Adsorption isotherms of ammonium on coir

Abstract

Coir (coconut mesocarp pith) is the fibrous material that constitutes the thick mesocarp (middle layer) of the coconut fruit (Cocos nucifera L.). It has ion‐exchange and gas adsorption properties that can be utilized to adsorb the important plant nutrient N in its NH₄ ⁺ and/or NH₃ form, protecting it from losses such as during composting of N‐rich wastes. The NH₄ ⁺ adsorption process and the pH buffering capacity of the coir were studied to quantify its effectiveness as an NH₄ ⁺ adsorbent. The one‐ and two‐surface Langmuir, van Bemmelen‐Freundlich, Temkin, and first‐order models were fitted to the NH₄ ⁺ sorption data at an equilibrium pH range of 4.6 to 5.1. Each model was found to describe the NH₄ ⁺ sorption data with comparable success (r²≥0.88), with the Langmuir and Temkin being superior (r²≥0.99). Although the equilibrium pH did not change much after adding buffers of pH 4 to 7 to the coir, there was a consistent increase in the amounts of NH₄ ⁺‐N sorbed with increasing pH, as estimated using the two‐surface Langmuir model. The estimated amounts of NH₄ ⁺‐N sorbed were 516 mmol kg^‐1 at pH 4.6, 521 mmol kg^‐1 at pH 4.63, 571 mmol kg^‐1 at pH 4.88, and 573 mmol kg^‐1 at pH 5.1. The coir showed a good buffering ability at pH range 3.7 to 10.4. The coir buffer strength, defined as the amount of OH” required to increase pH by one unit, was 11.3 cmol kg^‐1 for the pH range 3.7 to 8.4, and 22.1 cmol kg^‐1 for the pH range 8.4 to 10.4. The high CEC, surface area, and buffer strength of the coir indicated its high ability to retain cations and buffer against pH change.     

The fate of ammonium nitrogen applied to flooded rice as affected by zeolite addition

High rice (Oryza sativa L.) yields are closely related to plant absorption of a large amount of nitrogen (N). However, there is little information on the fate of N applied at the middle growth stages of rice. Labeled ¹⁵N ammonium sulfate was applied at the panicle formation stage in Experiment I, and 10 d after heading in Experiment II. Zeolite was also added at the concentration of 0, 0.01, and 0.1 kg kg^-1 to increase the cation exchange capacity (CEC) of the soil. The amount of ¹⁵N fertilizer in the soil surface water decreased exponentially and the fertilizer disappeared within 2 d after application. The soil that received zeolite at 0.1 kg kg^-1 exhibited significantly less ¹⁵NH₄ ⁺-N in the surface water and in the soil solution than the soil without the zeolite amendment. A significantly larger amount of exchangeable ¹⁵NH₄ ⁺-N was observed in the high zeolite-treatment of soil compared to the low zeolite-treatment of soil. The amount of exchangeable ¹⁵NH₄ ⁺-N increased initially, and thereafter decreased to traces 4 d after application in Experiment I, while 6 or 9 d after application in Experiment II. The disappearance of exchangeable ¹⁵NH₄ ⁺-N could be attributed mainly to the uptake by plants. The zeolite amendment or the time of N application did not significantly affect the amount of immobilized N. The rate of N adsorption was inhibited with increasing zeolite application. Moreover, zeolite application did not increase the recovery percentage of ammonium sulfate by rice plants. The total recovery of applied N ranged from 65 to 75%, irrespective of the zeolite treatments or the time of N application.     

Mineralization of Three Organic Manures Used as Nitrogen Source in a Soil Incubated under Laboratory Conditions

Abstract

The rate and timing of manure application when used as nitrogen (N) fertilizer depend on N‐releasing capacity (mineralization) of manures. A soil incubation study was undertaken to establish relative potential rates of mineralization of three organic manures to estimate the value of manure as N fertilizer. Surface soil samples of 0–15 cm were collected and amended with cattle manure (CM), sheep manure (SM), and poultry manure (PM) at a rate equivalent to 200 mg N kg^?1 soil. Soil without any amendment was used as a check (control). Nitrogen‐release potential of organic manures was determined by measuring changes in total mineral N [ammonium‐N+nitrate‐N (NH₄ ⁺–N+NO₃ ^?–N)], NH₄ ⁺–N, and accumulation of NO₃ ^?–N periodically over 120 days. Results indicated that the control soil (without any amendment) released a maximum of 33 mg N kg^?1soil at day 90, a fourfold increase (significant) over initial concentration, indicating that soil had substantial potential for mineralization. Soil with CM, SM, and PM released a maximum of 50, 40, and 52 mg N kg^?1 soil, respectively. Addition of organic manures (i.e., CM, SM, and PM) increased net N released by 42, 25, and 43% over the control (average). No significant differences were observed among manures. Net mineralization of organic N was observed for all manures, and the net rates varied between 0.01 and 0.74 mg N kg^?1 soil day^?1. Net N released, as percent of organic N added, was 9, 10, and 8% for CM, SM, and PM. Four phases of mineralization were observed; initial rapid release phase in 10–20 days followed by slow phase in 30–40 days, a maximum mineralization in 55–90 days, and finally a declined phase in 120 days. Accumulation of NO₃ ^?–N was 13.2, 10.6, and 14.6 mg kg^?1 soil relative to 7.4 mg NO₃ ^?–N kg^?1 in the control soil, indicating that manures accumulated NO₃ ^?–N almost double than the control. The proportion of total mineral N to NO₃ ^?–N revealed that a total of 44–61% of mineral N is converted into NO₃ ^?–N, indicating that nitrifiers were unable to completely oxidize the available NH₄ ⁺. The net rates of mineralization were highest during the initial 10–20 days, showing that application of manures 1–2 months before sowing generally practiced in the field may cause a substantial loss of mineralized N. The rates of mineralization and nitrification in the present study indicated that release of inorganic N from the organic pool of manures was very low; therefore, manures have a low N fertilizer effect in our conditions.     

Phosphate sorption by calcium‐bentonite as described by commonly used isotherms

Abstract

The one and two Langmuir, the Freundlich, and the Temkin isotherms were fitted to phsophorus (P) sorption data for P sorption by calcium (Ca)‐bentonite at different initial concentration and pH values of 3.8, 4.8, 6.0, 7.0, 8.0, and 9.0. Each was found to describe P sorption by Ca‐bentonite with comparable success. The effect of pH on P adsorption by Ca‐bentonite was studied and Langmuir, Temkin, and Freundlich isotherms were converted to the forms:

Langmuir: (Co‐X)X= 1/(0.0275–0.0025pH)(12.323–1.061pH) + (Co‐X)(12.323–1.016pH) Temkin: X = (2.45–0.211pH)In(AC) Freundlich: X = (1.324–0.146pH)C(^0.172+0044 _P ^H) where: X = (mmol P/kg) the amount of P sorbed per unit weight of soil, C = (μmol P/L) the P concentration in the equilibrium solution, and Co = ((μmol P/L) initial P concentration. It is noteworthy, that the maximum amount (Xm) of P that can be sorbed in a monolayer decreases by increasing of pH. Finally, the B constant of Temkin isotherms is indepented from pH changes.     

Comparison of Adsorption Isotherm Equations to Describe Boron Behavior in Soils Affected by Organic and Mineral Fertilization

The effects of different fertilization techniques—mineral [21% nitrogen (N)], organomineral (10% N), mycorrhiza inoculumns, wine-producing residues (three different formulas: distiller's residue, 2.2% N; anaerobic digestate, 2.8% N; and the same plus mycorrhizas inoculum), and compost by farm residues (2.0% N)—on adsorption of boron (B) were investigated. The soils, collected after a triennial lettuce (Lactuca sativa L. cv. ‘Bacio’) cultivation, were equilibrated using six B concentrations [0, 1, 5, 20, 50, and 100 mg B L^?1, as boric acid (H₃BO₃)]. The B adsorption was studied at two soil mass (m_s) to solution volume (v_s) ratios, m_s/v_s = 0.5 and 1, and the Langmuir, Eadie–Hofstee, Freundlich, and Temkin adsorption equations were fitted to the B adsorption data. The proportion of adsorbed B was gradually less in the more concentrated solutions, with differences in m_s/v_s ratio and in treatments: the percentage of B adsorbed was greater for m_s/v_s = 0.5 and for distiller's residue and mineral fertilizer. The Freundlich isotherm represented the measured B adsorption data well; at m_s/v_s = 0.5, the values of Freundlich adsorption maxima Xm varied from 93.14 to 111.88 mg kg^?1 (organomineral fertilizer and distiller's residue, respectively; at m_s/v_s = 0.5) and from 32.14 to 40.32 mg kg^?1 (mineral fertilizer and control, respectively; at m_s/v_s = 1). In our study, generally the B adsorption was greater with mineral fertilizers and distiller's residue, whereas the organomineral fertilizer led to a decrease in B adsorption. The parameters of adsorption isotherms were significantly correlated, at various degrees, with the exchangeable cation sodium. The adsorption isotherms were well explained by the lower soil mass to volume solution ratio in the order Freundlich > Temkin ≌ Langmuir > Headie–Hofstee.     

Zinc adsorption characteristics of selected calcareous soils of Iran and their relationship with soil properties

Abstract

The apparent recovery of applied zinc (Zn) by plants is very low in calcareous soils of Iran because most of it is retained by the soil solids. Subsamples of 24 surface soil (clay 130–530 g kg^‐1; pH 7.7–8.4; electrical conductivity 0.63–3.10 dS m^‐1; organic matter 6.0–22.0 g kg^‐1; cation exchange capacity 8–20 cmol kg^‐1; calcium carbonate (CaCO₃) equivalent 180–460 g kg^‐1) representing 13 soil series in three taxonomic orders were equilibrated with zinc sulphate (ZnSO₄) solutions and the amount of Zn disappeared from solution after a 24‐h shaking period was taken as that adsorbed (retained) by the soil solids. The adsorption data were fitted to Freundlich (X=AC^B) and Langmuir [X=(K‐bC)/(1+K#lbC)] adsorption isotherms. Backward stepwiseprocedure was used to obtain regression equations with isotherms coefficients as dependent and soil properties as independent variables. Freundlich A and Langmuir K were found to be highly significantly related to pH and clay and increasing as these soil properties increased. But Langmuir b was related only to clay and Freundlich B showed no significant relationship with any of the properties studied. The distribution coefficient (also called maximum buffering capacity), calculated as the product of Langmuir K and b, was also found to be highly significantly related to pH and clay. It is concluded that pH and clay content of calcareous soils are the most influential soil properties in retention of Zn.     

Estimating soil ammonium adsorption using pedotransfer functions in an irrigation district of the North China Plain

Extensive use of chemical fertilizers in agriculture can induce high concentration of ammonium nitrogen(NH4⁺_-N) in soil. Desorption and leaching of NH4⁺_-N has led to pollution of natural waters. The adsorption of NH4⁺_-N in soil plays an important role in the fate of the NH4⁺_-N. Understanding the adsorption characteristics of NH4⁺_-N is necessary to ascertain and predict its fate in the soil-water environment, and pedotransfer functions(PTFs) could be a convenient method for quantification of the adsorption parameters. Ammonium nitrogen adsorption capacity, isotherms, and their influencing factors were investigated for various soils in an irrigation district of the North China Plain. Fourteen agricultural soils with three types of texture(silt, silty loam, and sandy loam) were collected from topsoil to perform batch experiments. Silt and silty loam soils had higher NH4⁺_-N adsorption capacity than sandy loam soils.Clay and silt contents significantly affected the adsorption capacity of NH4⁺_-N in the different soils. The adsorption isotherms of NH4⁺_-N in the 14 soils fit well using the Freundlich, Langmuir, and Temkin models. The models’ adsorption parameters were significantly related to soil properties including clay,silt, and organic carbon contents and Fe²⁺ and Fe³⁺ ion concentrations in the groundwater. The PTFs that relate soil and groundwater properties to soil NH4⁺_-N adsorption isotherms were derived using multiple regressions where the coefficients were predicted using the Bayesian method. The PTFs of the three adsorption isotherm models were successfully verified and could be useful tools to help predict NH4⁺_-N adsorption at a regional scale in irrigation districts.     

Reducing ammonia loss from urea and improving soil-exchangeable ammonium retention through mixing triple superphosphate, humic acid and zeolite

Ammonia losses from soil following fertilization with urea may be large. This laboratory study compared the effect of four different, urea–triple superphosphate (TSP)–humic acid–zeolite, mixtures on NH₃ loss, and soil ammonium and nitrate contents, with loss from surface‐applied urea without additives. The soil was a sandy clay loam Typic Kandiudult (Bungor Series). The mixtures significantly reduced NH₃ loss by between 32 and 61% compared with straight urea (46% N) with larger reductions with higher rates of humic acid (0.75 and 1 g kg^?1 of soil) and zeolite (0.75 and 1 g kg^?1 of soil). All the mixtures of acidic P fertilizer, humic acid and zeolite with urea significantly increased soil NH₄ and NO₃ contents, increased soil‐exchangeable Ca, K and Mg, and benefited the formation of NH₄ over NH₃ compared with urea without additives. The increase in soil‐exchangeable cations, and temporary reduction of soil pH may have retarded urea hydrolysis in the microsite immediately around the fertilizer. It may be possible to improve the efficiency of urea surface‐applied to high value crops by the addition of TSP, humic acid and zeolite.     

Effect of Raw and NH4+-enriched Zeolite on Nitrogen Uptake by Wheat and Nitrogen Leaching in Soils with Different Textures

Leaching of nutrients in soil can change the surface and groundwater quality. The present study aimed at investigating the effects of raw and ammonium (NH₄⁺)-enriched zeolite on nitrogen leaching and wheat yields in sandy loam and clay loam soils. The treatments were one level of nitrogen; Z₀: (100 kg (N) ha^?1) as urea, two levels of raw zeolite; Z₁:(0.5 g kg^?1 + 100 kg ha^?1) and Z_2: (1 g kg^?1 + 100 kg ha^?1), and two levels of NH₄⁺-enriched zeolite; Z₃: (0.5 g kg^?1 + 80 kg ha^?1) and Z₄: (1 g kg^?1 + 60 kg ha^?1). Wheat grains were sown in pots and, after each irrigation event, the leachates were collected and their nitrate (NO₃^?) and NH₄⁺ contents were determined. The grain yield and the total N in plants were measured after four months of wheat growth. The results indicated that the amounts of NH₄⁺ and NO₃^? leached from the sandy loam soil were more than those from the clay loam soil in all irrigation events. The maximum and minimum concentrations of nitrogen in the drainage water for both soils were observed at control and NH₄⁺-zeolite treatments, respectively. Total N in the plants grown in the sandy loam was higher compared to plants grown in clay loam soil. Also, nitrogen uptake by plants in control and NH₄⁺-zeolite was higher than that of raw-zeolite treatments. The decrease in the amount of N leaching in the presence of NH₄⁺-zeolite caused more N availability for plants and increased the efficiency of nitrogen fertilizers and the plants yield.     

Methane oxidation in arable soil as inhibited by ammonium, nitrite, and organic manure with respect to soil pH

 The effects of inorganic N and organic manure, applied to a loamy arable soil, on CH₄ oxidation were investigated in laboratory incubation experiments. Applications (40 mg N kg^–1) of NH₄Cl, (NH₄)₂SO₄, and urea caused strong instantaneous inhibition of CH₄ oxidation by 96%, 80%, and 84%, respectively. After nitrification of the added N the inhibitory effect was not fully reversible, resulting in an residual inhibition of 21%, 16%, and 25% in the NH₄Cl, (NH₄)₂SO₄, and urea treatments, respectively. With large NH₄ ⁺ applications [240 mg N kg^–1 as (NH₄)₂SO₄] the residual inhibition was as high as 64%. Exogenous NO₂ ^– (40 mg NO₂ ^–-N kg^–1) initially inhibited CH₄ oxidation by 84%, decreasing to 41% after its oxidation. Therefore, applied NO₂ ^– was a more effective inhibitor of CH₄ consumption than NH₄ ⁺. Temporary accumulation of NO₂ ^– during nitrification of added N was small (maximum: 1.9 mg NO₂ ^–-N kg^–1) and thus of minor importance with respect to the persistent inhibition after NH₄ ⁺ or urea application. CH₄ oxidation after NaNO₃ (40 mg N kg^–1) and NaCl addition did not differ to that of the untreated soil. The effect of organic manures on CH₄ oxidation depended on their C/N ratio: fresh sugar beet leaves enhanced mineralization, which caused an instantaneous 20% inhibition, whereas after wheat straw application available soil N was rapidly immobilized and no effect on CH₄ oxidation was found. The 28% increase in CH₄ oxidation after biowaste compost application was not related to its C/N ratio and was probably the result of an inoculation with methanotrophic bacteria. Only with high NH₄ ⁺ application rates (240 mg N kg^–1) could the persistent inhibitory effect partly be attributed to a pH decrease during nitrification. The exact reason for the observed persistent inhibition after a single, moderate NH₄ ⁺ or urea application is still unknown and merits further study. Received: 31 October 1997     

Effect of Manure Types and Period of Incubation on Phosphorus-Sorption Indices of a Weathered Tropical Soil

Application of animal manures with inorganic phosphate (PO₄) fertilizer is proposed as one of the management options to improve availability and solubility of applied phosphate in weathered soil. We studied the effects of poultry, cattle, and goat manures at different incubation periods (0 to 120 days) on phosphorus (P) sorption indices of a weathered sandy clay loam soil. The soil P adsorption isotherms conformed to the H curve. Generally, the soil P-sorption efficiency decreased as the number of days of incubation increased irrespective of manure amendments. Manure application reduced the P-sorption efficiency of the soil; the lowest P-sorption efficiency was observed after 30 days of incubation. The data conformed to adsorption models in the order Temkin > Freundlich > Langmuir. Cattle, goat, and poultry manures reduced the adsorption constants in all models. Standard phosphate requirement and P-buffering capacity were also reduced with the application of the manures.     

Presidedress soil nitrogen test for corn in Virginia

Abstract

The presidedress soil nitrate test (PSNT) and the presidedress tissue nitrogen test (PTNT) have been developed to assess residual soil nitrogen (N) sufficiency for corn (Zea mays L.) in the humid eastern U.S. We conducted field studies at 47 sites during 1990 and 1991 to evaluate the use of the PSNT and PTNT for corn in Coastal Plain, Piedmont, and Appalachian Ridge and Valley regions of Virginia. Seven rates of fertilizer N (0, 45, 90, 135, 180, 225, and 270 kg/ha) were applied at corn height of 0.40 to 0.50 m and replicated four times in a randomized complete block design. Whole corn plants and soil to a depth of 0.30 m were sampled when corn height was 0.15 to 0.30 m to estimate available soil N prior to the application of fertilizer N treatments. Corn grain yield response to fertilizer N was used to assess residual soil N availability. Nitrogen concentration of whole corn plants at 0.15 to 0.30 m height was not an accurate indicator of plant‐available soil N. Corn yields were maximized without sidedress N at the 19 sites where soil NO₃‐N was at least 18 mg‐kg^‐1 and at the 17 sites where soil (NO₃+NH₄)‐N was at least 22 mg‐kg^‐1. The PSNT predicted corn N sufficiency regardless of soil physiographic region or surface texture; however, the critical values for NO₃‐N and (NO₃+NH₄)‐N were 3 to 5 mg‐kg^‐1 lower than those established in Pennsylvania and Maryland, where cooler soil temperatures may permit greater residence time of inorganic N.     

Nitrogen Mineralization of Two Manures as Influenced by Contrasting Application Methods under Laboratory Conditions

The decomposition and the associated nitrogen (N) dynamics of organic N sources are affected by their contact with soil. While several authors have examined the effect of surface application or incorporation of crop residues on their decomposition rate, less information is available about the relationship between the placement of animal manure and their N mineralization rate. This study investigated the influence of chicken manure and cattle manure placement on soil N mineralization. The manures were incorporated or surface applied at 175 mg N kg^?1, and N release was periodically determined over 56 days by measuring inorganic N [nitrate (NO₃ ^?) N and ammonium (NH₄ ⁺) N] in a 2 M potassium chloride (KCl) extract at a ratio of 1:10 (w/v). Results indicated that the control soil released a maximum of 64 mg N kg^?1 soil at day 21, a sixfold increase over the initial concentration, which indicates its substantial mineralization potential. Manure treatments showed an initial increase in net NO₃ ^?-N content at the start of the experiments (until day 7) before an extended period of immobilization, which ended at day 21 of the incubation. A small but positive net N mineralization of all manures was observed from 28 days of incubation. At each sampling time, the mean mineral N released from the control was significantly less (P < 0.01) than surface-applied chicken manure, incorporated chicken manure, and surface-applied cattle manure. Treatments exceptions were at days 21 and 28 where N immobilization was at its peak. In contrast, incorporation of cattle manure showed a different N-release pattern, whereby the mineral N amount was only significantly greater than the control soil at days 42 and 56 with 84 and 108 mg N kg^?1 soil respectively. Incorporation of chicken manure and cattle manure did not favor nitrification as much as surface application and cattle manure caused a much greater immobilization when incorporated than when surface applied.     

Removal of Ammonia from Aqueous Solutions,Ground Water,and Wastewater Using Mechanically Activated Clinoptilolite and Synthetic Zeolite-A: Kinetic and Equilibrium Studies

Natural zeolite clinoptilolite and synthetic zeolite Na-A were characterized using XRD and SEM to be used as adsorbents for ammonia from aqueous solutions, ground water, and sewage water. Clinoptilolite was mechanically activated for 2, 4, 6, and 8 h to study the effect of activation in enhancing the adsorption capacity. The adsorption by activated natural zeolite and synthetic zeolite is high pH dependent and achieve the best values at pH?=?7. The adsorption capacity of activated natural zeolite increases with increasing the activation from 2 to 8 h achieving removal percentage close to that obtained using synthetic zeolite. The equilibrium was obtained after 60 min for synthetic zeolite and all the activated natural zeolite (except 2-h-activated product, the equilibrium was achieved after 30 min). The kinetic studies reflected the high fitness of the adsorption results of activated natural zeolite products and synthetic zeolite with pseudo-second-order model rather than the other kinetic models. The obtained isotherms reflected the formation of S-type isotherm curve for the adsorption using mechanically activated clinoptilolite and L-type curve for the uptake using synthetic zeolite. The results represented well with Langmuir model followed by Temkin and Freundlich model for adsorption using synthetic zeolite. The uptake using mechanically activated clinoptilolite can be represented by Temkin model rather than both Langmuir and Freundlich models. Thermodynamic parameters indicate spontaneous endothermic adsorption of ammonia using all the zeolitic products under investigation. Finally, the mechanically activated natural zeolite and synthetic zeolite exhibit high efficiency in the removal of ammonia and other water pollutants from ground water and sewage water.     

Does the Ammonium Fixation Capacity of Soils Have a Significant Effect on the Nitrogen Nutrition of Wheat?

Pot experiments were conducted on three soils differing in their ammonium (NH₄ ⁺) fixation capacity [high = 161 mg NH₄-nitrogen (N) kg^?1 soil; medium = 31.5 mg NH₄-N kg^?1 soil; and no = no NH₄-N was additionally fixed], and the effect of N fertilizer forms and doses on wheat (Triticum aestivum L.) was investigated. Grain yields responded to almost all forms of N fertilizer with 80, 160, and 240 kg N ha^?1 in the high, medium, and no NH₄ ⁺ fixing soil process, respectively. Agronomic efficiency of applied N fertilizers was significantly greater in the no NH₄ ⁺ fixing soil. Thousand grain weights (TGW) of wheat grown on the high and medium NH₄ ⁺ fixing soil decreased with increasing N. Grain protein increased with increasing NH₄ ⁺ fixation capacity. Nitrogen doses and the forms of N fertilizers affected grain protein at a significance level. The combination of urea + ammonium nitrate (NH₄NO₃) was most effective in increasing grain protein content.     

Does the potential ammonium fixation of soils have an impact on the optimum nitrogen fertilizer rate?

Field experiments were conducted to determine the effect of nitrogen (N) fertilizer forms and doses on wheat (Triticum aestivum L.) on three soils differing in their ammonium (NH₄) fixation capacity [high = 161 mg fixed NH₄-N kg^?1 soil, medium = 31.5 mg fixed NH₄-N kg^?1 soil and no = nearly no fixed NH₄-N kg^?1 soil]. On high NH₄⁺ fixing soil, 80 kg N ha^?1 Urea+ ammonium nitrate [NH₄NO₃] or 240 kg N ha^?1 ammonium sulfate [(NH₄)₂SO₄]+(NH₄)₂SO₄, was required to obtain the maximum yield. Urea + NH₄NO₃ generally showed the highest significance in respect to the agronomic efficiency of N fertilizers. In the non NH₄⁺ fixing soil, 80 kg N ha^?1 urea+NH₄NO₃ was enough to obtain high grain yield. The agronomic efficiency of N fertilizers was generally higher in the non NH₄⁺ fixing soil than in the others. Grain protein was highly affected by NH₄⁺ fixation capacities and N doses. Harvest index was affected by the NH₄⁺ fixation capacity at the 1% significance level.     

NH4+-K+ co-loaded clinoptilolite as a binary fertilizer

ABSTRACT

Understanding the potential of clinoptilolite (CLI) for adsorption of NH₄⁺ and K⁺, providing appropriate fertilizer formula, and evaluation of the produced zeolitic nutrient sources (ZNSs) to meet the plant need are the main objectives of this study. Three ZNSs (NH₄⁺-saturated, K⁺-saturated and dual-purpose NH₄⁺-K⁺ saturated CLI) were produced, assessed, and compared with commercial N and K fertilizers (CFs) on corn growth in a greenhouse. The results indicated that CLI can potentially adsorb both NH₄⁺ and K⁺ to the maximum values of 25.00 mg-NH₄⁺ g^?1 and 47.61 mg-K g^?1, respectively, and chemisorptions mainly followed the process of adsorption. Saturation of zeolite by NH₄⁺ and K⁺ occurred after 10 and 15 d which lead to ZNSs with 2% and 5% of N and K, respectively. NH₄⁺-K⁺ saturated CLI contained 1% N and 1% K. The greenhouse experiment showed no significant difference between ZNSs and CFs on plant growth. However, the application of both N and K in the form of zeolitic sources significantly increased the uptake of N by the plant. The highest uptake of K (2.05 g pot^?1) occurred in plants supplied with both natural zeolite and CFs. The present results may benefit the future utilization of ZNSs in environmental friendly farming practices.     

Spatiotemporal Heterogeneity of Soil Available Nitrogen During Crop Growth Stages on Mollisol Slopes of Northeast China

Spatiotemporal heterogeneity of soil available nitrogen (AN) (sum of NO₃⁻–N and NH₄⁺–N) is the essential basis for soil management and highly correlates to crop yield. Both geostatistical and traditional analyses were used to describe the spatiotemporal distribution of AN in the 0–20‐cm soil depth on typical Mollisol slopes (S1 and S2) in Northeast China. The concentration of NO₃⁻–N dynamics at slope positions was typically opposite to NH₄⁺–N. The peak values of AN typically moved from the summit of the slope to the bottom from spring to autumn and were mainly influenced by the content of NO₃⁻–N (S1, 7·9–18·9 mg kg⁻¹; S2, 1·2–103·6 mg kg⁻¹), both of NO₃⁻–N (S1, 3·9–8·3 mg kg⁻¹; S2, 2·2–28·0 mg kg⁻¹) and NH₄⁺–N (S1, 21·4–30·5 mg kg⁻¹; S2, 2·1–23·3 mg kg⁻¹), and NH₄⁺–N (S1, 10·5–28·9 mg kg⁻¹; S2, 5·0–39·0 mg kg⁻¹) in the seedling stage, vegetative growth stage, and reproductive growth stage, respectively. The spatial autocorrelation of AN was strong and was mainly influenced by structural factors during crop growth stages. This was mainly determined by soil erosion–deposition (SED) and soil temperature–moisture (STM) in the seedling stage; this was also mainly influenced by SED, STM, crop type, and crop growth in the vegetative growth stage and by early STM and early SED in the reproductive growth stage. Generally, the content of AN, NO₃⁻–N, and NH₄⁺–N on the whole slope was mainly determined by the early SED and local fertilizer application, while their spatiotemporal heterogeneity, especially the evenness, was mainly changed by SED, STM, crop growth, and crop types on the slope scale. In order to increase more crop yields, additional N fertilizer application on both the summit and the bottom during the vegetative growth stage and conservation tillage systems or additional soil amendments on the back slopes was necessary. Copyright © 2016 John Wiley & Sons, Ltd.     

Added nitrogen interaction as affected by soil nitrogen pool size and fertilization – significance of displacement of fixed ammonium

Displacement of NH₄⁺ fixed in clay minerals by fertilizer ¹⁵NH₄⁺ is seen as one mechanism of apparent added nitrogen interactions (ANI), which may cause errors in ¹⁵N tracer studies. Pot and incubation experiments were carried out for a study of displacement of fixed NH₄⁺ by ¹⁵N‐labeled fertilizer (ammonium sulfate and urea). A typical ANI was observed when ¹⁵N‐labeled urea was applied to wheat grown on soils with different N reserves that resulted from their long‐term fertilization history: Plants took up more soil N when receiving fertilizer. Furthermore, an increased uptake of ¹⁵N‐labeled fertilizer, induced by increasing unlabeled soil nitrogen supply, was found. This ANI‐like effect was in the same order of magnitude as the observed ANI. All causes of apparent or real ANI can be excluded as explanation for this effect. Plant N uptake‐related processes beyond current concepts of ANI may be responsible. NH₄⁺ fixation of fertilizer ¹⁵NH₄⁺ in sterilized or non‐sterile, moist soil was immediate and strongly dependent on the rate of fertilizer added. But for the tested range of 20 to 160 mg ¹⁵NH₄⁺‐N kg^–1, the NH₄⁺ fixation rate was low, accounting for only up to 1.3 % of fertilizer N added. For sterilized soil, no re‐mobilization of fixed ¹⁵NH₄⁺ was observed, while in non‐sterile, biologically active soil, 50 % of the initially fixed ¹⁵NH₄⁺ was released up to day 35. Re‐mobilization of ¹⁵NH₄⁺ from the pool of fixed NH₄⁺ started after complete nitrification of all extractable NH₄⁺. Our results indicate that in most cases, experimental error from apparent ANI caused by displacement of fixed NH₄⁺ in clay is unlikely. In addition to the low percentage of only 1.3 % of applied ¹⁵N, present in the pool of fixed NH₄⁺ after 35 days, there were no indications for a real exchange (displacement) of fixed NH₄⁺ by ¹⁵N.