Evaluation of water potential,fertilizer placement and incubation time on volatilization losses of urea in two northern Idaho soils

Abstract

The increased use of urea as a nitrogen (N) fertilizer source in northern Idaho may require precautions to prevent potential losses via volatilization. The purpose of this study was to determine the effects of urea placement, water potential and time on volatilization losses of N in two northern Idaho soils under laboratory conditions maintained at 25°C. A completely randomized block factorial design with repeated measures [2 soils x 2 urea placement treatments x 4 soil water potentials x 3 replications‐measured at 0, 2, 4, 8, and 16 d] was utilized in this study. The two soils, a DeVoignes silt loam (fine silty, mixed nonacid, frigid Histic Humaquept) and a Santa silt loam (coarse silty, mixed, frigid Ochreptic Fragixeralf), were maintained at water potentials of ‐0.8, ‐2.0, ‐3.0 or ‐6.0 bars. Urea was either surface applied or incorporated into the soils at the rate of 200 kg/ha. Data were analyzed by SAS‐GLM and Omega squared (ω²) values were used to identify the impact of each main effect and interaction. The 4‐factor interaction of urea placement (NIT) x soil (SL) x water potential (WP) x time of incubation (IT), 4–3 factor interactions, 6–2 factor interactions and 4 main effects were found to be significant in this study. Due to the number of significant sources of variation, ω² values were used to assess their relative importance. The urea placement treatment accounted for 31.8% of the variation in this study as N losses after 16 d of incubation from the surface urea applications were 28.35% compared to 6.52% where urea was incorporated into the soil. The incubation time x urea placement interaction was the second most important factor and accounted for 21.98% of the observed variability. Volatilization losses were much greater at all incubation times in the surfaceapplied urea treatment when compared to incorporated urea. The differences in N lost by volatilization increased with time. Soil water potential also affected N volatilization as losses increased with increasing soil moisture levels. When the soil water content was not limiting, substantial volatilization occurred. This may be due to an increased urea hydrolysis rate as the moisture content increases. This study demonstrated that volatilization losses may be significant for surface applications of urea on some Idaho soils. To counter these losses incorporation of urea into the soil should be considered.     

Ammonia volatilization from ammonium sulphate,ammonium nitrate,and urea surface applied to winter wheat on a calcareous soil

Abstract

Ammonia (NH₃) volatilization losses from surface‐applied ammonium sulphate (AS), ammonium nitrate (AN), and urea to winter wheat and the effects of the NBPT [N‐(n‐butyl) thiophosphoric triamide], PG (Phospho‐gypsum), and PR (byproduct‐Pyrite) were determined in a field experiment. Effects on grain yield and protein content of the grain were also measured. Total NH₃ losses from AS, AN, and urea varied from 13.6–19.5%, 4.4–6.4%, and 3.9–12.0% depending on the compounds and their levels added to nitrogen (N) fertilizers, respectively. The compounds added to AS and AN increased NH₃‐N losses with respect to unamended fertilizers (control). On the other hand, while urea treatments with two tons of PG/ha increased NH₃ losses, the other compounds decreased the losses. The highest reductions of NH₃ loss were observed with NBPT 0.50% and NBPT 0.25% by 63.4% and 52.8%, respectively. Although the effect of nitrogeneous fertilizers on total N losses and protein content of wheat grain was found statistically significant (p<0.01), as the compounds applied with N fertilizers have had no significant effect. Also, a negative and highly significant correlation (r = ‐0.69???) was found between total N loss and protein content of the grain.     

Nitrogen losses by volatilization in a corn crop with two tillage systems in the Argentine Pampa

Abstract

Ammonia volatilization from soils is a complex process generally associated with surface applied nitrogen (N) fertilizer. The effect of conventional tillage and no tillage on NH₃ volatilization was evaluated on cultivated corn (Zea maize L.) field in Pampa Húmeda, Argentina. The objectives of this study were a) to determine the amount of N loss by volatilization (NH₃) from urea fertilized soils under two different tillage systems (conventional and no tillage) and two different fertilizer application methods (surface and incorporated application) and b) to relate volatilization losses with environmental factors and biochemical and microbiological properties. This experiment was conducted on a Vertic Argiudoll with a silty clay loam texture in the Argentine Pampa. The site has been in natural grassland for 8 years prior was planted to corn. Following the fertilizer application for conventional tillage and no tillage systems, the daily volatilization loss of NH₃ on the fertilized plots was highest during the first three days. Higher losses of NH₃ occurred in the no‐tillage treatments, with 11.5% and 6.2% of N‐urea lost when the fertilizer was surface applied and incorporated, respectively. For conventional tillage, 8.6 % of the N was lost when the fertilizer was surface applied and 5.4% when the fertilizer was incorporated. Surface application of urea stimulated urease enzyme activity. An opposite effect was observed when the urea was incorporated. Environmental changes conditioned the availability of energy substrates for microorganisms, which resulted in different rates of intensity of biochemical reactions in the soil. Multiple regression equations showed differences between surface applied urea and incorporated urea treatments due to the latter avoiding the direct exposure of the fertilizer to atmospheric conditions.     

Effects of Slow‐Release Fertilizers on Tomato Growth and Nitrogen Leaching

Tomatoes (Lycopersicon esculentum Mill.) were grown in 9.46‐L plastic pots in a glasshouse for evaluation of their growth and nitrogen (N) losses through leaching. Plants were fertilized with either ammonium nitrate (AN) or one of three slow‐release N fertilizers. The slow‐release N fertilizers were Georgia Pacific liquid 30‐0‐0 (L30), Georgia Pacific granular 42‐0‐0 (N42), and Georgia Pacific granular 24‐0‐0 (N24). Each fertilizer was applied at 112 low N rate (L) and 224 high N rate (H) kg N ha^?1. The pots were filled with either a sandy soil from Florida or a loam soil from Georgia. Increasing the N rate did not influence shoot biomass at 19 days after transplanting (DAT) and increased biomass production at 77 DAT. Shoot biomass differed significantly among fertilizer treatments. The accumulation of N in shoots was significantly influenced by fertilizer source, rate, and soil type. The plants grown in the loam soil accumulated significantly more N than those grown in the sandy soil with the same treatment. In the loam soil, the highest and lowest N accumulations occurred in the N42‐H and N24‐L treatments, respectively; and in the sandy soil the corresponding treatments were AN‐H and N24‐L. The amount of N leached varied with the different fertilizers, soils, and time. The net leaching of N ranged from ?0.4% to 6.3% of the fertilizer N applied for the loam soil and 6.5% to 32.9% for the sand soil. The net amount of N leached from the loam soil at both high and low application rates declined in the following order: AN > N24 > N42 > L30; the corresponding order for the sandy soil was AN‐H > N42‐H > L30‐H > N24‐H. L30 had the least leaching potential, and ammonium nitrate had the most. Slow‐release fertilizers had significantly less leaching N than did ammonia nitrate.     

Dicyandiamide (DCD) research in agriculture in the mid‐Atlantic region

Abstract

Numerous experiments have been conducted in Maryland and Pennsylvania since 1981 to determine if adding the nitrification inhibitor dicyandiamide (DCD) to an ammonium‐containing or producing N fertilizer source would increase the efficiency of that source with turfgrass, wheat, or corn. Greater yields per unit of fertilizer N were attained in three of eight experiments with wheat when DCD was included with an early spring application of N as urea or UAN. There was no significant beneficial effect of DCD on turf clipping yields or color in the 3 years of the turf study or on corn grain yields in the 22 field comparisons of N fertilizer with and without DCD. In five of the 22 comparisons with corn, there was a significantly lower grain yield with DCD than when it was not included. In three of these five cases, it was hypothesized that the lower yields with DCD were due to increased NH₃ volatilization from urea or urea‐ammonium nitrate solutions containing DCD that were surface‐applied to no‐till corn. It was concluded that there was little likelihood that the inclusion of a nitrification inhibitor such as DCD with N fertilizer would increase N fertilizer efficiency with corn or turf on the predominantly well‐drained silt loam soils in the two states.     

Ammonia volatilization from five nitrogen compounds used as fertilizers following surface application to soils

Measurements were made of the volatilization of ammonia from mono-ammonium phosphate (MAP), di-ammonium phosphate (DAP), ammonium sulphate (AS), ammonium nitrate (AN) and urea, applied to the surface of five contrasting soils. The compounds were applied as solids, at a rate equivalent to 100 kg N ha^?1, to samples of moist soil packed into columns (48 mm diameter) and placed individually in jars through which a stream of air was passed for a period of 8 d. Volatilization ranged from nil to 53% of the N applied, with both the nature of the compound and soil type having large effects. Taking all combinations into account, there was a close relationship between the extent of volatilization, expressed as a percentage of the ammonium or urea N, and the pH attained after 24 h by the corresponding mixtures of soil and compound. Using the results of these and other experiments, the proportion of fertilizer N volatilized as ammonia is estimated to be about 3.4% over the UK as a whole.     

Influence of ammonia fertilization on cotton production in conservation tillage systems

Abstract

Field studies were conducted to determine the influence of ammonia fertilization on cotton grown in conservation tillage systems. The studies were located on a Decatur silt loam (Rhodic Paleudult) in the Limestone Valley and a Norfolk sandy loam (Typic Paleudult) in the Coastal Plain of Alabama. Winter annual legumes, crimson clover (Trifolium incarnatum L. at the Norfolk site) and hairy vetch (Vicia villosa Roth at the Decatur site) were established as whole plots along with a winter fallow area. Sources of fertilizer differing widely in their NH₄+‐N contents were used for split plot treatments applied at time of cotton (Gossypium hirsutum L.) planting. Fertilizer treatments included calcium nitrate, ammonium nitrate, urea, urea with dicyandiamide, and a no N check. The cotton was planted with a strip‐till conservation planter. Nitrogen production by winter legumes was adequate to meet N requirements for cotton on the Decatur silt loam (67 kg N/ha) but not at the Norfolk sandy loam site (101 kg N/ha). Cotton populations were 24% higher in fallow than legume whole plots. Differences in plant growth and N concentrations were highly variable and treatment trends were not found. Seed cotton yields were 4% higher in fallow than legume plots. Maximum populations and yields were achieved with ammonium nitrate in fallow area and urea in legume areas.     

灌溉施用氮肥后氮素在土壤中的转化及淋失状况: 土柱模拟研究

A soil column method was used to compare the effect of drip fertigation (the application of fertilizer through drip irrigation systems, DFI) on the leaching loss and transformation of urea-N in soil with that of surface fertilization combined with flood irrigation (SFI), and to study the leaching loss and transformation of three kinds of nitrogen fertilizers (nitrate fertilizer, ammonium fertilizer, and urea fertilizer) in two contrasting soils after the fertigation. In comparison to SFI, DFI decreased leaching loss of urea-N from the soil and increased the mineral N (NH₄⁺-N + NO₃^--N) in the soil. The N leached from a clay loam soil ranged from 5.7% to 9.6% of the total N added as fertilizer, whereas for a sandy loam soil they ranged between 16.2% and 30.4%. Leaching losses of mineral N were higher when nitrate fertilizer was used compared to urea or ammonium fertilizer. Compared to the control (without urea addition), on the first day when soils were fertigated with urea, there were increases in NH₄⁺-N in the soils. This confirmed the rapid hydrolysis of urea in soil during fertigation. NH₄⁺-N in soils reached a peak about 5 days after fertigation, and due to nitrification it began to decrease at day 10. After applying NH₄⁺-N fertilizer and urea and during the incubation period, the mineral nitrogen in the soil decreased. This may be related to the occurrence of NH₄⁺-N fixation or volatilization in the soil during the fertigation process.     

Ammonia volatilization from nitrogen fertilizers with and without gypsum

Abstract. Ammonia volatilization with and without gypsum incorporation was measured in Gujranwala soil (Udic Haplustalf) in an incubation study using different nitrogen fertilizers e.g. urea, ammonium sulphate (AS), calcium ammonium nitrate (CAN), and urea nitrophos (UNP). Nitrogen from different fertilizers was applied at the rate of 200 mg N kg⁻¹ to two sets of soils in plastic bags (1.0 kg soil) and plastic jars (0.5 kg soil). Soil moisture was maintained at field capacity. Application of urea increased soil pH to 9, three hours after its addition. Ammonium sulphate and calcium ammonium nitrate had little effect on soil pH. Ammonium volatilization losses from fertilizers were related to the increase in soil pH caused by the fertilizers. Consequently maximum losses were recorded due to application of urea. Losses through ammonia volatilization were significantly lower with AS, CAN and UNP in descending order. Gypsum incorporation significantly reduced the losses. Therefore, application of gypsum to soil before urea may substantially improve N use efficiency for crop production by reducing N losses.     

Calcium chloride and ammonium thiosulfate as ammonia volatilization inhibitors for urea fertilizers

Abstract

Surface‐applied urea fertilizers are susceptible to hydrolysis and loss of nitrogen (N) through ammonium (NH₃) volatilization when conditions favorable for these processes exist. Calcium chloride (CaCl₂) and ammonium thiosulfate (ATS) may inhibit urease activity and reduce NH₃ volatilization when mixed with urea fertilizers. The objective of this study was to evaluate the effectiveness of CaCl₂ and ATS as urea‐N loss inhibitors for contrasting soil types and varying environmental conditions. The proposed inhibitors were evaluated in the laboratory using a closed, dynamic air flow system to directly measure NH₃ volatilization. The initial effects of CaCl₂ on ammonia volatilization were more accentuated on an acid Lufkin fine sandy loam than a calcareous Ships clay, but during volatilization periods of ≥ 192 h, cumulative N loss was reduced more on the Ships soil than the Lufkin soil. Calcium chloride delayed the commencement of NH₃ volatilization following fertilizer application and reduced the maximum N loss rate. Ammonium thiosulfate was more effective on the Lufkin soil than the Ships soil. For the Lufkin soil, ATS reduced cumulative urea‐N loss by 11% after a volatilization period of 192 h. A 20% (v/v) addition of ATS to urea ammonium nitrate (UAN) was most effective on the coarse textured Lufkin soil whereas a 5% addition was more effective on the fine textured, Ships soil. Rapid soil drying following fertilizer application substantially reduced NH₃ volatilization from both soils and also increased the effectiveness of CaCl₂ but not ATS. Calcium chloride and ATS may function as limited NH₃ volatilization inhibitors, but their effectiveness is dependent on soil properties and environmental conditions.     

Ammonia volatilization from nitrogen fertilizers surface-applied to corn (Zea mays) and grass pasture (Dactylis glomerata)

Summary The major agronomic concern with NH₃ loss from urea-containing fertilizers is the effect of these losses on crop yields and N fertilizer efficiency. In this 2-year study, NH₃ volatilization from surface-applied N fertilizers was measured in the field, and the effects of the NH₃ losses detected on corn (Zea mays L.) and orchardgrass (Dactylis glomerata L.) yield and N uptake were determined. For corn, NH₄NO₃ (AN), a urea-AN solution (UAN), or urea, were surface-broadcast at rates of 0, 56 and 112 kg N ha^–1 on a Plano silt loam (Typic Argiudoll) and on a Fayette silt loam (Typic Hapludalf). Urea and AN (0 and 67 kg N ha^–1) were surface-applied to grass pasture on the Fayette silt loam. Significant NH₃ losses from urea-containing N sources were detected in one of four corn experiments (12%–16% of applied N) and in both experiments with grass pasture (9%–19% of applied N). When these losses occurred, corn grain yields with UAN and urea were 1.0 and 1.5 Mg ha^–1, respectively, lower than yields with AN, and orchardgrass dry matter yields with urea were 0.27 to 0.74 Mg ha^–1 lower than with AN. Significant differences in crop N uptake between N sources were detected, but apparent NH₃ loss based on N uptake differences was not equal to field measurements of NH₃ loss. Rainfall following N application markedly influenced NH₃ volatilization. In corn experiments, NH₃ loss was low and yields with all N sources were similar when at least 2.5 mm of rainfall occurred within 4 days after N application. Rainfall within 3 days after N application did not prevent significant yield reductions due to NH₃ loss from urea in grass pasture experiments.     

Ammonia volatilization from Vertisols

Farmers want to minimize losses of nitrogen (N) by volatilization of ammonia when adding fertilizers and improve fertilizer recovery of N by plants. We aimed to quantify the losses of N through NH₃ volatilization as affected by soil moisture content, type of fertilizer, and placement method in Vertisols in Kenya, and conducted three experiments for the purpose under controlled conditions in the laboratory. We found that NH₃-N losses were greatest at 80% water holding capacity, which we ascribed to the ready availability of water to dissolve the fertilizer at that water content. The soil's cation exchange capacity (CEC) did not influence volatilization, whereas the soil's pH indicated the potential of the soil to volatilize ammonia. Ammonia losses from the fertilizers were in the order urea > ammonium sulphate > ammonium nitrate applied. Incorporating fertilizer within the 0–5 cm soil layer more than halved NH₃ volatilization but did not prevent it completely. These results indicate that soil pH, rather than CEC, is the main inherent characteristic influencing ammonia volatilization from Vertisols. Ammonium-based fertilizers should be incorporated within the 0–5 cm soil layer, or preferably somewhat deeper, to avoid losses via NH₃ volatilization, particularly in alkaline soils. Nitrate fertilizers are preferable to urea where the risks of NH₃ volatilization are large, provided due consideration is given to denitrification risks.     

Comparison of ammonium sulfate and urea as nitrogen sources in rice production

Wetland rice agriculture is the major anthropogenic source of methane, an important greenhouse gas. Methane emissions are less when ammonium sulfate (AS) rather than urea is the nitrogen (N) source. However, an agronomic advantage of AS over urea has not been established. The objectives of this study were: (i) to compare the effectiveness of AS, urea, and urea plus elemental sulfur (S) as sources of N in flooded rice culture, (ii) to compare fertilizer recovery of each source of N from application at preflood (PF) and panicle initiation (PI), and (iii) to determine if there is a response to S by rice grown on a soil with a less than optimum level of available S. ‘Cypress’ rice was . drill‐seeded in a Crowley silt loam soil (fine, montmorillonitic, thermic Typic Albaqualf) of 7.25 to 10.75 mg S kg^‐1. Ammonium sulfate, urea, or urea plus S was applied in split applications of 101 kg N ha^‐l PF and 50 kg N ha^‐1 PI. Microplots with retainers and ¹⁵N‐labeled N were used. Unlabeled N was used in field plots. Microplots were harvested at 50% heading, while field plots were harvested at maturity. Dry matter and total N accumulation at 50% heading and at maturity were similar regardless of N source. Grain dry matter yields were 8.54, 8.47, and 8.79 Mg ha^‐1 for AS, urea, and urea plus S treatments, respectively. Greater N recovery was generally found from N application at PI than at PF, but this was not reflected by an increase in grain yield. No response to S was detected, although grain yields were slightly higher when S‐containing fertilizers were used. Ammonium sulfate and urea were equally effective for flooded rice production in Louisiana.     

不同种类氮肥对紫色土表面电化学性质的影响

以紫色土为研究对象,采用土柱淋溶方法,研究了不同种类氮肥对紫色土表面电化学性质的影响。结果表明:氮肥处理的紫色土表面电荷量较原土大,增加量在0.05～0.7 cmol kg-1;在低氮水平(100、200 mg kg-1)下,紫色土表面电荷量为尿素硫铵硝铵;而在高氮水平(300、400 mg kg-1)下,表面电荷量为硫铵尿素硝铵。与原土相比,施肥处理的紫色土比表面积有所增加,其中施用100 mg kg-1尿素的增加量最大,较原土增加了78.04%,且尿素处理对土壤比表面积的影响显著高于其余两种氮肥处理;而400 mg kg-1硫铵处理的增加量最少,只增加了0.06%。在同一个施氮水平下,硫铵处理的土壤表面电荷密度和电场强度最大,而尿素处理的最小;低氮施肥处理对电荷密度和电场强度的影响明显高于高氮施肥处理。可见,不同氮肥种类和施氮水平由于电解质体系类型和浓度的差异,引起土壤pH变化,最终对土壤电化学性质产生影响,从而改变土壤养分的保蓄性和有效性。在本试验条件下,非电解质体系在低浓度下能显著影响紫色土表面电化学性质,而强电解质在高浓度下影响效果较为明显。     

不同氮肥形态的氨挥发损失比较

利用从德国引进的农田土壤氨挥发风洞法测定系统,对不同N肥形态的肥料进行对比实验。结果表明,在相同施N量条件下,硝酸铵、硝酸铵钙、硫硝酸铵的氨挥发损失分别比尿素减少22.5%、3.2%和8.3%,不同N肥的氨挥发损失差异很大。相同条件下,尿素的氨挥发损失为25.7%,添加DMPP后氨挥发损失为27.6%;硫硝酸铵的氨挥发损失为18.6%,添加DMPP后为20.6%;添加DMPP对尿素和硫硝酸铵的氨挥发影响不显著。     

Ammonia loss following surface application of urea fertilizers to a calcareous soil

Abstract

N loss by volatilization was measured for surface‐applied granular urea and ammonium nitrate, liquid urea‐ammonium nitrate and liquid acid urea in closed containers. Urea‐containing fertilizers lost between 10 and 451 of the N added within 10 days. The presence of a straw mulch accentuated the losses. N volatilization losses from acid urea solutions were significantly less than from granular urea. Addition of water following surface application of granular urea significantly reduced the loss of N as ammonia from the soil. The results of this laboratory study indicate that use of acid urea for surface application of N fertilizers may reduce N volatilization losses relative to granular urea, but losses still exceed those from ammonium nitrate.     

Reducing NH3, N2O and {\text{NO}}_3^ - –N losses from a pasture soil with urease or nitrification inhibitors and elemental S-amended nitrogenous fertilizers

A 3-month field experiment comparing nitrogen (N) losses from and the agronomic efficiency of various N fertilizers was conducted on a sandy loam (Typic Hapludand) soil at Ruakura AgResearch farm, Hamilton, New Zealand during October to December 2003. Three replicates of seven treatments: urea, urea + the urease inhibitor N-(n-butyl) thiophosphoric triamide (trade name Agrotain), urea + Agrotain + elemental sulphur (S), urea + double inhibitor [DI; i.e., Agrotain + dicyandiamide (DCD)], diammonium phosphate (DAP), DAP + S, each applied at 150 kg N ha⁻¹, and control (no N). After fertilizer application, soil ammonium () and nitrate () concentrations (7.5-cm soil depth), ammonia (NH₃) volatilization, nitrate () leaching, nitrous oxide (N₂O) emission, pasture dry matter, and N uptake were monitored at different timings. Urea applied with Agrotain or Agrotain + S delayed urea hydrolysis and released soil at a slower rate than urea alone or urea + DI. Urea applied with DI increased NH₃ volatilization by 29% over urea alone, while urea + Agrotain and urea + Agrotain + S reduced NH₃ volatilization by 45 and 48%, respectively. Ammonia volatilization losses from DAP were lower than those from urea with or without inhibitors. Total reduction in leaching losses for urea + DI and urea + Agrotain compared to urea alone were 89% and 47%, respectively. Application of S with urea + Agrotain reduced leaching losses by an additional 6%. Nitrous oxide emissions were higher from the DAP and urea alone treatments. Urea applied with DI and urea + Agrotain reduced N₂O emissions by 37 and 5%, respectively, over urea alone. Compared to urea alone, total pasture production increased by 20, 17, and 15% for urea + Agrotain + S, urea + Agrotain, and urea + DI treatments, respectively, representing 86, 71, and 64% increases in N response efficiency. Total N uptake in urea + Agrotain, urea + Agrotain + S, and urea + DI increased by 29, 22, and 20%, respectively, compared to urea alone. These results suggest that the combination of both urease and nitrification inhibitors may have the most potential to reduce N losses and improve pasture production in intensively grazed systems.     

Modeling of Nitrogen Losses Through Ammonia Volatilization in Second-season Corn

ABSTRACT

Knowledge on the behavior of cumulative N-NH₃ volatilization is important for defining the strategies to reduce the N losses, as well as increasing the efficiency of nitrogen fertilization in different environments. The present study, which uses nonlinear models, aims at assessing the cumulative N-NH₃ losses through volatilization by applying different rates of urea over time to two soils cultivated with second-season corn. Two experiments were carried out; one in a clayey Oxisol, and another in a sandy-clay loam Ultisol in a randomized block experimental design. N-NH₃ volatilization was quantified by using semi-open static chambers and spectrophotometry (salicylate blue). The cumulative N-NH₃ losses were similar at both rates of urea and in both soils assessed, ranging from 34.04% to 43.15% of the N applied. The highest N-NH₃ volatilization occurred from 1.03 to 6.48 days after applying the fertilizer, and the highest volatilization rates ranged from 0.90 to 2.91 kg ha^-1 d^-1. The shortest time to reach the highest volatilization rate, associated with the highest daily rate of N-NH₃ volatilization, was seen in the Ultisol. Although the volatilizations accumulated in both soils were similar, this result was only seen due to the climatic conditions after applying the fertilizer, which contributed to minimize the N-NH₃ losses. The use of nonlinear models has shown an appropriate data adjustment, providing parameters that help to understand the behavior of N-NH₃ volatilization accumulated over time in second-season corn.     

Response of tomato to rates and methods of placement of urea and ammonium sulfate as affected by dwell,a nitrification inhibitor

Abstract

The effectiveness of Dwell, a nitrification inhibitor, was tested in a greenhouse with two fertilizers and three Arizona soils. Tomato plants (Lycopersicum esculentum Mill., cv. Row Pak) were grown in ABS plastic columns 10 cm diameter and 50 cm long containing 4500 g soil. Urea and ammonium sulfate (AS) were applied at 112 and 224 kg N/ha and Dwell (5‐ethoxy‐3‐trichloromethyl‐l,2,4‐thiadiazole) was applied at rates of 0 and 1.27 kg/ha of active ingredient. Both fertilizers and Dwell were added by mixing uniformly or in a band. Dwell increased ? uptake by 41%. The highest ? uptake was with Dwell with the highest urea rate, but Dwell was effective with both fertilizers in all soils. The lowest response to Dwell was with AS‐Laveen loam treatment, whereas the highest response, but the lowest ? uptake, was with urea ‐ Vinton loamy sand treatment. Dwell did not affect the inorganic‐N contents of the soils.     

Effects of nitrification inhibitors on transformations of urea nitrogen in soils

The effects of three patented nitrification inhibitors on transformations of urea N in soils were studied by determining the effects of these compounds (10 μg/g of soil) on urea hydrolysis, ammonia volatilization. and production of ammonium, nitrite, and nitrate in soils incubated under aerobic conditions (30°C, 60% WHC) after treatment with urea (400 μg of urea N/g of soil). The inhibitors used (N-Serve, ATC, and CL-1580) had little, if any, effect on urea hydrolysis, but they retarded nitrification of the ammonium formed by urea hydrolysis and increased gaseous loss of urea N as ammonia. They also decreased the amount of (urea + exchangeable ammonium + nitrite + nitrate) — N found in urea-treated soils after various times.Two of the soils used accumulated substantial amounts of nitrite(> 160 μg of nitrite N/g of soil) when incubated under aerobic conditions after treatment with urea. Addition of nitrification inhibitors to these soils eliminated or substantially reduced nitrite accumulation and greatly retarded nitrate formation, but had little, if any, effect on the recovery of urea N as (urea + exchangeable ammonium + nitrite + nitrate + ammonia) — N after various times. This finding and other observations reported indicate that the “nitrogen deficits” observed in studies of urea N transformations in soils may not largely be due to gaseous loss of urea N through chemodenitrification and are at least partly due to volatilization and fixation of the ammonium formed by urea hydrolysis in soils. The work reported also indicates that N-Serve and other nitrification inhibitors may prove useful for reduction of the nitrite toxicity problems associated with the use of urea as a fertilizer but that application of such inhibitors in conjunction with fertilizer urea, when surface applied, may promote gaseous loss of urea N as ammonia.