0 引言
【研究意义】红壤性水稻土是我国南方最重要的土壤类型之一。红壤地区水热资源丰富,生产潜力大,水稻种植面积广,为我国粮食安全做出了重要贡献[1,2]。尽管红壤性水稻土耕作历史悠久,但是受成土母质、耕作方式和施肥措施不合理等因素的影响,中低产田的面积仍然占很大比例,土壤肥力水平总体偏低[3]。土壤肥力是水稻丰产的基础,大量研究表明,通过秸秆还田、种植绿肥和增施动物源有机肥等措施培肥土壤,不仅能够提高水稻产量,还能降低化肥的使用[4,5,6,7]。但是,不同肥力红壤性水稻土对水稻氮肥利用效率的影响尚不清楚。【前人研究进展】我国水稻氮肥回收率平均仅为30%[8,9],比其他主要水稻种植国家低15%—20%[10]。为提高水稻氮肥利用效率,前人已经从水稻品种、氮肥类型、施肥技术和水分管理等多个角度进行了大量的研究[11,12,13,14,15]。但是,有关土壤肥力对水稻氮肥利用效率及其去向的影响研究仍然很少。PENG等[16]研究表明,低肥力、中肥力和高肥力湖泊冲积性水稻土的氮肥回收率分别为16%、18%和25%,而氮肥损失率分别为77%、72%和64%,这说明提升土壤肥力不仅能提高氮肥回收率,还能降低氮肥的损失率。NORMAN等[17]的研究表明,在34—101 kg·hm-2的施氮量条件下,高肥力土壤水稻的氮肥回收率显著高于低肥力土壤,而当施氮量为134—168 kg·hm-2时,不同肥力土壤氮肥回收率基本无差异。其原因是低肥力土壤自身土壤氮素较低,且氮肥回收率受施氮水平的影响。王秀斌等[18]的研究发现,不管施氮水平高低,水稻氮肥回收率均是低产田高于中产田,中产田高于高产田,作者认为可能与水稻品种的耐肥性有关。但是,范立慧等[19]试验表明,高地力土壤第一年水稻的氮肥回收率均高于低地力土壤,而第二年的结果却相反,表明气象因子也可能影响水稻氮肥利用对土壤肥力的响应。许多针对旱作土壤的研究也表明,土壤肥力显著影响氮肥回收率和去向[20,21]。【本研究切入点】前人关于稻田土壤肥力对氮肥利用效率的研究大部分是利用差减法计算氮肥回收率,无法解析氮肥的真实回收率及其去向,因此无法揭示土壤肥力对氮肥利用、残留和损失的影响。此外,氮肥回收率受气候条件、地形和水分管理等多个因素的综合影响[22]。因此,前人基于田间不同肥力地块的对比研究无法排除其他因素的干扰而单独揭示土壤肥力水平对水稻氮肥回收率的影响。【拟解决的关键问题】本研究通过选取不同肥力的土壤,利用15N同位素示踪技术,采用盆栽试验,揭示了不同肥力红壤性水稻土对水稻产量、氮肥利用效率及其去向的影响,为红壤性水稻土的土壤培肥和合理施肥提供科学依据。1 材料与方法
1.1 试验土壤
2016年11月,在江西省红壤研究所内（江西省进贤县,28°15'30"N,116°20'24"E）广泛选取高、中、低不同产量水平的水稻田块,采集其耕层土壤样品（0—15 cm）,并标记采样地点。土壤样品带回室内风干,分别测定pH、有机质、全氮、碱解氮、速效磷、速效钾和土壤质地。以土壤有机质含量为筛选标准（土壤有机质含量相差10 g·kg-1左右）,选取母质相同（第四纪红色黏土）、质地相似的高、中、低3种不同肥力的土壤,其基本理化性质见表1。2016年12月采集所选取田块的耕层土壤样品,风干后过2 mm筛,用于2017年的盆栽试验。盆栽试验在江西农业大学试验站网室内进行（江西南昌,28°46′17″N,115°49′52″E）。网室采用铁丝网建造,长宽高分别为12、5和8 m。网室主要是防止鸟害,其光照、温度和降水与外界环境一致。但是,为了防止溢水造成氮素流失,本试验在降雨时以雨棚遮盖,采用人工灌溉。试验站年平均温度17.5℃、年平均降水量1 600 mm。Table 1
表1
表1不同肥力红壤性水稻土的基本理化性质
Table 1The basic physiochemical properties of the selected red paddy soils with different fertility
| 土壤肥力 Soil fertility | pH | 有机质 Organic matter (g·kg-1) | 总氮 Total N (g·kg-1) | 碱解氮 Alkaline N (mg·kg-1) | 速效钾 Available K (mg·kg-1) | 速效磷 Olsen P (mg·kg-1) | 砂粒 Sand (2-0.02 mm, %) | 粉粒 Silt (0.02-0.002 mm, %） | 黏粒 Clay (<0.002 mm, %) |
|---|---|---|---|---|---|---|---|---|---|
| 低肥力Low fertility | 5.48 | 19.9 | 1.2 | 137.2 | 174.7 | 17.9 | 22 | 56 | 22 |
| 中肥力Medium fertility | 5.39 | 29.6 | 1.8 | 191.5 | 170.5 | 21.2 | 23 | 55 | 22 |
| 高肥力High fertility | 5.31 | 38.9 | 2.3 | 241.4 | 239.6 | 22.4 | 22 | 54 | 24 |
新窗口打开
1.2 试验设计
试验设3种肥力水平,分别为低肥力（FL）、中肥力（FM）和高肥力（FH）,3种施氮水平,分别为0、0.10、0.15 g N·kg-1干土（对应大田施氮量为0、150和225 kg·hm-2,分别记作N0、N150和N225）。试验共9个处理,分别为FLN0、FLN150、FLN225、FMN0、FMN150、FMN225、FHN0、FHN150和FHN225,每个处理重复3次,采用完全随机设计。采用塑料桶进行盆栽试验,桶高21 cm,上部内径28 cm,底部内径20 cm,每盆装干土4 kg。水稻于2017年4月20日播种,品种为Y两优5867（籼型两系杂交稻品种）。采用大田育秧,5月18日移栽,每盆2穴,每穴1苗。氮肥采用丰度为20.16%的15N同位素标记尿素（上海化工研究院）。氮肥按基肥﹕蘖肥﹕穗肥=5﹕2﹕3分3次施用。所有处理磷、钾肥施用量相同,每千克干土施P2O5 0.06 g,K2O 0.1 g。磷、钾肥一次性基施,磷肥为钙镁磷肥,钾肥为氯化钾。整个水稻生长期保持2—3 cm淹水层,严控病、虫害和杂草。
1.3 样品采集与测定
水稻成熟后,将植株分为籽粒、茎叶和根系,于105℃杀青30 min,70℃烘干至恒重,并考察有效穗数、每穗粒数、结实率和千粒重。植株样品粉碎后测定氮素含量和15N丰度。同时,采集土壤样品,一部分风干后磨细用于测定土壤氮素含量及其15N丰度和固定态铵含量,另一部分鲜土4℃保存,48 h内测定微生物生物量氮、铵态氮和硝态氮。土壤和植株各器官氮素含量采用凯氏定氮仪测定,15N同位素丰度采用Finnigan-MAT-251型质谱仪测定。微生物生物量氮采用适于淹水土壤的常压氯仿熏蒸-浸提法[23]测定,浸提液中的总氮采用凯氏定氮仪测定。土壤固定态铵采用KOBr-KOH法[24]测定。铵态氮和硝态氮采用2 mol·L-1 KCl溶液浸提,连续流动分析仪（SKALAR SAN++,荷兰）测定。
1.4 数据处理与分析
基于15N示踪技术的植株氮素来源于土壤和肥料的比例根据Hauck和Bremner的方法[25]计算：植株氮素来源于氮肥的比例（Ndff, %）=（施氮处理植株15N丰度-空白处理植株15N丰度）/（氮肥15N丰度-氮肥自然丰度）×100; （1）
植株氮素来源于土壤的比例（Ndfs, %）=100-Ndff; （2）
植株吸收的肥料氮（mg·pot-1）=Ndff×植株总吸氮量; （3）
氮肥回收率（%）=植株吸收的肥料氮/施氮量×100; （4）
氮肥残留率（%）=（施氮处理土壤15N丰度-空白处理土壤15N丰度）/（氮肥15N丰度-氮肥自然丰度）×土壤全氮含量/施氮量×100; （5）
氮肥损失率（%）=（施氮量-水稻吸收氮肥量-土壤残留氮肥量）/施氮量×100。 （6）
此外,本研究还采用传统的差减法计算了氮肥对产量的贡献率（简称为氮肥贡献率）、土壤氮素依存率和氮肥的利用效率,计算方法见参考文献[29]。
采用DPS V7.05数据处理系统进行数据统计分析,采用最小显著性差异法（LSD）进行显著性检验（P<0.05）。
2 结果
2.1 土壤肥力和施氮量对水稻产量及其构成的影响
土壤肥力对水稻产量有极显著的影响（表2）。在相同施氮量条件下,土壤肥力越高水稻产量越高,且均达到显著水平。施氮量对水稻产量也有极显著的影响,相同土壤肥力条件下,施氮量越多,水稻产量也越高,除FHN150和FHN225处理外,差异均达到显著水平。土壤肥力和施氮量对水稻产量具有极显著的互作效应。与N0相比,N150和N225在FL、FM和FH上的增产率分别为63%和89%、40%和55%、17%和23%。Table 2
表2
表2土壤肥力（F）和施氮量（N）对水稻产量及其构成的影响
Table 2Effects of soil fertility (F) and N fertilization (N) on rice yield and its components
| 处理 Treatments | 产量 Grain yield (g/pot) | 有效穗数 Effective panicles/pot | 每穗实粒数 Spikelets per panicle | 结实率 Filled grain percentage (%) | 千粒重 1000-grain weight (g) |
|---|---|---|---|---|---|
| FLN0 | 23.6f | 9.3f | 108.6ab | 89.4bc | 26.5d |
| FLN150 | 38.5e | 15.3de | 101.9b | 88.7bc | 26.3d |
| FLN225 | 44.5d | 17.0d | 109.0ab | 89.0bc | 26.4d |
| FMN0 | 40.0e | 14.7e | 116.5a | 88.9bc | 26.7bcd |
| FMN150 | 55.9c | 19.3c | 114.5ab | 88.3c | 26.6cd |
| FMN225 | 62.1b | 22.0ab | 113.6ab | 88.3c | 26.5d |
| FHN0 | 55.3c | 21.7b | 115.5ab | 89.6b | 27.1a |
| FHN150 | 65.0ab | 22.3ab | 114.5ab | 91.5a | 27.0ab |
| FHN225 | 68.0a | 24.0a | 117.4a | 91.1a | 26.9abc |
| ANOVA（P） | |||||
| 肥力（F） | 0.0001 | 0.0001 | 0.0525 | 0.0001 | 0.0001 |
| 施氮量（N） | 0.0001 | 0.0001 | 0.6595 | 0.8117 | 0.3175 |
| 肥力×施氮量（F×N） | 0.0010 | 0.0033 | 0.9165 | 0.0366 | 0.9305 |
新窗口打开
土壤肥力和施氮量对有效穗数均有极显著的影响,且二者均有极显著的互作效应（表2）。相同施氮量条件下,有效穗数随土壤肥力的提升而增加。施氮肥对中、低肥力土壤的有效穗数有显著的增加作用,但在高肥力土壤上只有高施氮量（225 kg·hm-2）具有显著影响。土壤肥力对每穗粒数无显著影响,但呈增加趋势。施氮肥对每穗粒数亦无显著影响。土壤肥力对结实率和千粒重均有极显著影响,高肥力土壤的结实率和千粒重显著高于中、低肥力土壤。总体而言,水稻产量的增加主要是来自于有效穗数的提高。
土壤肥力和施氮量对水稻产量的氮肥贡献率和土壤氮素依存率均有极显著的影响（图1）。在N150施氮量下,氮肥对水稻产量的贡献率为15%—39%,而在N225施氮量下,氮肥贡献率为19%—47%。在N150施氮量下,土壤氮素依存率为61%—82%,而在N225施氮量下,土壤氮素依存率为52%—77%。在相同施氮量的条件下,土壤肥力越高,氮肥对水稻产量的贡献率越小,而水稻产量对土壤氮素的依存率越高。相同土壤肥力条件下,N225处理的氮肥贡献率显著高于N150处理,而土壤氮素依存率则低于N150处理。
显示原图|下载原图ZIP|生成PPT图1土壤肥力（F）和施氮量（N）对水稻产量的氮肥贡献率和土壤氮素依存率的影响
FL、FM、FH分别代表低、中和高肥力土壤。N150和N225分别代表施氮量为150和225 kg·hm-2。图柱上不同字母表示处理间在P<0.05水平上差异显著。误差线表示标准差。下图同
-->Fig. 1The N fertilizer contribution rate and soil N dependent rate of rice yield as affected by soil fertility (F) and N fertilization (N)
FL, FM, FH mean low, medium, and high fertility soils, respectively. N150 and N225 mean the N application rate at 150 and 225 kg·hm-2, respectively. Different letters indicate significant difference at P<0.05. Error bars indicate standard deviation. The same as following Figs
-->
2.2 土壤肥力和施氮量对水稻氮素吸收及其来源的影响
土壤肥力和施氮量对水稻总吸氮量均有极显著的影响（表3）。水稻植株总吸氮量随着土壤肥力的提升而显著增加,且施氮量越多吸氮量越高。土壤肥力和施氮量对水稻植株吸收的土壤氮素和肥料氮素的数量及其比例均有极显著的影响,且二者具有显著的互作效应。总体而言,植株吸氮量中来自肥料氮素的比例平均只有21%,而来自土壤氮素的比例达到79%。与总吸氮量变化一致,在相同施氮量的条件下,随着土壤肥力的提高,植株对土壤氮素和肥料氮素的吸收量均显著增加。在相同施氮量的条件下,随着土壤肥力的提高,植株吸氮量中来自肥料氮素的比例显著降低,而来自土壤氮素的比例显著提高。相同土壤肥力下,N225处理植株吸收肥料氮素的比例显著高于N150处理,而吸收土壤氮素的比例显著低于N150处理。Table 3
表3
表3土壤肥力（F）和施氮量（N）对水稻吸氮量及其来源的影响
Table 3Rice N uptake and its sources as affected by soil fertility (F) and N fertilization (N)
| 处理 Treatments | 总吸氮量 N uptake (mg/pot) | 肥料氮吸收量 Fertilizer N uptake (mg/pot) | 来自肥料氮的比例 Ndff (%) | 土壤氮吸收量 Soil N uptake (mg/pot) | 来自土壤氮的比例 Ndfs (%) |
|---|---|---|---|---|---|
| FLN0 | 443.0g | - | - | - | - |
| FLN150 | 723.5f | 163.5f | 22.6b | 560.0e | 77.4e |
| FLN225 | 854.1e | 260.9c | 30.5a | 593.2d | 69.5f |
| FMN0 | 904.9e | - | - | - | - |
| FMN150 | 1165.8d | 192.7e | 16.8e | 973.1c | 83.2b |
| FMN225 | 1352.3c | 291.0b | 21.5c | 1061.3b | 78.5d |
| FHN0 | 1184.5d | - | - | - | - |
| FHN150 | 1440.4b | 217.4d | 14.9f | 1223.1a | 85.1a |
| FHN225 | 1546.1a | 302.1a | 19.5d | 1244.0a | 80.5c |
| ANOVA（P） | |||||
| 肥力（F） | 0.0001 | 0.0001 | 0.0001 | 0.0001 | 0.0001 |
| 施氮量（N） | 0.0001 | 0.0001 | 0.0001 | 0.0001 | 0.0001 |
| 肥力×施氮量（F×N） | 0.2961 | 0.0404 | 0.0001 | 0.0101 | 0.0001 |
新窗口打开
2.3 土壤肥力和施氮量对肥料氮去向的影响
土壤肥力对水稻氮肥回收率有极显著的影响,且与施氮量有极显著的互作效应（图2）。水稻对氮肥的回收率为41%—54%,氮肥残留率为18%—30%,氮肥损失率为16%—39%。土壤肥力越高,相同施氮量处理的氮肥回收率越高。在低肥力土壤上,与N150处理相比,N225处理显著提高了氮肥回收率,在中肥力土壤上,二者没有显著差异,而在高肥力土壤中,N225处理却显著降低了氮肥回收率。土壤肥力和施氮量均极显著地影响氮肥残留率。土壤肥力越高,相同施氮量处理的氮肥残留率越高,而N225处理的氮肥残留率显著低于N150处理。土壤肥力和施氮量均极显著地影响氮肥的损失率,且二者有极显著的互作效应。土壤肥力越高,氮肥的损失率越低,而增加施氮量会增加氮肥的损失率。在低肥力土壤上,增加施氮量对氮肥损失率影响不显著,而在中、高肥力土壤中,增加施氮量显著增加氮肥损失率。
显示原图|下载原图ZIP|生成PPT图2土壤肥力（F）和施氮量（N）对氮肥去向的影响
-->Fig. 2The fate of fertilizer N as affected by soil fertility (F) and N fertilization (N)
-->
2.4 基于差减法计算的土壤肥力和施氮量对氮肥利用效率的影响
利用传统差减法计算氮肥的利用效率如图3。土壤肥力对氮肥的农学效率有极显著的影响。高肥力土壤的农学效率显著低于中、低肥力土壤。增加施氮量有降低氮肥农学效率的趋势,但未达到显著差异水平。氮肥表观回收率受土壤肥力的显著影响,且与施氮量有显著的互作效应。在N150处理下,氮肥表观回收率随土壤肥力的升高呈下降趋势,而在N225处理下,中肥力土壤上氮肥表观回收率最高。在中肥力土壤上,增加施氮量显著提高了氮肥表观回收率,而在其他两个肥力土壤没有显著差异,虽然呈略微降低趋势。土壤肥力和施氮量对氮肥偏生产力均有极显著的影响,且二者有极显著的互作效应。在相同施氮量条件下,随着土壤肥力的提升,氮肥偏生产力显著增加。在相同肥力土壤上,增加施氮量显著降低了氮肥偏生产力。随着土壤肥力的提升,氮肥偏生产力的下降速率增加,与N150处理相比,N225处理在FL、FM和FH土壤上的氮肥偏生产力分别下降了30%、35%和43%。相同施氮量条件下,提升土壤肥力能降低氮肥生理效率。在相同土壤肥力下,增加施氮量会降低氮肥生理效率。
显示原图|下载原图ZIP|生成PPT图3基于差减法计算的土壤肥力（F）和施氮量（N）对水稻氮肥利用效率的影响
-->Fig. 3N fertilizer efficiency based on the difference method as affected by soil fertility (F) and N fertilization (N)
-->
2.5 土壤肥力和施氮量对水稻根系重量的影响
土壤肥力和施氮量对水稻根系干重均有极显著的影响,二者亦具有显著的互作效应（图4）。总体而言,根系干重占总生物量的比例很低,比例只有9%—17%。土壤肥力越高,相同施氮量条件下根系干重越大。施氮量对水稻根系干重有显著的影响,在中、低肥力土壤上,施氮量越高根系干重越大,而在高肥力土壤上,施氮肥处理降低了根系干重。
显示原图|下载原图ZIP|生成PPT图4土壤肥力（F）和施氮量（N）对水稻根系干重的影响
-->Fig. 4Dry weight of root as affected by soil fertility (F) and N fertilization (N)
-->
2.6 土壤肥力和施氮量对土壤活性氮素的影响
土壤肥力和施氮量对土壤微生物量氮、硝态氮、铵态氮的含量均有显著影响（图5）。在相同施氮量条件下,微生物量氮、铵态氮和矿质氮变化随土壤肥力的提高而增加,且差异达到显著水平。在相同肥力土壤上,增加施氮量能增加微生物生物量氮和铵态氮的含量。除低肥力土壤外,增加施氮量对硝态氮含量无显著影响。
显示原图|下载原图ZIP|生成PPT图5土壤肥力（F）和施氮量（N）对土壤微生物量氮、铵态氮和硝态氮含量的影响
-->Fig. 5The concentration of soil microbial biomass N, ammonium N, and nitrate N as affected by soil fertility (F) and N fertilization (N)
-->
2.7 土壤肥力和施氮量对土壤固定态铵的影响
土壤肥力对固定态铵的含量有极显著的影响（图6）,在相同施氮量条件下,提升土壤肥力能显著增加固定态铵的含量。施氮量对固定态铵也有极显著的影响,在相同土壤肥力上,增加施氮量能增加固定态铵的含量,但N150和N225处理间差异不显著。土壤肥力和施氮量对固定态铵的含量有极显著的互作效应,即高肥力土壤增施氮肥对固定态铵含量的增加率显著低于中、低肥力土壤。
显示原图|下载原图ZIP|生成PPT图6土壤肥力（F）和施氮量（N）对土壤固定态铵含量的影响
-->Fig. 6The concentration of soil fixed ammonium as affected by soil fertility (F) and N fertilization (N)
-->
3 讨论
3.1 土壤肥力对水稻产量的影响
本研究表明,在不施氮肥的条件下,水稻基础产量的变化与土壤肥力的变化是一致的,这说明红壤性水稻土以土壤有机质为筛选指标来确定土壤肥力的高低是合理可行的。本研究表明,土壤肥力与施氮量对水稻产量具有显著的互作效应,增施氮肥均能增加水稻产量,但增产率随土壤肥力的升高而降低。这主要是因为土壤肥力越低,土壤供氮能力越弱（表3,图5）,植株对氮肥的响应越敏感,因此,氮肥的增产效果越显著[26]。这表明低肥力土壤增施氮肥的增产作用显著,而高肥力土壤适当降低施氮量,也能获得较高产量[27,28]。因此,要根据土壤肥力水平来确定适宜的施氮量[19]。3.2 基于差减法和示踪法的氮肥回收率的差异
本研究表明,传统差减法计算的氮肥回收率的变化趋势与示踪法计算的氮肥回收率的变化趋势不一致。主要原因是土壤肥力越高,水稻吸收更多的肥料氮,因此,在相同施氮量下,示踪法计算的氮肥回收率随土壤肥力的升高而升高（表3）[22]。在差减法中,决定氮肥回收率的是施氮处理与空白处理的吸氮量之差。而随着土壤肥力的提升,尽管施氮处理吸氮量和空白处理吸氮量均增加（表3）,但是,空白处理增加的速率远大于施氮处理,导致两者的差值减小,因而,氮肥回收率呈降低趋势。而在同位素示踪法中,氮肥回收率只与植株吸收的氮肥多少有关,因此,土壤肥力越高,植株吸收的化学氮肥越多,氮肥回收率也越高。从各处理吸收的土壤氮素（表3）可以看出,施氮刺激了植株吸收更多的土壤氮素,即氮肥的激发效应,例如FLN0处理的吸氮量为443.0 mg/pot,而示踪法计算的FLN150处理对土壤氮素的吸收量为560.0 mg/pot。因此,差减法高估了氮肥的贡献,掩盖了土壤肥力对氮肥吸收的影响,导致氮肥回收率远高于示踪法计算的氮肥回收率。而且,土壤肥力越低,氮肥的激发效应越强,导致相同施氮量下高肥力土壤的氮肥表观回收率低于低肥力土壤（图3）。同时,传统差减法计算的氮肥表观回收率没有将施氮量、作物吸氮量和土壤氮库变化联系起来,无法解析土壤残留氮肥对土壤氮库的补充作用,更不能反映氮肥在土壤-植物-大气系统中的损失情况[27]。因此,我们认为在研究氮肥的去向时,采用示踪法计算的氮肥回收率更为科学。此外,示踪法能够区分作物对化学氮肥的吸收率和残留率,有利于更为真实地认识目前我国的氮素利用效率[22]。
此外,FMN225的氮肥回收率高于FMN150,而在高肥力土壤上则相反（图3）。这可能是由于225 kg·hm-2的施氮量在中肥力土壤上属于适宜的施氮量,而在高肥力土壤上,此施氮量超过了适宜用量,导致氮肥损失严重,因而,FHN225的氮肥回收率低于FHN150。因此,对于低肥力土壤不仅要适当增施氮肥,更要培肥土壤,提高基础地力;而对于高肥力土壤在保证较高产量目标的条件下,确定适宜的施氮量以降低氮肥损失和维持土壤氮库平衡,从而维持较高的土壤生产力[27]。
3.3 土壤肥力对水稻氮肥吸收及其去向的影响
本研究表明,植株当季吸收的氮素来源于土壤的比例为70%—85%,而来源于氮肥的比例为15%— 30%。这说明植株当季吸收的氮素大多数来源于土壤[30,31]。本研究以土壤有机质划分土壤肥力的高低,而土壤有机质与土壤氮素含量高度相关。因此,土壤肥力越高,水稻植株总吸氮量中来自土壤氮的比例越大,而来自肥料氮的比例越小[20]。土壤肥力是导致氮肥利用、残留和损失差异的重要因素[32]。本研究表明,提升土壤肥力能提高氮肥回收率和残留率,降低损失率（图2）。主要原因有：第一,高肥力土壤能供给更多更均衡的土壤养分,包括氮磷钾等大量元素和其他微量养分。而且,高肥力土壤具有良好的土壤结构（虽然盆栽试验破坏了耕层结构,但过2 mm筛的土壤依然体现了土壤团聚体、孔隙度等物理结构的差异）[33],有利于根系的生长发育,扩大了根系的数量和吸收面积[34]。本研究中高肥力土壤供氮能力更强,即不施氮肥处理植株吸收的氮素更多（表3）,根系生物量也更多（图4）。第二,高肥力土壤的缓冲能力、阳离子交换能力和养分固持能力更强。本结果也表明高肥力土壤的活性氮和固定态铵的含量最高（图5,图6）;第三,高肥力土壤具有更多的碳源来固持氮素,从而使土壤碳循环和氮循环过程耦合的更为紧密。这表现在高肥力土壤有机质含量高,提高了微生物的数量和活性,固持了更多的活性氮,有利于减少氮肥损失[20]。本研究也表明高肥力土壤微生物量氮库也最高（图5）;第四,有研究表明较高肥力土壤有利于土壤微生物量氮的保蓄[35]。施肥后,土壤微生物初期固持的氮素,在其死亡后又重新被植物吸收利用[36]。因此,高肥力土壤能够更好地协调土壤供氮与植株需氮之间的关系,从而提高氮肥回收率,减少氮肥损失[21]。
本结果表明增施氮肥对不同肥力土壤的水稻氮肥回收率影响不同。在低肥力土壤上,增施氮肥（150 kg·hm-2 vs. 225 kg·hm-2）显著提高了氮肥回收率,在中肥力土壤上影响不显著,而在高肥力土壤上,增施氮肥显著降低了氮肥回收率（图2）。从表3可以看出,在低肥力土壤上,与施氮量150 kg·hm-2处理相比,225 kg·hm-2处理植株对肥料氮吸收量的增加率为60%,大于施氮量的增加率50%,因此氮肥回收率增加;在中肥力土壤上,增施氮肥后肥料氮吸收量的增加率为51%,与施氮量增加率接近,因此氮肥回收率差异不显著;而在高肥力土壤上,增施氮肥对肥料氮吸收量的增加率只有39%,远低于施氮量的增加率,因此氮肥回收率降低。而NORMAN等[17]研究发现,在34—168 kg·hm-2的施氮量范围内,高肥力土壤和低肥力土壤的氮肥回收率都持续增加。可能是因为其施氮量远低于本试验,且其土壤肥力水平也远低于本研究。因此,需要依据土壤肥力水平确定水稻适宜的施氮量。在低肥力土壤上适当增施氮肥既能增产又能提高氮肥回收率;而在高肥力土壤上则需要适当降低施氮量,在维持较高产量水平的条件下,既能增加氮肥回收率,又能降低氮肥损失[21]。
3.4 本研究的不足
本研究采用过筛后的土壤,并以土壤有机质为主的化学肥力指标作为土壤肥力的筛选标准,不能全面反应土壤结构、耕层特性等土壤物理肥力指标对水稻生长、氮素吸收的影响[37]。此外,盆栽试验与田间试验在耕层土壤属性、氮素损失途径、作物群体效应和微气象等方面差异较大,在田间条件下土壤肥力对水稻氮肥回收率的影响有待进一步研究。另外,不同水稻品种对氮素的吸收利用存在较大差异,是否存在品种与土壤肥力的互作效应还需要进一步研究[17]。如引言所述,以往对田间不同肥力地块的对比研究无法真正揭示土壤肥力水平对水稻氮肥回收率的影响,因此,我们建议可以利用现有长期施肥定位试验所形成的土壤肥力梯度,采用15N示踪技术阐明不同稻田肥力对水稻氮肥回收率及其去向的影响[20-21, 36]。最后,本研究仅采用了一种土壤类型和3个土壤肥力梯度,其他土壤类型和更多肥力水平土壤是否也表现出相同的规律还有待进一步研究。4 结论
对红壤性水稻土的研究表明,提高土壤肥力能显著增加水稻的有效穗数、产量、总吸氮量以及对土壤氮素和肥料氮素的吸收量,提高氮肥回收率和残留率,降低氮肥损失。低肥力土壤上增加施氮量增加了氮肥回收率,而高肥力土壤上增加施氮量降低了氮肥回收率。因此,通过培肥土壤并根据土壤肥力合理施用氮肥,不仅能提高水稻产量和氮肥利用效率,还能减少氮肥损失,降低环境污染,从而实现水稻的可持续生产。The authors have declared that no competing interests exist.
参考文献 原文顺序
文献年度倒序
文中引用次数倒序
被引期刊影响因子
| [1] | . 研究双季稻种植制度下长期不同施肥红壤性水稻土磷素含量及磷素有效性演变特征及其对土壤磷盈亏（磷平衡）的响应,为南方双季稻区红壤性水稻土科学施磷提供依据。以35年长期肥料定位试验为平台,研究不同施肥处理土壤全磷、有效磷及磷活化系数（PAC）的演变规律,计算不同处理土壤-作物系统每年磷素盈亏量及累积磷素盈亏量,探讨土壤全磷、有效磷及PAC与累积磷盈亏量的响应关系。结果表明,不施磷肥的CK和NK处理土壤全磷、有效磷和PAC随试验年限呈持平或下降趋势;不施磷肥仅施猪粪的NK＋PM处理土壤全磷呈缓慢上升趋势,有效磷和PAC呈下降趋势;施化学磷肥或化学磷肥配施稻草的NP、NPK、NP＋RS和NPK＋RS处理土壤全磷在试验前10年上升速率较快,之后25年上升速率变缓或随时间变化不显著,土壤有效磷在试验前5年急剧升高,之后随时间变化速率减缓或基本持平。CK、NK和NK＋PM处理35年土壤PAC平均值较试验初始值分别下降33.2%、29.7%和16.6%,NP、NPK、NP＋RS和NPK＋RS土壤PAC较初始值分别提高66.2%、60.6%、65.6%和52.9%。不施磷肥导致红壤性水稻土磷素亏缺,不施化学磷肥仅施猪粪土壤磷素基本持平,施用化肥磷及化肥磷配施稻草土壤磷素盈余。土壤全磷、有效磷及PAC与土壤磷累积盈亏量均呈极显著正相关关系,土壤每盈余磷100 kg hm^-2,全磷含量提高0.03 g kg^-1,有效磷提高1.20 mg kg^-1,土壤PAC上升0.09%。外源磷投入是影响土壤磷素及磷有效性的重要因素,在本试验条件下,长期不施磷或磷投入不足导致土壤磷亏缺,进而导致土壤磷及磷有效性降低,而化肥磷及有机无机磷配施促进了土壤磷盈余及土壤磷素肥力的提高。 . 研究双季稻种植制度下长期不同施肥红壤性水稻土磷素含量及磷素有效性演变特征及其对土壤磷盈亏（磷平衡）的响应,为南方双季稻区红壤性水稻土科学施磷提供依据。以35年长期肥料定位试验为平台,研究不同施肥处理土壤全磷、有效磷及磷活化系数（PAC）的演变规律,计算不同处理土壤-作物系统每年磷素盈亏量及累积磷素盈亏量,探讨土壤全磷、有效磷及PAC与累积磷盈亏量的响应关系。结果表明,不施磷肥的CK和NK处理土壤全磷、有效磷和PAC随试验年限呈持平或下降趋势;不施磷肥仅施猪粪的NK＋PM处理土壤全磷呈缓慢上升趋势,有效磷和PAC呈下降趋势;施化学磷肥或化学磷肥配施稻草的NP、NPK、NP＋RS和NPK＋RS处理土壤全磷在试验前10年上升速率较快,之后25年上升速率变缓或随时间变化不显著,土壤有效磷在试验前5年急剧升高,之后随时间变化速率减缓或基本持平。CK、NK和NK＋PM处理35年土壤PAC平均值较试验初始值分别下降33.2%、29.7%和16.6%,NP、NPK、NP＋RS和NPK＋RS土壤PAC较初始值分别提高66.2%、60.6%、65.6%和52.9%。不施磷肥导致红壤性水稻土磷素亏缺,不施化学磷肥仅施猪粪土壤磷素基本持平,施用化肥磷及化肥磷配施稻草土壤磷素盈余。土壤全磷、有效磷及PAC与土壤磷累积盈亏量均呈极显著正相关关系,土壤每盈余磷100 kg hm^-2,全磷含量提高0.03 g kg^-1,有效磷提高1.20 mg kg^-1,土壤PAC上升0.09%。外源磷投入是影响土壤磷素及磷有效性的重要因素,在本试验条件下,长期不施磷或磷投入不足导致土壤磷亏缺,进而导致土壤磷及磷有效性降低,而化肥磷及有机无机磷配施促进了土壤磷盈余及土壤磷素肥力的提高。 |
| [2] | . The acidity regimes of Red Soils in Yingtan, Jiangxi Province were examined by determining pH and pCa of the soil paste as well as determining pH in-situ. The results show that for upland soil profiles, the pH decreases gradually from the upper surface layer to the lower layer at a depth of 20 cm by 0.3 units, then decreases slightly until it does not change. For soil profiles under tea trees, the pH decreases gradually from the upper surface layer to the lower layer at a certain depth, then increases slightly with the increase in depth until it reaches a constant value. The distribution pattern of pH of the soil profiles under natural vegetation is similar to that of the soil profiles under tea trees. For paddy soil profiles, the pH increases from the upper layer to the lower layers within the depth of 0 40 cm by 1.37 units, then decreases gradually with increasing depth. For soil profiles under upland crops, tea trees, and natural vegetation, the pCa increases gradually from the surface layer to lower layers. However, in the paddy soil profiles, the pCa decreases from the upper surface downwards to a depth of 40 cm, then increases gradually with increasing depth. The lime potential (pH 0.5pCa) shows a similar trend as the pH. For a given soil, the measured pH value of the soil paste is lower by about 0.5 units than the value determined by the conventional method with a water-to-soil ratio of 5:1 or 10:1. The pH determined in-situ is even lower. The soil acidity status is principally determined by the balance between the leaching loss of base ions, especially calcium ions, and enrichment of these cations from the litter and agricultural measures. |
| [3] | . . |
| [4] | . Because the in situ incorporation of rice straw into paddy fields enhances CH4 emissions, the ex situ (or shifted) incorporation of rice straw into uplands may provide an alternative way of mitigating CH4 emissions and increasing crop productivity and soil organic carbon (SOC) accumulation. To evaluate the efficiency of this practice, three field trials were conducted in flooded paddies (FP), paddy-upland rotation (PU), and upland (UL) cropping systems in Taoyuan county, a subtropical region of China. All trials had three fertilization treatments: no fertilizer (Nil), chemical fertilizer only (NPK) and combined application of chemical fertilizer and rice straw (NPK+R in FP and NP+R in PU and UL). Results showed that the responses of crop yields to NPK in the UL trial (yields increased 2.4 to 4.1-folds relative to Nil) were greater than those of rice (increased 1.65 to 1.80-folds) in the FP and PU trial. Compared with NPK treatment, NPK+R constantly increased the grain yields of rice in the FP trial by 10% averagely, but not in PU trials. The effects of NP+R treatment on crop yields in the UL trial were significant (p<0.05) during the first 5–6 years. NPK treatments increased the SOC accumulation at a rate of 0.48Mgha611yr611 in the FP trial and 0.35Mgha611yr611 in the UL trial, but not in the PU trial. NPK+R treatments resulted in SOC accumulation rates of 1.00, 0.68, and 0.24tha611yr611, and 9.11%, 6.56%, and 6.45% of the total straw C input was converted to SOC in the FP, UL, and PU trials, respectively. The results suggested that the incorporation of rice straw was highly efficient on SOC accumulation and crop productivity in the uplands (as shown in the UL trial). We therefore recommend the ex situ incorporation of rice straw in the upland neighboring paddy fields as a way of utilizing excessive rice straw in the hilly area of subtropical China. |
| [5] | . Understanding the effects of external organic and inorganic components on soil organic C (SOC) and fertilizer N use efficiency (NUE, in kg of grain per kg of N applied) is essential for better stewardship of domesticated soils. We collected 106 paired-treatment data points from 28 long-term field fertilization trials of subtropical paddy soils with double-rice cropping systems in China. The effects of chemical fertilizer (NPK), NPK plus straw (NPK+s), and NPK plus manure (NPK+m) on rice yield, SOC density, and NUE were assessed. The greatest SOC sequestration rate was found with the use of NPK+m (0.67 Mg ha611yr611), whereas this value was lower with NPK+s (0.48 Mg ha611yr611) and NPK (0.30 Mg ha611yr611). The soil C sequestration rate decreased with the experimental time, leading to a sequestration period of 43, 65, and 55 years to reach a new equilibrium value of SOC for NPK, NPK+s and NPK+m, respectively. Under the same N input condition, the treatment with N fertilizer proportionally replaced by manure (NPK+m) could enhance both rice yield and NUE by 28% and 27%, respectively, whereas thein siturice straw incorporation (NPK+s) showed no distinct effect. Additional manure amendment on the basis of existing N fertilizer application rate did not have an effect on both rice yield and NUE. In contrast, additional rice straw incorporation decreased NUE by 24%, even though no distinct change of rice yield was found. Our results indicate that application of chemical fertilizer plus manure, rather than rice straw, to paddy fields is a promising practice to enhance SOC accumulation and improve rice yield, as well as the crop N use efficiency in subtropical rice production of China. |
| [6] | . |
| [7] | . Substituting a N-fixing legume for winter wheat has recently been suggested as a feasible method for mitigating N pollution from heavily-fertilized rice/wheat cropping system in the Taihu Lake Plain of southeast China. To understand the agronomic and environmental value of planting legumes instead of wheat, a 3-year consecutive field observation encompassing six crop seasons was conducted to compare crop yields, chemical N inputs, and N losses for three crop rotation systems; rice/wheat (the control), rice/fava bean, and rice/milk vetch. Our data showed that 52.6–59.5% of the annual N input could be saved in the two rice/legume rotations as a result of no N fertilization in the legume growing season and the replacement of 13.2–25.7% of chemical N by leguminous N via crop residue incorporation in the rice season. This reduction in N fertilizer not only produced equivalent or slightly more rice yields compared to the control, but also reduced N loss by half. In terms of N loss, ammonia (NH3) volatilization during the rice season and N runoff in the winter season for the two rice/legume rotations were greatly reduced by 31.3–38.0% and 82.1–86.0%, respectively compared to the control. A decreasing trend was also found in N leaching and nitrous oxide (N2O) in both seasons, NH3 volatilization in the winter season, and N runoff in the rice season for the two rice/legume rotations. The preliminary economic evaluation of yield benefits, fertilizer costs, and environmental costs related to N losses suggested that a mixed rice/fava bean and rice/milk vetch crop rotation (50% of each type) could ensure farmers’ returns and achieve a half-maximum reduction in environmental risk. These results demonstrate that substituting winter grain/forage legumes for wheat may be a technically feasible, low-input solution to the N pollution problems in the intensive rice-based cropping systems in the Taihu Lake Plain. |
| [8] | . Today, about 30% of world nitrogen (N) fertilizer is consumed by China. Rice crops in China consume about 37% of the total N fertilizer used for rice production in the world. Average rate of N application for rice production in China is high and fertilizer-N use efficiency is low compared with other major rice growing countries. Research progresses have been made internationally and domestically on the application method, fertilizer-N sources, computer-based decision support systems, and real-time N management in order to reduce N losses and increase fertilizer-N use efficiency. In addition to continuous increase in N rate and lack of adoption of new knowledge and technology in N management by farmers, we hypothesize that high indigenous soil N supply, adoption of hybrid and super rice cultivars, improper timing of N application, and practice of mid-season drainage could be the causes for the low fertilizer-N use efficiency in China. Future research work on improving fertilizer-N use efficiency of rice crop in China should focus more on improving cultivar's N responsiveness, optimizing the timing and rate of N application based on crop N status, and achieving optimal soil N supply capacity. |
| [9] | . China is the world’s largest consumer of synthetic nitrogen (N), where very low rates of fertilizer N recovery in crops have been reported, raising discussion around whether fertilizer N use can be significantly reduced without yield penalties. However, using recovery rates as indicator ignores a possible residual effect of fertilizer N—a factor often unknown at large scales. Such residual effect might store N in the soil increasing N availability for subsequent crops. The objectives of the present study were therefore to quantify the residual effect of fertilizer N in China and to obtain more realistic rates of the accumulative fertilizer N recovery efficiency (RE) in crop production systems of China. Long-term spatially-extensive data on crop production, fertilizer N and other N inputs to croplands in China were used to analyze the relationship between crop N uptake and fertilizer N input (or total N input), and to estimate the amount of residual fertilizer N. Measurement results of cropland soil N content in two time periods were obtained to compare the change in the soil N pool. At the provincial scale, it was found that there is a linear relationship between crop N uptake and fertilizer N input or total N input. With the increase in fertilizer N input, annual direct fertilizer N RE decreased and was indeed low (below 30% in recent years), while its residual effect increased continuously, to the point that 40–68% of applied fertilizer was used for crop production sooner or later. The residual effect was evidenced by a buildup of soil N and a large difference between nitrogen use efficiencies of long-term and short-term experiments. |
| [10] | . By improving fertilization, irrigation and crop cultivation managements, rice yield and N efficiency can be increased to some extent. However, the environmental impacts under different integrated management have been rarely evaluated. Field experiments with four management practices were conducted in the Taihu Lake region to assess an important N loss pathway from paddy fields-NH3 volatilization for two consecutive rice seasons. The four treatments included control with 0 N fertilizer (CK), local conventional production practice (CT), integrated high-efficiency practice (HE), and high-yield practice (HY) with more nutrient inputs (relative to CT). NH3 volatilization was measured and plant samples were collected for determining the dry matter yield and apparent nitrogen recovery (ANR) efficiency. During the two rice-growing seasons, the HE treatment had 47.8 and 39.7 percentage points lower total NH3 losses, whereas the HY treatment had 12.6 and 48.9 percentage points higher those than the CT treatment. The HE and HY treatments resulted in significantly higher grain yield and ANR in the two seasons. The HE treatment had 11.1 and 18.0 percentage points higher yields than CT, while the HY treatment had 34.6 and 40.4 percentage points higher those than the CT treatment in the 2 years. The ANR was improved by 9.2 and 26.2 percentage points for the HE treatment, and by 9.4 and 15.6 percentage points for the HY treatment compared with the CT treatment. Furthermore, the ratio of ammonia emission to grain yield for HE treatment was 53.6 and 49.1 percentage points lower than CT treatment, and 44.2 and 51.8 percentage points lower than HY treatment during the two seasons, respectively. Therefore, the integrated high-efficiency practice is effective in reducing NH3 loss and increasing rice yield and nitrogen use efficiency (NUE), and can be used for the sustainable development of rice production systems in the Taihu Lake region. |
| [11] | . The main objectives of this paper were to investigate the absorption and utilization of nitrogen applied at the panicle stage in rice for promoting and protecting spikelet and the effect of residual nitrogen on the utilization of nitrogen in the succeeding wheat crop in the rotation system. A field experiment was combined with a mini-plot experiment with15N labelled urea applied at the panicle stage in rice. The experiments included three nutrient management treatments: F, S1 and S2. 126kgNha611, 120kgN ha611, 72kgNha611labeled with 30 atom% excess15N were applied in rice, respectively. (1) Compare to conventional fertilizer management (F), the optimized fertilizer management (S1&S2) reduced the amount of nitrogen applications, whereas the rice and wheat yield did not decrease, and nitrogen use efficiency was improved. (2) At rice harvest, 4.7–10.7% of the fertilizer15N was found in the 0–20cm profile. The fertilizer15N absorbed by the wheat during the period from jointing to heading accounted for 37.0%-51.1% of the total15N absorbed. (3) The sum of the ratio of nitrogen absorption from the rice panicle fertilizer applied to the crops (rice and wheat) and ratio of soil residue nitrogen in the wheat field were ordered S2>S1>F. The optimized fertilization management reduced the loss of the rice nitrogen in the rice–wheat rotation system through improved recycling of rice panicle nitrogen applied in the crop-soil system. |
| [12] | . The loss of nitrogen (N) can be very high in rice ( Oryza sativa L.) fields, particularly in the irrigated rice cropping systems with very poor water control. Previous studies have reported very low (3002%) fertilizer N use efficiency by broadcasting in irrigated cropping systems. The effect of fertilizer N (prilled urea—PU) and briquettes—urea supergranules (USG) on rice yield performance and nutrient uptake was investigated in West Africa. Field experiments were carried out in Sourou valley in Burkina Faso in the wet season of 2012 and dry season of 2013. PU was broadcast applied and USG were point-placed deeply into the soil at 5–702cm using the same fertilizer N rates (5202kg02N02ha 611 ) and two different rice varieties (FKR 19 and NERICA 62N). The results indicate that Fertilizer Deep Placement (FDP) significantly increased grain yields, particularly in the wet season as compared with broadcasting. The FDP applied to NERICA 62N produced the highest tillers and panicles numbers, leading to more yields. In wet season, FDP significantly increased agronomic efficiency by 39.4302% over PU and physiological efficiency by 24.2302%. In the dry season, differences in the average nitrogen use efficiency (NUE) between FDP and PU were not significant. The studies suggest that FDP is genotype and season-specific, and that it can be used by farmers to improve NUE and increase grain yields in the irrigated rice cropping system. Further investigations are underway to understand seasonal and genetic effect on FDP performance. |
| [13] | . Alternate wetting and drying (AWD) irrigation has been widely adopted to replace continuous flooding (CF) irrigation for saving water and increasing water productivity in irrigated rice systems. There is limited information on the performance of controlled-release nitrogen fertilizer (CRNF) under AWD conditions. The objectives of this study were to investigate the effects of four N managements (control, N0; conventional urea at 240kgNha611, UREA; controlled-release bulk blending fertilizer at 240kgNha611, BBF; polymer-coated urea at 240kgNha611, PCU) under CF and AWD water regime on dry matter accumulation (DMA), grain yield, water and N use efficiencies (WUE/NUE) in late-season rice. Compared with CF, AWD significantly reduced the number of irrigation (5 in 2010 and 3 in 2011) and the amount of irrigation water (41.9% in 2010 and 28.0% in 2011). Thus, field water level was shallowed and rainwater storage capacity and usage were improved, leading to reduced surface runoff. AWD performed comparably to or better than CF on plant biomass (root, shoot, panicle, shoot, and whole rice), yield, WUE and NUE, while N fertilization significantly enhanced those parameters. BBF performed comparably with urea on DMA, yield, WUE and NUE, while PCU significantly improved those traits compared with BBF and urea. The interactions of W×N on DMA, grain yield, total N uptake, and NUE were not significant, while those on WUE were significant. The combined AWD and PCU treatment enhanced root and panicle dry matter accumulation and partitioning, effective panicles per m2, spikelets per m2, grain filling and harvest index. As a result, it increased grain yield and subsequently increased WUE and NUE with reduced water input by AWD and enhanced N utilization by PCU. Our results suggested that the new water and N management combination can be an effective means to save water, promote rice production, and improve WUE and NUE for late-season rice. |
| [14] | . A major challenge in rice (Oryza sativa L.) production is to achieve the dual goal of increasing food production and resource use efficiency. This study aimed to investigate if an improved crop management (ICM) could increase grain yield, N use efficiency (NUE), and water use efficiency (WUE). Three rice cultivars were field grown at either Yangzhou or Lianyungang, China. in 2009 and 2010. Three treatments, local farmers' practice (LFP), ICM, and N omission, were conducted. The ICM adopted two new techniques, that is, site-specific N management and irrigation using alternate wetting and moderate drying. Compared with the LFP, the ICM significantly increased percentage of productive tillers, crop growth rate, and contents of cytokinins in plants at mid and late growth stages, nonstructural carbohydrate accumulation in the stem at the heading time, and root oxidation activity, leaf area duration, photosynthetic rate of the flag leaf, and activities of key enzymes involved in sucrose-to-starch conversion in grains during grain filling. On average, the ICM increased grain yield by 14.4%, agronomic NUE (kg grain yield increase per kg N applied) by 64.1%, and WUE for irrigation (grain yield over amount of irrigation water) by 36.4% when compared with the LFP. We conclude that the ICM could increase not only grain yield but also NUE and WUE. Improved physiological performances at latter growth stages contribute to increases in grain yield and resource use efficiency. |
| [15] | . High N loss and low N use efficiency (NUE), caused by high N fertilizer inputs and inappropriate fertilization patterns, have become important issues in the rice (Oryza sativa L.) growing regions of southern China. Changing current farmer fertilizer practice (FFP, 225 kg ha–1 N as three applications, 40% as basal fertilizer, 30% as tillering fertilizer and 30% as jointing fertilizer) to one—time root—zone fertilization (RZF, 225 kg ha–1 N applied once into 10 cm deep holes positioned 5 cm from the rice root as basal fertilizer) will address this problem. A two—year field experiment covering two rice growing regions was conducted to investigate the effect of urea one—time RZF on rice growth, nutrient uptake, and NUE. The highest NH4+–N content for RZF at fertilizer point at 30 d and 60 d after fertilization were 861.8 and 369.9 mg kg–1 higher than FFP, respectively. Rice yield and total N accumulation of RZF increased by 4.3–44.9% and 12.7–111.2% compared to FFP, respectively. RZF reduced fertilizer—N loss by 56.3–81.9% compared to FFP. The NUEs following RZF (mean of 65.8% for the difference method and 43.7% for the labelled method) were significantly higher than FFP (mean of 35.7% for the difference method and 14.4% for the labelled method). In conclusion, RZF maintained substantial levels of fertilizer—N in the root—zone, which led to enhanced rice biomass and N uptake during the early growth stages, increased fertilizer—N residual levels and reduced fertilizer—N loss at harvest. RZF produced a higher yield increment and showed an increased capacity to resist environmental threats than FFP in sandy soils. Therefore, adopting suitable fertilizer patterns plays a key role in enhancing agricultural benefits. |
| [16] | . |
| [17] | . ABSTRACT Hybrid rice (Oryza sativa L.) hectarage has increased substantially in the southern United States and necessitated research into the N nutrition of this new type of rice and how it compares to the traditional pure-line rice. Consequently, a study was conducted utilizing N-15-labeled urea applied at a range of N rates on two silt loam soils differing in native soil N to evaluate and compare the N fertilizer uptake efficiency, the native soil N uptake, and total N uptake of a RiceTec hybrid and a pure-line rice cultivar. The hybrid (60.5 kg N ha(-1)) had greater soil N uptake compared with the pure-line cultivar (51.7 kg N ha(-1)). The hybrid had a higher fertilizer N uptake efficiency (FNUE) compared with the pure-line at the location with the lesser native soil N (62.2 vs. 56.2%, respectively), but had a similar FNUE at the location with the greater soil N (63.8 vs. 60.0%, respectively). Also, the pure-line had a higher FNUE and greater N fertilizer response at the location with the greater soil N while the hybrid had a similar FNUE at both locations. The greater total N uptake by the hybrid compared with the pure-line was due to greater soil N uptake at both locations and fertilizer N uptake at the location with the lower native soil N. The results suggest that if the native soil N is below a critical level a pure-line rice cultivar might benefit from a higher rate of N fertilization to maximize FNUE. |
| [18] | . <p>试验采用田间小区试验，设置7个氮肥用量(N 0、 60、 120、 180、 240、 300和360 kg/hm<sup>2</sup>)，研究了江西省高产田、 中产田和低产田双季稻最佳施氮量，以及不同施氮水平对水稻产量、 氮肥贡献率、 土壤氮素依存率和氮肥利用率的影响。结果表明，低产田、 中产田和高产田分别在施氮量为120、 180和240 kg/hm<sup>2</sup>处理取得高产； 氮肥贡献率在低产田和中产田上大于高产田，且分别在施氮处理为N 120、 180和240 kg/hm<sup>2</sup>达到最大；土壤氮素依存率为高产田>中产田>低产田，且在一定范围内随着施氮量的增加，土壤氮素依存率逐渐降低； 氮肥吸收利用率为低产田>中产田>高产田，氮肥农学效率、 氮肥生理利用率和氮肥偏生产力低、 中、 高产田间差异不大。高、 中、 低产田氮肥农学利用率、 氮肥吸收利用率和氮肥偏生产力随氮肥用量增加而降低，而氮肥生理利用率各施氮处理间变化不大。综合产量和氮肥利用率得出，低产田、 中产田和高产田双季稻适宜施氮量分别为N 120、 180和240 kg/hm<sup>2</sup>。</p> . <p>试验采用田间小区试验，设置7个氮肥用量(N 0、 60、 120、 180、 240、 300和360 kg/hm<sup>2</sup>)，研究了江西省高产田、 中产田和低产田双季稻最佳施氮量，以及不同施氮水平对水稻产量、 氮肥贡献率、 土壤氮素依存率和氮肥利用率的影响。结果表明，低产田、 中产田和高产田分别在施氮量为120、 180和240 kg/hm<sup>2</sup>处理取得高产； 氮肥贡献率在低产田和中产田上大于高产田，且分别在施氮处理为N 120、 180和240 kg/hm<sup>2</sup>达到最大；土壤氮素依存率为高产田>中产田>低产田，且在一定范围内随着施氮量的增加，土壤氮素依存率逐渐降低； 氮肥吸收利用率为低产田>中产田>高产田，氮肥农学效率、 氮肥生理利用率和氮肥偏生产力低、 中、 高产田间差异不大。高、 中、 低产田氮肥农学利用率、 氮肥吸收利用率和氮肥偏生产力随氮肥用量增加而降低，而氮肥生理利用率各施氮处理间变化不大。综合产量和氮肥利用率得出，低产田、 中产田和高产田双季稻适宜施氮量分别为N 120、 180和240 kg/hm<sup>2</sup>。</p> |
| [19] | . . |
| [20] | . This study addressed if long-term combined application of organic manure and inorganic fertilizers could improve the synchrony between nitrogen (N) supply and crop demand. (15) N-labeled urea was applied to micro-plots within three different fertilized treatments (no fertilizer, No-F soil; inorganic NPK fertilizers, NPK soil; and manure plus inorganic NPK fertilizers, MNPK soil) of a long-term field trial (1990-2009) in a dryland wheat field in the south Loess Plateau, China. After one season of wheat harvest, (15) N use efficiency was 20, 58, and 65 % in the No-F, NPK, and MNPK soil, respectively. During the early wheat growth stage, microbial immobilization of applied (15) N was significantly (P < 0.05) highest in the MNPK soil (15.3 %), higher in the NPK soil (12.6 %), and lowest in the No-F soil (7.4 %). Of the (15) N immobilized by the soil microbial biomass, 69 % (NPK soil) to 83 % (MNPK soil) was released between the stem elongation and flowering of wheat. Compared with the NPK soil, the MNPK soil had significantly (P < 0.05) higher grain yield. Our findings highlight that long-term application of organic manure with inorganic fertilizers cannot only improve the synchrony of N supply for crop demand but also increase N use efficiency and grain yield. |
| [21] | . . |
| [22] | . . |
| [23] | . A chloroform-fumigation extraction method with fumigation at atmospheric pressure (CFAP, without vacuum) was developed for measuring microbial biomass C (C BIO ) and N (N BIO ) in water-saturated rice soils. The method was tested in a series of laboratory experiments and compared with the standard chloroform-fumigation extraction (CFE, with vacuum). For both methods, there was little interference from living rice roots or changing soil water content (0.44–0.5565kg kg –1 wet soil). A comparison of the two techniques showed a highly significant correlation for both C BIO and N BIO ( P <0.001) suggesting that the simple and rapid CFAP is a reliable alternative to the CFE. It appeared, however, that a small and relatively constant fraction of well-protected microbial biomass may only be lysed during fumigation under vacuum. Determinations of microbial C and N were highly reproducible for both methods, but neither fumigation technique generated N BIO values which were positively correlated with C BIO . The range of observed microbial C:N ratios of 4–15 was unexpectedly wide for anaerobic soil conditions. Evidence that this was related to inconsistencies in the release, degradation, and extractability of N BIO rather than C BIO came from the observation that increasing the fumigation time from 465h to 4865h significantly increased N BIO but not C BIO . The release pattern of C BIO indicated that the standard fumigation time of 2465h is applicable to water-saturated rice soils. To correct for the incomplete recovery of C BIO , we suggest applying the k C factor of 2.64, commonly used for aerobic soils (Vance et al. 1987), but caution is required when correcting N BIO data. Until differences in fumigation efficiencies among CFE and CFAP are confirmed for a wider range of rice soils, we suggest applying the same correction factor for both methods. |
| [24] | . A method of determining fixed ammonium in soils is described. The soil sample is treated with alkaline KOBr solution to remove exchangeable ammonium and organic nitrogen compounds, and the residue is washed with 0.5M KCl and shaken with 5N HF:1N HCl for 24 hr, the ammonium released by the HF-HCl treatment being determined by steam distilling the soil-acid mixture with KOH. The KOBr treatment effects almost quantitative removal of organic soil nitrogen under conditions which preclude fixation by soil minerals of ammonium released from soil organic matter by this treatment, and evaluation tests indicate that the procedure used to estimate fixed ammonium in the KOBr-pretreatment residue is satisfactory. The method is simple and precise, and it has none of the observed defects of previous methods of estimating fixed ammonium in soils. It gives higher values than the Dhariwal-Stevenson, Bremner, and Mogilevkina methods, and lower values than the Rodrigues and Schachtschabel methods. A modification in which the HF-HCl treatment is performed at 100C for 30 min is described. |
| [25] | . |
| [26] | . 【目的】研究长期不同施肥措施对土壤基础地力和氮磷钾养分吸收利用效率的影响，探明土壤基础地力和氮、磷、钾养分吸收利用效率的相互关系。【方法】采集双季水稻种植制度下33年长期定位施肥试验的不施肥(CK)、施氮磷钾肥(NPK)和氮磷钾肥配施稻草(NPKS)3个处理的土壤，设置施肥与不施肥盆栽试验，监测水稻产量、土壤基础地力产量和基础地力贡献率、水稻氮磷钾养分吸收量、氮磷钾养分利用效率，分析氮、磷、钾利用效率对土壤基础地力贡献率的响应。【结果】早晚稻土壤基础地力产量和基础地力贡献率三个处理土壤大小顺序均为 NPKS > NPK > CK，NPKS处理土壤早晚稻两季平均基础地力产量和基础地力贡献率较 CK处理土壤分别增加113.8%和93.7%，NPK处理分别增加100.7%和81.9%。在同一施肥水平条件下，早、晚稻均以土壤基础地力较高的 NPKS处理氮、磷、钾肥偏生产力，土壤养分依存率，氮、磷、钾素收获指数较高，氮、磷、钾肥回收利用率，肥料农学效率，肥料对产量的贡献率则较低。回归分析表明，氮、磷肥回收利用率，氮、磷、钾肥农学效率，氮、钾素生理利用率均随土壤基础地力贡献率的提高呈显著或极显著降低；氮、磷、钾肥偏生产力，氮、磷、钾素土壤依存率随土壤基础地力贡献率的提高呈显著或极显著提高。【结论】长期施氮磷钾肥或长期氮磷钾肥配施稻草均能提高土壤基础地力，以长期氮磷钾肥配施稻草的效果更显著。在较高基础地力土壤上生产，可以在保证作物高产稳产的情况下实现减量化施肥，实现农业生产的可持续性。 . 【目的】研究长期不同施肥措施对土壤基础地力和氮磷钾养分吸收利用效率的影响，探明土壤基础地力和氮、磷、钾养分吸收利用效率的相互关系。【方法】采集双季水稻种植制度下33年长期定位施肥试验的不施肥(CK)、施氮磷钾肥(NPK)和氮磷钾肥配施稻草(NPKS)3个处理的土壤，设置施肥与不施肥盆栽试验，监测水稻产量、土壤基础地力产量和基础地力贡献率、水稻氮磷钾养分吸收量、氮磷钾养分利用效率，分析氮、磷、钾利用效率对土壤基础地力贡献率的响应。【结果】早晚稻土壤基础地力产量和基础地力贡献率三个处理土壤大小顺序均为 NPKS > NPK > CK，NPKS处理土壤早晚稻两季平均基础地力产量和基础地力贡献率较 CK处理土壤分别增加113.8%和93.7%，NPK处理分别增加100.7%和81.9%。在同一施肥水平条件下，早、晚稻均以土壤基础地力较高的 NPKS处理氮、磷、钾肥偏生产力，土壤养分依存率，氮、磷、钾素收获指数较高，氮、磷、钾肥回收利用率，肥料农学效率，肥料对产量的贡献率则较低。回归分析表明，氮、磷肥回收利用率，氮、磷、钾肥农学效率，氮、钾素生理利用率均随土壤基础地力贡献率的提高呈显著或极显著降低；氮、磷、钾肥偏生产力，氮、磷、钾素土壤依存率随土壤基础地力贡献率的提高呈显著或极显著提高。【结论】长期施氮磷钾肥或长期氮磷钾肥配施稻草均能提高土壤基础地力，以长期氮磷钾肥配施稻草的效果更显著。在较高基础地力土壤上生产，可以在保证作物高产稳产的情况下实现减量化施肥，实现农业生产的可持续性。 |
| [27] | . 【目的】研究双季稻种植制度下,连续3年施肥与不施肥对不同肥力土壤基础地力产量、基础地力贡献率、土壤氮磷钾表观平衡和土壤养分变化的影响,为不同肥力土壤基础地力培育及土壤肥力维持和提升提供参考。【方法】从32年长期施用不同肥料定位试验的不施任何肥料（CK）、施氮磷钾肥（NPK）和氮磷钾肥配施稻草（NPKS）处理采取土壤,分别代表3种不同肥力水平,设置连续3年施肥与不施肥处理的盆栽试验,监测双季水稻产量、土壤基础地力产量、基础地力贡献率和土壤氮磷钾养分的变化。【结果】在试验期间,不同肥力土壤的早晚稻基础地力产量、基础地力贡献率均表现为：NPKS处理土壤〉NPK处理土壤〉CK处理土壤,且随着试验年限的延长,不同肥力土壤之间的差异呈逐渐缩小趋势,到试验第3年,不同肥力土壤之间的差异变得不显著。无论施肥或不施肥,初始肥力越高的土壤经3年6季水稻种植,由作物收获带走的氮、磷、钾养分越多。不同肥力土壤在连续施肥条件或不施肥条件下,肥力养分变化规律存在较大差异,这种差异与水稻种植体系中养分输入-输出平衡状况有一定关系。【结论】初始肥力越高的土壤如果连续不施肥,其基础地力下降得越快。因此,对于地力水平较低的土壤应注重合理施肥,培育和提高农田土壤肥力和基础地力;地力水平较高的土壤也应注意高效合理补充养分,以维持土壤较高的肥力水平和持续生产力。 . 【目的】研究双季稻种植制度下,连续3年施肥与不施肥对不同肥力土壤基础地力产量、基础地力贡献率、土壤氮磷钾表观平衡和土壤养分变化的影响,为不同肥力土壤基础地力培育及土壤肥力维持和提升提供参考。【方法】从32年长期施用不同肥料定位试验的不施任何肥料（CK）、施氮磷钾肥（NPK）和氮磷钾肥配施稻草（NPKS）处理采取土壤,分别代表3种不同肥力水平,设置连续3年施肥与不施肥处理的盆栽试验,监测双季水稻产量、土壤基础地力产量、基础地力贡献率和土壤氮磷钾养分的变化。【结果】在试验期间,不同肥力土壤的早晚稻基础地力产量、基础地力贡献率均表现为：NPKS处理土壤〉NPK处理土壤〉CK处理土壤,且随着试验年限的延长,不同肥力土壤之间的差异呈逐渐缩小趋势,到试验第3年,不同肥力土壤之间的差异变得不显著。无论施肥或不施肥,初始肥力越高的土壤经3年6季水稻种植,由作物收获带走的氮、磷、钾养分越多。不同肥力土壤在连续施肥条件或不施肥条件下,肥力养分变化规律存在较大差异,这种差异与水稻种植体系中养分输入-输出平衡状况有一定关系。【结论】初始肥力越高的土壤如果连续不施肥,其基础地力下降得越快。因此,对于地力水平较低的土壤应注重合理施肥,培育和提高农田土壤肥力和基础地力;地力水平较高的土壤也应注意高效合理补充养分,以维持土壤较高的肥力水平和持续生产力。 |
| [28] | . . |
| [29] | . 【目的】研究江汉平原地区不同基础地力土壤和优化施肥对水稻产量和氮肥利用率的影响。【方法】以江汉平原水稻主推品种丰两优香一号为试验材料，通过3年田间小区试验，考察分析土壤基础地力不同的稻田优化施肥、农民习惯施肥和不施肥处理的产量、氮肥贡献率、土壤氮素依存率和氮肥利用率等的差异。【结果】土壤基础地力不同的稻田均是优化施肥处理的产量最高，与农民习惯施肥处理比较，高地力和低地力稻田优化施肥处理的产量分别平均提高6.9%和5.0%；与不施肥处理比较，产量分别平均提高17.3%和30.3%。与农民习惯施肥处理比较，优化施肥处理的氮肥吸收利用率、农学利用率和偏生产力均大幅度提高。高地力稻田土壤氮素依存率高、氮肥贡献率小、施肥增产的潜力小；低地力稻田土壤氮素依存率低、氮肥贡献率大、施肥增产的潜力大。【结论】优化施肥可以降低水稻产量对土壤基础地力的依赖，提高氮肥利用率。 . 【目的】研究江汉平原地区不同基础地力土壤和优化施肥对水稻产量和氮肥利用率的影响。【方法】以江汉平原水稻主推品种丰两优香一号为试验材料，通过3年田间小区试验，考察分析土壤基础地力不同的稻田优化施肥、农民习惯施肥和不施肥处理的产量、氮肥贡献率、土壤氮素依存率和氮肥利用率等的差异。【结果】土壤基础地力不同的稻田均是优化施肥处理的产量最高，与农民习惯施肥处理比较，高地力和低地力稻田优化施肥处理的产量分别平均提高6.9%和5.0%；与不施肥处理比较，产量分别平均提高17.3%和30.3%。与农民习惯施肥处理比较，优化施肥处理的氮肥吸收利用率、农学利用率和偏生产力均大幅度提高。高地力稻田土壤氮素依存率高、氮肥贡献率小、施肥增产的潜力小；低地力稻田土壤氮素依存率低、氮肥贡献率大、施肥增产的潜力大。【结论】优化施肥可以降低水稻产量对土壤基础地力的依赖，提高氮肥利用率。 |
| [30] | . Efficient management of rice () nutrition across soils ranging from organic to mineral soils varies widely due to large contributions of nutrients, including N, from the indigenous supply. This study tested the hypothesis that the indigenous N supply (INS) would increase if the SOC content of the rice paddy soil increased, evaluated across a wide range of soil organic carbon (SOC) content. The INS, defined as N uptake from N omission plots, was estimated from 54 plots over a three year period at two locations in the Sacramento-San Joaquin Delta over a range of SOC from 6 to 232 g SOC kg. Additionally ten N rate trials (0 to 160 kg N applied ha) were conducted concurrent with the N omission plots. The INS did not increase as SOC increased across the entire SOC gradient, and instead exhibited a concave quadratic trend across the SOC gradient; greatest in the 110 170 g SOC kgrange and lower in sites with less than 110 g SOC kgor more than 170 g SOC kg. Consequently, positive yield response to N fertilizer was observed in soils with low INS, with no positive yield response on soils with high INS. This study indicates that the INS can be predicted by the SOC content, hence fertilizer-N recommendations should include considerations for SOC content. |
| [31] | . Chemical N input is essential for high rice yields. However, low recovery efficiency of chemical fertilizer N with flooding irrigation in the anthropogenic-alluvial soil resulted in N lost from the rice field in Ningxia Irrigation Region in the upper reaches of the Yellow River. With the technique of stable isotope 15N-traced urea, we conducted two years experiment to estimate the recovery efficiency and loss of applied chemical fertilizer in a rice field. The three fertilizer N treatments included 300kgha611 (N300, the conventional application rate), 240kgha611 (the optimized N application amount, N240) and no N fertilizer application treatment (CK). We estimated the recovery of 15N-labelled urea in grain, straw and root of rice and residues in soil profile. The 15N not accounted for in the plant and soil was presumably lost. The results showed that more efficient use of N fertilizer could allow current N application rates to reduce by 20%. This would still maintain crop yields while substantially reducing N losses to the environment. The high N fertilizer application increased the N uptake by rice derived from fertilizer, and the amount of N rice taken up from soil reduced correspondingly, which resulted in the higher N surplus in soil. Under the conventional irrigation and fertilizer management level, the recovery rate of 15N-labelled urea in rice–soil system was about 48–49%. The 15N-labelled fertilizer recovery in rice plant (Ndff) was 26–30%. In the paddy soil profiles of 0–90cm, the residual of 15N-labelled fertilizer in soil (Ndfs) were 54–70kgha611, and N residual rate in soils were 18–23%. The annual N loss from the rice field in the Irrigation Region was 28,865tons. The distribution of 15N abundance variability in different soil profile indicated that fertilizer N leached into the deep soil layers along with irrigation water as a result of continuous yearly rice planting. Optimization of nitrogen fertilizer can significantly reduce the amount of N residuals and N loss from the paddy field. Compared with N300, optimized nitrogen fertilizer application could decrease the loss of fertilizer N by 22–34kgha611, and reduce the amount of N surplus by 26–33kgha611 while the dry matter of rice increased 8–15% and N uptake by rice increased 2–6%. Considering the high food production and the minimum environmental threat, we should fully take into account the optimization application by reducing fertilizer N inputs. However, the interaction between irrigation management and N application rate on N use efficiency in alkaline anthropogenic-alluvial soil needs to be further studied. |
| [32] | . 作为全球活性氮制造量和氮肥消费量均最大的国家,中国农业生态系统的氮平衡问题受到了国内外广泛的关注。普遍认为中国农田施氮过量问题突出,并产生了严重的环境污染。为全面了解中国农业生态系统氮的来源和去向,找出引起氮肥消费量高的原因,本研究运用氮循环基本原理,以2010年为例,根据近年来发表的文献和国家统计资料,详细讨论了不同空间尺度上中国农业生态系统的氮输出和输入,重点分析了作物-土壤系统氮循环与氮平衡的特征。2010年中国农业生态系统氮投入总体上过量,其数量基本上相当于经生物地球化学循环返回作物–土壤系统的氮量,大致在5 Tg N左右。在全国水平上,2010年化肥和有机肥带入农田的氮量,相等于作物吸氮量和农田氮损失量之和;由于化学氮肥流向的多样化,如林、牧、渔业和城市绿化等的氮肥消耗,以及部分经济作物包括果树和蔬菜,特别是设施蔬菜的高量施氮,总体上粮食作物过量施氮的问题并不十分突出。在耕地资源有限(占全球8%的耕地面积,养活20%的世界人口)、有机废弃物中氮养分循环利用率低于30%、豆科作物播种面积较少且生物固氮占农田总氮投入不足15%的情况下,中国的农业生产只有依靠氮肥。然而,中国氮肥消费存在着很大的地区差异,在土地生产力水平较高的黄淮海、长江中下游和珠江三角洲地区,单位农作物播种面积的施氮量显著高于全国平均水平。这些地区氮肥消费量较大与粮食单产高、复种指数高和豆科作物种植比例低有密切关系。因此,为保证人们不断增长的食物需求和膳食结构的改善,加之土壤基础肥力相对较低,农田化学氮肥投入较高具有一定的合理性。然而,农业生产过程中发生的氮损失,既浪费了资源,也污染了环境。损失进入大气和水中活性氮以及环境中新产生的活性氮,经生物地球化学循环过程以大气沉降和灌溉水返回农田,已经成为作物-土壤系统氮的重要投入项。由于农业生态系统中氮素转化过程的多样性和生物地球化学循环的复杂性,循环过程中的氮损失不可避免。只有通过在不同空间尺度上对氮素进行优化管理,才能将氮损失降低到最低。在保证粮食安全的基础上,尽可能地降低农田施氮的环境风险,需要多学科、多部门的协作与共同努力,在不同空间尺度上实现氮优化管理、达到降低农业生态系统氮肥投入的目的。 . 作为全球活性氮制造量和氮肥消费量均最大的国家,中国农业生态系统的氮平衡问题受到了国内外广泛的关注。普遍认为中国农田施氮过量问题突出,并产生了严重的环境污染。为全面了解中国农业生态系统氮的来源和去向,找出引起氮肥消费量高的原因,本研究运用氮循环基本原理,以2010年为例,根据近年来发表的文献和国家统计资料,详细讨论了不同空间尺度上中国农业生态系统的氮输出和输入,重点分析了作物-土壤系统氮循环与氮平衡的特征。2010年中国农业生态系统氮投入总体上过量,其数量基本上相当于经生物地球化学循环返回作物–土壤系统的氮量,大致在5 Tg N左右。在全国水平上,2010年化肥和有机肥带入农田的氮量,相等于作物吸氮量和农田氮损失量之和;由于化学氮肥流向的多样化,如林、牧、渔业和城市绿化等的氮肥消耗,以及部分经济作物包括果树和蔬菜,特别是设施蔬菜的高量施氮,总体上粮食作物过量施氮的问题并不十分突出。在耕地资源有限(占全球8%的耕地面积,养活20%的世界人口)、有机废弃物中氮养分循环利用率低于30%、豆科作物播种面积较少且生物固氮占农田总氮投入不足15%的情况下,中国的农业生产只有依靠氮肥。然而,中国氮肥消费存在着很大的地区差异,在土地生产力水平较高的黄淮海、长江中下游和珠江三角洲地区,单位农作物播种面积的施氮量显著高于全国平均水平。这些地区氮肥消费量较大与粮食单产高、复种指数高和豆科作物种植比例低有密切关系。因此,为保证人们不断增长的食物需求和膳食结构的改善,加之土壤基础肥力相对较低,农田化学氮肥投入较高具有一定的合理性。然而,农业生产过程中发生的氮损失,既浪费了资源,也污染了环境。损失进入大气和水中活性氮以及环境中新产生的活性氮,经生物地球化学循环过程以大气沉降和灌溉水返回农田,已经成为作物-土壤系统氮的重要投入项。由于农业生态系统中氮素转化过程的多样性和生物地球化学循环的复杂性,循环过程中的氮损失不可避免。只有通过在不同空间尺度上对氮素进行优化管理,才能将氮损失降低到最低。在保证粮食安全的基础上,尽可能地降低农田施氮的环境风险,需要多学科、多部门的协作与共同努力,在不同空间尺度上实现氮优化管理、达到降低农业生态系统氮肥投入的目的。 |
| [33] | . The ability to predict C cycle responses to temperature changes depends on the accurate representation of temperature sensitivity (Q10) of soil organic matter (SOM) decomposition in C models for different C pools and soil depths. Theoretically, Q10 of SOM decomposition is determined by SOM quality and availability (referred to here as SOM protection). Here, we focus on the role of SOM protection in attenuating the intrinsic, SOM quality dependent Q10. To assess the separate effects of SOM quality and protection, we incubated topsoil and subsoil samples characterized by differences in SOM protection under optimum moisture conditions at 25 C and 35 C. Although lower SOM quality in the subsoil should lead to a higher Q10 according to kinetic theory, we observed a much lower overall temperature response in subsoil compared with the topsoil. Q10 values determined for respired SOM fractions of decreasing lability within the topsoil increased from 1.9 for the most labile to 3.8 for the least labile respired SOM, whereas corresponding Q10 values for the subsoil did not show this trend (Q10 between 1.4 and 0.9). These results indicate the existence of a limiting factor that attenuates the intrinsic effect of SOM quality on Q10 in the subsoil. A parallel incubation experiment of 13C-labeled plant material added to top- and subsoil showed that decomposition of an unprotected C substrate of equal quality responds similarly to temperature changes in top- and subsoil. This further confirms that the attenuating effect on Q10 in the subsoil originates from SOM protection rather than from microbial properties or other nutrient limitations. In conclusion, we found experimental evidence that SOM protection can attenuate the intrinsic Q10 of SOM decomposition. |
| [34] | . Analyzing attainable yield (YA), yield gap (YG), and nutrient use efficiency (NUE) will help develop and inform agricultural policies and strategies to increase grain yield. Data from a total of 2218 on-farm rice experiments were collected between 2000 and 2013 from the main rice production areas of China. Common treatments in each study included the optimum nutrient management (OPT), farmers' fertilizer practices (FP) and nutrient omission treatments which were used to assess YG, yield response to nutrient (YR), and NUE. This study used meta-analysis and ANOVA to evaluate differences across the four rice planting seasons (early, middle, late, and single-season rice). The average YA from the OPT was 8.5tha611, and the yield gap between OPT and FP was 0.6tha611. The YR to nitrogen (N), phosphorus (P), and potassium (K) averaged 2.4, 0.9, and 1.0tha611across all sites, respectively. Results using the Pearson' correlation analysis showed significantly negative coefficients for YR to soil nutrient contents and soil organic matter. The large variations in YR were attributed to differences in climatic conditions and soil indigenous nutrient supplies. As compared to FP, the average recovery efficiency (RE) to N, P, and K with OPT increased by 10.1, 5.0 and 8.6 percent across all sites, respectively. In order to narrow the YG and increase NUE, effective soil, plant, nutrient management measures, advances in knowledge and technologies would be required to sustain higher crop production. |
| [35] | . 为阐明不同肥力区域,施氮水平对土壤微生物学特性的影响,采用室内分析法系统比较3个肥力条件下,5个施氮水平(不施氮、70％×优化施氮、优化施氮、130％×优化施氮和农民习惯性施氮)对土壤微生物生物量碳、氮以及酶活性的影响.结果表明:较高肥力有利于微生物生物量氮(MBN)的保蓄.随氮肥施用水平提高,微生物所同化的氮在各肥力区均有所增加,继续增大尿素用量(312 kg/hm2),中、低肥力土壤MBN的数值有所回落;而肥力差异未对微生物生物量碳(MBC)产生规律性的影响.低肥力条件下,施氮对MBC的影响表现为先抑制后促进的作用,高、中肥力则与之相反;优化施氮与农民习惯性施氮均有助于蔗糖酶和脲酶活性的提高;在高、低肥力区域,随施氮水平增加,过氧化氢酶活性先降低而后升高,与在中等肥力区所表现的规律恰好相反.与无氮对照(N0)相比,70％优化施氮对土壤蛋白酶活性有抑制作用,而随氮肥用量增加,蛋白酶活性渐趋升高,尿素用量为312 kg/hm2时的蛋白酶活性达最大值;适量施氮范围内(0～270 kg/hm2),增施尿素有利于碱性磷酸酶活性的提升. . 为阐明不同肥力区域,施氮水平对土壤微生物学特性的影响,采用室内分析法系统比较3个肥力条件下,5个施氮水平(不施氮、70％×优化施氮、优化施氮、130％×优化施氮和农民习惯性施氮)对土壤微生物生物量碳、氮以及酶活性的影响.结果表明:较高肥力有利于微生物生物量氮(MBN)的保蓄.随氮肥施用水平提高,微生物所同化的氮在各肥力区均有所增加,继续增大尿素用量(312 kg/hm2),中、低肥力土壤MBN的数值有所回落;而肥力差异未对微生物生物量碳(MBC)产生规律性的影响.低肥力条件下,施氮对MBC的影响表现为先抑制后促进的作用,高、中肥力则与之相反;优化施氮与农民习惯性施氮均有助于蔗糖酶和脲酶活性的提高;在高、低肥力区域,随施氮水平增加,过氧化氢酶活性先降低而后升高,与在中等肥力区所表现的规律恰好相反.与无氮对照(N0)相比,70％优化施氮对土壤蛋白酶活性有抑制作用,而随氮肥用量增加,蛋白酶活性渐趋升高,尿素用量为312 kg/hm2时的蛋白酶活性达最大值;适量施氮范围内(0～270 kg/hm2),增施尿素有利于碱性磷酸酶活性的提升. |
| [36] | . High soil organic matter content may improve synchronization between N supply and crop demand. To test this hypothesis, we compared the fate of N-15-labeled fertilizer in soil with different management history. The soils had received no fertilizer (No-F soil), inorganic N, P. and K fertilizer (NPK soil), or manure plus N, P. and K fertilizer (MNPK soil) as part of a 19-year long-term fertilization trial. The N use efficiency (NUE) of wheat (Triticum aestiyum L.) was 62% in the MNPK soil, higher than that in the NPK soil (50% NUE), and in the No-F soil (13% NUE). At wheat harvest, 38% of the fertilizer N-15 remained in the 0-100 cm depth of the MNPK soil, significantly less that the amount of fertilizer N-15 that remained in the NPK soil (45%) or in the No-F soil (88%). More than 50% of the fertilizer N-15 in the No-F soil had leached below the 20 cm depth by wheat harvest, significantly more than in the NPK or MNPK soils. The amount of immobilized N-15 at wheat stem elongation was significantly (P<0.05) greater in the MNPK soil than in the NPK soil. The mineralization of immobilized N-15 between stem elongation and flowering was also significantly higher in the MNPK soil than in the NPK soil (P<0.05). The succeeding maize (Zea mays L.) crop took up 9% of the fertilizer N-15 in the No-F soil, 6% of the fertilizer N-15 in the NPK soil, and 2% of the fertilizer N-15 in the MNPK soil. Combined soil profile and crop removal analyses at wheat harvest accounted for nearly 100% of the fertilizer N-15 for all three soils. However, only 45% of the fertilizer N-15 added to the No-F soil could be accounted for at maize harvest, significantly less than the recovery rate in the NPK (83%) and MNPK (85%) soils (P<0.01). These results indicate that the fertilizer N-15 was mainly lost from these soils during the maize growing season. We conclude that the combined application of manure and inorganic fertilizers improves synchrony between N supply and crop demand, thus reducing N losses from agriculture. (C) 2012 Elsevier B.V. All rights reserved. |
| [37] | . 2006和2007年，在桶栽条件下，以早稻（三系籼型杂交稻金优253）为试材，应用15N示踪技术研究了稻草还田免耕、免耕、稻草还田常耕、常耕4种栽培方式对水稻氮素吸收利用与分配特性的影响。结果表明，1）水稻植株吸收的氮肥数量及其在体内的分配与土壤耕作方式密切相关； 免耕提高了水稻对肥料氮的吸收比率及在子粒和根中的分配比率，但降低了在叶和茎中的分配比率。2）免耕水稻产量和氮素吸收总量与常耕水稻差异不显著，但免耕水稻吸收的氮素中来源于肥料的比例比常耕水稻的大； 免耕水稻的氮肥回收效率高于常耕水稻，但氮素的稻谷生产效率差异不明显。3）稻草还田对氮肥的吸收利用有显著的影响。免耕条件下，稻草还田降低了基肥和分蘖肥氮素的积累量，增加了穗肥氮素积累量，氮肥总积累量呈下降趋势； 常耕条件下，稻草还田提高了各个时期的肥料氮素积累量，氮肥的总积累量增加显著。4）稻草还田提高了免耕水稻和常耕水稻产量，2007年其差异达显著水平。免耕条件下稻草还田降低了氮素的回收效率，但常耕条件下稻草还田提高了氮肥的回收效率。 . 2006和2007年，在桶栽条件下，以早稻（三系籼型杂交稻金优253）为试材，应用15N示踪技术研究了稻草还田免耕、免耕、稻草还田常耕、常耕4种栽培方式对水稻氮素吸收利用与分配特性的影响。结果表明，1）水稻植株吸收的氮肥数量及其在体内的分配与土壤耕作方式密切相关； 免耕提高了水稻对肥料氮的吸收比率及在子粒和根中的分配比率，但降低了在叶和茎中的分配比率。2）免耕水稻产量和氮素吸收总量与常耕水稻差异不显著，但免耕水稻吸收的氮素中来源于肥料的比例比常耕水稻的大； 免耕水稻的氮肥回收效率高于常耕水稻，但氮素的稻谷生产效率差异不明显。3）稻草还田对氮肥的吸收利用有显著的影响。免耕条件下，稻草还田降低了基肥和分蘖肥氮素的积累量，增加了穗肥氮素积累量，氮肥总积累量呈下降趋势； 常耕条件下，稻草还田提高了各个时期的肥料氮素积累量，氮肥的总积累量增加显著。4）稻草还田提高了免耕水稻和常耕水稻产量，2007年其差异达显著水平。免耕条件下稻草还田降低了氮素的回收效率，但常耕条件下稻草还田提高了氮肥的回收效率。 |
