Uptake of 15N by wetland rice in response to application of 15N-labelled Sesbania rostrata and urea

 Pot experiments were carried out to evaluate the response of rice to Sesbania rostrata green manure N as compared to urea fertilizer N under flooded conditions. After growing S. rostrata for 21 days with a ¹⁵N-labelled N source, the labelled Sesbania was applied to wetland rice as a green manure and the uptake of ¹⁵N from this substrate was compared to that from labelled urea. Rice was cultivated twice in the same pots. The rice was grown for a period of 49 days in each case, separated by a period of 21 days when the soil was allowed to dry. The ¹⁵N content of the soil and shoots and roots of rice was determined and ¹⁵N balances established. The total N content of the shoots and roots of rice was determined by a non-tracer method. The percentage recovery of ¹⁵N from shoot material which was derived from urea N was more than twice that from S. rostrata. The recovery of ¹⁵N from the pots receiving both green manure and urea was low, and not significantly different from that recovered from the green manure treatment. As much as 64.5–73.5% and 40.1–41% of the ¹⁵N remained in the soil which had received green manure or urea, respectively. The overall recoveries of ¹⁵N varied between 86.5% and 94.4%. At the second harvest, the oven-dry weight of shoots was significantly (P<0.05) higher in green-manure treated pots, but the total N content did not differ significantly. Labelled N remaining in the soil after amendment with the green manure was much more available to the rice crop than that remaining after the addition of urea-N. The total recovery of labelled N (shoots plus roots) amounted to 65.5% and 74%, respectively of the residual labelled N in the two S. rostrata treatments (i.e. 19.55 mg ¹⁵N pot^–1 and 39.10 mg ¹⁵N pot^–1) and 23.2% and 23.2% of the residual labelled N in the two urea treatments (i.e. 19.55 mg ¹⁵N pot and 39.10 mg ¹⁵N pot^–1), respectively. Received: 8 December 1997     

Biomass production of tree fallows and their residual effect on maize in Zimbabwe

The rotation of maize (Zea mays) with fast-growing, N₂-fixing trees (improved fallows) can increase soil fertility and crop yields on N-deficient soils. There is little predictive understanding on the magnitude and duration of residual effects of improved fallows on maize yield. Our objectives were to determine the effect of fallow species and duration on biomass production and to relate biomass produced during the fallow to residual effects on maize. The study was conducted on an N-deficient, sandy loam (Alfisol) under unimodal rainfall conditions in Zimbabwe. Three fallow species — Acacia angustissima, pigeonpea (Cajanus cajan), and Sesbania sesban — of one-, two-, and three-year duration were followed by three seasons of maize. Pigeonpea and acacia produced more fallow biomass than sesbania. The regrowth of acacia during post-fallow maize cropping provided an annual input of biomass to maize. Grain yields for the first unfertilized maize crop after the fallows were higher following sesbania (mean = 4.2 Mg ha^–1) than acacia (mean = 2.6 Mg ha^–1). The increased yield of the first maize crop following sesbania was directly related to leaf biomass of sesbania at the end of the fallow. Nitrogen fertilizer did not increase yield of the first maize crop following one- and two-year sesbania fallows, but it increased yield following acacia fallows. Nitrogen fertilizer supplementation was not required for the first maize crop after sesbania, which produced high-quality biomass. For acacia, which produced low-quality biomass and regrew after cutting, N fertilizer increased yield of the first post-fallow maize crop, but it had little benefit on yield of the third post-fallow maize crop.This revised version was published online in November 2005 with corrections to the Cover Date.     

Soil nitrogen availability as affected by fallow-maize systems on two soils in Kenya

Simple methods for the measurement of nitrogen (N) availability are needed to assess the effect of low-input, organically based land management systems on the N supply of tropical soils. Our objectives were to determine the effect of contrasting land-use systems (LUS) on soil N availability and to identify measures of N availability that correlated with maize (Zea mays L.) grain yield. The LUS at the two sites in Kenya involved growth of a maize crop following 17 months of either: (1) Sesbania sesban (L.) Merr. tree growth (sesbania fallow), (2) natural regrowth of vegetation without cultivation (natural fallow), (3) three crops of unfertilized maize (maize monoculture), or (4) bare uncultivated soil (bare fallow). Soil was collected before the post-fallow maize crop was sown. The LUS had no effect on total soil N or amount of N in the heavy fraction soil organic matter (SOM) (>150 μm, >1.37 Mg m^–3). Sesbania and natural fallows, as compared to maize monoculture, increased the N in light fraction SOM (>150 μm, <1.13Mgm^–3), N in intermediate fraction SOM (>150 μm, 1.13 to 1.37 Mg m^–3), ammonium-N and aerobic N mineralization at a depth of 0–15 cm. Maize yields were highest following the sesbania fallow. Nitrate-N, inorganic-N (ammonium plus nitrate) and anaerobic N mineralization correlated with maize grain yield at both sites. The relationship between maize yield and pre-season nitrate-N improved when the depth of soil sampling was increased to 1 m at one site (an Alfisol), but did not improve at the site with anion adsorption in the subsoil (an Oxisol). The sesbania fallow was more effective than the natural fallow in increasing available soil N. Maize yield was better related to pre-season nitrate than N in size-density fractions of SOM. Received: 5 May 1997     

毛萼田菁茎瘤的形成和固氮活性的研究

毛萼田菁(S.rostrata)喜高温、高湿生态环境,在温度20℃以上、相对湿度70—80％的条件下生长迅速,植株可达3.5米以上。 毛萼田菁的茎瘤形成于茎上蛰伏的不定根发生点。当合适的根瘤菌从不定根发生点裂口入侵后,刺激不定根原基周围的皮层细胞分裂形成含菌组织而发育成茎瘤。茎瘤的固氮活性随茎瘤和其中类菌体的发育和衰败而升降。植株的共生固氮周期呈抛物线。茎瘤的固氮活性为根瘤的2.3倍,单株茎瘤的固氮量为根瘤的46倍。植物的光合作用对茎瘤的形成和固氮强度有决定性影响。在正常光照下发育的茎瘤的固氮活性约为包扎遮光下发育的茎瘤固氮活性的1.5倍。     

普通田菁的共生固氮特性

普通田菁(Sesbania cannabina)在苗龄10天左右主根开始结瘤,根瘤呈马蹄形至鸡冠状,深红,大小为0.5cm×1.0cm;苗龄65天,主根瘤开始衰败,苗龄35天侧根显瘤,侧根瘤多为球状,少数呈马蹄形,生长期长达80天以上。乙炔还原法测定表明:湿润和旱栽田菁根瘤固氮酶活性的变化比较一致,苗龄60～65天出现活性高峰,分别为16.45微克分子乙烯/株·小时和16.43微克分子乙烯/株·小时。在淹水条件下,固氨酶活性在苗龄,60～80天之间出现两个高峰,其峰值分别为19.91和14.51微克分子乙烯/株·小时。同时,比色测定的结果也表明。在不同的栽培条件下,根瘤豆血红蛋白含量的消长与固氮酶活性变化相一致。在适宜的栽培条件下,普通田菁的固氮周期可长达120天以上,湿润栽培下每季田菁的总固氮量估计可达13g/m~2。     

田菁改良重度盐渍化土壤的效果分析

为评价田菁改良重度盐渍化土壤的效果,试验设置4个处理：（1）只种植田菁(T);（2）种植田菁,施用二铵450 kg/hm²(TA);（3）种植田菁,施用磷石膏2250 kg/hm²(TG);（4）不种植田菁的空白处理作对照(CK)。结果表明：施用磷石膏能够显著促进田菁生长(P<0.05),TG处理地上部、地下部生物量较T、TA处理分别增加了14.24%、24.77%和8.32%、12.39%,施用二铵对田菁生长的促进作用不显著。种植田菁能够显著降低重度盐渍化土壤含盐量、容重,提高土壤速效氮、速效钾、水溶性有机质(DOC)含量,及土壤大团聚体含量、平均重量直径(MWD)、总孔隙度(P<0.05),TG处理改良效果最大。相关分析表明,盐渍化土壤含盐量、Na⁺含量、DOC、有机质是维系盐渍化土壤结构的关键性状,降低土壤含盐量、Na⁺含量,提高DOC、有机质含量是盐渍化土壤改良方向。种植田菁,同时施用磷石膏是一种快速提升重度盐渍化土壤肥力的有效方法。     

田菁种子发芽条件研究

通过温水及浓硫酸浸泡处理,以及采用不同的发芽床,观察田菁[Sesbania cannabina (Retzius) Poiret]种子的发芽势和发芽率的变化规律。结果表明：温水浸泡各处理间达到显著差异,其中30℃、12 h的发芽势和发芽率最高,分别达到56%和75%;浓硫酸浸泡各处理间差异不显著,其中处理15 min的发芽势和发芽率最高,分别达到73%和84%;不同发芽床间的差异不显著,其中纸床的发芽势和发芽率最高,分别达到64%和75%;本试验中,以浓硫酸处理种子效果最佳。     

云南省田菁根瘤菌及根瘤内生细菌遗传多样性研究

本研究采用BOX-PCR指纹图谱和16SrDNA全序列分析,对45株分离自田菁的根瘤菌及根瘤内生细菌进行了菌株多样性研究,BOX-PCR指纹图谱分析结果表明,在78%的相似性水平上,待测菌株分成了4个遗传群,其中群Ⅰ和群Ⅳ分别与根癌土壤杆菌(Agrobacterium tumefaciens)和大肠杆菌(Escherichia coli)聚在一起,其它群没有与参比菌株聚群。选取每群的代表菌株进行16SrDNA全序列测定。结果表明:待测菌株归于6个属,分别是贪铜菌属(Cupriavidus)、拜纳蒙纳斯属(Balneimonas)、土壤杆菌属(Agrobacterium)、克罗诺杆菌(Cronobacter)、肠杆菌属(Enterobacter)和泛菌属(Pantoea),菌株表现了丰富的遗传多样性;其中分离自田菁的根瘤菌隶属于贪铜菌属(Cupriavidus)和拜纳蒙纳斯属(Balneimonas)尚未见其它文章报道。     

Effect of Sesbania rostrata on Nitrogen Uptake and Yield of Lowland Rice

Nitrogen inputs into rice fields can be increased by cultivation of green manure crops. Many Sesbania species have been generally grown by the rice farmers in India and these green manures are capable of contributing significant amount of nitrogen in 45 to 90 days period by their association with the nitrogen fixing symbiotic bacterium – Rhizobium . Field experiments conducted at the Tamil Nadu Agricultural University, Coimbatore, India, during Dry and Wet seasons in 1987–88 with medium duration (145 days) rice variety CO 43. Sesbania rostrata produced higher biomass on 60th day after sowing and accumulated higher percentage of nitrogen. Application of fertilizer nitrogen with S. rostrata have increased the nitrogen uptake and yield of rice.     

Control pollination and pollen management in Sesbania sesban (L.) Merr.

Sesbania sesban was amiable to controlled cross pollination when the emasculation and pollination operations were performed in the morning. A medium of 10% sucrose solution was found to be optimal for in vitro germination of the pollen grains. The pollen is quite tolerant of orthodox storage conditions enabling controlled crosses to be performed among accessions that flower in differing seasons of the year.