稻田养萍模式下不同施氮量对稻田氨挥发及红萍生物固氮作用的影响

红萍对水体铵态氮浓度较为敏感，稻田放养红萍模式下，红萍的生物固氮作用及其抑制氨挥发的作用对不同施氮量的响应未知。红萍为水生蕨藻共生体，具有很强的生物固氮能力。红萍可作为优质绿肥放养于稻田，以替代部分化学氮肥，起到节能减排的效应。为明确稻田养萍模式下不同施氮量对红萍生物固氮作用和田间氨挥发的影响，采用盆栽试验设置了0、75、150、225、300kg/hm²共5个施氮(以纯N量计)水平，监测了稻田放养红萍和水稻单种各处理的氨挥发量、生物固氮速率和水稻产量。结果表明：(1)同一施氮水平下，稻田放养红萍可显著降低氨挥发日通量峰值及氨挥发总量。在施氮量为225 kg/hm²时，稻田放养红萍对氨挥发总量的抑制作用最大，与水稻单种相比，抑制幅度可达83.2%。(2)红萍的生物固氮速率及固氮总量与施氮量呈线性负相关关系，随施氮量的增加，固氮速率和固氮量逐渐降低，施氮量300 kg/hm²并放养红萍处理得到的固氮速率及总量同不施氮肥不养萍处理之间无显著差异。(3)与不养萍处理相比，放养红萍组各处理的水稻产量都明显增加，其中施氮量为225...     

我国大豆的生物固氮潜力研究

【目的】根瘤菌与大豆共生结瘤固氮是大豆的重要氮素来源之一,而我国在大豆生产中普遍过量使用化学氮肥,不仅增加了生产成本,而且严重抑制了大豆的生物固氮效率。因此在生产中充分发挥生物固氮作用、 合理施用化学氮肥、 降低大豆生产成本是我国发展大豆产业的重要措施,本文对我国大豆主产区生物固氮潜力及其分布特征进行了研究,旨在了解不施氮肥条件下不同大豆产区生物固氮的最大供氮能力,为大豆的合理施肥和充分发挥生物固氮作用提供理论依据。【方法】采用15N自然丰度法,在2011年和2012年测定了在不施用氮肥条件下我国4个大豆主产区包括黑河、 大庆、 长春、 铁岭、 济宁、 延安、 南宁等7个试验点在内的大豆生物固氮效率、 生物固氮量及其对产量的贡献。15N自然丰度法的原理是利用非固氮参照作物从土壤中吸收的15N丰度高于固氮植物,根据两者的15N自然丰度差异估算出固氮植物的生物固氮率。所选的非固氮参照作物必须同大豆生长季一致,并且各试验点选用同一种非固氮植物以保证各地数据的可比性。通过查阅文献,有研究使用玉米作为参照作物,并且符合上述要求,因此本研究选择玉米作为非固氮参照作物。【结果】在不施氮肥条件下,我国大豆在正常降水年份的生物固氮效率为47%～70%,其中铁岭最高为60%～70%,黑河最低为47%～54%;大豆的生物固氮量在N 92～150 kg/hm2之间变化,其中籽粒中的生物固氮量占总固氮量的65%～81%,生物固氮量最高的试验点为长春,最低的试验点为延安;生物固氮对产量的贡献在1039～1867 kg/hm2之间,其中最高的试验点为长春,最低的试验点为延安;在延安试验点苗期～开花期极度干旱的2011年,大豆缺水严重抑制了根瘤菌的数量和固氮酶的活性,其生物固氮效率、 固氮量及对产量的贡献均达极低水平,分别为15%和N 24 kg/hm2和245 kg/hm2。【结论】我国大豆不同主产区的生物固氮潜力存在较大差异,并且具有明显的分布规律。生物固氮效率以温带的铁岭为最高,向北至寒温带的黑河、 向南到亚热带的南宁均呈现逐渐降低的趋势。受种植密度等因素的影响,大豆生物固氮量及其对产量贡献的分布规律与生物固氮效率不完全一致,其中东北地区最高,其次是济宁和南宁,延安最低。     

氮肥减施配施菌剂对水稻生长及土壤有效养分的影响

为明确滨海盐渍型水稻土在氮肥减量施用条件下,微生物菌剂促进土壤养分释放和对水稻生长影响的机制,以盐丰47水稻为供试作物,采用盆栽试验方法,研究在氮肥减量30%条件下,化肥配施固氮螺菌和复合微生物菌剂对苗期水稻生长和土壤养分有效性的影响。结果表明:化肥配施微生物菌剂明显提高水稻生物量,增加水稻株高、根长、根体积、根表面积等根系发育指标。与常规施肥相比,在氮肥用量减少30%条件下配施微生物菌剂可以提高土壤有效磷和速效钾含量,提高幅度分别为2.71%～17.67%和0.73%～18.17%,土壤碱解氮含量变化相对较少,差异不明显。微生物菌剂可以替代部分化肥对水稻生长的促进作用,氮肥配施复合微生物菌剂处理比配施固氮螺菌的效果更好。研究结果对化肥合理减施、保障作物产量和合理应用微生物菌剂有重要意义。     

禾本科植物联合固氮的研究现状及应用前景

氮是限制农业生产的最重要因素之一。随着人工固氮技术的发展,氮肥的施用在提高作物产量、解决人类温饱问题的同时,导致了土壤板结、酸化、氮素流失及温室气体排放(N2O)等环境问题。与人工合成氨相比,生物固氮是一种绿色经济的固氮方式,其包括共生固氮和非共生(自生固氮及联合固氮)固氮,且每年固定的氮可占总固定量的50%以上。与共生固氮相比,非共生固氮存在范围广,如甘蔗、水稻、玉米和小麦等禾本科作物均能进行非共生固氮(联合固氮)。本文主要从禾本科植物的联合固氮菌种类及其作用机理、固氮活性及调控方式以及联合固氮菌的资源及应用3个方面进行综述,发现相比较共生固氮而言,联合固氮菌易受到土著微生物、氮素水平等环境因素影响,其研究难度更大,需要筛选纯化更多的联合固氮菌,为其固氮机制研究提供良好材料;氮、磷、钼、铁等肥料的适量添加可有效促进固氮菌的固氮效率;固氮菌不仅可以提高土壤固氮量,而且有利于植物根系激素调节,从而增加植物抗病抗逆能力,促进植物更健康的生长。本文最后对禾本科植物联合固氮的农艺管理措施及固氮菌剂的实际应用方面做了展望,以期为提高禾本科植物联合固氮效率及推动生物固氮菌在农业生产中的应用提供理论依据。     

氮肥对大豆结瘤固氮、籽粒产量和蛋白质含量的影响

  【目的】  合理施用氮肥不仅可提高大豆结瘤固氮能力,还可减少农业污染,实现大豆生产的高产优质高效。研究施氮时期和施氮量对大豆结瘤固氮、产量及蛋白质含量的影响,为大豆高产优质提供理论基础及科学依据。  【方法】  采用盆栽试验,供试大豆品种为‘东生35’,试验设2个氮肥施用时期(V2期和R1期)和3个氮肥施用量[N 0、5、100 mg/(kg, 土)],表示为N0、N5和N100。在大豆R2期(盛花期)和R5期(鼓粒期)取样分析了地上部干物质积累量、根瘤数量、根瘤干重和固氮酶活性。在R8期(成熟期)调查了大豆籽粒产量和蛋白质含量。  【结果】  施氮时期和施氮量对大豆地上干物质积累、结瘤和固氮能力均有显著影响。不论是V2期还是R1期施氮,大豆地上部干物质积累量均随着施氮量的增加而增加,而根瘤干重、数量则呈降低的趋势。R1期施氮条件下,N100处理的大豆盛花期根瘤数量和根瘤干重比N0分别下降了42.3%和32.8%,而固氮酶活性则均以N5处理最高;V2期施氮条件下,N5处理的大豆固氮酶活性在R2期和R5期较N0处理分别增加15.3%和27.1%。大豆籽粒产量和蛋白质含量均以N5处理最高,籽粒蛋白质含量较N0处理增加了6.3%～9.4%。结构方程结果表明,施氮量正向调控固氮酶活性,间接影响大豆产量;负向调控根瘤数量,间接影响大豆籽粒蛋白质含量。施氮时期直接负向调控大豆籽粒产量,正向调控籽粒蛋白质含量。  【结论】  合理施氮有利于大豆高产优质,早期(V2期)施用氮肥有利于大豆产量提升,而推迟到始花期(R1期)施用氮肥更有利于大豆固氮和籽粒蛋白质含量的增加。盆栽条件下,施氮量对大豆产量和蛋白质含量的影响大于施肥时期,施氮量均以控制在N 5 mg/(kg, 土)为宜。     

有机无机肥配施对水稻氮素利用率与氮流失风险的影响

农田土壤–作物系统对畜禽粪便有一定的消纳作用,有机粪肥与无机氮肥配施是未来农业生产中进一步增加产量、减少化肥施用和保护环境的重要生产模式。本研究采用盆栽试验,分析在施用一定量有机粪肥基础上,不同无机氮肥用量对水稻产量、氮素利用率和氮流失风险的影响,探讨有机肥与无机氮肥的最优比例,为有机肥施用条件下稻田无机氮肥的合理施用提供科学依据。结果表明:与单施有机肥(M)相比,配施0.8倍的无机氮肥效果最佳,水稻产量、株高、分蘖数、籽粒吸氮量和氮肥利用率达最高。有机肥作底肥时,水稻生长前期田面水无机氮浓度随配施无机氮肥量的增加而增加,而后期配施无机氮肥各处理田面水氮素浓度则随着氮肥施用量的增加呈现先降低后升高趋势,其中,增施0.4倍、0.6倍和0.8倍无机氮肥时稻田田面水氮素浓度较单施有机肥处理分别降低17.5%、11.9%和9.3%,差异达显著水平(P0.05)。与单施无机氮肥处理(N)相比,同样以0.8倍无机氮肥+有机肥处理作物产量和氮肥利用率最高,田面水氮浓度降低了30.2%,差异达显著水平(P0.05)。综上,消纳有机肥基础上,在满足作物需氮量的前提下,无机氮肥与其配比为1︰1时,既可以提高水稻增产潜力,又降低稻田氮素流失风险和适当减少稻田无机氮肥施用量。     

生物固氮研究中的蛋白质组学

生物固氮为全球的植物提供75％的氮素，是生命科学中的重大课题。蛋白质组学新思想、新技术的引入，为固氮研究的发展注入了新的活力。本综述主要介绍蛋白质组学在自生固氮菌、根瘤菌及其与豆科植物结瘤固氮中的蛋白质组学的研究概况，以助于在我国生物固氮研究中应用这一有力工具，推动和发展其基础和应用的创新性研究。     

利用15N2直接标记法研究水稻种植对稻田固氮量和固氮活性的影响

稻田固氮对土壤维持肥力有着重要的作用,但水稻种植与固氮菌及其活性之间的关系尚不清楚。本试验利用~(15)N_2直接标记法测定了下位砂姜土发育的简育水耕人为土在种水稻和不种水稻条件下的生物固氮量,及其在土壤不同层次(0～1、1～5、5～15 cm)和水稻中的分配,并通过实时荧光定量PCR技术测定了土壤中固氮菌nifH DNA及RNA基因数量。结果表明:种水稻处理显著提高了土壤各层固氮量,尤其提高了1～5 cm和5～15 cm土层土壤固氮量对总固氮量的贡献;种水稻处理的总固氮量是不种水稻处理的10.3倍;水稻植株中生物固定的氮占总固氮量的31.48%;在0～1 cm土层,种水稻处理显著提高了nifH RNA基因数量,而对nifH DNA基因数量的增加不显著。可见,水稻种植没有增加固氮菌的数量,稻田固氮量的增加是因为水稻种植极大地促进了固氮菌nifH基因的表达,提高了固氮菌的固氮活性。     

南方稻田紫云英作冬绿肥的增产节肥效应与机制

本文对我国南方稻田紫云英作冬绿肥以及紫云英与稻草共同利用的增产和节肥效应及其植物营养学、土壤微生物学等相关作用机制进行综述。2008—2019年间开展的11个联合定位试验结果 (n = 930) 表明，冬种紫云英在不减肥或者减肥20%条件下增产效果显著，水稻产量增加幅度分别为6.53%和4.15%；在减施40%化肥时可保障水稻与常规施肥相比不减产。紫云英的增产和节肥效应随种植年限的增加而增强，5个联合定位试验连续7年的监测结果表明，冬种紫云英减施40%化肥条件下，紫云英种植第一年相对常规施肥增产0.87%，至种植第7年增幅为3.98%。紫云英与稻草联合利用是近些年稻区推行的重要技术模式，2016—2019年间开展的7个联合定位试验结果 (n = 342) 表明，紫云英–稻草联合还田相对于单独稻草还田，水稻产量增加了11.71%。本文分别从优化水稻产量构成、促进水稻养分吸收、提升土壤肥力3方面阐释了紫云英作冬绿肥的增产、节肥机制。稻田冬种紫云英可增加水稻有效穗数和每穗实粒数，优化了产量构成。与常规施肥相比，紫云英配施减量化肥的水稻吸氮量增加了6.4%～6.9%，氮肥利用率提高了6.6%～31.1%。稻田种植紫云英使土壤碳、氮库得到培育，土壤活性有机碳含量和碳转化酶活性提高，土壤速效养分、土壤物理性状明显改善。以有机质和全氮为例，相比常规施肥处理，种植翻压紫云英后减施20%和40%化肥处理的土壤有机质含量分别增加3.95%和4.15%，土壤全氮含量分别增加1.22%和1.74%。在紫云英调控土壤微生物及氮转化机制方面，冬种绿肥有利于土壤微生物的生长繁殖，增强与微生物活性密切相关的土壤酶活性，并通过改变土壤微生物的群落结构及功能微生物影响土壤养分循环。紫云英配施减量化肥可提高土壤固氮菌丰度，通过合理的调控措施可优化紫云英的生物固氮作用。硝化作用对冬绿肥的响应在不同类型土壤中有较大差异，碱性水稻土中冬种绿肥可通过抑制硝化作用降低氮素淋失风险，氨氧化微生物群落结构的变化是冬绿肥影响硝化作用的重要机制。通过近十多年来的研究，逐渐明晰了我国南方稻田冬种紫云英的增产、节肥效应及其机制，为今后稻田绿肥的效应与机制研究提供了重要借鉴和参考。     

不同年限有机栽培对土壤生物固氮活性的影响

氮是对作物生长和产量维持最重要的元素。有机农业无化学肥料投入,生物固氮是氮素最重要的来源之一。然而到目前为止,有机栽培对农田土壤微生物固氮活性的影响尚不清楚。本文以20年常规栽培花椰菜农田土壤为对照,比较经10年、14年、20年有机栽培后土壤微生物固氮活性的变化,并通过多元统计分析探究了影响土壤生物固氮活性的因素。研究结果表明,在7天的测定周期中,与常规栽培相比,10年和14年有机栽培降低了前期土壤生物固氮速率,但整个周期累积固氮在量各处理间无显著差异。不同年限有机栽培对土壤生物固氮速率和累积固氮量影响显著,整体而言14年有机栽培的最低,10年和20年有机栽培间的差异因培养时间而异。培养结束时,常规栽培土壤固氮速率接近于0,有机栽培的花椰菜土壤则仍保持较高活性。皮尔森相关分析和冗余分析（RDA）表明,NH₄+、NO₃?及Olsen P含量是影响有机栽培土壤生物固氮活性的关键因素;其中,NO₃?对固氮有抑制作用,Olsen P则促进了土壤生物固氮活性的增加。     

On-Farm Participatory Technology Development Effects on Resource Conservation Technologies in Rainfed Upland Paddy in Himachal Pradesh,India

Rice is a major cereal crop in Himachal Pradesh, a Himalayan state of India, where paddy acreage is about 78,000 ha with a low average yield of 19.62 q ha^?1 due to rainfed upland farming. High seeding rates and poor resource-use efficiency of conventional fertilizer nitrogen (N) management practices in rainfed upland paddy have also been major production constraints in rainfed upland ecosystems. To validate and refine the production technology on seed rate and fertilizer N management, the Farm Science Centre, Sundernagar, India, conducted numerous on-farm trials (OFTs) during 2006–2010 under an on-farm participatory technology development approach to enhance resource use efficiency through these resource conservation technologies and boost the paddy productivity in the region. Results of two OFTs conducted during Kharif 2006 in the Mandi District of Himachal Pradesh on different seed rates under different sowing methods on VL Dhan-221 and Sukaradhan-1 (HPR-1156) cultivars suitable for rainfed upland conditions revealed that the seed rate at 80 kg ha^?1 sown in rows 20 cm apart resulted in the greatest average paddy productivity to the tune of 25.6 q ha^?1 besides greater profitability, followed by a seed rate at 60 kg ha^?1 sown in rows 20 cm apart (25.2 q ha^?1), over the earlier State Agricultural University (SAU)–recommended practice, that is, seed rate at 100 kg ha^?1 in rows 20 cm apart. This refinement in the seed rate was accepted by the participating farmers of the region. The greatest average benefit/cost (B/C) ratio was observed in plots with seed rate at 60 kg ha^?1 sown in rows 20 cm apart. Based on these results and data compilation from other locations of the state, now the SAU has refined the seed rate from earlier recommendation of 100 kg ha^?1 to 60 kg ha^?1 in rows 20 cm apart as well as 80 kg ha^?1 through broadcast method under rainfed upland paddy in Himachal Pradesh. Results of two OFTs conducted during Kharif 2009 on integrated nutrient management in rainfed upland paddy revealed that farmyard manure (FYM) at 10 t ha^?1 + nitrogen, phosphorus, and potassium (N, P, K) at 15:30:30 kg ha^?1 at sowing followed by 15 kg N ha^?1 15 days after sowing (DAS) and remaining the N [i.e., 30 kg N ha^?1] at tillering (45–50 DAS) resulted in the greatest grain yield of 29.85 and 31.67 q ha^?1 in VL Dhan-221 and HPR-1156, respectively, with respective greater yields of 35.99 and 36.51% over farmers’ practice, besides better profitability. To further standardize fertilizer N split doses and assess their effect on paddy productivity, another OFT was conducted during Kharif 2010 under rainfed upland paddy conditions in HPR-1156. The results revealed that NPK at 60:30:30 kg ha^?1 (whole of P and K as basal, 50% N at 15 DAS, 25% N each at 45–50 DAS and 70–75 DAS splits) resulted in better grain yield (34.3 q ha^?1) and net profitability (?29,786 ha^?1) over other treatments. Overall, it is concluded that these resource conservation technologies developed under the OFT participatory approach can enhance the rainfed upland paddy productivity and strongly show that there is dire need to split the N requirement of rainfed upland paddy in 2–3 splits to reduce the fertilizer N losses, enhance resource-use efficiency, and increase productivity and profitability in Himachal Pradesh, India.     

Effects of preceding compost application on the nitrogen budget in an upland soybean field converted from a rice paddy field on gray lowland soil in Akita,Japan

Abstract

The annual nitrogen (N) budget was measured in a soybean-cultivated upland field during the first year after conversion from a paddy field on gray lowland soil, which is typically found on the Sea of Japan side of northern Japan. Forage rice was cultivated on lysimeter fields for 4 consecutive years with applications of chemical fertilizer, immature compost, or mature compost (the control, immature compost, and mature compost plots, respectively), and then the fields were converted to upland fields for soybean (Glycine max [L.] Merrill cultivar Ryuho) cultivation. Input (seed, bulk N deposition, and symbiotic dinitrogen [N₂] fixation) and output (harvested grain, leached N via drainage water, and nitrous oxide emission) N flows were measured, and the field N budget was estimated from the difference between the input and output. The soybean plants in the immature and mature compost plots grew well and had higher yields (498–511 g m)^?2) compared to the control plot (410 g m)^?2). Total N accumulation in the soybean plants derived from N₂ fixation (g N m)^?2) in the mature compost plot (27.7) was higher than those in the control (18.1) and immature compost plots (19.9). Percentages of soybean N accumulation derived from N₂ fixation ranged from 53% to 74%. N derived from symbiotic N₂ fixation accounted for more than 90% of the total N input, whereas harvested grain accounted for approximately 85% of the total N output. N leaching mainly occurred during the fallow period, accounting for 13–15% of the total N output. The annual N budgets were negative (?10.0,?14.2, and ?6.4 g N m)^?2 year)^?1 for the control, immature compost, andmature compost plots, respectively). The Nloss from the immature compost plot was higher than that of the control plot, because the N output in harvested grain was higher, and the N input by N₂ fixation was similar between plots. While the N loss from the mature compost plot was lower than that of the control plot because the N output in harvested grain was higher, as was the case in the immature compost plot, the N input by N₂ fixation was also higher. Preceding compost application—whether immature or mature compost—to paddy fields increased the subsequent soybean yield during the first year after conversion. This result suggests that N loss and the following decrease in soil N availability in the field could be mitigated by increased N₂ fixation resulting from mature compost application with an appropriate application practice.     

Status of paddy soils as affected by paddy rice and upland soybean rotation in northeast Japan,with special reference to nitrogen fertility

To investigate the current available nitrogen (N) and chemical properties of paddy soils affected by crop rotation between irrigated paddy rice (Oryza sativa L.) and upland soybean [Glycine max (L.) Merr.] (paddy-upland rotation), topsoils were collected from 22 fields of four different farmers in the northeastern region of Japan. Regardless of organic material application, a significant negative correlation was found between available soil N and an increase in the proportions of upland seasons to total crop seasons after the initiation of paddy-upland rotation. Soil total N and total carbon (C) also tended to decrease with an increase in upland frequency. In fields with repeated applications of cattle manure compost, the soil available N was higher than in fields where only crop residue was applied. A significant negative correlation was also found between the soil available N:total N ratio and upland frequency. This indicates that the part of soil N related to available N was notably lost by the use of paddy fields as upland fields. In order to sustain available soil N over the minimum suitable level of 80?mg?kg^?1, upland frequency should not exceed 65% when only crop residues and no other organic materials are applied. The upland frequency can be raised by the repeated application of organic materials which maintain a higher level of available soil N. The results imply that care should be taken to maintain the N fertility of paddy soil at a suitable level in paddy-upland rotation, and that upland frequency and organic materials applied are important factors to do this.     

水旱轮作条件下免耕土壤微生物特性研究

通过野外调查和室内分析,研究了水旱轮作条件下,不同免耕年限土壤微生物数量和生物量的变化特点及其影响因素。结果发现:（1）旱作和水作后,免耕土壤细菌数量显著低于常规耕作。随着免耕年限延长,旱作后土壤细菌数量呈先降低再增加的趋势,免耕5～6 a时最低;而水作后,不同免耕年限间无显著差异。（2）旱作后,免耕土壤真菌和放线菌数量显著高于常规耕作,而水作后,真菌和放线菌数量较常规耕作显著降低。随着免耕年限的延长,旱作后土壤真菌数量呈先降低再增加的趋势,免耕7～8 a时最低;土壤放线菌数量在免耕5～6 a后趋于稳定。水作后,土壤真菌和放线菌数量呈显著负相关。（3）旱作和水作后,免耕土壤微生物量碳和氮显著高于常规耕作,两者呈极显著正相关,变化趋势一致。随着免耕年限延长,旱作后,土壤微生物量碳、氮呈逐渐降低的趋势;水作后,土壤微生物量碳、氮呈先增加再降低的趋势。     

N2 fixation of nodules and N absorption by soybean roots associated with ridge tillage on poorly drained upland fields converted from rice paddy fields

Abstract

Sowing on elevated ridges is effective in reducing wet injury of soybean plants cultivated in upland fields converted from rice paddy fields. Therefore, we investigated the effect of ridge tillage (RT) on soybean N accumulation properties. We compared the amounts of plant N associated with N₂ fixation of nodules and from soil and fertilizer in the RT treatment with amounts in conventional tillage (CT) in two fields in 2002–2003. Both fields were upland fields converted from rice paddy fields (Typic Hydraquents). The main difference between the fields was the presence of a field underdrain. The amounts of Rb and K accumulated in the shoots were also determined to estimate soybean root distribution. The grain yields with RT increased in both fields from 106% to 129% compared with CT. Increased pod number and seed weight were the major factors responsible for the yield increase. anova indicated that RT significantly increased the activities of both N₂ fixation of nodules and N absorption by roots until R1 (flowering stage). The ratio of Rb and K accumulated in the shoots indicated that with RT, the root distribution was more abundant in the superficial layers compared with CT. Thus, RT reduced wet injury during the rainy season that overlapped the flowering stage. Nitrogen accumulation from N₂ fixation until the R7 stage with RT was significantly higher than that with CT. We concluded that RT was effective in increasing N₂ fixation of nodules in poorly drained upland fields converted from rice paddy fields.     

东北地区滨海盐渍土型稻田土壤有机氮组分的研究

用Bremner法测定东北地区滨海盐渍土型开垦5年、30年稻田土壤和邻近未开垦稻田的旱地土壤的有机氮各组分含量。结果表明:(1)在0~60 cm土层,3种土壤非酸解性全氮含量及其占全氮比率明显大于酸解性全氮,但总体上以表层土壤(0~20 cm)为最高。(2)与未开垦旱地土壤相比,种稻5年和30年均使表层土壤酸解全氮含量明显下降,但种稻5年使土壤酸解氨基酸态氮和氨基糖态氮的含量及其占全氮比率明显增加,使氨态氮和未知态氮的含量及其占全氮比率明显下降;而种稻30年则均使土壤酸解各组分氮含量及其占全氮比率明显下降。(3)与未开垦旱地土壤相比,种稻5年和30年稻田土壤酸解全氮含量及其占全氮比率均随土层深度的增加而逐渐降低,但2种稻田土壤酸解各组分氮含量及其占全氮比率的剖面分布则无明显的变化规律。     

Nitrogen accumulation in soybean [Glycine max (L.) Merr.] is increased by manure compost application in drained paddy fields as a result of increased soil nitrogen mineralization

The application of manure compost is an effective way to increase soybean [Glycine max (L.) Merr.] yield and nitrogen (N) fertility in drained paddy fields. We investigated changes in soil N mineralization during soybean cultivation using reaction kinetics analysis to determine the contribution of increased N mineralization after manure compost application (at a rate of 0 to 6?kg?m^?2) on N accumulation and seed yield of soybean under drained paddy field conditions. The seed yield and N accumulation decreased markedly in the second and third year of the experiment, but soil N mineralization increased in both years. No decrease in soil N mineralization occurred even after two soybean crops. Soil N availability was not the main cause of decreased soybean yield in the second and third years. The differences in plant aboveground N content between plots with and without manure compost was similar to the increase in N mineralization caused by manure compost application in the second and third years. The application of 6?kg?m^?2 of manure compost increased the amount of ureide-N and nitrate-N in soybean in the third year. Our results suggest that manure compost application increases soil N mineralization and soybean N₂ fixation, resulting in increased N accumulation and seed yield. However, the soybean yield remained less than 300?g?m^?2 in the second and third years (i.e., below the yield in the first year) at all levels of manure compost application due to the remarkable decrease of N accumulation in the second and the third crops.     

Effect of soil physical properties on soybean nodulation and N2 fixation at the early growth stage in heavy soil field in Hachirougata Polder,Japan

We studied the effect of the soil physical properties on soybean nodulation and N₂ fixation in the heavy soil of an upland field (UF) and an upland field converted from a paddy field (UCPF) in the Hachirougata polder, Japan. Seeds of the soybean cultivar Ryuho were sown in each field with or without inoculation of Bradyrhizobium japonicum A1017. The soybean plants were sampled at 35 (V3) and 65 (Rl) d after sowing (DAS), and then nodulation and the percentage of N derived from N₂ fixation in the xylem sap were determined. The soil physical properties were different between UF and UCPF, especially the air permeability and soil water regime. Nodule growth was restricted in UCPF irrespective of rhizobial inoculation, though rhizobial infection was not inhibited by the unfavorable soil physical conditions. Soybean plant growth was closely related to the nodule mass and N₂ fixation activity, and the inoculation of a superior rhizobium strain was effective only at 35 DAS. These results indicate that soybean nodulation and N₂ fixation was considerably affected by the physical properties of heavy soil, and that it is important to maintain the N₂ fixation activity and inoculate the soybean plants with a superior rhizobium strain at a later growth stage in order to increase soybean production in heavy soil fields.     

Uptake of carbon and nitrogen through roots of rice and corn plants,grown in soils treated with 13C and 15N dual-labeled cattle manure compost

Nitrogen and carbon dynamics in paddy and upland soils for rice cultivation and in upland soil for corn cultivation was investigated by using ¹³C and ¹⁵N dual-labeled cattle manure compost (CMC). In a soil with low fertility, paddy and upland rice took up carbon and nitrogen from the CMC at rates ranging from 0.685 to 1.051% of C and 17.6–34.6% of N applied. The ¹³C concentration was much higher in the roots than in the plant top, whereas the ¹⁵N concentration differed slightly between them, indicating that organic carbon taken up preferentially accumulated in roots. The ¹³C recovery in the plant top tended to be higher in upland soil than in paddy soil, whereas ¹⁵N applied was recovered at the same level in both paddy and upland soils. In the experiment with organic farming soil, paddy rice took up C and N from the CMC along with plant growth and the final recovery rates of ¹³C and ¹⁵N were 2.16 and 17.2% of C and N applied. In the corn experiment, a very large amount of carbon from the CMC was absorbed, accounting for at least 7 times value for rice. The final uptake rates of ¹³C and ¹⁵N reached about 13 and 10% of C and N applied, respectively. Carbon emission from the CMC sharply increased by 2 weeks after transplanting and the nitrogen emission was very low. It is concluded that rice and corn can take up an appreciable level of carbon and nitrogen from the CMC through roots.     

Ferric iron transformation in soils with rotation of irrigated rice-upland crops and effect on soil tillage properties

We examined the relationship between the form of iron and the tillability (defined as the degree of ease of pulverizing a soil into small clods) of soils in upland fields that had been converted from paddy fields. The amount of iron (Fe.e) extractable with acetate buffer (pH 3.0) decreased from 0.959 g kg_-1 in a field that has been continuously used as a paddy field to 0.104 g kg-I in a field that had been converted into an upland field for a period of 5 y. There was no significant change in the free iron oxide content under upland conditions. These results indicate that ferric iron oxides are gradually crystallized to less reactive forms after the conversion of a paddy field into upland conditions. Both soil tillability (represented by the mean clod diameter after tillage) and the stability of the soil microstructure (represented by the sediment volume) also increased during the 3-y period after conversion and then remained constant for the last 2-y period of the study. On the basis of these results, two mechanisms for the improvement of soil tillability can be proposed as follows: crystallization of ferric iron oxides increased their resistance to microbiological reduction and due to this stabilization the iron oxides as a cementing reagent that contributed to the soil microstructure, which in turn affected the soil tillability. During the first year after drainage, however, there was no significant correlation between the soil tillability and amount of Fe_ac, presumably because the soil was not sufficiently dry in the first year after conversion, and the iron oxides did not affect appreciably the soil structure.