A Comparison of Diffusion-Conductimetric and Distillation-Titration Methods in Analyzing Ammonium- and Nitrate-Nitrogen in the KCl-Extracts of Georgia Soils

Soil mineral (or inorganic) nitrogen (SMN), which primarily exists as exchangeable and soluble ammonium (NH4⁺) and the nitrate (NO₃^?) ions, represents readily available nitrogen for plant growth. Over the years a 2M potassium chloride (KCl) solution has become the extraction solution of choice for extracting SMN. In the research and service laboratories, either distillation-titration method (DTM) or colorimetric method (CM) is virtually the standard to measure NH₄⁺- and NO₃^?-N in the 2M KCl soil extracts. However, being a time-consuming and labor intensive method, DTM generally has a very low throughput. Likewise, CM is affected by interferences from pH variation, color, turbidity, presence of organic species, and some other constituents in the extracts. In contrast, diffusion conductivity method (DCM) is a less expensive and high throughput one, which is also relatively free from common interferences. In this study, we, therefore, compared the extraction efficiency of various KCl concentrations and performance of diffusion conductivity method (DCM) with DTM in measuring NH₄⁺-N and NO₃^?-N in KCl extracts of 32 agricultural soils of Georgia. A 0.2M KCl solution extracted statistically similar amounts of NH₄⁺-N and NO₃^?-N as did 2M KCl, suggesting that a 10-fold dilute KCl solution than the standard 2M KCl might be good enough to extract and estimate the most of SMN. For the analyses of NH₄⁺- and NO₃^?-N in the KCl extracts, the DCM produced results statistically similar to those produced by DTM. The deviation between the results given by DCM and DTM was no more than ±10%. Thus, DCM appears to be an attractive alternative to the labor intensive and time-consuming DTM for measuring NH₄⁺- and NO₃^?-N in the KCl extract of soils in the research and service laboratories.     

Leaching Methods Can Underestimate Mineralization Potential of Soils

Aerobic incubations to estimate net nitrogen (N) mineralization typically involve periodic leaching of soil with 0.01 M calcium chloride (CaCl₂), so as to remove mineral N that would otherwise be subject to immobilization. A study was conducted to evaluate the accuracy of leaching for analysis of exchangeable ammonium (NH₄⁺)-N and nitrate + nitrite (NO₃^?+ NO₂^–)-N, relative to conventional extractions using 2 M potassium chloride (KCl). Ten air-dried soils were used, five each from Illinois and Brazil, that had been amended with NH₄⁺-N (1 g kg^?1) and NO₃^–-N (0.6 g kg^?1). Both methods were in good agreement for inorganic N analysis of the Brazilian Oxisols, whereas leaching was significantly lower by 12–48% in recovering exchangeable NH₄⁺-N from Illinois Alfisols, Mollisols, and Histosols. The potential for underestimating net N mineralization was confirmed by a 12-wk incubation experiment showing 9–86% of mineral N recoveries from three temperate soils as exchangeable NH₄⁺.     

Agro-Industry Sludge as a Potential Organic Fertilizer for Prompt Nitrogen Release

The aim of this study was to evaluate the sustainability of an agro-industry sludge as a nitrogen (N) fertilizer in perennial crops by assessing its dynamics of release of: 1) N as ammonium (NH₄⁺)- and nitrate (NO₃^?)-N, and 2) carbon as soil respiration. In incubation assay, application of agro-industry sludge promoted the maximum NH₄⁺-N concentration (50 mg kg^?1) 2 h after application, then it decreased with time until day 26. NO₃^?-N increased, reaching the maximum between day 60 and day 100, according to a second degree function. Agro-industry sludge showed a slower release of NO₃^?-N compared with urea. Soil basal respiration and cumulative amount of carbon dioxide were higher in sludge from day 71 on. In field, soil NO₃^?-N increased after fertilization treatments and was higher in Calcari Stagnic Cambisols soil. Sludge showed a potential lower environment impact in terms of mineral N release, than urea.     

石灰性土壤起始NO3——N对土壤供氮能力测定方法的影响

在陕西省的澄城、永寿、杨陵 3地区选取有机质、全N、硝态N含量差异较大的 17个石灰性土壤 ,分别在淋洗与未淋洗土壤起始NO3--N后 ,利用盆栽试验探讨土壤NO3--N淋洗前、后 ,不同方法测定的已矿化N和可矿化N与小麦吸N量之间的相关性。结果表明 ,未淋洗土壤起始NO3--N ,用KCl直接浸取、KCl煮沸法所浸取以及通气培养前CaCl2 所淋洗的起始NO3--N均与小麦吸N量密切相关 ,相关系数 (r)分别为 0.934 ,0.856和 0.862 ,均达1%显著水准。与此相反 ,通气培养、淹水培养、沸水煮沸、碱性高锰酸钾、酸性高锰酸钾及碱解扩散等方法所提取的可矿化N与小麦吸N量间无显著相关。淋洗土壤起始NO3--N后 ,用KCl直接浸取、KCl煮沸法浸取以及通气培养前CaCl2 所淋洗的起始NO3--N与小麦吸N量之间的相关系数明显降低 ,达不到 5%的显著水准。而通气培养、淹水培养、沸水煮沸、碱性高锰酸钾、酸性高锰酸钾及碱解扩散等方法所提取的可矿化N与小麦吸N量之间相关系数却明显提高 ,都达到 5%或 1%的显著水平。其中变化最明显的是淹水培养 1周矿化出的NH4+-N、通气正式培养 2周矿化出的NO3--N及碱解扩散出的NH4+-N ,其与小麦地上部吸N量之间的相关系数 (r)分别由淋洗前的0.443,0.119,0.259增加到淋洗后的 0.866 ,0.767,0.763。说明可矿化N反映土壤供N能力不佳是因为受起始NO3--N的干扰和影响，在土壤NO3--N含量较高的情况下，要正确评价可矿化N测定方法必须考虑NO3--N的作用。     

Interactions between Inorganic Nitrogen Nutrition and Root Development

Root development responds not only to the quantity of inorganic nitrogen in the rhizosphere, but to its form, NH₄⁺ or NO₃^?. Root growth of tomato showed a hyperbolic response to soil levels of inorganic nitrogen: very few roots were found in soil blocks depleted in inorganic nitrogen, roots proliferated as soils increased to 2 μg NH₄⁺-N g^?1 soil or 6 μg NO₃^?-N g^?1 soil, and root growth declined in soils with the higher levels of inorganic nitrogen. High NH₄⁺ concentrations inhibited root growth, but low concentrations promoted the development of an extensive, fine root system. Supply with NO₃^? as the sole nitrogen source led to a more compact root system. These differences in root morphology under NH₄⁺ and NO₃^? nutrition may be mediated through pH. Rice and maize roots absorbed NH₄⁺ most rapidly right at the apex and appeared to assimilate this NH₄⁺ in the zone of elongation. During NH₄⁺ assimilation, root cells must release protons, and the resulting acidification around the walls of cells in this region should stimulate root extension. By contrast, NO₃^? absorption reached a maximum in the maturation zone of rice and maize roots, and this NO₃^? was probably assimilated in more basal regions. Absorption of NO₃^? requires proton efflux, whereas NO₃^? assimilation requires proton influx. The net result under NO₃^? nutrition was only subtle shifts in rhizosphere pH that probably would not influence root elongation. The signal through which roots detect changes in rhizosphere NH₄⁺ and NO₃^? levels is still obscure. It is proposed that a product of nitrogen metabolism such as nitric oxide serves as a signal.     

Soil inorganic nitrogen composition and plant functional type determine forage crops nitrogen uptake preference in the temperate cultivated grassland,Inner Mongolia

ABSTRACT

Plant nitrogen (N)-acquisition strategy affects soil N availability, community structure, and vegetation productivity. Cultivated grasslands are widely established to improve degraded pastures, but little information is available to evaluate the link between N uptake preference and forage crop biomass. Here an in-situ ¹⁵N labeling experiment was conducted in the four cultivated grasslands of Inner Mongolia, including two dicots (Medicago sativa and Brassica campestris) and two monocots (Bromus inermis and Leymus chinensis). Plant N uptake rate, shoot- and root biomass, and concentrations of soil inorganic-N and microbial biomass-N were measured. The results showed that the root/shoot ratios of the dicots were 2.6 to 16.4 fold those of the monocots. The shoot N concentrations of the dicots or legumes were 40.6% to 165% higher than those of the monocots or non-legumes. The four forage crops in the cultivated grassland preferred to uptake more NO₃^?-N than NH₄⁺-N regardless of growth stages, and the NH₄⁺/NO₃^? uptake ratios were significantly lower in the non-legumes than in the legumes (p < 0.05). Significant differences in the NH₄⁺-N rather than NO₃^?-N uptake rate were observed among the four forages, related to plant functional types and growth stages. The NH₄⁺ uptake rate in the perennial forages exponentially decreased with the increases in shoot-, root biomass, and root/shoot ratio. Also, the plant NH₄⁺/NO₃^? uptake ratio was positively correlated with soil NH₄⁺/NO₃^? ratio. Our results suggest that the major forage crops prefer to absorb soil NO₃^?-N, depending on soil inorganic N composition and belowground C allocation. The preferential uptake of NO₃^?-N by forages indicates that nitrate-N fertilizer could have a higher promotion on productivity than ammonium-N fertilizer in the semi-arid cultivated grassland.     

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.     

DEVELOPMENT OF A SOIL N TEST FOR FERTILIZER REQUIREMENTS FOR WHEAT

Optimal fertilizer nitrogen (N) rates result in economic yield levels and reduced pollution. A soil test for determining optimal fertilizer N rates for wheat has not been developed for Quebec, Canada, or many other parts of the world. Therefore, the objectives were to determine: 1) the relationship among soil nitrate (NO^? ₃)- N, soil ammonium (NH ⁺ ₄)- N and N fertilizer on wheat yields; and 2) the soil sampling times and depths most highly correlated with yield response to soil NO^? ₃-N and NH ⁺ ₄-N. In a three year research work, wet and dried soil samples of 0- to 30- and 30- to 60-cm depths from 20 wheat fields that received four rates of N fertilizer at seeding and postseeding (plants 15 cm tall) were analyzed for NH ⁺ ₄-N and NO^? ₃ -N using a quick-test (N-Trak) and a standard laboratory method. Wheat yield response to N fertilizer was limited, but strong to soil NO^? ₃-N.     

Effect of ammonium-, nitrite- and nitrate nitrogen on anaerobic nitrogenase activity in soil

Sandy loam soil, with added glucose, was incubated anaerobically under N₂ and subjected to repeated 1-h C₂H₂ reduction assays. In the presence of 1% glucose the addition of 50 μg NH₄⁺ ?N/g or of 20 μg NO^?₃ N/g (untreated soil contained 1.2 μg NH⁺₄?N and 7.10 μg NO^?₃-N/g) caused at least some suppression of nitrogenase activity. Activity developed when the KCl-extractable soil inorganic nitrogen concentration dropped below 35 μg/g. In the presence of 0.1 or 0.05% glucose the addition of 5 μg NH⁺₄?N/g caused some suppression of nitrogenase activity. However, activity developed when the soil NH₄⁺-N concentration dropped below about 4 μg/g. With 0.1% glucose and 5 μg added NO^?₂ N/g, activity did not develop until the soil NO^?₂ -N concentration dropped to zero. Added NO^?₃ N was rapidly reduced and denitrified to NO^?₂- N, N₂O-N and NH⁺₄ N and furthermore caused some inhibition of CO₂ evolution. The data from NH₄^?-addition experiments are consistent with a nitrogenase repression/ derepression threshold of 4 and 35μg NH⁺₄-N/g at 0.05 and 1% glucose concentrations, respectively. The data from NO^?₂- and NO^?₃-addition experiments suggest a combination of repression and toxicity effects in the presence of added NO^?₃ N.     

Development of a Soil N Test for Fertilizer Requirements for Corn Production in Quebec

Corn requires high nitrogen (N) fertilizer use, but no soil N test for fertilizer N requirement is yet available in Quebec. Objectives of this research were (1) to determine the effects of soil nitrate (NO₃ ^?)-N, soil ammonium (NH₄ ⁺)-N, and N fertilizer rates on corn yields and (2) to determine soil sampling times and depths most highly correlated with yields and fertilizer N response under Quebec conditions. Soil samples were taken from 0- to 30-cm and 30- to 60-cm depths at seeding and postseeding (when corn height reached 20 cm) to determine soil NH₄ ⁺ and NO₃ ^? in 44 continuous corn sites fertilized with four rates of N in two replications using a quick test (N-Trak) and a laboratory method. The N-Trak method overestimated soil NO₃ ^?-N in comparison with the laboratory method. Greater coefficients of determination were observed for soil NO₃ ^?-N analyses at postseeding compared with seeding.     

Nitrogen Availability from Compost in High Tunnel Tomato Production

High yield agricultural systems, such as high tunnel (HT) vegetable production, require a large supply of soil nutrients, especially nitrogen (N). Compost is a common amendment used by HT growers both to supply nutrients and to improve physical and biological soil properties. We examined commercially-available composts and their effects on soil N, plant N uptake, and tomato yield in HT cultivation. In addition, a laboratory study examined N and carbon (C) mineralization from the composts, and the usefulness of compost properties as predictors of compost N mineralization was assessed under field and laboratory conditions. The field study used a randomized complete block design with four replications to compare four compost treatments (all added at the rate of 300 kg total N ha^?1) with unamended soil and an inorganic N treatment (110 kg N ha^?1). Tomatoes were grown in Monmouth, Maine during the summers of 2013 and 2014. Compost NO₃^?-N and NH₄⁺-N application rates were significantly correlated with soil NO₃^?-N and NH₄⁺-N concentrations throughout the growing season. Marketable yield was positively correlated with compost total inorganic N and NO₃^?-N in both years, and with NH₄⁺-N in 2014. There were no significant differences among composts in percentage of organic N mineralized and no correlations were observed with any measured compost property. In the laboratory study, all compost-amended soils had relatively high rates of CO₂ release for the initial few days and then the rates declined. The compost-amended soils mineralized 4%–6% of the compost organic N. This study suggested compost inorganic N content controls N availability to plants in the first year after compost application.     

Nitrogen Source and Concentration Affect Growth and Performance of Bedding-Plant Impatiens

ABSTRACT

Impatiens (Impatiens wallerana Hook. f.) is the most important annual bedding plant in the United States, based on wholesale dollar volume. Production of high-quality plants requires optimization of the nutrition regimen during growth, especially the total nitrogen (N) concentration and the ratio of N sources. The objective was to determine the N concentration and the nitrate (NO₃ ^??N):ammonium (NH₄ ⁺?N) ratio of N source that optimized bedding-plant impatiens growth and flower development. Four N concentrations (3.5, 7, 10.5, and 14 mmol N · L^?1) were used in factorial combination with four ratios of NO₃ ^??N:NH₄ ⁺?N (4:0, 3:1, 1:1, and 1:3). Application of treatments was made for 30 d. Then for 10 d only deionized water was applied to reduce salt buildup. Substrate pH was lowest (4.9) with the NH₄ ⁺?N source and electrical conductivity (EC) highest, but never > 2.4 dS m^?1. Nitrogen concentration and N source displayed an interaction for most growth parameters. Shoot fresh and dry weights and flower bud number were maximized at the 1:3 NO₃ ^??N:NH₄ ⁺?N ratio with a N concentration of 10.5 mmol L^?1. However, plant diameter, leaf number, and leaf chlorophyll content responded quadratically to N form ratio, with the 1:1 ratio optimum at a concentration of 10.5 mmol N· L^?1.     

Regression equations to monitor inorganic nitrogen changes in fallow and wheat soils

Soil NH⁺₄-N and NO^?₃-N at five soil depths (0–10, 10–20, 20–40, 40–60, 60–80 cm) and some environmental variables were measured in a field trial under fallow and wheat for 9 months.Significant linear and quadratic relationships were obtained relating soil NH⁺₄-N, NO^?₃-N, NH⁺₄-N + NO^?₃-N, and NH⁺₄-N + NO^?₃ + total-N uptake by wheat to soil heat accumulation (temperature), moisture, and rainfall. R² values generally decreased with soil depth and the maximum value (37%) was obtained for NO^?₃-N changes in the topsoil (0–10 cm).Although a considerable amount of variation in the inorganic values recorded is not included in the equations, our results suggest that the development of the above relationships particularly of the quadratic type are useful to predict crop requirements for N by measurement of environmental variables in the field.     

Nitrogen transformation from three soil organic amendments in a sandy soil

Abstract

A sandy soil was amended with various rates (20 – 320 g air-dry weight basis of the amendments per kg of air-dry soil) of chicken manure (CM), sewage sludge (SS), and incinerated sewage sludge (ISS) and incubated for 100 days in a greenhouse at 15% (wt/wt) soil water content. At the beginning of incubation, NH₄-N concentrations varied from 50 – 280 mg kg^?1 in the CM amended soil with negligible amounts of NO₃-N. Subsequently, the concentration of NH₄-N decreased while that of NO₃-N increased rapidly. In soil amended with SS at 20 – 80 g kg^?1 rates, the NO₃-N concentration increased sharply during the first 20 days, followed by a slow rate of increase over the rest of the incubation period. However, at a 160 g kg^?1 SS rate, there were three distinct phases of NO₃-N release which lasted for160 days. In the ISS amended soil, the nitrification process was completed during the initial 30 days, and the concentrations of NH₄-N and NO₃-N were lower than those for the other treatments. The mineralized N across different rates accounted for 20 – 36%, 16 – 40%, and 26 – 50% of the total N applied as CM, SS, and ISS, respectively.     

减氮配施有机物质对土壤氮素淋失的调控作用

采用室内土柱模拟试验方法,研究不同氮肥施用下1m土体中氮素的分布和移动特征,揭示土壤氮素动态变化规律。结果表明:FN(农民习惯施无机氮用量)、RN(根据土壤养分供应和作物需求确定的推荐无机氮用量)显著增加了土壤上层NH_4^+-N和NO_3^--N向下层淋失。RN+HA(与推荐无机氮纯养分相等的锌腐酸尿素)和RN40%+OMB(推荐无机氮肥减60%基础上配施自制有机调理物质)可延长上层土壤NH_4^+-N峰值出现时间,降低下层NH_4^+-N。淋溶结束后,等氮量下增施HA较RN降低60cm以下NH_4^+-N残留29.7%～54.2%;降低60—80cm NO_3^--N累积17.4%。RN40%+OMB处理无机氮肥用量最小,0—20cm的NH_4^+-N最高,40—100cm稳定在2.0mg/kg左右;0—20,20—40cm土层NO_3^--N较RN+HA增加12.3%和2.0%,显著降低40cm以下NO_3^--N残留。RN+HA和RN40%+OMB较RN的土壤总无机氮残留分别减少7.4%和20.2%,降低表观淋失率。因此,RN40%+OMB可较好地抑制氮素下移,降低氮素淋失风险,为减少氮素淋失、明确合理氮肥施用方式提供科学依据。     

太湖地区氮肥用量对土壤供氮、水稻吸氮和地下水的影响

利用矿化培养与田间试验的方法,探讨了太湖地区长期施氮条件下,氮肥用量对土壤供氮、水稻吸氮与环境的影响。初步试验结果表明:多年施用氮肥能够提高土壤的供氮能力,并随施N量的增加而增加。增加氮肥用量能够提高稻株含氮量和吸氮量,但氮素向谷粒的转移率降低,试验区水稻氮肥用量以225～270kghm-2左右为佳。稻田田面水和渗漏液的N素养分动态变化显示,施N会造成田面水NH4 N和NO3-N含量的短暂升高,但不同施N量之间相差并不显著。稻田渗漏液中的氮以硝态氮为主,通常在淹水泡田后的7d内有一个NO3-N含量的峰值期,NO3-N含量在1.62～2.75mgL-1之间,约10d后降至0.5mgL-1以下;NH4 N含量变化有随施N量而增加的趋势,高峰期通常出现在分蘖末期,其余时间NH4 N含量在0.2mgL-1以下。     

A Single Law to Describe Atmospheric Nitrogen Bulk Deposition versus Rainfall Amount: Inputs at the Seine River Watershed Scale

Atmospheric nitrogen species (NH₄-N and (NO₃+NO₂)-N) were determined in weekly samples of atmospheric bulk deposition (dry plus wet), collected in France at seven sites over the course of a year. Rural, semi-rural and industrialised-urban sites were chosen in the Seine river watershed from the Seine estuary to upstream from Paris. Mean NH₄-N concentrations varied from 0.7 to 1.7 mg L^-1. Mean (NO₃+NO₂)-N concentrations were approximately 0.5 mg L^-1 for all sites except Paris (0.7 mg L^-1), which has a local impact on the fallout contamination from urban emissions. The relation between concentration and rainfall amount obeys a power law, in the form of y = ax ^b. When the nitrogen sources are very local, this relationship turns into a dilution law. Annual atmospheric nitrogen deposition (NH₄-N+(NO₃+NO₂)-N) was calculated and varied from 7.8 kg ha^-1 yr^-1 in the neighbourhood of a rural town to 17.3 kg ha^-1 yr^-1 in a very industrialised harbour. 58% of the atmospheric nitrogen deposition occurred during ‘spring + summer’ period. The total nitrogen atmospheric input to the Seine estuary, via direct deposition + indirect input via the watershed, was estimated to about 5% of the total nitrogen load within the Seine river basin.     

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.     

Nitrification Inhibitor,Fertilizer Rate,and Temperature Effects on Nitrous Oxide Emission and Nitrogen Transformation in Loamy Sand Soil

An incubation study investigated the effects of nitrification inhibitors (NIs), dicyandiamide (DCD), and neem oil on the nitrification process in loamy sand soil under different temperatures and fertilizer rates. Results showed that NIs decreased soil nitrification by slowing the conversion of soil ammonium (NH₄⁺)-nitrogen (N) and maintaining soil NH₄⁺-N and nitrate (NO₃^?)-N throughout the incubation time. DCD and neem oil decreased soil nitrous oxide (N₂O) emission by up to 30.9 and 18.8%, respectively. The effectiveness of DCD on reducing cumulative soil N₂O emission and retaining soil NH₄⁺-N was inconsistently greater than that of neem oil, but the NI rate was less obvious than temperature. Fertilizer rate had a stronger positive effect on soil nitrification than temperature, indicating that adding N into low-fertility soil had a greater influence on soil nitrification. DCD and neem oil would be a potential tool for slowing N fertilizer loss in a low-fertility soil under warm to hot climatic conditions.     

氮肥基追比对小麦产量、土壤水氮分布及利用的影响

为解决区域土壤质地类型针对性氮肥施用问题,在轻壤土和黏壤土上分别设置不施氮肥,氮肥基追比3∶7,4∶6,5∶5,6∶4和7∶3处理,研究小麦产量、水氮利用效率以及土壤含水量、贮水量、NH_4~+-N、NO_3~--N动态变化规律。结果表明:轻壤质土壤氮肥基追比4∶6的处理小麦产量、水分利用效率、氮肥生产效率最高分别为8 265.3 kg/hm~2,27.6 kg/(hm~2·mm),34.4 kg/kg。黏壤质土壤氮肥基追比5∶5的处理小麦产量、水分利用效率、氮肥生产效率最高分别为8 363.2 kg/hm~2,28.3 kg/(hm~2·mm),34.8 kg/kg。小麦不同生育期各土层含水量垂直分布变化较大,轻壤质土壤含水量在9.3%～26.2%,而黏壤质为9.7%～27.6%;小麦全生育期内土壤贮水量呈先升高后降低趋势,黏壤质土壤贮水量高于轻壤质。氮素追施量越多土壤表层NH_4~+-N与NO_3~--N含量越高,且随土层加深土壤NH_4~+-N与NO_3~--N含量降低,受降水影响轻壤质土壤NH_4~+-N与NO_3~--N更易于向土层深处淋溶,成熟期黏壤质各土层的NH_4~+-N和NO_3~--N含量均多于轻壤质。说明黏壤质土壤保水保氮肥能力强于轻壤质,氮肥基追比可以适当增加。