Reduced NH3 Loss Research Articles

Organic and Inorganic Amendments to Reduce Ammonia Losses from Liquid Hog Manure

AbstractLiquid hog manure (Sus scrofa domesticus) is in common use as a fertilizer or a soil conditioner in agricultural production. Liquid hog manure (LHM) suffers from N loss through volatilization of ammonia (NH3), however. Reduction of NH3 loss from 4% total solids LHM was studied using added Sphagnum peat moss (Sphagnum fuscum peat), sulfuric acid, phosphoric acid, monocalcium phosphate monohydrate (MCPM), elemental S, and calcium carbonate. Cumulative losses of NH3‐N ranged between 0 and 711 mg N kg−1 LHM applied. Elemental Sulfur and calcium carbonate (CaCO3) treatments induced greater NH3 losses compared with the nonamended LHM, whereas acidic treatments including Sphagnum peat moss (SM) reduced NH3 losses by at least 74.6%. Volatilization of NH3 from LHM increased as the pH of amended LHM treatment increased. The relationships between cumulative (15 d) NH3 volatilized and initial pH of amended LHM varied, depending on the amendment. The nutrient values of amended LHM stored for 25 d under continuous aeration were assessed on two soils mapped as Chicot (fine loamy, mixed, nonacid, mesic Typic Hapludoll) and Uplands (coarse loamy, mixed, nonacid, Typic Haplorthod) from eastern Canada. Treatment of LHM with SM at greater than 1% (w/w) reduced NH3 volatilization. Added CaCO3 increased NH3 loss. In general, amendments did not reduce effectiveness of LHM‐N for barley (Hordeum vulgare L.) growth. An exception was the 1% SM + 2% CaCO3 amendment that reduced plant growth.

Effect of tillage practices and hay straw on ammonia volatilization from nitrogen fertilizer solutions

Urea (U) fertilizer solutions applied on soil surface lose nitrogen through ammonia (NH3) volatilization, and such losses may be influenced by tillage practices and by the presence of crop residues. Ammonia measurements in corn (Zea mays L.) fields were initiated and continued for 9 d in July 1988 and 1989 to assess the effects of three tillage practices used in corn production (conventional, CT; reduced, RT; and zero tillage, ZT) and urea-ammonium nitrate (UAN) formulations on the volatilization of NH3 from UAN solutions. The UAN formulations were 33% U — 67% ammonium nitrate (AN) and 50% U — 50% AN. These UAN formulations indicate proportion, as percentage, of total N derived from U and AN, respectively. The experiments were conducted on two agricultural soils of Quebec [Macdonald sandy loam (Humic Gleysol), and St. Benoit sandy loam (Eutric Brunisol)]. Cumulative NH3 losses over 9 d ranged from 0.8 to 9.5% of applied N. On both soils, NH3 losses from 50–50 UAN were higher than the 33–67 UAN by 13.5, 14.6 and 23.9% on CT, RT, and ZT, respectively. Reduced NH3 loss with CT was attributed in part to lower crop residues than with ZT treatments. In a separate experiment to evaluate the effect of plant residues on NH3 loss, chopped timothy hay (Phleum pratense L.) was used to provide a greater surface cover and a uniform spreading of residues. Hay straw surface-applied to a conventionally tilled St. Benoit soil had to reach a threshold level somewhere between 750 and 1500 kg ha−1 to increase N losses compared to no added hay treatment. Key words: UAN solution, ammonia volatilization, tillage, hay straw

Effect of urease inhibitors on urea hydrolysis and ammonia volatilization

Two laboratory incubation experiments were conducted to study the effects of the urease inhibitors hydroquinone (HQ), phenyl phosphorodiamidate (PPDA), and N-(n-butyl) thiophosphoric triamide (NBPT) in retarding the hydrolysis of urea, in the evolution of mineral N, and in reducing NH3 loss through volatilization, under aerobic and waterlogged conditions, both at 25°C. NBPT generally exceeded PPDA and HQ in the ability to delay urea hydrolysis and NHinf4sup+accumulation under aerobic conditions, whereas PPDA retarded these activities more effectively under anaerobic conditions. HQ was less effective than the other two urease inhibitors. Under aerobic conditions, 20% of the applied urea was lost through NH3 volatilization after 5 days in the system without an inhibitor. With the addition of HQ and PPDA, the volatilization was delayed by 1 day but not eliminated. NBPT effectively decreased the NH3 loss, from 20 to 3% of the applied urea. A more severe N loss (40%) occurred in the waterlogged system. HQ had little effect on NH3 volatilization. PPDA decreased the NH3 loss from 40 to less than 20% of the applied urea. The effectiveness of NBPT decreased under anaerobic conditions. It was concluded that urease inhibitors can reduce NH3 volatilization following the application of urea. However, environmental conditions might have an important influence on the effectiveness of these inhibitors.

Regulation Mechanisms and Field Implications of Ammonia Bonding with Various Crystalline Salts

Ammonia volatilization following surface application of urea or inorganic NH4 salts can be reduced by the addition of CaCl2, MgCl2, or MgSO4 salts. The mechanisms for this phenomenon are reported to be: (i) precipitation of CO2-3 by Ca2+ or Mg2+, preventing (NH4)2CO3 formation and (ii) Ca2+ depression of soil pH by suppression of the dissociation of the CaCO3-Ca(OH)2 buffer system. Using Fourier-transform infrared (FTIR) spectroscopy, this study demonstrates that, for systems containing limited quantities of water (adsorbed water only), the CaCl2 or MgCl2 salts act as proton donors to NH3, forming stable MH2OOH·H4N·Cl2 (M = Ca or Mg) compounds. However, the ability of a metal cation to act as a proton donor is diminished when the cation-anion bond increases in strength (ionic character of the bond is diminished while covalent character is increased). These findings are consistent with NH3-volatilization data reported in the literature. The present study shows, via a different mechanism, that Ca salts of low solubility (e.g., CaSO4·2H2O) should not be effective in reducing NH3 losses. On the other hand, Ca or Mg salts of high solubility ought to be effective in reducing NH3 losses from surface-applied urea or NH4 fertilizers.

Ammonia losses from surface-placed mixtures of urea-calcium-potassium salts in the presence of phosphorus

Phosphorus compounds frequently are mixed with urea containing materials for economy in fertilizer operations. There is little published information on NH3 losses from surface application of these mixtures. However, there is evidence that P can react and precipitate with adsorbed and added Ca and increase the potential for NH3 loss. This paper compares NH3 losses from surface applied urea plus KCl or CaCl2 in the presence of 5 common P sources. The N, with Ca, K, and P salts, was surface-applied to a calcareous (Harkey) and an acid soil (Cuthbert) in a laboratory and the NH3 losses determined by passage of the exhaust air through a 2% boric acid solution. Ammonia losses were increased with (in the presence of KCl or CaCl2) KH2PO4 (KP) (calcareous soil only) and K2HPO4 (K2P), unaffected by Na5P3O10 (PP) but decreased with Ca(H2PO4)2 (CaP) and H3PO4 (HP) (No HP or PP applied to the acid soil). Urea which hydrolyses in environments with lower soluble and desorbable Ca levels is susceptible to higher NH3 losses. The effectiveness of KCl for control of NH3 loss depended on the existence of desorbable Ca to react with the decomposing urea. Therefore the deleterious impact of P on NH3 loss was greater with KCl than with CaCl2. Adding Ca directly with the urea made additional Ca available for reaction with P and urea. Monocalcium phosphate (CaP) alone with urea, in a calcareous soil, did not reduce NH3 loss; however, NH3 loss was reduced in the acid soil. The addition of CaCl2 with urea + CaP reduced NH3 loss more than CaCl2 with urea. The HP reaction with CaCO3 was more rapid and complete than occurred with the acidic CaP. Sodium tripolyphosphate (PP) with urea had little impact on NH3 loss over that produced by the KCl or CaCl2 salts alone. The HP and CaP chemicals did not appear to function strictly as acid sources (calcareous soil). The Harkey soil has 8% CaCO3 which would appear adequate to neutralize any acidity introduced by the P fertilizers. The explanation may lie in double salt formation between the Ca-urea-P materials.

The influence of formula modifications and additives on ammonia loses from surface-applied urea-ammonium nitrate solutions

Urea-ammonium nitrate (UAN) solution fertilizers are subject to N loss through ammonia (NH3) volatilization. This loss may be reduced by manipulation of the proportion of urea and by use of additives to reduce urea hydrolysis or increase fertilizer solution acidity. This research was design to study the effect of urea proportion in UAN solutions, added ammonium thiosulfate (ATS), and aquechem liquor (an industry by-product) on NH3 loss from N solutions surface-applied to a range of agricultural soils. NH3 volatilization from urea (U), ammonium nitrate (AN), and UAN solutions surface-applied on six eastern Canadian soils was investigated. Ammonia loss from urea solutions ranged from 23 to 55% of the applied N. Increased AN-N in UAN solutions caused a reduction of NH3 loss greater than the reduction in urea. Less volatilization was observed with N solutions of higher acidity. This effect was more pronounced on a sandy soil than on clay soil. When ATS was added to UAN solution, a further reduction of NH3 losses was observed. This reduction ranged from 12 to 23.5% in Dalhousie clay and Ste. Sophie sand soils, respectively. Addition of aquachem liquor (AqL) to the UAN solution did not consistently reduce NH3 loss.

Ammonia volatilization from urea nitricphosphate and urea applied to the soil surface

Urea nitricphosphate (UNP) is an N-P fertilizer prepared by solubilizing phosphate ore with nitric acid and conditioning the product with urea. The product is acidic, and its nutrient analysis is 23-12-0. Urea makes up 74% of the N component of this material and the remainder comes from the nitrate added as nitric acid. In volatilization trials, UNP lost significantly less N than did urea in a noncalcareous soil (13 and 31% respectively). In calcareous soils the urea-N component of UNP exhibited loss patterns similar to those of urea. Soil pH remained stable at the center of the granule placement site during UNP hydrolysis, thereby reducing NH3 loss, whereas the pH of the same soil treated with urea rose almost 1.9 units. The urea component of UNP appeared to diffuse from the center of the acidic microsite allowing hydrolysis to take place and permitting limited NH3 volatilization to occur. UNP appears to be an attractive NP fertilizer in terms of nutrient analysis and resistance of the N component to volatile N losses as NH3.

Measuring Nitrogen Losses from Lowland Rice Using Bulk Aerodynamic and Nitrogen‐15 Balance Methods

AbstractManagement practices, designed to reduce ammonia (NH3) volatilization and total N loss from flooded rice fields, after application of urea, were assessed in the dry season at Mabitac, Philippines. The assessment was made in replicated 4.8‐m × 5.2‐m plots by determining NH3 and total fertilizer N losses with bulk aerodynamic and 15N balance methods, respectively. The bulk aerodynamic method was first evaluated by comparison of ammoniacal‐N concentrations, pH values, and equilibrium NH3 concentrations for a 50‐m diam, circular area and small plots receiving the same fertilizer treatment. Good agreement was obtained so the bulk aerodynamic method was used to determine NH3 loss from the small plots receiving the different management treatments. Ammonia loss was high when urea was broadcast into floodwater 10 d after transplanting—48 and 56% of the applied N was volatilized as NH3 during the first 8 d after application of 53 and 80 kg N ha−1, respectively. Total N losses were 60 and 59%, respectively. Ammonia loss was reduced slightly (to a mean of 43% of the applied N for the two application rates) by broadcasting the fertilizer into 0.05‐m‐deep floodwater and incorporating it into the soil by harrowing before transplanting. Removal of the floodwater before applying urea onto saturated soil and incorporation by harrowing reduced NH3 loss to a mean of 9% and total fertilizer N loss to a mean of 33%. Fertilizer N recovery by rice plants was significantly increased by incorporation without surface water.

Effects of initial soil calcium content on ammonia losses from surface-applied urea and calcium-urea

Ammonia loss from surface-applied urea occurs because urea hydrolysis increases the pH of the placement site microenvironment. Addition of Ca-salts with urea will control or reduce the microsite pH, thus reducing NH3 losses. The degree of Ca-saturation of the cation exchange sites may influence the ratio of calcium:urea required to control ammonia loss. A laboratory study was conducted to determine if adsorbed Ca or CaCO3 additions (acid soils only) had a measureable impact on Ca control of NH3 loss from surface applied urea at various Ca:urea ratios.

Ammonia Volatilization from Surface‐applied Urea as Affected by Several Phosphoroamide Compounds

AbstractIn an attempt to reduce ammonia (NH3) losses from surface applied urea to ultimately increase plant N use efficiency, a field experiment was conducted to compare the effects of six phosphoroamide urease inhibitors on NH3 volatilization from urea surface applied to no‐till (NT) and conventionally tilled (CT) soils. Urea prills (200 kg N ha−1) with and without phosphoroamide inhibitors (4.0 kg a.i. ha−1) were broadcast on the surface of microplots. Ammonia evolution was measured using a semiopen‐static system in which the volatilization chambers were moved periodically to compensate for soil environmental changes induced by the enclosures. Environmental and soil conditions affected the cumulative and daily losses of N. Losses were greater and more rapid under warm, moist soil conditions than hot and dry conditions. The low specific humidity during the hot, dry conditions prevented complete dissolution of prills until 6 d after application thus reducing hydrolysis and NH3 volatilization. Phenylphosphorodiamidate (PPD) most consistently reduced cumulative NH3 losses on NT and CT. Ammonia loss with the addition of PPD was 10 to 54% of the NH3 loss with unamended urea in three of four tests. Trichloroethyl phosphorodiamidate and N‐(diaminophosphinyl)‐cyclohexane were the only other compounds to significantly reduce NH3 losses compared to unamended urea, but these compounds were effective in only one‐half the tests. Both field and laboratory studies showed significantly greater NH3 losses from urea applied to residue covered soil than to bare soil. Addition of PPD or thiophosphoric triamide to residue reduced N losses to 43 and 39% of applied urea‐N, respectively. The effectiveness of PPD in retarding NH3 losses was decreased as the soil pH increased from 5.6 to 7.2.

Effect of Phenylphosphorodiamidate on Immobilization and Ammonia Volatilization

AbstractLaboratory incubation experiments were conducted to evaluate the ability of the urease inhibitor phenylphosphorodiamidate (PPD) to reduce NH3 volatilization and immobilization of urea (100 mg N kg−1 of soil). Application of 20 mg PPD kg−1 of soil effectively inhibited urea hydrolysis for approximately 4 d in both soil and oat straw‐amended soil systems. This delayed urea hydrolysis reduced NH3 losses after 7 d from 82 to 19% in the straw‐amended soil, and from 26 to 14% in the soil system. When urea was applied to soil incubated in closed vessels, only 80% of the applied urea could be recovered as inorganic N after 3 d of incubation. This apparent immobilization of N was prevented for 7 d by application of PPD. Immobilization of N in the straw‐amended soil exceeded 40% within 7 d, but the onset of these losses was delayed for at least 3 d by PPD. These results demonstrate that losses of surface‐applied urea via both NH3 volatilization and immobilization can be prevented by application of an effective urease inhibitor.

Effect of Phenylphosphorodiamidate on Ammonia Volatilization as Affected by Soil Temperature and Rates and Distribution of Urea

AbstractLaboratory incubation studies were conducted to evaluate the ability of phenylphosphorodiamidate (PPD) to inhibit urea hydrolysis and control NH3 volatilization losses. Complete hydrolysis of the uninhibited urea occurred within 8 d at all temperatures studied, and resulted in volatilization of more than 25% of the applied N within 10 d. Application of 20 mg PPD kg−1 of soil essentially prevented urea hydrolysis and resultant NH3 losses for 1, 2, 4, 8, and 17 d at 35, 25, 15, 10, and 5°C, respectively. This delay in the onset of NH3 losses due to PPD application kept NH3 losses during the first 10 d to <7% of the applied N at the three lower temperatures, but had little effect upon NH3 losses at 25 and 35°C. Such limited effectiveness of PPD at higher temperatures will no doubt reduce its utility for application to soils with surface temperatures above 25°C. Application of lower concentrations of urea gave reduced NH3 losses, both with and without PPD, likely due to a greater ability of other N transformations to compete for the reduced ammonium pools. Ammonia losses were also reduced, with and without PPD, when the urea was distributed throughout a larger soil volume, presumably due to a greater proportion of the urea being hydrolyzed below the immediate soil surface.

Compaction of metal salt-urea complexes with triple superphosphate

It has been the experience of the fertilizer industry that urea should not be cogranulated or blended with superphosphate because urea reacts with monocalcium phosphate monohydrate (MCP·H2O) in superphosphate to form an adduct. This reaction releases the water of hydration and causes the product to become wet and sticky or severely caked during storage. The objectives of this study were [1] to test the feasibility of preventing or retarding the reaction by complexing the urea with various salt hydrates and [2] to measure ammonia volatilization from metal salt-urea complexes on the soil surface. Three metal salt-urea complexes — Al(urea)6(NO3)3, Fe(urea)6(NO3)3, and Mn(urea)4Cl2 — were prepared and cogranulated by compaction with pure MCP·H2O or triple superphosphate (TSP) at a mole ratio of MCP:urea as 1:2. These materials were then compared with the same material without metal salts in terms of changes in free water content during a storage period of 6 weeks. Without metal salts a rapid and significant increase in free water content of the cogranulated MCP·H2O + urea or TSP + urea was observed. The increases in free water content were found to range from 1.5% to 1.8%, corresponding to approximately 63% and 78% of the added MCP·H2O that reacted with urea in the cogranulated products. On the other hand, little change or only a slight increase (less than 0.5%) in free water content was observed with the cogranulated metal salt-urea complexes. Ammonia volatilization losses from urea on the soil surface were measured in a period up to 14 d with two soils: Windthorst (pH 7.6) and Savannah (pH 7.0). The fertilizer materials used were granular. In Windthorst soil, the amounts of NH3-N lost were 25% for prilled urea, 11% for Mn(urea)4Cl2, and essentially none for Mn(urea)4Cl2 compacted with TSP at a mole ratio of MCP:urea as 1:1 or 1:2. In Savannah soil, the amounts of NH3-N lost were 39% for prilled urea, 24% for Mn(urea)4Cl2, 15% for Fe(urea)6(NO3)3, and less than 6% for each of the two metal salt-urea complexes compacted with TSP. The acidity that resulted from metal complexing of urea reduced NH3 volatilization from hydrolyzed urea in soils, and additional acidity produced from hydrolysis of MCP·H2O further reduced NH3 losses when materials were applied as multicomponent granules (metal salt + urea + TSP).

Effect of Environmental Factors on Ammonia Volatilization from a Urea-Fertilized Soil

A greenhouse experiment using 15N followed by wind tunnel experiments using a micrometeorological technique were conducted to identify some of the factors that contribute most significantly to ammonia (NH3) volatilization in a simulated semiarid environment following application of urea. An Aridic Calciustolls with high urease activity was subjected to a variety of initial soil moisture contents, rainfall patterns, wind speeds, air-humidity, and urea application methods. Losses of broadcast urea-N in the greenhouse at 42-d harvest, presumably due to NH3 volatilization, were reduced from 40% with a first rain of 1 cm (7 d after fertilizer application) to 13% with a first rain of 4 cm. Nitrogen losses were increased by 8% when initial soil moisture was increased from 21% (≅ permanent wilting point or PWP) to 31%. Wind tunnel experiments verified that nitrogen can be conserved either by heavy initial rain events (showing no NH3 volatilization with application of 2.5 cm rain immediately after urea application) or by banding of urea at a depth of 2.5 cm. Losses were maximized by maintaining adequate moisture in the topsoil for urea hydrolysis without inducing leaching, either by humidifying the air between 80 and 95% or by applications of 8 mm rain every 3 d. Increasing wind velocity from 1.7 to 3.4 ms−1 reduced NH3 loss from 19 to 7.5%, likely due to more rapid drying of the soil surface.

Substitution of Ammonium and Potassium for Added Calcium in Reduction of Ammonia Loss from Surface‐applied Urea

AbstractAmmonia (NH3) volatilization loss from surface application of urea must be reduced if urea is to gain further acceptance for use in pastures and on other non‐ or low‐tillage systems which do not permit soil incorporation. The method used to reduce NH3 loss should not increase costs of the N fertilizer significantly. Preferably, the material used should itself be a fertilizer nutrient.The nitrate salts of the monovalent cations NH+4, K+, and Na+ were tested as substitutes for chloride or nitrate salts of Ca2+ to depress NH3 losses when mixed with surface‐applied urea. Ammonia losses were measured from soils with different cation exchange capacities (CEC) in the laboratory, with residual N quantified by growing sudangrass on the variously treated soils under greenhouse conditions.Laboratory and/or greenhouse data indicate that NH3 loss from surface‐applied urea was most effectively reduced by Ca salts. Substitution of K, Na, and NH4 salts for Ca salts was increasingly effective as soil CEC increased. Monovalent salts were effective in reducing NH3 losses if the soil had exchangeable Ca2+ + Mg2+. In sand, however, monovalent salts did not reduce NH3 losses. The order of effectiveness on nonsandy soils was Na+ = K+ > NH+4 in reducing NH3 loss.Potassium as KNO3 or KCl can be used effectively to partially replace (Ca + Mg) nitrate or chloride salts with urea to reduce NH3 losses. Ammonium nitrate was ineffective in reducing NH3 losses except where high N application rates were used or where little or no soil CEC existed. The efficacy of NH4NO3 seemed to be due to its acidic nature more than displacement of exchangeable Ca2+ + Mg2+.

A Comparison of Calcium Carbonate Precipitation and pH Depression on Calcium‐Reduced Ammonia Loss from Surface‐Applied Urea

AbstractThe role of calcium (Ca) in reducing ammonia (NH3) loss from soil by way of calcium carbonate (CaCO3) precipitation and soil pH depression was investigated by applying increasing rates of urea with fixed ratios of Ca/N in the laboratory and greenhouse. Soil pH, Ca precipitation, and the rate of hydrolysis of added urea were related to reduction of NH3 loss.Calcium/nitrogen ratios of 0.25 were equally effective in reducing NH3 loss independent of N application rates. Higher ratios of Ca/N at at 55 and 110 kg N/ha application rates did not further depress NH3 loss. At application rates of 550 and 1,100 kg N/ha, Ca levels above a Ca/N ratio of 0.25 resulted in additional large depressions of NH3 loss. This additional effect was due to a depression in soil pH from increased Ca activity and a dramatically reduced rate of urea hydrolysis. The chemical reaction of Ca with urea was complete at a Ca/N ratio of 0.25. Additional Ca, if added with a high enough rate of urea (550 and 1,100 kg N/ha) remained soluble and reduced the soil pH and was responsible for one half of the total reduction in NH3 loss.Greenhouse data showed that the addition of Ca with urea increased plant recovery of fertilizer N more than predicted from laboratory data. Nitrogen rates as low as 55 kg/ha, applied in a surface band or as large granules, resulted in improved plant recovery of added N. Broadcast applications at 165 kg N/ha also resulted in good fertilizer N recovery at Ca/N ratios of 0.25 and 0.50.

Ammonia Losses from Surface‐Applied Urea and Ammonium Fertilizers as Influenced by Rate of Soluble Calcium

AbstractPrevious research has shown that applying large amounts of soluble Ca with urea and NH4 fertilizers depressed ammonia (NH3) losses extensively. This paper reports effects of varying amounts of Ca on reduction of this loss. Ammonia loss was progressively less with increasing Ca/N ratios. In the greenhouse, a Ca/urea‐N equivalent ratio of 0.25 reduced NH3 losses to 11% of applied N. In the laboratory, this ratio reduced NH3‐N losses to 42% of applied N; without Ca, N losses were 75%.Soluble Ca was effective in reducing NH3 losses from urea when surface applied to both acid and calcareous soils. Increased acidity from the application of soluble Ca salts on acid soils reduced the amount required to reduce NH3 losses. Soluble Ca applied with (NH4)2SO4 (AS) and NH4NO3 (AN) also reduces NH3 losses from calcareous soils. Reduction of NH3 losses from AN was due solely to lowered soil pH values. However, reduction of NH3 loss from urea and AS was possibly due both to CaCO3 precipitation and soil pH depression.

Ammonia Volatilization from Surface Applications of Ammonium Compounds to Calcareous Soils: VI. Effects of Initial Soil Water Content and Quantity of Applied Water

AbstractAmmonia losses from (NH4)2SO4 (AS) and NH4NO3 (AN) applied to the surface of initially wet and initially dry soils, when followed by irrigation, were generally greater from the initially wet soils, especially when water application rates were < 2.5 cm. The greatest NH3 loss occurred at the lowest water addition and the least loss at the highest water addition. The addition of 20.3 cm of water to a Harkey silty clay loam did not reduce NH3 loss below that found with the addition of 5.1 cm of water. Ammonium was moved deeper into the soil by water in the initially wet soil than into the initially dry soil.Approximately a twofold increase in NH3 loss was observed following the application of AS and AN to the soil through irrigation water compared with NH3 loss following broadcast fertilizer application and subsequent irrigation. Again, initial soil water content influenced total NH3 loss with greater loss occurring from initially wet soil.A direct relationship was found between the loss of water and NH3 in sand. This relationship was not changed by placing a barrier to capillary water and N movement in the soil profile. The barrier greatly reduced absolute NH3 and H2O losses but did not influence the ratio of NH3 to H2O loss.

Ammonia Volatilization and Nitrogen Utilization from Sulfur‐coated Ureas and Conventional Nitrogen Fertilizers

AbstractAmmonia volatilization was measured on acid and calcareous soils receiving sulfur‐coated ureas (SCU) and highly soluble N fertilizers. Surface and mixed applications of SCU‐30 (30% dissolution rate), SCU‐20 (20% dissolution rate), uncoated (NH2)2CO, NH4NO3, and (NH4)2SO4 were made with and without lime to a fallowed acid fine sand. Without lime, top dressed NH4NO3, SCU‐20, SCU‐30, and (NH4)2SO4 lost < 1% while (NH2)2CO lost 18.5% of added N in 14 days. Topdressing lime with N caused more NH3 loss from (NH4)2SO4 than from (NH2)2CO during the intial 48 hours. However, accumulative losses for 14 days were 51.5, 22.5, 9.0, and 1.7% from (NH2)2CO, (NH4)2SO4, SCU‐30, and SCU‐20, respectively. Incorporating the lime with the soil prior to N addition reduced NH3 loss > 50% as compared to surface application, but mixing N with the limed acid soil did not reduce NH3‐N losses. Mixing SCU with the soil appeared to increase release rate of N over topdressing, but this effect was not detected in plant response. Nitrogen uptake by corn (Zea mays L.) on the acid soil substantiated some of the conclusions regarding measured NH3‐N losses.Ammonia losses from N mixed with the finer textured calcareous clay loam were generally insignificant. Surface applied (NH2)2CO and (NH4)2SO4 lost significant amounts of NH3‐N, while losses from SCU and NH4NO3 were negligible.

The Influence of Cation Exchange Capacity and Depth of Incorporation on Ammonia Volatilization from Ammonium Compounds Applied to Calcareous Soils

AbstractThe objective of this study was to determine the influence of soil cation exchange capacity (CEC) and depth of incorporation on NH3‐N volatilization from NH4+‐N compounds applied to calcareous soil. This study was conducted in the laboratory on soils with a wide range of CEC. An increasing CEC resulted in decreasing NH3 losses. Ammonium sulfate produced higher soil pH values and NH3 losses than did NH4NO3. The pH of the soil decreased with increasing NH4NO3 application rates. With NH4NO3, percent NH3‐N losses decreased with increasing application rate; however, with (NH4)2SO4, percent NH3‐N losses increased as the application rates increased.Incorporation of the NH4+‐compounds into the soil reduced NH3 losses. Increasing depths of NH4+‐incorporation resulted in reduced NH3 loss. Losses decreased as the CEC of soil increased. The effectiveness of soil depth in reducing NH3 loss was associated with soil water content. Decreasing the soil water increased the effectiveness of soil incorporation for reducing NH3 losses.Two regression equations were developed to describe NH3 losses with respect to CEC, soil pH, time, NH4+‐N application rate and temperature. Correlation coefficients were 0.86 and 0.81 for (NH4)2SO4 and NH4NO3 systems, respectively.