Yield,N Uptake and N Utilization of Early Maturing,Drought and Striga-Tolerant Maize Varieties under Low N Conditions

Performance under sub-optimal nitrogen (N) conditions, of early maturing maize cultivars bred for tolerance to drought and Striga parasitism in the Nigerian savanna is not known. This study evaluated the tolerance of selected early maturing drought and Striga-tolerant maize cultivars to low N conditions in Northern Nigeria. The cultivars were evaluated at 30 and 100 kg N ha^?1. The varieties were compared with an improved maize cultivar that is not tolerant to drought and Striga. Maize grain yield was 26% higher at 100 kg N ha^?1 than at 30 kg N ha^?1 in 2010 and 161% higher100 kg Nha^?1 than at 30 kg Nha^?1 in 2011. The drought and Striga-tolerant varieties produced consistently higher yields than the non-drought-tolerant variety particularly at 30 kg Nha^?1. These cultivars also accumulated higher amount of N, had higher N-uptake efficiency or N-utilization efficiency than the non-drought-tolerant variety ACR 95 TZE-COMP4 C3. Grains yield at low nitrogen rate was associated with high ears m^?2, high dry matter accumulation, high grains m^?2, suggesting that these traits are linked to low-N tolerance. The good performance of the drought-tolerant maize varieties under low N suggests that varieties developed for drought tolerance may be tolerant to low-N conditions.     

氮肥减量后移对玉米产量和氮素吸收利用及农田氮素平衡的影响

田间试验研究了不同土壤氮素供应水平和底追比例对玉米籽粒产量、土壤硝态氮和农田氮素平衡的影响.与农民习惯施肥(N 240 kg·hm-2,基肥和大喇叭口追肥为1∶2)相比,氮肥减量10％(N 216 kg· hm-2)和20％ (N 192kg·hm-2)处理的玉米产量并没有降低,而氮肥利用效率显著增加.氮肥减量后移可使耕层无机氮供应较好地与作物吸收同步,降低收获期0～100 cm土层的硝态氮积累,减少氮素的田间表观损失,提高氮肥利用效率.在本试验条件下,氮肥减量20％(N 192 kg·hm-2),基追比例1∶3∶1处理的植株产量、地上部植株氮肥吸收利用率、氮肥农学利用率均较高,0～100 cm土层未出现硝态氮明显累积,氮素表观损失量最少,是最佳施氮运筹模式.     

Influence of Long-term Tillage,Straw, and N Fertilizer Management on Crop Yield,N Uptake,and N Balance Sheet in Two Contrasting Soil Types

Field experiments (established in autumn 1979, with monoculture barley from 1980 to 1990 and barley/wheat–canola–triticale–pea rotation from 1991 to 2008) were conducted on two contrasting soil types (Gray Luvisol [Typic Haplocryalf] loam soil at Breton; Black Chernozem [Albic Agricryoll] silty clay loam soil at Ellerslie) in north-central Alberta, Canada, to determine the influence of tillage (zero tillage and conventional tillage), straw management (straw removed [S_Rem] and straw retained [S_Ret]), and N fertilizer rate (0, 50 and 100 kg N ha^?1in S_Ret, and only 0 kg N ha^?1in S_Rem plots) on seed yield, straw yield, total N uptake in seed + straw (1991–2008), and N balance sheet (1980–2008). The N fertilizer urea was midrow-banded under both tillage systems in the 1991 to 2008 period. There was a considerable increase in seed yield, straw yield, and total N uptake in seed + straw with increasing N rate up to 100 kg N ha^?1 under both tillage systems. On the average, conventional tillage produced greater seed yield (by 279 kg ha^?1), straw yield (by 252 kg ha^?1), and total N uptake in seed + straw (by 6.0 kg N ha^?1) than zero tillage, but the differences were greater at Breton than Ellerslie. Compared to straw removal treatment, seed yield, straw yield, and total N uptake in seed + straw tended to be greater with straw retained at the zero-N rate used in the study. The amounts of applied N unaccounted for over the 1980 to 2008 period ranged from 1114 to 1846 kg N ha^?1 at Breton and 845 to 1665 kg N ha^?1 at Ellerslie, suggesting a great potential for N loss from the soil-plant system through denitrification, and N immobilization from the soil mineral N pool. In conclusion, crop yield and N uptake were lower under zero tillage than conventional, and long-term retention of straw suggests some gradual improvement in soil productivity.     

Kinetics of C and N mineralization, N immobilization and N volatilization of organic inputs in soil

C and N mineralization data for 17 different added organic materials (AOM) in a sandy soil were collected from an incubation experiment conducted under controlled laboratory conditions. The AOM originated from plants, animal wastes, manures, composts, and organic fertilizers. The C-to-N_AOM ratios (η_AOM) ranged from 1.1 to 27.1. Sequential fibre analyses gave C-to-N ratios of soluble (η_Sol), holocellulosic (η_Hol) and ligneous compounds (η_Lig) ranging from 1.1 to 57.2, 0.8 to 65.2, and 3.5 to 25.3, respectively. Very different patterns of net AOM-N mineralization were observed: (i) immobilization for four plant AOM; (ii) moderate mineralization (4-15% AOM-N) for composts; (iii) marked mineralization (11-27% AOM-N) for 1 animal AOM, 1 manure and 2 organic fertilizers; and (iv) high rates of transformations with possible gaseous losses for some N-rich AOM.The Transformation of Added Organics (TAO) model proposed here, described AOM-C mineralization (28 °C, 75% WHC) from three labile (L′), resistant (R) and stable (S) compartments with the sole parameters P′_L and P_S=fractions of very labile and stable compounds of AOM, respectively. Dividing the C-compartments by their C-to-N estimates supplied the remaining N_AOM fraction (RAONF). A P_im parameter split the TAO nitrogen fraction (TAONF=added N-RAONF) into two compartments, immobilized (imN) and inorganic (inorgN) N. A P_im>0 value meant that all the TAONF plus a fraction (P_im−1) of native soil inorganic N was immobilized. Additional N mineralization was predicted when necessary from imN by first order kinetics (constant k_remin). The TAO version with two parameters P_im and k_remin allowed us to predict very different patterns of N mineralization and N immobilization. In a few cases, a further first order kinetic law (constant k_v) was added to predict N volatilization from inorgN. Two hypotheses were tested: (i) η_L′, η_R, η_S (C-to-N of L′, R and S)=η_Sol, η_Hol, η_Lig, respectively, (ii) η_L′=η_R=η_S=η_AOM. The first hypothesis was validated by these data, and the second was a good approximation of the former one. In all the cases, predictions were in good agreement with measured values.     

氮肥减施对稻-麦轮作体系作物氮素吸收、利用和土壤氮素平衡的影响

田间试验研究了稻-麦轮作体系中减施氮肥对作物氮素吸收、利用和土壤氮素平衡的影响。结果表明,与当地习惯施肥(小麦:N 225 kg/hm2,基肥与分蘖肥各半;水稻:N 210 kg/hm2,基肥和分蘖肥为3∶2)相比,减氮20%～30%处理产量并没有降低,而氮肥当季利用率、氮素农学利用率以及氮素偏因子生产力则有所增加;而且,氮肥分次追施,能增加子粒产量,并减少氮肥成本。虽然减氮20%～30%处理0—40 cm土层无机氮含量较习惯施肥处理降低,但是并没有降低植株地上部对氮素的吸收。在小麦和水稻收获期,减施氮肥处理0—100 cm土壤无机氮残留量低于习惯施肥处理;且稻-麦轮作系统中氮的表观损失主要发生在水稻季。初步认为,在长江中下游平原稻-麦轮作体系氮素过量施用地区,第一个轮作周期减施氮肥20%～30%不仅不影响产量,而且可提高氮素利用率,有利于保护环境。     

旱地土壤矿质氮和可矿化氮与土壤供氮能力的关系

在具有典型半干旱气候特征的陕西永寿选取22个不同肥力水平的田块,分层采集0－100cm土样,研究矿质氮、可矿化氮和土壤供氮能力之间的关系。结果表明,NH4－M与可矿化氮之间没有明显关系;15－80cmNO3－N与各层可矿化氮显著相关,0－15cm和80－100cmNO3－N与之大多相关不显著。通径分析表明,30－45cm的可矿化氮和NO3－N对作物吸氮量的直接贡献最大（后者稍低于前者）;其次是60－80cm的NO3－No0-100cmNO3-N总的直接和间接贡献均大于可矿化氮。作为土壤供氮指标,0－45cm可矿化氮和0-100cmNO3-N都可靠,尤以后者效果更好。     

Simultaneous determination of total C,total N,and 15N on soil and plant material

Abstract

Availability of labor and laboratory instrumentation has frequently limited use of isotopes in N management research. Recent innovations in laboratory instrumentation have made it possible to simultaneously determine total C, total N, and ¹⁵N concentrations in plant, soil, and water samples. An automatic C and N analyzer was interfaced with a continuous‐flow mass spectrometer for purposes of routine analytical determinations. Compared to manual procedures, the automated procedure was rapid, accurate, and gave reproducable results both over time and between adjacent samples. Ball‐mill preparation of samples greatly increased precision of determinations and is recommended to improve sample homogeneity.     

不同施氮量对夏玉米产量、氮肥利用率及氮平衡的影响

通过田间小区试验研究了不同施氮量对夏玉米产量、氮肥利用率、硝酸盐淋溶及氮平衡的影响。结果表明，施氮对夏玉米子粒有显著的增产作用，但随施氮量的增加产量变化不大。氮肥利用率在9．2％-22．6％之间，随施氮量的增加而降低。施氮可明显提高0-160cm剖面土壤NO3^--N含量，而且随深度的增加NO3^--N含量呈降低趋势，累积峰主要在20—60cm之间。玉米收获后，随着施氮量的增加氮素的损失量增加，各施氮处理的硝态氮残留量在121～221kg／hm^2之间，以N250处理的残留量最高，残留率近65％。     

不同施氮量对夏玉米产量、氮肥利用率及氮平衡的影响

通过田间小区试验研究了不同施氮量对夏玉米产量、氮肥利用率、硝酸盐淋溶及氮平衡的影响。结果表明,施氮对夏玉米子粒有显著的增产作用,但随施氮量的增加产量变化不大。氮肥利用率在9.2%~22.6%之间,随施氮量的增加而降低。施氮可明显提高0~160 cm剖面土壤NO3--N含量,而且随深度的增加NO3--N含量呈降低趋势,累积峰主要在20~60 cm之间。玉米收获后,随着施氮量的增加氮素的损失量增加,各施氮处理的硝态氮残留量在121~221 kg/hm2之间,以N250处理的残留量最高,残留率近65%。     

Availability of N from Casuarina residues and inorganic N to maize, using 15N isotope techniques

 The contribution of N from Casuarina equisetifolia (casuarina) residues to maize with inorganic N (ammonium sulphate) supplementation was studied in a pot experiment using ¹⁵N labelling techniques. A single rate of N application of 100 mg N kg^–1 soil was applied as N-ammonium sulphate in combination with casuarina residues in the proportions 100 : 0; 75 : 25; 50 : 50; 25 : 75 and 0 : 100, respectively. The directly ¹⁵N-labelled casuarina residue and indirect labelling (unlabelled casuarina + ¹⁵N soil) were compared to estimate the proportion and amount of N derived from the residue and fertilizer. The application of ammonium sulphate at a high rate significantly affected shoot dry matter (P<0.05) and likewise reduced the contribution of soil-derived N compared to residues. Total recoveries by maize of residue N and applied fertilizer N averaged 11% and 24%, respectively. Residue and fertilizer use efficiencies were not influenced by the addition of different rates of fertilizer or residue. The estimation of the contribution of N from different sources showed that direct measurement of the ¹⁵N-labelled organic source was more reliable. Received: 10 September 1997     

氮肥后移对土壤氮素供应和冬小麦氮素吸收利用的影响

采用田间试验研究了氮肥后移对土壤氮素供应和冬小麦氮素吸收利用的影响。结果表明,与农民习惯施氮（N 300 kg/hm2,基肥和拔节肥各占1/2）比较,氮肥后移处理（N210kg/hm2,基肥、拔节肥和孕穗肥各占1/3）在不降低小麦产量的同时,大大提高了氮肥利用率,且全生育期氮素表观损失极低。过量施用氮肥(N 300 kg/hm2)明显提高了60 cm以下土层硝态氮含量,增加了其向地下水淋溶迁移的风险。氮肥后移可提高小麦成熟期0-20cm土层硝态氮积累量,降低其在20-100cm土层的积累。基于冬小麦不同生育阶段的氮素吸收量而进行氮肥后移是可行的,氮肥后移可节省氮肥30%,是较为理想的施氮方式。     

氮肥后移对冬小麦产量、氮肥利用率及氮素吸收的影响

为改变小麦“一炮轰”施肥存在的弊端,通过两个田间试验,研究了不同氮肥后移模式对冬小麦产量、氮肥利用率及氮素吸收、累积的影响,旨在了解冬小麦对氮素吸收和转运规律,为实现冬小麦超高产和合理施肥提供依据。结果表明,与传统“一炮轰”施肥技术相比,氮肥后移可以提高冬小麦的子粒产量、穗数及氮肥利用率,以N4处理（50%作为基肥,50%返青后追施）最高,两个试验点产量分别达到3857和8240kg/hm2,增产25.8%和17.3%,穗数增加6.0%和18.1%,氮肥利用率提高111.8%和107.4%。冬小麦氮素累积主要集中在返青后期至灌浆期阶段,因此在保证基肥的条件下,返青期后追施氮肥显得尤为重要。表明在本试验条件下,比较合理的氮肥施肥模式为50%作为基肥,50%返青后追施。     

Grain yield,seed weight,seed N concentration,and nodule activity of soybean as influenced by defoliation and N fertilizer

It is unknown if nitrogen (N) fertilizer application will ameliorate the yield loss associated with severe defoliation of soybean [Glycine max (L.) Merr.] at the R5 stage of growth. The objective of this field study was to investigate the interaction of N fertilization rate and extent of defoliation on soybean yield, seed weight, seed N concentration, and nodule activity. Field experiments were conducted in 1988 and 1989 on a Drummer silty clay loam (Typic Haplaquolls). Treatment variables were three cultivars: BSR 101, Chamberlain, and Elgin 87; three N fertilizer rates applied one day after defoliation: 0, 84, and 168 kg N ha^‐1 as urea; and three levels of defoliation: 0, 50, and 75%. Grain yield was not significantly affected by N rate but did decrease with defoliation. Fertilizer N did not ameliorate the yield reduction associated with defoliation. Seed weight decreased linearly with increasing defoliation. Plants exposed to the most severe defoliation produced seed which weighed 1 g 100^‐1 seed less than seed from nondefoliated plants. In 1989 seed weight of only the nondefoliated plants increased slightly with N rate, seed weight was not affected by N rate for any other year by defoliation treatment combination. Seed N concentration was not affected by N rate. Seed N concentration increased with defoliation in 1988 but not in 1989. Seed N concentration was not affected by defoliation in 1989. N fertilizer application and defoliation decreased nodule activity. Defoliated plants utilized nitrates in preference to dinitrogen fixation. Fertilizer N increased the concentration of nitrates in the plant, but the increase did not ameliorate the yield loss. Developing pods and seed are the predominate sink. The additional energy presumably required for dinitrogen fixation did not exacerbate the yield loss.     

缓/控释氮肥对夏玉米氮代谢、氮素积累及产量的影响

采用田间试验研究了缓/控释氮肥和不同施氮次数对夏玉米氮代谢、氮素吸收及产量的影响。结果表明,施氮显著增加了穗位叶硝酸还原酶活性、游离氨基酸含量、叶绿素含量和氮素积累量,提高了百粒重,增产20.93%~27.04%。与习惯两次施氮相比,一次性施用缓/控释氮肥和"苗肥30%+大口肥30%+吐丝肥40%"三次施氮的灌浆期游离氨基酸含量分别高2.77 mg g-1和4.07 mg g-1,氮素积累量分别提高了4.18%和9.74%,氮肥利用率分别提高了2.95和6.88个百分点,产量分别增加了4.88%和5.05%,实现了夏玉米增产和高效施肥。     

OPTIMAL N FERTILIZATION,USING TOTAL AND MINERAL N,AFFECTING CORN (ZEA MAYS L.) GRAIN N UPTAKE

Measurement of total and mineral nitrogen (N), resulted by the presence of soil organic matter, would make the more precise determination of N fertilization possible with respect to the amounts of N absorbed by crop grains. Such a test requires a wide range of soil properties and observations. Accordingly, in a three-year experiment, grain N uptake and soil total and mineral N were determined using different analytical methods (standard laboratory and the N-Trak quick method). The other experimental treatments consisted of sampling time (seeding and postseeding where plants were about 30 cm tall), sampling depths (0–30 and 30–60 cm) as well as the condition of samples (wet or dry). Using regression equations the effects of N fertilization and soil total and mineral N on the uptake of grain N was investigated. Accordingly, the proposed N test predicted the optimum N fertilizer amounts of 236 to 271 kg ha^?1 for corn production.     

Rhizosphere activity, grass species and N availability effects on the soil C and N cycles

We examined whether grass species and soil nitrogen (N) availability could enhance Carbon (C) and N turnover during root litter decay in grassland. Three species with increasing competitiveness (Festuca ovina, Dactylis glomerata and Lolium perenne) were grown at two N fertiliser levels in an undisturbed grassland soil, in which soil organic fractions derived for the last 9 years from Lolium root litter which was ¹³C-depleted. During the subsequent experimental year, the C turnover was calculated using the respective δ¹³C values of the old and new C in the root phytomass, in two Particulate Organic Matter (POM) fractions above 200 μm and in the lightest part of the aggregated soil fraction between 50 and 200 μm. Soil N availability was monitored during the regrowth periods with ion exchange resins (IER). The C decay rates of each particle size fraction were calculated with a simple mechanistic model of C dynamics. The N mineralisation immobilisation turnover (MIT) was characterised by dilution of ¹⁵N-labelled fertiliser in the N harvestThe C:N ratio and the residence time of C in the fractions decreased with particle size. The presence of a grass rhizosphere increased the decay rate of old C. Accumulation of new C in particle size fractions increased with species competitiveness and with N supply. Species competitiveness increased C turnover in the aggregated fraction, as a result of greater accumulation of new C and faster decay of old C. Fertiliser N increased N turnover and C mineralisation in the SOM. Species competitiveness decreased soil -N exchanged with the IER and increased dissolved organic C (DOC) content. The nature of the current rhizosphere is thus an important factor driving C and N transformations of the old root litter, in relation with grass species strategy. Plant competitiveness may stimulate the C and N turnover in the more evolved SOM fractions in a similar way to the mineral N supply.     

气候-土壤-作物之间氮形态契合在氮肥管理中的关键作用

采用合理的作物养分管理措施对粮食安全保障、土壤与农业可持续发展和生态环境保护至关重要。正确的养分管理策略应是针对某一特定气候-土壤-作物条件选择特定的肥料品种、用量、施用时间和施用位置。然而,当前的氮肥管理措施大多未考虑作物氮形态喜好特性、土壤氮素转化特点以及气候条件等因素的影响,以致在实际生产中效果欠佳。本文提出最大化满足作物氮形态喜好,氮肥形态、土壤氮素转化特点以及气候条件高度契合才能显著提高氮肥利用率,同时降低施氮量、减少活性氮向环境的扩散;气候-土壤-作物之间氮形态契合程度也是引进新的作物或者实施新的施肥措施的重要依据。本文为因地制宜地制定农业减氮增效措施指出了另一个方向。