Research on nitrogen (N) mineralization from organic residues is important to understand N cycling in soils. Here we review research on factors controlling net N mineralization as well as research on ...laboratory and field modeling efforts, with the objective of highlighting areas with opportunities for additional research. Among the factors controlling net N mineralization are organic composition of the residue, soil temperature and water content, drying and rewetting events, and soil characteristics. Because C to N ratio of the residue cannot explain all the variability observed in N mineralization among residues, considerable effort has been dedicated to the identification of specific compounds that play critical roles in N mineralization. Spectroscopic techniques are promising tools to further identify these compounds. Many studies have evaluated the effect of temperature and soil water content on N mineralization, but most have concentrated on mineralization from soil organic matter, not from organic residues. Additional work should be conducted with different organic residues, paying particular attention to the interaction between soil temperature and water content. One- and two-pool exponential models have been used to model N mineralization under laboratory conditions, but some drawbacks make it difficult to identify definite pools of mineralizable N. Fixing rate constants has been used as a way to eliminate some of these drawbacks when modeling N mineralization from soil organic matter, and may be useful for modeling N mineralization from organic residues. Additional work with more complex simulation models is needed to simulate both gross N mineralization and immobilization to better estimate net N mineralized from organic residues.
Some crops, like blueberries, require a pH of 4 to 5. Irrigation of acid‐loving crops with alkaline water can raise pH and cause micronutrient deficiencies. Diseases like citrus greening ...(Huanglongbing) are more severe at higher soil pH values. Application of acidifying fertilizers to lower soil pH may therefore benefit crop growth in such instances and release calcium from calcareous soils to remove sodium. Therefore, a good understanding of the processes involved and the amount of acidification from various fertilizer materials is needed. We show with an anion–cation balance of recent plant uptake data that the alkalinity released from plant uptake of nutrients alone gave a value of 2 kg CaCO3 equivalents of alkalinity per kilogram of N uptake, in close agreement with Association of Official Analytical Chemists values of 1.8. We also provide equations and calculations and a summary table that allows a user to compare the acidifying capacity of commonly available N and S fertilizers.
The use of urea fertilizers in grasslands is likely to increase in areas with concentrated animal feeding operations as restrictions on manure applications are implemented. Concerns have been raised ...about the economic and environmental impacts of NH3 loss from these urea fertilizers. This study evaluated NH3 losses from Nitamin (a urea polymer), urea-NH4NO3 (UAN), and granular urea applied to tall fescue (Festuca arundinacea Schreb.) plots at 50 kg N ha-1 in fall and spring for 2 yr. Fertilizers were applied to circular plots (30-m diameter) and NH3 loss was measured by the modified passive flux method for 69 to 120 d after application. In a separate laboratory study, Nitamin, UAN, and urea were surfaced applied to fescue thatch at 100 kg N ha-1 and treatments were incubated at 24°C and 90% relative humidity for 31 d. In fall applications, urea lost more NH3 (19% in 2004, 46% in 2005) than UAN or Nitamin, which were not different from each other (6% in 2004, 34% in 2005). In contrast, there were no differences among fertilizers in spring applications, with average losses of 13% in 2005 and 17% in 2006. In the laboratory study, urea lost significantly more NH3 (24%) than UAN or Nitamin, which were not different from each other (average 9% loss). These results indicate that Nitamin and UAN undergo similar NH3 losses, and that both fertilizers may lose less NH3 than urea under conditions favorable to volatilization.
Broiler (Gallus gallus domesticus) litter is subject to ammonia (NH3) volatilization losses. Previous work has shown that the addition of gypsum to broiler litter can increase nitrogen mineralization ...and decrease NH3 losses due to a decrease in pH, but the mechanisms responsible for these effects are not well understood. Therefore, three laboratory studies were conducted to evaluate the effect of gypsum addition to broiler litter on (i) urease activity at three water contents, (ii) calcium carbonate precipitation, and (iii) pH. The addition of gypsum to broiler litter increased ammonium concentrations (p < 0.0033) and decreased litter pH by 0.43 to 0.49 pH units after 5 d (p < 0.0001); however, the rate of urea hydrolysis in treated litter only increased on Day 0 for broiler litter with low (0.29 g H2O g−1) and high (0.69 g H2O g−1) water contents, and on Day 3 for litter with medium (0.40 g H2O g−1) water content (p < 0.05). Amending broiler litter with gypsum also caused an immediate decrease in litter pH (0.22 pH units) due to the precipitation of calcium carbonate (CaCO3) from gypsum‐derived calcium and litter bicarbonate. Furthermore, as urea was hydrolyzed, more urea‐derived carbon precipitated as CaCO3 in gypsum‐treated litter than in untreated litter (p < 0.001). These results indicate that amending broiler litter with gypsum favors the precipitation of CaCO3, which buffers against increases in litter pH that are known to facilitate NH3 volatilization.
Core Ideas
The rate of urea hydrolysis briefly increases when gypsum is added to broiler litter.
Treating broiler litter with gypsum causes an immediate decrease in litter pH.
Calcium carbonate precipitation in gypsum‐amended litter decreases litter pH.
A major concern of the broiler industry is the volatilization of ammonia (NH3) from the mixture of bedding material and broiler excretion that covers the floor of broiler houses. Gypsum has been ...proposed as a litter amendment to reduce NH3 volatilization, but reports of NH3 abatement vary among studies and the mechanism responsible for decreasing NH3 volatilization is not well understood. The goal of this study was to evaluate the effect of adding 20 or 40% flue-gas desulfurization gypsum (FGDG) to broiler litter on pH, electrical conductivity (EC), water potential, urea-degrading bacteria abundance, NH3 and carbon dioxide (CO2) evolution, and nitrogen (N) mineralization in several 21-d experiments. The addition of FGDG to broiler litter increased EC by 24 to 33% (P < 0.0001), decreased urea-degrading bacteria by 48 to 57% (P = 0.0001) and increased N mineralization by 10 to 11% (P = 0.0001) as compared to litters not amended with FGDG. Furthermore, the addition of FGDG to broiler litter decreased NH3 volatilization by 18 to 28% (P < 0.0001), potentially resulting from the significantly lower litter pH values compared to un-amended litter (P < 0.0001). Findings of this study indicate that amending broiler litter with 20% FGDG can decrease NH3 volatilization and increase the fertlizer value of broiler litter.
Soil pH buffering capacity, described here as lime buffer capacity (LBC), is a fundamental soil property needed to estimate the change in soil pH after a known quantity of acidity or alkalinity is ...added to soil. Its rapid determination can be useful for many purposes, for example, estimating the lime needed to raise pH or acid needed to lower pH to a desired level. The objective of the present study was to evaluate the statistical relationship developed in previous studies between LBC from 30-min equilibration with Ca(OH)2 (LBC30) and LBC from 5-d equilibration with Ca(OH)2 (LBCeq) on a larger set of soils from Georgia. Five days was considered adequate time for true pH equilibrium and obtaining a true LBC. Eighty-seven soils from Georgia were treated with Ca(OH)2 using standard procedures for both equilibrium times, and the statistical relationship between the two LBCs were developed. The relationship developed in the first study was further tested in a second incubation of 67 soils to determine its accuracy in achieving a target pHCaCl2 of 6.0. The data from the second incubation indicated that the target pH was exceeded by an average of 0.11 pH units and that the average pH spread around the acquired pH was ±0.1 pH unit. The results suggest that the prediction of soil pH buffering capacity based on the proposed protocols will be sufficiently accurate for making agricultural lime application recommendations.
In the United States, approximately 600,000 ha of pine trees are fertilized with urea each year, with NH3 volatilization losses ranging from <1% to >50% depending on environmental conditions. ...Previous work showed that the timing of rainfall after urea application plays a significant role in controlling NH3 loss, but the effect of other environmental variables is not well understood. We conducted 10 29-d studies under different environmental conditions during 2 yr to identify important variables controlling NH3 loss from urea applied to loblolly pine (Pinus taeda L.) at 200 kg N ha–1. Ammonia loss was measured with dynamic chambers that adjusted the rate of air flow through the system based on wind speed at 1 cm above the soil surface. Regression analysis indicated that a variable related to the initial water content of the forest floor and a variable related to the relative humidity (RH) during the study explained 85 to 94% of the observed variability in NH3 loss. Relatively high initial water content followed by consistently high RH led to large NH3 losses. In contrast, low initial water contents resulted in slow rates of NH3 loss, which increased when elevated RH led to an increase in the water content of the forest floor. These results indicate that RH can play a significant role in NH3 loss by accelerating urea dissolution and by increasing or decreasing the water content of the forest floor, which in turn can affect the rate of urea hydrolysis.
We report the observation of a compact binary coalescence involving a 22.2-24.3 M black hole and a compact object with a mass of 2.50-2.67 M (all measurements quoted at the 90% credible level). The ...gravitational-wave signal, GW190814, was observed during LIGO's and Virgo's third observing run on 2019 August 14 at 21:10:39 UTC and has a signal-to-noise ratio of 25 in the three-detector network. The source was localized to 18.5 deg2 at a distance of Mpc; no electromagnetic counterpart has been confirmed to date. The source has the most unequal mass ratio yet measured with gravitational waves, , and its secondary component is either the lightest black hole or the heaviest neutron star ever discovered in a double compact-object system. The dimensionless spin of the primary black hole is tightly constrained to ≤0.07. Tests of general relativity reveal no measurable deviations from the theory, and its prediction of higher-multipole emission is confirmed at high confidence. We estimate a merger rate density of 1-23 Gpc−3 yr−1 for the new class of binary coalescence sources that GW190814 represents. Astrophysical models predict that binaries with mass ratios similar to this event can form through several channels, but are unlikely to have formed in globular clusters. However, the combination of mass ratio, component masses, and the inferred merger rate for this event challenges all current models of the formation and mass distribution of compact-object binaries.
We report on the population of 47 compact binary mergers detected with a false-alarm rate of <1yr^(−1) in the second LIGO–Virgo Gravitational-Wave Transient Catalog. We observe several ...characteristics of the merging binary black hole (BBH) population not discernible until now. First, the primary mass spectrum contains structure beyond a power law with a sharp high-mass cutoff; it is more consistent with a broken power law with a break at 39.7^(+20.3)(-9.1)M or a power law with a Gaussian feature peaking at 33.1^(+4.0)(-5.6)M (90% credible interval). While the primary mass distribution must extend to ~65M or beyond, only 2.9^(+3.5)(-1.7)M% of systems have primary masses greater than 45M. Second, we find that a fraction of BBH systems have component spins misaligned with the orbital angular momentum, giving rise to precession of the orbital plane. Moreover, 12% to 44% of BBH systems have spins tilted by more than 90°, giving rise to a negative effective inspiral spin parameter, χeff. Under the assumption that such systems can only be formed by dynamical interactions, we infer that between 25% and 93% of BBHs with nonvanishing |χeff| > 0.01 are dynamically assembled. Third, we estimate merger rates, finding RBBH = 23.9^(+14.3)(-8.6) Gpc^(-3) yr^(-1) for BBHs and RBNS = 320^(+490)(-240) Gpc^(-3) yr^(-1) for binary neutron stars. We find that the BBH rate likely increases with redshift (85% credibility) but not faster than the star formation rate (86% credibility). Additionally, we examine recent exceptional events in the context of our population models, finding that the asymmetric masses of GW190412 and the high component masses of GW190521 are consistent with our models, but the low secondary mass of GW190814 makes it an outlier.
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