were much smaller in GG 44 , which could limit the response of BX given the relationship of BX and soil C contents 65 . Second, soil microbial biomass showed no significant change in SG but significantly increased under N fertilization in GG 39 .…”

“…Pearson correlation coefficients between SOC, TN, C/N, MBC, MBN, MBC/MBN, and glycosidase activities (i.e., AG, BG, BX, CBH) under three N fertilization treatments (NN, LN and HN) in two bioenergy croplands (SG and GG). Bold values denote significant correlation coefficients at P < 0.05. www.nature.com/scientificreports/ 15-47%) as they appeared to be higher than that for soil moisture, total pore space, pH, SOC, TN, δ 13 C and δ 15 N 30,44,76 and substantially lower than that for extractable soil Fe and Mn 52 . However, substantially different CVs were evident between enzymes in this study.…”

“…The experimental site marks a warm humid temperate climate with an average annual temperature of 15.1 °C, and total annual precipitation of 1200 mm 42 . The crop type and N fertilization treatments were included in a randomized block design 37 , 39 , 43 , 44 . The two crop types were Alamo SG ( Panicum virgatum L.) and GG ( Tripsacum dactyloides L.).…”

Investigating microplastic dynamics in soils: Orientation for sampling strategies and sample pre‐procession

“…Hence, a sampling strategy must be designed not only just according to the research question but also according to the size of the investigated spatial unit. One option to achieve adequate spatial representation of a particular study area could be the prior calculation of the sample number required for the specific research question and the planned statistical tests on the basis of pilot-sampling and geostatistical analyses (Li, 2019;Li et al, 2020). However, to date, such strategies have not been transferred to research on microplastic dynamics in soils, probably because analytical methods are still very costly.…”