Impact of urease and nitrification inhibitor on NH4+ and NO3− dynamic in soil after urea spring application under field conditions evaluated by soil extraction and soil solution sampling

The application of mineral nitrogen (N) fertilizers is one of the most important management tools to ensure and increase yield in agricultural systems. However, N fertilization can lead to various ecological problems such as nitrate () leaching or ammonia and nitrous oxide emissions. The application of N stabilizers (i.e., inhibitors) combined with urea fertilization offers an effective option to reduce or even prevent N losses due to their regulatory effect on ammonium () and release into the soil. The present field experiment therefore aimed at soil N speciation dynamics after urea spring fertilization (225 kg N ha^?1) in the presence of a urease inhibitor (UI), a nitrification inhibitor (NI), both inhibitors (UI+NI) or when no inhibitor was applied at all. The study focused on the distribution of N species among soil matrix and soil solution. Plant cultivation was completely omitted in order to avoid masking soil N turnover and speciation by plant N uptake and growth dynamics. Application of UI clearly delayed urea hydrolysis in the top soil, but a complete hydrolysis of urea took place within only 10 days after fertilization (DAF). Nitrification was significantly reduced by NI application, leading to higher and lower concentrations in treatments with NI. Due to sorption of to the soil matrix a significantly larger fraction of was always detected in the soil extracts compared to soil solution. However, while in soil extracts the impact of NI application was less apparent and delayed, in soil solution a quick response to NI application was observed as revealed by significantly increased soil solution concentrations of . Because of the “asymmetric” soil phase distribution soil solution was predominant over only initially after fertilization even in inhibitor treatments (≈ 8 to 10 DAF). Nevertheless, inhibitor application tended towards closer ratios of to concentration in soil solution and hence, might additionally affect concentration dependent processes like plant N uptake and root development. Despite cold spring conditions urea application along with UI and/or NI did not indicate a limited supply of plant available and .     

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.     

硝化抑制剂对春玉米氮素利用及土壤pH值和无机氮的影响

通过大田试验,研究了黑土区春玉米施用硝化抑制剂对土壤pH值、土壤铵态氮和硝态氮变化、硝化抑制率、产量及氮素利用率的影响。试验结果表明:硝化抑制剂处理中,混合物B的中水平添加量处理(B2)玉米产量较一次性全施肥处理(AF)能够增产且增产率最高,为5.60%,氮素利用率较追肥处理(TP)提高5.43%,硝化抑制作用和增产的效果明显;施用硝化抑制剂可使土壤pH值缓慢阶梯式下降;土壤含水率与土壤铵态氮含量呈负相关性(P0.01);土壤铵态氮含量与土壤pH值呈显著正相关;所选用的两种硝化抑制剂的配方中,B2和A3(混合物A的低水平添加量)处理的增产和硝化抑制效果最佳。     

Evaluation of selected medicinal plant materials and dicyandiamide on nitrification of urea‐derived ammonium under laboratory conditions

Background : Poor utilization of urea fertilizer and N losses from agriculture lands demands alternate fertilization practices to reduce N losses and improve utilization, i.e., application of nitrification inhibitors. Aims : This study was aimed to evaluate and compare the influence of dicyandiamide (DCD) and selected medicinal plant materials and on N transformations, nitrification inhibition and recovery of applied N. Methods : Treatments included: urea nitrogen (UN), UN + DCD, UN + Gingiber officinale, UN + Viola odorata, UN + Sewertia chirata, UN + Azadirachta indica, UN + Sphaenathus indicus, UN + Allium sativus, UN + Artemisia absenthium, UN + Fumaria indicus, UN + Caesalpinea bondusella, UN + Barberis lyceum, and an un‐amended control. Urea was applied at 200 mg N kg^?1 soil, while DCD and medicinal plant materials were applied at of 1% and 20% of applied urea, respectively. Results : Medicinal plant materials inhibited nitrification of urea‐derived ${\mathrm{NH}}_4^{+}\text{-}N$. On an average of medicinal plant materials treatments, 51% of ${\mathrm{NH}}_4^{+}\text{-}N$ was still present in soil compared to 17% ${\mathrm{NH}}_4^{+}\text{-}N$ in UN treatment without medicinal plant materials after 28 days. Similarly, ${\mathrm{NO}}_3^{-}\text{-}N$ was 76.54 mg kg^?1 in UN treatment compared to 34.40 mg kg^?1 in UN + medicinal plant materials treatments, indicating 55% reduction in nitrification. Apparent nitrogen recovery (ANR) in UN treatment was 65% compared to 74% in UN + DCD treatment. ANR in treatments, where UN was amended with medicinal plant materials, varied between 58 to 70%. Conclusions : The use of DCD and medicinal plant materials with UN significantly reduced ${\mathrm{NH}}_4^{+}\text{-}N$ oxidation and nitrification ( ${\mathrm{NO}}_3^{-}\text{-}N$). In general, medicinal plant materials were more effective in regulating N transformations and, thus, offer a suitable alternate fertilization practice to reduce N losses and improve fertilizer utilization.     

Effect of the nitrification inhibitor nitrapyrin on the fate of nitrogen applied to a soil incubated under laboratory conditions

The aim of this study was to examine the effect of the nitrification inhibitor nitrapyrin on the fate and recovery of fertilizer nitrogen (N) and on N mineralization from soil organic sources. Intact soil cores were collected from a grassland field. Diammonium phosphate (DAP) and urea were applied as N sources. Cores were equilibrated at –5 kPa matric potential and incubated at 20 °C for 42 to 56 days. Changes in NH₄⁺‐N, accumulation of NO₃^–‐N, apparent recovery of applied N, and emission of N₂O (acetylene was used to block N₂O reductase) were examined during the study. A significant increase in NH₄⁺‐N released through mineralization was recorded when nitrapyrin was added to the control soil without N fertilizer application. In the soils to which N was added either as urea or DAP, 50–90 % of the applied N disappeared from the NH₄⁺‐N pool. Some of this N (8–16 %) accumulated as NO₃^–‐N, while a small proportion of N (1 %) escaped as N₂O. Addition of nitrapyrin resulted in a decrease and delay of NH₄⁺‐N disappearance, accumulation of much lower soil NO₃^–‐N contents, a substantial reduction in N₂O emissions, and a 30–40 % increase in the apparent recovery of added N. The study indicates that N recovery can be increased by using the nitrification inhibitor nitrapyrin in grassland soils at moisture condition close to field capacity.     

脲酶/硝化抑制剂对尿素氮在白浆土中转化的影响

采用室内恒温培养方法,研究了脲酶抑制剂（NBPT）、硝化抑制剂（DMPP）及其协同对尿素氮在三江平原白浆土中转化作用效果。研究表明,在白浆土中NBPT有效作用时间小于13 d,作用时间较在棕壤和黑土中短;对土壤中铵态氮、硝态氮及表观硝化率影响与普通尿素基本一致。NBPT与DMPP组合缓释尿素施入4-7 d,能够有效抑制脲酶活性,减缓尿素水解;只添加DMPP与添加NBPT与DMPP协同作用对抑制铵态氮硝化作用效果相同,二者能保持土壤中NH4+-N高含量时间超过80 d。DMPP作用时间可达80 d以上,能有效抑制NH4+-N向NO3--N的转化;在第80 d,土壤中仍有54.58%～56.85%的氮以铵态氮形式存在,表观硝化率只有50%左右。DMPP抑制硝化作用效果十分显著,因此,在白浆土中施用添加NBPT缓释尿素、DMPP缓释尿素、NBPT与DMPP缓释尿素时,应首选添加1%DMPP的缓释尿素肥料。     

DMPP硝化抑制效果受其浓度、施用方式及土壤基质势的影响

The efficacy of nitrification inhibitors depends on soil properties and environmental conditions. The nitrification inhibitor 3.4-dimethylpyrazole phosphate （DMPP） was investigated in a sandy loam and a loamy soil to study its effectiveness as influenced by inhibitor concentration, application form, and soil matric potential. DMPP was applied with concentrations up to 34.6 mg DMPP kg^-1 soil as solution or as ammonium-sulfate/ammonium-nitrate granules formulated with DMPP. DMPP inhibited the oxidation of ammonium in both soils, but this effect was more pronounced in the sandy loam than in the loamy soil. When applied as solution, increasing DMPP concentrations up to 7 mg DMPP kg^-1 soil had no influence on the inhibition. The effectiveness of DMPP formulated as fertilizer granules was superior to the liquid application of DMPP and NH4^＋, particularly in the loamy soil. Without DMPP, a decline in soil matric potential down to -600 kPa decreased nitrification in both soils, but this effect was more pronounced in the sandy loam than in the loamy soil. DMPP was most effective in the sandy loam particularly under conditions of higher soil moisture, i.e., under conditions favorable for nitrate leaching.     

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。     

Mitigation of nitrous oxide emissions in spray-irrigated grazed grassland by treating the soil with dicyandiamide, a nitrification inhibitor

Abstract. Nitrous oxide (N₂O) from animal excreta in grazed pasture systems makes up a significant component (c. 10%) of New Zealand's total greenhouse gas inventory. We report an effective method to decrease N₂O emissions from animal urine patches by treating the soil with the nitrification inhibitor dicyandiamide (DCD), in a simulated grazed dairy pasture system under spray irrigation. The soil was a free-draining Lismore stony silt loam (Udic Haplustept loamy skeletal) and the pasture was a mixture of perennial ryegrass ( Lolium perenne ) and white clover ( Trifolium repens ). By treating the soil with DCD, N₂O emissions were decreased by 76% following urine application in the autumn, from 26.7 kg N₂O-N ha⁻¹ without DCD to an average of 6.4 kg N₂O-N ha⁻¹ with DCD over the 6-month experimental period. N₂O flux was decreased by 78% following urine application in the spring, from 18 kg N₂O-N ha⁻¹ without DCD to 3.9 kg N₂O-N ha⁻¹ with the application of DCD over the 3-month period. A single application of DCD immediately after urine was sufficient to effectively mitigate N₂O emissions from the urine. The results showed that repeated applications of DCD after urine application, or mixing DCD with urine, offered no advantage over a single application of DCD immediately after urine deposition.     

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。     

西藏高原自然生态系统转化为农田后提高了土壤的净矿化和净硝化

A comparative study was conducted to determine the NH4^＋ and NO3^- concentrations in soil profiles and to examine the net nitrogen （N） mineralization and nitrification in adjacent forest, grassland, and cropland soils on the Tibetan Plateau. Cropland soil showed significantly higher inorganic N concentrations in soil profiles compared with forest and grassland soils. NO3^- -N accounted for 70%-90^ of inorganic N in cropland soil, while NH4^＋ -N was the main form of inorganic N in forest and grassland soils. The average net N mineralization rate at 0 20 cm depth was approximately twice in cropland soil （1.48 mg kg^-1 d^-1） as high as in forest （0.83 mg kg^-1 d^-1） or grassland soil （0.72 mg kg^-1 d^-1）. Cropland showed strong net nitrification, with the net rate almost equal to the total net N mineralization. Urea addition stimulated soil respiration, particularly in forest soil. Most urea-N, however, remained as NH4^＋ in forest and grassland soils, while NO3^- was the main form of inorganic N to increase in cropland soil. Higher rates of net nitrification in cropland soils suggest that land use change on the Tibetan Plateau may lead to high N losses through nitrate leaching.     

Effect of soil solarization on subsequent nitrification activity at elevated temperatures

Soil solarization is a nonchemical method of soil disinfection achieved by covering the soil surface with sheets of vinyl plastic to generate elevated soil temperature, generally over 45°C. Such elevated temperatures may be detrimental to some nitrifying microorganisms and favorable to others. However, little information exists to indicate how nitrification activity in soil is affected after solarization. We performed several experiments to investigate the effects of soil solarization on nitrification activity. We found that: (1) if a soil was subjected to pretreatment of 45 or 50°C for as little as 1 d, nitrification activity in a subsequent incubation at 30°C was less than that of a soil that did not receive any high-temperature pretreatment. However, if a soil received pretreatments of 45 or 50°C for more than 7 d, nitrification activity in a subsequent incubation at 45 or 50°C was greater than that of soil that did not receive high temperature pretreatment. (2) Nitrification activity in three kinds of soil taken from 0–5 cm depth after solarization treatment was greater at 45°C than 30°C. (3) Nitrification activity at 45°C in soil that had received solarization in the preceding year was greater than that in soil that had not been subjected to solarization. This was consistent with the fact that the population densities of ammonia oxidizers were greater in soils that had been subjected to solarization. These results suggest that soil solarization induces nitrifying microorganisms that are more active at 45–50°C than they are at 30°C, and that the effect of solarization on nitrification persists until the next crop season.     

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。     

Effect of labile and recalcitrant carbon on heterotrophic nitrification in a subtropical forest soil

Carbon (C) is an important factor controlling heterotrophic nitrification in soil, but the effect of individual C components (e.g., labile and recalcitrant C) is largely unclear. We carried out a C amendment experiment in which either labile C (glucose) or a recalcitrant C (cellulose and biochar) was added to a subtropical forest soil. A ¹⁵N-, ¹³C-tracing and MiSeq sequencing study was performed to investigate soil gross heterotrophic nitrification rates, carbon utilization for soil respiration and microbial biomass production and microbial composition, respectively. After 2 days, results showed a significant increase of gross heterotrophic nitrification rate in glucose (GLU) (on average 3.34 mg N kg⁻¹ day⁻¹), cellulose (CEL) (on average 0.21 mg N kg⁻¹ day⁻¹) and biochar (BIO) (on average 0.13 mg N kg⁻¹ day⁻¹) amendment in comparison with the unamended soil (CK) (on average 0.01 mg N kg⁻¹ day⁻¹; p < 0.05). The contribution of heterotrophic nitrification to total soil nitrification was significantly larger in GLU (average 85.86%), CEL (average 98.52%) and BIO (average 81.25%) treatments compared with CK (average 33.33%; p < 0.01). After 2-month amendment, the gross rates remarkably decreased in GLU (average 0.02 mg N kg⁻¹ day⁻¹), and the contribution to total nitrification (average 8.73%) were significantly lower than that in CK (p < 0.05). A decrease in the proportion of heterotrophic nitrification to total nitrification in soil was also observed in CEL (average 38.40%) and BIO (6.74%) treatments. Nevertheless, BIO amendment (compared to CK, GLU and CEL) showed the highest gross heterotrophic nitrification rate, accompanied by a notably higher abundance of specific heterotrophic nitrifiers, i.e. Trichoderma, Aspergillus and Penicillium. These results point to a stimulatory effect of C addition on soil heterotrophic nitrification in the short term, while the stimulatory impact of C amendment diminishes with the decline in easily available C. In addition, a shift of the microbial composition in the long term can possibly be sustained for longer if additional recalcitrant C is available to heterotrophic nitrifiers. The dynamic response of heterotrophic nitrification to labile and recalcitrant C in this study offered an explanation for the positive effect of plantation and plant root exudation on the process.     

尿素不同配施处理对棕壤茶园土壤尿素转化及硝化作用影响的研究

采用好气土壤培养试验,以单施尿素为对照,研究了尿素配施双氰胺（UD）、菌剂（UJ）、复混肥（UY）、菌剂+复混肥（UYJ）以及表面覆盖茶末（UF）处理对尿素转化和硝化作用的影响,测定了土壤铵态氮、硝态氮、脲酶活性、氨氧化菌数量并计算表观硝化率,结果表明:各种处理均能提高土壤中铵态氮含量,降低硝态氮含量,延迟脲酶活性高峰期,减小表观硝化率,抑制氨氧化菌。其中以覆盖茶末（UF）处理效果最好,其土壤铵态氮含量最高,硝态氮和硝化率最低;其次为UD处理,配施DCD能明显推迟脲酶活性高峰出现时间并降低前期活性,同时能显著抑制氨氧化菌生长。此外,比较UYJ和UJ处理结果可以推测:在有机质丰富的茶园中施用菌剂来抑制硝化作用的效果不显著。     

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。     

硝化抑制剂对海南岛几种野生蔬菜干物质积累的影响

本文探讨了含有硝化抑制剂DMPP的长效肥料ENTEC对三种野生蔬菜(苋菜、闭鞘姜、仙人掌)干物质积累的影响。结果表明:①ENTEC对闭鞘姜干物质积累有显著影响。仙人掌干物质积累较尿素处理提高26%。②三种蔬菜生长过程中均表现为ENTEC处理下的最高生长速率到达时期推迟,干物质积累主要时期延长。     

Abiotic factors regulating nitrification in a Swedish arable soil

Summary The effects of temperature, water potential and ammonium concentrations were studied in field and laboratory experiments on arable soil. The two field experiments used different sampling intervals, one at daily (short-term) and the other at monthly (long-term) intervals. In the short-term field experiment, the numbers and activities of nitrifiers were assessed before and after natural rain or irrigation. The nitrifiers were apparently outcompeted by heterotrophs during the first days after wetting the soil. Potential nitrification was affected only slightly by changes in water potential, whereas the numbers of ammonium and nitrite oxidizers appeared more sensitive to these changes. The numbers of ammonium and nitrite oxidizers correlated strongly during the daily samplings. The potential nitrite-oxidation rates correlated with water potentials whereas the potential ammonium oxidation rates did not. Extractable ammonium decreased in proportion to increasing nitrate concentrations in both the rain-fed and the irrigated plots. In the long-term field experiments, the numbers of ammonium oxidizers correlated with water potentials but not with in situ temperature or with ammonium concentrations. The potential ammonium-oxidation rates correlated with water potentials and with ammonium-oxidizer numbers. The potential nitrite-oxidation rates correlated strongly with the potential ammonium-oxidation rates. The field experiments implied that nitrite oxidizers obtained substrate from ammonium oxidizers but also from nitrate reduction. In laboratory experiments nitrate accumulated at a Q ₁₀ of about 2 and the V _max for nitrification was observed at a water potential of –0.11 MPa (65% of water-holding capacity). The K _m for ammonium oxidation at pH 8.2 was 1.72 mg l^–1 soil water.     

Coating of essential oils onto prilled urea retards its nitrification in soil

Increased use of nitrogenous fertilizers in agriculture has led to the increased pollution of ground water and atmosphere. Certain plant products can be used as coating materials onto urea to reduce the N losses. We evaluated the effectiveness of citronella and palmarosa grass oils as nitrification inhibitors in a soil incubation study. The treatments (14) were combinations of 4 N sources (neem, citronella and palmarosa oil coated prilled ureas, and uncoated prilled urea), 2 coating thicknesses of oils (500 and 1000 mg kg^?1) and 2 N levels (75 and 150 kg N ha^?1), replicated thrice in a randomized block design. N levels at 75 and 150 kg ha^?1 were equivalent to 34 and 68 mg N kg^?1 soil, respectively. Results showed that N sources citronella (CCPU₁₀₀₀) and neem oil (NCPU₁₀₀₀) coated prilled ureas at 1000 mg kg^?1 coating thickness with 75 kg ha^?1 released similar amount of ammonical-N to uncoated prilled urea at 150 kg N ha^?1, suggesting the beneficial effect of coated ureas. The highest nitrification inhibition (%) was recorded with NCPU₁₀₀₀, the reference nitrification inhibitor, which was significantly greater to all the other N sources at 7 days after incubation (DAI), and at par to CCPU₁₀₀₀ at 14 and 21 DAI.     

Effect of indaziflam on microbial activity and nitrogen cycling processes in an orchard soil

Indaziflam is a preemergent herbicide widely used for the control of weeds in pecan (Carya illinoinensis) orchards in the southwestern region of the United States. Given the paucity of data regarding the effect of indaziflam on the biochemical properties of soils supporting pecan production, this study was conducted to evaluate the effects of different application rates of indaziflam on soil microbial activity, diversity, and biochemical processes related to nitrogen (N) cycling. During two consecutive growing seasons (2015 and 2016), soil samples were obtained from experimental mesocosms consisting of soil-filled pots where pecan saplings were grown and treated with indaziflam applied at two different rates (25 and 50 g active ingredient (ai) ha^-1, with the higher rate being slightly lower than the recommended field application rate of 73.1 g ai ha^-1). Soil samples were collected approximately one week before and one week after herbicide application for determination of soil microbial biomass and diversity, N mineralization, and β-glucosaminidase activity. Soil samples collected from the control mesocosms without herbicide application were treated in the laboratory with two rates of indaziflam (75 and 150 g ai ha^-1) to determine the immediate effect on microbial activity. No significant effect of herbicide treatment on soil respiration and microbial biomass was detected. The results showed a slight to moderate decrease in microbial diversity (7% in 2015 and 44% in 2016). However, decreased β-glucosaminidase activity with herbicide treatment was observed in soils from the mesocosms (33%) and soils treated with indaziflam in the laboratory (45%). The mineral N pool was generally dominated by ammonium after indaziflam application, which was consistent with the drastic decrease (75%) in nitrification activity measured in the laboratory experiment. The results of this study indicate that indaziflam, even when applied at higher than recommended rates, has limited effects on soil microbial activity, but may affect N cycling processes.