Ammonia volatilization losses from different fertilizers and effect of several urease inhibitors,CaCl2 and phosphogypsum on losses from urea

The extent of ammonia volatilization losses from urea, ammonium sulphate (AS), and diammonium phosphate (DAP) were determined in soil incubation studies. The effects of some urease inhibitors (thiourea, hyroquinone, 2–4 dinitro phenol and boric acid) and CaCl₂ and phosphogypsum additions on ammonia loss from urea were also studied. Total ammonia volatilization losses were 32.6%, 3.1% and 2.3% of the N applied to the soil as urea, AS and DAP, respectively. Among the chemicals examined in the study, 500 mg H₃BO₃ in 1 kg of the soil decreased the ammonia loss from urea by 21% in comparison with the control. When 50 mg/kg soil of thiourea, 2–4 dinitro phenol or hydroquinone were applied, ammonia volatilization losses were found to be 10%, 3% and 0% less than urea applied alone, respectively. When 2500 mg CaCl₂ was applied to 1 kg of soil with urea, ammonia loss was decreased by 5%. The lowest hydrolysis rate (65%) occurred with the boric acid treatment. The differences between the hydrolysis rates of the other treatments were not statistically significant. Phosphogypsum was found the most effective agent in reducing ammonia losses from urea. When phosphogypsum was mixed at 2.3 times as much as the urea, ammonia loss was about 85% less than that of urea applied alone. Obviously, further work is needed to find out the potential of both boric acid and phosphogypsum as reducing agents of ammonia losses from urea.     

Ammonia volatilization from fertilizers applied to irrigated wheat soils

A series of experiments using flow chambers was undertaken in the field to investigate the effects of stubble and fertilizer management, soil moisture and precipitation on ammonia volatilization following nitrogen application on chromic luvisols. In the first factorial experiment, urea at 100 kg N ha^–1 was applied to the soil surface one, three and six days following irrigation; there were four rice stubble management systems comprising stubble burnt, stubble burnt then rotary hoed, stubble rotary hoed into the soil and stubble retained on the surface. Cultivation almost halved ammonia loss. The higher loss from uncultivated plots was ascribed to an alkaline ash bed on burnt plots, and to higher soil moisture and some retention of urea prills in the crop residue above the soil surface of the stubble retention plots. Average volatilization over a 12 day period following urea application from plots fertilizer one, three or six days after irrigation was 16, 15 and 4 kg N ha^–1, respectively. Daily application of up to 1.7 mm of water did not reduce volatilization and 35 kg N ha^–1 was lost within five days of fertilization. Daily precipitation of 6.8 mm reduced loss to 14 kg N ha^–1. This quantity of rain is uncommon in the region and it was concluded that showery conditions are unlikely to reduce volatilization. The third experiment demonstrated that the quantity of stubble on the soil surface had no effect on volatilization, and all plots lost 25% of applied nitrogen. In the fourth experiment, 100 kg N ha^–1 as urea or ammonium nitrate was either broadcast onto the surface or stubble retention plots, or placed, and partly covered to simulate topdressing with a disc implement. Partial burial of urea reduced ammonia volatilization from 36 to 7 kg N ha^–1, while partial burial of ammonium nitrate reduced loss from 4 to 0 kg N ha^–1.     

The effect of fertiliser type and application rate on denitrification losses from cut grassland in Northern Ireland

Denitrification losses were measured using the acetylene inhibition technique adapted for a coring procedure. Two soils under a cut ryegrass sward were used. One soil was a freely-drained clay loam receiving under 900 mm rainfall annually, the other soil being a poorly-drained silty clay receiving over 1100 mm rainfall annually. Swards at each site received up to 300 kg N ha^–1 yr^–1 of calcium ammonium nitrate (CAN), urea or a new fertiliser mixture GRANUMS (30% ammonium nitrate, 30% urea, 10% ammonium sulphate, 30% dolomite). For both soils the rate of denitrification exceeded 0.1 kg N ha^–1 day^–1 only when the air-filled porosity of the soil was < 30% v/v and soil nitrate was > 2 mg N kg^–1 in the top 10cm of the profile and when soil temperature at 10 cm was > 4°C. When the soils dried such that their air-filled porosity was > 30% v/v, denitrification rates decreased to < 0.08 kg N ha^–1 day^–1. Highest rates (up to 3.7 kg N ha^–1 day^–1) were observed on the clay soil following application of 94 kg N ha^–1 CAN to soil near field capacity in early summer 1986. Losses from CAN were approximately 3 times those from urea for a given application. Denitrification losses from the GRANUMS treatment were, overall, intermediate between those from CAN and urea but the daily losses more closely resembled those from the CAN treatment. The impeded drainage on the clay soil, where soil moisture contents remained close to field capacity throughout the year, showed denitrification losses roughly 3 times those observed on the more freely drained clay-loam for any given treatment. Over a 12-month period, N losses arising from denitrification were 29.0 and 10.0 kg N ha^–1 for plots receiving 300 kg N ha^–1 CAN and urea, respectively, on the well drained clay-loam and 79.0 and 31.1 kg N ha^–1 respectively, for identical plots on the poorly drained clay soil. Annual denitrification losses from control plots were < 1 kg N ha^–1 on both soils.     

Movement and transformations of fertigated nitrogen below trickle emitters and their effects on pH in the wetted soil volume

The movement and transformations of ammonium-, urea- and nitrate-N in the wetted volume of soil below the trickle emitter was studied in a field experiment following the fertigation of N as ammonium sulphate, urea and calcium nitrate. Effects on soil pH in the wetted volume were also investigated.During a fertigation cycle (emitter rate 2lh^–1) applied ammonium was concentrated in the surface 10 cm of soil immediately below the emitter and little lateral movement occurred. In contrast, because of their greater mobility in the soil, fertigated urea and nitrate were more evenly distributed down the soil profile below the emitter and had moved laterally in the profile to 15 cm radius from the emitter. The conversion of applied N to nitrate-N was more rapid when urea rather than ammonium-N was applied suggesting that the accumulation of large amounts of ammonium below the emitter in the ammonium sulphate treatment probably retarded nitrification.Following their conversion to nitrate-N, both fertigated ammonium sulphate and urea caused acidification in the wetted soil volume. Acidification was confined to the surface 20 cm of soil in the ammonium sulphate treatment, however because of its greater mobility, fertigation with urea (2lh^–1) resulted in acidification occurring down to a depth of 40 cm. Such subsoil acidity is likely to be very difficult to ameliorate. Increasing the trickle discharge rate from 2lh^–1 to 4lh^–1 reduced the downward movement of urea and encouraged its lateral spread in the surface soil. As a consequence, acidification was confined to the surface (0–20 cm) soil.     

Fate of Fertilizer15N applied as urea and ammonium sulphate in opium poppy (Papaver somniferum L.) grown under greenhouse conditions

Laboratory incubation and greenhouse experiments were conducted to investigate the comparative effectiveness of urea and ammonium sulphate in opium poppy (Papaver somniferum L.) using¹⁵N dilution techniques. Fertilizer treatments were control (no N), 600 mg N pot^–1 and 1200 mg N pot^–1 (12 kg oven dry soil) applied as aqueous solution of urea or ammonium sulphate. Fertilizer rates, under laboratory incubation study were similar to that under greenhouse conditions. A fertilizer¹⁵N balance sheet reveals that N recovery by plants was 28–39% with urea and 35–45% with ammonium sulphate. Total recovery of¹⁵N in soil-plant system was 77–82% in urea. The corresponding estimates for ammonium sulphate were 89–91%. Consequently the unaccounted fertilizer N was higher under urea (18–23%) as compared to that in ammonium sulphate (9–11%). The soil pH increased from 8.2 to 9.4 with urea whereas in ammonium sulphate treated soil pH decreased to 7.3 during 30 days after fertilizer application. The rate of NH₃ volatilization, measured under laboratory conditions, was higher with urea as compared to the same level of ammonium sulphate. The changes in pH of soil followed the identical trend both under laboratory and greenhouse conditions.     

Relative susceptibility of conventional and experimental nitrogen sources to ammonia loss from flooded rice fields

Urea, the most common N source in Asia, is prone to high loss as ammonia when applied to tropical flooded rice (Oryza sativa L.). Chemical or physical modifications of urea could offer potential in reducing ammonia loss. Two field studies were conducted to identify conventional and experimental N-containing sources loss prone to ammonia less than prilled urea. Relative susceptibility to ammonia loss was inferred from equilibrium ammonia vapor pressure, pNH₃. For the sources studied, ammonia formation and presumably loss were least for guanylurea sulfate (GUS) and sulfur-coated urea (SCU). The slow mineralization and acidifying effect of GUS resulted in negligible ammonia concentration in the floodwater. Amendment of urea with either 5 or 10% paraformaldehyde (ureaform) reduced pNH₃, but never by more than 55%. Coating urea with phosphate rock tended to be less effective than amendment with paraformaldehyde in reducing pNH₃. There was no significant difference in the pNH₃, and presumably ammonia loss, for urea phosphate (17-44-0), urea-urea phosphate (34-17-0), and urea. About 3 days after fertilization, the floodwater pH tended to become higher with NP sources than with urea. This elevation in pH was apparently due to the stimulation of algal photosynthetic activity by added P, and it may explain the failure of a phosphoric acid amendment to urea (urea phosphate) in reducing pNH₃. Ammonia disappearance from broadcast diammonium phosphate (DAP) and ammonium phosphate sulfate (16-20-0) was complete within 3 days after N application, whereas ammonia remained in floodwater for up to 7 days following broadcast application of urea and ammonium sulfate.     

Ammonia volatilization from point-placed urea in upland,sandy soils

The upland fertilization practice in Africa of placing N fertilizer below the soil surface near the plant might be facilitated through use of urea supergranules (USG). Since little is known about N losses from point-placed urea on light-textured African soils, laboratory studies were conducted in a forced-draft system to determine (a) the influence of soil properties on ammonia loss from USG and (b) to compare N loss from USG with that from broadcast N sources. Ammonia loss from 1.1 g USG placed at a 4-cm soil depth ranged from 2.9 to 62% of the added N on six light-textured soils. Ammonia loss was correlated with soil clay content (r = –0.93^**) but not with pH. A more detailed study on a soil from Niger revealed significantly less ammonia loss from either surfaced applied urea (18%) or surface-applied calcium ammonium nitrate (7%) than from USG placed at a 4-cm depth (67%). Amendment of surface-applied urea with 1.7% phenyl phosphorodiamidate (PPD), a urease inhibitor, essentially eliminated ammonia loss (1.9%). An¹⁵N balance confirmed that ammonia volatilization was the major loss mechanism for all N sources. The results suggest that point-placed urea may be prone to ammonia volatilization loss on light-textured African soils moistened by frequent light rainfall. In such cases, broadcast application of urea, CAN, or urea amended with PPD may be less prone to N loss.     

Comparison of several nitrogen fertilisers applied in surface irrigation systems. I. Crop response

The effect of several N carriers applied in the surface irrigation water on the growth, yield and N status of maize was studied in 2 seasons. The carriers applied in the water included anhydrous ammonia, ammonium sulphate, ammonium nitrate, potassium nitrate and urea and they were compared with a preplant band application of anhydrous ammonia and a control treatment. All N treatments received 100 kg N ha^–1. The site used in the second experiment was less responsive to N fertiliser than the first site and the crop growth in the second season was affected by an attack of charcoal rot (Macrophomina phaseolina).Urea, as a N source for fertigation, was superior to the ammonium forms, while the nitrate carriers were the least efficient. Water-run urea increased the maize yield by 27% when compared with the band application in the first season but was 6% lower in the second season. Fertigation allowed N to be applied during the grand period of growth when N stress was most likely to occur. This technique for applying N fertiliser to surface irrigated crops has been adopted by commercial growers.     

Fate of fertilizer nitrogen applied to wheat under simulated mediterranean environmental conditions

Triticum aestivumThe fate of fertilizer nitrogen applied to dryland wheat was studied in the greenhouse under simulated Mediterranian-type climatic conditions. Wheat, L., was grown in 76-cm-deep pots, each containing 50–70 kg of soil, and subjected to different watering regimes. Two calcareous clay soils were used in the experiments, Uvalde clay (Aridic Calciustoll) and Vernon clay (Typic Ustochrept). Fertilizer nitrogen balance studies were conducted using various¹⁵N-labeled nitrogen sources, including ammonium nitrate, urea, and urea amended with urea phosphate, phenyl phosphorodiamidate (a urease inhibitor), and dicyandiamide (a nitrification inhibitor). Wheat yields were most significantly affected by available water. With additional water during the growing period, the recovery of fertilizer nitrogen by wheat increased and the fraction of fertilizer nitrogen remaining in the soil decreased. In the driest regimes, from 40 to 65% of the fertilizer nitrogen remained in the soils. In most experiments the gaseous loss of fertilizer nitrogen, as estimated from unaccounted for¹⁵N, was not significantly affected by water regime. The¹⁵N not accounted for in the plant and the soil at harvest ranged from 12 to 25% for ammonium nitrate and from 12 to 38% for regular urea. Direct measurement of labeled ammonia loss from soil indicated that ammonia volatilization probably was the main N loss mechanism. Low unaccounted-for¹⁵N from nitrate-labeled ammonium nitrate, 4 to 10%, indicated that N losses due to denitrification, gaseous loss from plants, or shedding of anthers and pollen were small or negligible. Amendment of urea with urea phosphate to form a 36% N and 7.3% P product was ineffective in reducing N loss. Dicyandiamide did not reduce N loss from urea presumably because N was not leached from the sealed pots and denitrification was insignificant. Amendment of urea with 2% phenyl phosphorodiamidate reduced N loss significantly. However, band placement of urea at as 2-cm soil depth was more effective in reducing N loss than was amendment of broadcast urea with phenyl phosphorodiamidate.     

Fate of nitrogen applied in different fertilizers to the surface of a calcareous soil in Syria

¹⁵N-labelled ammonium sulphate or¹⁵N-labelled urea were each applied in solutionat a rate of 30 kg N ha^-1 to the surface of 20soil cores (52 mm internal diameter × 100 mm deep)located on a field experiment at the ICARDA station,Tel Hadya, Syria. Recovery of ¹⁵N-label in theammonium, nitrate, organic and/or urea-N pools in thesoil was measured on days 0, 1, 2, 5 and 13 afterapplication. Total recovery of ¹⁵N was initially100%, but by day 13 after application it had declinedto 51% with urea and 73% with ammonium sulphate.Ammonium nitrate labelled either as ammonium or asnitrate was also applied to the soil surface of 8other cores at the same time. ¹⁵N recovery in thefour soil N pools was measured only on day 12 afterapplication. Total recovery of ¹⁵N-label was 75%with labelled ammonium and 57% with labelled nitrate.Volatilization of ammonia from this calcareous soil(pH 8.1) is one probable mechanism of N loss fromammonium and urea fertilizers: with nitrate bothleaching beyond the base of the core (i.e. 100 mm) and denitrification were responsible for Nlosses. These large losses of N immediately afterapplication have implications for fertilizermanagement practices.     

Ammonia volatilization from drill sown rice bays

Ammonia volatilization losses and other N transformations were studied in drill sown rice bays fertilized with urea at various times between permanent flooding (PF) and panicle initiation (PI). Ammonia loss was measured directly with flow chambers and indirectly through application of Freney et al.'s (1985) model. Both techniques indicated that ammonia volatilization was negligible from fields fertilized immediately before PF. Applying 100 kg urea-N ha^–1 to floodwater one day after flooding significantly increased floodwater ammoniacal-N and urea-N content, however the concentrations fell rapidly over the following five days. Fertilizer-N dissolved in the floodwater was in the urea rather than the ammoniacal-N form, indicating slow hydrolysis until it moved into the soil. Floodwater on plots receiving urea one day after PF frequently had more than double the NO₃-N concentration of plots fertilized before flooding.Applying up to 140 kg urea-N ha^–1 at PI increased floodwater ammoniacal-N concentrations from almost zero to over 27 g m^–3, but three days after fertilization there was less than 3 g m^–3 present. Fertilization also increased NH₄-N concentration in the top 40 mm of soil. Higher ammoniacal-N concentration at PI suggests higher urease activity. Floodwater pH at PI was low, with a mean daily maximum of 7.8 and this reduced ammonia loss to less than 1% of the applied N.The results indicate that volatilization from fields fertilized prior to PF is minimal because of the low floodwater pH and ammoniacal-N concentration, while low floodwater pH restricts volatilization from fields topdressed at PI.     

The manufacture and evaluation of granular potassium chloride fertilizers

A finely divided red potassium chloride (KCl) (particle size distribution: 79% <0.5 mm, 20% 1-0.5 mm and 1% 1–2 mm) was granulated by adding eight readily available and relatively inexpensive binders using a rotating drum in the laboratory. The binders used were: urea, pulp and paper waste liquor containing lignosulphonate, urea + pulp and paper waste liquor, Borrebond powder (a commercial product containing lignosulphonate), urea + formaldehyde, ammonium sulphate, ammonium sulphate + pulp and paper waste liquor and a waste liquor containing ammonium sulphate from a Ferritin production plant. Of these, except for urea and urea + pulp and paper waste liquor which produced KCl granules having low critical relative humidity at 30°C (CRH) (<55%) and Borrebond which produced KCl granules of low crushing strength (1.1 kg for 2–3 mm granules) the other five binders produced granules with good size distributions, high crushing strengths (2.0–2.5 kg for 2–3 mm granules), CRH (65–70%) and suitable nutrient contents (K, 46–50%, Cl, 42–47%). These values are very close to those of the standard chipped KCl (crushing strength, 2.5 kg; CRH, 65–70%; K, 50%; Cl, 47%).Crushed chipped KCl (74% <1 mm, 25% 1–2 mm, 1% 2–3 mm) when cogranulated in the pilot plant with the 5 binders found successful in the laboratory, produced granules having similar characteristics as the corresponding ones produced in the laboratory. Granules produced both in the laboratory and the pilot plant had lower abrasion resistance (higher % degradation) than chipped KCl. The abrasion resistance however markedly increased when the fines (<1.4 mm) in the granules were removed.Glasshouse trials using barley as test crop demonstrated that the agronomic values of the KCl prototype granules produced with the 5 binders were similar to chipped KCl and granules produced from the feedstock KCl and water.     

Evaluation and model of temperature and rainfall effects on response to N sources applied to grassland in spring

Direct and residual effects of urea and calcium ammonium nitrate (CAN) on dry matter (DM) response were measured at a total of 12 application times in early spring over three years. The variation in the direct effect was described by models that included temperature and long-term rainfall for CAN and, additionally, short-term rainfall for urea. The operative temperature was the accumulated mean daily air temperature for combined intervals pre-application and postapplication of N. The effect of rainfall was apparent only when the data were adjusted for temperature.Simulation studies with the models indicated that, although the influence of temperature was dominant, rainfall modified it strongly in terms of the relative efficiencies of the two N sources and the magnitude of response. For instance, the temperature-induced increase in DM response to urea between cold and normal years was 402 kg ha^–1 for a specified period, whereas differences between dry and wet years were decreases of 166 and 259 kg ha^–1 in the case of urea and CAN, respectively. Short-term rainfall had a positive effect on response to urea.The experimental values varied widely both between and within years. The direct effect of the application of urea at 50 kg N ha^–1 varied from 0 to 750 kg DM ha^–1, and the residual effect varied from 0 to 1620 kg DM ha^–1. The corresponding values for apparent N recovery varied from 0.1 to 45% and from 7 to 68%, respectively. The efficiency of urea was comparable to, and in instances better than, CAN.     

Relationships between ammonia volatilization and nitrogen fertilizer application rate,intake and excretion of herbage nitrogen by cattle on grazed swards

Grazed pastures emit ammonia (NH₃) into the atmosphere; the size of the NH₃ loss appears to be related to nitrogen (N) application rate.The micrometeorological mass balance method was used to measure NH₃ volatilization from rotationally grazed swards on three plots in the autumn of 1989 and throughout the 1990 growing season. The aim of the research was to derive a mathematical relationship between NH₃ volatilization and N application rate, which would vary between soil type and weather conditions. In both years the plots received a total of 250, 400 or 550 kg N ha^–1 as calcium ammonium nitrate (CAN) split over 6 to 8 dressings. The number of grazing cycles ranged from 7 to 9 for the three N plots.In the last two grazing cycles of 1989, NH₃ losses were 3.8, 12.0 and 14.7 kg N ha^–1 for the 250N, 400N and 550N plots, which was equivalent to 5.3%, 13.9% and 14.4% of the amount of N excreted on the sward, respectively. In 1990, NH₃ losses were 9.1, 27.0 and 32.8 kg N ha^–1 for the 250N, 400N and 550N plots, which was equivalent to 3.3%, 6.9% and 6.9% of the N excreted, respectively. Differences in urine composition between the plots were relatively small. Rainfall and sward management affected the size of the NH₃ volatilization rate. Volatilization of NH₃ was related to N excretion and N application rate.A calculation procedure is given to enable the estimation of NH₃ volatilization from N application rate. Adjustments can be made for grazing efficiency, grazing selectivity, N retention in milk and liveweight gain, concentrate N intake and milking duration. Losses of NH₃ increase progressively with an increase in N application rate until herbage yield reaches a maximum at an application rate of about 500 kg N ha^–1 yr^–1.     

A microplot study of the fate of15N-labelled ammonium nitrate and urea applied at two rates to ryegrass in spring

Confined microplots were used to study the fate of¹⁵N-labelled ammonium nitrate and urea when applied to ryegrass in spring at 3 lowland sites (S1, S2 and S3). Urea and differentially and doubly labelled ammonium nitrate were applied at 50 and 100 kg N ha^–1. The % utilization of the¹⁵N-labelled fertilizer was measured in 3 cuts of herbage and in soil to a depth of 15 cm (soil_0–15).Over all rates, forms and sites, the % utilization values for cuts 1, 2, 3 and soil_0–15 were 52.4, 5.3, 2.4 and 16.0% respectively. The % utilization of¹⁵N in herbage varied little as the rate of application increased but the % utilization in the soil_0–15 decreased as the rate of application increased. The total % utilization values in herbage plus soil_0–15 indicated that losses of N increased from 12 to 25 kg N ha^–1 as the rate of N application was increased from 50 to 100 kg N ha^–1.The total % utilization values in herbage plus soil_0–15 over both rates of fertilizer N application were 84.1, 80.8 and 81.0% for urea compared with 74.9, 72.5 and 74.4% for all ammonium nitrate forms at S1, S2 and S3 respectively. Within ammonium nitrate forms, the total % utilization values in herbage plus soil_0–15 over both rates and all sites were 76.7, 69.4 and 75.7% for¹⁵NH₄NO₃, NH₄ ¹⁵NO₃ and¹⁵NH₄ ¹⁵NO₃ respectively. The utilization of the nitrate moiety of ammonium nitrate was lower than the utilization of the ammonium moiety.The distribution of labelled fertilizer between herbage and soil_0–15 varied with soil type. As the total utilization of labelled fertilizer was similar at all sites the cumulative losses due to denitrification and downward movement appeared to account for approximately equal amounts of N at each site.     

Ammonia volatilization losses from fertilizers applied to acid soil in the field

Losses of ammonia by volatilization from ammonium sulphate and urea applied to soil were studied in field conditions.Losses from ammonium sulphate generally were not large; ammonia volatilization is thus unlikely to be an important pathway of nitrogen loss from cropped soils, and does not explain the low responses to nitrogen fertilizer of wheat grown in the higher rainfall cropping areas of South-Eastern Australia.Losses of nitrogen from ammonium sulphate were not greatly affected by meteorological variables, rate of application, water applicaton or incorporation into soil.The above variables all affected losses of nitrogen from urea, by influencing the rates of solution and hydrolysis of urea, and volatilization of ammonia. Losses ranged from 4 to 50% of the applied urea-nitrogen. Losses of urea-nitrogen were large when evaporation rates were high, and large variations occurred in the rates at which urea could be hydrolyzed.Extrapolation of the results to grazing conditions suggests that ammonia volatilization may result in large losses of nitrogen from short pastures in dry conditions.     

Granulation of finely crystalline ammonium sulphate using calcium oxide and sulphuric acid

Two types of finely crystalline ammonium sulphate (particle size distributions: white type 7% 2–3 mm, 45% 1–2 mm, 48% <1 mm; blue type 1% 2–3 mm, 8% 1–2 mm, 91% <1 mm) were granulated by adding calcium oxide and concentrated sulphuric acid using a rotating drum in the laboratory and pilot plant. The granules had satisfactory physical and chemical properties.The granules made in the pilot plant with 25 kg ammonium sulphate, 0.5 kg CaO, 1.26 litres of water and 0.9 to 1.125 litres of 98.5% H₂SO₄ had 80 to 97% of the granules within the size range of 1–3 mm, abrasion resistance of 0.4 to 0.8% <1 mm, crushing strength of 1.4 to 2.3 kg, critical relative humidity of 65–70%, pH 1.8 to 1.9 and N, S and Ca contents of 19, 24 and 1%. The quality of the granules when stored for 6 months alone or blended together with common fertilizers did not change.A glass house trial using barley demonstrated that the agronomic values of 4 prototype ammonium sulphate granules produced in the laboratory were similar to 3 standard granular ammonium sulphate fertilizers.The process of granulation which could easily be adopted in superphosphate manufacturing plants is recommended for plant scale testing.Provisional New Zealand Patent (No 236,025) applied for.     

The effect of N fertilizer forms on nitrous oxide emissions from UK arable land and grassland

Nitrous oxide emission factors (EFs) were calculated from measurements of emissions from UK wheat crops and grassland, that were part of a wider research programme on N loss pathways and crop responses. Field studies were undertaken in 2003, 2004 and 2005??a total of 12 site-seasons. Nitrous oxide emissions were measured by the closed static chamber method, following the application of various N fertilizer forms (ammonium nitrate (AN), calcium ammonium nitrate (CAN), urea (UR), urea ammonium sulphate and urea ammonium nitrate) at the recommended rates. Emission factors for the growing season (March?CSeptember) ranged from less than 0.1?C3.9?%. In the 2nd year, measurements continued at three sites until the following February; the resulting annual EFs were one-third greater, on average, than those for the growing season. There was some evidence that N₂O emissions from UR were smaller than from AN or CAN, but when this was adjusted for loss of ammonia by volatilization, there was generally little difference between different forms of N. Emissions from UR modified by the addition of the urease inhibitor nBTPT (UR?+?UI) were lower than corresponding emissions from nitrate forms, except under conditions where emissions were generally low, even allowing for indirect emissions, suggesting that the use of a urease inhibitor can provide some mitigation of N₂O, as well as NH₃, emissions. The emission data broadly bear out the relationships obtained in earlier UK studies, showing a strong dependence of N₂O emission on soil wetness, temperature and the presence of sufficient mineral N in the soil, which decreases rapidly after N application mainly as a result of plant uptake. Overall net mean EFs for the whole season (after subtracting background emissions from unfertilized controls) covered a range wider than the 0.3?C3.0?% range of IPCC (2006).     

The effects of nitrogen fertilizer form on the plant availability of phosphate from soil,phosphate rock and mono-calcium phosphate

A glasshouse trial using lettuce as the test crop, and laboratory incubations were used to evaluate the influence of various nitrogen fertilizers on the availability of phosphate from an unfertilized loamy sand soil and from the same soil fertilized with Sechura phosphate rock or monocalcium phosphate. The order in which nitrogen fertilizer form increased plant yield and P uptake from soil alone and from soil fertilized with the rock was ammonium sulphate > sulphurised urea > ammonium nitrate > urea > potassium nitrate. For each rock application (both 30 and 60 mg/pot) and for soil alone, increased P uptake by the plant correlated well with decreased soil pH. In soil fertilized with the soluble P form, monocalcium phosphate, the form of the nitrogen fertilizer had little effect on plant P uptake. Subsequent laboratory incubation studies showed that increased dissolution of soil-P or Sechura phosphate rock did not occur until acidity, generated by nitrification or sulphur oxidation of the fertilizer materials, had lowered soil pH to below 5.5. A sequential phosphate fractionation procedure was used to show that in soils treated with the acidifying nitrogen fertilizers, ammonium sulphate and urea, there was considerable release of Sechura phosphate rock P to the soil, amounting to 42% and 27% of the original rock P added, respectively.     

Ammonium nitrate wastewater treatment by coupled membrane electrolysis and electrodialysis

A process coupling membrane electrolysis and electrodialysis is implemented to treat ammonium nitrate wastewater. Membrane electrolysis produces ammonia and nitric acid while electrodialysis reconcentrates the depleted salt solution. Ammonia is removed continuously by in situ stripping; thus allowing gas production with a constant current efficiency (about 70%). Nitric acid up to 8 mol L^–1 is obtained. The current efficiency of acid production depends on nitric acid concentration. When this concentration varies from 1 to 8 mol L^–1 the average current efficiency is about 58%. Electrodialysis produces a rejected stream containing less than 3 × 10^–3 mol L^–1 of ammonium nitrate.