Effects of some environmental factors on ammonia volatilization from simulated livestock urine applied to soil

Summary The proportion of the N that was volatilized as ammonia during 8 days, following the application of simulated livestock urine to soil, increased from 25 to 38% as the temperature of incubation was increased from 4° to 20°C in a system with a continuous flow of air at 70% relative humidity. However, volatilization was reduced if the application was followed by simulated rain; the reduction was greater as the amount of rain increased (up to at least 16 mm) and became less with an increasing length of time (up to 2–3 days) after the application of the urine. The effects of the soil water content before application of the urine, and of the relative humidity of the air, were generally small but volatilization was reduced by a combination of air-dry soil with a low relative humidity. Volatilization was slight (7%) when the flow of air was restricted to 0.5 h in every 12 h but, with an air flow for 12 h in every 24 h, the volatilization was much closer to that with a continuous flow for the whole 8-day period. When cool or dry conditions were imposed for 8 days and then more favourable conditions were instituted for a second period of 8 days, there was a substantial increase in volatilization following the change.     

Effects of plant material on ammonia volatilization from simulated livestock urine applied to soil

Summary The volatilization of ammonia from simulated urine applied to small columns of soil was reduced by the presence of ryegrass growing in the soil. The ryegrass had been sown 18 weeks previously and had been cut on seven occasions to a height of 5–6 cm with the cut herbage removed. Cumulative volatilization over 8 days amounted to 39% of the urinary N from bare soil, and 23% in the presence of the ryegrass. In contrast, the volatilization of ammonia was increased by dead leaf litter placed on the soil surface, apparently due to the increase in surface area for urease activity and volatilization. Differences in the C:N ratio of the leaf litter over the range 13:1–29:1 had little effect on the extent of ammonia volatilization. When living ryegrass and dead leaf litter were examined together, the reduction in volatilization due to the ryegrass was the dominant effect.     

Effect of urease inhibitors on urea hydrolysis and ammonia volatilization

Summary Two laboratory incubation experiments were conducted to study the effects of the urease inhibitors hydroquinone (HQ), phenyl phosphorodiamidate (PPDA), and N-(n-butyl) thiophosphoric triamide (NBPT) in retarding the hydrolysis of urea, in the evolution of mineral N, and in reducing NH₃ loss through volatilization, under aerobic and waterlogged conditions, both at 25°C. NBPT generally exceeded PPDA and HQ in the ability to delay urea hydrolysis and NH _inf4 ^sup+ accumulation under aerobic conditions, whereas PPDA retarded these activities more effectively under anaerobic conditions. HQ was less effective than the other two urease inhibitors. Under aerobic conditions, 20% of the applied urea was lost through NH₃ volatilization after 5 days in the system without an inhibitor. With the addition of HQ and PPDA, the volatilization was delayed by 1 day but not eliminated. NBPT effectively decreased the NH₃ loss, from 20 to 3% of the applied urea. A more severe N loss (40%) occurred in the waterlogged system. HQ had little effect on NH₃ volatilization. PPDA decreased the NH₃ loss from 40 to less than 20% of the applied urea. The effectiveness of NBPT decreased under anaerobic conditions. It was concluded that urease inhibitors can reduce NH₃ volatilization following the application of urea. However, environmental conditions might have an important influence on the effectiveness of these inhibitors.     

Effect of amending urea fertilizer with chemical additives on ammonia volatilization loss and nitrogen-use efficiency

 Effects of amending urea with pyrite (Py) or potassium chloride (KCl) alone and in combination with copper sulphate (CuSO₄) on NH₃ volatilization and N-use efficiency in an Alfisol were evaluated. NH₃ volatilization from surface-applied urea fertilizers was measured using a closed dynamic air flow system. Kinetics of NH₃ volatilization over a 10-day period showed that the peak rate of NH₃ loss was on day 3 with the unamended urea, whilst it occurred on day 4 with all amended urea fertilizers. Total NH₃ loss from the unamended urea was 48% of the applied N, which was reduced to 38 and 40% with U+Py and U+KCl, respectively. A further reduction in N loss was recorded with U+Py+CuSO₄ (34%) and U+KCl+CuSO₄ (36%). The inhibition of NH₃ with U+Py+CuSO₄ and U+KCl+CuSO₄ was markedly high, at 30 and 25%, respectively. As compared to urea, all amended urea fertilizers resulted in a significantly higher dry matter yield, N uptake and apparent N recovery (ANR) efficiency by sunflower. An increase of 28 and 24% units in ANR over urea could be obtained with U+Py+CuSO₄ and U+KCl+CuSO₄, respectively. Since the chemical additives also have a fertilizer value besides being effective in controlling NH₃ loss from urea and improving N-use efficiency, their use as amendment to urea could be a viable option. Received: 5 August 1999     

Influence of iron pyrites and dicyandiamide on nitrification and ammonia volatilization from urea applied to loess brown earths (luvisols)

Laboratory incubation study showed that iron pyrites retarded nitrification of urea-derived ammonium (NH₄ ⁺), the effect being greatest at the highest level (10000 mg kg^–1 soil). Nitrification inhibition with 10000 mg pyrite kg^–1 soil, at the end of 30 days, was 40.3% compared to 55.9% for dicyandiamide (DCD). The inhibitory effect with lower rates of pyrite (100–500 mg kg^–1) lasted only up to 9 days. Urea+pyrite treatment was also found to have higher exchangeable NH₄ ⁺-N compared to urea alone. DCD-amended soils had the highest NH₄ ⁺-N content throughout. Pyrite-treated soils had about 7–86% lower ammonia volatilization losses than urea alone. Total NH₃ loss was the most with urea+DCD (7.9% of applied N), about 9% more than with urea alone. Received: 11 November 1995     

施用尿素、有机-无机复混肥和包膜有机肥对几种水稻田土表水层pH的影响

采用不同类型的3种水稻田土壤进行模拟培养,研究施用尿素、有机-无机复混肥和包膜有机肥对土表水层pH变化的影响。实验表明:淹水培养5天以后土表水层pH变化趋势明显。水稻田土壤类型不同,培养期间土表水层pH变化差异显著。在培养后5～15天期间,不施肥对照、施用包膜有机肥处理和施用复混肥处理,红壤、灰潮土和盐碱土土表水层pH都明显上升;施用尿素处理在灰潮土和盐碱土上土表水层pH值略微下降,而在红壤上仍呈上升趋势。     

交替灌溉施肥对夏玉米土壤氨挥发的影响

为了解交替灌溉施肥条件下土壤氮素平衡过程,提高氮肥利用率,采用密闭法研究了夏玉米农田土壤氨挥发速率和挥发量。结果表明：夏玉米拔节期追肥灌水后,不同处理的氨挥发速率峰值（1.68～3.97 kg/hm2×d）出现在第2天,而后迅速下降并进入低挥发阶段;抽雄期追肥灌水后,水肥异区交替灌溉施肥处理的氨挥发速率呈现上下波动变化;玉米拔节期追肥灌水的氨挥发量和损失率远远小于抽雄期。在灌水量350 m3/hm2、施肥量256.08 kg/hm2时的氨挥发量最低。与常规灌水施肥处理相比,水肥异区交替灌溉施肥处理可明显减少氨挥发损失。     

长期有机无机肥配施对冬小麦籽粒产量及氨挥发损失的影响

【目的】黄淮海地区作为华北平原重要的农业生产区,氮肥投入量大、利用率低的现象较为普遍,氮肥损失和农业面源污染严重。本研究在长期肥料定位试验基础上,连续多年监测不同施肥处理下冬小麦田氮素挥发损失量及其规律,探讨减少黄淮海地区麦田氨挥发的有效施肥方式,为提高冬小麦产量及肥料利用效率提供科学依据。 【方法】2011～2015 年利用水肥渗漏研究池进行试验,以石麦 15 (SM15) 为材料,以不施氮肥 (CK) 为对照处理,在同等施氮量下设置单施尿素 (U)、单施牛粪 (M) 和尿素牛粪 1∶1 配施 (U + M) 3 种氮肥配比处理,随机区组设计。采用通气法连续 4 年原位监测不同施肥处理下小麦氨挥发损失量、小麦籽粒产量及氮肥利用率。 【结果】2011～2015 年氨挥发损失量年际间变化较大,最大变幅可达 19.69 kg/hm2,年际间施肥后氨挥发速率变化规律趋势相似。不同施肥处理对土壤氨挥发有显著影响,冬小麦季氨挥发主要发生在施肥后 15 d 内,拔节期追肥的氨挥发速率显著高于播种期施用基肥。四年间氨挥发损失量平均达 7.26～42.40 kg/hm2,与不施氮肥相比,施氮处理的氨挥发损失量升高 1.40～4.84 倍,表明施用氮肥显著促进土壤氨挥发;施氮处理的氮肥损失率以 U 处理最高,达到 19.5%,M 处理最低,为 5.7%,U + M 处理为 12.3%,介于两处理之间,U + M 处理和 M 处理的氮肥损失率较 U 处理四年平均分别降低了 37.0% 和 71.1%,表明单施有机肥或有机无机肥配施可显著抑制氨挥发损失。2011～2015 年各施肥处理冬小麦产量均以 U + M 处理最高,达 9461.5 kg/hm2,较 U 和 M 处理分别增产 6.8% 和 9.1%。各处理的冬小麦籽粒吸氮量、地上部吸氮量同样以 U + M 处理最大,较 U 和 M 处理分别提高 7.1%、12.6% 和 5.4%、12.9%。U + M 处理的氮肥利用率在四年均最高,达 41.96%,较 U 和 M 处理分别提高 16.5%～19.6% 和 38.6%～58.7%。 【结论】综合籽粒产量及氮素利用效率,有机无机肥配施比单施化肥能显著降低氨挥发损失,提高籽粒产量和氮肥利用率,有利于实现冬小麦高产与肥料高效的协同,可作为黄淮海区域小麦生产中的增产增效的优化施肥方式。     

Effect of blending urea with pyrite or coating urea with polymer on ammonia volatilization loss from surface-applied prilled urea

Laboratory studies on a sandy clay loam (Typic Ustochrept) alkaline soil showed that NH₃ volatilization loss from surface-applied prilled urea during an 8-dya incubation under aerobic conditions was 27.5% of applied N (400 kg N ha^-1) and was reduced to 8.9% when the urea was blended physically with pyrite in a 1:2 ratio; under anaerobic conditions the values for urea and pyrite-urea were 19.3 and 16.9%, respectively. Other treatments tested were urea-gypsum, neemcake-coated urea and polymer-coated urea. A 6% polymer coating showed the least NH₃ volatilization under anaerobic conditions and was next best to pyrite-urea under aerobic conditions. A 3% polymer coating was slightly inferior to the 6% coating. Urea-gypsum and neemcake-coated urea did not differ very much from urea alone under anaerobic conditions, but under aerobic conditions neemcake-urea showed a significantly lower total NH₃ loss compared to prilled urea alone and urea-gypsum.     

有机肥无机肥配施对稻田氨挥发和水稻产量的影响

在南方红壤区双季稻田进行田间试验,研究等氮、磷、钾量条件下,有机无机肥配施对稻田氨挥发及水稻产量的影响。结果表明,有机无机肥配合施用能显著地降低稻田氨挥发,减少氮素损失,提高氮肥利用率。单施化肥(尿素),其氨挥发损失达37.8%,而单施有机肥和有机无机肥各半配合施用,氨挥发损失分别为0.7％-1.0％和7.2％-18.2％。田间氨挥发持续的时间,早稻约在施肥后20d,晚稻为9-10d。虽然有机无机肥各半配合施用的水稻产量与单施化肥的相近,均比对照提高约70％,但前者的氮损失少,其氮肥利用率为34.9％,高于化肥处理(33.2％)和有机肥处理(28.0%)。有机无机肥配合施用对提高水稻产量和降低氮肥环境负效应的综合效应最佳。     

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.     

The interdependence of ammonia volatilization and denitrification as nitrogen loss processes in flooded rice fields in the Philippines

Summary The relative importance of ammonia volatilization and denitrification as loss processes following the application of urea to flooded rice by the traditional method was assessed at four sites with different characteristics in the Philippines. The effect of reducing ammonia loss on denitrification and total N loss was also studied. The total N loss was determined by a ¹⁵N-balance method and ammonia volatilization was assessed by a bulk aerodynamic method following the application of urea to small plots (4.8×5.2 m). As run-off was prevented and leaching losses were negligible, the denitrification loss was assessed as the difference between total N loss and ammonia loss. When urea was broadcast into the floodwater at transplanting, the ammonia loss varied from 10% to 56% of the applied N. Loss was smallest at Aguilar where wind speeds were low and the greatest at Mabitac where floodwater pH values and temperatures were high and the winds were strong. The ammonia loss was reduced at all sites by incorporating the urea into the soil by harrowing. However, the reduction achieved varied markedly between sites, with the largest reduction (from 56% to 7% loss of the applied N) being observed at Mabitac. The total N lost from the basal application into the floodwater ranged from 59% to 71% of the applied N. Incorporating the urea by harrowing reduced the total N loss at two sites, increased the total N loss at the third site, and had no effect at the fourth site. The denitrification losses ranged widely (from 3% to 50% of the applied N) when urea was broadcast into the floodwater at the four sites. The denitrification loss was low when the ammonia loss was high (Mabitac) and high when the ammonia loss was low (Aguilar). Reducing ammonia losses by incorporating the urea into the flooded soil resulted in increased denitrification losses at three of the sites and appeared to have no effect on denitrification at the fourth site. The results show that reducing the ammonia loss by incorporating urea into the soil does not necessarily result in reduced total N loss, and suggest that the efficiency of fertilizer N will be improved only when both N-loss processes are controlled simultaneously.     

不同吸附特性的稻草生物炭对稻田氨挥发和水稻产量的影响

秸秆生物炭具有改善土壤生态环境、土壤蓄水保肥和减少温室气体排放等正效应,但其石灰效应会加大稻田氨挥发损失。为充分发挥生物炭吸铵特性,降低其石灰效应的不利影响,对不同热解温度（300、500、700 ℃）和酸化水平（pH值=5、7、9）稻草生物炭处理下的田面水NH4+-N浓度、氨挥发和水稻产量进行了研究。结果表明：偏酸性（pH值=5）、中性（pH值=7）生物炭处理在基肥期和分蘖肥期均能显著降低田面水NH4+-N峰值浓度（P<0.05）,降幅达16.90%～35.60%。全生育期稻田氨挥发损失占施氮量的15.14%～26.05%（2019年）、15.10%～19.00%（2020年）。稻田增施热解温度为700 ℃、酸化水平为5（pH值=5）的生物炭（C700P5）降氨效果最好,两年氨挥发分别显著降低22.93%、12.61%（P<0.05）。高温热解配合偏酸性、中性生物炭（C700P5、C700P7）增产效果显著,增产率达9.92%～13.50%,结构方程模型表明,其增产原因是生物炭酸化处理降低了稻草生物炭的石灰效应,而热解温度调整提高了生物炭阳离子交换量（Cation Exchange Capacity,CEC）,进而降低了田面水NH4+-N浓度和氨挥发损失,最终提高了水稻地上部氮素积累和水稻产量。研究可揭示不同热解温度和酸化水平制备的生物炭在稻田中的应用潜力,并为稻田合理施用生物炭和减少化肥施用量提供理论依据。     

Effect of nitrogen inputs to cereals on nitrate leaching from sandy soils

Abstract. The effect of nitrogen fertilizer inputs to cereal crops on nitrate leaching after harvest was tested on 21 experiments on sandy soils in England. At small nitrogen fertilizer rates leaching increased very little with increasing inputs, while at high rates more than half of any additional nitrogen could be accounted for as increase in nitrate leached. In many cases the response fitted two straight lines. Nitrogen offtake in grain also fitted two straight lines, with a form which complemented the leaching response. The gradient averaged 0.52 kg N in grain for every additional 1kg N applied below the break point, but only 0.05 kg/kg above. The break points were generally close to or above the economic optimum N input. The effect of inputs on leaching could he quantitatively related to nitrogen offtake in grain, assuming a constant ratio of nitrogen in grain to total nitrogen uptake. The results show that fields receiving N inputs in excess of the economic optimum cause a disproportionately large nitrate loss. However because of uncertainty in predicting the break point in advance, modest further reduction in leaching will occur by reducing inputs to somewhat below the expected economic optimum.     

Effects of phosphoroamides on ammonia volatilization and nitrite accumulation in soils treated with urea

Summary We compared the effects of N-(n-butyl) thiophosphoric triamide (NBPT), N-(diaminophosphinyl)-cyclohexylamine (DPCA), phenylphosphorodiamidate (PPD), and hydroquinone on transformations of urea N in soils. The ability of these urease inhibitors to retard urea hydrolysis, ammonia volatilization, and nitrite accumulation in soils treated with urea-decreased in the order NBPT > DPCA PPD > HQ. When five soils were incubated at 30°C for 14 days after treatment with urea (1 mg urea N g^–1 soil), on average, the gaseous loss of urea N as ammonia and the accumulation of urea N as nitrite were decreased from 52 to 5 % and from 11 to 1%, respectively, by addition of NBPT at the rate of 10 g g^–1 soil (0.47 parts of NBPT per 100 parts of urea). The data obtained support previous evidence that NBPT is more effective than PPD for reduction of the problems encountered in using urea as a fertilizer and deserves consideration as a fertilizer amendment for retarding hydrolysis of urea fertilizer in soil.     

控释掺混肥结合增密对水稻氮肥利用效率和氨挥发的影响

为探究控释掺混肥结合增密对水稻产量、氮素吸收、施肥经济效益和氨挥发损失的影响,该研究以扬籼优418为供试材料,设不施氮对照（CK）、常规施氮（Farmer''s Fertilization Practice,FFP）、优化施氮（Optimized Nitrogen Application,OPT）、控释掺混肥（Controlled Release Blended Fertilizer,CRBF）和控释掺混肥结合增密（Controlled Release Blended Fertilizer Combined with Dense Planting,CRFDP）共5个处理,对比分析了不同处理的水稻产量及构成因子、氮素吸收和氮肥利用效率、经济效益和氨挥发损失的差异。结果发现,CRFDP处理的水稻有效穗数和每穗实粒数显著高于其他处理（P<0.05）,较FFP分别增加26.1%和18.7%。CRFDP处理较FFP处理水稻增产33.3%。与FFP相比,CRFDP的氮肥吸收利用率、氮肥偏生产率、氮肥农学利用率分别提高160%、22.8 kg/kg、16.27 kg/kg。CRFDP较CRBF处理的氮肥吸收利用率显著提高10.0个百分点,氮肥偏生产率、氮肥农学利用率和氮素生理利用率则没有显著差异（P>0.05）;与FFP处理相比,3个优化施氮处理（OPT、CRBF和CRFDP）在氮肥用量降低20%的情况下,水稻每公顷净收益增加3 328～8 968元,其中CRFDP处理的水稻产值和净收益最高。施氮显著提高了水稻生长季的田面水铵态氮浓度和土壤脲酶活性,与FFP处理相比,CRFDP处理的氨挥发强度和累积氨挥发损失分别降低62.5%和46.3%。综上,控释掺混肥与增密结合可兼顾水稻高产、氮肥高效利用和氨减排。研究结果可为水稻高产及环境友好和资源高效的水稻种植新模式数据支持和理论支撑。     

Effect of timing of simulated rainfall on ammonia volatilization from urea, applied to soil of varyingmoisture content

Ammonia volatilization from granular urea applied at 10gNm⁻² to pasture was investigated using an enclosure method. Misting 0, 4 or 16 mm of water on to the soil at field capacity within 3 h of urea application resulted in total NH₃ losses of 2.81, 0.92 and 0.18 g N m⁻² respectively. Further delaying the watering reduced this effect until at 48 h, volatilization was lowered from 3.33 to only 3.09gNm⁻² with 16mm of water. Hydrolysis and NH₃ loss were rapid. Similar trends occurred at a lower initial soil moisture content.
On air-dry soil (0.06 g H₂O/g soil), hydrolysis was slow (73 ± 14% of the urea remained after 30 days) and volatilization, while gradual, accounted for 33% of applied urea-N after 30 days. Addition of 16 mm of water 48 and 96 h after urea application was followed by a period of rapid hydrolysis and volatilization, resulting in a total loss of 2.59 and 2.40gNm⁻² respectively. Repeated addition of 2mm of water produced bursts of hydrolysis and NH₃ loss until completion of hydrolysis when additional water had no effect. A total loss after 30 days of 3.94 g N m⁻² occurred in this 2 mm treatment.     

专用缓释肥的土壤氨挥发特性及其对辣椒氮磷钾吸收利用的影响

采用室内扩散模拟试验研究了施用大颗粒尿素(PUR)、辣椒专用复混肥(LCCF)、辣椒专用缓释复混肥(LSRF)土壤的氨挥发特性,并采用土培试验研究了LSRF、LCCF、普通复合肥(OCCF)、市场非包膜缓释复合肥(MSRF)对‘渝椒五号’和‘改良早丰’辣椒产量、氮磷钾养分吸收利用、土壤有机质及酶活性的影响,探讨LSRF的应用效果。结果显示,室内扩散模拟试验中,前28 d氨释放速率总体表现为PURLCCFLSRF不施肥(CK),28 d以后LSRF的氨释放速率略高于PUR和LCCF处理。培养70 d时,PUR、LSRF和LCCF的氨挥发量分别为71.87 mg·kg-1、54.29 mg·kg-1和63.49 mg·kg-1,LSRF比PUR和LCCF分别降低了24.5%和11.7%。土培试验中,LSRF处理显著提高了2个辣椒品种的果实重量,‘渝椒五号’和‘改良早丰’分别较OCCF处理增产64.7%和33.8%。与OCCF处理相比较,LSRF处理增加了土壤有机质含量、土壤脲酶、蔗糖酶和过氧化氢酶活性,提高了辣椒对氮磷钾养分的吸收利用。‘渝椒五号’和‘改良早丰’LSRF处理的氮素表观利用率较OCCF处理分别增加62.5%和123.1%,‘改良早丰’和‘渝椒五号’LSRF处理的磷素表观利用率分别较OCCF处理提高了14.0倍和3.2倍,钾素表观利用率分别较OCCF处理提高了28.7%和120.9%。     

Effects of different lime application rates and time on some chemical properties of an acid soil in Ghana

Abstract. Finely ground calcium carbonate was applied at six rates (0–7.0 t/ha) to samples from four depths of an acid tropical soil (Oxisol). The mixtures were kept moist and maintained at 18 °C for a period of 30 days. There was a significant increase (> 28%) in soil pH at all the sampling depths. Extractable P also increased significantly (> 90%). Significant positive correlations between pH, extractable P and liming rate were obtained ( r > 0.9, P = 0.01). The effect of time was significant only on the 10th day after liming, when soil pH had stabilized. Exchangeable Al was completely eliminated on the 5th day after liming, when most of the soil samples had pH values > 5.0. The results clearly indicate that liming, as a management practice, could be used to alleviate or prevent acidification of Oxisols like the soil studied.     

Effects of the urease inhibitor N-(n-butyl)phosphorothioic triamide in low concentrations on ammonia volatilization and evolution of mineral nitrogen

Laboratory incubation experiments were conducted to study the influence of increasing concentrations of N-(n-butyl)phosphorothioic triamide (NBPT) on NH₃ volatilization and rate of urea hydrolysis and evolution of mineral N in Ozzano, Rimini and Carpi soils with different physicochemical characteristics. Low concentrations of NBPT reduced NH₃ losses due to volatilization after urea fertilization and the effectiveness of the inhibitor was related to the soil characteristics (e.g. high concentrations of organic C and sand). After 15 days of incubation, no significant reductions of losses were found for any of the NBPT concentrations employed in Rimini soil. The application of NBPT led to a considerable reduction of the formation of nitrite. This process was completely annulled with the highest dose of NBPT (0.5% w/w_urea) in the Carpi soil after 15 days. In Rimini soil, however, the use of NBPT was less effective in influencing nitrite formation. The use of NBPT favoured accumulation of nitrate proportional to the NBPT concentration employed while it had no influence on the NH _inf4 ^sup+ fixation by 2:1 layer silicates. The data obtained support previous evidence that NBPT is effective in reducing the problems encountered in using urea as fertilizer. However, environmental conditions and soil physicochemical characteristics may have an important influence on the effectiveness of NBPT.