Surface-applied Urea Research Articles

Evaluating How Enhanced Efficiency Nitrogen Fertilizers Improve Agricultural Sustainability: Greenhouse Multi-Phase Tracking System

The vast consumption of nitrogen-based fertilizers is a significant source of environmental pollutants in all phases. While enhanced-efficiency nitrogen fertilizers (EENFs) improve N-use efficiency and reduce environmental impact, their performance depends on local conditions. Here, we present a relatively simple soil–fertilizer–plants greenhouse setup for the multi-phase tracking of N species of the effects of EENFs. We compared the environmental and agronomic performance of three urea-based EENFs (urea embedded with urease inhibitors, 2-month, and 4-month controlled release urea) and the common split surface application of the granulated urea. We tested the fertilizer applications on basil seedlings for three consecutive growing cycles. The analyses carried out included nitrogen recovery in plant biomass, soil, drainage, and NH3 and N2O emissions. This multi-phase research indicates that tested EENFs perform better than the standard surface-applied urea. The four-month controlled-release urea fertilizer matched the basil N demand the best, significantly increasing yield and improving nitrogen use efficiency while reducing NO3− leaching and NH3 and N2O emissions. The presented soil–fertilizer–plants experimental setup provides a relatively easy-to-handle system for the comprehensive tracking of N dynamics, including plant response. It allows stakeholders to estimate and improve fertilization sustainability.

Efficacy of a newN-(n-butyl) thiophosphoric triamide formulation in reducing ammonia volatilization from urea-based fertilizers

N-(n-Butyl)thiophosphoric triamide (NBPT) has been reported to reduce ammonia volatilization from surface-applied urea and urea ammonium nitrate (UAN). A new NBPT formulation (ARM U™, 18% NBPT) that contains a polymer allowing for lower application rate of NBPT was evaluated for its efficacy relative to Agrotain®(30% NBPT) and Arborite®(24% NBPT). Trials consisted of (i) a greenhouse study that compared two rates of ARM U-treated urea (360 and 540 mg NBPT kg−1urea) with Arborite- or Agrotain-treated urea (480 and 600 mg NBPT kg−1urea, respectively) and (ii) a field study that compared urea and UAN treated with either ARM U (360 mg NBPT kg−1urea) or Agrotain (600 mg NBPT kg−1urea) at two sites. Static chambers fitted with acid-charged discs were used to measure ammonia volatilization at six or seven dates over 28 d. In the greenhouse study, ammonia volatilization was reduced by 96% with either ARM U or Agrotain and 95% with Arborite. In the field study, ARM U and Agrotain reduced ammonia volatilization from urea by 80% and 66%, respectively, across sites. Similarly, ammonia volatilization from UAN was reduced by 46% and 60% with ARM U and Agrotain, respectively. Despite the lower NBPT application rates with ARM U, ammonia reduction by ARM U, Agrotain, and Arborite was not significantly different. The addition of ARM U to urea and UAN enabled lower application rate of NBPT without compromising its efficacy.

Ammonia losses following surface application of enhanced-efficiency nitrogen fertilizers and urea

The so-called “enhanced-efficiency N fertilizers” were developed to mitigate ammonia losses from surface-applied urea (UR) and thereby increase N use efficiency and crop yield. However, research is needed to assess the efficiency of these products in mitigating ammonia emission. The aim of this study was to compare volatilization losses of ammonia following application of UR treated with B and Cu (B-Cu-UR), UR treated with dicyandiamide (DCD) and N-(n-butyl) thiophosphoric triamide (NBPT) (DCD-NBPT-UR), UR treated with humic substances (HS-UR), UR treated with NBPT (NBPT-UR), polymer S-coated UR (PSCUR), S-coated UR (SCUR), and untreated and uncoated UR (UR). Fertilizers (at a rate of 2355 mg N kg−1) were applied over the soil surface, and volatilized ammonia was quantified for 60 d under controlled conditions using a static closed chamber. Use of DCD-NBPT-UR increased ammonia emissions in comparison to UR by blocking nitrification and keeping the soil pH high, the latter resulting from UR hydrolysis. Urease complexation by the inhibitor and gradual N release resulted in low losses of ammonia by NBPT-UR and PSCUR, respectively. Compared to UR, BCu-UR delayed and slightly decreased ammonia volatilization. HS-UR, SCUR, and UR fertilizers had similar ammonia losses. Humic substances most likely did not act on urea-N complexation or even on decreasing urease activity, whereas immediate release of the nutrient by SCUR was noted. NBPT-UR and PSCUR could substitute for UR, aiming to mitigate ammonia volatilization.

Impact of the oasis effect on wind tunnel measurements of ammonia volatilization from urea

The validity of emission factors derived from small-scale measurements of ammonia (NH3) volatilization has been questioned in the literature because gaseous NH3 concentration gradients differ at the edge of the measurement plot and may result in higher emissions than at field scale. We studied this “oasis effect” using two very long (22 m) wind tunnels constructed indoors over soil plots fertilized with surface-applied urea (20 g N m−2). We hypothesized that NH3 flux would be highest at the start of the tunnel and decrease with distance. Air NH3 concentration was measured every 2 m along each tunnel for 2 wk after urea application; NH3 flux did not decrease along the length of the tunnels. Of the 60 measurement periods, when there was significant NH3 volatilization, only two had a significant nonlinear relationship (P ≤ 0.05) between NH3 concentration and distance. For the other periods, the NH3 concentration increased linearly with distance (P ≤ 0.05). The background NH3 concentration difference between halves of the tunnels was not significantly related to NH3 flux difference (P > 0.1). Our results indicate that wind tunnel measurements of NH3 volatilization fertilized using urea are not impacted by a measurable oasis effect.

Ammonia volatilization following nitrogen fertilization with enhanced efficiency fertilizers and urea in loblolly pine (Pinus taeda L.) plantations of the southern United States

Ammonia (NH3) volatilization losses following surface application of urea and three enhanced efficiency nitrogen (N) containing fertilizers (EEFs) were compared in six thinned mid-rotation loblolly pine (Pinus taeda L.) stands across the southern United States. All fertilizer treatments were labeled with 15N (∼370‰, 0.5 AP) and applied during two different seasons (spring, summer) in 2011 to open chamber microcosms. Individual microcosms were sampled 1, 15 and 30days after fertilization to estimate remaining 15N. Losses of fertilizer N were determined using a mass balance calculation. Significantly less N loss occurred following fertilization with EEFs compared to urea after all sampling days for both seasons. Because root uptake was eliminated in the microcosms and there was no leaching of 15N below the microcosms, the most likely loss pathway of the 15N from the microcosms was NH3 volatilization. There were generally no differences among the individual EEFs. Following spring application, the mean NH3 volatilization during the 30day experiment ranged from 4% to 26% for the EEFs compared to 26–40% for urea. In summer, mean NH3 volatilization for EEFs ranged from 8% to 23% compared to 29–49% for urea. This research highlights the potential of EEFs to reduce loss of fertilizer N in forest systems, potentially increasing fertilizer N use efficiency in these pine plantations.

Value of copper, zinc, and oxidized charcoal for increasing forage efficiency of urea N uptake

Volatilization losses reduce the efficiency of surface-applied urea for crop N uptake, and can be controlled using urease inhibitors to retard hydrolysis or by the presence of other amendments that enhance retention of NH4+ formed by urea hydrolysis. A greenhouse study was conducted to evaluate the effectiveness of oxidized charcoal (OCh; 150gkg−1 fertilizer) applied with or without Cu and/or Zn (∼0.5–2gkg−1 fertilizer), and of Cu and/or Zn applied without OCh, for increasing uptake of urea 15N by a common tropical pasture grass, capim-Mombaça (Panicum maximum Jacq. Cv. Mombaça), grown on a coarse-textured Oxisol. Cuttings were collected 5, 14, 28, 42, and 56days after surface placement of amended or unamended urea pellets to estimate dry matter production, total N uptake, and 15N recovery. Soil sampling was carried out in conjunction with the first and fourth cuts to evaluate exchangeable NH4+ and NO3− concentrations. At the concentrations studied, OCh was more effective than Cu and/or Zn for prolonging NH4+-N availability in urea-treated soil; however, OCh alone or in combination with Zn and Cu had no effect on biomass production or N recovery and can safely be eliminated as a useful option for pasture improvement. The most promising amendment was Zn, which significantly increased total N uptake and the efficiency of urea N fertilization. The use of Zn in conjunction with urea has practical potential to improve forage production on tropical soils.

Effect of Mixed Urease Inhibitors on N Losses From Surface-applied Urea

The effect of mixed urease inhibitors on NH3 volatilization from surface-applied urea was studied. The results showed that mixed urease inhibitors could effectively reduce NH3 volatilization. Mixed urease inhibitors of 0.05% N-(n-butyl)thiophosphoric triamide (NBPT) and 0.05% N-(n-propyl) thiophosphoric triamide (NPPT) reduced NH3 volatilization of23.8% or 28.8% compared with the treatments with single NBPT or NPPT. Mixed inhibitors showed more effectiveness on slowing urea hydrolysis and maintaining lower soil NH4+ concentration for a long time than single inhibitor.

Applied Model for Estimating Potential Ammonia Loss from Surface-Applied Urea

Ammonia loss from urea fertilizer is a major concern to farmers all over the world. Various environmental factors such as temperature, soil water content, wind speed, pH, rainfall, relative humidity, cation exchange capacity (CEC), soil organic matter, and others influence ammonia volatilization loss. The objective of this work was to establish a model for estimating ammonia loss utilizing published data. Also, using current day inputs (temperature, wind speed, and known soil pH) estimates could relate risk to producers considering surface applications of urea fertilizer without incorporation. Linear models for soil pH and ammonia loss, ambient temperature and ammonia loss, and wind speed and ammonia loss were determined based on more than 40 published articles. Final estimates of ammonia loss from surface applications of urea employed an additive effects model using inputs for pH, temperature, and wind speed. Web access to this model can be located at www.nue.okstate.edu/ammonia_loss.htm.

Effects of Fertilizer Additives on Ammonia Loss after Surface Application of Urea–Ammonium Nitrate Fertilizer

The purpose of this study was to measure the effect of additives on ammonia loss when used with urea–ammonium nitrate fertilizer (UAN). The fertilizer additives were ammonium thiosulfate (ATS), calcium thiosulfate (CaTS), N-(N-butyl) thiophosphoric triamide (Agrotain, AG), AG + CaTS, or a maleic-itaconic copolymer (Nutrisphere-N, NSN). Four greenhouse studies were conducted, with small fertilizer droplets applied to bare soil, large fertilizer droplets applied to bare soil, small fertilizer droplets applied to soil with 50% straw cover, and large fertilizer droplets applied to soil with 50% straw cover. Ammonia volatilizing from the soil surface was trapped in phosphoric acid and determined by steam distillation. Averaged across all four experiments, the percentage reductions of ammonia loss after 14 days, compared to unamended UAN, were 40% for UAN + ATS, 40% for UAN + CaTS, 51% for UAN + AG, 65% for UAN + AG + CaTS, and 11% for UAN + NSN.

Improving formulated nitrogen, phosphorus and potassium compound fertilizer using zeolite

Ammonia volatilization from urea and ammonium containing compound fertilizers cause higher cost of fertilization in agriculture. In this study, an incubation experiment was carried out to compare the effect of different ratios of compound fertilizer amended with clinoptilolite zeolite on NH3 volatilization, soil exchangeable NH4 and available NO3 contents on Bekenu Series (Tipik Tualemkuts) with surface-applied urea without additives. Treatments with zeolite significantly reduced NH3 loss when compared with urea without addictives. They also improved retention of exchangeable NH4 and NO3 and this was possible because zeolite favoured formation of ammonium and nitrate over ammonia. There is a potential for compound fertilizer with zeolite to improve nitrogen efficiency by lowering ammonia volatilization and increasing accumulation of exchangeable NH4 and NO3. Key words: Ammonia volatilization, compound fertilizers, clinoptilolite zeolite, soil exchangeable ammonium, available nitrate.

Effect of N, P and K humates on dry matter of Zea mays and soil pH, exchangeable ammonium and available nitrate

Ammonia volatilization from surface-applied urea reduces urea-N use efficiency in crop production and it also pollutes the environment; it is an economic loss. A greenhouse study was conducted to confirm the effect of similar fertilizer formulations (N, P and K humates) on soil pH, exchangeable ammonium, available nitrate retention and dry matter of Zea mays cultivated on an acid soil (Typic Paleudults). The fertilizers were applied 10 days after planting (DAP) in each pot containing 10 kg of soil. Soil and plant samples (stems, leaves and roots) were collected at 31 DAP. Soil samples were analyzed for pH, ammonium, and nitrate content. Urea amended with humic acid (HA), acidified (HA+FA) and humin without TSP and MOP were not effective in increasing the dry matter production of the test crop. Urea amended with fulvic acid (FA) alone significantly increased plant dry matter. Complete fertilizer consisting urea, triple superphosphate (TSP) and mono triphosphate (MOP) amended with or without HA, FA, acidified HA and FA and humin significantly increased the dry matter of the test crop with significant retention of soil exchangeable ammonium. However, only the complete fertilizer with and without HA and humin amendment significantly retained soil available nitrate. The findings in this study may only be applicable to similar acid soils. The outcome of this study may contribute to the improvement of urea N use efficiency as well as reducing environmental pollution. Key words: Humic acids, fulvic acids, triple superphosphate, muriate of potash, soil exchangeable ammonium, available nitrate, Zea mays, dry matter.

Ammonia volatilization losses from surface-applied urea with urease and nitrification inhibitors

Urease inhibitor (UI) and nitrification inhibitor (NI) have the potential to improve N-use efficiency of applied urea and minimize N losses via gaseous emissions of ammonia (NH3) to the atmosphere and nitrate (NO3−) leaching into surface and ground water bodies. There is a growing interest in the formulations of coating chemical fertilizers with both UI and NI. However, limited information is available on the combined use of UI and NI applied with urea fertilizer. Therefore the aim of this study was to investigate the effects of treating urea with both UI and NI to minimize NH3 volatilization. Two experiments were set up in volatilization chambers under controlled conditions to examine this process. In the first experiment, UR was treated with the urease inhibitor NBPT [N-(n-butyl) thiophosphoric acid triamide] at a rate of 1060 mg kg−1 urea and/or with the nitrification inhibitor DCD (dicyandiamide) at rates equivalent to 5 or 10% of the urea N. A randomized experimental design with five treatments and five replicates was used: 1) UR, 2) UR + NBPT, 3) UR + DCD 10%, 4) UR + NBPT + DCD 5%, and 5) UR + NBPT + DCD 10%. The fertilizer treatments were applied to the surface of an acidic Red Latosol soil moistened to 60% of the maximum water retention and placed inside volatilization chambers. Controls chambers were added to allow for NH3 volatilized from unfertilized soil or contained in the air that swept over the soil surface. The second experiment had an additional treatment with surface-applied DCD. The chambers were glass vessels (1.5 L) fit with air inlet and outlet tubings to allow air to pass over the soil. Ammonia volatilized was swept and carried to a flask containing a boric acid solution to trap the gas and then measured daily by titration with a standardized H2SO4 solution. Continuous measurements were recorded for 19 and 23 days for the first and second experiment, respectively. The soil samples were then analyzed for UR–, NH4+–, and NO3−–N. Losses of NH3 by volatilization with unamended UR ranged from 28 to 37% of the applied N, with peak of losses observed the third day after fertilization. NBPT delayed the peak of NH3 losses due to urease inhibition and reduced NH3 volatilization between 54 and 78% when compared with untreated UR. Up to 10 days after the fertilizer application, NH3 losses had not been affected by DCD in the UR or the UR + NBPT treatments; thereafter, NH3 volatilization tended to decrease, but not when DCD was present. As a consequence, the addition of DCD caused a 5–16% increase in NH3 volatilization losses of the fertilizer N applied as UR from both the UR and the UR + NBPT treatments. Because the effectiveness of NBPT to inhibit soil urease activity was strong only in the first week, it could be concluded that DCD did not affect the action of NBPT but rather, enhanced volatilization losses by maintaining higher soil NH4+ concentration and pH for a longer time. Depending on the combination of factors influencing NH3 volatilization, DCD could even offset the beneficial effect of NBPT in reducing NH3 volatilization losses.

Ammonia Volatilization from Urea and Mitigation by NBPT following Surface Application to Cold Soils

Urea is frequently surface applied to winter wheat (Triticum aestivum L.) during cold weather months (October–April) in the semiarid northern Great Plains. This study was conducted to quantify NH3 volatilization loss from surface-applied urea (100 kg N ha−1) and urea amended with N-(n-butyl) thiophosphoric triamide (NBPT) during this period. Ammonia emissions were quantified by a micrometeorological integrated horizontal flux method with samplers placed on a mast in the center of circular plots (20-m radius). Cumulative NH3 losses from urea varied but averaged 20.5% of applied N across 12 trials. The largest losses (30–44% of applied N) occurred after urea was applied to high-water-content soil surfaces, followed by a period of slow drying with little or no precipitation. Emissions occurred for a prolonged period often lasting >42 d. Periods (1–2 wk) of high NH3 flux (>30 g N ha−1 h−1) frequently occurred when mean daily soil temperatures (1-cm depth) were –2 to 5°C. In one trial, 24.3% of applied N was lost after urea was applied to a 140-mm snowpack. Ammonia losses were moderated by applying urea to dry soil surfaces. If precipitation events that followed were light (<8 mm), losses were reduced to 10 to 20% of applied N. If the events were heavy (>18 mm), then losses were <10%. Coating urea with NBPT (1 g kg−1) reduced cumulative NH3 losses by 66%. Volatilization protection lasted 2 to 3 wk on acidic soils, and >7 wk on an alkaline soil. This study demonstrated that significant NH3 losses from surface-applied urea could occur during cold weather months.

English

&nbsp; In agricultural lands, the loss of NH3&nbsp;from surface-applied urea and micronutrient deficiencies are the two most common problems, which can be solved by using coated urea with micronutrients and biodegradable natural materials. These coatings can improve the nutrient status in the soil and simultaneously reduce nitrogen loss from urea. To control ammonia loss and urea&rsquo;s hydrolysis process, two laboratory studies were conducted to compare the effects of using coated urea with that of using only urea. Both studies consisted of consecutive incubation experiments that were conducted on the same Typic Paleudult soil (Serdang Series). Eight treatments (labeled as Urea, UPS1, UPS2, UPS3, UAG1%, UAG2%, UG1% and UG2%) in study 1 and six treatments (labeled U, UPSCu, UAGCu, UGCu, UCu, and UCuZn) in study 2 were prepared and used to determine the effects of various concentrations of natural materials and the inhibitory effects of micronutrients on both ammonia loss and the hydrolysis process. The NH3&nbsp;loss was measured by forced draft techniques; the soil&rsquo;s exchangeable ammonium, available nitrate and urea-N were determined by using standard procedures. The outcomes of the study did not show any significant difference among various concentrations of natural material. Coated urea treatments significantly reduced ammonia loss by 30 to 40% in study 1 and by 40 to 67% in study 2 in comparison to urea alone. The same observation was made with respect to urea hydrolysis. All of the coated urea treatments significantly slowed down the hydrolysis process in comparison to urea. The outcomes of the study may improve urea fertilizer by reducing the loss of NH3&nbsp;volatilization. &nbsp; Key words:&nbsp;Biodegradable polymers, coated urea, CuSO4, NH3&nbsp;volatilization loss, urease inhibitor, urea.

Evaluation of coated urea for ammonia volatilization loss, nitrogen mineralization and microsite pH in selected soil series

The increase in microsite soil pH due to surface application of urea to the soil is an important reason of ammonia volatilization loss and fast hydrolysis process. The use of Cu and Zn with biodegradable materials coatings were assumed to reduce ammonia volatilization losses by reducing soil pH and slowing down hydrolysis process. The present study was conducted to evaluate the effects of coated urea with the combination coatings of Cu, Zn, palm stearin, agar and gelatine on microsite pH. For this purpose, six urea treatments named; uncoated urea or control, Cu and palm stearin coated urea, Cu and agar coated urea, Cu and gelatine coated urea, Cu coated urea, Cu and Zn coated urea were prepared and evaluated for their effects on microsite pH, ammonia volatilization loss and mineralization of N in three tropical soil. For the each soil; soil properties, soil microsite pH, ammonia volatilization loss and N mineralization were determined with slandered methods. The results reveal that the microsite pH in the three soils varied significantly due to the variability in texture. The pH of microsite treated with coated urea was lower than the uncoated urea treatments in each soil. The reduction in the microsite soil pH was associated with urea hydrolysis. The rate of mineralization (30%) and ammonia volatilization (50%) reduced in the soils where the pH was low or stable on the fertilizer microsite after adding the fertilizer treatments. The results of this study proved the positive effectiveness of coating material and potential to control fast hydrolysis process and ammonia volatilization losses. Key words: Ammonia volatilization, microsite pH, nitrogen, urease inhibitors.

Urea hydrolysis and lateral and vertical movement in the soil: effects of urease inhibitor and irrigation

A glasshouse-based study was conducted to investigate the effect of urease inhibitor N-(n-butyl) thiophosphoric triamide (‘Agrotain’) and irrigation on urea hydrolysis and its movement in a Typic Haplustept silt loam soil (in 72 repacked soil cores). Half (36) of these cores were adjusted to soil moisture contents of 80% field capacity (FC) and the remaining 36 cores to 50% FC. Granular urea with or without Agrotain was applied at a rate equivalent to 100 kg N ha−1. There were three replicates to these two sets of soil cores. After 1 day of treatment application, soil cores of the 50% FC were adjusted to 80% FC by applying surface irrigation. Twelve pots were destructively sampled at each day after 1, 2, 3, 4, 7 and 10 days of treatment application to determine urea hydrolysis and its lateral and vertical movement in different soil layers. Agrotain-treated urea delayed urea hydrolysis during the first 7 days after its application. This delay in urea hydrolysis caused by Agrotain enabled added urea, which is uncharged, to move away from the surface soil layer to the sub-surface soil layer both vertically and laterally. In contrast, most urea hydrolysed to soil NH4+ within 2 days of its application. Irrigation after 1 day resulted in further urea movement both laterally and vertically from the surface soil layer (0–10 mm) to the sub-soil layer (30–50 mm) in Agrotain-treated urea. These results suggest that Agrotain delayed urea hydrolysis and allowed more time for rainfall or irrigation to move added urea from the surface layer to sub-soil layers where it is likely to make good contact with plant roots. This distribution of urea in the rooting zone has the potential to enhance N use efficiency and minimize N losses associated with ammonia volatilization from surface-applied urea.

Minimizing ammonia loss from urea through mixing with zeolite and acid sulphate soil

Ammonia volatilization is a major cause of nitrogen loss from surface applied urea. While all top dressed ammonia and ammonium-based fertilizers can be volatized, the potential is greatest with urea and fluid containing urea. This laboratory study compared the effect of four different urea-zeolite-acid sulphate soil mixtures on NH3 volatilization and, soil exchangeable NH4 and available NO3 contents of an acid soil with surface-applied urea without additives. The soil used in the study was a sandy loam Typic Paleudults (Nyalau Series). The mixtures significantly minimized NH3 loss by 6 to 15% compared to urea alone. These treatments also significantly increased soil exchangeable NH4 and available NO3 contents compared to urea without additives. The increase in the formation of NH4+over NH3 and the temporary decrease in soil pH retarded urea hydrolysis at the microsite immediately around the fertilizer. Surface applied urea fertilizer efficiency could be increased by mixing it with zeolite and acid sulphate soil. Key words: Ammonia loss, urea, zeolites, acid sulphate soils.

Ammonia volatilization in no-till system in the south-central region of the State of Paraná, Brazil

Ammonia (NH3) volatilization can reduce the efficiency of urea applied to the surface of no-till (NT) soils. Thus, the objectives of this study were to evaluate the magnitude of NH3 losses from surface-applied urea and to determine if this loss justifies the urea incorporation in soil or its substitution for other N sources under the subtropical climatic conditions of South-Central region of Paraná State, Brazil. The experiment, performed over four harvesting seasons in a clayey Hapludox followed a randomized block design with four replicates. A single dose of N (150 kg ha-1) to V5 growth stage of corn cultivated under NT system was applied and seven treatments were evaluated, including surface-applied urea, ammonium sulfate, ammonium nitrate, urea with urease inhibitor, controlled-release N source, a liquid N source, incorporated urea, and a control treatment with no N application. Ammonia volatilization was evaluated for 20 days after N application using a semi-open static system. The average cumulative NH3 loss due to the superficial application of urea was low (12.5 % of the applied N) compared to the losses observed in warmer regions of Southeastern Brazil (greater than 50 %). The greatest NH3 losses were observed in dry years (up to 25.4 % of the applied N), and losses decreased exponentially as the amount of rainfall after N application increased. Incorporated urea and alternative N sources, with the exception of controlled-release N source, decreased NH3 volatilization in comparison with surface-applied urea. Urea incorporation is advantageous for the reduction of NH3 volatilization; however, other aspects as its low operating efficiency should be considered before this practice is adopted. In the South-Central region of Paraná, the low NH3 losses from the surface-applied urea in NT system due to wet springs and mild temperatures do not justify its replacement for other N sources.

Effects of urease and nitrification inhibitors added to urea on nitrous oxide emissions from a loess soil

AbstractUrea fertilizer‐induced N2O emissions from soils might be reduced by the addition of urease and nitrification inhibitors. Here, we investigated the effect of urea granule (2–3 mm) added with a new urease inhibitor, a nitrification inhibitor, and with a combined urease inhibitor and nitrification inhibitor on N2O emissions. For comparison, the urea granules supplied with or without inhibitors were also used to prepare corresponding supergranules. The pot experiments without vegetation were conducted with a loess soil at (20 ± 2)°C and 67% water‐filled pore space. Urea was added at a dose of 86 kg N ha–1 by surface application, by soil mixing of prills (&lt;1 mm) and granules, and by point‐placement of supergranules (10 mm) at 5 cm soil depth. A second experiment was conducted with spring wheat grown for 70 d in a greenhouse. The second experiment included the application of urea prills and granules mixed with soil, the point‐placement of supergranules and the addition of the urease inhibitor, and the combined urease plus nitrification inhibitors at 88 kg N ha–1. In both experiments, maximum emissions of N2O appeared within 2 weeks after fertilization. In the pot experiments, N2O emissions after surface application of urea were less (0.45% to 0.48% of total fertilization) than from the application followed by mixing of the soil (0.54% to 1.14%). The N2O emissions from the point‐placed‐supergranule treatment amounted to 0.64% of total fertilization. In the pot experiment, the addition of the combined urease plus nitrification inhibitors, nitrification inhibitor, and urease inhibitor reduced N2O emissions by 79% to 87%, 81% to 83%, and 15% to 46%, respectively, at any size of urea application. Also, the N2O emissions from the surface application of the urease‐inhibitor treatment exceeded those of the granules mixed with soil and the point‐placed‐supergranule treatments receiving no inhibitors by 32% to 40%. In the wheat growth experiment, the N2O losses were generally smaller, ranging from 0.16% to 0.27% of the total fertilization, than in the pot experiment, and the application of the urease inhibitor and the combined urease plus nitrification inhibitors decreased N2O emissions by 23% to 59%. The point‐placed urea supergranule without inhibitors delayed N2O emissions up to 7 weeks but resulted in slightly higher emissions than application of the urease inhibitor and the urease plus nitrification inhibitors under cropped conditions. Our results imply that the application of urea fertilizer added with the combined urease and nitrification inhibitors can substantially reduce N2O emissions.

Enhancing the Urea-N Use Efficiency in Maize (Zea mays) Cultivation on Acid Soils using Urea Amended with Zeolite and TSP

Problem Statement: Ammonia loss significantly reduces urea-N use efficiency in crop production. Efforts to reduce ammonia loss are laboratory oriented, as such limited in reflecting actual field conditions. This paper reports the effects of urea amended with triple superphosphate (TSP) and zeolite (Clinoptilolite) on soil pH, soil nitrate, soil exchangeable ammonium, dry matter production, N uptake, fresh cob production and urea-N uptake efficiency in maize (Zea mays) cultivation on an acid soil in actual field conditions. Approach: The treatments evaluated were: (i) Normal N, P, K application (74.34 g urea, 27.36 g TSP, 24.12 g KCl) (T1), (ii) Urea-TSP mixture (74.34 g urea+27.36 g TSP)+24.12 g KCl (T2), (iii) 74.34 g urea+27.36 g TSP+9.0 g zeolite (T3), (iv) 74.34 g urea+27.36 g TSP+13.5 g zeolite (T4) and (v) No fertilization (T5). Note, the same amount of 24.12 g KCl was used in T3 and T4 plots. Standard procedures were used to determine the selected chemical properties of zeolite, soil, TSP and urea. The pH of the urea, zeolite, soil and TSP were determined in a 1:2.5 soil: distilled water suspension and/or 0.01 N CaCl2 using a glass electrode. The CEC of the zeolite was determined by the CsCl method. Soil CEC was determined by leaching with 1 N ammonium acetate buffer adjusted to pH 7.0 followed by steam distillation. Soil samples at harvest were analyzed for pH using the method previously outlined. Exchangeable ammonium and nitrate at harvest were extracted from the soil samples by the method of Keeney and Nelson and the amount determined using a LACHAT Autoanalyzer. Total N of the plant tissues (stem and leaf) was determined by the Micro-Kjeldhal method. Results: Urea amended with TSP and zeolite treatments and Urea only (urea without additives) did not have long term effect on soil pH and accumulation of soil exchangeable ammonium and nitrate. Treatments with higher amounts of TSP and zeolite significantly increased the dry matter (stem and leaf) production of Swan (test crop). All the treatments had no significant effect on urea-N concentration in the leaf and stem of the test crop. In terms of urea-N uptake in the leaf and stem tissues of Swan, only the treatment with the highest amount of TSP and zeolite significantly increased urea-N uptake in the leaf of the test crop. Irrespective of treatment, fresh cob production was statistically not different. However, all the treatments with additives improved Urea-N uptake efficiency compared to urea without additives or amendment. Conclusion: Urea amended with TSP and zeolite has a potential of reducing ammonia loss from surface-applied urea.