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The persistence of antimicrobial resistant (AMR) genes in the soil-environment is a concern, yet practices that mitigate AMR are poorly understood, especially in grasslands. Animal manures are widely deposited on grasslands, which are the largest agricultural land-use in the United States. These nutrient-rich manures may contain AMR genes. The aim of this study was to enumerate AMR genes in grassland soils following 14-years of poultry litter and cattle manure deposition and evaluate if best management practices (rotationally grazed with a riparian (RBR) area and a fenced riparian buffer strip (RBS), which excluded cattle grazing and poultry litter applications) relative to standard pasture management (continuously grazed (CG) and hayed (H)) minimize the presence and amount of AMR genes. Quantitative PCR (Q-PCR) was performed to enumerate four AMR genes (ermB, sulI, intlI, and blactx-m-32) in soil, cattle manure, and poultry litter environments. Six soil samples were additionally subjected to metagenomic sequencing and resistance genes were identified from assembled sequences. Following 14-years of continuous management, ermB, sulI, and intlI genes in soil were greatest (P < 0.05) in samples collected under long-term continuous grazing (relative to conservation best management practices), under suggesting overgrazing and continuous cattle manure deposition may increase AMR gene presence. In general, AMR gene prevalence increased downslope, suggesting potential lateral movement and accumulation based on landscape position. Poultry litter had lower abundance of AMR genes (ermB, sulI, and intlI) relative to cattle manure. Long-term applications of poultry litter increased the abundance of sulI and intlI genes in soil (P < 0.05). Similarly, metagenomic shotgun sequencing revealed a greater total number of AMR genes under long-term CG, while fewer AMR genes were found in H (no cattle manure) and RBS (no animal manure or poultry litter). Results indicate long-term conservation pasture management practices (e.g., RBS and RBR) and select animal manure (poultry litter inputs) may minimize the presence and abundance of AMR genes in grassland soils. [ABSTRACT FROM AUTHOR]

Soil microorganisms are important for maintaining soil health, decomposing organic matter, and recycling nutrients in pasture systems. However, the impact of long-term conservation pasture management on soil microbial communities remains unclear. Therefore, soil microbiome responses to conservation pasture management is an important component of soil health, especially in the largest agricultural land-use in the US. The aim of this study was to identify soil microbiome community differences following 13-years of pasture management (hayed (no cattle), continuously grazed, rotationally grazed with a fenced, un-grazed and unfertilized buffer strip, and a control (no poultry litter or cattle manure inputs)). Since 2004, all pastures (excluding the control) received annual poultry litter at a rate of 5.6 Mg ha−1. Soil samples were collected at a 0–15 cm depth from 2016–2017 either pre or post poultry litter applications, and bacterial communities were characterized using Illumina 16S rRNA gene amplicon sequencing. Overall, pasture management influenced soil microbial community structure, and effects were different by year (P < 0.05). Soils receiving no poultry litter or cattle manure had the lowest richness (Chao). Continuously grazed systems had greater (P < 0.05) soil community richness, which corresponded with greater soil pH and nutrients. Consequently, continuously grazed systems may increase soil diversity, owing to continuous nutrient-rich manure deposition; however, this management strategy may adversely affect above ground plant communities and water quality. These results suggest conservation pasture management (e.g., rotationally grazed systems) may not improve microbial diversity, albeit, buffer strips were reduced nutrients and bacterial movement as evident by low diversity and fertility in these areas compared to areas with manure or poultry litter inputs. Overall, animal inputs (litter or manure) increased soil microbiome diversity and may be a mechanism for improved soil health. [ABSTRACT FROM AUTHOR]

Biochars form recalcitrant carbon and increase water and nutrient retention in soils; however, the magnitude is contingent upon production conditions and thermo-chemical conversion processes. Herein we aim at (i) characterizing switchgrass (Panicum virgatum L.)-biochar morphology, (ii) estimating water-holding capacity under increasing ratios of char: soil; and, (iii) determining nutrient profile variation as a function of pyrolysis conversion methodologies (i.e. continuous, auger pyrolysis system versus batch pyrolysis systems) for terminal use as a soil amendment. Auger system chars produced at 600°C had the greatest lignin portion by weight among the biochars produced from the continuous system. On the other hand, a batch pyrolysis system (400 °C - 3h) yielded biochar with 73.10% lignin (12 fold increases), indicating higher recalcitrance, whereas lower production temperatures (400°C) yielded greater hemicellulose (i.e. greater mineralization promoting substrate). Under both pyrolysis methods, increasing biochar soil application rates resulted in linear decreases in bulk density (g cm-3). Increases in auger-char (400 °C) applications increased soil water-holding capacities; however, application rates of >2 Mt ha-1 are required. Pyrolysis batch chars did not influence water-holding abilities (P>0.05). Biochar macro and micronutrients increased, as the pyrolysis temperature increased in the auger system from 400 to 600 °C, and the residence time increased in the batch pyrolysis system from 1 to 3 h. Conversely, nitrogen levels tended to decrease under the two previously mentioned conditions. Consequently, not all chars are inherently equal, in that varying operation systems, residence times, and production conditions greatly affect uses as a soil amendment and overall rate of efficacy. [ABSTRACT FROM AUTHOR]

Tree species and fertilization sources may affect the soil organic carbon (SOC) and fertility in agroforestry (AF) systems in temperate regions, but this remains unexplored. This study assesses the longitudinal trends in the SOC and major nutrients in a 17-year AF site established on an Ultisol in Fayetteville, AR. We evaluated how management and fertilization (mineral vs. organic) affect the soil's physical and chemical properties using the tree species: red oak (Quercus rubra L.) and pecan Carya illinoinensis (Wangenh.) K. Koch. Long-term applications of poultry litter increased the soil pH, whereas the Mg and S concentrations decreased compared to the baseline levels (1999). Poultry litter increased the soil P concentration in 53% compared to the baseline levels and reduced the soil C:N ratio. After 17 years, increased Ca, SOC, and N concentrations were observed in the soils under the pecan stands that received poultry litter. Positive correlations occurred between the SOC and N (r = 0.96) as well as the Ca (r = 0.71) and P (r = 0.61) at a soil depth of 0–15 cm. Our findings demonstrated that the changes in SOC and fertility in the AF soils vary according to tree species and fertilization, mostly due to distinctive leaf litter and nutrient inputs. Organic matter accumulation increased the SOC retention and nutrient availability in the temperate AF systems. [ABSTRACT FROM AUTHOR]

Treating manure with aluminum sulfate (alum) is a best management practice (BMP) which reduces ammonia (NH3) emissions and phosphorus (P) runoff from poultry litter. However, the price of alum has increased markedly in recent years, creating a need for less expensive products to control NH3 volatilization. The objective of this study was to evaluate the effects of a new litter amendment made from alum mud, bauxite, and sulfuric acid (alum mud litter amendment or AMLA) on NH3 emissions, litter chemistry, and poultry production in a pen trial. Three separate flocks of 1000 broilers were used for this study. The first flock of birds was used to produce the poultry litter needed for the experiment. The second and third flocks of birds were allocated to 20 pens in a randomized block design with four replicates of five treatments: (1) control, (2) 49 kg AMLA/100 m2 incorporated, (3) 98 kg AMLA/100 m2 incorporated, (4) 98 kg AMLA/100 m2 surface applied, and (5) 98 kg alum/100 m2 incorporated. Ammonia flux measurements and litter samples were collected from each pen at day 0, 7, 14, 21, 28, 35, and 42. The average litter pH for both flocks was higher in untreated litter (7.92) compared to incorporating alum (7.32) or AMLA (7.18). The two flocks' average NH4-N concentrations at day 42 were 38% and 30% higher for the high rates of incorporated alum and AMLA compared to the untreated litter. Compared with untreated litter, AMLA reduced overall NH3 emissions by 27% to 52% which was not significantly different from reductions in emissions by alum (35%). Alum mud litter amendment reduced cumulative NH3 losses from litter as much as, and in some cases more than, alum applied at the same rate. These data indicate that AMLA, which can be manufactured for lower price than alum, is an effective alternative litter amendment for reducing NH3 emissions from poultry litter. [ABSTRACT FROM AUTHOR]

Digestate and its derived composts are valuable organic fertilizers for growing vegetables and field crops. However, the impacts on enzymatic activities and microbial resources acquisition pattern are not well addressed. This study investigated ecoenzymatic activities and microbial resource acquisition patterns following these organic fertilizations for sunflower cultivation. The experiment involved applying digestate, five compost types derived from digestate, and inorganic N fertilizer (NINORG), with a control plot having no treatment. Activities of nine enzymes related to C-, N-, P-, and S- acquiring were measured at three development stages: seedling, pre-blooming, and harvest. Across all treatments, resource allocations, especially for C-, N-, and P- acquisitions, increased with plant development, correlating positively with microbial biomass, soil organic carbon, and soil nutrients contents, showing the heightened energy and nutrient sources stimulated microbial growth, prompting increased resource allocation to meet elevated demands, particularly in later crop developmental stages. Stoichiometric analysis revealed greater investments in P compared to N and C, persisting throughout the study period, with P acquisitions at least four-fold greater than N and at least seven times greater than C. This pattern was greatly impacted at harvest for all treatments except NINORG and control, with a reduced investment rate for P- acquisition compared to that of C-, N-, albeit the C: N:P ratio was still far short of the global mean 1:1:1 ratio. The strong negative correlation between available P and vector angle (p<0.001) indicated that the addition of bioavailable P through organic amendments helped reduce the gap towards the ideal ratio. In summary, on soils with imbalanced microbial nutrient and energy demands, organic amendments intensified microbial growth, resulting in heightened nutrient acquisition. However, the declining trend in P acquisition rates compared to C and N over the cropping period suggests possible adjustments with the help of organic fertilizations. Organic fertilizers, by addressing energy-nutrient imbalances, can contribute to a healthier soil ecosystem under conventional farming systems. • Responses of enzyme activities to digestate and composts applications were evaluated. • All enzymatic activities greatly increased with digestate and compost applications. • Enzymatic activities increased during the cropping period with compost and digestate treatments. • Ecoenzymatic stoichiometry revealed microbial P was the most limited compared to N and C. • Organic fertilizations enhanced P availability but reduced microbial P limitation. [ABSTRACT FROM AUTHOR]