Linking soil microbial community structure to potential carbon mineralization: A continental scale assessment of reduced tillage

Potential carbon mineralization (Cmin) is a commonly used indicator of soil health, with greater Cmin values interpreted as healthier soil. While Cmin values are typically greater in agricultural soils managed with minimal physical disturbance, the mechanisms driving the increases remain poorly understood. This study assessed bacterial and archaeal community structure and potential microbial drivers of Cmin in soils maintained under various degrees of physical disturbance. Potential carbon mineralization, 16S rRNA sequences, and soil characterization data were collected as part of the North American Project to Evaluate Soil Health Measurements (NAPESHM). Results showed that type of cropping system, intensity of physical disturbance, and soil pH influenced microbial sensitivity to physical disturbance. Furthermore, 28% of amplicon sequence variants (ASVs), which were important in modeling Cmin, were enriched under soils managed with minimal physical disturbance. Sequences identified as enriched under minimal disturbance and important for modeling Cmin, were linked to organisms which could produce extracellular polymeric substances and contained metabolic strategies suited for tolerating environmental stressors. Understanding how physical disturbance shapes microbial communities across climates and inherent soil properties and drives changes in Cmin provides the context necessary to evaluate management impacts on standardized measures of soil microbial activity

Carbon-sensitive pedotransfer functions for plant available water

Currently accepted pedotransfer functions show negligible effect of management-induced changes to soil organic carbon (SOC) on plant available water holding capacity (θAWHC), while some studies show the ability to substantially increase θAWHC through management. The Soil Health Institute\u27s North America Project to Evaluate Soil Health Measurements measured water content at field capacity using intact soil cores across 124 long-term research sites that contained increases in SOC as a result of management treatments such as reduced tillage and cover cropping. Pedotransfer functions were created for volumetric water content at field capacity (θFC) and permanent wilting point (θPWP). New pedotransfer functions had predictions of θAWHC that were similarly accurate compared with Saxton and Rawls when tested on samples from the National Soil Characterization database. Further, the new pedotransfer functions showed substantial effects of soil calcareousness and SOC on θAWHC. For an increase in SOC of 10 g kg–1 (1%) in noncalcareous soils, an average increase in θAWHC of 3.0 mm 100 mm–1 soil (0.03 m3 m–3) on average across all soil texture classes was found. This SOC related increase in θAWHC is about double previous estimates. Calcareous soils had an increase in θAWHC of 1.2 mm 100 mm–1 soil associated with a 10 g kg–1 increase in SOC, across all soil texture classes. New equations can aid in quantifying benefits of soil management practices that increase SOC and can be used to model the effect of changes in management on drought resilience

Per-plant eco-physiological responses of maize to varied nitrogen availability at low and high plant densities

Although maize (Zea mays L.) routinely experiences both intra- and inter-specific competition for limited resources, most plant-plant interaction studies have principally focused on maize-weed interactions. Thus very few investigations have considered the impacts of plant crowding and nitrogen (N) availability on maize intra-specific competition. The primary objective of this two-year field study near West Lafayette, IN was to investigate the per-plant eco-physiological responses of modern maize genotypes to varied N availability (0, 165, and 330 kg side-dress N ha-1) at low and high plant densities (54,000 and 104,000 plants ha-1, respectively) by measuring responses among dominated [lowermost 25% per-plant grain yield (GYP)], intermediate, and dominant (uppermost 25% GYP) individual plants in each treatment combination. Parameters measured at the per-plant level included R1 green leaf area (LAP), R1 SPAD, anthesis-silking interval (ASIP), GYP, R6 total aboveground biomass (TBP), and harvest index (HIP). In both years, severe intra-specific competition for soil N in the highly crowded, low-N environment resulted in low R1 LAP and SPAD values, high ASIP values, and reduced GYP, R6 TBP, and HIP values, particularly among dominated plants. Intense competition in this environment also led to (i) high dominant group/dominated group mean ratios for most parameters; (ii) high plant-to-plant variability for R1 SPAD, ASIP, GYP, and HIP; and (iii) high frequencies of barren and low-yielding plants. Insufficient N at high plant densities thus encouraged the formation of plant hierarchies composed of markedly dominated individuals with diminished source capability and severely impaired biomass partitioning to developing grain

Per-plant eco-physiological responses of maize to varied nitrogen availability at low and high plant densities

Although maize (Zea mays L.) routinely experiences both intra- and inter-specific competition for limited resources, most plant-plant interaction studies have principally focused on maize-weed interactions. Thus very few investigations have considered the impacts of plant crowding and nitrogen (N) availability on maize intra-specific competition. The primary objective of this two-year field study near West Lafayette, IN was to investigate the per-plant eco-physiological responses of modern maize genotypes to varied N availability (0, 165, and 330 kg side-dress N ha-1) at low and high plant densities (54,000 and 104,000 plants ha-1, respectively) by measuring responses among dominated [lowermost 25% per-plant grain yield (GYP)], intermediate, and dominant (uppermost 25% GYP) individual plants in each treatment combination. Parameters measured at the per-plant level included R1 green leaf area (LAP), R1 SPAD, anthesis-silking interval (ASIP), GYP, R6 total aboveground biomass (TBP), and harvest index (HIP). In both years, severe intra-specific competition for soil N in the highly crowded, low-N environment resulted in low R1 LAP and SPAD values, high ASIP values, and reduced GYP, R6 TBP, and HIP values, particularly among dominated plants. Intense competition in this environment also led to (i) high dominant group/dominated group mean ratios for most parameters; (ii) high plant-to-plant variability for R1 SPAD, ASIP, GYP, and HIP; and (iii) high frequencies of barren and low-yielding plants. Insufficient N at high plant densities thus encouraged the formation of plant hierarchies composed of markedly dominated individuals with diminished source capability and severely impaired biomass partitioning to developing grain

Nitrous oxide emissions in Midwest US maize production vary widely with band-injected N fertilizer rates, timing and nitrapyrin presence

Nitrification inhibitors have the potential to reduce N _2 O emissions from maize fields, but optimal results may depend on deployment of integrated N fertilizer management systems that increase yields achieved per unit of N _2 O lost. A new micro-encapsulated formulation of nitrapyrin for liquid N fertilizers became available to US farmers in 2010. Our research objectives were to (i) assess the impacts of urea–ammonium nitrate (UAN) management practices (timing, rate and nitrification inhibitor) and environmental variables on growing-season N _2 O fluxes and (ii) identify UAN treatment combinations that both reduce N _2 O emissions and optimize maize productivity. Field experiments near West Lafayette, Indiana in 2010 and 2011 examined three N rates (0, 90 and 180 kg N ha ^−1 ), two timings (pre-emergence and side-dress) and presence or absence of nitrapyrin. Mean cumulative N _2 O–N emissions ( Q _10 corrected) were 0.81, 1.83 and 3.52 kg N _2 O–N ha ^−1 for the rates of 0, 90 and 180 kg N ha ^−1 , respectively; 1.80 and 2.31 kg N _2 O–N ha ^−1 for pre-emergence and side-dress timings, respectively; and 1.77 versus 2.34 kg N _2 O–N ha ^−1 for with and without nitrapyrin, respectively. Yield-scaled N _2 O–N emissions increased with N rates as anticipated (averaging 167, 204 and 328 g N _2 O–N Mg grain ^−1 for the 0, 90 and 180 kg N ha ^−1 rates), but were 22% greater with the side-dress timing than the pre-emergence timing (when averaged across N rates and inhibitor treatments) because of environmental conditions following later applications. Overall yield-scaled N _2 O–N emissions were 22% lower with nitrapyrin than without the inhibitor, but these did not interact with N rate or timing