三种硝化抑制剂在石灰性土壤中的应用效果比较

在人工气候室内采用25℃黑暗培养法研究双氰胺(DCD)、3,4-二甲基吡唑磷酸(DMPP)及2-氯-6-三氯甲基吡啶(Nitrapyrin)在石灰性土壤中的硝化抑制效果。结果表明:施用DCD、DMPP、Nitrapyrin的土壤NH4+-N含量较单施硫酸铵的土壤(对照)分别提高228.45~244.85 mg/kg(砂土)、209.75~254.79 mg/kg(黏土),NO3--N含量较对照分别降低93.85%~94.99%(砂土)、91.82%~95.38%(黏土)。表观硝化率随培养进程增加缓慢,培养期间只增加了1.28%~2.09%(砂土)、2.72%~8.40%(黏土),而对照增加了86.00%(砂土)、80.89%(黏土)。3种硝化抑制剂均显著抑制了石灰性土壤中硫酸铵水解铵硝化作用的进行,并且在砂土中的硝化抑制率高于黏土,硝化抑制效果最好的为DMPP处理,0.54%Nitrapyrin处理次之但用量最小,0.27%Nitrapyrin和10.8%DCD处理抑制效果相对较弱。     

石灰和双氰胺对红壤酸化和硝化作用的影响及其机制

施用石灰是改良酸性土壤的重要措施,但其对土壤硝化作用的增强不仅加速土壤酸化,也增加硝态氮流失风险.传统的硝化抑制剂双氰胺(Dicyandiamide,DCD)能否在石灰改变pH的条件下始终有效抑制硝化是当前红壤区生产中亟需解决的问题.采用短期土壤培养试验,探讨了不同用量石灰与DCD配合施用对土壤酸化和硝化作用的影响及其...     

三种硝化抑制剂抑制土壤硝化作用比较及用量研究

【目的】硝化抑制剂是调控土壤氮素转化与硝化作用微生物群落结构的有效途径。本文通过室内模拟试验对3种硝化抑制剂在不同剂量下的硝化抑制效果进行研究,旨在筛选出效果最佳的剂型与剂量,为石灰性土壤硝化抑制剂的合理应用提供依据。 【方法】培养试验在生长箱内进行,25℃黑暗条件培养;盆栽试验在温室内进行。供试硝化抑制剂为双氰胺（DCD）、3,4-二甲基吡唑磷酸盐（DMPP）和2-氯-6-三氯甲基吡啶（Nitrapyrin）,DCD和DMPP用量均设定为纯氮（N）量的0（CK）、1.0%、2.0%、3.0%、3.5%、4.0%、4.5%、5.0%、6.0%和7.0%;Nitrapyrin用量分别为纯氮量的0、0.1%、0.125%、0.2%、0.25%、0.3%、0.35%、0.4%、0.45%和0.5%,三种硝化抑制剂均设10个水平,每个水平3次重复。盆栽试验氮加入量为每公斤风干土0.50 g,三种硝化抑制剂用量分别为纯氮用量的5%、1%、0.648%。调查比较了三者的硝化抑制效果及对土壤氮素转化的影响及其对小青菜鲜重的生物学效应;采用变性梯度凝胶电泳（DGGE）法分析了不同硝化抑制剂对土壤AOA、AOB群落结构的影响。 【结果】DCD、DMPP、Nitrapyrin均可显著抑制土壤硝化作用（P＜0.05）,各硝化抑制剂处理土壤的NH₄+-N含量分别较对照提高了46.2~256.1 mg/kg、291.8~376.7 mg/kg、3.68~372.9 mg/kg。DCD与DMPP处理的硝化抑制率分别为49.3%~79.4%和96.4%~99.4%,DCD表现出明显的剂量效应,但DMPP在1%~7%浓度范围内的剂量效应不明显。Nitrapyrin在0.1%~0.2%浓度范围内有明显的剂量效应。0.25%~0.5% Nitrapyrin的硝化抑制率为98.9%~99.9%,其硝化抑制效果与DMPP处理相同。DCD、DMPP、Nitrapyrin处理的小青菜地上部分鲜重分别比氮肥处理（ASN）提高了12.7%、11.1%、17.6%。施用硝化抑制剂可改变土壤AOA和AOB群落结构,且对AOA群落结构的影响大于AOB,不同硝化抑制剂之间对AOA和AOB群落结构的影响无差异。 【结论】3种硝化抑制剂的硝化抑制效果表现为Nitrapyrin≥DMPP>DCD,均对AOA与AOB群落结构产生明显影响。各硝化抑制剂处理均可提高小青菜地上部鲜重、叶片Vc含量及可显著提高小青菜叶片氨基酸含量（P＜0.05）。综合比较,Nitrapyrin硝化抑制效果好于DMPP,DCD效果最差,推荐用量为基于纯氮0.25%的Nitrapyrin添加量。     

硝化抑制剂类型和剂量对不同类型土壤硝化抑制作用机理的研究

氮肥配施硝化抑制剂是提高氮肥利用率、减少活性氮损失和降低环境代价风险的有效措施。为探讨不同硝化抑制剂类型和剂量对不同类型土壤硝化作用的机理,采用室内土壤培养试验,对3种硝化抑制剂[双氰胺(DCD)、3,4-二甲基吡唑磷酸盐(DMPP)和2-氯-6-(三氯甲基)吡啶(NP)]设置不同剂量,研究其对我国不同区域典型土壤(红壤、水稻土、潮土)硝化过程无机氮含量、土壤pH值及土壤表观硝化率变化特征的影响。结果表明,与单施硫酸铵处理相比,3种硝化抑制剂均能抑制水稻土和潮土中铵态氮向硝态氮的转化,且对潮土铵态氮向硝态氮转化抑制效果优于水稻土,而对红壤硝化作用的抑制效果均不明显,3种土壤pH值差异是影响硝化抑制剂作用效果的主因。此外,DCD和NP随着用量的增加,对水稻土和潮土的硝化抑制效果越明显,而DMPP对2种土壤硝化抑制作用无明显的剂量效应。在水稻土中,NP的抑制效果强于DMPP和DCD;在潮土中,DCD的抑制效果优于NP和DMPP,这可能是由于不同硝化抑制剂类型硝化抑制机理性的差异以及其自身特性的差异导致的。综上,针对特定土壤类型筛选适宜的硝化抑制剂类型和用量对农业优化氮肥管理、提高氮肥利用率尤为重要。     

双氰胺对不同质地红壤中碳酸氢铵的硝化抑制作用研究

通过室内好气培养试验,研究了双氰胺(DCD)对施入不同质地红壤中碳酸氢铵的硝化抑制作用。结果表明,添加DCD明显提高了相应处理的铵态氮含量,降低了硝态氮含量。无论加入DCD与否,砂壤土中碳酸氢铵的硝化时间大约都需7周;轻粘土中碳酸氢铵的硝化时间为35.d,加入硝化抑制剂后硝化时间可延长2周;而中壤土中至培养结束时仍有较高的铵态氮,故铵的硝化时间有待进一步研究。DCD对碳酸氢铵的硝化抑制效果中壤土优于砂壤土、轻粘土;在砂壤土和轻粘土中,DCD对低浓度铵态氮处理的硝化抑制效果好;而在中壤土中对高浓度的抑制效果好。     

两种硝化抑制剂对土壤氮转化的影响

为比较硝化抑制剂双氰胺、硫代硫酸钾对土壤氮的硝化抑制效果,明确其对土壤氮转化作用效应,采用室内培养试验方法,研究了双氰胺、硫代硫酸钾及其配施对土壤矿质氮动态变化、硝化作用及氮回收率的影响。结果表明,单施氮肥土壤硝化作用活跃,77.7%的化肥氮以铵态氮形式从矿质氮库消失,其中56.6%的氮形成硝态氮。氮肥配施双氰胺、硫代硫酸钾分别显著降低矿质氮库铵态氮消失量74.1%(P0.01)和16.6%(P0.05),同时配施双氰胺和硫代硫酸钾处理铵态氮出现增加现象。氮肥配施双氰胺及同时配施2种抑制剂均不同程度地抑制氮的硝化作用,抑制率分别为35.5%~98.7%和82.2%~103.5%,硝化作用延滞时间均在20 d以上。氮肥配施硫代硫酸钾的硝化抑制率为1.6%~62.6%,硝化作用延滞时间为10 d。双氰胺硝化抑制效应优于硫代硫酸钾,且2种抑制剂同时配施作用效果优于其单独施用。施用硫代硫酸钾可促进土壤NO2--N积累,双氰胺可抑制NO2--N生成。氮肥配施双氰胺及同时配施两种抑制剂处理显著增加土壤矿质氮含量、降低其他去向氮含量同时显著提高土壤矿质氮回收率14.7%(P0.05)和12.0%(P0.05)。总体上,抑制剂双氰胺在铵态氮转化、硝化作用抑制及提高矿质氮回收率等方面作用效果均优于硫代硫酸钾,硫代硫酸钾与双氰胺配施在硝化抑制作用方面具有协同效应。该研究结果可为双氰胺、硫代硫酸钾在农田氮素面源污染控制中的应用提供科学依据,但对2种抑制剂硝化抑制特性的全面了解,尚需在田间试验条件下进行进一步的研究和验证。     

土壤pH值和含水量对土壤硝化抑制剂效果的影响

硝化抑制剂如2-氯-6-三氯甲基吡nitrapyrin,通常与氮肥配施来抑制硝化作用提高农田中肥料的利用率,但是其抑制效果会受到土壤理化性质的影响。采用新工艺重新合成后的新型nitrapyrin纯度高达98%,由于杂质减少而具有更好的硝化抑制效果。为了研究土壤pH值和含水量对新型nitrapyrin抑制效果的影响,明确nitrapyrin适合施用的土壤条件,采用室内培养试验,研究了在不同的土壤pH值和含水量下nitrapyrin对无机氮含量动态变化和硝化作用强度的影响,以及其硝化抑制率的变化规律。结果表明:随着土壤pH值的升高,铵态氮含量降低,硝态氮含量和表观硝化率呈现上升的趋势,并且在所有pH值处理下氮肥配施nitrapyrin均显著地降低了矿质氮库铵态氮的转化量,均不同程度地抑制了硝化作用;在培养的第9天,nitrapyrin在pH值7.70处理下对硝化作用抑制效果最好,硝化抑制率达到91.53%,但硝化抑制率的降低速率在高pH值处理上更快;在培养的第45天,当pH值为4.66时,硝化抑制率为36.43%,显著高于其他处理;在整个培养过程中,施用nitrapyrin能显著抑制各处理的硝化作用,硝化抑制率在不同土壤含水量上的表现为:40%WHC60%WHC80%WHC。可见,nitrapyrin更加适合施用在酸性土壤以及旱地土壤上,该研究可以为新型硝化抑制剂nitrapyrin在农田中施用的最优条件提供理论依据。     

几种吡啶类化合物对土壤硝化的抑制作用比较

为了探明吡啶类化合物对土壤硝化作用的抑制效应,采用室内微宇宙试验,研究了2-氯-6(三氯甲基)硫酸盐、2-氯-6(三氯甲基)盐酸盐、吡啶混合物和吡啶X类化合物对潮土、红壤和水稻土中铵态氮硝化的抑制作用。结果表明,在35 d培养期内,吡啶类化合物处理土壤硝态氮含量明显低于对照(未添加吡啶类化合物),吡啶类化合物对土壤中铵态氮的硝化抑制率介于2.91%~91.92%,抑制强度先逐渐升高后降低,在培养21 d时抑制强度达到峰值。不同类型吡啶类化合物对土壤中铵态氮的硝化抑制效果存在差异,吡啶盐酸盐类化合物优于其他几类化合物;吡啶类化合物对土壤中铵态氮的硝化抑制作用与土壤类型有关,对3种土壤中铵态氮的硝化抑制作用表现为潮土>水稻土>红壤。就同一土壤而言,硝化抑制强度随着吡啶类化合物用量的增加而增加。     

添加DCD对雨养区春玉米产量、 氧化亚氮排放及硝态氮残留的影响

【目的】田间条件下氮肥中添加硝化抑制剂双氰胺(dicyandiamide,DCD)对氧化亚氮排放和硝态氮含量变化的影响尚不清楚,研究不同施氮模式对玉米产量、 氧化亚氮排放以及对土壤深层硝态氮残留和氮肥农学效率等的影响,对提高氮肥利用效率、 减少农业源温室气体排放具有重要意义。【方法】试验于2013年4月至2014年9月,在中国科学院长武黄土高原农业生态试验站进行,供试作物为春玉米,品种为先玉335,半覆膜种植。试验设4个处理: 传统施氮(Con)、 减量施氮(Opt)、 减量施氮+硝化抑制剂(Opt+DCD)、 不施氮(N0),定期采集土样和氧化亚氮气体,利用流动分析仪和气象色谱仪测定土壤矿质氮和氧化亚氮的含量,采用SAS软件对不同处理的产量和各个指标进行方差分析。【结果】Opt和Opt+DCD在保持产量的同时,显著影响氧化亚氮排放和硝态氮残留。Opt处理的硝态氮含量峰值降低13.7%,而Opt+DCD处理降低硝态氮峰值19.0%。其次,施氮模式还影响硝态氮峰值出现的时间: Con(190.1 mg/kg)率先出现, 其次是Opt(164.0 mg/kg)和Opt+DCD(132.9 mg/kg)。Opt显著降低了氧化亚氮的排放,降幅为29.4%,而在Opt基础上添加DCD可进一步降低氧化亚氮排放28.1%。在雨季,硝态氮含量和氧化亚氮排放随降雨而出现波动。尽管Opt降低了铵态氮峰值,但在Opt基础上,添加DCD提高了铵态氮峰值。4种施氮模式土壤剖面0100 cm和100200 cm的硝态氮残留量分别介于33.5~148.9和24.8~92.8 kg/hm2之间,平均值分别为78.5和56.4 kg/hm2。土壤剖面0200 cm的硝态氮残留量以Con最大,为225.9 kg/hm2,与Con相比,Opt和Opt+DCD的硝态氮残留量降幅分别为48.0%~59.0%、 29.4%~57.5%。Opt和Opt+DCD之间硝态氮残留差异不显著(P0.05)。【结论】不同施氮模式对玉米产量、 矿质氮和氧化亚氮的动态变化以及氮肥农学效率具有显著影响,但是Opt和Opt+DCD在施氮量减少20%的同时,不仅没有显著降低玉米产量,还进一步降低了土壤剖面硝态氮的残留量和农业源温室气体的排放。因此在黄土高原雨养农业区,添加DCD是一种科学有效的施肥管理方式。     

用于黑土的稳定性氯化铵的适宜硝化抑制剂和氮肥增效剂组合

【目的】本文研究添加不同种类硝化抑制剂的高效稳定性氯化铵氮肥在黑土中的施用效果，旨在筛选出适合旱作黑土的高效稳定性氯化铵态氮肥。【方法】在氯化铵中分别添加硝化抑制剂3,4-二甲基吡唑磷酸盐 (DMPP)、双氰胺 (DCD)、2-氯-6-三甲基吡啶 (Nitrapyrin，CP)、氨保护剂 (N-GD) 和1种氮肥增效剂 (HFJ) 及其组合，制成9种稳定性氯化铵氮肥。以不施氮肥 (CK) 和施普通氯化铵 (CK-N) 为对照，以9种稳定性氯化铵为处理进行了等氮量盆栽试验。在玉米苗期、大喇叭口期、灌浆期和成熟期测定了土壤中铵态氮和硝态氮含量，在玉米成熟期测定植株生物量、籽粒产量和氮素含量，计算铵态氮肥的表观硝化率、硝化抑制率、氮肥农学效率、氮肥偏生产力。【结果】1) 与CK-N处理相比，9个处理均显著提高玉米的产量，HFJ的效果均为最显著，可增加玉米籽粒产量3.99倍，提高氮肥吸收利用率4.98倍，显著高于8个硝化抑制剂处理 (P < 0.05)。CP + DMPP和CP + DCD处理提高玉米籽粒产量1.90～2.11倍，两个处理之间无显著差异；CP + DMPP玉米生物量显著高于CP处理，而与DMPP和DCD处理无显著差异；CP + DMPP玉米氮肥吸收利用率显著高于CP和DMPP处理，显著提高3.71倍 (P < 0.05)；2) CP + DMPP和CP + DCD土壤中铵态氮含量提高2.09～2.42倍，且显著高于CP、DMPP和DCD处理 (P < 0.05)，而硝态氮含量和土壤表观硝化率均显著降低24%和66%～68%，与CP和DCD处理存在显著差异 (P < 0.05)；苗期CP + DMPP和CP + DCD硝化抑制率高达23.9%～24.3%，显著高于CP和DCD (P < 0.05)。【结论】在黑土中，氯化铵中添加硝化抑制剂组合的硝化抑制率显著高于添加单一抑制剂，能够有效减缓土壤中铵态氮向硝态氮的转化，减少土壤中氮素损失，降低环境污染。CP + DMPP组合玉米的氮肥吸收利用率显著高于CP + DCD组合。氮肥增效剂HFJ显著增加玉米的氮素吸收量，提高氮肥利用率，从而使玉米获得高产并获得较高的收获指数和经济系数。因此，综合考虑产量和抑制硝化作用等因素，黑土区氯化铵作为玉米生产用氮肥时，建议首选添加氮肥增效剂HFJ来保证作物的高产和氮肥高利用率，也可以添加硝化抑制剂组合CP + DMPP，或者CP + DCD制备稳定性氯化铵来提高氯化铵的增产效果和氮肥利用率，减少氮素损失，降低环境污染。     

Effects of 4-amino 1,2,4-triazole, dicyandiamide and encapsulated calcium carbide on nitrification inhibition in a subtropical soil under upland and flooded conditions

 Nitrification inhibition of soil and applied fertilizer N is desirable as the accumulation of nitrates in soils in excess of plant needs leads to enhanced N losses and reduced fertilizer N-use efficiency. In a growth chamber experiment, we studied the effects of two commercial nitrification inhibitors (NIs), 4-amino 1,2,4-triazole (ATC) and dicyandiamide (DCD), and a commonly available and economical material, encapsulated calcium carbide (CaC₂) (ECC) on the nitrification of soil and applied NH₄ ⁺-N in a semiarid subtropical Tolewal sandy loam soil under upland [60% water-filled pore space (WFPS)] and flooded conditions (120% WFPS). Nitrification of the applied 100 mg NH₄ ⁺-N kg^–1 soil under upland conditions was retarded most effectively (93%) by ECC for up to 10 days of incubation, whereas for longer periods, ATC was more effective. After 20 days, only 16% of applied NH₄ ⁺-N was nitrified with ATC as compared to 37% with DCD and 98% with ECC. Under flooded soil conditions, nitrates resulting from nitrification quickly disappeared due to denitrification, resulting in a tremendous loss of fertilizer N (up to 70% of N applied without a NI). Based on four indicators of inhibitor effectiveness, namely, concentration of NH₄ ⁺-N and NO₃ ^–-N, percent nitrification inhibition, ratio of NH₄ ⁺-N/NO₃ ^–-N, and total mineral N, ECC showed the highest relative efficiency throughout the 20-day incubation under flooded soil conditions. At the end of the 20-day incubation, 96%, 58% and 38% of applied NH₄ ⁺-N was still present in the soil where ECC, ATC and DCD were used, respectively. Consequently, nitrification inhibition of applied fertilizer N in both arable crops and flooded rice systems could tremendously minimize N losses and help enhance fertilizer N-use efficiency. These results suggest that for reducing the nitrification rate and resultant N losses in flooded soil systems (e.g. rice lowlands), ECC is more effective than costly commercial NIs. Received: 25 May 2000     

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.     

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.     

Nitrous oxide emissions from two dairy pasture soils as affected by different rates of a fine particle suspension nitrification inhibitor, dicyandiamide

In grazed pasture systems, a major source of N₂O is nitrogen (N) returned to the soil in animal urine. We report in this paper the effectiveness of a nitrification inhibitor, dicyandiamide (DCD), applied in a fine particle suspension (FPS) to reduce N₂O emissions from dairy cow urine patches in two different soils. The soils are Lismore stony silt loam (Udic Haplustept loamy skeletal) and Templeton fine sandy loam (Udic Haplustepts). The pasture on both soils was a mixture of perennial ryegrass (Lolium perenne) and white clover (Trifolium repens). Total N₂O emissions in the Lismore soil were 23.1–31.0 kg N₂O-N ha⁻¹ following the May (autumn) and August (late winter) urine applications, respectively, without DCD. These were reduced to 6.2–8.4 kg N₂O-N ha⁻¹ by the application of DCD FPS, equivalent to reductions of 65–73%. All three rates of DCD applied (7.5, 10 and 15 kg ha⁻¹) were effective in reducing N₂O emissions. In the Templeton soil, total N₂O emissions were reduced from 37.4 kg N₂O-N ha⁻¹ without DCD to 14.6–16.3 kg N₂O-N ha⁻¹ when DCD was applied either immediately or 10 days after the urine application. These reductions are similar to those in an earlier study where DCD was applied as a solution. Therefore, treating grazed pasture soils with an FPS of DCD is an effective technology to mitigate N₂O emissions from cow urine patch areas in grazed pasture soils.     

Nitrification and utilization of fertilizer nitrogen by highbush blueberry

Nitrification rates and nitrogen (N) recovery by 3 year‐old highbush blueberry ( Vaccinium corymbosum L. cv. Bluecrop) were compared following applications of ammonium sulfate with or without the nitrification inhibitor dicyandiamide (DCD) on a sandy loam soil with pH 4.8. Ammonium sulfate solutions containing 7.9 grams N (10.2 atom % ¹⁵N), with or without 0.6 g DCD, were applied to the soil surface beneath bushes. Concentrations of fertilizer derived nitrate were significantly lower in DCD treated soils 2 weeks following application, but DCD had no effect on total nitrate levels or fertilizer derived nitrate later in the season. Uptake of fertilizer‐N by blueberry plants was observed by collecting fruit during the growing season and assessing N partitioning within whole plants at the end of the season using ¹⁵N as a label for fertilizer N. The DCD had no effect on fertilizer derived or total N levels in plants. Plants recovered an average of 3% of applied N by the end of the season.     

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.     

Evaluation of ecological doses of the nitrification inhibitors 3,4-dimethylpyrazole phosphate (DMPP) and 4-chloromethylpyrazole (ClMP) in comparison to dicyandiamide (DCD) in their effects on dehydrogenase and dimethyl sulfoxide reductase activity in soils

Risk assessment of the nitrification inhibitors (NIs) 3,4-dimethylpyrazole phosphate (DMPP), 4-chloromethylpyrazole (ClMP), and dicyandiamide (DCD) on nontarget microbial activity in soils was determined by measuring dehydrogenase and dimethyl sulfoxide reductase activity (DHA, DRA, respectively) in three differently textured soils under laboratory conditions. Dehydrogenase activity was measured with standard procedure recommended to evaluate side effects of environmental chemicals on general microbial activity in soils. The kinetic of inhibition were obtained by dose–response relationships and used to calculate the no observable effect levels (NOEL values) and the effective doses at 10% and 50% inhibition (ED₁₀ and ED₅₀), respectively. Negative effects on DHA and DRA, respectively, were observed only at rates approximately 40–100 times higher than the concentrations recommended in the field. Both DHA and DRA were affected more in the sandy than in the silty or clayey soil. Consequently, NOEL, ED₁₀, and ED₅₀ values were considerably higher in the clayey than in the silty or sandy soil. The heterocyclic N compounds DMPP and ClMP, respectively, were more effective in inhibiting DHA and DRA than DCD. At application rates used in the field as well as at concentration up to 25 to 90 times higher, the NIs concerned failed to affect general soil microbial activity in soils. Among the three NIs tested, the not marketed ClMP exhibited the strongest negative effects on soil microbial activity. At recommended application rates, the NIs tested should be considered as enviromentally safe.     

Evaluation of Two Products Recently Introduced as Nitrification Inhibitors

This study compared the relative effectiveness of two products recently introduced as nitrification inhibitors with other materials used to inhibit nitrification. Four soils were treated with 0, 0.2, 1, 5, and 25 mg kg^?1 of nitrapyrin (NP), a new microencapsulated nitrapyrin product (ENP), dicyandiamide (DCD), a new maleic-itaconic polymer product (MIP), and ammonium thiosulfate (ATS). The soils were also treated with 200 mg N kg^?1 as urea, and percent inhibition of nitrification determined after 2 or 4 weeks of incubation. After 4 weeks, similar levels of nitrification inhibition were provided by 1 mg kg^?1 of NP (72%), 5 mg kg^?1 of ENP (79%), and 25 mg kg^?1 of DCD (73%), averaged across soil. After 4 weeks with a sandy soil, the highest rate of MIP and ATS provided 15 and 36% inhibition, respectively. MIP and ATS were ineffective at inhibiting nitrification when added to the other three soils.

Abbreviations: ATS: ammonium thiosulfate; DCD: dicyandiamide; ENP: encapsulated nitrapyrin; MIP: maleic-itaconic polymer; NP: nitrapyrin; UAN: urea-ammonium nitrate liquid fertilizer