Semiarid land rehabilitation by direct drilling in the South Island,New Zealand—plant species and establishment technology

Large areas of the east coast and inland basins of the South Island, New Zealand, are affected by periodic drought and/or semiarid climatic conditions, particularly during cyclic El Niño climatic events. The severity of these environmental conditions places great stress on introduced and native pasture species and frequently results in poor establishment of new pastures using standard drilling techniques. The objective of this study was to determine effective, practical means of rehabilitating semiarid land (about 470 mm annual rainfall) on a site in Central Otago. A comparison of two direct drilling methods, a novel strip‐seeder drill and a standard hoe‐coulter drill, was conducted in a trial initiated during spring 1998. Five drought‐tolerant forage species were established: wheatgrass (Thinopyron intermedium), tall oat grass (Arrhenatherum elatius), birdsfoot trefoil (Lotus corniculatus), hairy dorycnium (Dorycnium hirsutum) and bluebush (Kochia prostrata). For the 2000/2001 growing season, species established with the strip‐seeder drill had an overall mean herbage biomass of 235 g m ⁻² , three‐times that for the hoe‐coulter drill (77 g m ⁻² , P < 0·001). Differences in herbage biomass between species were observed, with hairy dorycnium (mean 328 g m ⁻² ) producing significantly (P < 0·001) more herbage biomass than the other species. After the third spring, the percentage ground cover recorded from transects across the strip‐seeder drill plots (cf. the hoe‐coulter drill) was: wheatgrass—41 per cent (10 per cent); tall oat grass—44 per cent (25 per cent); birdsfoot trefoil—25 per cent (5 per cent); hairy dorycnium—50 per cent (19 per cent); and bluebush—4 per cent (0 per cent). The native plant content of the resident vegetation was reduced as a result of the drilling treatments and also when fertilizer was added to undistrubed pasture. The strip‐seeder drill is capable of providing superior plant growth on dryland sites even during adverse drought conditions. It produces a furrow approximately 16 cm wider than the hoe‐coulter drill, exerts a greater shattering effect on the soil structure and places fertilizer at depth. It is suggested that this assists plant establishment by providing good seedling protection from wind and sun, and subsequent plant growth by allowing easier root penetration to the subsoil where nutrients and moisture are available. Copyright © 2004 John Wiley & Sons, Ltd.     

水稻秸秆-薄膜连续叠加覆盖对三叶鬼针草的控制效果

入侵植物三叶鬼针草(Bidens pilosa L.)严重危害我国农林畜牧业的生产。为探究生态高效控制三叶鬼针草的方法,开展了水稻秸秆与塑料薄膜相结合覆盖控制入侵杂草的研究。试验在以三叶鬼针草和马唐[Digitaria sanguinalis(L.)Scop.]为主的自然杂草荒地进行,设置不同稻秆覆盖量(0kg·m~(-2)、1kg·m~(-2)、1.5kg·m~(-2)),于冬季进行稻秆覆盖,春季在稻秆覆盖的基础上覆盖薄膜。通过测定秸秆覆盖中期(2月12日)和薄膜覆盖中期(4月12日)的午间土壤温度、土壤相对含水量和近地表空气温湿度等环境指标和杂草生物量、种子萌发量、杂草群落结构和土壤种子库等群落指标,探究该方法控制入侵杂草的效果和机制。结果表明:冬季水稻秸秆覆盖显著降低了草地午间土壤温度、近地表空气温度、三叶鬼针草生物量和种子萌发量、优势杂草盖度和从属种的种类和数量;覆盖1.5 kg·m~(-2)稻秆的处理对各类指标的影响程度均大于1 kg·m~(-2)的处理。春季叠加薄膜覆盖导致浅层土壤高温干燥、近地表空气高温高湿;叠加薄膜覆盖处理使三叶鬼针草的土壤种子密度在0～5cm的土层内显著低于未做覆盖处理的对照,降低了79.49%;叠加薄膜覆盖处理的入侵杂草全部死亡且无种子萌发。说明冬季采用水稻秸秆覆盖,春季再叠加覆盖薄膜能有效防控三叶鬼针草的生长蔓延,在薄膜覆盖之前,覆盖1.5 kg·m~(-2)稻秆的处理对三叶鬼针草的防控效果要好于1 kg·m~(-2)的处理,在薄膜覆盖处理后,两个稻秆覆盖量处理对三叶鬼针草的防控效果均达到100%。本研究结果可为不同季节采用不同的控制方法及其组合模式防控入侵杂草的扩散提供参考。     

德兴铜矿尾矿库植被重建后的土壤肥力状况和重金属污染初探

德兴铜矿是我国的超大型铜矿,尾矿砂的排放是其主要的环境问题之一,目前主要堆积于尾矿库中。1号尾矿库于1986年服役期满后共堆积矿砂2.15×107 m3,面积约210 hm2。20世纪90年代后期,在坝坡约30 hm2覆有客土的地区进行了一系列植被重建的试验研究工作,本文报道了1998年开始在旱稻(OryzaLinn.)、花生(Arachis Linn.)、香根草(Vetiveria zizanioidesNash)和湿地松(Pinuselliottii Engelm.)等18种不同植被组合条件下的土壤基本农化性状(pH、有机质(OM)、铵态氮、速效P、速效K)以及0.05 mol L-1 HCl可提取态重金属在3~4年时间内的变化情况,结果表明,坝坡土壤N、P、K严重不足,且保水、保肥能力弱,需要不断地进行培肥和改良。三年多来,土壤pH总体上无显著变化;OM第三年有显著上升,约为第一年的127%;NH4 N成直线下降,第二年和第三年分别为第一年的72.9%和43.0%;随着耕作实践的推移,速效P和速效K显著上升,但仍旧处于较低水平。重金属(主要是Cu)污染严重,Cu、Zn、Pb、Cd在植物中有明显积累。研究结果强调了试验区在植被重建中不宜种植食用植物,以避免食物链的污染。     

Effect of sodium‐vinasse application on seed germination and growth of three species differing in salt tolerance

Abstract

The produced vinasse from molasses of sugar beets contains high amounts of nitrogen, potassium, and sodium (Na‐vinasse). In a pot experiment involving plant species of different tolerance to soil salts (cotton, corn, and beans), applications up to 10 t vinasse ha^‐1 did not significantly affect the seed germination, and had a positive effect on plant growth of all species. Increasing the vinasse application to 20 t ha^‐1 had no effect on seed germination of cotton and increased its growth. In contrast, a 20 t ha^‐1 application delayed the time of germination and inhibited corn and bean growth up to one month. Subsequently, plant growth increased and plant height 52 days after sowing was similar to that with the 10 t ha^‐1 treatment. For the bean plants, the negative effect of the 20 t ha^‐1 application continued and resulted in a higher dry matter in leaves, but lower dry matter in stems and fruits compared to the untreated soil. A replacement of potassium by sodium in cotton and corn plants was also observed at this vinasse application. Very high application of vinasse (100 t ha^‐1) resulted in a damage of cotton and bean seeds, while a higher portion of corn seeds germinated (64%). However, corn seeds that germinated collapsed after a few days. Among the three species studied, cotton plants absorbed the highest amount of sodium, corn plants the highest amount of potassium and those of bean the highest amount of nitrogen.     

Use of Germination and Seedling Performance Bioassays for Assessing Revegetation Strategies on Bauxite Residue

Bauxite residues from the extraction of alumina from bauxite ore are stored in residue disposal areas. These areas require revegetation and the major constraints and suitable plant species will differ with each site. Germination bioassays were used on bauxite residue from the Aughinish Alumina Ltd. refinery to determine properties inhibitory to seed germination and seedling development. Unamended residue was characterised as having high pH, sodicity, salinity and Al content. These properties had negative tests on seed germination and performance. Amendment of the residue improved chemical properties and greatly increased seedling performance in four test species. Decreased sodicity content in the residue extract resulted in seedling growth greater than achieved in the control. Lolium perenne and Trifolium pratense were identified as useful species for revegetation of amended bauxite residue.     

Microbial CO2 production, CH4 dynamics and nitrogen in a wetland soil (New York State, USA) associated with three plant species (Typha, Lythrum, Phalaris)

Plants furnish soil with organic carbon (OC) compounds that fuel soil microorganisms, but whether individual plant species – or plants with unique traits – do so uniquely is uncertain. We evaluated soil microbial processes within a wetland in which areas dominated by a distinct plant species (cattail –Typha sp.; purple loosestrife –Lythrum salicaria L.; reed canarygrass –Phalaris arundinacea L.) co‐mingled. We also established an experimental plot with plant shoot removal. The Phalaris area had more acidic soil pH (7.08 vs. 7.27–7.57), greater amount of soil organic matter (19.0% vs. 9.0–11.5%), and the slowest production rates of CO₂ (0.10 vs. 0.21–0.46 μmol kg⁻¹ s⁻¹) and CH₄ (0.040 vs. 0.054–0.079 nmol kg⁻¹ s⁻¹). Nitrogen cycling was dominated by net nitrification, with similar rates (17.2–18.9 mg kg⁻¹ 14 days⁻¹) among the four sampling areas. In the second part of the study, we emplaced soil cores that either allowed root in‐growth or excluded roots to evaluate how roots directly affect soil CO₂ and CH₄. The three plant species had similar amounts of root growth (ca 290 g m⁻² year⁻¹). Fungal biomass was similar in soils with root in‐growth versus root exclusion, regardless of dominant plant species. Rates of soil CO₂ production did not differ with root in‐growth versus root exclusion, and added glucose increased CO₂ production rates by only 35%. Root in‐growth did lead to greater rates of CH₄ production; albeit, addition of glucose had much greater effect on CH₄ production (1.24 nmol kg⁻¹ s⁻¹) compared with controls without added glucose (0.058 nmol kg⁻¹ s⁻¹). Our data revealed relatively few subtle differences in soil characteristics and processes associated with different plant species; albeit, roots had little effect, even inhibiting some microbial processes. This research highlights the need for both field and experimental studies in long‐established monocultures of plant species to understand the role of plant biodiversity in soil function.     

Selection of Adequate Species for Degraded Areas by Oil‐Exploitation Industry as a Key Factor for Recovery Forest in the Ecuadorian Amazon

One of the requirements for the forest restoration of soils disturbed by the oil‐exploitation industry is that saplings be able to endure soil‐adverse conditions. In this study, saplings of 20 species susceptible to be used in reforestation programs were evaluated for their ability to grow on substrates derived from soils disturbed by petroleum extractions in the Ecuadorian Amazon. Seeds of each species were planted in germination trays. Once seedlings reached 5 cm in height they were transplanted to plastic bags with three treatment substrates: two derived from petroleum‐exploitation activity (soils from mud and drill cutting cells and from areas surrounding oil wells) and a control soil. Plant survival rate, stem height, and diameter were measured on a weekly basis until 14 weeks after transplantation, when we harvested the plants and also measured plant biomass and calculated the Dickson quality index for each species. Oil‐exploitation by‐product substrates impaired the performance of many saplings, with the substrate from mud and drill cutting cells being the one that most affected plant performance. Only saplings of five native species in the Amazon basin—Apeiba membranaceae, Cedrelinga cateniformis, Inga densiflora, Myroxylon balsamum, and Pouroma cecropiifolia—exhibited high or similar Dickson quality index values in all soil treatments and performed better than the rest. The use of these five species in remediation of soils disturbed by petroleum extraction in the Amazon basin could prove important because of their high potential to adapt to these disturbed sites. Copyright © 2016 John Wiley & Sons, Ltd.     

Growth and nutrition of Holcus lanatus in bauxite residue amended with combinations of spent mushroom compost and gypsum

Bauxite residues are very slow to naturally vegetate due to nutrient deficiency and high sodicity. In order to test the effectiveness of amendments at promoting revegetation, bauxite residue was amended with varying rates of compost to increase fertility (0, 60, 80 and 120 t ha⁻¹) and gypsum to reduce sodicity (0, 40 and 90 t ha⁻¹). Amended residue was sown with Holcus lanatus, a perennial grass. Following a 1‐year growth period, substrate properties, plant performance and plant nutrient uptake were assessed. Compost application substantially increased substrate N, P, K and Mn concentrations, while gypsum application greatly reduced sodicity and improved nutrient uptake for Mn and P. Compost amendment was essential for sustainable plant growth. Foliar deficiencies in N, P and Mg may persist with lower compost application rates, requiring the addition of supplemental fertiliser for healthy plant growth. Copyright © 2010 John Wiley & Sons, Ltd.     

栽培方式对菘蓝农艺性状及产量和品质的影响

栽培方式对中药材产量和品质影响较大。本研究为了探讨河西走廊绿洲灌溉区菘蓝的最佳栽培方式,通过田间试验,采用栽培模式(平作和垄作)和覆膜方式(不覆膜、覆白膜和覆黑膜)二因素随机区组试验设计,设置6个处理。按照播种至收获每月一次定期采集菘蓝植株样品,测定了6种栽培方式下菘蓝根农艺性状指标、板蓝根产量及检测成分(R,S)-告依春含量。结果表明,不同栽培方式对菘蓝根长、根直径、单株根干重的累积动态、板蓝根产量和质量均具有显著影响。垄作覆黑膜栽培菘蓝根的快速生长持续期最长,根系最发达,根长、根直径和单株根干重均较高。板蓝根产量以垄作覆黑膜栽培最高(4 514.4 kg·hm~(-2)),垄作覆白膜产量最低(3 116 kg·hm~(-2));(R,S)-告依春含量以垄作覆白膜最高(2.61 g·kg~(-1)),垄作不覆膜最低(1.37 g·kg~(-1))。在不同栽培方式下,菘蓝主根长、根直径和单株根干重生长随生长时间均呈现"S"型生长趋势,符合Logistic生长模型。河西走廊绿洲灌区菘蓝收获板蓝根适宜栽培方式为垄作覆黑膜栽培。     

EFFECTS OF SOIL SALINITY IN THE GROWTH OF AMBROSIA ARTEMISIIFOLIA BIOTYPES COLLECTED FROM ROADSIDE AND AGRICULTURAL FIELD

Morphological differences were observed between roadside (R) and agricultural field (F) biotypes of Ambrosia artemisiifolia, in which R-type seedlings were shorter and produced larger and heavier seeds under greenhouse grown conditions. Previous findings indicated that A. artemisiifolia R-types exhibited greater salt tolerance with respect to germination. However, the impact of biotype and salt tolerance on morphological variation has not been investigated in A. artemisiifolia plants. After performing replicated greenhouse experiments with both biotypes, it was shown that salinity level was a critical factor influencing both seedling and mature plant size and this response was dependent upon biotype. The R-type exhibited slight but significant increases in growth at low/mild salinity levels (50–100 mM) compared with non-saline conditions, while the F-type exhibited significantly reduced growth at the low/mild salinity levels. The reductions in growth of F-type plants in low/mild salinity were similar to those reductions of R-types observed in non-saline conditions. As both biotypes produced seeds at low/mild salinity levels, we conclude that low/mild salinity affects A. artemisiifolia plant size and overall growth rate, and secondly, certain F-type plants may acclimate to the roadside environment over time by reducing their size while producing larger seed under saline conditions. It is possible that this species may exhibit changes in morphology after several generations of exposure to saline roadside conditions. Toxicity due to salt treatment at high salinity (400 mM) was observed in both biotypes, whereas the R-type was more tolerant to both low and high salinity levels with respect to seed germination. Differential A. artemisiifolia growth responses which occur from seed germination to plant maturity may be partially attributed to its ability to tolerate saline soil conditions both under greenhouse and field conditions. This ability to tolerate saline conditions may be especially important in early spring when roadside soils experience increased salinity, caused by de-icing salt treatments applied during the winter season.     

EFFECT OF NANOSCALE ZINC OXIDE PARTICLES ON THE GERMINATION,GROWTH AND YIELD OF PEANUT

An investigation was initiated to examine the effects of nanoscale zinc oxide particles on plant growth and development. In view of the widespread cultivation of peanut in India and in other parts of the globe and in view of the potential influence of zinc on its growth, this plant was chosen as the model system. Peanut seeds were separately treated with different concentrations of nanoscale zinc oxide (ZnO) and chelated bulk zinc sulfate (ZnSO₄) suspensions (a common zinc supplement), respectively and the effect this treatment had on seed germination, seedling vigor, plant growth, flowering, chlorophyll content, pod yield and root growth were studied. Treatment of nanoscale ZnO (25 nm mean particle size) at 1000 ppm concentration promoted both seed germination and seedling vigor and in turn showed early establishment in soil manifested by early flowering and higher leaf chlorophyll content. These particles proved effective in increasing stem and root growth. Pod yield per plant was 34% higher compared to chelated bulk ZnSO₄. Consequently, a field experiment was conducted during Rabi seasons of 2008–2009 and 2009–2010 with the foliar application of nanoscale ZnO particles at 15 times lower dose compared to the chelated ZnSO₄ recommended and we recorded 29.5% and 26.3% higher pod yield, respectively, compared to chelated ZnSO₄. The inhibitory effect with higher nanoparticle concentration (2000 ppm) reveals the need for judicious usage of these particles in such applications. This is the first report on the effect of nanoscale particles on peanut growth and yield.     

Comparison of Pioneer and Native Woodland Species Growing on Top of an Engineered Landfill,Hong Kong: Restoration Programme

This study dealt with a restoration project conducted at South‐East New Territories Landfill in Hong Kong, in order to screen suitable tree and shrub species (both native and pioneer species) for revegetation. For engineered landfills, landfill gas migration and leachate contamination to the topsoil are rarely problematic, but the lack of nutrients and moisture and poor physical soil conditions may jeopardize potential woodland establishment. The growth performance of 25 woody plant species subjected to 12 different soil amelioration and seedlings planting methods was compared. The results showed that the general performance (mortality rate, apical height, crown diameter and basal diameter) of pioneer species (notably Acacia species) was much better than that of native species in all blocks of woodland mix and scrub mix. The notch planting method was effective in helping seedling roots to have better contact with soil for water uptake, which subsequently increased the survival rates of seedlings, leading to a better tree coverage. Soil ameliorations (horticultural soil with fertilizer and horse and pig manure) generally increased the seedling survival rate and improved plant growth. Tree coverage on all the plant trial blocks was mainly established by the three Acacia species. A planting distance of 1 m was recommended for woodland establishment, and such dense seedlings planting would achieve a better tree coverage under a shorter period of time (than the distance of 3 m). Difficulties in woodland establishment were discussed, and the strategies for achieving a better tree growth were recommended. Copyright © 2015 John Wiley & Sons, Ltd.     

黄麻土工布覆盖对花岗岩红壤表土坡面侵蚀特性的影响

[目的]探究黄麻土工布覆盖条件下花岗岩红壤表土坡面侵蚀特性,为花岗岩红壤区坡面土壤侵蚀防治提供科学依据。[方法]通过室内模拟降雨试验,在2个坡度(5°和15°坡度)、3种密度(无覆盖,6 cm×6 cm及3 cm×3 cm网格)的黄麻土工布覆盖条件下,研究极端降雨条件下(90 mm/h)花岗岩红壤表土的坡面侵蚀特性,并观测径流系数、土壤侵蚀速率、泥沙颗粒变化规律及富集率等指标。[结果]坡面径流随降雨历时增加而增加,土壤侵蚀速率则相反,表明侵蚀过程是一个分离受限的过程。和对照组相比,黄麻土工布覆盖在不同试验条件下都具有明显的减流减沙作用。另外,由侵蚀泥沙的粒径分选规律可知,坡面土壤中的黏粒和粉粒大小的颗粒倾向于被优先选择性搬运,其结果致使坡面石英粗颗粒富集,在缓坡(5°)与高密度黄麻土工布覆盖条件下(3 cm×3 cm网格)尤为突出。坡面石英粗颗粒随降雨历时增加不断富集进一步增加了原位坡面的侵蚀抗性,产生了土壤侵蚀速率随降雨历时不断降低的现象。[结论]高密度黄麻土工布的覆盖能够有效地减流减沙,增加原位坡面抗蚀性,是一种有效的水土保持措施,在今后的土壤侵蚀防治和劣地恢复工作中应该被重视。     

2-methylisoborneol and geosmin,the main sources of soil odor,inhibit the germination of brassicaceae seeds

The effects of 2-methylisoborneol (MIB) and geosmin, the main sources of soil odor produced by microorganisms, on plant seed germination were examined for 15 kinds of Brassicaceae seeds including radish (Raphanus sativus var. radicula). Authentic MIB or geosmin was used at the concentration of 100 mg L^-1 in the assay, the effects were quantitatively indexed based on four parameters of cumulative seed germination: the final germination percentage, germination onset, weighted mean rate, germination index. MIB and geosmin inhibited germination of all kinds of seeds tested for these parameters. Radish variety “Comet” was the most affected of all of the tested plant seeds. The estimated 50% inhibitory concentration values on germination of “Comet” were 70.5 and 7.5 mg L^-1 for MIB and geosmin, respectively. We also conducted the primary characterization of the inhibition by MIB and geosmin on “Comet” seeds. Our findings were as follows: (1) onset of seed imbibition was not affected; (2) germination of seeds pre-imbibed in the control solution until approx. 2 h before germination onset was inhibited by subsequent MIB or geosmin treatment; (3) growth of seedlings was not significantly affected; (4) the germination was restored by stratification, gibberellin A₃ treatment, or seed coat removal; and (5) light irradiation affected the degree of inhibition. These results suggest that inhibition by MIB and geosmin is restricted to the germination process, at least in the early stage of growth, that they act as growth -regulating substances.     

Growth and selenium uptake of range plants propagated in uranium mine soils

High soil selenium (Se) levels have been found in association with uranium deposits in Texas. A concern that high Se concentrations may be found in forages grown on reclaimed mine lands prompted this investigation. A native soil sampled near the mining area, and overburden materials sampled from two Se enriched uranium mine spoil sites were compared in a plant growth study in the greenhouse. Shoot yields and shoot Se concentration in each of ten grasses common to the region were determined from plants harvested three weeks after germination and from shoot regrowth harvested four weeks after the first harvest. Shoot weights were reduced for 5 of the 10 species growing in soils with medium and high Se status. Total shoot weights of Cynodon dactylon and Panicum coloratum from two harvests were consistently highest in all soil materials and are highly recommended for use as a stabilizing cover crop for lands disturbed from uranium mining. Generally, no correlation was observed between shoot weight and plant Se concentration or uptake in the 10 species. However, plant tissue Se concentrations in all species for at least one of the two harvest dates were above the 5 mg kg^‐1 concentration considered potentially harmful to grazing livestock. Therefore, none of these species would be a suitable forage for livestock grazing on reclaimed Se‐enriched uranium mining overburden.     

Involvement of nitrogen in salt resistance of Atriplex portulacoides is supported by split‐root experiment data and exogenous application of N‐rich compounds

Using a split‐root system, we aimed to identify the limiting factors for the growth of the halophyte Atriplex portulacoides L. under extreme salinity (800 mM NaCl) conditions. One half of the root system was immersed in complete nutrient solution at 0 or 800 mM NaCl and the other half was immersed in NaCl‐free medium, containing all nutrients or deprived of potassium (K⁺) or calcium (Ca²⁺) or nitrogen (N). Data indicate that at high salinity levels A. portulacoides growth is limited by the restrictions imposed by NaCl on N uptake. Next, the alleviation of the adverse impact by salt stress (800 mM NaCl) on plant growth was investigated through urea (U) and/or thiourea (TU) external addition through foliar application. Whether separately or supplied together, both components mitigated the negative impact of salinity on the plant growth by significantly improving the photosynthetic activity parameters [CO₂ assimilation rate, stomatal conductance and maximum quantum efficiency of PSII photochemistry (F_v/F_m)], as well as shoot N concentration and the photosynthetic nitrogen‐use efficiency (PNUE). A concomitant increase of protein and free amino acid concentrations was also observed. As a whole, the present study highlights the significance of N in A. portulacoides response to high salinity and suggests that combined application of U and TU could promote the growth of this halophyte potentially useful for saline soil reclamation and revegetation purposes.     

EFFECT OF ARSENIC ON GERMINATION,PHOTOSYNTHESIS AND GROWTH PARAMETERS OF TWO WINTER WHEAT VARIETIES IN IRAN

□ Effects of different arsenic (As) concentration (0–30 mg L^?1) on seed germination, root tolerance index, relative shoot height, root and shoot biomass, photosynthetic pigments and arsenic accumulation in two wheat varieties were investigated. Low concentrations of arsenic (0–2.5 mg L^?1) stimulated germination percentage, shoot and root elongation, plant biomass as well as chlorophyll content as compared with control, however, these factors all decreased gradually at high concentrations of arsenic (5–30 mg L^?1). ‘Zarin’ variety had a significantly higher tolerance to arsenic than ‘Sardari.’ Arsenic accumulation by plants root and shoot increased with the increasing arsenic concentrations in medium, which ‘Zarin’ had a higher ability to absorb and translocate arsenic to the shoots. Root accumulated more arsenic than shoot. The similar trend of chlorophyll content and wheat growth under different arsenic concentration suggesting that arsenic toxicity affects the photosynthesis which ultimately results in the reduction of wheat growth and yield.     

Effects of Culture Filtrates of Rhizobacteria Isolated from Wild Lupine on Germination,Growth, and Biological Nitrogen Fixation of Lupine Seedlings

Abstract

In order to select potential Plant Growth Promoting Rhizobacteria (PGPRs), a selection of strains from the predominant genera in the rhizosphere of four lupine species, based on genetic divergence criteria, carried out in a previous study, yielded 11 Aureobacterium (Aur), four Cellulomonas (Cell), two Arthrobacter (Arth), two Pseudomonas (Ps), and six Bacillus (Bc) strains. Cell‐free culture filtrates of each bacterium were assayed for effects on germination, growth, and biological nitrogen fixation (BNF) of Lupinus albus L. cv. Multolupa seeds or seedlings. Four (Aur 6, Aur 9, Aur 11, and Cell 1) of the twenty‐five strains assayed promoted germination. Aureobacterium 6 and Aur 9 also increased root surface, total nitrogen content, and BNF. As a result of the screening, and considering all the variables studied, Aur 6 can be considered a plant growth promoting rhizobacterium and is suitable for further field trials in other plants and in different production systems.     

Nutrient‐rich compost versus nutrient‐poor vermicompost as growth media for ornamental‐plant production

A comparative study on the suitability of one compost and two vermicomposts, obtained from the same batch of tomato‐crop waste, as growth media for ornamental plant production was carried out. Each material was mixed with Sphagnum peat at 100 : 0, 75 : 25, 50 : 50, 25 : 75, and 0 : 100 (peat control) proportions by volume. Two ornamentals (Calendula officinalis, Viola cornuta) were sown and grown in the 13 substrates. Substrates were characterized physically and chemically. Seed germination, total leaf chlorophyll (SPAD units), plant growth, and plant nutrient concentrations were determined. The compost and the vermicomposts were markedly different from peat. Compost and the vermicomposts had greater bulk density and lower total porosity than peat. Compost had larger aeration and lower water‐holding capacity than vermicomposts and peat. Compost and vermicomposts were alkaline (pH = 8.8 on average) whilst peat was acidic (pH = 5.9). Electrical conductivity was low in peat (0.23 dS m^–1) and vermicomposts (0.65 dS m^–1), and high in compost (2.85 dS m^–1) due to the high concentrations of K⁺ and SO$ _4^{2-} $ . Mixing compost and vermicomposts with peat produced substrates with intermediate characteristics. Physical properties were within adequate range for all mixes except for the compost ones. pH was within adequate range only in pure peat, and salinity was extremely high in the compost mixes. Compost was phytotoxic, as shown by the strong reduction of seed germination, chlorophyll content, and plant growth of both ornamentals. Vermicomposts did not affect seed germination but reduced plant growth, though much less than compost. Mixing these materials with peat improved germination and growth. The diluted materials (compost at the 25 : 75 and vermicomposts at the 50 : 50 and 25 : 75 proportions) produced good‐quality plants.