Control of ammonia volatilization with N‐(N‐butyl) thiophosphoric triamide in loamy sands

Abstract

In a laboratory study, ammonia (NH₃) was trapped from 10 g soil units treated with 10 mg urea‐N, 10 mg urea‐N plus 50 ug N‐(n‐butyl) thiophosphoric triamide (NBPT), or 10 mg urea‐N plus 50 ug phenyl‐phosphorodiamidate (PPD). The soil was a Dothan loamy sand with pH levels adjusted to 6.0, 6.5, and 6.9 prior to N application. After 12 days, NBPT reduced NH₃ volatilization 95 to 97%, while PPD reduced it 19 to 30%. Although NH₃ loss was positively related to initial soil pH, there was no interaction between pH and urease inhibitor. In a field study, NH₃ was trapped in semi‐closed chambers from 134 kg N/ha surface applied to corn (Zea mays L.) 6 weeks after planting. Nine days after N application, NH₃ losses were 20.5, 1.5, 1.5, and 0.2 kg N/ha from urea, urea plus 0.25% NBPT, urea plus 0.50% NBPT, and ammonium nitrate, respectively. Covariance analysis showed that percent organic matter was negatively related to NHL losses. The soil properties, initial pH, CEC, and percent sand, did not vary enough to affect NH₃ volatilization. In conclusion, in both the laboratory and the field, NBPT exhibited strong control of NH₃ volatilization, and could thereby prevent significant loss of surface‐applied urea‐N to crops.     

Determination of total sulphur in soil using in‐ductively coupled plasma‐atomic emission spectrometry

Abstract

Total sulphur in soils was determined by ignition with a NaHCO₃/Ag₂O mixture, extraction with HC1 and measurement of sulphur by inductively coupled plasma‐atomic emission spectrometry. Significant spectral interference from other extracted elements (mainly iron and aluminium) was corrected using an off‐peak background reading. Recovery of sulphur added to soil as K₂SO₄ was complete and barium did not interfere when added in amounts equivalent to 2000 μg g^‐1 soil. The total sulphur values for a range of New Zealand pastoral soils determined by this method were on average 104% (SEM=1,4) of the values obtained by the NaOBr oxidation method of Tabatabai & Bremner (1). The method enables analysis of relatively large sample numbers.     

Preparation of Ammonium‐15N and Nitrate‐15N Samples by Microdiffusion for Isotope Ratio Analysis by Optical Emission Spectrometry

Abstract

A diffusion method for the preparation and measurement of ¹⁵N abundance of ammonium and nitrate in KCl extracts of soil using optical emission spectrometry (OES) was compared with conventional continuous flow isotope ratio mass spectrometry (IRMS). There were highly significant correlations between the values obtained by using OES and IRMS. The 99% confidence interval of the intercept included the value 0 and the 99% confidence interval of the slope included the value 1 for both nitrate and ammonium measurements, suggesting that the results from the two methods did not differ significantly. In another experiment, ¹⁵N values of nitrate and ammonium from soil extracts prepared by using the standard distillation procedures for OES were compared against the microdiffusion preparation method. Again, there was a highly significant correlation between the values: the 95% confidence interval of the intercept included the value 0, and the 95% confidence interval of the slope included the value 1, again suggesting that the two methods did not differ significantly. It was concluded that the diffusion technique is an appropriate and simple method of sample preparation for inorganic N analysis of KCl extracts using OES.     

The persistence of 2‐chloro‐6‐(trichloromethyl)‐pyridine in soil

Abstract

The half‐life of 2‐chloro‐6‐(trichloromethyl)‐pyridine in three soils varied from 43 to 77 days at 10 C and from 9 to 16 days at 20 C. The Q₁₀ values were highest in coarse textured soils.     

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     

Loss‐on‐Ignition in the Determination of Pools of Organic Carbon in Soils of Forests and Afforested Arable Fields

Abstract

Loss‐on‐ignition (LOI) and concentration of organic carbon (Cc) were determined on pristine forest soils and soils from afforested arable fields. The objectives were to investigate the relation between the Cc of soil estimated indirectly from LOI and true Cc from dry combustion (C_LECO) and further to evaluate how the applied analytical method affects the carbon pool estimates. According to results, LOI was a good indicator of Cc in the organic layer. As regards mineral soil, however, C_LECO/LOI ratio significantly decreased with increasing depth, and the ratio changed differently in soils underlying forest sites as opposed to the soils from former fields. The results indicate that estimation of carbon pools from conversion factors would lead to considerable bias and that direct measurement of Cc is preferable to the use of any Cc/LOI ratio. The results also emphasize the need for elimination of carbonate carbon when measuring Cc from the soil of arable fields.     

Determination of exchangeable acidity,carbonate ions and change of buffer in triethanolamine‐buffered solutions percolated through soil samples containing carbonates

Abstract

The content of dissolved carbonates and exchanged acidity in triethanolamine‐buffered BaCl₂‐solutions which were percolated through soil samples containing carbonates is determined by two titration‐procedures to pH 4.0 and 10.25. because a single titration value gives no information of the amounts of both ionic species in solution. The amount of dissolved carbonates calculated on the bases of these titration‐procedures, however, is smaller than that determined by measuring the content of inorganic carbon in solution. The difference is attributed to the sorption of protonized triethanolamine‐buffer during percolation, which leads to an underestimation of CEC when measured by re‐exchanged Ba⁺⁺, whereas the amount of exchangeable bases is overestimated due to dissolution of carbonates. The amount of exchanged acidity calculated from the data obtained is surprisingly high and is at least partly attributed to the existence of HCO₃ ^‐ ‐sorbed on the surface of (wet) soils.     

Growth and Accumulation of Nitrogen and Potassium in Flue‐Cured Tobacco as Affected by Calcium Nitrate and Ammonium Nitrate

The process of biomass, nitrogen (N), and potassium (K) accumulation over time as affected by N forms is poorly understood. The objective of this study was to identify the effects of N form on growth as well as on N and K nutrition of flue‐cured tobacco plants (Nicotiana tobaccum L.). The plants were grown in a greenhouse with pots of soil for 117 days after 200 days of preculture. Three treatments (calcium nitrate [Ca(NO₃)₂], ammonium nitrate (NH₄NO₃), and ammonium nitrate plus straw (NH₄NO₃ + straw)) were used. The results showed that there were no significant differences in shoot dry mass of tobacco among the three treatments during the entire growth stage except at 30 and 117 days after transplanting. At these two growth stages, shoot biomass with the Ca(NO₃)₂ treatment was significantly less than that with NH₄NO₃ with or without straw. The NH₄NO₃ + straw plants had more mature leaves and greater leaf dry weight than the other two treatments. At an early stage (before 66 days), N concentration of Ca(NO₃)₂‐fed plants was less than with the other two treatments. The leaf K concentration and shoot K content of NH₄NO₃ and NH₄NO₃ + straw plants were more than with the Ca(NO₃)₂ treatment before maturity. Also, K concentration in mature leaves with these two treatments was greater than with Ca(NO₃)₂ treatment. All these results indicated that NH₄NO₃ application had benefits to the maturity and K accumulation in leaves of tobacco.     

Determination of trace elements in Saudi Arabian soils by inductively coupled plasma mass spectrometry (ICP‐MS)

Abstract

Saudi Arabian soil samples from different locations have been collected and analyzed for traces of barium (Ba), cobalt (Co), nickel (Ni), titanium (Ti), vanadium (V), silver (Ag), gold (Au), copper (Cu), lithium (Li), and lead (Pb). Inductively coupled plasma mass spectrometry (ICP/MS) has been found to be useful for soil analysis. Two commonly used digestion methods, one employing nitric acid and the other aqua regia, are employed for sample pretreatment. Percentage recovery of added element quantities are found to be within the 97.4 to 101.2% range for Ba, Co, Ni, Ti, and V using aqua regia digestion and within the 95.0 to 05.0% range for Ag, Au, Cu, Li, and Pb when using the nitric acid digestion method. The percentage relative standard deviation (% RSD) for five replicate samples for the two digestion procedures is less than 5% for the analyzed elements.     

Kinetic Characteristics of Nitrate Uptake by Wheat and Rape and Their Determination

15－day old seedlings of wheat and rape were grown in a series of solutions with different concentrations of KNO3 for a definite period of time.The changes in NO3^- concentration of the solutions were determined by the double ion-selective electrode method,and then the amount of NO3^- taken up by the plants was estimated and values of Km and Imax of the Michealis-Mentan equation were calculated.Results show that both the method and conditions of determination affected the values of Km and Imax.For example,the Km value was appreciably reduced when the volume of culture solution was increased or when the duration of nutrient uptake was shortened;the Km value obtained with short-term depletion method was higher than that obtained with long-term one.Similar Variations were found for the values of Imax.There was a considerable difference in the characteristics of uptake kinetics between wheat and rape when determined under the same conditions of determination.The isotherm of NO3^- uptake by wheat could be separated into saturated and unsaturated parts,and when the concentration of NO3^- exceeded 180μM,the relationship between the rate of NO3^- uptake and NO3^- concentration tended to be linear.However,the isotherm of NO3^- uptake by rape was found to fit the Michealis-Menten equation and no linear relationship could be found.     

Nitrate determination in sugar beet sap extracted with Pb (CH3COO)2‐PbO using an ion‐selective electrode

Abstract

Nitrates were directly determined in sugar beet sap, extracted with 0.04 M Pb(CH₃COO)₂ ‐ 0.02 M PbO, using an ion‐selective electrode. Nitrate levels as low as 5 mg/kg of fresh plant weight could be accurately determined with a high degree of precision. As an additional advantage, this method can be automated so that nitrates in sugar beet sap can be determined simultaneously with Na, K, aminoacid‐nitrogen, and sugar.     

Determination of molybdenum in wet‐ashed digests of plant material using flameless atomic absorption

Abstract

A procedure using matrix‐compensated Mo standards to determine Mo in plant tissue by flameless atomic absorption is described. Concentration ranges of macroelements (N,P,K,Ca,Mg), microelements (Cu,B,Zn,Mn,Al,Fe), and HC1O₄. typical of those found in HNO₃‐HC1O₄ plant tissue digests were examined for their effect on the observed analytical value of Mo. The mean of 20 Mo determinations of NBS orchard leaves SRM 1571 was 0.28 ± 0.01 ppm Mo compared to the NBS certified value of 0.3 ± 0.1 ppm Mo. Recovery of Mo added to digests of orchard leaves and alfalfa tops ranged from 95 to 105%.     

Spatial Inference of Nitrate Concentrations in Groundwater

We develop a method for multiscale estimation of pollutant concentrations, based on a nonparametric spatial statistical model. We apply this method to estimate nitrate concentrations in groundwater over the mid-Atlantic states, using measurements gathered during a period of 10 years. A map of the fine-scale estimated nitrate concentration is obtained, as well as maps of the estimated county-level average nitrate concentration and similar maps at the level of watersheds and other geographic regions. The fine-scale and coarse-scale estimates arise naturally from a single model, without refitting or ad hoc aggregation. As a result, the uncertainty associated with each estimate is available, without approximations relying on high spatial density of measurements or parametric distributional assumptions.     

Recovery of 15N‐Labeled Nitrate Injected into Deep Subsoil by Maize in a Calcareous Alluvial Soil on the North China Plain

Abstract

Recovery of residual nitrogen (N) from the subsoil by maize (Zea mays L.) was studied by injecting ¹⁵N‐labeled nitrate at 110 cm for treatments with and without N fertilizer in a calcareous soil on the North China Plain. The results show that the recovery of ¹⁵N‐labeled nitrate diffusing in the 90‐ to 130‐cm soil horizon was 11.9% with N fertilizer application and 6.7% without N application in maize. Nitrogen fertilizer applied to topsoil stimulated growth of maize roots in the subsoil, thus increasing the recovery of ¹⁵N‐labeled nitrate. In the relatively dry growing season in this experiment, the ¹⁵N‐labeled nitrate did not move downward because there was no downward water flow at 110 cm. Hence, under dry weather conditions, the maize crop can re‐utilize a small part of the residual soil nitrate in deep soil layers. Most of the nitrogen uptake was in the 0‐ to 80‐cm layer during the experiment.     

Determination of Optimum Rate and Growth Stage for Foliar‐Applied Phosphorus in Corn

Abstract

Foliar applications of fertilizer phosphorus (P) could improve use efficiency by minimizing soil applications. Nine experiments were conducted in 2002 and 2003 to determine foliar P rates and appropriate growth stages for application. Treatments comprised of 10 factorial combinations of three foliar P application timings and four rates of foliar P. Foliar application times were V4 (collar of fourth leaf visible), V8 (collar of eighth leaf visible), and VT (last branch of the tassel completely visible but silks not yet emerged) corn growth stages. Foliar P rates were 0, 2, 4, and 8 kg ha^?1. Foliar P applied at the VT growth stage improved grain and forage P concentration, which was reflected in increased grain yield in some of the experiments. A foliar P rate of 8 kg ha^?1 improved yield to some extent and forage and grain P concentration more than the smaller rates. The results suggest that foliar P could be used as an efficient P‐management tool in corn when applied at the appropriate growth stage and rate.     

Determination of organic matter content in arid‐zone soils using a simple “loss‐on‐ignition” method

Abstract

A simple and rapid procedure for the determination of organic matter content in mineral soils by loss‐on‐ignition without pretreatment was studied. Attention was given to the possible effect of inorganic compounds abundant in mineral soils on the estimation of organic matter content by this method. Both fast heating (DTA‐TGA type) studies and prolonged heating procedures were employed on natural and “synthetic”; soils. The results were compared to those obtained by the dichromate wet‐oxidation method widely used in soil laboratories for organic matter determination. In a group of 91 soils collected from various mineral soils in Israel, and having OM contents between 0.09 and 13.23%, a correlation coefficient of 0.972 was obtained for the linear regression between organic matter content measured by the proposed method and organic carbon measured by the dichromate wet‐oxidation method.     

Effect of N‐(n‐butyl)thiophosphoric triamide added to peat and leather in urea‐based fertilizers on urea hydrolysis and ammonia volatilization

Abstract

A laboratory experiment evaluated the rate of urea hydrolysis and ammonia volatilization from urea (U) mixed in organo‐mineral (O‐M) fertilizers. These fertilizers were incubated in soil in the presence or absence of N‐(n‐butyl)thiophosphoric triamide (NBPT) as a urease inhibitor. Two organic matrices, leather (L) and peat (P), were used to prepare the O‐M fertilizers. In the absence of NBPT, the highest ammonia losses and the fastest rate of urea hydrolysis were in the soil treated with the fertilizer containing leather (UL₅₀). Significantly lower ammonia losses occurred with peat‐based fertilizers. Although the fertilizer containing peat (UP₅₀) stimulated the rate of urea hydrolysis with respect to the urea alone, no increase in ammonia volatilization was detected. NBPT‐containing fertilizers were stored for different times (0,7, 30, and 60 days) and temperatures (25°C and 40°C), and the NBPT recovery was monitored by extraction and analysis by HPLC. The NBPT recovery decreased by increasing either the storage time or the storage temperature. Differences among the fertilizers occurred after storage at 40°C for 30 or 60 days. With UN, in spite of about 25% extracted amount of NBPT, the ammonia losses did not increase with respect to the non‐stored fertilizer. On the contrary, no inhibitor was recovered from either of the O‐M fertilizers (UNL and UNP). However, in the presence of leather, NBPT reduced the volatilization losses by 35 to 40%, whereas in the presence of peat, a complete loss of NBPT efficiency occurred. In general, either the inhibitor recovery or efficiency were affected by the storage conditions or the type of organic matrix.     

Growth and nitrogen (N2) fixation response of arrowleaf clover to mineral nitrogen and 2(N‐morpholino)‐ethanesulfonic acid at low pH

Evaluation of legume response to acidic conditions can be difficult when using nutrient solutions because of fluctuations in solution pH. The organic buffer 2(N‐morpholino)‐ethanesulfonic acid (MES) has been used for stabilizing pH in nutrient solution studies. We evaluated the effectiveness of MES (5.0 mM) to stabilize solution culture at pH 5.5 with and without mineral N (0 or 1.0 mM NH₄NO₃) and its influence on growth and N₂ fixation of arrowleaf clover (Trifolium vesiculosum Savi). The buffer maintained pH stability ± 0.1 pH units in the presence or absence of mineral N. In the absence of mineral N, the quantity of N₂ fixed by plants grown with MES was not significantly different from that fixed by plants grown without MES. However, with mineral N, N₂ fixation was reduced 37% with addition of MES. Tissue analysis indicated a small increase in Ca and Mg concentration for plants grown with MES. Caution should be exercised in the use of MES in studies of N₂‐fixing legumes when mineral N is included.     

Comparison of Extraction Procedures Used in Determination of Phosphorus Species by 31P‐NMR in Chilean Volcanic Soils

Abstract

Four procedures were employed to extract phosphorus (P) from volcanic soils for ³¹P‐NMR experiments. The procedures involve 0.5 M NaOH extraction, 0.5 M NaOH and Chelex 100 cation exchange resin extraction, NaOH‐EDTA extraction, and HCl‐NaOH two step sequential extraction with Chelex 100 clean up. Results showed that inorganic‐P, monoester‐P, diester‐P and pyrophosphate were present. Their detection was dependent on the extraction procedure used.

The NaOH procedure gives only a broad and vaguely defined signal with poor signal to noise ratio. The incorporation of Chelex 100 in the extraction enhanced the signal to noise ratio and allowed the distinction of inorganic‐P, monoester‐P, diester‐P and pyrophosphate. The two step sequential extraction involving HCl, NaOH, and Chelex 100 significantly improve the signal to noise ratio. The NaOH‐EDTA extraction procedure is efficient only in samples with low OC contents.

When soils have low OC content, any of the four extraction procedures can be successfully used. If the OC and the Fe concentration in the extracted solutions are high, the Chelex 100 became essential in clean up the metallic ions. Both the NaOH and Chelex 100 and the HCl‐NaOH‐Chelex produced satisfactory results and the later procedure by far the best resolved spectra.