Water and nutrient dynamics of a paddy soil of Bangladesh

The objectives of the study were the changes in water tension, redox potential, and the pH value of a silty Eutric Gleysol from young river sediments near Mymensingh, the nutrient concentration of soil solution, as well as the supply of nutrients by rain, irrigation and fertilizing, and the uptake of nutrients by rice during the year. In the case of nitrogen, a moderate loss was observed, caused by the leaching of NH₄, and significant losses due to volatilisation and denitrification. Fertilized P was enriched in the soil. The leaching of Ca, K, Mg, Na, Cu, Fe, Mn, and Zn was clearly higher than the addition by rain, irrigation and fertilization. It is concluded, that the loss of nutrients was caused by weathering.     

宁夏引黄灌区稻田氮素浓度变化与迁移特征

过量施氮与不合理灌水是农田面源污染加剧的主要原因。为了寻求较优的水氮管理模式以促进农业生产和减少农田退水对黄河水体的污染, 在宁夏引黄灌区典型稻田中开展了不同水氮条件下稻田氮素迁移转化规律研究。结果表明: 不同水氮条件下稻田田面水NH₄⁺-N 与NO₃^--N 浓度伴随施肥出现明显峰值, NO₃^--N 峰值出现时间较NH₄⁺-N 晚, 且变化较平缓。3 次追肥时期和整个生育期田面水NH₄⁺-N 平均浓度与施氮量和灌水量都呈显著相关, 田面水NO₃^--N 平均浓度与施氮量呈显著正相关, 与灌水量相关性不显著。稻田30 cm与60 cm 深度的直渗水NH₄⁺-N 浓度受施肥影响较大, 与田面水NH₄⁺-N 浓度变化规律相似, 90 cm 处直渗水NH₄⁺-N 浓度峰值出现较为滞后, 且浓度较上层土体低, 120 cm 处直渗水NH₄⁺-N 浓度大体呈现持续上升趋势,整个生育期直渗水NH₄⁺-N 平均浓度与施氮量呈显著相关, 仅30 cm 处NH₄⁺-N 平均浓度与灌水量呈负相关, 其他土层深度不显著。30 cm 与60 cm 直渗水NO₃^--N 浓度在首次灌水后急剧下降, 在施肥后有较小幅度上升, 90 cm 与120 cm 直渗水NO₃^--N 浓度下降缓慢, 仅30 cm 处NO₃^--N 平均浓度与施肥量显著正相关。总的结果表明减少施肥或灌水均可达到减少农田氮素淋失的目的。     

Ammonium-nitrate dynamics in the critical zone during single irrigation events with untreated sewage effluents

Purpose

Previous studies in the Mezquital Valley evidenced that irrigation with untreated sewage effluent supplies two- to tenfold larger nitrogen doses to crops than common fertilizer recommendations. However, nitrate concentrations in the groundwater are only slightly above threshold concentrations for drinking water. To understand the N dynamics in this agroecosystem, we quantified nitrogen inputs, outputs, and transformations within the rooting zone and in the vadose zone down to the aquifer (i.e., in the critical zone).

Materials and methods

Single irrigation events were monitored in three different fields cropped with either annual rye grass (Lolium rigidum) or oats (Avena sativa L.) harvested for fodder. For each irrigation event, the total amount of water entering and leaving the field was quantified with a flowmeter. Soil pore water was collected with either microsuction cups or observation wells and groundwater was sampled at two wells. All water samples were analyzed for total nitrogen (Nt), ammonium nitrogen (NH₄ ⁺–N), nitrate nitrogen (NO₃ ^?–N), chloride (Cl^?1), and pH. Organic N was calculated as the difference between total N and inorganic N. The water tension and the soil water content were monitored before, during, and after the irrigation with tensiometers and TDR probes, respectively, installed at different depths and at three sites within each field. Batch experiments were conducted to assess the NH₄ ⁺ adsorption capacity of the soils.

Results and discussion

The irrigations added 537 to 727 kg ha^?1 N in form of organic N (40 %) and NH₄ ⁺–N (60 %) to the fields. Crops absorbed 65 % of the N and 31 to 66 kg NO₃ ^?–N ha^?1 leached out beyond the rooting zone (>40 to 130 cm). Batch experiments evidenced an ammonium adsorption capacity of 43 and 53 % of the input ammonium mass. Nitrification dominated over denitrification as the water infiltrated through the soil, evidenced by changes in nitrate concentrations and pH values in the soil pore water. The behavior of the total N/Cl ratio with depth indicated possible N losses due to NH₃ volatilization at the field surface, a temporal withdrawal of N from the soil solution due to NH₄ ⁺–N adsorption in the rooting zone, as well as probable denitrification losses in the vadose zone.

Conclusions

Although the studied agroecosystem muses the large N inputs relative efficiently, between 7 and 10 % of the added N with each irrigation leaches beyond the crop root zone as nitrate. This is triggered by overflow irrigation, since up to 8,699,000 L of water with N concentrations of up to 50 mg total N L^?1 infiltrate rapidly through macropores beyond the rooting zone. Additionally, ammonia volatilization and denitrification seem to be occurring. The latter could provide a self-cleaning potential to the system, if it reaches N₂ and needs further verification. Nevertheless, N inputs to the system should match crop uptake to avoid groundwater and atmospheric pollution.

     

不同植稻年限土壤剖面基本性质与水-氮分布的关系

在江汉平原典型农业区选定不同水稻种植年限(2、18、100a)的稻田,采用野外调查与室内分析相结合的方法,量化不同稻田土壤剖面基本性质和水–氮分布特征,以揭示内在原因,探讨适宜不同水稻种植年限稻田的水–氮管理方式,为提高稻田水–氮利用率和减少稻田面源污染提供科学依据。结果表明:对于不同水稻种植年限农田,土壤剖面基本性质差异明显。耕作层和犁底层厚度随水稻种植年限的延长而增加;土壤有机质在耕作层富集,且随水稻种植年限的延长含量增加;耕作层土壤容重随水稻种植年限的延长而减小,犁底层土壤容重则增大;受耕作和淋溶条件的影响,犁底层和心土层的黏粒含量随水稻种植年限的延长而增加;饱和导水率(Ks)随水稻种植年限的延长而降低,犁底层Ks差异较大,2、18、100a稻田犁底层Ks分别为37.02、8.45、3.11cm/d。土壤剖面基本性质的差异影响水–氮的剖面分布特征。土壤水分和硝态氮含量随水稻种植年限的延长而增加,2、18、100 a稻田土壤剖面(0～100 cm)平均含水量分别为0.39、0.46、0.54cm3/cm3,硝态氮含量分别为3.75、6.27、9.85mg/kg。铵态氮储量远低于硝态氮储量,且受水稻种植年限影响较小;2、18、100 a稻田土壤剖面铵态氮与硝态氮储量比值分别为0.61、0.39和0.30。在灌溉和施肥方式上,水稻种植年限短的稻田适合少量多次的管理方式以减少渗漏损失;而年限长的稻田可适当提高单次灌溉量以减少灌溉次数,进而减少劳力消耗。     

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.     

Effect of nitrogen fertilization and irrigation on soil microbial activities and population dynamics — a field study

In a field experiment, net nitrogen (N) mineralization and immobilization were studied in relation to: 1) population dynamics and activities of N-metabolizing soil microbial communities, 2) changes in substrate-induced respiration (SIR) and 3) potential urease acitvity. Nitrogen fertilization (80 kg NO₃-N ha^-1) without irrigation induced additional N mineralization up to 280 kg N ha^-1. Net N-mineralization was weakly correlated to cell numbers of ammonifying and NH₄⁺-oxidizing microorganisms. Potential urease activity, respiration activity, and substrate-induced respiration activity were not correlated with the amount of mineralized nitrogen. Irrigation significantly increased potential urease activity of the soil microflora. Substrate induced respiration activity and basal respiration activity of the soil microflora were highest in the unfertilized and non irrigated treatment. But greatest differences were detected between the two sampling dates. NO₂^--oxidizing and ammonifying microbial populations increased, while populations of NH₄⁺-oxidizing and denitrifying microorganisms decreased with time. The results of this study demonstrate the interaction of nitrogen fertilizer application and irrigation on population dynamics of N-transforming soil microorganisms and microbial activities under field conditions. Detailed microbiological investigations of this type improve our understanding of nitrogen transformations in soil and suggest possible reasons of nitrogen losses, so that N fertilizer can be used more effectively and N losses be reduced.     

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.     

Gaseous losses of fertilizer nitrogen from a citrus orchard in the red soil hilly region of Southeast China

The gaseous losses of fertilizer nitrogen (N) applied to agroecosystems are a major contributor to a host of environmental problems, inefficient production systems, and decreased N-use efficiency. These losses lead to the wastage of resources, increasing the greenhouse effect and harming human health. The red soil hilly region of Southeast China houses the biggest orchard area of the world, and nitrogen fertilizers are usually heavily applied to the orchard systems in China. Therefore, this study aimed to measure the gaseous losses of the fertilizer N by ammonia (NH₃) volatilization and denitrification losses using the venting method and acetylene inhibition method respectively, and to assess the potential environmental risk of NH₃ and nitrous oxide (N₂O) emission from this orchard system based on the recent orchard management practices. An experiment was conducted in an Ougan citrus (Citrus reticulata Blanco ‘Suavissima’) orchard in the red soil hilly region of Southeast China. Three fertilization treatments, including the control (no N fertilizer, CK), poultry manure (at a rate of 6.3 t/ha, OM), and conventional fertilization (OM 6.3 t/ha + chemical fertilizer 393 kg N/ha, CF), were used. In all treatments, the fertilizers were incorporated into the soil after application. The test results, which were continuously determined within one year, indicated that the NH₃ volatilization losses accounted for 4.5% of the OM nitrogen (OM-N) and 2.9% of the CF nitrogen (CF-N), whereas the denitrification N losses accounted for 2.1% of the OM-N and 2.9% of the CF-N. Overall, the total gaseous N losses (including NH₃ volatilization losses and denitrification N losses) were 5.8% in the CF treatment. A relatively higher N₂O flux, accounting for 1.8% of the CF-N, emitted from the CF treatment.     

Soil nitrogen and denitrification potential as affected by land use and stand age following agricultural abandonment in a headwater catchment

Changes in vegetation and soil properties because of agricultural abandonment may affect soil nitrogen (N) and associated processes. We investigated soil N (total N: TN, inorganic N: NH₄–N and NO₃–N) and denitrification potential in cropland, pine plantations and abandoned agricultural land along a secondary succession sequence (grassland→shrubland→secondary forest) in a headwater catchment in the Qinling Mountains, northwest China. The results show that the soil denitrification potential differed significantly among the five land‐use types with the highest potential in the secondary forest, followed by grassland, shrubland, cropland and plantations. The denitrification potential of the 20‐ to 40‐cm layer was significantly lower compared with the topsoil (0–20 cm) across all land‐use types. TN, soil organic matter (SOM) and NH₄–N increased significantly with stand age, whereas there was an opposite trend in soil pH. However, the denitrification potential did not relate to stand age in a linear manner. We conclude that changes in soil TN, SOM and pH during vegetation succession following agricultural abandonment are critical controls on the denitrification potential.     

春小麦调亏灌溉对土壤氮素养分的影响

本文对河西绿洲灌区春小麦调亏灌溉两年后的土壤碱解氮和全氮的变化进行了研究,并用配对样本t检验(双尾检验)对小麦收获时土壤氮素养分指标年际间的差异及其与全生育期调亏供水量间的关系进行了回归分析,旨在为该区春小麦调亏灌溉对土壤氮素养分的影响研究提供一些可靠的信息.结果发现,春小麦调亏灌溉对2003年和2004年两个试验年度0～20cm、20～40cm及O～40cm土层土壤氮素养分有显著影响;而小麦收获时土壤氮素养分指标配对样本t检验发现,2004年0～20cm土层土壤全氮、碱解氮,20～40cm土层全氮,0～40cm土层全氮显著高于2003年,然而20～40cm土层碱解氮、0～40cm土层碱解氮在2003年和2004年问差异不显著.0～40cm土层土壤全氮量与小麦全生育期供水量呈线性负相关,而碱解氮则与全生育期供水量呈线性正相关.     

A 15N tracing technique-based analysis of the fate of fertilizer N: a 4-year case study in eastern China

The fate of fertilizer N applied with different irrigation amounts in tobacco fields was quantitatively studied by applying ¹⁵N double-labelled NH₄NO₃ in lysimeters. The ¹⁵N (fertilizer N originating from the fertilizer applied in 2011) in tobacco plants, ¹⁵N in soils and ¹⁵N loss were observed continuously from 2011 to 2014. The results showed that 21.6% of ¹⁵N was utilized by tobacco plants, 72.1% remained in the 0–60 cm soil layer and 6.3% was lost from the soil–plant system after the first season’s harvest (2011) of flue-cured tobacco. During the four seasons from 2011 to 2014, cumulative utilization of ¹⁵N by tobacco plants was 34.3%, while 54.2% remained in the 0–60 cm soil layer, and 11.5% was lost via mechanisms such as leaching and volatilization. The fate of ¹⁵N in terms of accumulation in plants and soils or losses from the soil–plant system from 2012 to 2014 was greatly affected by the fertilizer and irrigation management strategies in 2011. The results of this investigation suggest that the major amount of fertilizer N applied during the first season remains available in the soil for utilization by tobacco plants after 4 years.     

生物炭改性黏土的渗水渗气特性及其函数关系

黏土中施加生物炭可改变土体的孔隙结构。生物炭掺量和干密度均会对土体的渗透系数产生影响,准确确定生物炭-黏土混合土的渗透系数对满足填埋场上覆层的功能需求就显得格外重要。采用自主研发设计的柔性壁水-气联合渗透测试装置,测定不同生物炭掺量和干密度的生物炭-黏土混合土的饱和渗透系数和渗气系数,得到生物炭掺量、干密度与渗气系数和渗水系数间的关系曲线。建立生物炭掺量和干密度双变化条件下的渗气渗水函数,并通过验证组验证该函数的适用性。研究结果表明：在干密度较小时,对比纯黏土的渗水率,添加5%、10%、15%和20%生物炭处理后的土样渗水系数k_w值分别为8.25×10^-17、8.89×10^-17、10.40×10^-17和18.25×10^-17 m²,掺20%生物炭土样的渗透率增加了将近一个数量级。渗气渗水函数基于易测定的渗气率作为自变量,同时又考虑了干密度和生物炭掺量的影响,能快速、准确地确定土样的渗水系数。结合验证组试验得出,利用该函数计算得到的渗水系数和试验实测值吻合程度较好,表明该函数具有一定的适用性。本研究结果可为快速、准确确定渗水系数,定量描述非饱和土孔隙中水气运动之间的相互影响提供理论支撑。     

自然降雨下玉米秸秆堆沤还田对滇中小流域坡耕地氮素流失的影响

为探究自然降雨下不同堆沤方式秸秆还田对小流域坡耕地径流泥沙及氮素流失的影响,以滇中二龙潭流域坡耕地为研究对象,设置9种不同玉米秸秆堆沤方式,分别为CK及8种处理,各处理包括2种秸秆还田量(0.75,1.5 kg/m^2)、2种秸秆粒度(1,5 cm)、2种秸秆堆沤方式(水或水与尿素堆沤),研究烤烟坡耕地产流产沙及氮素流失特征。结果表明:(1)在4场具有典型产流的降雨中,施用较高秸秆还田量(1.5 kg/m^2)和粗颗粒秸秆(5 cm),均可有效减少坡耕地产流产沙量(10.06%~38.60%和10.07%~38.60%);(2)施用较低秸秆还田量(0.75 kg/m^2)、粗颗粒秸秆(5 cm)及未添加尿素堆沤的秸秆径流TN、NO3--N浓度低于施用高秸秆还田量(1.5 kg/m^2)、细颗粒秸秆(1 cm)及添加尿素堆沤的处理(1.96%~32.79%和3.97%~40.89%);(3)各处理下NO3--N/TN、NH4+-N/TN、PN/TN分别为63.64%~86.18%,5.31%~13.86%和5.33%~25.80%,表明坡耕地地表径流氮素主要流失形式为NO3--N,溶解态氮是径流中的主要氮素污染物;(4)施用较低秸秆还田量(0.75 kg/m^2)、粗颗粒(5 cm)秸秆、未加尿素堆沤的秸秆,泥沙TN流失浓度降低(16.87%~48.15%);(5)施用较高秸秆还田量、粗颗粒秸秆及未添加尿素堆沤可有效降低滇中坡耕地氮素的流失风险(0.32%~35.05%和54.52%~77.23%)。TN径流和泥沙流失中,以径流输出为主,占TN流失量的50.09%~71.67%。为了减少该流域氮素流失量,可选择施用较高秸秆还田量(1.5 kg/m^2)和粗颗粒(5 cm)秸秆,并依据烤烟不同生长期的吸收情况和土壤养分情况等选择少量或不添加尿素堆沤进行秸秆还田。     

Dynamic changes of nitrogen and phosphorus losses in ephemeral runoff processes by typical storm events in Sichuan Basin, Southwest China

This study was carried out in the Xujiawan watershed in Sichuan Province, China. The area is characterized by easy weathering of bedrock (sedimentary sandstone and shale) and vulnerability to erosion due to coarse soil texture and weak soil structure. The objective of this study was to understand the dynamics of nitrogen (N) and phosphorus (P) losses during typical storm events. The results showed that runoff generation was sudden and ephemeral, giving rise to flash floods with sharp, narrow hydrographs and short time lags in this type of agricultural ecosystems. The time lag effect of runoff formation depended on soil conditions before storm events. Suspended solids (SS) concentration peaks occurred at the beginning of the storm flow and decreased as rainfall progressed. Meanwhile, SS losses increased at the beginning of runoff flow, then decreased due to flow volume change. Concentrations of NO₃⁻-N were four times higher than NH₄⁺-N in runoff. NO₃⁻-N concentrations first decreased as runoff volume increased until reaching relatively low concentrations, then increased again as runoff volume decreased. Both NH₄⁺-N and dissolved phosphorus (DP) in runoff remained at low concentrations with a small magnitude of variation. Suspended particulate nitrogen (SN) was the dominant N form. Losses of NO₃⁻-N were higher than NH₄⁺-N in the dissolved nitrogen (DN). Suspended particulate nitrogen losses were several times higher than DN in the early period of runoff formation, but the ratio of SN/DN decreased gradually as rainfall progressed, and by the end of the storm event the rate was lower than 1, indicating DN took the main form after the early physical flush. In the early period of storm events, suspended particulate phosphorus (SP)/DP was above 70 and decreased as rainfall progressed, but remained higher than 1, which showed that SP was the main form of P loss. The transport of N, and particularly P, was intimately linked to sediment in the runoff, indicating an obvious soil erosion-associated nutrient transport, especially in relation to P loss.     

太湖地区稻麦轮作条件下施用包膜尿素的氮素循环和损失

A field experiment was conducted to investigate the fate of ^15N-labeled urea and its residual effect under the winter wheat （Triticum aestivum L.） and summer maize （Zea mays L.） rotation system on the North China Plain. Compared to a conventional application rate of 360 kg N ha^-1 （N360）, a reduced rate of 120 kg N ha^-1 （N120） led to a significant increase （P 〈 0.05） in wheat yield and no significant differences were found for maize. However, in the 0-100 cm soil profile at harvest, compared with N360, N120 led to significant decreases （P 〈 0.05） of percent residual N and percent unaccounted-for N, which possibly reflected losses from the managed system. Of the residual fertilizer N in the soil profile, 25.6%-44.7% and 20.7%-38.2% for N120 and N360, respectively, were in the organic N pool, whereas 0.3%-3.0% and 11.2%-24.4%, correspondingly, were in the nitrate pool, indicating a higher potential for leaching loss associated with application at the conventional rate. Recovery of residual N in the soil profile by succeeding crops was less than 7.5% of the applied N. For N120, total soil N balance was negative; however, there was still considerable mineral N （NH4^＋-N and NO3^--N） in the soil profile after harvest. Therefore, N120 could be considered ngronomically acceptable in the short run, but for long-term sustainability, the N rate should be recommended based on a soil mineral N test and a plant tissue nitrate test to maintain the soil fertility.     

淹水稻田氮的损失

A field microplot experiment was conducted during the tillering stage of paddy rice to investigate nitrogen(N) Iosses from flooded rice fields following fertilizer application. After application of ammonium bicarbonate, most of nitrogen in the flood water was present as NH₄-N and its concentration varied widely with time. Concentrations of both NO₃-N and NO₂-N in the floodwater were low due to the weakened nitrification. Under flooded anaerobic reducing conditions, soil solution concentrations of NO₃-N and NH₄-N were nothigh, ranging from 0.6 mg L^-1 to 4.8 mg L^-1, and decreased with soil depth. However, the ground water wasstill contaminated with NO₃-N and NH₄-N. Rainfall simulation tests showed that the N losses via runoff inrice fields were closely related to the time intervals between fertilizer applications and rainfall events. Whena large rain fell for a short period after fertilizer application, the N losses via runoff could be large, which could have a considerable effect on surface water quality. Both irrigation and N fertilizer application must be controlled and managed with great care to minimize N losses via runoff from agricultural land.     

下层土壤反硝化作用的研究

在夏玉米生长期间 ,采用乙炔抑制 -原状土柱培养方法研究了北京褐土下层 (15～ 6 0cm)土壤的反硝化作用 ,并探讨影响该层土壤反硝化作用的主要因素。试验结果表明 ,施氮量越高 ,反硝化量越大。随着土壤层次的加深 ,反硝化量呈直线下降 ,但在亚表层土壤 (15～ 30cm)反硝化值仍保持了较高的量 ,约相当于表层的 10 .7%～ 33.5 % ;下层土壤 (15～ 6 0cm)的总反硝化量约相当于表层土壤的 14%～ 51%。加入碳源无论对表层土壤还是下层土壤 ,其反硝化损失氮量大大增加 ,尤其是对下层土壤增加的趋势更为明显。在计算夏玉米季土壤反硝化损失氮量时 ,如果忽略下层土壤的反硝化作用 ,肯定会低估其数值     

Considering Residual Soil Mineral Nitrogen in Corn Fertilizer Recommendations in an Irrigated Mediterranean Area

Management of nitrogen (N) fertilization for economic crop production in water-stressed areas relies heavily on irrigation. The objectives were to determine the depth distribution of mineral N (N_min) at pre-plant and post-harvest seasons and assess the residual mineral N pool as a potential source of plant-available N for irrigated corn (Zea mays L.) in southern Turkey. Pre-plant and post-harvest composite soil samples were collected randomly from farmer’s fields at 0–30, 30–60 and 60–90 cm depths, respectively, analyzed for nitrate (NO₃) and ammonium (NH₄) concentrations, and the N_min values were correlated with corn yields and N uptake. Results showed that substantial amounts of pre-plant (76 to 94 kg N_min/ha) and post-harvest (70–78 kg N_min/ha) N_min accumulation at different soil depths. However, the N_min did not correlate with crop yields and N uptake. Results suggested that residual N_min could be the ?basis for recommending N fertilization to support crop production.     

利用膜进样质谱法测定不同氮肥用量下反硝化氮素损失

利用膜进样质谱仪(MIMS)测定了太湖流域典型稻田不同氮肥施用梯度下,土壤反硝化氮素损失量,同时也对氨挥发通量进行了观测。根据两年的田间试验结果得到:在常规施氮处理(N300)下,每年平均有54.8 kg/hm~2 N通过反硝化损失,有约54.0 kg/hm~2 N通过氨挥发损失,分别占肥料施用量的18.3%和18.0%,两者损失量相当。通过反硝化和氨挥发损失的氮素量随着氮肥用量增加而增加,田面水的NH_4~+-N、NO_3~–-N、DOC和pH浓度影响稻田土壤反硝化速率。在保产增效施氮处理(N_270)下,氮肥施用量比常规减少10%,水稻产量增加了5.5%,而通过反硝化和氨挥发损失的氮素量分别下降了1.1%和3.1%,氮肥利用率提高了约5.5%。在增施氮肥处理(N375)下,因作物产量增加使得氮肥利用率比N300增加,但通过氨挥发和反硝化的氮素损失量也最大。因此,通过综合集约优化田间管理措施,降低氮肥用量,可实现增产增效的目的。     

Water management in various crop production systems related to soil tillage

Soil tillage, of different types and intensity and performed at different antecedent soil moisture conditions, is an important tool for agricultural water management. Tillage systems have important applications for increasing irrigation efficiency, enhancing the effectiveness of drainage systems, improving water quality, decreasing runoff losses and minimizing soil erosion, increasing runoff losses for water harvesting and supplemental irrigation, and decreasing percolation losses and creating aquatic environments for rice cultivation. The versatility and diversity of applications of tillage systems depend on the choice of tillage techniques. No-tillage methods with residue mulches are useful to conserve soil water. Chisel tillage and subsoiling methods along with ridge-tillage techniques are useful in increasing irrigation efficiency. No-tillage systems are useful in decreasing sediment density and transport of sediment laden pollutants in runoff, and puddling and wet tillage techniques or soil compaction are used in rice cultivation. Finally soil compaction and techniques to increase water repellence are useful for water harvesting for subsequent use in supplemental irrigation.