Effect of urea pellet size and dicyandiamide on residual ammonium in field microplots

Abstract

Nitrification of urea can be slowed by adding a nitrification inhibitor or by fertilizer localization. The purpose of this research was to compare the effects of urea pellet size (0.01, 0.1, and 1.0 g) and level of dicyandiamide (DCD) addition (0, 1, 2, 5, and 10% of N as DCD‐N) on residual ammonium in field microplots. Trials were conducted at ten locations in North Dakota during 1988 and 1989. Adding DCD to 0.01 g urea pellets slowed nitrification at all locations and the lower rates of DCD (1–2% of N as DCD‐N) often performed as well as higher rates. Increasing urea pellet size to 1.0 g was more effective in inhibiting nitrification than adding DCD to 0.01 g pellets. Increased pellet size plus addition of DCD led to a very slow nitrification. A 1.0 g urea pellet containing 1–2% of N as DCD‐N should be a practical fertilizer formulation where a very slow nitrification is required.     

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.     

Dicyandiamide (DCD) as a nitrification inhibitor for rice culture in the United States

Abstract

Efficient nitrogen (N) fertilizer management for paddy rice production is difficult because of potentially high N losses from denitrification, NH₃ volatilization, and leaching. The use of a nitrification inhibitor, by slowing the rate of nitrification of NH₄ ⁺‐N sources prior to flooding, offers the potential to reduce denitrification losses that occur after flooding. Dicyandiamide (DCD) is one such nitrification inhibitor. The objective of this series of studies was to evaluate DCD for its effectiveness as a nitrification inhibitor in paddy rice production across an array of soils, management systems, and climate conditions.

Studies were conducted on fine‐ and medium‐textured soils in Arkansas, California, Louisiana, Mississippi, and Texas. Dicyandiamide was coated onto or formulated with urea (7 or 10% of total N as DCD‐N) and applied either broadcast pre‐plant incorporated or broadcast as a topdress application prior to flooding at the 4‐ to 5‐leaf development stage of the rice plant. These treatments were compared with urea applied either pre‐plant incorporated or in multiple applications timed to the peak N demand periods of rice. An array of N rates were used to model the yield response to levels of N. Similar studies utilizing ¹⁵N‐enriched urea were also conducted.

The studies indicated that use of DCD delayed nitrification and tended to result in rice grain yield increases as compared with urea applied pre‐plant without DCD in drill‐seeded rice; however, proper application of urea in split applications gave more consistent results. In water‐seeded continuously flooded rice culture, use of DCD was advantageous only if the flood was delayed for more than 14 days after urea application. The ¹⁵N‐enriched studies indicated that highest N fertilizer recovery was associated with split topdress urea applications; however, addition of DCD resulted in increased immobilization of fertilizer N and release of soil N.     

Effect of dicyandiamide on the form and recovery of 15N‐labeled urea in the delayed flood soil system

Abstract

Dicyandiamide (DCD) is a nitrification inhibitor that has been proposed for use in drill‐seeded rice. Immobilization of fertilizer NH₄ ⁺‐N by soil microorganisms under aerobic conditions has been found to be significantly enhanced in the presence of a nitrification inhibitor. The objective of this laboratory study was to determine if DCD significantly delayed nitrification of urea‐derived N, and if this enhanced immobilization of the fertilizer N in the delayed‐flood soil system inherent to dry‐seeded rice culture. Nitrogen‐15‐labeled urea solution, with and without DCD (1: 9 w/w N basis), was applied to a Crowley silt loam (Typic Albaqualf) and the soil was incubated for 10 weeks in the laboratory. The soil was maintained under nonflooded conditions for the first four weeks and then a flood was applied and maintained for the remaining six weeks of incubation. The use of DCD significantly slowed the nitrification of the fertilizer N during the four weeks of nonflooded incubation to cause the (urea + DCD)‐amended soil to have a 2.5 times higher fertilizer‐derived exchangeable NH₄+‐N concentration by the end of the fourth week. However, the higher exchangeable NH₄+‐N concentration had no significant effect on the amount of fertilizer N immobilized during this period. Immobilization of the fertilizer N appeared to level off during the nonflood period about the second week after application. After flooding, immobilization of fertilizer N resumed and was much greater in the (urea + DCD)‐amended soil that had the much higher fertilizer‐derived exchangeable NH₄ ⁺‐N concentration. Immobilization of fertilizer N appeared to obtain a maximum in the urea‐amended soil (18%) about two weeks after flooding and for the (urea + DCD)‐amended soil (28%) about four weeks after flooding.     

Effect of dicyandiamide on growth and nutrient uptake of cotton

Abstract

The nitrification inhibitor dicyandiamide (DCD) offers potential for improving efficiency of N applications to cotton grown on sandy soils of the southeastern Coastal Plain. Research has indicated that cotton is sensitive to DCD. The purpose of this greenhouse experiment was to investigate the effect of DCD on growth and nutrient uptake of DPL 90 cotton grown for 73 days in pots containing a typical Coastal Plain soil (Norfolk sandy loam, Typic Paleudult). Nitrogen (50 mg kg^‐1) as NaNO₃ or urea, and DCD (0, 2.5, 5, 10, 15 and 20 mg kg^‐1) were applied to the soil at first true leaf and plants were harvested 58 days later. Sodium nitrate increased leaf dry weight and total dry weight of plants 9.1 and 6.0%, respectively, over urea fertilized plants. Leaf area, dryweight, and stem dry weight were reduced linearly with DCD. Fertilization with urea increased concentrations of leaf P, K, and Mn and reduced the concentration of Mg in leaf tissue. Dicyandiamide increased leaf N, P, and K concentrations but reduced concentrations of Ca, Mg, and Mn. Uptake rates (μg^‐1 g^‐1 fresh root day^‐1) of Ca and Mg were increased 7.5 and 13.7%, respectively, with NaNO₃ vs. urea, while P uptake rate was 15.5% greater for urea‐fertilized plants vs. NaNO₃‐fertilized plants. Dicyandiamide reduced Ca and Mg uptake rates. Phosphorus uptake rates were increased by DCD when urea was the N source. The effects of DCD on cotton growth and nutrient uptake generally resulted from the compound itself and were not an indirect result of nitrification inhibition. Although significant reductions in plant growth did not occur unless DCD exceeded that normally applied with recommended N rates on this soil, these results suggest a need for caution when applying DCD to cotton grown on sandy soils.     

Laboratory evaluation of dicyandiamide as a soil nitrification inhibitor

Abstract

Laboratory studies to evaluate dicyandiamide (DCD) as a soil nitrification inhibitor showed that it is considerably more effective than several compounds that have been patented or proposed as fertilizer amendments for retarding nitrification of fertilizer nitrogen (N) in soil, but is considerably less effective than 2‐ethynylpyridine, nitrapyrin (N‐Serve), etridiazole (Dwell), 3‐methylpyrazole‐l‐carboxamide (MPC), or 4‐amino‐l,2,4‐triazole (ATC). Other findings in studies reported were as follows: a) DCD is more effective for inhibiting nitrification of ammonium‐N than of urea‐N; b) the effectiveness of DCD as a nitrification inhibitor is markedly affected by soil temperature and soil type and is limited by the susceptibility of DCD to leaching; c) DCD has very little, if any, effect on urea hydrolysis, denitrification, or seed germination in soil; d) products of DCD decomposition in soil (guanylurea and guanidine) have little, if any, effect on nitrification compared with DCD; e) in the absence of leaching, the persistence of the inhibitory effect of DCD on nitrification decreases with increase in soil temperature from 10 to 30°C, but the inhibitory effect of 50 μg DCD g^‐1 soil is substantial even after incubation of DCD‐treated soils at 20 or 30°C for 24 weeks.     

Alternatives to regular urea for abating N losses in lettuce production under sub-tropical climate

Alternative fertilization practices are needed for reducing gaseous and leaching N losses at high urea application rates. The objective of this study was to compare gaseous N emissions (N₂O and NH₃) and NO₃ ^? concentrations in the soil solution during two successive lettuce cropping seasons under contrasting fertilization practices. Treatments were fertilization with regular urea (U), urea treated with urease [N-(n-butyl) thiophosphoric triamide (NBPT)] and nitrification [dicyandiamide (DCD)] inhibitors (UIs), non-acidified pig slurry compost (PSC), acidified pig slurry compost (APSC), and an unfertilized control (C). Acidification of pig slurry during composting had no impact on soil cumulative N₂O emissions during the cropping seasons. The use of composts resulted in emission factors (EFs) (PSC, 0.09% of applied N; APSC, 0.16%) an order of magnitude smaller than with regular urea (1.63%). Similarly, adding NBPT and DCD to urea reduced the N₂O EF from 1.63 to 0.37% of applied N and fertilizer-induced NH₃ emissions from 30.2 to 3.4% of applied N. Composts and UI resulted in yield-scaled N₂O emissions that were 33 to 49% lower than the unfertilized control and 64 to 73% lower than the regular urea estimates, indicating a greater efficiency of supplied N with composts and UI. Nitrate concentration of the soil solution (at 0.1 and 0.3 m) in PSC, APSC, and UI plots was similar to the control and up to 17 times lower than with regular urea, indicating reduced risks for leaching losses. We conclude that, as compared to regular urea, the use of composted pig slurry, with and without acidification, and the addition of NBPT and DCD inhibitors to urea are good practices to reduce environmental N losses from lettuce production under sub-tropical climate.     

The effect of dicyandiamide and neem cake on the nitrification of urea-derived ammonium under field conditions

Summary Dicyandiamide (DCD) and neem cake were evaluated for their efficiency in inhibiting nitrification of prilled urea-derived NH ₄ ⁺ –N in a wheat field. Prilled urea was blended with 10% and 20% DCD-N or 10% and 20% neem cake and incorporated into the soil just before the wheat was sown. Both DCD and neem cake partially inhibited nitrification of prilled urea-derived NH ₄ ⁺ ; DCD was better than neem cake. The nitrification-inhibiting effects of DCD lasted for 45 days, while that of neem cake lasted for only 30 days. Blending the prilled urea with DCD (20% on N basis) was most effective in inhibiting the nitrification of urea-derived NH ₄ ⁺ , both in terms of intensity and duration, and maintained substantially more NH ₄ ⁺ –N than the prilled urea alone and 20% neem-cake-blended urea for a period of 60 days.     

Dicyandiamide effects on nitrification and total inorganic soil nitrogen in sandy soils

Abstract

Inhibition of nitrification in soil results in a decreased ratio of nitrate‐nitrogen (NO₃‐N) to ammonium‐nitrogen (NH₄‐N). If the conditions for NO₃‐N loss by leaching or denitrification exist, nitrification inhibitors should increase concentrations of total inorganic soil nitrogen (N) (TISN) (NH₄‐N + NO₃‐N). This can then result in plants taking up more N and developing more crop yield or biomass. This study examined whether inhibition of nitrification by dicyandiamide (DCD) would result in increased concentrations of TISN under field conditions. The effects of DCD on soil N were evaluated in hyperthermic sandy soils planted to potato (Solanum tuberosum L., cv. Atlantic). Treatments were factorial combinations of N as ammonium nitrate (NH₄NO₃) at 67, 134, and 202 kg N ha^‐1 and DCD at 0, 5.6, and 11.2 kg DCD ha^‐1. Soil NH₄‐N, NO₃‐N, and TISN concentrations were determined for up to five potato growth stages at two locations for two years for a total of 16 determinations (cases), i.e., four were not determined. The N form ratio [NO₃‐N/(NH₄‐N + NO₃‐N] x 100 was decreased in 10 of 16 cases, indicating that nitrification was inhibited by DCD. With two of these 10 cases, TISN concentration increased, but with four others, TISN concentration decreased with at least one N rate. With four of these 10 cases, inhibition of nitrification had no effect on TISN concentration. Under the conditions of these field studies, DCD inhibited nitrification more often than not. Inhibition of nitrification was, however, more likely to reduce TISN concentration than to increase it. This may have been due to DCD effects on immobization of applied NH₄‐N.     

3,4二甲基吡唑磷酸盐和双氰胺在黑钙土中对尿素氮转化的作用效果

采用室内培养试验,以普通尿素为对照,研究双氰胺(DCD)、3,4-二甲基吡唑磷酸盐(DMPP)和缓释尿素在东北黑钙土中对尿素氮转化的作用效果。结果表明,缓释尿素对尿素水解有一定的限制作用。0.5%DMPP对抑制氨氧化作用效果最好,保持低表观硝化率时间最长,硝化抑制率最高,有效作用时间最长,最佳有效抑制时间为42 d,有效作用时间可达63 d,显著好于2%DCD;2%DCD也有显著的抑制效果,保持低表观硝化率时间较长,硝化抑制率较高,最佳抑制时间为35 d,有效作用时间超过56 d,缓释尿素最佳作用时间为7 d,有效作用时间可达35 d。作用效果为添加0.5%DMPP+尿素添加2%DCD+尿素缓释尿素普通尿素。     

DCD 在不同质地土壤上的硝化抑制效果和剂量效应研究

通过硝化抑制剂抑制土壤硝化作用是实现作物铵硝混合营养和提高氮肥利用率的重要途径之一。本试验采用室内模拟的方法, 在人工气候室(25 ℃)黑暗培养条件下, 应用新疆石灰性土壤研究了不同剂量的双氰胺(dicyandiamide, DCD)在砂土、壤土、黏土3 种不同质地土壤中对土壤硝态氮、铵态氮转化的影响及DCD 的剂量效应和硝化抑制效果。处理30 d 内, 各剂量DCD 处理对砂土的硝化抑制率为96.5%~99.4%(平均值为98.3%), 在黏土上为66.9%~85.6%(平均值为77.6%), 在壤土上为49.3%~79.4%(平均值为67.7%), 总体硝化抑制率表现为砂土>黏土>壤土。在砂土上DCD 的剂量效应不明显, DCD 用量从纯氮的1.0%增加到7.0%时, 土壤中硝态氮含量仅增加1.9~10.7 mg·kg^-1(培养30 d 时); 而在壤土和黏土中, 土壤硝态氮含量随DCD 浓度的增加而显著下降, 存在明显剂量效应。这说明施用DCD 可显著抑制新疆石灰性土壤的硝化作用过程, 在砂土、壤土、黏土中DCD 的最佳浓度分别为纯氮用量的6.0%、7.0%和7.0%, 并在培养30 d 内发挥显著作用。     

Plant availability of magnesium and phosphorus from struvite with concurrent nitrification inhibitor application

Struvite (MgNH₄PO₄.6H₂O) and nitrification inhibitors are applied to soils to, respectively, provide nutrients and reduce nitrogen (N) loss. Given its low N composition (5.7%) relative to that of phosphorus (P, 12.6%) and magnesium (Mg, 9.9%), struvite could be added to soil concurrently with N fertilizers as a source of P and Mg. Nutrient release from struvite could be impacted if nitrification of its ammonium component is reduced by a nitrification inhibitor. Accordingly, a pot trial gauged whether struvite‐fertilized ryegrass had comparable Mg or P uptake and shoot yields with treatments receiving conventional Mg and P fertilizers. Struvite precipitated from milk industry wastewater, or conventional fertilizers, were added to a soil–sand mixture of low fertility. The inhibitor dicyandiamide (DCD) was added to assess its effect on P uptake by ryegrass. Relative to Epsom salt, struvite led to increased Mg uptake without significantly affecting shoot biomass, indicating luxury consumption. Regarding shoot yield and P uptake, struvite was as effective as triple super phosphate. DCD significantly reduced P uptake in the first harvest; the inhibited nitrification of the ammonium is surmised to have diminished struvite dissolution. In later harvests, DCD led to a trend (albeit not statistically significant) of increased biomass; this N‐rich (66% N) compound was probably biodegraded and utilized as an N source. The impact of DCD on P uptake in this experiment was short‐lived. Nevertheless, DCD degradation occurs less rapidly in field conditions, potentially affecting early P supply which is vital for optimum yield.     

氮素与抑制剂双控释尿素的制备及其对土壤供氮能力和小麦产量的影响

  【目的】  包衣和添加抑制剂是常用的制备缓控释肥料的手段。尝试同时使用这两种方法,制备更加可控氮素释放与转化的新型肥料,并研究其在小麦上的应用效果。  【方法】  采用先在大颗粒尿素 (2.5～3.5 mm) 表面涂层,再用树脂包膜的方法制备含不同抑制剂的树脂包膜尿素。依据不同抑制剂,制备了无涂层 (CU)、脲酶抑制剂HQ涂层 (CRU1)、硝化抑制剂DCD涂层 (CRU2) 和HQ + DCD组合涂层 (CRU3) 4种新型树脂包膜尿素。通过扫描电镜观测了4种包膜尿素的微观结构,采用静水释放的方法测定了养分和抑制剂的缓释性能。在山东省潍坊和泰安两地布置冬小麦等氮磷钾施用量和相同施肥方法的田间试验,以普通大颗粒尿素为对照,在冬小麦苗期、拔节期、开花期、灌浆期和成熟期采集耕层土壤样品,测定速效氮含量,并于小麦成熟期测定产量及构成因素。  【结果】  1) 制备的4种包膜尿素成膜完整,包膜厚度均匀,表面光滑且膜层致密,树脂包膜材料能完整地覆盖在肥核的表面,膜表面有微孔,成为尿素和抑制剂向膜外释放的通道;尿素与抑制剂交接处结合严密,无间隙产生,抑制剂在包膜层的完全包围之中,可实现对尿素和抑制剂释放的同时控制。2) 包膜与抑制剂结合可有效控制尿素溶出。静水释放条件下,4种包膜尿素的氮素初期溶出率分别为7.59%、1.96%、2.12%、0.89%,尿素控释期依次是42、56、56、56天;CRU1的HQ释放期为28天,CRU2的DCD释放期为14天,CRU3中HQ和DCD的释放期分别为42和14天。相比较而言,CRU3的氮素释放期长于CRU1和CRU2,抑制剂的释放期也长于CRU1和CRU2,因此缓释效果大于CRU1和CRU2。3) 与大颗粒尿素对照 (U) 相比,4个包膜尿素处理在小麦苗期能维持土壤中NH₄+-N的适宜浓度,开花期后显著增加土壤NH₄+-N含量,保障了氮素的持续供应;而在小麦整个生育期内均显著降低土壤NO₃–-N含量,从而减少氮素淋溶损失。含HQ涂层的CRU1、CRU3处理能在小麦生育期内维持土壤脲酶活性处于较低水平;含DCD涂层的CRU2、CRU3处理能够抑制土壤NH₄+-N向NO₃–-N的转化,显著降低土壤NH₄+-N表观硝化率。与CU相比,CRU1、CRU2和CRU3处理的小麦产量在潍坊试验点分别显著增加23.38%、23.13%和38.79%,在泰安试验点分别增加6.36%、9.52%和28.57%。  【结论】  先在大颗粒尿素表面包裹抑制剂涂层,再包裹树脂,可在尿素表面形成完整且均匀的膜,而且在膜表面仍有一定量的微孔,实现尿素与抑制剂释放的同时控制。小麦整个生育期,与施用单一抑制剂的包膜尿素处理相比,施用含两种抑制剂 (CRU3) 的包膜尿素处理的土壤氮素持续供应能力更强,小麦产量最高;而且土壤硝态氮水平一直较低,也减少了氮素淋溶损失的可能。     

肥料添加剂降低N2O排放的效果与机理

如何降低氮肥施入农田后的N2O排放,实现氮肥增产效应的同时降低其对环境的负面影响是全球集约化农业生产中重要的科学问题,氮肥添加剂是有效途径之一。本研究采用室内静态培养法,在调节土壤水分含量和温度等环境因素的条件下,研究不同肥料添加剂对华北平原典型农田土壤N2O排放的影响及其机制。结果表明,N2O排放通量的峰值大约出现在施氮后的第24 d,肥料混施较肥料表施的出峰时间提前。与单施尿素处理相比,添加硝化抑制剂DMPP或DCD能分别降低N2O排放总量99.2%和97.1%; 添加硫酸铜对N2O排放的抑制作用不显著; 添加秸秆会增加N2O排放总量60.7%,而在添加秸秆的土壤中施加硝化抑制剂DMPP能够显著降低N2O排放量至无肥对照水平。说明华北平原农田土壤中N2O的产生主要是由硝化作用驱动,同时也可看出,添加硝化抑制剂是N2O减排的有效措施。     

几种硝化抑制剂和包硫尿素(SCU)对土壤N素形态和小麦产量的影响

采用土壤盆栽法,研究了双氰胺(DCD)、硫脲(THU)和硫脲甲醛树脂(TFR)以及包硫尿素(SCU)对土壤氮素形态和小麦产量的影响。试验共设不施氮(CK)、单施尿素、包硫尿素(SCU)、以及尿素分别与DCD、THA、TUF的3个浓度梯度(分别按尿素用量的0.5%、1%、2%)配合施用共12个处理。结果表明:随添加浓度的增加,硝化抑制作用逐渐增强,高剂量硝化抑制剂显著降低土壤NO-3-N含量,在2%添加浓度下,DCD、THU、TFR的土壤NO-3-N浓度分别比单施尿素降低29%、22%和14%,对土壤表观硝化率的抑制强度也是2%DCD2%THU2%TFR;SCU处理与2%DCD作用强度接近,且在施用早期就体现抑制效果,并在追肥后第74 d土壤表观硝化率显著低于使用硝化抑制剂的处理(P0.05);硝化抑制剂和SCU都可以使土壤NH+4-N含量稳定在较高的水平,抑制剂用量越多,土壤NH+4-N含量越高;与单施尿素相比,尿素+DCD模式,均可提高小麦产量,且在0.5%、1%、2%添加浓度,都达到显著水平(P0.05);THU在1.0%和2.0%添加浓度,小麦产量显著高于单施尿素,但增产效果次于DCD。总体上,包硫尿素(SCU)比硝化抑制剂在控释氮素方面效果更持久,而3种硝化抑制剂中,在控制土壤NH+4-N转化、土壤硝化抑制方面,DCD和THU优于TFR;作为外源添加物的抑制剂长期应用可能对土壤环境造成潜在的危害,不同硝化抑制在土壤中的形态归趋和长期作用还有待进一步研究。     

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

Urea 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 (<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.     

Nitrification Inhibitor,Fertilizer Rate,and Temperature Effects on Nitrous Oxide Emission and Nitrogen Transformation in Loamy Sand Soil

An incubation study investigated the effects of nitrification inhibitors (NIs), dicyandiamide (DCD), and neem oil on the nitrification process in loamy sand soil under different temperatures and fertilizer rates. Results showed that NIs decreased soil nitrification by slowing the conversion of soil ammonium (NH₄⁺)-nitrogen (N) and maintaining soil NH₄⁺-N and nitrate (NO₃^?)-N throughout the incubation time. DCD and neem oil decreased soil nitrous oxide (N₂O) emission by up to 30.9 and 18.8%, respectively. The effectiveness of DCD on reducing cumulative soil N₂O emission and retaining soil NH₄⁺-N was inconsistently greater than that of neem oil, but the NI rate was less obvious than temperature. Fertilizer rate had a stronger positive effect on soil nitrification than temperature, indicating that adding N into low-fertility soil had a greater influence on soil nitrification. DCD and neem oil would be a potential tool for slowing N fertilizer loss in a low-fertility soil under warm to hot climatic conditions.     

Decomposition rate of dicyandiamide and nitrification inhibition

Abstract

Degradation of dicyandiamide (DCD) was assayed in laboratory studies at 8, 15, and 22 C in a Decatur silt loam and in a Norfolk loamy sand. Dicyandiamide was very short lived at 22 C, with half‐lives of 7.4 and 14.7 days in the Decatur and Norfolk soils, respectively. In the Norfolk soil at 8 C, half‐life increased to 52.2 days. In a nitrificaton study of both soils at 22 C, 80 mg (NH₄)₂SO₄‐N kg^‐1 of soil was applied with 20 mg DCD‐N kg^‐1 of soil and 100 mg kg^‐1 (NH₄)₂S0₄‐N was added with 5% nitrapyrin. Distinct lag phases preceded zero order nitrification with the inhibitor treatments. Lag periods were 2 and 2.6 times the half life of DCD in the degradation study for Decatur and Norfolk soils, respectively. Like most nitrification inhibitors, the effectiveness of DCD decreases with increasing temperature. In the Norfolk loamy sand, nitrification inhibition by DCD was equal to nitrapyrin for up to 42 days, but in Decatur silt loam, DCD was less potent to nitrapyrin as a nitrification inhibitor.     

Exchangeable ammonium and nitrate from different nitrogen fertilizer preparations in polyacrylamide-treated and untreated agricultural soils

 High molecular weight, anionic polyacrylamide (PAM) is currently being used as an irrigation water additive to significantly reduce soil erosion associated with furrow irrigation. PAM contains amide-N, and PAM application to soils has been correlated with increased activity of soil enzymes, such as urease and amidase, involved in N cycling. Therefore we investigated potential impacts of PAM treatment on the rate at which fertilizer N is transformed into NH₄ ⁺ and NO₃ ^– in soil. PAM-treated and untreated soil microcosms were amended with a variety of fertilizers, ranging from common rapid-release forms, such as ammonium sulfate [(NH₄)₂SO₄] and urea, to a variety of slow-release formulations, including polymerized urea and polymer-encapsulated urea. Ammonium sulfate was also tested together with the nitrification inhibitor dicyandiamide (DCD). The fertilizers were applied at a concentration of 1.0 mg g^–1, which is comparable to 100 lb acre^–l, or 112 kg ha^–1. Potassium chloride-extractable NH₄ ⁺-N and NO₃ ^–-N were quantified periodically during 2–4 week incubations. PAM treatment had no significant effect on NH₄ ⁺ release rates for any of the fertilizers tested and did not alter the efficacy of DCD as a nitrification inhibitor. However, the nitrification rate of urea and encapsulated urea-derived NH₄ ⁺-N was slightly accelerated in the PAM-treated soil. Received: 16 January 1998