The use of cover crops for nutrient conservation

Field experiments were conducted in 1990 and 1991 on a sandy loam soil at Ayr and a loam soil at Woodstock to evaluate the effectiveness of cover crops for nutrient conservation. Three cover crops, oilseed radish, annual ryegrass and red clover were established in 1990 in or following harvest of barley and winter wheat to which 1/2, 1 and 2x the recommended rates of N had been applied. Attempts to establish cover crops in corn were largely unsuccessful. Cover crops were sampled periodically to determine biomass production and N and P uptake. Soil and soil solution samples were taken periodically in the fall of 1990 and spring of 1991 and analyzed for NH4+ and NO3 nitrogen. Corn was grown on all plots in 1991 without N addition to evaluate the release of N from the cover crops. The potential for contribution of N and P to surface runoff by leaching from cover crops during the winter and spring was evaluated in laboratory leaching studies using a rainfall simulator.Agriculture Canad

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

Linkage disequilibrium, SNP frequency change due to selection, and association mapping in popcorn chromosome regions containing QTLs for quality traits

Abstract The objectives of this study were to assess linkage disequilibrium (LD) and selection-induced changes in single nucleotide polymorphism (SNP) frequency, and to perform association mapping in popcorn chromosome regions containing quantitative trait loci (QTLs) for quality traits. Seven tropical and two temperate popcorn populations were genotyped for 96 SNPs chosen in chromosome regions containing QTLs for quality traits. The populations were phenotyped for expansion volume, 100-kernel weight, kernel sphericity, and kernel density. The LD statistics were the difference between the observed and expected haplotype frequencies (D), the proportion of D relative to the expected maximum value in the population, and the square of the correlation between the values of alleles at two loci. Association mapping was based on least squares and Bayesian approaches. In the tropical populations, D-values greater than 0.10 were observed for SNPs separated by 100-150 Mb, while most of the D-values in the temperate populations were less than 0.05. Selection for expansion volume indirectly led to increase in LD values, population differentiation, and significant changes in SNP frequency. Some associations were observed for expansion volume and the other quality traits. The candidate genes are involved with starch, storage protein, lipid, and cell wall polysaccharides synthesis

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