四环素类抗生素在土壤和堆肥中的吸附和降解

Two agricultural soils were collected from Dahu and Pinchen counties and swine manure compost (SMC) from Ping-tung County in Taiwan, China to investigate the sorption and dissipation of three tetracyclines (TCs), i.e., oxytetracycline (OTC), tetracycline (TC) and chlortetracycline (CTC), in compost, soils and soil/compost mixtures with different organic carbon (OC) contents. There were seven treatments in total. TCs were most strongly adsorbed to SMC in all treatments due to the high OC content. When SMC was present in the soils, the sorption of TCs was significantly enhanced, which might be attributed to the increased OC content and CEC. The adsorption of TCs showed non-linear adsorption isotherms and fitted well to the Freundlich model. After 49 d of incubation at 25 ℃ in soils and soil/compost mixtures in the dark, TCs elapsed in all substrates, with the time required for 50% degradation (DT₅₀) between 20 and 41 d, and the time for 90% degradation (DT₉₀) between 68 and 137 d. Soil amended with compost enhanced the stability of TCs and reduced their mobility. The dissipation of TCs in a soil environment was slow, indicating that these compounds might be persistent in soil.     

油蒿群落土壤碳酸钙和脱氢酶对土壤有机质的响应

Little attention has been paid to the role of soil organic matter (OM) in the formation of pedogenic carbonate in desert soils. The relationships among soil OM, soil dehydrogenase activity (DHA), and soil CaCO₃ in a plant community dominated by Artemisia ordosica, located on the eastern boundary of Tengger Desert in the Alxa League, Inner Mongolia, China, were studied to understand whether OM was directly involved in the formation of pedogenic carbonate. The results showed that DHA and CaCO₃ positively correlated with OM content, and DHA, OM, and CaCO₃ were correlated with each other in their spatial distribution, indicating that abundant OM content contributed to the formation of CaCO₃. Therefore, the formation of pedogenic CaCO₃ was a biotic process in the plant community dominated by A. ordosica.     

用熏蒸提取法校正酸性红壤的KEC值

Commonly used K_EC value (0.45) of the fumigation-extraction (FE) method was obtained on the basis of temperate neutral soils. To ascertain its applicability to acidic red soils widespread in southern China and other subtropical regions, the K_EC value was investigated based on 8 acidic red soils by in situ labelling of native soil microorganisms using ¹⁴C-labelled glucose. Realistic K_EC value for red soils could be obtained by in situ ¹⁴C-labelling as long as an incubation period of 72 h is adopted after addition of ¹⁴C glucose to soil. The single K_EC values for the eight red soils ranged from 0.27 to 0.35 and averaged 0.31. Lower K_EC value obtained in red soils probably resulted from different soil quality, compared with other types of soil, which causes possible changes in microbial community structure and extractability of cellular component. Microbial biomass C contents of the eight red soils measured using a unique and constant K_EC value of 0.45 decreased by 22.2%~40% in comparison to those using variable K_EC values. The results suggest that microbial biomass C would be significantly underestimated using the present K_EC value and a calibration of the K_EC value is necessary for red soils.     

磷的吸附和表面电荷特征及其与华南地区某些土壤矿物的关系

The phosphate adsorption and surface charge characteristics of the tropical and subtropical soils derived from different parent materials in China were determined, and their relations to soil mineralogy were analysed. The results showed that all soil phosphate adsorption curves were well fitted by Freundlich equation and Langmuir equation. The maximum buffering capacity of P ranged from 66 to 9 880 mg kg^-1, with an increasing order of purple soil, skeletal soil, red soil, lateritic red soil, yellow soil and latosol; and the highest value was 149 times the lowest value, which indicated great differences among these soils in phosphate adsorption and supplying characteristics. The pH₀ (zero point of charge) values obtained by salt titration-potential titration varied from 3.03 to 5.49, and the highest value was found in the latosol derived from basalt whereas the lowest value was found in the purple soil. The correlation analysis indicated that the main minerals responsible for phosphate adsorption in the soils were gibbsite, amorphous iron oxide and kaolinite; and the pH₀ was mainly controlled by kaolinite, gibbsite and oxides.     

电解质阴离子和pH对可变电荷土壤硫酸盐吸附的影响

The effects of three electrolyte anions, ionic strength and pH on the adsorption of sulfate by two variable charge soils, with different surface charge properties were studied. Under the conditions of the same pH and ionic strength the effect of electrolyte anions on the adsorption of sulfate was in the order of Cl^- > NO₃^- > ClO₄^-, indicating the difference of the nature among these three anions. For Ferralsol in the same concentration of chloride and perchloride solutions, the two sulfate adsorption-pH curves could intersect at certain pH value. When pH was higher than the intersecting point, more sulfate was adsorbed in the perchloride solution, while when it was lower than the intersecting point, more sulfate was adsorbed in the chloride solution. In different concentrations of electrolyte solution, the curves of the amount of oxy-acid anion adsorbed, which changed with pH, could intersect at a certain pH, which is termed point of zero salt effect (PZSE) on adsorption. The nature of electrolyte anions influenced obviously the appearance of PZSE for sulfate adsorption. For ferralsol the curves of adsorption converged to about pH 7 in NaCl solution seemed to intersect in NaNO₃ solution and to have a typical PZSE for sulfate adsorption in NaClO₄ solution. For Acrisol the three curves of adsorption were nearly parallel in NaCl and NaNO₃ solutions and converged to pH 6.5 in NaClO₄ solution.     

甲硫嘧磺隆在土壤中的吸附和解吸特性研究

Methiopyrsulfuron is a new low-rate sulfonylurea herbicide for weed control in wheat; however, there is a lack of published information on its behavior in soils. In this study, methiopyrsulfuron adsorption and desorption were measured in seven soils sampled from Heilongjiang, Shandong, Jiangxi, Sichuan, Anhui, and Chongqing provinces of China using a batch equilibrium method. The Freundlich equation was used to described its adsorption and desorption. Adsorption isotherms were nonlinear with the values of Kf-ads, the Freundlich empirical constant indicative of the adsorption capacity, ranging from 0.75 to 2.46, suggesting that little of this herbicide was adsorbed by any of the seven soils. Soil pH and organic matter content (OM) were the main factors influencing adsorption; adsorption was negatively correlated with pH and positively correlated with OM. Methiopyrsulfuron desorption was hysteretic on the soils with high OM content and low pH.     

中国陕西省施有机肥黄土NH4+固定的热力学性质

Some thermodynamic properties of NH₄⁺ fixation by loess soil in plowing and clay layers are discussed. The results indicate that the four ion adsorption equations commonly used can describe the properties of NH₄⁺ fixation in these soils under constant temperature. Among the four adsorption equations, the single-surface Langmuir equation is the best. When the concentration of NH₄Cl solution is 10^-1 mol below, the Freundlich equation can be used. The changes of apparent standard free energy (ΔG°), enthalpy (ΔH°) and entropy (ΔS°) illustrate that NH₄⁺ fixation in soil is an endothermic adsorption and spontaneous reaction, and the process can be enhanced by a higher temperature and clay content in soil. The "proper value of NH₄⁺ fixation by soil (K₁ × q_m) increased with increasing clay content and temperature. The heat of NH₄⁺ fixation in soil (Q_m) confirms the conclusions made in this paper.     

初始浓度对六氯苯在土壤中的吸附-解吸的影响及解吸

Adsorption and desorption are important processes that influence the transport, transformation, and bioavailability of hexachlorobenzene (HCB) in soils. To examine the adsorption-desorption characteristics of HCB, equilibrium batch experiments were carried out using two soils (red soil and paddy soil) with different initial HCB concentrations (0.25, 0.50, 0.75, 1.00, 1.50, 2.50, 3.50, and 5.00 mg L^-1) by using 0.01 mol L^-1 calcium chloride as the background solution. The successive desorption experiments (48, 96, 144, 192, and 240 h) were conducted after each adsorption equilibrium experiment. The results revealed that adsorption and desorption isotherms of HCB on two soils were nonlinear, which can be best described by the Freundlich equation with the square of the correlation coefficient (r²) ranging from 0.97 to 0.99. Desorption of HCB from the two soils exhibited hysteresis at all HCB concentrations because the Freundlich desorption coefficients were always higher than the Freundlich adsorption coefficients. The hysteretic effect was enhanced with increasing initial HCB concentration, and positive hysteresis was observed at different concentrations.     

钙盐诱导下土壤锰和铁的释放及其对胡椒的生物有效性

Releases of manganese and iron ions from an albic soil (Albic-Udic Luvisol), a yellow-red soil (Hap-Udic Ferrisol) and a yellow-brown soil (Arp-Udic Luvisol) induced by calcium salt addition and their bioavailability to pepper (Capsicum frutescens L.) were studied in a pot experiment. Addition of Ca(NO₃)₂ decreased soil pH and increased both exchangeable and DTPA (diethylenetriamine pentaacetic acid)-extractable Mn and Fe in soils. Meanwhile, total Mn accumulation in the shoots of Capsicum frutescens L. on the salt-treated soils increased significantly (P< 0.01) compared with the control, suggesting that salt addition to soil induced Mn toxicity in Capsicum frutescens L. Although exchangeable and DTPA-extractable Fe increased also in the salt-treated soils, Fe uptake by the shoots of Capsicum frutescens L. decreased. The effect of added salts in soils on dry matter weight of pepper varied with the soil characteristics, showing different buffer capacities of the soils for salt toxicity in an order of yellow-brown soil > albic soil > yellow-red soil. Fe/Mn ratio in shoots of Capsicum frutescens L. decreased with increasing salt addition for all the soils, which was ascribed to the antagonistic effect of Mn on Fe accumulation. The ratio of Fe/Mn in the tissue was a better indicator of the appearance of Mn toxicity symptoms than Mn concentration alone.     

电解质对酸性土壤铝的溶解及铝形态在土壤溶液中的分布的影响

KCl, CaCl₂, NH₄Cl, NaCl, K₂SO₄ and KF solutions were used for studying the effects of cations and anions on the dissolution of aluminum and the distribution of aluminum forms respectively. Power of exchanging and releasing aluminum of four kinds of cations was in the decreasing order Ca²⁺ >K⁺ >NH₄⁺ >Na⁺. The dissolution of aluminum increased with the cation concentration. The adsorption affinity of various soils for aluminum was different. The aluminum in the soil with a stronger adsorption affinity was difficult to be exchanged and released by cations. The Al-F complexes were main species of inorganic aluminum at a low concentration of cations, while Al³⁺ became major species of inorganic aluminum at a high concentration of cations. The results on the effect of anions indicated that the concentrations of total aluminum, three kinds of inorganic aluminum (Al³⁺, Al-F and Al-OH complexes) and organic aluminum complexes (Al-OM) when SO₄^2- was added into soil suspension were lower than those when Cl^- was added. The dissolution of aluminum from soils and the distribution of aluminum forms in solution were affected by the adsorption of F^- on the soil. For soils with strong affinity for F^-, the concentrations of the three inorganic aluminum species in soil solution after addition of F^- were lower than those after addition of Cl^-; but for soils with weak affinity for F^-, the concentrations of Al³⁺ and Al-OM were lower and the concentrations of Al-F complexes and total inorganic aluminum after addition of F^- were higher than those after addition of Cl^-. The increase of F^- concentration in soil solution accelerated the dissolution of aluminum from soils.     

施入粉煤灰和污泥对酸性淋溶土镉和铅吸附的影响

The safe recycling of fly ash (FA) and sewage sludge (SS) in the agricultural processes comprises an important environmental technology on waste management. Soils amended with FA and SS may change their ability to adsorb heavy metals due to either increase of soil pH or decomposition of sludge-borne organic matter. Thus, Cd and Pb sorption was investigated by 1-month incubation under soil moisture content at field capacity and room temperature with an acidic Typic Haploxeroalf from central Greece amended with varying amounts of FA and SS. Batch experiments were conducted by equilibrating the soil samples with CaCl₂ solutions containing 0-400 mg Pb L^-1 or 0-100 mg Cd L^-1. The results showed that the Freundlich equation described well the Cd and Pb sorption. Distribution coefficient (K_d) values of Pb were higher than those of Cd in all the treatments of this study. Application of FA increased K_d values for Cd and Pb to 8.2 and 2.3 times more than the controls, respectively. Simultaneous applications of FA and SS caused a K_d increase of 3.8 and 2.1 times compared to the treatments that received only SS for Cd and Pb, respectively. Treatment of SS alone did not significantly change Cd and Pb sorption compared to the controls. The sorption reactions seemed to be mainly affected by soil pH, which was revealed by the significant correlations of Cd and Pb sorption with soil pH. These suggested that fly ash was very useful as a low-cost adsorbent for Cd and Pb and could be used as an ameliorant for biosolid-amended acidic soils.     

Wheat yield prediction by zero sink and equilibrium-type soil phosphorus tests

Diffusive gradients in thin films (DGT) measurements have been shown to outperform other phosphorus (P) tests in soils with strong P sorption, but this has not been confirmed for moderately weathered European soils. We compared the performance of DGT in predicting wheat grain yield in Swedish long-term fertility experiments with those of standard intensity (water-extractable P (P-H₂O)) and quantity (ammonium lactate-extractable P (P-AL)) tests. A Mitscherlich-type model was used to fit wheat yield response to P application rates (0, 15, 30 or 35, and 45 kg P ha^-1 year^-1) in each individual trial replicate to estimate the maximum yield. For trials with clear plateau-type yield responses and the goodness of fit (R²) > 0.75, relative yields (RYs) were calculated for each P treatment and plotted against the soil P test results (n=143). The goodness of the Mitscherlich-type fits decreased in the following order:DGT-measured P (P-DGT) (R²=0.35) > P-H₂O (R²=0.18) > P-AL (R²=0.13). When excluding soils with P-AL:P-DGT ≥ 0.1 L g^-1, R² was considerably improved to 0.55 for P-AL, 0.46 for P-H₂O, and 0.65 for P-DGT (n=61). At 95% of maximum yield, the upper limit of P deficiency for P-DGT was 44.8 (the soils with P-AL:P-DGT < 0.1 L g^-1) and 61.9 μg L^-1 (all soils), falling within the range reported for other European and Australian soils (6.0-142 μg L^-1). We show that in the investigated Swedish soils, DGT performed better than the quantity and intensity tests, which is attributed to its ability to capture P diffusion and resupply from the soil solid phase, similar to plant roots in the rhizosphere.     

Variability in pattern and hydrogen isotope composition (δ2H) of long-chain n-alkanes of surface soils and its relations to climate and vegetation characteristics: A meta-analysis

The average chain length (ACL), carbon preference index (CPI), and hydrogen isotope composition (δ²H) of long-chain n-alkanes in sediments have been used to retrieve information about the paleoclimate. Despite their importance as in-between media from leaves to sediments, n-alkanes of surface soils have not been systematically analyzed at large scale. Such an investigation of the spatial variation of n-alkane properties in soil and their dependence on climatic and botanic (e.g., vegetation type) factors could provide a rationale for a better estimation of the past environment. We synthesized the patterns and δ²H of long-chain n-alkanes in soil (δ²H^n-alkanes) with regard to vegetation types (cropland, grassland, shrubland, and woodland) and environmental factors using data from peer-reviewed papers. Our results showed that the ACL and CPI of soil C₂₇–C₃₃ n-alkanes were not suitable indicators for differentiating vegetation types at large scale; instead, ACL significantly correlated with water conditions such as mean annual precipitation (MAP) and Palmer drought severity index (PDSI), and CPI significantly correlated with temperature without significant influence of vegetation type. The variation (i.e., standard deviation) of fractionation between the δ²H values in annual precipitation and in soil n-alkanes (ε_rain-soil) was smaller than that reported in leaves; therefore, soils were better suited to quantifying the general growing conditions of plants at a certain site. The fractionation ε_rain-soil correlated with climatic conditions as described by the PDSI and relative humidity (RH). This correlation agreed with the change in leaf water enrichment with changing RH taken from the literature and was independent of the vegetation type at large scale. This meta-analysis may provide useful information for the variations of the patterns and δ²H_n-alkanes values in surface soils.     

不同液土比和温度条件下塿土铵离子吸附

Effects of NH₄⁺ concentration, solution/soil ratio and temperature on NH₄⁺ adsorption were studied in a Eum-Orthic Anthrosol. The slopes of the soil NH₄⁺ adsorption isotherms and the fitted n, the coefficient for the adsorption intensity, and k, the coefficient related to adsorption capacity, of the Freundlich equation increased with increasing solution/soil ratio (SSR) and with decreasing temperature (T). For the range of experimental conditions, the value of ∂q/∂c, the rate of change of the amount of NH₄⁺ adsorbed in the soil solid phase (q) with respect to the equilibrium concentration of NH₄⁺ in soil solution (c), was 0.840, indicating that q increased with increasing c. From 2 to 45 ℃, ∂q/∂SSR, the rate of change of q with respect to SSR, decreased from 2.598 to 1.996, showing that q increased with increasing SSR, while its increasing rate decreased with temperature. From SSR 1:1 to 20:1, ∂q/∂T, the rate of change of q with respect to T, decreased from -0.095 to -0.361, indicating that q decreased with increasing temperature, and at the same time the negative effect of temperature became larger as SSR increased. Thus under the experimental conditions the order of importance in determining the amount of NH₄⁺ adsorbed in the soil solid phase was ∂q/∂SSR > ∂q/∂c > |∂q/∂T|, indicating that the greatest effect on the amount of NH₄⁺ adsorbed was with the solution/soil ratio; the equilibrium concentration of NH₄⁺ had a lesser effect; and temperature had the least effect.     

氯离子在土壤中的扩散: Ⅱ.动力学及热力学性质

The amounts of chloride ions diffused in four soils of different textures at the same water content under different temperature and at varied time were measured by the diffusion cell method using ³⁶Cl-labelled CaCl₂ solution. Five kinetic models were used to fit the dynamic process of the diffusion of chloride ions in the soils. It was found that Elovich equation or power function equation was the best model to describe the process. The pseudothermodynamic parameters, i.e. the net reaction energy, the activation entropy, activation enthalpy and activation free energy of the diffusion, were derived from the absolute reaction-rate theory. The results showed that these parameters decreased in the order of loessal soil > black lu soil > lou soil > yellow cinnamon soil, which indicated that the force and the heat-energy barrier to be overcome for diffusion decreased, the diffusion rate increased and the disorder of the soil-solution-ion system due to diffusion decreased successively with the texture becoming heavier in the four soils.     

pH对土壤重金属吸附动力学的影响

The pH effect on the sorption kinetics of heavy metals in soils was studied using a constant flow leaching method. The soil samples were red soil collected from Yingtan, Jiangxi, and yellow-brown soil from Nanjing, Jiangsu. The heavy metals tested were zinc and cadmium. Assuming that the experimental data fitted to the following kinetic rate equation: 1/c·dx/dt = kx_∞-kx, the rate constant k of sorption could be determined from the slope of the straight line by plotting of 1/c·dx/dt vs. x. The results showed that the pH effect on the rate constants of heavy mental sorption in soils was very significant. The values of k decreased with increasing pH. The sorptions were more sensitive to pH in red soil than in yellow-brown soil.     

土壤Se的分级与Se的植物有效性的关系

Nine soils with distinct properties and Se levels were selected to test a fractionation procedure of soil Se based on sequential extraction. Soil Se was fractionated into readily available Se (fraction Ⅰ, extracted by 0.5 M NaHCO₃), slowly available Se (fraction Ⅱ, extracted by 0.1 M NaOH-0.1 M Na₄P₂O₇), amorphous oxide-occluded Se (fraction Ⅲ, extracted by acid ammonium oxalate), free oxide-occluded Se (fraction Ⅵ, extracted by dithionite-citrate-bicarbonate buffer solution) and residual Se (fraction Ⅴ, determined by HNO₃-HClO₄ digestion of the final soil residue). The recovery of soil Se (the sum of all fractions over total soil Se determined independently) by this procedure was from 88.1% to 110.9%, mean 99.2%±6.4% for the test soils. The sum of fractions Ⅰ and Ⅱ, provided a good measure of available Se in soils and the percentage of fraction Ⅰ plus Ⅱ over the total soil Se, tentatively defined as Se availability index, could be used to indicate soil Se status and predict Se deficiency.     

Inhibition of ammonia-oxidizing bacteria promotes the growth of ammonia-oxidizing archaea in ammonium-rich alkaline soils

Disparities in the substrate affinity and tolerance threshold for ammonia have been believed to play a key role in driving niche differentiation between ammonia-oxidizing archaea (AOA) and bacteria (AOB); however, recent surveys argue that direct competition between AOA and AOB is also important in this phenomenon. Accordingly, it is reasonable to predict that diverse AOA lineages would grow in ammonium (NH₄⁺)-rich alkaline arable soils if AOB growth is suppressed. To test this hypothesis, a microcosm study was established using three different types of alkaline arable soils, in which a high NH₄⁺ concentration (200 μg N g^-1 dry soil) was maintained by routinely replenishing urea and the activities of AOB were selectively inhibited by 1-octyne or 3,4-dimethylpyrazole phosphate (DMPP). Compared with amendment with urea alone, 1-octyne partially retarded AOB growth, while DMPP completely inhibited AOB. Both inhibitors accelerated the growth of AOA, with significantly higher ratios of abundance of AOA to AOB observed with DMPP amendment across soils. Nonmetric multidimensional scaling analysis (NMDS) indicated that different treatments significantly altered the community structures of both AOA and AOB and AOA OTUs enriched by high-NH₄⁺ amendment were taxonomically constrained across the soils tested and closely related to Nitrososphaera viennensis EN76 and N. garnensis. Given that these representative strains have been demonstrated to be sensitive to high ammonia concentrations, our results suggest that it is the competitiveness for ammonia, rather than disparities in substrate affinity and tolerance threshold for ammonia, that drives niche differentiation between these phylotypes and AOB in NH₄⁺-rich alkaline soils.     

巴基斯坦小麦-玉米轮作系统下低有机碳土壤中异丙隆和阿特拉津的吸附、淋洗潜力

Pesticide leaching is a great threat in low organic carbon soils when subjected to improper irrigation scheduling. Limited data are available on the sorption and leaching potential of pesticides in agricultural soils of Pakistan with low soil organic carbon (SOC). Lysimeter and field studies were conducted with and without manure application at two irrigation levels in a wheat-fallow-maize rotation in Faisalabad, Punjab, Pakistan. Isoproturon was applied to wheat 55 d after sowing at 1 kg active ingredient (a.i.) ha^-1, while atrazine was sprayed on maize 30 d after sowing at 0.774 kg a.i. ha^-1. Soil was sampled from three depths (0--35, 35--70, and 70--110 cm) for the field study and four depths (0--35, 35–70, 70--115, and 115--160 cm) for the lysimeter study, 280 and 65 d after application of isoproturon and atrazine, respectively. The soil-water partition coefficients (K_d) of isoproturon and atrazine ranged from 0.3 to 1.2 and 0.4 to 1.5 L Kg^-1, respectively, and increased linearly with increase in SOC contents. The organic carbon-normalized soil-water partition coefficient (K_oc) of isoproturon and atrazine averaged 246.1 and 184.9 L kg^-1, respectively, being higher with low spiking concentration. Isoproturon residues measured 280 d after application ranged from 2.1% to 3.6% of the applied mass in the lysimeter study and from 1.5% to 3.1% under field conditions. Atrazine residues 65 d after application ranged from only 0.62% to 0.78% and from 0.88% to 0.82% in the lysimeter and field studies, respectively. The lowest levels of residues for both pesticides were observed with frequent irrigation applied to manure-amended soil. A pesticide leaching risk screening tool, the ground water ubiquity score (GUS), indicated that in the absence of manure under both irrigation levels, isoproturon has a leaching potential (GUS = 2.8), while with the application of manure it has a very low leaching risk. Atrazine GUS ranged from 1.7 to 1.9, indicating a very low risk of leaching.     

灌溉施用氮肥后氮素在土壤中的转化及淋失状况: 土柱模拟研究

A soil column method was used to compare the effect of drip fertigation (the application of fertilizer through drip irrigation systems, DFI) on the leaching loss and transformation of urea-N in soil with that of surface fertilization combined with flood irrigation (SFI), and to study the leaching loss and transformation of three kinds of nitrogen fertilizers (nitrate fertilizer, ammonium fertilizer, and urea fertilizer) in two contrasting soils after the fertigation. In comparison to SFI, DFI decreased leaching loss of urea-N from the soil and increased the mineral N (NH₄⁺-N + NO₃^--N) in the soil. The N leached from a clay loam soil ranged from 5.7% to 9.6% of the total N added as fertilizer, whereas for a sandy loam soil they ranged between 16.2% and 30.4%. Leaching losses of mineral N were higher when nitrate fertilizer was used compared to urea or ammonium fertilizer. Compared to the control (without urea addition), on the first day when soils were fertigated with urea, there were increases in NH₄⁺-N in the soils. This confirmed the rapid hydrolysis of urea in soil during fertigation. NH₄⁺-N in soils reached a peak about 5 days after fertigation, and due to nitrification it began to decrease at day 10. After applying NH₄⁺-N fertilizer and urea and during the incubation period, the mineral nitrogen in the soil decreased. This may be related to the occurrence of NH₄⁺-N fixation or volatilization in the soil during the fertigation process.