Carbon and nitrogen cycling and soil quality under long-term crop rotation and tillage

Crop rotation and tillage can have substantial impact on the soil environment, the microbial community, and the cycling of C and N. Understanding the relationship between soil organic matter dynamics and the agronomic practices of crop rotation and tillage is key to identifying management that has the potential to enhance the production of the soils of the Midwest. In order to evaluate how tillage influences soil biology, a global meta-analysis was conducted to compare the effect of conventional tillage on microbial properties to that of no-till. Overall, greater microbial biomass and enzyme activities were found under no-till compared to conventional tillage; however, the metabolic quotient was greater in conventional tillage. This indicates that individual microbes in tilled soil are more active compared to those in no-till soils. Despite these results, a large amount of variability remained that was not able to be explained, possibly as a result of the highly variable nature of the biological measures. While a meta-analysis provides a greater inference space, field research can provide greater understanding of the impact of agronomic practices on soil processes and soil quality within a region. Long-term crop rotation and tillage experimental sites were evaluated to assess the influence of both crop rotation and tillage on highly fertile Illinois soils. Using univariate analysis, the second chapter assesses the impact of these agronomic practices on C and N within soil organic matter and microbial biomass. Crop rotations with higher C:N residues and no-till led to greater soil organic carbon and total nitrogen; however, despite the role of microbes in C and N cycling, microbial biomass was not affected by these agronomic practices as expected based on the results of the meta-analysis. The final chapter evaluates how effective these and several other properties are to serve as indicators of soil quality. The results of a principal component analysis indicated that for both crop rotation and tillage, soil parameters related to C and N cycling were very influential and have great potential as soil quality indicators. Different usage of nitrogenous fertilizers among crop rotations and the stratification of these fertilizers under no-till are other significant aspects of these agronomic practices that were highlighted by the multivariate analysis

Role of inherent soil characteristics in assessing soil health across Missouri

Soil health indicator values vary based on parent material, native vegetation, and other soil forming factors; therefore, useful interpretations require consideration of inherent soil characteristics. Our objective was to evaluate the distribution of soil health indicators across soil and climate gradients throughout the state of Missouri through a statewide cover crop cost-share program. Soil samples (0–7 cm) were collected from 5,300 agricultural fields and analyzed for several soil health indicators. Comparisons were made among six regions in the state based on Major Land Resource Area and county boundaries. Results varied for soil organic carbon (C), active C, potentially mineralizable nitrogen, water stable aggregates, and cation exchange capacity by region and corresponded with soil forming factors. Interpretation of soil health indicators must account for regional factors, recognizing that areas with different inherent values have a different potential for soil health

Carbon and Nitrogen Content of Soil Organic Matter and Microbial Biomass under Long-Term Crop Rotation and Tillage in Illinois, USA

Crop rotation and tillage alter soil organic matter (SOM) dynamics by influencing the soil environment and microbes carrying out C and N cycling. Our goal was to evaluate the effect of long-term crop rotation and tillage on the quantity of C and N stored in SOM and microbial biomass. Two experimental sites were used to evaluate four rotations—continuous corn (Zea mays L.) (CCC), corn-soybean (Glycine max [L.] Merr.) (CS), corn-soybean-wheat (Triticum aestivum L.) (CSW), and continuous soybean (SSS), each split into chisel tillage (CT) and no-till (NT) subplots. The CSW rotation increased soil organic carbon (SOC) content compared to SSS; SSS also reduced total nitrogen (TN) compared to other rotations. Levels of SOC and TN were 7% and 9% greater under NT than CT, respectively. Rotation did not affect microbial biomass C and N (MBC, MBN) while tillage reduced only MBN at 10–20 cm compared to NT, likely related to dispersion of N fertilizers throughout the soil. Despite the apparent lack of sensitivity of microbial biomass, changes in SOC and TN illustrate the effects of rotation and tillage on SOM dynamics. The inclusion of crops with high C: N residues and no-till use both support higher C and N content in the top 20 cm of the soil

Long-term crop rotation and tillage effects on soil greenhouse gas emissions and crop production in Illinois, USA

Two of the most important agricultural practices aimed at improving soil properties are crop rotations and no-tillage, yet relatively few studies have assessed their long-term impacts on crop yields and soil greenhouse gas (GHG) emissions. The objective of this study was to determine the influence of tillage and crop rotation on soil GHG emissions and yields following 15 years of treatment implementation in a long-term cropping systems experiment in Illinois, USA. The experimental design was a split-plot RCBD with crop rotation as the main plot: (continuous corn [Zea mays L.] (CCC), corn-soybean [Glycine max (L.) Merr.] (CS), continuous soybean (SSS), and corn-soybean-wheat [Triticum aestivum L.] (CSW); with each phase of each crop rotation present every year) and tillage as the subplot: chisel tillage (T) and no-tillage (NT). Tillage increased the yields of corn and soybean. Tillage and crop rotation had no effect on methane (CH4) emissions (p = 0.4738 and p = 0.8494 respectively) and only rotation had an effect on cumulative carbon dioxide (CO2) (p = 0.0137). However, their interaction affected cumulative nitrous oxide (N2O) emissions significantly (p = 0.0960); N2O emissions from tilled CCC were the greatest at 6.9 kg-N ha−1-yr−1; while emissions from NT CCC (4.0 kg-N ha−1-yr−1) were not different than both T CS or NT CS (3.6 and 3.3 kg-N ha−1−yr−1, respectively). Utilizing just a CS crop rotation increased corn yields by around 20% while reducing N2O emissions by around 35%; soybean yields were 7% greater and N2O emissions were not affected. Therefore results from this long-term study indicate that a CS rotation has the ability to increase yields and reduce GHG emissions compared to either CCC or SSS alone, yet moving to a CSW rotation did not further increase yields or reduce N2O emissions