A survey of symbiotic nitrogen fixation by white clover grown on metal contaminated soils

There is conflicting evidence about toxic effects of heavy metals in soil on symbiotic nitrogen fixation. This study was set-up to assess the general occurrence of such effects. Soils with metal concentration gradients were sampled from six established field trials, where sewage sludge or metal salts have been applied, or from a transect in a sludge treated soil. Additional contaminated soils were sampled near metal smelters, in floodplains, in sludge amended arable land and in a metalliferous area. Symbiotic nitrogen fixation was measured with ¹⁵N isotope dilution in white clover (Trifolium repens L.) grown in potted soil that was not re-inoculated, and using ryegrass (Lolium perenne L.) as reference crop. The fraction nitrogen in clover derived from fixation (N_dff) varied from 0 to 88% depending on soil. Pronounced metal toxicity on N_dff was only confirmed in a sludge treated soil where nitrogen fixation was halved from the control value at soil total metal concentration of 737 mg Zn kg⁻¹, 428 mg Cu kg⁻¹ and 10 mg Cd kg⁻¹. The N_dff was significantly reduced by increasing metal concentration in soils from two other sites where N_dff was low throughout and where these effects might be attributed to confounding factors. No significant effects of metals on N_dff were identified in all other gradients even up to elevated total metal concentration (e.g. 55 mg Cd kg⁻¹). The variation of N_dff among all soils (n=48), is mainly explained by the number of rhizobia in the soil (log MPN, log (cells g⁻¹ soil)), whereas correlations with total or soil solution metal concentrations were weak (R²<0.25). The is significantly affected by the presence or absence of the host plant at the sampling site. No effects of metals were identified at even at total Zn concentrations of about 2000 mg Zn kg⁻¹, whereas metal toxicity could be identified at lower most probable number (MPN) values. This survey shows that the metal toxicity on symbiotic nitrogen fixation cannot be generalized and that survival of a healthy population of the microsymbiont is probably the critical factor.     

Short-Term Agronomical Effects of Olive Oil Pomace Composts on Pisum arvense L. and Trifolium subterraneum L. and Impacts on Soil Properties

Olive oil pomace (OLP) contains organic matter and nutrients that could be recycled by composting and supplying it to crops, solving the problem of disposal.

The effects of two OLP composts (C1 and C2) were assessed on two leguminous forage crops commonly cropped in the local livestock farms. In particular, C1 was applied on proteic pea and C2 on clover, compared with a mineral fertilizer (Min) and a commercial organic–mineral fertilizer (Org-min). The influence of composts on some soil chemical properties was also investigated.

The application of C1 significantly increased proteic pea dry weight at the end of the cycle by 27.2% and 52.0% and grain yield by 23.2% and 43.6%, in comparison with Org-min and Min, respectively. The clover dry weight during the entire cycle was lower in C2, in comparison with the other treatments, while no significant difference was found between C2 and the Org-min treatment both in yield and plant height.

Soil nitrate decreased from the beginning to the end of the trial in C1 and C2 plots by 22.8% and 50.9%, respectively. Soil phosphorous content significantly increased in Min by 32.4 and 41.7% compared to C1 and C2, respectively. These results showed that the substitution of commercial fertilizers with compost could be an environmentally sustainable solution. The high presence of heavy metals in compost should not affect soil application at least in this short-term trial.     

不同施肥处理对红车轴草生长发育的影响

[目的]探讨不同肥料配施对红车轴草生长发育的影响。[方法]以从美国引进的红车轴草Agivasion为供试品种,在大田条件下设置不施肥、单施N、NP配施和NPK配施4个处理,研究不同施肥处理对红车轴草生长发育的影响。[结果]施肥促进了红车轴草的生长发育,如：株高增加,尤以NP配施的促进作用最大;促发分枝,以NPK配施的促进效应最好;促进根颈增粗,以NP配施、NPK配施的效应较好。施肥在0.01水平上极显著促进红车轴草的茎、叶干物质积累和单株产量增长,促进效应以NPK配施〉NP配施≈单施N〉〉CK,各施肥处理之间单株产量差异不显著。[结论]合理施肥可促进红车轴草的生长发育。     

Genetic diversity of a natural population of Rhizobium leguminosarum biovar trifolii analysed from field nodules and by a plant infection technique

We compared trapping of Rhizobiumleguminosarum biovar trifolii isolates under field soil and non-soil environmental conditions. Isolates were obtained from white clover (Trifoliumrepens L.) and red clover (T. pratense L.) grown directly in the field and from plants inoculated with soil from the same site using a plant infection technique. Isolates were identified by genomic polymerase chain reaction (PCR) fingerprinting using primers derived from the enterobacterial repetitive intergenic consensus (ERIC) sequences. The isolates trapped from soil dilutions in the laboratory included a number of major ERIC types that were not found in the field trapped nodules, suggesting that sampling of clover Rhizobium strains from soil dilutions may not be representative of the field nodulating population.     

香根草·苜蓿和三叶草对土壤盐分的影响

[目的]为了比较香根草、苜蓿和三叶草对土壤盐分吸收能力的优劣。[方法]采用不同等级的NaCl溶液或K2CO3溶液,定期定量浇灌栽培在同质地土壤上的香根草、苜蓿和三叶草。通过5个月试验研究,分析香根草的成活率、分蘖率和香根草、苜蓿和三叶草的生物量积累率及植株体内的盐分含量,并比较了香根草、苜蓿和三叶草吸收土壤中盐分的质量和能力。[结果]香根草、苜蓿和三叶草都对土壤中盐分有吸收能力,且苜蓿对土壤盐分吸收能力最强,香根草对土壤盐分吸收能力次之,三叶草对土壤盐分吸收能力最弱。[结论]香根草、苜蓿和三叶草对土壤中盐分的吸收能力与土壤盐度有关,同时对土壤中盐分的吸收是有选择性的。     

间种白三叶草和稻草覆盖控制丘陵茶园杂草效果

开展丘陵茶园杂草生态控制,可减少对茶园土壤水分和养分的消耗,避免使用化学除草剂。连续2年的田间试验,野外应用小样方多点采样调查茶园杂草种群数量、生物量、平均株高和茶芽密度等指标,结合实验室的茶叶内含成分分析和感官评审。结果表明:茶园共有杂草16科31属31种,春季(4月)以生长速度较慢、生物量小、株高在30cm以下的杂草为主,夏季(7月)以生长快、植株高和生物量大恶性杂草为主,秋季(9月)恶性杂草开始减少,酢浆草、白花蛇舌草等生物量小、株高矮的杂草逐渐增多;稻草覆盖处理茶园春、夏和秋季3个观测时期杂草物种丰富度(S)、多样性(H)、均匀度(J)等指数均高于清耕对照,优势集中性指数(C)低于清耕对照;间种白三叶草处理春、夏和秋季3个观测时期杂草总数量和生物量均显著低于清耕对照,夏、秋季杂草平均株高显著低于清耕对照;稻草覆盖和间种白三叶草处理春季茶芽重和产量显著高于清耕对照,鲜叶中游离氨基酸含量高于清耕对照,茶叶感官评审得分高于清耕对照处理。这表明稻草覆盖和间种白三叶草能改变茶园杂草群落结构,有效控制杂草生长,增加茶叶产量和改善茶叶品质。     

Evaluation of the effect of eprinomectin in young dairy heifers sub-clinically infected with gastrointestinal nematodes on grazing behaviour and diet selection

Inappetence is commonly associated with parasitism and has been observed in both housed and pastured ruminants. In seeking a functional explanation for these observations, it has been hypothesised that parasitized animals may feed more selectively in order to proportionally increase the protein content of their diet and thus partially compensate for their reduced feed intake. Support for this theory is found principally in studies in housed animals under carefully controlled experimental conditions. Grazing animals face a far more heterogeneous environment and a multiplicity of potentially confounding factors that could influence diet selection. Controlled grazing of adjacent monocultures of grass and clover can mitigate some of these variables and was used in the current study to examine the dietary preference of dairy heifers with sub-clinical parasitic gastroenteritis when compared to those receiving regular anthelmintic treatments. Grazing behaviour and herbage intake rates were determined through the use of jaw-movement recorders, direct observation and short-term liveweight change. Consistent with previous observations and despite evidence that nematode burdens were low in the untreated control heifers, a reduction in daily grazing time of 56 min (P = 0.054) was observed in the control animals. There was, however, no evidence that the control heifers showed greater preference for clover compared with ryegrass: partial preference for clover was 73.0% in the untreated controls and 75.5% in the treated heifers. Furthermore control heifers were observed grazing the clover swards significantly (P = 0.032) less frequently than the treated heifers. This study provides additional evidence in grazing cattle for parasite-induced inappetence, manifest as a reduction in grazing time and in subtle changes in ingestive behaviour. The observed partial preference for clover in both treated and control cattle was not significantly affected by the level of parasitism.     

Nitrous oxide emissions and methane oxidation by soil following cultivation of two different leguminous pastures

 Nitrous oxide (N₂O) emissions and methane (CH₄) consumption were quantified following cultivation of two contrasting 4-year-old pastures. A clover sward was ploughed (to 150–200 mm depth) while a mixed herb ley sward was either ploughed (to 150–200 mm depth) or rotovated (to 50 mm depth). Cumulative N₂O emissions were significantly greater following ploughing of the clover sward, with 4.01 kg N₂O-N ha^–1 being emitted in a 48-day period. Emissions following ploughing and rotovating of the ley sward were much less and were not statistically different from each other, with 0.26 and 0.17 kg N₂O-N ha^–1 being measured, respectively, over a 55-day period. The large difference in cumulative N₂O between the clover and ley sites is presumably due to the initially higher soil NO₃ ^– content, greater water filled pore space and lower soil pH at the clover site. Results from a denitrification enzyme assay conducted on soils from both sites showed a strong negative relationship (r=–0.82) between soil pH and the N₂O:(N₂O+N₂) ratio. It is suggested that further research is required to determine if control of soil pH may provide a relatively cheap mitigation option for N₂O emissions from these soils. There were no significant differences in CH₄ oxidation rates due to sward type or form of cultivation. Received: 1 November 1998     

Effect of spring fertilization on ecosystem services of organic wheat and clover relay intercrops

Nitrogen (N) deficiency and weed infestation are main factors limiting yield and yield stability in organic wheat. Organic fertilizers may be used to improve crop performance but off-farm input costs tend to limit profitability. Instead, forage legumes may be inserted into the crop rotation to improve the N balance and to control weed infestation. In opposition to simultaneous cropping, relay intercropping of legumes in organic winter wheat limits resource competition for the legume cover crop, without decreasing the performance of the associated wheat.The aim of this study is to evaluate the effect of spring organic fertilization on the performance of intercropped legumes and wheat, and on services provided by the legume cover.Two species of forage legumes (Trifolium pratense L. and Trifolium repens L.) were undersown in winter wheat (Triticum aestivum L. cv Lona) in five organic fields during two consecutive crop seasons. Organic fertilizer was composed of feather meal and applied on wheat at legume sowing. The cover crop was maintained after the wheat harvest and destroyed just before sowing maize.Spring organic nitrogen fertilization increased wheat biomass (+35%), nitrogen (+49%), grain yield (+40%) and protein content (+7%) whatever the intercropping treatment. At wheat harvest, red clover biomass was significantly higher than white clover one (1.4 vs. 0.7 t ha⁻¹). Nitrogen fertilization decreased forage legume above-ground biomass at wheat harvest, at approximately 0.5 t ha⁻¹ whatever the specie. No significant difference in forage legume biomass production was observed at cover killing. Nitrogen accumulation in legume above-ground tissues was significantly higher for white clover than for red clover. Both red and white clover species significantly decreased weed infestation at this date. Nitrogen fertilization significantly increased weed biomass whatever the intercropping treatment and decreased nitrogen accumulation in both clover species (−12%).We demonstrated that nitrogen fertilization increased yield of wheat intercropped with forage legume while the performance of legumes was decreased. Legume growth was modified by spring fertilization whatever the species.     

三叶草不同品种叶结构特征与抗旱性的关系

为评价三叶草3个品种抗旱能力的强弱,了解其叶解剖结构与抗旱性的关系,以黑龙江乡土白三叶(Trifolium repens L.)以及2个引进品种瑞文德(T.repens L.)和普通红三叶(T.pretense L.)为材料,田间播种后正常管理,于当年选取成株叶,采用石蜡切片法,分析3个品种叶解剖结构与抗旱性的关系。结果表明:测定的10项指标中有6项指标,包括栅栏组织厚度、栅海比值、上表皮厚度、角质层厚度、主脉导管直径,以及木质部面积与维管束面积比值在品种间差异显著,可作为评价三叶草抗旱性的理想指标,应用隶属函数值法综合评价其抗旱能力由强到弱依次为黑龙江乡土白三叶>瑞文德>普通红三叶。