Non-exchangeable NH Research Articles

Nitrogen use efficiency and residual effect of fertilizers with nitrification inhibitors

Abstract Blending fertilizers with nitrification inhibitors (NI) is a technology to reduce nitrogen (N) losses. The application of NI could increase the soil N supply capacity over time and contribute to an enhancement of N use efficiency (NUE) in some cropping systems. The objectives were to determine in a field experiment located in Central Spain (i) the effect of NI-fertilizers applied to maize ( Zea mays L.) during two seasons on yield, N content and NUE compared to conventional fertilizers, (ii) the soil residual effect of NI-fertilizers in a non-fertilized sunflower ( Helianthus annuus L.) planted during a third season, and (iii) the possible sources of residual N via laboratory determinations. The maize was fertilized with ammonium sulfate nitrate (ASN) and DMPP (3,4-dimethylpyrazole phosphate) blended ASN (ENTEC ® ) at two levels (130 and 170 kg N ha −1 ). A control treatment with no added N fertilizer was included to calculate NUE. The second year, DMPP application allowed a 23% reduction of the fertilizer rate without decreasing crop yield or grain quality. In addition, the sunflower planted after the maize scavenged more N in treatments previously treated with ENTEC ® than with traditional fertilizers, increasing NUE in the cropping systems. After DMPP application, N was conserved in non-ready soil available forms during at least one year and subsequently released to meet the sunflower crop demand. The potential N mineralization obtained from aerobic incubation under controlled conditions of soil samples collected before sunflower sowing was higher for ENTEC ® than ASN or control treatments. A higher δ 15 N in the soil indicated larger non-exchangeable NH 4 + fixation in soils from the plots treated with ENTEC ® or ASN-170 than from the ASN-130 or the control. These results open the opportunity to increase NUE by designing crop rotations able to profit from the effect of NI on the soil residual N.

Influence of pre-crop and root architecture on the mobilization of non-exchangeable NH<sub>4</sub><sup>+</sup>

It is well established that non-exchangeable NH<sub>4</sub><sup>+</sup> is an important N source for plants. However, release from clay minerals only occurs when the NH<sub>4</sub><sup>+</sup> concentration of the mineral environment declines below a certain level. This may be conditioned by the growing plant. Although root development differs depending on plant species, the influence of root architecture on the mobilization of non-exchangeable NH<sub>4</sub><sup>+</sup> is still open to question. We found that mobilization of non-exchangeable NH<sub>4</sub><sup>+</sup> was higher under oilseed rape as compared to barley; oilseed rape even has allorhize and fescue homorhize roots. This observation could be proved by labeling soil samples with <sup>15</sup>NH<sub>4</sub><sup>+</sup>, which were incubated in soil holders under oilseed rape and barley. The higher mobilization of non-exchangeable NH<sub>4</sub><sup>+</sup> by oilseed rape is therefore assumed to be caused by higher release of H<sup>+</sup>, displacing interlayer NH<sub>4</sub><sup>+</sup>. Although allorhize roots from pre-crops create more stable biopores with an increasing diameter and living roots of the subsequent crop enter these biopores, we could not find an influence of the pre-crop on the mobilization of non-exchangeable NH<sub>4</sub><sup>+</sup>.

Ammonium fixation and release by clay minerals as influenced by potassium

It is postulated that stabilized ammonium fertilizers improve fertilizer-N utilization by crops, leading thus to higher yields with the same fertilizer rate, especially on sandy soils. However, it must be taken into consideration that in clayey soil at least a part of the NH<sub>4</sub><sup>+</sup> ions may be fixed by 2:1 clay minerals, thus delaying the effect of the N fertilizer. Because NH<sub>4</sub><sup>+</sup> and K<sup>+</sup> have similar size and valence properties and therefore compete for the same non-exchangeable sites of 2:1 clay minerals, we investigated the influence of time and K<sup>+</sup> application rate on both fixation and release of NH<sub>4</sub><sup>+</sup>. Fixation of NH<sub>4</sub><sup>+</sup> ions was higher when K<sup>+</sup> was applied after NH<sub>4</sub><sup>+</sup>, while the influence of the K<sup>+</sup> application rate was less pronounced. Mobilization of non-exchangeable NH<sub>4</sub><sup>+</sup> was retarded when K<sup>+</sup> was applied at the high rate after NH<sub>4</sub><sup>+</sup>. At the first harvest yield formation of ryegrass was neither influenced by the amount as well as the application time of K<sup>+</sup>, because plant available N was not growth limiting, while yield of the second harvest was significantly higher with the low K<sup>+</sup> application rate after NH<sub>4</sub><sup>+</sup>. After the second harvest the blocking effect of K<sup>+</sup> on the release of non-exchangeable NH<sub>4</sub><sup>+</sup> was attenuated and the highest yields of the third cut were reached in the treatments with the high K<sup>+</sup> application rate after NH<sub>4</sub><sup>+</sup>. Total dry matter yield was highest when K<sup>+</sup> was applied at the low rate after NH<sub>4</sub><sup>+</sup>. Our results show that K<sup>+</sup> governs fixation and release of non-exchangeable NH<sub>4</sub><sup>+</sup>, which should be taken into consideration when applying ammonium containing N fertilizers like ammonium sulfate, ammonium sulfate nitrate and ENTEC. Thus K<sup>+</sup> can affect N availability when N is applied as NH<sub>4</sub><sup>+</sup> in both the short and long term.

Modification of the standard method for determination of non-exchangeable NH<sub>4</sub>-N in soil

It is well accepted that non-exchangeable NH<sub>4</sub>-N plays an important role in the N dynamics of arable soils. However the widely-used Silva/Bremner method for determining this N fraction is very time consuming and the use of the hazardous hydrofluoric acid (HF) is indispensable. In the modification the use of HF is avoided and the quantity of analysed samples per unit of time could be increased by a factor of 2.5. After pretreating soil samples with KOBr to destroy soil organic matter soil samples are dried and the content of non-exchangeable NH<sub>4</sub>-N is measured using a CNS analyzer. The results of the analysis of 3 out of 4 different soils show no significant differences between both methods.  

Fixation and release of ammonium in flooded rice soils as affected by redox potential

In pot experiments with two typical paddy soils, we studied the significance of ammonium fixation under waterlogged conditions and the availability of this N fraction for wetland rice. Special attention was given to the influence of redox potential ( E h) on the fixation and release of NH + 4, since the E h has been shown to affect the charge conditions of certain expandable clay minerals and may alter their cation exchange capacity (CEC). The results demonstrate that ammonium formed by mineralization after flooding was converted, to a substantial degree, into a non-exchangeable form when sufficient amounts of expandable 2:1 minerals were present. The newly fixed NH + 4 was protected from N losses via nitrificationn–denitrification processes, which may occur, especially during the drying and rewetting of the soil, but was completely available to the following rice crop. The release of fixed NH + 4 was highest in the rhizosphere of rice plants (where the E h was greatly increased by the O 2 secretion of the roots) and decreased with growing distance from the roots. Correlations between the E h and the concentration of non-exchangeable NH + 4 indicate that fixation and mobilization of ammonium are strongly influenced by the redox potential in paddy soils.

Equilibrium and Kinetic Study of Ammonium Adsorption and Fixation in Sodium‐Treated Vermiculite

AbstractAmmonium fixation in vermiculite affects the movement of N in many soils. The effects of particle size, solution concentration, pH, and associated anions on NH+4 fixation in vermiculite are also important information for reducing N leaching from soils. In this study, the retention of NH+4 on the exchangeable and nonexchangeable sites of Montana vermiculite was determined in batch experiments. In the NH+4‐K+ exchange isotherm, the exchangeable sites of the vermiculite exhibited a preference for K+ to NH+4, while the nonexchangeable sites preferred NH+4 to K+. The nonexchangeable sites of the sand fraction had a higher preference for NH+4 at lower solution NH+4 concentration and a lower preference at higher NH+4 concentration. An opposite case was observed for the NH+4 concentration effect on the preference of nonexchangeable sites in the clay fraction. The retention isotherm of total NH+4 in the vermiculite exhibited S‐shape curves that can be described by the “two‐surface” Langmuir‐Freundlich equation. In the kinetic study, the clay fraction adsorbed the largest amount of exchangeable NH+4, but the silt fraction fixed the most NH+4 on its nonexchangeable sites. The retention of NH+4 in vermiculite increased with solution NH+4 concentration. Ammonium adsorption on the exchangeable sites increased at low solution pH, while NH+4 fixation was unaffected by pH change. The effect of associated anions was insignificant, except they caused a pH difference in solution.

Kinetics of Nonexchangeable Ammonium Release from Soils

AbstractThe rate of nonexchangeable NH4+ release from soils can have a significant effect on N dynamics and environmental quality. Nonexchangeable NH4+ is that N fraction which is fixed in the interlayers of clay minerals. The objective of this study was to determine the kinetics of nonexchangeable NH4+ release from two topsoils from Germany [Giessen Ap (Aqualf) and Hungen Ap (Alfisol)] and from two subsoils, one from Germany [Hungen C (Alfisol)] and one from Kentucky [Shrouts Bt (Hapludalf)]. Calcium‐saturated, freeze‐dried soils were extracted with H‐resin for 0.25 to 384 h. Sodiumethylmercurythio‐salisylate (Thimerosal) was added to the soil/H‐resin suspension to inhibit microbiological ammonification. The kinetics of nonexchangeable NH4+ release from the soils were biphasic and were best described by Elovich and heterogeneous diffusion models. The release of nonexchangeable NH4+ as a percentage of total nonexchangeable NH4+ in the soils ranged from 4 to 25% and was lower in subsoils than in topsoils. This was ascribed to the higher levels of indigenous nonexchangeable NH4+ in the subsoils, which is more tightly held than recently fixed nonexchangeable NH4+.

Depletion of non-exchangeable NH 4-N in the soil—root interface in relation to clay mineral composition and plant species

Experiments were carried out with 10 soils with different clay contents and different clay composition to investigate the dynamics of non-exchangeable NH + 4 and 1 M HCl extractable NH + 4, respectively, in the vicinity of the roots. The experimental plant was rape ( Brassica napus). In addition the influence of plant species on the mobilization of non-exchangeable NH + 4 was investigated with ryegrass ( Lolium multiforum) and red clover ( Trifolium pratense) on a soil with a higher proportion of smectites and vermiculite. The depletion zone of non-exchangeable NH + 4 as well as 1 M HCl extractable NH + 4 extended to about 3 mm from the root zone in soils with a higher proportion of smectites and vermiculite, while in soils with mainly illites the depletion of both N fractions in the root vicinity was negligible. The depletion was less pronounced for red clover. It is suggested that the release of ammonium from the interlayers depends on clay mineral characteristics as well as on plant species.

Nonexchangeable Ammonium and Potassium Determination in Soils with a Modified Sodium Tetraphenylboron Method

AbstractThe mechanism of NH+4 and K+ fixation by clay minerals is similar, yet different analytical methods are used to estimate nonexchangeable (fixed) amounts of these nutrients in soils. Sodium tetraphenylboron (NaBPh4) facilitates the release of nonexchangeable NH+4 and K+ by precipitation of these ions as NH4BPh4 and KBPh4. A NaBPh4 method was modified and evaluated as a common procedure for determination of nonexchangeable NH+4 and K+ in 10 midwestern soils that were either untreated or NH+4 − or K+‐saturated (treated with 2 M solutions of NH4Cl or KCl to saturate fixation sites with NH+4 or K+). Experiments were conducted to evaluate Cu2+ (CuCl2) as a substitute for Hg2+ (HgCl2) in the recovery of NH+4 and K+ released by NaBPh4 in soils. A 7‐d incubation with the modified NaBPh4 method (CuCl2 instead of HgCl2) released most of the NaBPh4‐ extractable NH+4 and K+. In untreated soils, the NaBPh4 method extracted 71% of NH+4 released by the conventional HF/HCl method. Nonexchangeable NH+4 release by both methods was related in untreated (r2 = 0.98) and NH+4‐saturated (r2 = 0.95) soils. Recently fixed NH+4 in the NH+4‐saturated soil was equally accessible to both methods. The NaBPh4 method extracted up to 10 times more nonexchangeable K+ than the conventional 1 M HNO3 method in both the untreated and K+‐saturated soils. Recently fixed K+ in the K+‐saturated soil was equally accessible to both methods, except in high‐fixing soils where K+ was held too strongly to be released by HNO3. The results show that the modified NaBPh4 method can be used as a common procedure to estimate nonexchangeable forms of both NH+4 and K+.

AVAILABILITY OF 15N-LABELED NONEXCHANGEABLE AMMONIUM TO SOIL MICROORGANISMS

Soils containing appreciable amounts of 2:1 clay minerals frequently contain a substantial portion of their total N as nonexchangeable NH; trapped within the interlayers of these clay minerals. Moreover, NH; applied as fertilizer to these soils may be rapidly fixed. A laboratory study was conducted to assess the role of soil microorganisms in the release of clay-fixed NH; and its eventual accumulation in forms suitable for plant uptake in two alluvial soils of the lower Mississippi floodplain. Experiments involving 15 N-labeled NH 4 + , initially present solely as nonexchangeable 15 NH 4 + , showed that indigenous heterotrophic microorganisms readily assimilated this N when the availability of a C substrate created demand. When Commerce silt loam initially containing 180 mg of clay-fixed 15NH 4 + -N kg −1 was incubated for 28 days, 48 % of fixed 15 N was recovered as microbial biomass N (12 %) and as exchangeable NH 4 + -N (36 %). The 15 NH 4 + released was not rapidly refixed by clays, even though only small amounts were nitrified. Fumigation to inhibit soil biological activity resulted in a substantial reduction in the release of fixed 15 NH 4 + . In contrast, the addition of 4000 mg of mannitol-C kg −1 to stimulate biological activity enhanced the release of fixed 15 N and stimulated its subsequent nitrification. Experiments using two C-amended soils containing 90 or 180 mg of fixed 15 NH 4 + -N kg −1 showed that 64 to 96 % of this N was released in 28 days. Measures of microbial respiration indicated that recently fixed NH; was 23 to 46 % as available as NH 4 + added directly to soil as a neutral salt and considerably more available than native fixed NH 4 + . The conclusion that heterotrophic microorganisms play a principal role in the release of recently fixed NH; was supported by experiments showing that addition of N in this form stimulated microbial activity and growth. These findings suggest that the activity of heterotrophic microorganisms may conserve soil N by promoting the release of recently fixed NH 4 + , primarily near the surface of roots that supply C to these organisms

Release of nonexchangeable NH 4 ‐N after planting of ryegrass in relation to soil content and as affected by nitrate supply

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Quantity‐Intensity Relationships of Soil Ammonia in Long‐Term Rotation Plots

AbstractReports of release of nonexchangeable NH+4 from soils under some conditions and reports that management practices can change the affinity of the exchange complex for NH+4 indicate a need to reevaluate the commonly accepted practice of determining exchangeable NH+4 to assess the availability of NH+4 to plants. To address this need, quantity‐intensity (Q/I) relationships were studied in soil samples from two Iowa soils, a Webster clay loam (fine‐loamy, mixed, mesic Typic Haplaquoll) and a Galva silty clay loam (fine‐silty, mixed, mesic Typic Hapludoll) in long‐term experiments having various crop‐rotation and N‐fertilizer treatments. The observed Q/I relationships gave no evidence for release of nonexchangeable NH+4. Potassium‐exchangeable NH+4 concentrations were well correlated with measurements of labile NH+4 (r = 0.91, P < 0.01) and equilibrium activity ratios for NH+4 (r = 0.89, P < 0.01). No significant relationship was found between relative affinity of the exchange complex for NH+4 and organic C within each soil. Soil management practices influenced NH+4 availability as evaluated by KCl‐exchangeable NH+4 and Q/I parameters, but did not change the relative affinity of the exchange complex for NH+4. Overall, indexes of NH+4 availability based on determinations of K‐exchangeable NH+4 were similar to those derived from studies of Q/I relationships.

Short-term nitrogen reactions following the addition of urea to a grass-legume association

This experiment was made throughout one growing season to study soil N reactions in the field shortly after the application of 15N-labelled urea (85 kg N ha −1) to a grass-legume association under Mediterranean conditions. Ureolysis occurred within 2 days after application, with the highest NH + 4- 15N concentration observed at 2 days. The rates of nitrification and labelling of microbial biomass N reached maximum values during the decrease in the concentration of labelled ammonium: the release of microbial N metabolites from biomass N was marked after 9 days. About 59.5% (48.4% as organic N and 11.1% as non-exchangeable NH + 4-N) of the initially-applied N was accounted for in the 0–40 cm topsoil layer at the time of the first forage harvest. Microbial N immobilization was greater than N uptake by the plants (12.3% of the total urea-N at the first harvest) and limited N losses. Biomass-N values determined by the fumigation-extraction method (FE) were 4 and 2.5 times higher than those obtained by the fumigation-incubation method (FI).

Nonexchangeable Ammonium Nitrogen Contribution to Plant Available Nitrogen

AbstractRecent European research has shown that nonexchangeable NH+4‐N may be released from soil and utilized by crops. Surface and subsoil samples were collected from agriculturally important soils of Coastal Plain, Piedmont, and Ridge and Valley regions of Virginia to determine the relative importance of different soil N fractions for supplying N to wheat (Triticum aestivum L. em Thell) grown in the greenhouse. Exchangeable and nonexchangeable NH+4‐N, NO‐3‐N, total N, organic matter contents and an index of organic N availability were measured on all samples. Plant available N was measured by N uptake of successive wheat crops grown in the greenhouse. Multiple linear regression models for different groups of samples were used to determine the significance of the different soil N fractions to the plant available N supply, and to predict N uptake by wheat. Best models were selected considering fit, significance of the regression coefficients, and predictive ability. Collinearity effects on the models were reduced by using Principal Components regression. All the soils provided significant amounts of N to the wheat in both the first and second crops. Exchangeable NH+4‐N and NO‐3‐N were the major initial sources of plant available N. Nonexchangeable NH+4‐N contents were highest in fine‐textured soils, and/or soils with large amounts of previously‐added N fertilizers. This soil N fraction was a significant contributor to the plant available N supply for all soil groups, and amounts up to 129 mg kg−1 soil were measured. Interaction of nonexchangeable NH+4‐N with readily‐available N was found in all soil groups. Nonexchangeable NH+4‐N should be considered as a potential plant available N source in future research.

Importance of soil type on the release of nonexchangeable NH 4 + and availability of fertilizer NH 4 + and fertilizer NO 3 -

Nitrogen uptake from non-exchangeable NH4+ byLolium multiflorum and availability of fertilizer NH4+ and fertilizer NO3- were studied in pot experiments with three different soil types. The luvisol derived from loess released considerable amounts of non-exchangeable NH4+ when cropped. In this soil fertilizer NH4+ was only weakly fixed and was as available to the crop as fertilizer NO3-. The recovery of fertilizer NH4+ was even higher than the recovery of fertilizer NO3-. In the fluvisol (alluvial soil) and in the cambisol (brown earth from basalt) N recovery was higher from NO3- fertilizer than from NH4+ fertilizer. In these soils NH4+ fertilizer was strongly fixed by 2:1 clay minerals and thus less available to the grass. Particularly in the basaltic soil the content of non-exchangeable NH4+ was low and so was the release of nonexchangeable NH4+. At the same time this soil showed the strongest fixation of fertilizer NH4+. Release and refixation of fertilizer NH4+ in the loess soil appears to be an important feature of this soil type with a beneficial effect on soil nitrogen turnover and availability.

Wheat Fallow Tillage Systems' Effect on a Newly Cultivated Grassland Soils' Nitrogen Budget

The objective of this study was to examine soil nitrogen (N) losses from grassland soil as affected by time since the beginning of cultivation. A native grassland site was cultivated for winter wheat (Triticum aestivum L.) production in a crop-fallow rotation under three tillage systems; no-till, stubble mulch, and plow (bare fallow). The experiment was located in Western Nebraska on a Duroc loam (fine silty, mixed, mesic, Pachic Haplustolls). After 12 yr of cultivation, losses of soil N from the 0 to 30 cm depth were 3% for no-till, 8% for stubble mulch, and 19% for the plow tillages. Potential loss by erosion was small because of protection from wind by the surrounding grasslands. These results suggest decreased stirring of the soil resulted in major N savings beyond erosion losses. The sum of NO−3-N greater than that found below the sod control plus crop removal of N accounted for essentially all of the soil N lost from stubble mulch and plow tillages. In the no-till environment, crop removal of N and leached NO−3-N accounted for more N than had been lost from the soil since cultivation began. Plow tillage system resulted in leaching of 100 kg ha−1 more NO−3-N than occurred with no-till or stubble mulch. Soil N in the 0-to 30-cm soil depth was fractionated into exchangeable NH+4-N, nonexchangeable NH+4-N, and nonhydrolyzable N. The nonexchangeable and exchangeable NH+4-N fractions were not affected by cultivation. The nonhydrolyzable N fraction was reduced by all forms of tillage and accounted for a substantial part of the soil N losses.

The Release of Nonexchangeable Ammonium (15N Labelled) in Wetland Rice Soils

AbstractThe release of nonexchangeable (fixed) NH+4 was studied for three representative rice soils of the Philippines. Soil samples from these soils were treated with 15NH+4 in the laboratory so that they contained appreciable amounts of nonexchangeable NH+4 in 15N form. Special soil holders were filled with the labelled soil and incubated in the wetland rice soils from July to October at a depth of 0.2 m. During this period of incubation, highly significant amounts of labelled nonexchangeable NH+4 were released from all three soils. For the Maligaya silty clay loam and Guadalupe clay, both containing vermiculite, the total release of nonexchangeable NH+4 was higher than the release of labelled nonexchangeable NH+4 showing that non‐labelled NH+4 was released as well. 15N analysis of the rice plants showed that the nonexchangeable labelled NH+4 was subsequently available to the crop. Assuming a soil bulk density of 1 and a rooting depth of 0.2 m release of nonexchangeable NH+4 from the Maligaya silty clay loam ranged from 80 to 100 kg N ha−1, while for the Guadalupe clay and Santa Rita clay the net release of nonexchangeable NH+4 amounted to about 20 to 40 kg N ha−1, respectively. It is concluded that nonexchangeable NH+4 may play a major role in N nutrition of rice crops grown in wetland rice soils rich in vermiculite.

Distribution and isotope composition of nitrogen in Bay of Quinte (Lake Ontario) sediments

The concentrations and isotopic compositions of the various forms of nitrogen in silty clay sediments from the Bay of Quinte (Lake Ontario) have been determined. The total organic-N content is high throughout the sediment profiles and generally decreases with depth. On the contrary, exchangeable NH + 4-N concentration is quite low and tends to increase with depth in two out of three sediment cores examined. The concentration of non-exchangeable NH + 4-N and the 6 N HCl hydrolyzable NH + 4-N are relatively constant with depth. Among the N fractions analyzed, the exchangeable NH + 4-is most enriched in 15N. In most cases, the δ 15 N values of the N fractions remain relatively constant with sediment depth. There is no apparent correlation of δ 15 N values with the N concentration for any of the individual N fractions. The observed ranges in the δ 15 N values are: exchangeable NH + 4, + 5–+10‰; 6 N HCl hydrolyzable total N and 6 N HCl hydrolyzable NH + 4-N, + 3.5–+5.5‰.