The behaviour of Nitrogen fertilizers in neutral and acid loess soils I. Transport and transformations of nitrogen

A study to investigate the transport and the transformation of two N¹⁵-tagged N-fertilizers (Ca(NO₃₎₂ and (NH₄₎₂SO₄) was carried out in the laboratory at 4° and 23°C. Undisturbed soil columns from the upper 30 cm of neutral agricultural and acid forest loess soils were used. An unsaturated steady state water flow in the columns was established and maintained by a darcian flow of 5mm of water/day. The effluent collected from each column after two days, was analysed for NO₃- and NH₄+. The data collected were used to obtain the Breakthrough Curves (BTCs). The BTCs after NO_3- fertilizers from agricultural soil approached the ideal symmetrical curves from non-reacting solutes. While those from acid forest soil were somewhat flat and ended with pronounced tails. -Transformation of the applied NH_4- fertilizer to NO_3-N was much higher in agricultural soil than in acid forest soil. Even at lower temperature, nitrification in agricultural soil was active though at a reduced rate while in forest soil, nitrification rate was extremely low and appeared to be independent of temperature.     

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.     

Amount and speciation of N leached from a sandy soil fertilized with urea,liquid digestate,struvite and NH4-enriched chabazite zeolite-tuff

The large use and the bad management of fertilizers that are applied to soil for improving crop production have dramatically impaired soil, water, and air quality. To meet the requirements to reduce nitrogen (N) losses and all the related negative impacts on the environment and food production, it is mandatory to substitute or at least partially substitute the use of inefficient and unsustainable fertilizers with more efficient alternatives. The aim of this paper was to address the amount and speciation of the N released by a sandy soil fertilized with “slow-release fertilizers” and traditional fertilizers (urea and liquid digestate) by means of a series of column leaching experiments. The slow-release alternatives were represented by NH₄-enriched zeolitic tuff and struvite, both obtained by recovering the N from liquid digestate. The treatments consisted of sandy soil fertilized with (i) urea (U) (ii) liquid digestate (LD), (iii) NH₄-enriched zeolitic tuff (N-CHA) and (iv) struvite (STRV). Eight different flushing events were performed over 38 days, leachates were collected and analysed for total Kjeldahl N, organic-N, NH₄⁺-N, NO₃⁻-N, NO₂⁻-N and pH. U and LD lost the majority of N within the first 2 flushing events as organic N and NH₄⁺-N, respectively. On the other hand, STRV and N-CHA lost less N over the whole course of the experiment and with more balanced speciation. The mass balance outlined that after the experiment, native soil N was mined in U and LD treatments while in N-CHA and STRV a fraction of N from the fertilizers was still present. The results showed a slow release of N which can be used more efficiently in agricultural applications, minimizing the N losses.     

不同肥料结构对红壤稻田氮素迁移的影响

不同肥料结构对红壤稻田淹水层、不同深度渗漏水、外排水和土壤剖面中氮素的含量、形态及其动态变化的影响研究结果表明 ,各处理淹水层、外排水和渗漏水中NH4+-N含量明显高于NO3--N。淹水层中N的含量 ,水稻生育前期以单施化肥的高 ,约相当于配施有机肥的 1.18～ 1.20倍 ,而水稻生育后期 ,后者为前者的 1.11～ 1.2 1倍。各处理外排水中N素的输出量均以苗期最高 ,单施化肥明显大于配施有机肥。土壤剖面中NH4+-N向下迁移比碱解N更为明显 ,且配施有机肥的远高于单施化肥的 ,而NO3--N则相反。不同深度渗漏水中NO3--N的比例 ,上层 (30cm)低于下层 (50cm) ,随水逸出的N量各处理渗漏水均小于外排水 ;随水输入的N量远低于随水输出的N量 ,且以单施化肥的N亏损最大。水稻未利用的N量也以单施化肥的最大 ,约为配施有机肥的 1.0 9倍。     

Influence of catchment characteristics,forestry activities and deposition on nitrogen export from small forested catchments

The ability to predict nitrogen export from forested catchments is essential in order to evaluate the effects of anthropogenic activities on the trophic status of lakes and sea areas, and to extrapolate the results to catchments from which no measurements are available. Data from 20 forested catchments (0.3–42 km²) in Finland and Sweden during the 10-year period 1979–88 were used to develop empirical multivariate regression models of average NO₃-N, NH₄-N and organic N export fluxes as a function of geomorphological, meteorological, hydrological, deposition and forest management variables. A combination of high inorganic N deposition or air temperature and a low extent of organic soils was related to (R² = 0.64) high losses of NO₃-N. A strong correlation between N deposition and air temperature makes it difficult to distinguish the effects of one variable from the other. Retention of deposited nitrogen is still high in most of the catchments. High losses of NH₄-N had the strongest correlation with forestry activities and stream density. A combination of drainage percentage and temperature was related to (R² = 0.53) losses of NH₄-N. The most important factors explaining spatial variability of organic N losses were clearly forestry activities. A combination of high percentage of drainage and clear-cutting was related to (R² = 0.81) high organic N losses. However, within the catchments, large-scale forest management practices were needed before any clear effect on spatial variability was detected. All the equations obtained were influenced by the choice of a limited number of catchments. No causal relationships between losses and the explaining variables can be inferred from this type of study.     

Evaluation of Biochar Effects on Nitrogen Retention and Leaching in Multi-Layered Soil Columns

Biochar can play a key role in nutrient cycling, potentially affecting nitrogen retention when applied to soils. In this project, laboratory experiments were conducted to investigate the adsorption properties of bamboo charcoal (BC) and the influence of BC on nitrogen retention at different soil depths using multi-layered soil columns. Results showed that BC could adsorb ammonium ion predominantly by cation exchange. Ammonium nitrogen (NH₄ ⁺-N) concentrations in the leachate of the soil columns showed significant differences at different depths after ammonium chloride application to the columns depending on whether BC had been added. Addition of 0.5% BC to the surface soil layer retarded the downward transport of NH₄ ⁺-N in the 70-day experiment, as indicated by measurements made during the first 7 days at 10 cm, and later, in the experimental period at 20 cm. In addition, application of BC reduced overall cumulative losses of NH₄ ⁺-N via leaching at 20 cm by 15.2%. Data appeared to suggest that BC could be used as a potential nutrient-retaining additive in order to increase the utilization efficiency of chemical fertilizers. Nonetheless, the effect of BC addition on controlling soil nitrogen losses through leaching needs to be further assessed before large-scale applications to agricultural fields are implemented.     

水分状况与供氮水平对土壤可溶性氮素形态变化的影响

采用通气培养试验,研究比较了两种水稻土在不同水分和供氮水平下的矿质氮(TMN)和可溶性有机氮(SON)的变化特征。结果表明,加氮处理及淹水培养均显著提高青紫泥的NH4+-N含量;除加氮处理淹水培养第7 d外,潮土NH4+-N含量并未因加氮处理或淹水培养而明显升高。无论加氮与否,控水处理显著提高两种土壤的NO3--N含量,其中潮土始见于培养第7 d,青紫泥则始于培养后21 d;加氮处理可显著提高淹水培养潮土NO3--N含量,却未能提高淹水培养青紫泥NO3--N含量。两种土壤的SON含量从开始培养即逐步升高,至培养21～35 d达高峰期,随后急剧下降并回落至基础土样的水平;SON含量高峰期,潮土SON/TSN最高达80%以上,青紫泥也达60%。综上所述,潮土不仅在控水条件下具有很强硝化作用,在淹水条件下的硝化作用也不容忽视,因此氮肥在潮土中以硝态氮的形式流失的风险比青紫泥更值得关注;在SON含量高峰期,两种土壤的可溶性有机氮的流失风险也应予以重视。     

Soil N transformation mechanisms can effectively conserve N in soil under saturated conditions compared to unsaturated conditions in subtropical China

The connection between moisture and nitrogen (N) transformation in soils is key to understanding N losses, particularly nitrate (NO₃^?) losses, and also provides a theoretical framework for appropriate water management in agricultural systems. Thus, we designed this study to provide a process-based background for management decision. We collected soil samples from the long-term field experiment in subtropical China, which was designed to examine tobacco and rice rotations under a subtropical monsoon climate. The field experiment was established in 2008 with four treatments: (1) no fertilization as control; (2) N, phosphorus (P), and potassium (K) fertilizers applied at recommended rates; (3) N fertilizers applied at rates 50% higher than the recommended amounts and P and K fertilizers applied at recommended rates; and (4) N, P, and K fertilizers applied at recommended rates with straw incorporated (NPKS). Soil samples were collected during the unsaturated tobacco-cropping season and saturated rice-cropping season and were incubated at 60% water holding capacity and under saturated conditions, respectively. Two ¹⁵N tracing treatments (¹⁵NH₄NO₃ and NH₄¹⁵NO₃) and a numerical modeling method were used to quantify N transformations and gross N dynamics. Autotrophic nitrification was stimulated by N fertilizer both under unsaturated and saturated conditions. The rate of NO₃^? consumption (via immobilization and denitrification) increased under the NPKS treatment under saturated conditions. Secondly, the rates of processes associated with ammonium (NH₄⁺) cycling, including mineralization of organic N, NH₄⁺ immobilization, and dissimilatory NO₃^? reduction to NH₄⁺, were all increased under saturated conditions relative to unsaturated conditions, except for autotrophic nitrification. Consequently, NO₃^?-N and NH₄⁺-N concentrations were significantly lower under saturated conditions relative to unsaturated conditions, which resulted in reduced risks of N losses via runoff or leaching. Our results suggest that under saturated conditions, there is a soil N conservation mechanism which alleviates the potential risk of N losses by runoff or leaching.     

Short-term effects of ammonium nitrogen in upland pasture soil affected or not affected by cattle

The short-term effects of excessive NH₄⁺-N on selected characteristics of soil unaffected (low annual N inputs) and affected (high annual N inputs) by cattle were investigated under laboratory conditions. The major hypothesis tested was that above a theoretical upper limit of NH₄⁺ concentration, an excess of NH₄⁺-N does not further increase NO₃⁻ formation rate in the soil, but only supports accumulation of NO₂⁻-N and gaseous losses of N as N₂O. Soils were amended with 10 to 500 μg NH₄⁺-N g⁻¹ soil. In both soils, addition of NH₄⁺-N increased production of NO₃⁻-N until some limit. This limit was higher in cattle-affected soil than in unaffected soil. Production of N₂O increased in the whole range of amendments in both soils. At the highest level of NH₄⁺-N addition, NO₂⁻-N accumulated in cattle-affected soil while NO₃⁻-N production decreased in cattle-unaffected soil. Despite being statistically significant, observed effects of high NH₄⁺-N addition were relatively weak. Uptake of mineral N, stimulated by glucose amendment, decreased the mineral N content in both soils, but it also greatly increased production of N₂O.     

控释氮肥养分控释效果及合理施用研究

试验采用{3,3}单形重心设计方法,研究了普通尿素和2种包膜尿素D90、D60配比对土壤NH4+-N、NO3--N及矿质态氮(Nmin)含量的影响。结果表明,供试的7种包膜肥料初期溶出率均12.0%,微分溶出率在0.26%～2.49%之间。各处理土壤NH4+-N含量均随时间逐渐降低,而NO3--N和Nmin含量随时间逐渐增加。整个培养期内单独施用尿素处理,土壤NH4+-N、NO3--N及Nmin含量最高;2种控释肥单施或其配比施用土壤NH4+-N、NO3--N及Nmin含量最低;尿素与控释肥配合施用,土壤NH4+-N、NO3--N及Nmin含量居中。不同时期内土壤NH4+-N的来源不同,0～20d内,尿素对土壤NH4-N含量贡献最大;30～50d内,土壤NH4+-N主要来自D60;整个培养期内尿素对土壤NO3--N和Nmin的贡献均最大。肥料配比中随着尿素比例的减少,土壤NH4+-N、NO3--N及Nmin均逐渐减少。研究结果初步验证了混料设计在肥料配比研究中的可行性。     

A nitrogen dynamic hydroponic culture on performance and quality of water spinach (Ipomoea aquatica)

Abstract

In view of the unreasonable application of chemical fertilizers in agriculture and the groundwater pollution caused by nitrogen (N) leaching, a nitrogen dynamic hydroponic culture was used to simulate the dynamics variation of ammonium nitrogen (NH₄-N) and nitrate nitrogen (NO₃-N) in the leaching loss soil. Solutions with different ratio of NO₃-N and NH₄-N (100:0, 70:30, 50:50, 30:70 and 0:100) were prepared as well as the same solutions that not containing NO₃-N .Water spinach was chosen to culture in the two solutions that differ from NO₃-N every two (E2) or five days (E5) to observe the growth, quality and nutrient solution uptake. In terms of the growth, uptake of N source, N use efficiency and the chemical indicators, plants grown in the balanced solution all showed the best results. The nitrogen dynamic hydroponic culture showed some differences between E2 and E5 in some aspects. Under the same N source level, plants in E2 showed a better growth and higher NO₃-N uptake than E5. On the other hand, the uptake of NH₄-N seemed to be affected significantly by the interchanged frequency, which showed the same variations of glutamine synthetase activity. The activity of nitrate reductase and glutamine synthetase showed the coexist of NO₃-N and NH₄-N could play synergistic effect. It is not recommended to supplement NO₃-N frequently in the case of N leaching loss, which has little impact on the growth and may lead to the hard taste and groundwater pollution.     

Simulation of soil freezing-thawing cycles under typical winter conditions: implications for nitrogen mineralization

Purpose

Seasonal freezing-thawing cycles (FTCs) are common phenomena in middle- and high-latitude regions that may have a strong effect on soil nitrogen (N) mineralization. As yet, little information is available about N mineralization of cultivated soils affected by FTCs, especially during non-growing seasons. It is proposed that N transformation of boreal farmland soil should be well responsive to FTCs because their microbial community and physiochemical characteristics are easily influenced by human agricultural activities. To examine this hypothesis, laboratory simulation experiments were carried out to investigate the effects of different amplitudes, frequencies, and moisture regimes of FCTs on soil N mineralization dynamics, to provide a better understanding of the mechanisms influencing the effect of FTCs on soil N availability during the non-growing season.

Materials and methods

In a laboratory simulation study, cultivated black soil (BL) and brown soil (BR) (Haplic Phaeozems and Haplic Luvisols, respectively; World Reference Base for Soil Resources 1988) were collected from two provincial experimental stations to assess the dynamics of N mineralization under four FTC factors (five levels for freezing temperature, two levels for thawing temperature, five levels for freezing-thawing frequency, and three levels for soil moisture regime).

Results and discussion

There were marked variations in inorganic N pools, microbial biomass N (MBN), and net N mineralization rate (NNMR) for both soils during the FTCs. In both soils, ammonium N (NH₄-N) and nitrate N (NO₃-N) concentrations, as well as NNMR, significantly increased with the decrease in freezing temperature, but the opposite was observed for MBN. However, fluctuating thawing temperature had no significant influence on the available N forms measured. As FTCs’ frequency increased, the NH₄-N, NO₃-N concentrations, and NNMR substantially decreased in both soils, while the MBN concentration initially increased and then declined, reaching the peak at the sixth FTC. The available N fractions in both soils had different response patterns as soil water content rose, showing a considerable increase of NH₄-N, a distinct decrease of NO₃-N, a steady increase for NNMR, and an initial increase followed by a decreasing trend for MBN.

Conclusions

This study has demonstrated that FTCs during the non-growing season in temperate regions can accelerate N mineralization via increases in freezing-thawing amplitude and freezing-thawing duration. Therefore, there is a potential risk of N losses over the early spring thawing period.

     

小麦苗期施入氮肥在土壤不同氮库的分配和去向

应用盆栽试验和15N标记技术研究了小麦苗期施入N肥后土壤不同N库的动态。结果表明 ,施肥后 28d ,作物所吸收的土壤N占总吸N量的 58.1% ,吸收的肥料N占 41.9%。作物对肥料N的利用率达到 55.3% ,N肥在土壤中的残留率为 24.3% ,损失率为 20.4%。施肥后短期以NH4+-4 N存在的肥料N占施N量的 50.5% ,随着硝化作用的进行和作物的吸收 ,土壤中的NH4+-N显著下降。NO3--N在第 7d达到高峰 ,表现为先升高后降低的趋势 ,说明施肥后在 7d以前有强烈的硝化作用发生。施肥后 2d ,以固定态铵存在的肥料N占 33.7% ,至 28d ,仅占施入N量的 2.4% ,说明前期固定的铵在作物生长后期又重新释放出来供作物吸收。在施肥后第 7d ,肥料N以微生物N存在的量占施肥量的 15.2% ;至 28d来自肥料N的微生物N也几乎被耗竭 ,仅占施N量的 2.4%。随作物生长 ,肥料N在各个土壤N库中的数量均显著下降。在其它N库几乎被耗竭的情况下 ,至施肥后 28d主要以有机N的形式残留。在不种作物的条件下 ,土壤N素的矿化量很低 ,作物的吸收作用导致土壤有机N库不断矿化 ,施入N肥后 ,土壤N素的矿化量增加 ,表现为明显的正激发效应     

Isotopic evaluation of the role of arbuscular mycorrhizae in the nitrogen preference in Chinese fir seedlings

Chinese fir seedlings grow well in shrubland (including deciduous forest) soils without or less fertilizer application, but they sometimes harbor disease and show symptoms of nitrogen deficiency in ploughed (including several rotation of Chinese fir plantation) soils, where agricultural practice and clear-felling reduce the abundance and diversity of mycorrhizal fungi, and lead to destruction of mycorrhizae. Based on measurements of foliar δ¹⁵N or foliar δ¹⁵N_fol-soil in seedlings collected from 33 nurseries, we compared the effect of an AM-mediated process on nitrogen resource use between shrubland and ploughed soils. In mycorrhizal seedlings growing in shrubland soils, both foliar δ¹⁵N and foliar δ¹⁵N (fol-soil) were significantly higher than those in ploughed soils, likely because of enhanced high δ¹⁵N/NO₃^? absorption through AM-mediated pathways. Those results showed that foliar δ¹⁵N typically reflected the isotopic signature of the source pools of N. We suggest that the dominant N form taken up by fir seedlings growing in ploughed soils was NH₄⁺-N rather than NO₃^?-N, where colonized root epidermis play an important role in exploiting soil N resource. However, the N form taken up by fir seedling growing in shrubland soils was primarily NO₃^?-N compared to NH₄⁺-N, which is attributed to the high efficiency in an AM-mediated process rather than the dominance of N species in the different habitats. It is conceivable that combined colonized root epidermis with AM-mediated process may be more important than root epidermis alone in exploiting different forms of N in nursery soils. Therefore, in low N and acidic ecosystems, species other than the dominant N-NH₄⁺, should be considered to satisfy the N demand for Chinese fir survival and growth, while the efficiency of an AM-mediated process should be determined by soil abiotic conditions.     

Transformations of nitrogen fertilizers in soil

The effects of ¹⁵N-labelled urea, (NH₄)₂SO₄ and KNO₃ on immobilization, mineralization, nitrification and ammonium fixation were examined under aerobic conditions in an acid tropical soil (pH 4.0) and in a neutral temperate soil (pH 6.8). Urea, (NH₄)₂SO₄ and KNO₃ slightly increased net mineralization of soil organic nitrogen in both soils. There was also an apparent Added Nitrogen Interaction (ANI) i.e. added labelled NH₄-N stood proxy for unlabelled NH₄-N that would otherwise have been immobilized. So far as immobilization and nitrification were concerned, urea and (NH₄)₂SO₄ behaved very similarly in each soil. Immobilization of NO₃-N was negligible in both soils. Some of the added labelled NH₄-N was rapidly fixed, more by the temperate soil than by the tropical soil. This labelled fixed NH₄-N decreased during incubation, in contrast to labelled organic N, which did not decline.     

林分类型和氮添加对亚热带森林土壤氧化亚氮排放的影响

为揭示亚热带森林土壤N₂O排放对林分类型和氮添加的响应特征,选取位于福建省三明市的中亚热带米槠次生林、杉木人工林和马尾松人工林土壤为研究对象,分别设置无氮添加(N0 mg/kg)、低氮添加(N10 mg/kg)、中氮添加(N25 mg/kg)和高氮添加(N50 mg/kg)4个氮添加水平,进行微宇宙培养试验,测定土壤N₂O排放。结果表明：与无氮添加处理相比,氮添加整体上降低3种林分土壤pH,增加土壤NH₄⁺-N和NO₃^--N含量。无氮添加处理中杉木人工林和马尾松人工林土壤N₂O累积排放量分别为9.67和9.62 mg/kg,显著高于米槠次生林土壤N₂O累积排放量6.81 mg/kg。低氮添加处理中杉木人工林和马尾松人工林土壤N₂O累积排放量显著高于米槠次生林。但在中氮和高氮添加处理中,3种林分土壤N₂O累积排放量均无显著性差异。不同氮添加处理均促进3种林分土壤N     

Contrasting response of two forest soils to nitrogen input: rapidly altered NO and N2O emissions and nirK abundance

Denitrification represents one of the main microbial processes producing the primary and secondary greenhouse gases nitrous oxide (N₂O) and nitric oxide (NO) in soils. It is well established that abiotic factors like the soil water content and the availability of nitrogen (N) are key parameters determining the activity of denitrifiers in soils. However, soils differing regarding their characteristics such as the content of C_org, the soil texture or the pH value may respond in specific manners to equivalent changes in soil moisture and N input. Thus, short-term incubation experiments were performed to test and compare the capacity of two contrasting Austrian forest soils to respond to mineral N application at increased soil water contents. Soils from the pristine Rothwald forest (rich in C_org) and the more acidic Schottenwald forest (poor in C_org) were amended with either NH ₄ ⁺ -N or NO ₃ ^? -N and were incubated at 40% and 70% water-filled pore space for 4 days. Changes in mineral N pools, nitrite reductase activity and NO and N₂O emission rates were measured, and the abundance and structural community composition of the functional group involved in nitrite reduction were analysed via quantitative real-time polymerase chain reaction and terminal restriction fragment length polymorphism analysis of the nirK gene. Rapid and distinct activity responses to increased soil moisture and altered mineral nitrogen availability were observed in two contrasting forest soils. In both soils, nitrogen oxide emission rates were stimulated by N inputs and, depending on the soil moisture status, either NO or N₂O emission was prevailing. However, different N cycling processes appeared to predominate in either soil under equivalent treatment. Nitrogen oxide emissions peaked following NO ₃ ^? application in Schottenwald soils but were the highest after NH ₄ ⁺ application in Rothwald soils. Denitrifying (nirK) communities differed significantly in Rothwald and Schottenwald soils; however, changes in the community structure were marginal during the short-term incubation. Abundances of nirK genes remained unaffected by N application in either soil. The soil water content affected nirK gene abundances only in Rothwald soil, indicating a distinct reaction of nitrite reducing communities in the two soils.     

Impact of Organic Amendments on Groundwater Nitrogen Concentrations for Sandy and Calcareous Soils

Experiments were conducted on calcareous and sandy soils to investigate the effects of organic amendments for vegetable production on groundwater nitrogen (N) concentration in south Florida. The treatments consisted of applying yard and food residuals compost, biosolids compost, a cocompost of the municipal solid waste and biosolids, and inorganic fertilizer. Nitrate nitrogen (NO₃-N), ammonium nitrogen (NH₄-N), and total N concentrations were collected for a period of two years for both soils. Statistical analysis results revealed that for the three species tested, there were no significant differences among treatments. NO₃-N concentrations for all treatments remained less than the maximum contamination level (10 mg/L). NO₃-N transport to groundwater was higher in calcareous soil (mean=5.3 mg/L) than in sandy soil (mean=0.6 mg/L). NH₄-N concentrations ranged from 0 to 13.6 mg/L throughout the experiment. Calcareous soil had lower NH₄-N concentrations (mean=0.1 mg/L) than sandy soils (mean=0.7 mg/L). Total N ranged from 0.4 to 21.7 mg/L for all treatments for both soils reflecting high adsorption of dissolved organic N in both soils. Overall, results indicated that all the compost treatments were comparable to inorganic fertilizer with regard to N leaching and N concentrations in the groundwater while producing similar or higher yields.     

冬小麦-夏玉米轮作体系中不同施氮水平对玉米生长及其根际土壤氮的影响

在河北衡水潮土上进行田间试验,以当地习惯高氮用量(小麦季施N 300 kg/hm2,玉米季施N 240 kg/hm2)为对照,研究冬小麦-夏玉米轮作体系中减少氮肥用量对玉米季植株生长、氮素吸收及根际土壤中无机氮与微生物量氮的影响。结果表明,两季作物氮肥施用量减少25%和40%,对玉米产量、生物量及植株体内氮累积量未产生明显影响,氮肥利用率提高。不同氮肥施用量对根际和非根际土壤铵态氮含量的影响不显著;减少氮肥施用量,对玉米根际土壤硝态氮含量也没有明显影响。在玉米苗期、抽雄期和成熟期,习惯高施氮量处理的非根际土壤硝态氮含量较高,其中抽雄期,非根际土壤硝态氮含量较氮肥减施40%用量处理高出近一倍,但非根际土壤微生物量氮水平含量明显降低。氮肥减施未影响根际土壤微生物量碳、氮含量,反而增加了非根际土壤微生物量碳、氮水平。在高肥力的潮土上,冬小麦/夏玉米轮作体系中适当减施氮肥并未影响玉米根际土壤氮素水平,可保证玉米稳产,实现减氮增效。     

Effects of substituting chemical fertilizers with manure on rice yield and soil labile nitrogen in paddy fields of China: A meta-analysis

Substituting chemical fertilizers with manure is an important method for efficient nutrient management in rice cropping systems of China.Labile nitrogen(N) is the most active component of the soil N pool and plays an essential role in soil fertility.However,the effects of manure substitution on soil labile N in rice cropping systems and their relationships with soil properties,fertilization practices,and climatic conditions remain unclear and should be systematically quantified.Here,we investiga...