0 引言
【研究意义】氮肥在农田生态系统中的投入和支出平衡对农业可持续发展至关重要,而农民为了获得更高的作物产量,盲目的过量施用氮肥导致氮肥利用率低,同时造成了严重的环境污染,例如地表富营养化、地下水和蔬菜中硝态氮含量超标、温室气体排放量增加等问题[1]。在华北平原地区,冬小麦-夏玉米轮作是主要的轮作模式,冬小麦季氮的平均施用量已经达到369 kg·hm-2[2],远超过作物对氮的需求量。另外,作物前期生长对养分需求较小,在传统的施肥过程中,有一半的氮肥会作为基肥在作物前期施入土壤,造成浪费[3]。我国目前当季氮肥利用率低,仅为35%[4],平均每年大约有180 kg·hm-2的氮通过氨挥发、硝化与反硝化等途径损失在环境中[5],而累积在土壤中的氮主要以硝态氮的形式存在[6,7,8],非常容易因为降雨或者大量灌溉向深层土壤迁移,造成深层土壤硝态氮累积增加[2,9-10],进而造成氮淋溶威胁地下水安全[11]。氮素施用主要以尿素为主,尿素施入土壤后在脲酶的作用下会迅速水解并发生大量氮损失[12],在小麦-玉米轮作体系中,土壤中硝态氮在60—200 cm土层中已经出现明显的累积和迁移[13,14]。所以氮肥品种,施用数量以及施用时间是保证作物产量和提高氮肥利用效率的关键[4],其中,缓/控释肥用于大田主要粮食作物已经成为当前减量施氮,提高氮肥利用率并维持土壤氮素平衡的重要途径,也是未来农业可持续发展的重要途径。【前人研究进展】研究者主要从肥料品种本身上寻找解决问题的方法,根据包膜材料控制养分的释放速率和释放时间,将其分为缓释肥和控释肥[1,15]。其中,控释肥因为其释放养分的时间和速率满足了作物在整个生育期对养分的需求[16,17,18],还因为其一次性施肥的特点降低了传统基追分施增加的劳动成本,成为降低氮肥使用量而提高其利用率的主要途径之一。提高作物产量和氮肥利用率是选用控释肥的基本目标,最主要的目标是要降低氮在土壤中的残留和向深层土壤的迁移,减少氮肥对环境产生的风险。已经有研究表明,施用树脂包膜的尿素能够显著增加玉米、水稻等作物的产量,提高氮肥利用效率[6,19],而冬小麦这样长生育期的作物对控释肥养分的释放速率以及氮肥利用效率的要求也会更高[19,20,21]。【本研究切入点】之前的研究大多集中在控释肥对作物产量、品质的影响以及氮肥的回收利用率等方面,忽略了施用控释肥后土壤氮的累积和其迁移的情况。【拟解决的关键问题】本试验是在保证小麦、玉米稳产或者少量增产的前提下,在小麦-玉米轮作体系中施用减量氮肥的控释尿素,能减少氮肥损失,并降低土壤中硝态氮的累积和其向深层土壤的迁移,降低其对环境的污染风险,为绿色农业发展提供理论依据。1 材料与方法
1.1 基本概况
试验地位于山东省微山岛乡上庄村,经纬度为：34°39'34" N,117°14'46" E。该地区常年平均降水为697 mm。试验作物为冬小麦济麦22号,2014年10月6日播种,2015年6月20日收获,夏玉米为郑单958,2015年6月28日播种,10月4日收获。供试土壤为潮土,黏壤土。表层0—20 cm土层的基础理化性状：pH 7.3,有机质含量为20.75 g·kg-1,Olsen-P含量为6.86 mg·kg-1,有效钾含量为89.69 mg·kg-1,硝态氮含量为9.64 mg·kg-1,0—100 cm土层中硝态氮累积量为50 kg·hm-2。1.2 试验设计与田间管理
小麦施肥处理：CK（不施用氮肥的空白处理,0-90-60,每公顷N、P2O5、K2O纯养分含量）;CRF（144-90-60,控释肥处理,氮投入量为优化施肥处理的80%）;OPT（180-90-60,优化施肥处理）。玉米施肥处理：CK（0-60-60）;CRF（168-60-60）;OPT（210-60-60）。田间操作根据当地习惯,肥料包括普通尿素（N 46%）和树脂包膜尿素（N 42%,金正大）、重钙（P2O5 44%）、氯化钾（K2O 60%）。其中,普通尿素分基施和追施两次,施用量基,追肥各半,追施分别在小麦返青期和玉米拔节期进行开沟施用。磷钾肥和包膜控释肥一次性基施。每个处理设置3次重复,小区面积36 m2,各小区随机区组排列。小麦生育期内不进行人工灌溉,各处理其他管理措施均等同于大田生产。
1.3 田间收获与指标测定
于作物成熟期收获整株作物,按器官分开,105℃杀青30 min,60℃烘至恒重,称取干重。通过凯氏定氮法测定植株样品全氮。于小麦的返青期、拔节期、孕穗期和收获期以及玉米的苗期、拔节期、灌浆期和成熟期按照20 cm土层采集0—100 cm土壤剖面土,用环刀法测定不同土层土壤容重,鲜土用2 mol·L-1 KCl溶液（土水比1﹕5）浸提,并通过氮素连续流动分析仪（TRAACS 2000, Bran and Luebbe, Norderstedt, Germany）测定硝态氮和铵态氮。1.4 统计及分析方法
采用Excel、SigmaPlot进行数据处理和绘图,采用SPSS16.0（Duncan P<0.05）（SPSS Inc.,Chicago,IL,USA）进行显著方差分析。氮肥表观利用率（REN）=(U-U0)/F×100%
式中,U为施肥后作物收获时地上部的氮肥吸收量,U0为未施肥时作物收获时地上部的氮肥吸收量,F为氮肥的投入量。
氮肥表观损失（N loss）=Nmin,initial + Norganic + Nfer - Nmin, harvest - Nuptake
式中,Nmin, initial和 Nmin, harvest分别表示种植前和收获后0—100 cm土层无机氮含量;Norganic表示假定不施氮肥处理的氮素损失为零,并根据氮素平衡计算土壤氮的矿化量;Nfer表示氮肥的投入量;Nuptake表示地上部氮的吸收量[22]。
相对氮累积速率（RNAR）=(N2-N1)/[(T2-T1)N1]
式中,N1 和 N2分别表示在第一（T1）、第二次（T2）收获时土壤中的氮含量。
2 结果
2.1 不同施肥措施对氮肥吸收利用的影响
从表1可见,小麦季和玉米季的OPT和CRF处理的产量均显著高于对照处理,地上部总吸氮量也均显著高于对照处理,但是OPT和CRF之间没有显著差异（表1）。Table 1
表1
表1小麦/玉米产量和总吸氮量
Table 1The grain yield and total N uptake for wheat and maize
| 处理 Treatment | 产量Grain yield (t·hm-2) | 总吸氮量Total N uptake (kg·hm-2 ) | ||
|---|---|---|---|---|
| 小麦 Wheat | 玉米 Maize | 小麦 Wheat | 玉米 Maize | |
| CK | 4.97±0.14b | 5.79±0.20b | 113.70±11.54b | 89.2±5.95b |
| CRF | 7.58±0.35a | 8.31±0.46a | 178.75±12.87a | 148.79±8.35a |
| OPT | 7.87±0.71a | 7.57±0.38a | 209.22±19.84a | 142.53±6.74a |
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在小麦季,CRF和OPT处理的氮肥表观利用率没有显著差异,分别为45%和53%。而CRF处理0—100 cm土层的氮肥表观损失量较低,为46.94 kg·hm-2,显著低于 OPT处理（表2）。在玉米季,CRF的氮肥表观利用率略高于OPT,但处理之间没有显著差异。CRF处理0—100 cm土壤硝态氮出现盈余,为19.35 kg·hm-2,而此时OPT处理氮肥表观损失量为53.78 kg·hm-2,显著高于CRF（表2）。
Table 2
表2
表2小麦/玉米不同处理的氮肥表观利用率和0—100 cm土层氮肥表观损失量
Table 2The apparent N recovery efficiency and the apparent N loss in 0-100 cm soil layer of the different treatments for wheat and maize
| 处理 Treatment | 氮肥表观利用率 REN (%) | 0—100 cm氮肥表观损失量 Apparent N loss in 0-100 cm soil (kg·hm-2) | |
|---|---|---|---|
| 小麦 Wheat | CRF | 45.17±8.93a | 46.94±6.62b |
| OPT | 53.07±11.02a | 97.66±19.83a | |
| 玉米 Maize | CRF | 35.47±4.97A | -19.35±22.40A |
| OPT | 25.40±3.21A | 53.78±13.27B |
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2.2 不同生育时期土壤硝态氮累积变化
随着小麦生长,CRF处理的0—100 cm土层中硝态氮的含量一直和对照处理CK保持一致,在拔节期出现最低累积量14 kg·hm-2,而后随着小麦生长累积量逐渐升高,在收获期达到80 kg·hm-2;相反,OPT处理的0—100 cm土层中,硝态氮含量在小麦的孕穗期明显高于其他处理,达到峰值214 kg·hm-2,在收获时硝态氮含量下降为105 kg·hm-2（图1）。在玉米季,不同处理间0—100 cm土层中的CRF和CK硝态氮含量变化趋势一致,在整个生育期CRF处理的硝态氮含量平均高出CK 110 kg·hm-2,OPT处理在灌浆期达到峰值312 kg·hm-2;在玉米成熟收获时,CRF和OPT土壤硝态氮含量相同,均达到165 kg·hm-2（图2）。
显示原图|下载原图ZIP|生成PPT图1小麦季不同生育时期硝态氮在0—100 cm土层中的累积量
RS：青期;JS：拔节期;BS：孕穗期;HS：收获期。下同
-->Fig. 1The content of NO3--N in the 0-100 cm soil layer at the different growth stages for wheat
RS: Regreening stage; JS: Jointing stage; BS: Booting stage; HS: Harvest stage. The same as below
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显示原图|下载原图ZIP|生成PPT图2玉米季不同生育时期硝态氮在0—100 cm土层中的累积量
-->Fig. 2The content of NO3--N in the 0-100 cm soil layer at the different growth stages for maize
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2.3 硝态氮在土壤中的迁移速率
小麦季土壤中硝态氮的相对累积速率在不同土层中存在显著差异。施氮处理OPT和CRF的相对累积速率随着土层加深呈现出先升高后降低的规律,并在40—60 cm土层达到峰值,显著高于其他土层中硝态氮的相对累积速率。OPT在40—60 cm土层中每季达到93 kg·hm-2,是CRF处理的2倍多（图3）。小麦收获之后播种玉米,玉米季土壤中硝态氮累积速率的变化和小麦季完全不同。在0—20 cm表层土壤中,硝态氮的相对累积速率虽然显著高于其他土层,但是CRF的相对累积速率也仅为每季2 kg·hm-2,OPT和CK为1 kg·hm-2,在20—40 cm以及40—60 cm,除了OPT土层中出现较小的累积,其他处理在20—100 cm土层中均出现了小幅度的负增长现象（图4）。
显示原图|下载原图ZIP|生成PPT图3小麦季不同处理硝态氮在不同土层中的相对累积速率
不同大写字母表示不同土层间平均值差异显著（P<0.05）。下同
-->Fig. 3The relative accumulated rates of NO3--N in the soil layers of the different treatments for wheat
Different capital letter indicate significant difference among the soil layers for mean value (P<0.05). The same as below
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显示原图|下载原图ZIP|生成PPT图4玉米季不同处理硝态氮在不同土层中的相对累积速率
-->Fig. 4The relative accumulated rates of NO3--N in the soil layers of the different treatments for maize
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3 讨论
虽然CRF的施氮量仅为OPT的80%,但是并没有降低小麦、玉米的产量和地上部总氮吸收量（表1）,说明在优化施肥量的基础上减施20%的氮肥能够保证作物不减产,符合目前华北平原小麦、玉米适宜的理论施氮量[23,24]。氮肥利用率随施氮量增加而降低,损失率相应增加[22,25],本试验条件下,OPT的施氮量虽然是优化施氮量,但是因为施用的是尿素,在土壤中极易造成损失进而污染环境。小麦季中OPT处理氮肥的表观利用率虽然较高,但是氮肥的损失量也高（表2）,相反,包膜控释肥料由于释放养分缓慢,在整个生育期土壤中的硝态氮变化相对比较平缓,在整个生育期根层土壤硝态氮量较稳定[19,26]。王文岩[27]、栗丽等[28]研究也证实控释肥能够在减施25%氮肥的条件下保证产量并提高氮肥利用率,同时也能维持土壤氮素平衡。从化肥氮投入量和作物地上部氮输出量发现,在本试验中小麦/玉米一年两熟的轮作体系中,CRF的氮总输入量为312 kg·hm-2,地上部总吸氮量为326 kg·hm-2,而OPT的总输入为390 kg·hm-2,输出为351 kg·hm-2,根据CHEN等[29,30]建立的高产条件下土壤-作物系统综合管理技术,本试验中OPT处理的施氮量虽然在理论推荐施氮量的范围内,但仍然存在较高的氮累积或者损失的风险,CRF的施氮量相对更为合理。另外,由于OPT追施尿素,小麦和玉米生长后期0—100 cm土层中有明显的硝态氮累积,在作物收获后,硝态氮却又明显回落,从CRF和OPT处理的表观损失量（表2）可以看出,CRF减少的20%的氮实际也是减少了氮的损失量。硝态氮在土壤剖面中的累积量和淋容量会随着施氮量的增加而增加[31,32,33],淋溶量不仅受水分的影响,也和作物根系生长的时空性相关。在本试验中,OPT处理0—100 cm的土层中,硝态氮的含量在小麦季拔节期和玉米灌浆期追施氮肥后都有明显累积,小麦季整个生育期中硝态氮的相对累计速率在40—60 cm土层表现最强烈,高达93 kg·hm-2,说明硝态氮向深层土壤迁移在小麦季主要集中在40—60 cm土层,于淑芳等[20]研究也表明,在首季小麦季时,施用速效性氮肥后硝态氮向下迁移主要集中在60 cm土层,即使在高氮投入的设施菜田中,施用控释肥后,硝态氮残留主要集中在表层根系分布的区域,减少了其向下层土壤的淋洗[34]。因此,40—60 cm土层可能是0—100 cm土层中氮素迁移的敏感层,硝态氮在土壤中累积和迁移发生初期主要集中在40—60 cm土层。在之后玉米季连续施用氮肥后,所有施肥处理其硝态氮含量均呈现不断增加的趋势（图2）,而此时土层中硝态氮只有在0—20 cm表层发生较小幅度的累积,而在20—100 cm土层中出现了小幅度的负增长（图4）,在玉米收获时,所有施氮处理0—100 cm的硝态氮含量已经维持在了较高水平,说明此时20—100 cm土层中的硝态氮仍然在向更深层的土壤迁移,发生了淋溶[32,33]。CRF处理0—100 cm土层中硝态氮累积量在小麦季和CK保持一致,由于连续的施加氮肥,在玉米季其含量也开始升高,并从表层土壤向下迁移,但是迁移速率远不及OPT处理（图3、4）。上述结试验结果说明,在小麦-玉米轮作中,控释肥在土壤中残留硝态氮减少,在保证耕层养分供应满足作物需求的情况下减少了硝态氮向深层土壤的迁移。在西欧等发达国家规定的氮肥优化管理体系中,作物收获后0—100 cm土层中氮素残留应不超过50 kg·hm-2 [20],在中国针对华北平原小麦/玉米轮作体系中优化管理的氮素盈余量参考值为100 kg·hm-2 [35]。本试验在试验前0—100 cm土层中的硝态氮含量为50 kg·hm-2,在小麦/玉米轮作收获后CRF和OPT处理的硝态氮含量均为165 kg·hm-2,盈余量为115 kg·hm-2,结果非常接近,这也就充分说明本试验中减施20% 氮的控释肥能更好地降低对土壤以及地下水环境污染的风险。
4 结论
和优化施肥相比较,包膜控释肥不仅可以实现和作物种子一次性施入土壤,减少劳动力达到省工的目的;另外,在保证作物产量和地上部吸氮量的同时,减施20%氮量的控释肥还减少了硝态氮在土壤中的残留量,降低了硝态氮向深层土壤迁移的速率,也进一步降低了对环境污染的风险。The authors have declared that no competing interests exist.
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被引期刊影响因子
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| [2] | . . |
| [3] | . Nitrogen dynamics and budgets in a clay loam soil (Meadow Aqualf) in the North China Plain were investigated in a winter wheat ( Triticum aestivum L.) and maize ( Zea mays L.) cropping system comparing the effects of four N rates (0, 120, 240 and 360 kg N ha 611 as urea) applied twice to each crop over 2 years. Ammonium nitrogen (NH 4-N) in the soil profile remained at a low and constant level (except in the surface 20 cm layer) following application of fertilizer N. In contrast, nitrate nitrogen (NO 3-N) levels were significantly altered by the rate of applied N. A strong tendency of NO 3-N to move from the surface layer to the lower layers (20–100 cm) was observed during the wheat and maize growth seasons in treatments of 240 and 360 kg N ha 611 per crop (N240 and N360). The amounts of NO 3-N accumulated in the soil profile were significantly higher in N240 and N360 than those in N0 and N120 (treatments receiving 0 and 120 kg N ha 611 per crop). After 2 years, soil NO 3-N levels at 0–300 cm depth in N120, N240 and N360 amounted to 336, 815 and 1141 kg ha 611, respectively, with more than half of these amounts distributed in the 100–300 cm layer. The calculated total N balance indicates that most fertilizer N was available as NO 3-N in the top 300 cm of the soil profile using traditional fertilization and irrigation practices. Over the subsequent 2 years, N losses were calculated to be relatively low in N120 but significantly higher in N240 and N360. Measured gaseous N losses showed that NH 3 volatilization and denitrification comprised only a small fraction of total N losses during the 2-year rotation, while NO 3-N leaching from the top 100 cm of the soil profile accounted for most N losses across all N rates and experimental years. The N budget showed that accumulation and/or leaching of NO 3-N below 100 cm depth (beyond the reach of most roots) was the main pathway for N losses in the winter wheat–maize cropping system. The recommended N application rate of 120 kg N ha 611 minimized soil NO 3-N accumulation and leaching losses while maintaining high yields and N utilization by winter wheat and maize. |
| [4] | . Fertilizer use plays an important role in crop production to ensure food security in China. At the same time, the relatively low nutrient use efficiency resulted in negative impact on environment quality. Therefore, scientific use of nutrient resources and improvement in fertilizer use efficiency is an important scientific issue rated to national food security and environment quality. This review paper discussed China’s basic situation with large population, limited arable land, relatively low land productivity and fragile ecosystem, analyzed fertilizer demand to meet the rapid increase in crop production, overviewed current use of organic and inorganic nutrient resources, and revealed N loss from chemical fertilizer application and its impact on environment. Based on deep understanding of the existing problems and great challenge China is facing, the authors proposed a new fertilizer recommendation strategy-“regional fertilizer rate control with adjustment at field level”, developed regionalized nutrient management for small size farm operation system and precision fertilization for large scale farm operation. The current situation and existing problems in slow/controlled release fertilizers and in organic nutrient resources were also discussed. For sustained increase in crop production to support food security and to protect the environment, the technic strategy was proposed, including increase of land productivity, improvement of all nutrient resources using advanced science and technology, realization of regionalized fertilizer recommendation based on land productivity. Favorable policies and continuous financial support to fertilizer related science and technology development was also suggested. . Fertilizer use plays an important role in crop production to ensure food security in China. At the same time, the relatively low nutrient use efficiency resulted in negative impact on environment quality. Therefore, scientific use of nutrient resources and improvement in fertilizer use efficiency is an important scientific issue rated to national food security and environment quality. This review paper discussed China’s basic situation with large population, limited arable land, relatively low land productivity and fragile ecosystem, analyzed fertilizer demand to meet the rapid increase in crop production, overviewed current use of organic and inorganic nutrient resources, and revealed N loss from chemical fertilizer application and its impact on environment. Based on deep understanding of the existing problems and great challenge China is facing, the authors proposed a new fertilizer recommendation strategy-“regional fertilizer rate control with adjustment at field level”, developed regionalized nutrient management for small size farm operation system and precision fertilization for large scale farm operation. The current situation and existing problems in slow/controlled release fertilizers and in organic nutrient resources were also discussed. For sustained increase in crop production to support food security and to protect the environment, the technic strategy was proposed, including increase of land productivity, improvement of all nutrient resources using advanced science and technology, realization of regionalized fertilizer recommendation based on land productivity. Favorable policies and continuous financial support to fertilizer related science and technology development was also suggested. |
| [5] | . Abstract3鈭 relative to ammonium- or urea-based N fertilizers. Organic fertilizers can improve soil fertility and quality, but long-term application at high rates can also lead to more nitrate leaching, and accumulation of P, if not managed well. Well-managed combination of chemical and organic fertilizers can overcome the disadvantages of applying single source of fertilizers and sustainably achieve higher crop yields, improve soil fertility, alleviate soil acidification problems, and increase nutrient-use efficiency compared with only using chemical fertilizers. Crop yield can be increased through temporal diversity using crop rotation strategies compared with continuous cropping and legume-based cropping systems can reduce carbon and nitrogen losses. Crop yield responses to N fertilization can vary significantly from year to year due to variation in weather conditions and indigenous N supply, thus the commonly adopted prescriptive approach to N management needs to be replaced by a responsive in-season management approach based on diagnosis of crop growth, N status and demand. A crop sensor-based in-season site-specific N management strategy was able to increase Nuptake efficiency by 368% over farmers鈥 practices in the North China Plain. Combination of these well-tested nutrient management principles and practices with modern crop management technologies is needed to develop sustainable nutrient management systems in China that can precisely match field-to-field and year-to-year variability in nutrient supply and crop demand for both single crops and crop rotations to not only improve nutrient-use efficiency but also increase crop yield and protect the environment. In addition, innovative and effective extension and service-providing systems to assist farmers in adopting and applying new management systems and technologies are also crucially important for China to meet the grand challenge of food security, nutrient-use efficiency and sustainable development. |
| [6] | . 在大田条件下研究了树脂包膜控释肥(CRF)和硫包膜控释肥(SCF)对夏玉米产量、田间氨挥发及氮肥利用率的影响.结果表明:控释肥能显著提高玉米产量.在相同施肥量(N、P、K量相同)情况下,全量控释肥CRF(1428 kg.hm-2)和SCF(1668 kg.hm-2)分别比全量普通复合肥CCF(1260 kg.hm-2)增产13.15%和14.15%;控释肥施肥量减少25%(CRF1071 kg.hm-2;SCF 1251 kg.hm-2)时,分别比CCF增产9.69%和10.04%;控释肥施肥量减少50%时(CRF 714 kg.hm-2;SCF 834 kg.hm-2),其产量与CCF无显著差异.对夏玉米田间土壤原位氨挥发进行研究表明,控释肥处理氨挥发速率上升缓慢,最大挥发高峰出现时间比普通肥处理晚7 d,土壤氨挥发量在0.78~4.43 kgN.hm-2,比普通肥处理(9.11 kgN.hm-2)减少51.34%~91.34%.控释肥的氮肥利用率和农学效率也均显著高于普通肥处理. . 在大田条件下研究了树脂包膜控释肥(CRF)和硫包膜控释肥(SCF)对夏玉米产量、田间氨挥发及氮肥利用率的影响.结果表明:控释肥能显著提高玉米产量.在相同施肥量(N、P、K量相同)情况下,全量控释肥CRF(1428 kg.hm-2)和SCF(1668 kg.hm-2)分别比全量普通复合肥CCF(1260 kg.hm-2)增产13.15%和14.15%;控释肥施肥量减少25%(CRF1071 kg.hm-2;SCF 1251 kg.hm-2)时,分别比CCF增产9.69%和10.04%;控释肥施肥量减少50%时(CRF 714 kg.hm-2;SCF 834 kg.hm-2),其产量与CCF无显著差异.对夏玉米田间土壤原位氨挥发进行研究表明,控释肥处理氨挥发速率上升缓慢,最大挥发高峰出现时间比普通肥处理晚7 d,土壤氨挥发量在0.78~4.43 kgN.hm-2,比普通肥处理(9.11 kgN.hm-2)减少51.34%~91.34%.控释肥的氮肥利用率和农学效率也均显著高于普通肥处理. |
| [7] | |
| [8] | . 采用田间微区1 5N示踪试验研究了肥料氮在冬小麦、夏玉米当季和后茬的去向。结果表明 ,在供试土壤的肥力水平和生产条件下 ,N 12 0kg hm2 的施肥水平已经达到了较高产量 ,再增加氮肥施用量作物产量不再增加 ;其氮肥利用率和残留率均显著高于施氮量为N 36 0kg hm2 ,损失率则远低于后者 ;在一季作物生长后仍有 2 0 .9%～4 8 4 %肥料氮残留于 0～ 10 0cm土层 ,这些残留的肥料氮在后茬的利用率不足 8% ,至施肥后第 2或第 3茬作物 ,仍有部分肥料氮残留于土壤。在低施氮量时 ,肥料氮以NO-3 N残留的量很低 ,在高施氮量时 ,残留氮除以有机态、微生物态氮形式存在外 ,以NO-3 N形式存在的比例也很高 ;在氮素损失途径中 ,淋洗损失可能占有相当重要的地位。 . 采用田间微区1 5N示踪试验研究了肥料氮在冬小麦、夏玉米当季和后茬的去向。结果表明 ,在供试土壤的肥力水平和生产条件下 ,N 12 0kg hm2 的施肥水平已经达到了较高产量 ,再增加氮肥施用量作物产量不再增加 ;其氮肥利用率和残留率均显著高于施氮量为N 36 0kg hm2 ,损失率则远低于后者 ;在一季作物生长后仍有 2 0 .9%～4 8 4 %肥料氮残留于 0～ 10 0cm土层 ,这些残留的肥料氮在后茬的利用率不足 8% ,至施肥后第 2或第 3茬作物 ,仍有部分肥料氮残留于土壤。在低施氮量时 ,肥料氮以NO-3 N残留的量很低 ,在高施氮量时 ,残留氮除以有机态、微生物态氮形式存在外 ,以NO-3 N形式存在的比例也很高 ;在氮素损失途径中 ,淋洗损失可能占有相当重要的地位。 |
| [9] | . Excessive nitrogen (N) fertilization and decreasing N recovery rates by crops have caused dramatic increases in nonpoint source pollution from agriculture in China. The rate of N fertilization across the country varies widely among regions and crops, depending on the stage of economic development. For example, N application rates in the eastern regions and on cash crops are far higher than in western regions of the country and on cereal crops. Moreover, N application rates in wealthier regions are higher than recommended by the Chinese Academy of Sciences. To successfully achieve environmental protection as well as high crop yields, China must formulate relevant agricultural policies to encourage farmers in economically developed areas to reduce their N fertilization rate while also issuing conventional fertilization recommendations for small-scale farming systems and the expanding cultivation of cash crops. |
| [10] | . 运用统计资料和调查研究资料,揭示中国氮肥用量在地区之间和作物之间分配的不平衡现象.经济 发达的东南部地区和城郊地区氮肥施用量远高于西北部地区,经济作物远高于粮食作物,氮肥短缺和过量施用并存.中国北方某些地区土壤剖面硝态氮的大量累积对 水体环境构成了某种程度的威胁.由于大田作物获得较高产量的"平均适宜施氮量(N 150~180 kg/hm2)"与氮素环境安全指标尚有一定距离,中国完全可以实现水体环境安全和农业高产优质的双重目标.氮肥对水体环境的影响主要是由不合理大量施用 氮肥造成的.因此,中国应制定施肥技术标准和法规,鼓励农民降低氮肥用量. . 运用统计资料和调查研究资料,揭示中国氮肥用量在地区之间和作物之间分配的不平衡现象.经济 发达的东南部地区和城郊地区氮肥施用量远高于西北部地区,经济作物远高于粮食作物,氮肥短缺和过量施用并存.中国北方某些地区土壤剖面硝态氮的大量累积对 水体环境构成了某种程度的威胁.由于大田作物获得较高产量的"平均适宜施氮量(N 150~180 kg/hm2)"与氮素环境安全指标尚有一定距离,中国完全可以实现水体环境安全和农业高产优质的双重目标.氮肥对水体环境的影响主要是由不合理大量施用 氮肥造成的.因此,中国应制定施肥技术标准和法规,鼓励农民降低氮肥用量. |
| [11] | . Using a scientific assessment concept of sustainability in crop-production based on the entropy production minimization principle of thermodynamics, formation and non-use of soluble and volatile (by-)products of the nutrient cycles within the system are interpreted as indicators or measures of the low efficiency/sustainability of recent forms of intensive agriculture. The simultaneous high energy input in modern crop production systems further shows the difference between these and quasi-stationary natural systems with maximum bioproduction having minimum energy dissipation and entropy production. Using balance sheets and dynamic approaches, the practical implications regarding the nitrogen cycle in central Europe (FR Germany) and China are exemplified and discussed. The average N balance of arable systems in Germany shows surplus N amounts of 110–130 kg N ha -1 yr -1 . A high N immobilization in accordance with deepened top soil layers has governed N balances in Germany since about 1960. In China Nbalance surpluses in intensive agricultural (double-cropping) systems on the southern edge of the Loess Plateau now reach 125–230 kg N ha -1 yr -1 . In field experiments, mineral N contents in the profiles (0–1.2 m depth) were 72–342 and 78–108 kg ha -1 at harvest of summer maize and winter wheat, respectively. In the Taihu region in eastern China, surpluses in the N balance (rice-wheat double cropping) amount to 217–335 kg N ha -1 yr -1 . N min contents in the 0–0.9 m profiles of between 50 and 100 kg N ha -1 were frequently found after winter wheat harvest. In two separate investigations of ground and well water samples in China, nitrate contents exceeded the critical WHO value for drinking water in 38–50% of the locations investigated. |
| [12] | . A field experiment located in Taihu Lake Basin of China was conducted, by application of urea or a mixture of urea with manure, to elucidate the interception of nitrogen (N) export in a typical rice field through “zero-drainage water management” combined with sound irrigation, rainfall forecasting and field drying. N concentrations in floodwater rapidly declined before the first event of field drying after three split fertilizations, and subsequently tended to return to the background level. Before the first field drying, total particulate nitrogen (TPN) was the predominant N form in floodwater of plots with no N input, dissolved inorganic nitrogen (DIN) on plots that received urea only, and dissolved organic nitrogen (DON) on plots treated with the mixture of urea and manure. Thereafter TPN became the major form. No N export was found from the rice field, but total nitrogen (TN) of 15.8 kg/hm was remained, mainly due to soil N sorption. The results recommended the zero-drainage water management for full-scale areas for minimizing N export. |
| [13] | . . |
| [14] | . 为了提高氮肥和水分利用效率，该文在甘肃河西灌区试验地点，采用田间小区试验，研究了不同氮水平（0、225、450kg／hm^2）和灌水量（750、1125、1500m^3／hm^2）对小麦／玉米间作土壤硝态氮累积和水氮利用效率的影响。结果表明，不同氮肥和灌水量对小麦带土壤硝态氮含量和累积量影响较小，对玉米带影响显著。随氮肥用量增加，玉米带土壤硝态氮含量和累积量增加，随灌水量和氮肥用量增加，0～60cm土壤硝态氮相对累积量增加，60～140cm土层降低。氮肥当季利用率、氮肥生产率、氮肥产投比都是以225kg／hm^2氮水平较高，但不同灌水量差别不大。WUE（水分利用效率）以W75nN225最高，W1500N0最低，随灌水量增加WUE降低。 . 为了提高氮肥和水分利用效率，该文在甘肃河西灌区试验地点，采用田间小区试验，研究了不同氮水平（0、225、450kg／hm^2）和灌水量（750、1125、1500m^3／hm^2）对小麦／玉米间作土壤硝态氮累积和水氮利用效率的影响。结果表明，不同氮肥和灌水量对小麦带土壤硝态氮含量和累积量影响较小，对玉米带影响显著。随氮肥用量增加，玉米带土壤硝态氮含量和累积量增加，随灌水量和氮肥用量增加，0～60cm土壤硝态氮相对累积量增加，60～140cm土层降低。氮肥当季利用率、氮肥生产率、氮肥产投比都是以225kg／hm^2氮水平较高，但不同灌水量差别不大。WUE（水分利用效率）以W75nN225最高，W1500N0最低，随灌水量增加WUE降低。 |
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