Optimizing the Nitrogen Management Strategy for Winter Wheat in the North China Plain Using Rapid Soil and Plant Nitrogen Measurements

Excessive nitrogen (N) fertilizer with improper split-application in small-scale farming is widespread for reducing N use efficiency and polluting the environment. The objective of this study was to develop a strategy for providing winter wheat with twice-topdressing N by quickly measuring the soil and plant N status. During the period 2009–2011, a field experiment was conducted for winter wheat cultivar Zhongmai-175 in the North China Plain. The mineral N (Nmin) pool at a soil depth of 0–90 cm and topdressing N twice, as total N supply, was gradually increased from 0 to 420 kg N ha^–1 to mimic the farmers´ practices. Measurements with the Soil Plant Analysis Development (SPAD) meter were taken on the uppermost fully expanded leaf, and the SPAD index was expressed relative to SPAD readings of sufficiently fertilized plants. Grain yield exhibited linear-plus-plateau responses to total N supply with a significant difference between years, the r² ranged from 0.73 to 0.94. With a basal N application of 30 kg ha^–1, the soil Nmin at 0–90 cm supplemented by twice-topdressing N (1:1 ratio) at Zadoks growth stage (ZGS) 22–23 in early spring and ZGS 47–52 was required at 150–165 kg N ha^–1 to achieve a maximum grain yield of 3.9–5.3 t ha^–1. The SPAD index exhibited a strong exponential response to N supply irrespective of plant growth stage and year (r² = 0.95–0.97); the value of 0.94 was critical in denoting N deficiency from sufficiency status. The N topdressing at ZGS 47–52 could be precisely modified/estimated by the equation y = 161.7–218x^5.16, where x is the SPAD index. Since SPAD readings varied significantly from year to year, our study suggests that it might be difficult to precisely manage field N for winter wheat.     

不同施氮玉米田土壤线虫群落特征及对土壤质量的指示作用

在甘肃省玉米生产中存在长期过量施用氮肥的问题,导致农产品品质下降、地下水污染、耕地土壤质量退化等问题,土壤线虫作为指示生物能在一定程度上反映出土壤生态系统的质量状况.在甘肃省榆中县玉米田进行了0(CK)、5、10、15 g N/(m2·a)4个不同施氮水平的处理,分析了各处理对土壤线虫群落的多度、属丰富度、成熟度指数、...     

旱地春玉米地表覆盖对土壤硝态氮残留的影响

在山西晋中旱塬进行了6年定点定位田间春玉米试验,研究了旱地不同地表覆盖栽培模式对土壤硝态氮残留累积的影响。结果表明,不同覆盖耕作处理对春玉米吸氮量有显著影响,地表覆盖处理春玉米吸氮量均显著高于无覆盖处理,比无覆盖处理增加10.04%~26.29%;种植春玉米6a后,无覆盖(CK)、渗水地膜覆盖(S)、渗水地膜与行间秸秆覆盖(SJ)、普通地膜覆盖(P)、普通地膜与行间秸秆覆盖(PJ)和秸秆覆盖(J)处理中0—300cm土层硝态氮储量依次为818.32,555.42,450.25,421.49,511.49,399.96kg/hm2,CK处理NO3--N主要分布于60-220cm土层,S、SJ、P、PJ和J处理NO3--N主要分布于160—300cm土层;不同降水年型,地表覆盖均能降低氮素在土壤中的累积,但其累积深度有所不同;干旱年份,地表覆盖处理增加0—100cm土层土壤硝态氮的累积,有效降低深层土壤硝态氮的累积;丰水年,地表覆盖处理增加了深层土壤中的硝态氮累积,甚至部分肥料氮已被淋洗到玉米根区以外。因此,应采取合理的覆盖耕作措施减少土壤剖面中NO3--N的累积量。     

土壤类型和施氮量对连作春玉米产量及氮素平衡的影响

以吉林省春玉米连作体系为研究对象,采用多因素方差分析的方法,对多年田间定位试验结果进行分析比较,以探讨土壤类型变异对土壤―作物系统氮素平衡的影响。通过在相同气候条件下,2种土壤类型(黑土(黏化湿润均腐土)和风砂土(湿润冲积新成土))上开展的连续4年的氮肥施用量(0、168、312 kg hm~(-2))田间定位试验,研究了不同土壤类型间玉米产量、氮素矿化、残留及氮素表观损失的差异。结果表明,土壤类型显著影响玉米产量,黑土的玉米籽粒产量较高(6 469~10 106 kg hm~(-2)),平均为8 623 kg hm~(-2),风砂土的玉米籽粒产量较低(1 386~8 196kg hm~(-2)),平均为5911 kg hm~(-2);黑土和风砂土玉米籽粒产量的年际间(2009―2012年)变异系数分别为13.4%和59.1%,黑土的玉米籽粒产量稳定性显著大于风砂土;黑土连续4季氮素总表观矿化量为328 kg hm~(-2),为风砂土的2.2倍;受土壤质地影响,黑土收获后0~100 cm土层土壤矿质氮残留量为99~321 kg hm~(-2),显著高于风砂土(38~77 kg hm~(-2));在中等施氮(168 kg hm~(-2))条件下,黑土与风砂土的氮肥表观损失量无显著差异,分别为320 kg hm~(-2)和315 kg hm~(-2);当施氮量增加至312 kg hm~(-2)时,黑土和风砂土的氮肥表观损失量均显著增加,且风砂土的氮肥表观损失量达到827 kg hm~(-2),显著高于黑土。由于受土壤质地和土壤供肥能力的影响,土壤类型会对玉米产量、氮素矿化和表观损失有一定的影响,因此,在氮肥优化管理中应考虑土壤类型的变异。     

畦灌不同施肥模式对夏玉米田间水氮分布的影响

为了探究夏玉米畦灌条件下适宜的灌溉施肥模式,在大田试验条件下对不同施肥方式(液施和撒施)、液施不同施肥时机和不同入畦流量下土壤水氮空间分布状况及其变化趋势进行了研究。结果表明,灌后2d土壤水分空间分布差异明显小于硝态氮,适当增大入畦流量有助于改善沿畦长方向土壤水分空间分布均匀性。灌后2d不同处理间作物有效根系层土壤硝态氮和土壤水分的贮存效率(土壤有效根系层土壤硝态氮占0—100cm土层中硝态氮的比重)变化都不明显。入畦流量相同时,液施情况下硝态氮沿畦长分布均匀性(介于86.1%~96.9%之间)高于撒施(介于89.3%~89.7%之间)。基于入畦单宽流量为4L/(s·m)、灌水至畦长33%处时均匀施肥的畦灌施肥模式,玉米根系层中土壤水氮含量比重较高,而且土壤水分与土壤硝态氮沿畦长分布均匀性最好,从而形成了有助于作物吸收的均匀的土壤水氮空间分布状态。     

地下部分隔对蚕豆/玉米间作氮素吸收和土壤硝态氮残留影响

利用田间试验,探讨了地下部分隔对蚕豆/玉米间作氮素吸收和土壤硝态氮残留的影响,结果表明:蚕豆/玉米间作,蚕豆不分隔条件下籽粒和秸秆吸氮量比分隔分别增加20 10%,34 43%;玉米不分隔条件下籽粒吸氮量与分隔近似,但秸秆吸氮量比分隔减少13 04%;蚕豆和玉米不分隔条件下土壤硝态氮累积量都高于分隔。蚕豆/空带间作,蚕豆不分隔籽粒吸氮量高于分隔,但土壤硝态氮累积量没有差异。空带/玉米间作,地下部分隔与否,作物吸氮量和土壤硝态氮累积量都没有差异。     

减量施氮及秸秆深埋对春玉米地土壤电导率和硝态氮淋溶的影响

通过在中国科学院长武黄土高原农业生态试验站半覆膜种植春玉米大田试验,研究了减氮及秸秆深埋对土壤电导率、土壤硝态氮淋溶和玉米产量的影响,旨在为提高氮肥利用效率和保护环境提供理论依据。试验设5个处理3个重复,处理包括不施氮(CK)、常规施氮(CON1,N 250kg/hm2)、常规施氮加秸秆(CON2,N 250kg/hm2+秸秆)、减量施氮(CR1,N 200kg/hm2)和减量施氮加秸秆(CR2,N 200kg/hm2+秸秆)。测量了春玉米各生育期土层剖面土壤电导率、收获期土壤硝态氮含量和春玉米产量。结果表明:土壤电导率在分蘖期、拔节期40—150cm土层出现峰值,在抽穗期、成熟期40—200cm土层出现峰值,峰值范围下移。在0—150cm土层范围内,土壤电导率整体呈现CON2CON1,CR2CR1。在0—150cm土层范围内,常规施氮土壤电导率高于减量施氮。与常规施氮相比,减量施氮减少了土壤剖面硝态氮含量,同时,采取秸秆深埋措施也能减少土壤剖面硝态氮含量,并延缓硝态氮的淋溶下移。与常规施氮相比,减量20%施氮增产9.59%。施氮条件下,秸秆深埋时,有利于提高作物产量,提高氮肥增产潜力。秸秆深埋有利于提高土壤电导率,减少土壤硝态氮含量,阻控土壤硝态氮向下淋溶,提高玉米产量。     

秸秆与地膜覆盖条件下旱作玉米田土壤氮组分生长季动态

研究不同覆盖措施下农田土壤全氮及其活性和半活性组分在作物生长季的动态变化,有助于深入理解农田土壤氮循环过程。基于黄土高原8年春玉米覆盖定位试验,系统分析了土壤全氮、矿质氮、微生物量氮、潜在可矿化氮以及颗粒有机氮在玉米不同生育期的动态特征。试验包括全生育期9 000kg/hm2秸秆覆盖、全生育期地膜覆盖和不覆盖对照3个处理。结果表明:(1)除硝态氮和铵态氮在苗期上升外,秸秆和地膜覆盖下土壤全氮及其组分含量在春玉米生育期基本呈苗期下降、拔节期上升、大喇叭口—抽雄期下降、灌浆和收获期回升的变化趋势;(2)与对照相比,秸秆覆盖提高了大多数生育时期0—40cm土层全氮和硝态氮含量及0—20cm土层铵态氮含量,提高各生育时期0—40cm土层微生物量氮、潜在可矿化氮以及颗粒有机氮含量;(3)地膜覆盖较对照提高大多数生育时期0—40cm土层硝态氮和0—20cm土层铵态氮含量,降低作物生育后期0—20cm土层全氮和0—40cm土层颗粒有机氮含量,降低大多数时期0—40cm土层微生物量氮和10—20cm土层潜在可矿化氮含量;(4)除了地膜覆盖下20—40cm土层颗粒有机氮相对含量在作物不同生育期差异不显著外,秸秆和地膜覆盖下0—40cm土层微生物量氮、潜在可矿化氮、颗粒有机氮对土壤全氮的动态均有重要贡献。总之,黄土高原的春玉米田秸秆覆盖具有明显的提升土壤全氮及其组分含量的作用,有助于培肥地力和土壤固氮;地膜覆盖则降低了作物生育后期土壤全氮及其组分含量,同时显著提高了土壤硝态氮水平,导致农田土壤氮素淋溶风险提高。     

春玉米产量、氮肥效率及土壤矿质氮对施氮的响应

为了提高氮肥增产效益,减少对环境的污染,通过田间试验研究了施氮量对春玉米产量、氮肥效率及土壤矿质氮的影响。结果表明,施氮量较低时,春玉米籽粒产量随施氮量增加显著增加,当施氮量高于180 kg·hm-2时,产量保持不变或有减少趋势。氮肥农学利用率、氮素吸收效率、氮素偏生产力和氮收获指数均随着施氮量增加显著降低,氮肥表观利用率和氮肥生理利用率均先增加后降低。从苗期到收获期,施氮处理0~60 cm土层硝态氮含量呈现"上升—下降—上升—下降—稳定"的变化趋势,而60~120 cm土层硝态氮在春玉米生长后期有增加的趋势。随着土层加深,土壤硝态氮含量呈波浪式下降,施氮量240 kg·hm-2和300 kg·hm-2处理在60~100 cm土层硝态氮含量均显著高于其他处理。随着施氮量增加,0~120 cm土层硝态氮累积量显著增加,当施氮量超过240kg·hm-2时,土层中累积的硝态氮存在着较大的淋溶风险。综合考虑产量、氮肥效率和环境效应,179~209 kg N·hm-2是本试验条件下春玉米的合理施氮量。     

Measuring Soil Nitrogen Mineralization under Field Conditions

Land application of animal manure is known to alter rates of nitrogen (N) mineralization in soils, but quantitative information concerning intensity and duration of these effects has been difficult to obtain under field conditions. We estimated net effects of manure on N mineralization in soils under field conditions in a completely randomized design, at six field sites, by comparing liquid swine (Sus scrofa) manure treatments to plots receiving no manure. Soil samples were collected immediately after manure application to determine inorganic N concentrations, and those samples were also incubated 28 d in the laboratory to determine amounts of N mineralized from the soil. Analyses and incubation were repeated on a second set of samples collected after various times, depending on the site. Differences in inorganic N concentrations were significant among treatments at all six locations for the first sampling and five of the six locations for the second sampling. In comparison, significant differences in inorganic N concentrations measured after 28 d of laboratory incubation were observed for only two of the six sites for each sampling time. Our results illustrate how to distinguish between the effects manure has on rates of N mineralization in soils and rates at which manure N is mineralized.     

Plant Density and Nitrogen Effects on Maize Phenology and Grain Yield

ABSTRACT

Nitrogen (N) and plant density are considered some of the most important factors affecting crop phenology (days to tasseling, silking, and maturity), morphology (leaves plant^?1, seeds ear^?1, ears 100 plants^?1) and grain yield. The effects of plant density and N on phenology, morphology, and yield of maize (Zea mays L.) at Peshawar in northwestern Pakistan were evaluated during 2002 to 2004. The 2 × 3 × 6 factorial experiment was designed having two plant densities (60,000 and 100,000 plants ha^?1) and three N levels (60, 120, and 180 kg N ha^?1) applied to main plots, while six split application of N in different proportions were applied to subplots in two equal, three equal, three unequal, four equal, five equal and five unequal splits at sowing and with 1st, 2nd, 3rd, and 4th irrigation at two week intervals. All the phenological characteristics were significantly affected by year, plant density, rate and timing of nitrogen application. Year and plant density had no significant effect while rates and split application of N had significant effects on the leaf number plant^?1 and seed number ear^?1. Year, plant density and N rate had significant effects while N splits had no significant effects on the number of ears 100 plants^?1 of maize. Significantly higher grain yield was observed under high plant densities, high N rate and split application of N, while its response to year effects was statistically non-significant. Tasseling, silking and physiological maturity were delayed and maximum grain yield was obtained from those plots maintained at higher plant density. Delaying in the phenological characteristics while increasing the number of leaves and seeds plant^?1, and number of ears 100 plant^?1 through high rate and split application of N results in maximum yield of maize at Peshawar. This study suggested that maize production can be maximized through high plant density and high N split application.     

不同施氮水平对春玉米氮素利用及土壤硝态氮残留的影响

过量施用氮肥造成的环境问题日益严重,氮肥合理使用成为了人们研究的热点。通过研究不同施氮水平对春玉米氮素利用及土壤硝态氮残留的影响,为氮肥的合理利用提供依据。通过在北京市通州区农业技术推广站进行田间小区试验,研究了不同施氮量（0、50、100、200和300kg·hm^-2）对春玉米产量及氮素利用效率、氮平衡和土壤硝态氮累积量的影响。结果表明：（1）春玉米在施氮量为200kg·hm^-2时达到最高产量,为9006．4kg．hm^-2,不同氮肥水平的氮肥利用率在19．7％-25．8％之间,在100kg·hm^-2时的利用效率最高,达到25．8％。（2）作物吸氮量随输入量的增加而增加,氮盈余主要以土壤残留为主,表观损失在氮盈余中的比例虽小,但随施氮量的增加而增加的趋势更加明显。（3）硝态氮在180cm土层中的累积量随氮素输入量的增加而显著增加,在300kg·hm^-2时达到最高值,为195kg·hm^-2,在施氮水平为100kg·hm^-2时作物生长的需要就基本上能够得到满足,而在高施氮水平下（200和300kg·hm^-2）时土壤中的硝态氮出现富集现象,对环境形成一定的威胁。     

滴灌施氮对春玉米氮素吸收、土壤无机氮含量及氮素平衡的影响

为解决吉林省半干旱区滴灌施肥条件下氮肥合理施用问题,通过2年(2015—2016年)田间试验,研究了覆膜滴灌条件下施氮量(0,70,140,210,280,350kg/hm~2)对春玉米产量、氮素吸收利用、土壤剖面无机氮含量变化及氮素平衡的影响。结果表明:施氮量在70~210kg/hm~2范围内玉米产量随施氮量的增加显著增加,当施氮量超过210kg/hm~2后,处理间产量无显著差异;将玉米产量(y)与施氮量(x)拟合,得出最佳施氮量分别为195.1,201.0kg/hm~2。施氮显著提高了玉米各生育时期氮积累量,其中灌浆期和成熟期氮积累量以施氮量210kg/hm~2处理最高。氮素当季回收率、农学利用率和偏生产力均随施氮量的增加而下降。玉米成熟期0-200cm剖面土壤硝态氮和铵态氮含量随土层深度增加呈逐渐下降的趋势;施氮提高了0-200cm土壤硝态氮和铵态氮含量,其中施氮量280,350kg/hm~2处理40-200cm土层硝态氮含量显著高于其他施氮处理。玉米吸氮量、土壤无机氮残留量和氮表观损失量与施氮量呈极显著的正相关;玉米吸氮量、土壤无机氮残留量和氮表观损失量分别占增加纯氮的21.6%~23.3%,33.0%~37.4%,41.0%~43.7%。综上所述,在本试验条件下,综合产量、氮素吸收利用、土壤剖面无机氮含量变化及氮素平衡等因素,在吉林省半干旱区滴灌施肥适宜施氮量应控制在195~210kg/hm~2。     

Nitrogen Availability for Maize from a Rolling Pampa Soil After Addition of Biosolids

Abstract

The objective of this paper was to evaluate the influence of different rates of biosolids on the soil nitrogen (N) availability for maize and its residuality. A field experiment was developed in a typic Argiudol located in the NE of the Buenos Aires Province. Maize was sown for two consecutive years 1997–1999. Biosolids from a sewage treatment plant of Buenos Aires outskirts were superficially applied to the soil and incorporated by plowing. There were eight treatments: Check; 8, 16, and 24 Mg of dry biosolid ha^?1; 8 and 16 Mg of dry biosolid ha^?1 applied one year before, 100 and 150 kg N ha^?1 of calcium ammonium nitrate (CAN). The sampling and determinations were done during the second maize cycle. At presowing (PS), sowing (S), 6 expanded leaves (V6), 12 expanded leaves (V12), and Flowering (Fl) composite soil samples from 0–40 cm depth were obtained to determine ammonium and nitrate contents. At Fl maize plants were sampled in order to determine total biomass and N content. The N‐nitrate content in the soil was significantly increased by the biosolids application (p < 0.05), and varied for each increment depending on the biosolids rates and the phenological stage. After 30 days from the incorporation the increases of 1.19, 1.34, and 2.05% were observed for N‐nitrates for 8, 16, and 24 Mg ha^?1, respectively. The contribution of mineral N from the biosolids was 2.48, 6.46, and 5.01 kg N Mg^?1 when the rates were incremented from 0–8, 8–16, and 16–24 Mg ha^?1, respectively. The nitrogen mineralization followed a release pattern with a maximum value of 296 kg N‐nitrate ha^?1 at sowing for 24 Mg ha^?1. Since then, the release of mineral nitrogen decreased significantly till Fl. The N‐nitrates values variation with the temperature adjusted to polinomic functions. The mineral N released from the biosolids increased as a response to the increment of soil temperature and then decreased due to the maize nitrogen absorption and the potentially mineralized nitrogen exhaustion. The application of 150 kg N ha^?1 as CAN incremented significantly the soil N‐nitrate content and equalized 16 and 24 Mg of dry biosolids ha^?1 at V6. But, no synchronism between the high nitrate releasing from biosolids and the increment in the nitrogen absorption by maize was observed. This fact generates a surplus of nitrate that incremented the potential of nitrogen loss by lixiviation. We observed a residual effect from the biosolids that were applied the previous year. This contribution represented the 35% of the maize requirements and was similar to the nitrate content observed in Bio 16. The biosolids might be a valuable source of nitrogen for maize crop if the synchronism between the soil supply and maize demand is observed in order to avoid nitrates surplus.     

Soil Acidity Changes in Bulk Soil and Maize Rhizosphere in Response to Nitrogen Fertilization

The capacity of nitrogen (N) fertilizers to acidify the soil is regulated principally by the rate and N source. Nitrogen fertilizers undergo hydrolysis and nitrification in soil, resulting in the release of free hydrogen (H⁺) ions. Simultaneously, ammonium (NH₄ ⁺) absorption by roots strongly acidifies the rhizosphere, whereas absorption of nitrate (NO₃ ^?) slightly alkalinizes it. The rhizosphere effects on soil acidity and plant growth in conjunction with N rate are not clearly known. To assess the impact of these multiple factors, changes in the acidity of a Typic Argiudol soil, fertilized with two N sources (urea and UAN) at two rates (equivalent to 100 and 200 kg N ha^?1), were studied in a greenhouse experiment using maize as the experimental plant. Soil pH (measured in a soil–water slurry), total acidity, exchangeable acidity, and exchangeable aluminum (Al) were measured in rhizospheric and bulk soil. Plant biomass and foliar area (FA) were also measured at the V₆ stage. Nitrogen fertilization significantly reduce the pH in the bulk soil by 0.3 and 0.5 units for low and high rates respectively. Changes in the rhizosphere (the “rhizospheric effect”) resulted in a significant increase in soil pH, from 5.9 to 6.2. The rhizospheric effect × N source interaction significantly increased exchangeable acidity in the rhizosphere relative to bulk soil, particularly when UAN was added at a low rate. Only total acidity was significantly increased by the fertilizer application rate. In spite of the bulk soil acidification, no significant differences in exchangeable aluminum were detected. Aerial biomass and FA were significantly increased by the higher N rate, but N source had no effect on them. Although changes in acidity were observed, root biomass was not significantly affected.     

田间施肥引起浅层土中氮的蓄积试验分析

田间施肥后,未挥发和被作物吸收的剩余N素易淋失运移,引起在浅层包气带土壤中的蓄积,且又易再释放进入下层土或地下水中形成污染,并主要受气候、土质结构、微生物作用等的影响。认识和掌握上述规律现象,将有助于研究农田施肥引起地下水污染的治理方法。对田间超量施肥灌溉后,作历时近1年的浅层包气带土壤中N的蓄积试验研究,结果显示:短期内土壤中N的显著蓄积主要发生在土层1.5m以浅部位,随时间、深度及入渗水量的变化而波动。这为探索根治由此引起的地下水污染,提供了较好的应用基础和科学依据。     

Comparing Nitrate-N Losses through Leaching by Field Measurements and Nitrogen Balance Estimations

Nitrogen (N) balance method is a valuable tool for estimating N losses. However, this technique could lead to incorrect estimates of the amount of nitrate (NO₃^?N) leaching if processes relevant to N losses are not considered properly. The aim of this study was to compare NO₃^?-N leaching losses estimated using an N balance (nonrecovered N, Nne) with data of NO₃^?-N leaching losses (Nl). The experiment was made on a Typic Argiudoll soil planted with corn (five growing seasons) under 0, 100, and 200 kg N ha^?1. The ceramic soil-water suction samplers were installed (1 m deep). Drainage was estimated by the LEACH-W model. The greatest overestimation with the N balance method occurred for years with annual rainfall below the historical average and at times of high NO₃^?-N availability. Future research should focus on investigating mechanisms of N losses relevant under limited water availability.     

施氮及种植模式对玉米氮素利用效率和土壤硝态氮含量的影响

通过田间试验,比较了"小麦/玉米/大豆"体系中的套作玉米与相同种植规格的单作玉米在不同施氮量下(0,90,180,270kg/hm2,分别记为N0、N90、N180、N270)的产量、生物量、氮积累量、氮肥利用率及土壤硝态氮变化。结果表明:(1)单、套作玉米地上部生物量及籽粒产量均随施氮量的增加先增加后略有降低,与N0处理相比,N90、N180、N270处理玉米产量单作玉米分别高18.9%,31.4%,29.4%,套作玉米分别高40.0%,70.1%,64.1%。(2)N0、N90处理下玉米产量套作比单作分别低18.5%,4.0%,其地上部吸氮量套作比单作低11.6%,6.2%;而N180、N270处理下玉米产量套作比单作分别高5.9%,3.4%,套作玉米吸氮量也略高于单作。(3)随施氮量增加单、套作玉米的氮肥吸收利用率及农学利用率均逐渐降低,套作玉米的氮肥吸收利用率及农学利用率平均分别为39.7%和17.6kg/kg,而单作玉米分别为34.1%和9.9kg/kg,套作比单作分别高16.4%和77.8%。(4)单、套作玉米土壤硝态氮含量均随生育时期推进呈先增高后降低的趋势;玉米种植行(窄行)土壤硝态氮在玉米播种时是套作比N0~N270各处理对应单作分别低19.7%,14.4%,14.1%,20.0%;玉米收获期时,N0处理仍是套作低于单作,其余处理为套作高于单作;玉米宽行各时期土壤硝态氮含量在套作单作间差异较大,这是由于套作玉米的前作小麦施肥、生长及后作大豆生长的影响所致。综上说明,玉米应适量施氮,单套作玉米应有不同的施肥策略以适应各自不同的土壤营养环境。     

滴灌水氮对土壤残留有效氮及玉米产量的影响

通过大田试验研究膜下滴灌施用不同水氮对玉米产量及收获后土壤残留有效氮的影响,寻求适宜的水氮耦合量,为达到高产、高效与低土壤氮损失量、残留量相协调的目标提供初步理论。结果表明:1 351~1 465 m~3/hm~2的低灌水量不能有效发挥氮对产量的贡献。灌水1 400~1 800 m~3/hm~2、施氮280~290 kg/hm~2时水对产量提升速度最快而与氮无协同增产效应。灌水1 800~2 100 m~3/hm~2、施氮250~280 kg/hm~2能获得比较高的产量和水氮协同增产效应。收获后1 m土层有效氮分布为由浅向深逐层减少,不同水氮施用量主要影响40~100 cm的残留量。施氮量增加,有效氮残留量增大,用量240 kg/hm~2以内残留量增长缓慢,继续施氮增长迅速。1 351~1 465 m~3/hm~2的低灌水量下肥料氮转化为土壤氮少,残留有效氮少。1 802~2 071 m~3/hm~2的灌水量促进肥料氮向土壤氮转化,随水迁移增大了40~100 cm土壤有效氮。灌水量达2 197~2 315 m~3/hm~2后,1 m土层有效氮残留量减少、深层损失量增大。优选水氮耦合量包含于近似椭圆的区域,交集区灌水2 016~2 100 m3/hm~2,施氮228~250 kg/hm~2可作为松辽平原到内蒙古高原过渡地带膜下滴灌种植玉米的适宜水氮耦合量。     

玉米秸秆覆盖麦田下的土壤温度和土壤水分动态规律

玉米秸秆覆盖冬小麦田后，冬季和早春季节对土壤温度有明显的增温作用，有利于保护小麦安全越冬，春季则有降温作用，影响春季小麦的分蘖和生长，覆盖处理能有效地抑制土壤无效蒸发，提高麦田的水分利用率；覆盖量为3000kg/hm^2时，有增产作用，覆盖量为6000kg/hm^2，有一定的减产作用。