Evaluation of some phosphoroamides as soil urease inhibitors

Summary The effectiveness of six phosphoroamides for retardation of urea hydrolysis in soils was studied by determining the effects of 10 g g^–1 soil of each compound on the amounts of urea hydrolyzed when soils treated with urea were incubated at 10°, 20°, 30°, and 40°C for 3, 7, and 14 days. The phosphoroamides used wereN-(diaminophosphinyl)-cyclohexylamine,N-benzyl-N-methyl phosphoric triamide, diethyl phosphoric triamide, trichloroethyl phosphorodiamidate, dimethyl phosphoric triamide, andN-butyl phosphorothioic triamide [N-(n-butyl) thiophosphoric triamide]. The soils used were selected to obtain a range in properties, and the effects of the six phosphoroamides studied were compared with those of two compounds known to be among the most effective compounds thus far proposed for retardation of urea hydrolysis in soils (phenylphosphorodiamidate and hydroquinone). The data obtained showed that all six of the phosphoroamides evaluated compared favorably with hydroquinone as soil urease inhibitors and that two of them [N-butyl phosphorothioic triamide andN-(diaminophosphinyl)-cyclohexylamine] were superior to phenylphosphorodiamidate for retardation of urea hydrolysis in soils at 20°, 30°, or 40°C.     

Effect of N-(n-butyl) thiophosphoric triamide on hydrolysis of urea by plant,microbial, and soil urease

Summary Comparison of the effects of N-(n-butyl) thiophosphoric triamide (NBPT) and phenylphosphorodiamidate (PPD) on hydrolysis of urea by plant (jackbean), microbial (Bacillus pasteurii), and soil urease showed that whereas NBPT was considerably more effective than PPD for inhibiting hydrolysis of urea added to soil, it was much less effective than PPD for inhibiting hydrolysis of urea by plant or microbial urease. Studies to account for this observation indicated that NBPT is rapidly decomposed in soil to a compound that is much more effective than NBPT for inhibition of urease activity and that this compound is N-(n-butyl) phosphoric triamide.     

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.     

Potential of phenylphosphorodiamidate and N‐(N‐butyl) thiophosphoric triamide for inhibiting urea hydrolysis in simulated oxidized and reduced soils

Abstract

A laboratory study was conducted to assess the effectiveness of phenylphosphorodiamidate (PPD) and N‐(n‐butyl) thiophosphoric triamide (NBT) in retarding urea hydrolysis in four flooded rice soils under simulated oxidized and reduced conditions. Urea (400 μg N g^‐1soil) with PPD or NBT (2.0% w/w) was added to preincubated soils and analyzed for urea content 1, 3, 5, 7 and 15 days after N application. N‐(n‐butyl) thiophosphoric triamide was more effective in delaying urea hydrolysis under oxidizing conditions and at 5 days 57% of the added urea remained in the oxidized soils compared to only 4% under reduced soil conditions. In three soils, PPD was observed to be effective under reducing soil constraints. At 5 days 56 and 31% of the added urea was unhydrolyzed under reducing and oxidizing soil conditions, respectively, with the addition of PPD. For two soils 48% of the added urea remained at the 15 day sampling for the urea + NBT treatment     

Effects of nitrification inhibitors on germination of various seeds in soil

Summary The effects of 19 nitrificiation inhibitors on germination of seeds in soil were investigated. The nitrification inhibitors tested were sodium azide, potassium azide, potassium ethyl xanthate, nitrapyrin (N-Serve), etridiazole (Dwell), 3-mercapto-1,2,4-triazole (MT), 2-amino-4-chloro-6-methylpyrimidine (AM), 2,4-diamino-6-trichloromethyl-s-triazine, 2-mercaptobenzothiazole (MBT), 4-amino-1,2,4-triazole (ATC), sodium thiocarbonate (STC), guanylthiourea (ASU), thiourea (TU), dicyandiamide (DCD), sulfathiazole (STC), phenylacetylene, 2-ethynyl-pyridine, 3-methylpyrazole-l-carboxamide (MPC), and ammonium thiosulfate (ATS). Germination tests were performed with seeds of alfalfa (Medicago sativa L.), wheat (Triticum aestivum L.), rye (Secale cereale L.), barley (Hordeum vulgare L.), sorghum [Sorghum bicolor (L.) Moench], oats (Avena sativa L.), and corn (Zea mays). Only 2 of the 19 nitrification inhibitors studied (potassium azide and sodium azide) reduced germination of the seeds tested when applied at the rate of 12.5 g g^–1. The other inhibitors studied had no effect on the germination of wheat, alfalfa, barley, corn, oat, rye, or sorghum seeds when they were applied at the rate of 125 g g^–1 soil, and most of them had no effect on seed germination when applied at the rate of 625 g g^–1 soil.     

Problems in the use of urea as a nitrogen fertilizer

Abstract. N -( n -butyl) thiophosphoric triamide (NBPT) is the most effective compound currently available for retarding hydrolysis of urea fertilizer in soil and for decreasing ammonia volatilization and nitrite e accumulation in soils treated with urea. It is a poor inhibitor of plant or microbial urease, but decomposes quite rapidly in soil with formation of N -( n -butyl) phosphoric triamide, which is a potent inhibitor of urease activity.
The adverse effects of urea fertilizers on seed germination and seedling growth in soil are due to ammonia produced through hydrolysis of urea by soil urease. They can be eliminated by addition of a urease inhibitor to these fertilizers.
The leaf-burn commonly observed after foliar fertilization of soybeans with urea results from accumulation of toxic amounts of urea in the soybean leaves rather than formation of toxic amounts of ammonia through urea hydrolysis by leaf urease. Leaf-burn is accordingly increased rather than decreased by addition of a urease inhibitor to the urea fertilizer applied.     

Suppression of methane oxidation in aerobic soil by nitrogen fertilizers,nitrification inhibitors,and urease inhibitors

Concentrations of CH₄, a potent greenhouse gas, have been increasing in the atmosphere at the rate of 1% per year. The objective of these laboratory studies was to measure the effect of different forms of inorganic N and various N-transformation inhibitors on CH₄ oxidation in soil. NH ₄ ⁺ oxidation was also measured in the presence of the inhibitors to determine whether they had differential activity with respect to CH₄ and NH ₄ ⁺ oxidation. The addition of NH₄Cl at 25 g N g^-1 soil strongly inhibited (78–89%) CH₄ oxidation in the surface layer (0–15 cm) of a fine sandy loam and a sandy clay loam (native shortgrass prairie soils). The nitrification inhibitor nitrapyrin (5 g g^-1 soil) inhibited CH₄ oxidation as effectively as did NH₄Cl in the fine sandy loam (82–89%), but less effectively in the sandy clay loam (52–66%). Acetylene (5 mol mol^-1 in soil headspace) had a strong (76–100%) inhibitory effect on CH₄ consumption in both soils. The phosphoroamide (urease inhibitor) N-(n-butyl) thiophosphoric triamide (NBPT) showed strong inhibition of CH₄ consumption at 25 g g^-1 soil in the fine sandy loam (83%) in the sandy clay loam (60%), but NH ₄ ⁺ oxidation inhibition was weak in both soils (13–17%). The discovery that the urease inhibitor NBPT inhibits CH₄ oxidation was unexpected, and the mechanism involved is unknown.     

15N-Urea Efficiency in Maize as Influenced by Humic Substances and Urease Inhibitors Treatments

Urea treated with urease inhibitors (UI) in association with humic substances (HS) is expected to improve urea efficiency by reducing ammonia losses and also provide the benefits of HS such as improve nitrogen (N) recovery by plants. Ammonia volatilization (AV), ¹⁵N recovery efficiency in the soil (NRE) and ¹⁵N use efficiency (NUE) were evaluated in maize (Zea mays L.) in a greenhouse pot trial. Treatments consisted of ¹⁵N-urea treated with UI (0, 0.4% boron (B) +0.15% copper (Cu), 0.64% B, and NBPT (N-(n-butyl) thiophosphoric triamide)) and three levels of HS (0%, 0.6%, and 1.2%). A control treatment (without N) was also included. N treatments were applied at V4 (vegetative leaf stage 4) on soil surface. HS was not efficient on AV reduction, NBPT had the greatest reduction in AV, and B had higher efficiency on AV reduction than Cu. At V8 (vegetative leaf stage 8), NBPT had the greatest NUE followed by B. At VT (tassel fully emerged), NUE from urea treated with NBPT reduced when increased levels of HS, and NBPT had the greatest NRE. UI in association with HS treated-urea does not reduce AV and it does not improve NUE by maize in vegetative stages.     

Nitrogen Fertilization of Soybean Affects Root Growth and Nodulation on Two Soil Types in Mississippi

Greenhouse studies were conducted to evaluate the influence of nitrogen (N) sources [urea + ?N-(n-butyl) thiophosphoric triamide, NBPT (urease inhibitor) and polymer-coated urea (PCU)] and rates on soybean root characteristics, nodule formation, and biomass production on two soil types (silt loam and clay) commonly cropped to soybean in Mississippi. About 15% less belowground biomass was produced in clay soil than in silt loam soil directly corresponding to all other root parameters including root length, root area, root diameter, and nodule number. Pooled across N rates, N additions resulted in 19% and 52% decrease in belowground biomass and number of nodules, respectively, across soils compared to soybean receiving no N. The N rate was the most critical factor as it influenced all root growth parameters. Number of nodules were 24% greater with PCU than urea + NBPT. Nitrogen additions and clay soil negatively impacted soybean root growth, nodulation, and belowground biomass production.

Abbreviations: Polymer-coated urea, PCU; N-(n-butyl) thiophosphoric triamide, NBPT     

Persistence of the inhibitory effects of phosphoroamides on urea hydrolysis in soils

Abstract

The persistence of the inhibitory effects of three phosphoroamides [N‐(n‐butyl) thiophosphoric triamide (NBPT), phenylphosphorodiamidate (PPD), and thiophosphoryl triamide (TPT)] on urea hydrolysis in soils was assessed by measuring the ability of four soils to hydrolyze urea after they had been treated with 5 μg phosphoroamide/g soil and incubated at 15°C or 30°C for 0, 3, 7, 14, or 28 days. The soils used differed markedly in pH, texture, and organic‐matter content. The data obtained showed that the persistence of the effects of the phosphoroamides studied decreased with increase in soil temperature from 15°C to 30°C and that whereas the effect of PPD decreased with increase in the time of incubation, the effects of NBPT and TPT sometimes increased before decreasing with increased time of incubation. These observations are in harmony with the recent findings that PPD is a potent inhibitor of urease activity, but decomposes in soils with formation of phenol, which is a relatively weak inhibitor of urease activity, whereas NBPT and TPT do not inhibit urease activity but decompose in soil with formation of their oxon analogs, which are potent inhibitors of urease activity. The inhibitory effect of NBPT on urea hydrolysis was considerably more persistent than that of PPD or TPT and was significant even after incubation of NBPT‐treated soil at 15°C or 30°C for 28 days.     

EFFECTIVENESS OF SEEDROW-PLACED N WITH POLYMER-COATED AND NBPT-TREATED UREA FOR CANOLA AND WHEAT

Seedrow-placed urea minimizes soil disturbance in reduced tillage systems, but it generally decreases seedling emergence (or stand density) at nitrogen (N) rates adequate for optimum crop yield. Two three-year field experiments were conducted on canola (Brassica napus L.) and spring wheat (Triticum turgidum L.) at Melfort Research Farm, Saskatchewan, Canada, to determine the influence of N rate (40, 80 and 120 kg N ha^?1), N source [untreated urea (urea), polymer-coated urea (ESN), and urea treated with Dicyandiamide (DCD) and N-(n-butyl) thiophosphoric triamide (NBPT or Agrotain^TM) (SuperU) in 2007, or NBPT only (AgrotainU) in 2008 and 2009], and placement (side-banded N and seedrow-placed N, using knives to create 2 cm wide band), plus a zero-N control, on seedling emergence, seed and straw yield, protein concentration (PC) in seed, and N uptake in seed and straw. For both crops, side-banded N had no detrimental effect on seedling emergence compared to the zero-N control for all rates and sources. Seedrow-placed ESN had little or no effect on seedling emergence of wheat or canola. Conversely, seedrow-placed urea, SuperU or AgrotainU reduced seedling emergence for wheat at the 80 and 120 kg N ha^?1 rates and reduced canola seedling emergence substantially at all rates, but particularly at the 80 and 120 kg N ha^?1. Seed yield and N uptake were generally greater with ESN than urea and also SuperU or AgrotainU, when the fertilizers were seedrow-placed at high N rates. The findings suggest the effectiveness of ESN in providing greater seedrow-placed N application options for producers.     

Effects of arbuscular mycorrhizal inoculation on growth,yield, nitrogen,and phosphorus nutrition of nodulating bean varieties in two soil substrates of contrasting fertility

A pot experiment was conducted to study the response of nodulated bean (Phaseolus vulgaris L.), vars. Ceca and Montalbán, to inoculation with the arbuscular‐mycorrhizae (AM) Glomus spurcum strain IES‐3 and G. mosseae strain IES‐8 in two non‐sterilized non‐amended soil substrates (S‐l and S‐2) of contrasting fertility. S‐l was an acid soil (pH 5.0) with 77% exchangeable aluminum (Al), low available phosphorus (P) (3.5 ug g^‐1 dry soil) and 1.8% organic matter. S‐2 was a soil with pH 7.0, 7.9 μg P g^‐1 dry soil, 9.6% organic matter and no exchangeable Al. Plants growing in S‐1 (S‐1 plants) and S‐2 (S‐2 plants) soils were sampled at the beginning of the flowering stage. S‐1 and S‐2 plants were nodulated by the rhizobial populations native of each soil. S‐1 plants of both varieties did not respond to AM inoculation in term of shoot and root mass, P content, relative abundance of ureides (RAU) and seed yields. Only the total chlorophyll, chlorophyll‐a, chlrophyll‐a/b ratio and nodule mass were significantly enhanced in AM‐inoculated plants. Increased total reducing sugars concentration was detected in roots of S‐1 plants inoculated with G. mosseae. S‐2 plants displayed significantly higher shoot and nodule mass as well as increased total chlorophyll, chlorophyll‐a, chlorophyll‐a/b ratio and P content than S‐1 plants, regardless of the variety and AM inoculation. S‐2 plants of the var Ceca showed a two fold increase in seed yields but similar RAU values (>60%) when compared to S‐1 plants of the same variety. In contrast, the significant increase in RAU detected in S‐2 plants of the var Montalban was not translated into higher seed yields. In S‐2, the productivity of plants of the var Ceca doubled that of the var Montalban. For both bean varieties the highest significant P content and seed yield were observed exclusively in S‐2 plants inoculated with G. mosseae. This Glomelean strain enhanced the sink‐source ratio of the S‐2 plants as evidenced by the higher total reducing sugar concentration in the root mass. Arbuscular‐mycorrhizae inoculation significantly decreased the acid phosphatase activity in the rhizosphere of S‐1 and S‐2 plants, respectively, pointing toward a negative effect of foreign AM on the native microbial biomass. The effectiveness of the rhizobial populations native of each soil type and the weak response elicited by G. mosseae in S‐2 plants do not justify, at present, the inclusion of foreign inocula in the bean crops carried out at S‐1 and S‐2 soils of the Sucre State of Venezuela. Results also indicated the higher adaptability of var Ceca to conditions prevailing in S‐1 and S‐2.     

Effect of urease and nitrification inhibitors on ammonia volatilization and abundance of N‐cycling genes in an agricultural soil

The effect of the combined application of urease and nitrification inhibitors on ammonia volatilization and the abundance of nitrifier and denitrifier communities is largely unknown. Here, in a mesocosm experiment, ammonia volatilization was monitored in an agricultural soil treated with urea and either or both of the urease inhibitor N‐(n‐butyl) thiophosphoric triamide (NBPT) and the nitrification inhibitor 3,4‐dimethylpyrazole phosphate (DMPP), with 50% and 80% water‐filled pore space (WFPS). The effect of the treatments on the abundance of bacteria and archaea was estimated by quantitative PCR (qPCR) amplification of their respective 16S rRNA gene, that of nitrifiers using amoA genes, and that of denitrifiers by qPCR of the norB and nosZI denitrification genes. After application of urea, N losses due to NH₃ volatilization accounted for 23.0% and 9.2% at 50% and 80% WFPS, respectively. NBPT reduced NH₃ volatilization to 2.0% and 2.4%, whereas DMPP increased N losses by up to 36.8% and 26.0% at 50% and 80% WFPS, respectively. The combined application of NBPT and DMPP also increased NH₃ emissions, albeit to a lesser extent than DMPP alone. As compared with unfertilized control soil, both at 50% and 80% WFPS, NBPT strongly affected the abundance of bacteria and archaea, but not that of nitrifiers, and decreased that of denitrifiers at 80% WFPS. Regardless of moisture conditions, treatment with DMPP increased the abundance of denitrifiers. DMPP, both in single and in combined application with NBPT, increased the abundance of nitrification and denitrification genes.     

Soil salt and NaCl have different effects on seed germination of the halophyte Suaeda salsa

Seed germination is a key life‐history stage of halophytes. Most studies on seed germination of halophytes have focused on the effects of a single salt, while little information is available on the effects of mixed salt in the natural habitat. Due to the contribution of multiple ions in saline soil, we hypothesized that the effect of mixed salt on seed germination will differ from that of a single salt and the mechanism of how germination is affected will differ as well. The effects of mixed salt and NaCl on germination, water imbibition, and ionic concentrations of seeds of Suaeda salsa (L.) Pall. were compared at various salinity levels. Germination percentage (GP) and rate (GR) decreased with increasing salinity level, regardless of salt type. There was no difference in GP or GR between mixed salt and NaCl when the salinity level was below 20 dS m^?1. Above 20 dS m^?1, GP and GR in NaCl were lower than those in mixed salt. At the same salinity level, Na⁺ concentration in seeds was higher in NaCl than that in mixed salt, but the reverse was true for Ca²⁺ and Mg²⁺ concentrations. Imbibition rate for seeds in NaCl was lower than that in mixed salt at the same salinity level. Addition of Ca²⁺ and Mg²⁺ alleviated the inhibition of NaCl on seed germination. In conclusion, our results suggest that the effects of soil salts and NaCl on seed germination are different, and using NaCl instead of soil salt might not be realistic to show the effect of saline stress on seed germination of halophytes in the natural habitat.     

Response of turfgrass to urea-based fertilizers formulated to reduce ammonia volatilization and nitrate conversion

Stabilized urea fertilizers are currently being marketed for use in turfgrass, as a more efficient alternative to standard urea that minimizes adverse impacts on the environment. These fertilizers have been evaluated for reducing N losses and increasing grain yield in crop plants, but their effects in turf are not well characterized. The efficacy of two stabilized urea fertilizers containing urease and nitrification inhibitors, N-(n-butyl) thiophosphoric triamide and dicyandiamide or butenedioc-methylenesuccinic acid copolymer, in reducing N losses was studied for a 56-day period in a mixed stand of Kentucky bluegrass (Poa pratensis L.) and perennial ryegrass (Lolium perenne L.) using ¹⁵?N-enriched fertilizers. Turf responded to a 49-kg ha^?1 N input with increased color, quality, and biomass production. No benefit of nitrification and urease inhibitors compared to urea was observed for clipping production, N use efficiency, or turfgrass color and quality. Though the efficacy of urease and nitrification inhibitors has been demonstrated both in the laboratory and for row crops, inhibitors appear to be of limited value for enhancing N use efficiency in turf.     

Impact of urease and nitrification inhibitors on nitrous oxide emissions from fluvo-aquic soil in the North China Plain

Little information is available on the effects of urease inhibitor, N-(n-butyl)thiophosphoric triamide (NBPT), and nitrification inhibitor, dicyandiamide (DCD), on nitrous oxide (N₂O) emissions from fluvo-aquic soil in the North China Plain. A field experiment was conducted at the Fengqiu State Key Agro-Ecological Experimental Station, Henan Province, China, to study the influence of urea added with NBPT, DCD, and combination of both NBPT and DCD on N₂O emissions during the maize growing season in 2009. Two peaks of N₂O fluxes occurred during the maize growing season: the small one following irrigation and the big one after nitrogen (N) fertilizer application. There was a significant positive relationship between ln [N₂O flux] and soil moisture during the maize growing season excluding the 11-day datasets after N fertilizer application, indicating that N₂O flux was affected by soil moisture. Mean N₂O flux was the highest in the control with urea alone, while the application of urea together with NBPT, DCD, and NBPT + DCD significantly lowered the mean N₂O flux. Total N₂O emission in the NBPT + DCD, DCD, NBPT, and urea alone treatments during the experimental period was 0.41, 0.47, 0.48, and 0.77 kg N₂O–N ha⁻¹, respectively. Application of urea with NBPT, DCD, and NBPT + DCD reduced N₂O emission by 37.7%, 39.0%, and 46.8%, respectively, over urea alone. Based on our findings, the combination of DCD and NBPT together with urea may reduce N₂O emission and improve the maize yield from fluvo-aquic soil in the North China Plain.     

Responses of biotic and abiotic effects on conservation and supply of fertilizer N to inhibitors and glucose inputs

Fertilizer N can be conserved through immobilization by microorganisms (biotic process) and fixation by soil clay minerals (abiotic process), and then subsequently remineralized and released. These processes are significantly affected by inhibitors, and available C application. In this study, a 96-day incubation experiment was conducted to assess the effects of microbial immobilization and ammonium fixation on conservation and supply of urea-N with the nitrification inhibitor (DMPP: 3,4-dimethylpyrazole phosphate), urease inhibitor (NBPT: N-(n-butyl) thiophosphoric triamide), and glucose additions. The results showed that urea-derived soil microbial biomass nitrogen (SMBN) consistently increased with DMPP input, whereas NBPT increased urea-derived SMBN in the absence of glucose but decreased it in the presence of glucose. Both inhibitors enhanced the effects of fixed NH₄⁺ on conservation and supply of urea-N in all cases, and retarded the release of fixed NH₄⁺. Glucose addition intensified the competition for NH₄⁺ between microbial immobilization and mineral fixation, as well as reduced the availability of urea-N and native soil N, resulting in a negative added N interaction at the initial incubation stage. From 12 to 96 days, the release of fixed NH₄⁺ was 2.6-fold greater than the mineralization of organic N (including SMBN and non-microbial organic N) in the non-glucose treatments, whereas the latter was 2.7-fold greater than the former in the glucose treatments. Taken together, our study indicates both microbial immobilization and mineral fixation are important processes by which N is stabilized in soil. Clarification of fertilizer N transformation induced by these biotic and abiotic processes can provide helpful implications for quantifying N cycle and optimizing agricultural nutrient management.     

The effect of soil ph on the activity of oryzalin and metribuzin on five common weeds in no‐till crop production

Abstract

Metribuzin [4‐amino‐6‐tert‐buty1–3‐(methylthio)‐as‐triazine‐5(4H)‐one] and oryzalin (3,5‐dinitro‐N ⁴ N ⁴‐dipropylsufanilamide) at two rates each were applied to pots of Cecil sandy loam soil adjusted to pH levels of 5.8, 6.2, 6.8, and 7.2 containing five weed species. Redroot pigweed (Amaranthus retroflexus L.) and large crabgrass [Digitaria sanguinalis (L.) Scop.] were completely controlled by both herbicides at all rates and all pH levels. Sicklepod (Cassia obtusifolia L.) was controlled by metribuzin, but not completely, by oryzalin. Jimsonweed (Datura stramonium L.) and tall morningglory [Ipomoea purpurea (L.) Roth] were not controlled by either herbicide. Soil pH had no effect on jimsonweed control with either herbicide. Morningglory was best controlled by both herbicides at higher soil pH.     

Soil volatile fungistasis and volatile fungistatic compounds

Fungistasis is a widespread phenomenon that can be mediated by soil microorganisms and volatile organic compounds (VOCs). The relationship between soil microorganisms and VOCs is still unclear, however, and many fungistatic compounds remain to be identified. We assessed the effects of soils (soil direct fungistasis) and VOCs produced by natural soils (soil volatile fungistasis) on the spore germination of several fungi. Both strong soil direct fungistasis and soil volatile fungistasis were observed in a wide range of soils. Soil fungistasis and VOC fungistasis were significantly correlated (P<0.001). The volatile fungistatic activity of soils stopped after autoclaving. Some VOCs were identified by using solid-phase microextraction-gas chromatography/mass spectrum. VOC composition and in vitro antagonism of relatively pure commercial compounds also were measured. Some VOCs, trimethylamine, 3-methyl-2-pentanone, dimethyl disulfide, methyl pyrazine, 2,5-dimethyl-pyrazine, benzaldehyde, N,N-dimethyloctylamine and nonadecane, were produced by various fungistatic soils. Moreover, antifungal activity test of above VOCs showed that trimethylamine, benzaldehyde, and N,N-dimethyloctylamine have strong antifungal activity even at low levels (4-12 mg l⁻¹).     

Zinc‐biofortified seeds improved seedling growth under zinc deficiency and drought stress in durum wheat

High zinc (Zn) concentration of seeds has beneficial effects both on seed vigor and human nutrition. This study investigated the effect of Zn biofortification on growth of young durum wheat (Triticum durum cv. Yelken) seedlings under varied Zn and water supply. The seeds differing in Zn concentrations were obtained by spraying ZnSO₄ to durum wheat plants at different rates under field conditions. Three groups of seeds were obtained with the following Zn concentrations: 9, 20, and 50 mg Zn kg^?1. The seeds differing in Zn were tested for germination rate, seedling height, shoot dry matter production, and shoot Zn concentration under limited and well irrigated conditions in a Zn‐deficient soil with and without Zn application. In an additional experiment carried out in solution culture, root and shoot growth and superoxide dismutase activity (SOD) of seedlings were studied under low and adequate Zn supply. Low seed Zn concentration resulted in significant decreases in seedling height both in Zn‐deficient and sufficient soil, but more clearly under water‐limited soil condition. Decrease in seed germination due to low seed Zn was also more evident under limited water supply. Increasing seed Zn concentration significantly restored impairments in seedling development. Drought‐induced decrease in seedling growth at a given seed Zn concentration was much higher when soil was Zn‐deficient. Increasing seed Zn concentration also significantly improved SOD activity in seedlings grown under low Zn supply, but not under adequate Zn supply. The results suggest that using Zn‐biofortified seeds assures better seed vigor and seedling growth, particularly when Zn and water are limited in the growth medium. The role of a higher antioxidative potential (i.e., higher SOD activity) is discussed as a possible major factor in better germination and development of seedlings resulting from Zn‐biofortified seeds.