氮磷钾配比对木薯养分吸收动态及产量影响

【目的】木薯是重要的粮食作物,也是优质的淀粉工业原材料,被认为是非粮生物质能源的最合适原料。氮、 磷、 钾含量水平显著影响木薯产量,但有关木薯养分阶段性累积特征及其对生物量和产量形成影响的相关研究仍较少。本文比较了不同肥料配比情况下,木薯生物量, 氮、 磷、 钾累积量变化趋势,探讨了不同生育期氮、 磷、 钾含量及累积量的重要性及施肥对其影响。【方法】以我国主栽木薯品种华南205为材料,2009年在广东省郁南县丘陵坡地开展田间施肥试验,共设CK、 NP、 NK、 PK、 NPK 5个施肥处理。于苗期、 块根形成期、 块根生长早期、 块根快速膨大期和成熟期调查生物量和氮、 磷、 钾含量,得出氮、 磷、 钾累积动态。以各时期氮、 磷、 钾含量及累积量作为原始变量进行主成分分析,判断各时期氮、 磷、 钾含量及累积量的重要性,并分析不同肥料配比对各时期氮、 磷、 钾含量及累积量的影响。【结果】华南205的生物量累积动态呈S型曲线, 生物量在苗期较小,进入块根形成期后快速提高,当进入成熟期后增长逐渐减缓。氮肥对生物量影响最大,其次是钾肥,磷肥的影响最小。木薯氮含量的变幅为3.99%~0.93%, 磷含量为0.82%~0.26%, 钾含量为1.39%~0.89%。氮、 磷、 钾含量均在苗期最高,且随着生育期的推进不断降低,尤以氮含量降幅最大。不同氮、 磷、 钾肥料配比显著影响木薯的氮、 磷、 钾含量。PK处理的氮含量较NPK处理降低了32.96%,NK处理的磷含量较NPK处理降低了16.21%,NP处理的钾含量较NPK处理降低了50.37%。氮、 磷、 钾累积量与产量显著相关。主成分分析表明木薯整个生育期的营养状况与块根形成期的氮含量、 苗期的钾含量及块根生长阶段的磷含量相关性最大。氮、 磷、 钾的吸收累积量随着木薯生长不断提高,其中块根形成期、 块根生长早期、 块根快速膨大期的氮累积量较大,块根形成期、 块根快速膨大期的磷累积量较大,块根生长早期、 块根快速膨大期、 成熟期的钾累积量较大。主成分分析表明块根快速膨大期的氮、 磷、 钾累积量对整个生育期养分累积影响显著,同时,苗期及块根生长早期的氮、 钾累积量对养分累积总量影响也较大。【结论】木薯氮、 磷、 钾含量随着植株生长不断下降,而累积量却不断提高。不同氮、 磷、 钾肥料配比显著影响木薯的氮磷钾含量及累积量、 物质累积及产量形成,其中氮肥的影响最大,其次是钾肥,磷肥的影响最小。综合分析表明,苗期、 块根形成期、 块根生长早期为氮、 磷肥的最佳施用时期,块根形成期、 块根生长早期及块根快速膨大期为钾肥的补充阶段。     

Impact of quality and quantity of biochar and hydrochar on soil Collembola and growth of spring wheat

The effects of biochar (maize biochar – MBC, wood biochar – WBC) and unfermented or fermented hydrochar (HTC) on the euedaphic Collembola Protaphorura fimata and on spring wheat were investigated in greenhouse experiments. The impact of char type, amount of fermented HTC, and MBC-Collembola interactions were assessed. Generally, shoot and root biomass as well as abundance of P. fimata were not affected by the different chars. However, with increasing amounts of fermented HTC the abundance of P. fimata declined, whereas shoot biomass of wheat increased. Moreover, MBC altered root morphology and resulted in thicker roots with higher volume. The latter was not apparent when Collembola were present.     

氮钾配施对芋头产量和品质的影响

采用二次饱和D-最优设计,研究了氮钾肥配施对芋头产量和品质的影响,并建立了以氮、钾肥施用量为变量因子,芋头产量和品质为目标函数的二元二次数学模型。模型解析表明,氮、钾肥对芋头产量和品质均有显著影响,且钾肥的影响大于氮肥;氮、钾肥之间存在显著的交互效应。在氮(N)、钾(K2O)施用量分别为261.75kg/hm2、757.50kg/hm2以内,产量随施肥量的增加逐渐提高,超过此施用量,则产量下降。在本试验条件下,施肥量为N34.5～531.0kg/hm2,K2O.526.8～1057.2kg/hm2,芋头产量可达30000kg/hm2以上。     

Activity and degradation of streptomycin and cycloheximide in soil

Streptomycin and cycloheximide were added (3 and 2 mg g^-1 dry soil, respectively) single and in combination to a forest soil to follow their possible degradation and their effects on soil mineralization-immobilization processes. After 0, 1, 2, 4, 7, and 10 days of incubation at 25°C and 60% water-holding capacity, measurements were taken of microbial biomass C and N, the evolution of CO₂, exchangeable NH _inf4 ^sup+ , 0.5M K₂SO₄-extractable organic C, and total N in both unfumigated and CHCl₃-fumigated soil. The results indicated that during the first 2 days of incubation, soil microorganisms were killed by the antibiotics and/or by CHCl₃ and used subsequently as a substrate by the survivors. Thereafter, surviving microorganisms probably also started to use biocidal molecules as an energy and nutrient source. The ratios of biomass C to biomass N and of CO₂ evolved to net NH _inf4 ^sup+ produced indicated that both biocides had non-target effects for most of the incubation. Thus, streptomycin and cycloheximide are not suitable in determining the relative contribution from fungi and bacteria to mineralization-immobilization processes in soils.     

氟 对玉米产量品质及土壤性质的影响

适量氟对动物和人类健康有益, 而过量氟对动物和人类健康有害。为研究氟对玉米产量品质及土壤性质的影响, 采用盆栽试验研究了添加0、100 mg·kg^-1、200 mg·kg^-1、500 mg·kg^-1、1 000 mg·kg^-1 和1 500 mg·kg^-1 氟(NaF)对玉米产量、粗蛋白和淀粉含量及土壤pH、水溶性钙和微生物数量的影响。结果表明: 随氟处理浓度的增加玉米产量显著降低, 减产9.9%~85.4%; 玉米籽粒蛋白质含量显著增加, 从91.8 g·kg^-1 增加到108.8 g·kg^-1。加入氟100 mg·kg^-1 和200 mg·kg^-1 时, 淀粉含量表现为下降趋势,而当加入氟500 mg·kg^-1、1 000 mg·kg^-1 和1 500 mg·kg^-1 时, 淀粉含量表现为上升趋势。玉米不同部位氟含量基本上随氟浓度的增加而增加, 玉米根部和籽粒含氟量与氟添加量的相关性达极显著水平, 相关系数分别为r_根=0.998^**和r_粒=0.915^**; 叶含氟量与氟添加量的相关性达显著水平, r_叶=0.852^*; 玉米不同部位氟含量的大小顺序为根>叶>叶鞘>茎>籽粒。氟浓度在200 mg·kg^-1 时, 籽粒含氟量已超过无公害农产品标准1.0 mg·kg^-1。石灰性土壤添加氟后, 可使土壤pH 增加,从8.05 增加到8.70; 水溶性钙含量显著下降, 由2.71 g·kg^-1 下降到1.02 g·kg^-1。随氟浓度的增加土壤放线菌数量显著降低, 与对照相比, 降低0.92%~65.22%; 低浓度的氟可以促进土壤细菌、真菌的生长, 而高浓度的氟可以抑制细菌、真菌的生长。     

Allocation and dynamics of C and N within plant–soil system of ash and beech

Forest management requires a profound understanding of how tree species affect C and N cycles in ecosystems. The large C and N stocks in forest soils complicate research on the effects of tree species on C and N pools. In‐situ ¹³C and ¹⁵N labeling in undisturbed, natural forests enable not only tracing of C and N fluxes, but also reveal insight into the interactions at the plant‐soil‐atmosphere interface. In‐situ dual ¹³C and ¹⁵N pulse labeling of 20 beeches (Fagus sylvatica L.) and 20 ashes (Fraxinus excelsior L.) allowed tracing the fate of assimilated C and N in trees and soils in an unmanaged forest system in the Hainich National Park (Germany). Leaf, stem, root, and soil samples as well as microbial biomass were analyzed to quantify the allocation of ¹³C and ¹⁵N for 60 d after labeling and along spatial gradients in the soil with increasing distance from the stem. For trees of similar heights (≈ 4 m), beech (20%) assimilated twice as much as ash (9%) of the applied ¹³CO₂, but beech and ash incorporated similar ¹⁵N amounts (45%) into leaves. The photosynthates were transported belowground through the phloem more rapidly in beech than in ash. Ash preferentially accumulated ¹⁵N and ¹³C in the roots. In contrast, beech released more of this initially assimilated ¹³C (2.0% relative ¹³C allocation) and ¹⁵N (0.1% relative ¹⁵N allocation) via rhizodeposition into the soil than ash (0.2% relative ¹³C, 0.04% relative ¹⁵N allocation), which was also subsequently recovered in microbial biomass. These results on C and N partitioning contribute to an improved understanding of the effects of European beech and ash on the C and N cycles in deciduous broad‐leaved forest. Differences in C and N allocation patterns between ash and beech are one mechanism of niche differentiation in forests containing both species.     

Effect of acetylene and ethylene gases released from encapsulated calcium carbide on growth and yield of wheat and cotton

Calcium carbide (CaC₂) is a rich source of the nitrification inhibitor acetylene (C₂H₂) and plant hormone ethylene (C₂H₄). C₂H₄ formed from biotic reduction of C₂H₂ released from CaC₂ may accumulate in soil at physiologically active concentrations. Laboratory studies were conducted to evaluate the potential of encapsulated CaC₂ for gradually releasing C₂H₂ and its product C₂H₄ in soil. The GC-FID analysis revealed that encapsulated CaC₂ released a copious amount of C₂H₂ (up to 23700 nmol kg⁻¹ soil), which was gradually reduced to C₂H₄ over a period of time via a strictly biotic reaction as no C₂H₄ was detected in CaC₂-amended sterilized soil. Ammonium oxidation was suppressed by the encapsulated CaC₂ indicating that C₂H₂ acted as a nitrification inhibitor. Results of pot trials conducted in the net house indicated that encapsulated CaC₂ applied at 30 mg kg⁻¹ soil significantly increased the number of tillers (up to 45.5%), root weight (up to 14.9%), straw (up to 32.8%) and grain yield (up to 37.3%) of wheat over the fertilizer application alone. In the case of cotton, the number of bolls, root, shoot and seed weight were also significantly increased in response to the application of encapsulated CaC₂. Moreover, application of encapsulated CaC₂ resulted in greater N-use efficiency (NUE) (up to 61.1%) by both wheat and cotton crops than that observed at the same rates of N fertilizer alone. These findings imply that CaC₂ affects plant growth through hormonal action of C₂H₄ as well as improved NUE; however, the latter factor might be a relatively more contributing. It is desirable that CaC₂ is formulated for gradually slow release of C₂H₂ and C₂H₄ in soil air.     

Effects of experimental acidification and alkalinization on soil and growth and health of Acer saccharum Marsh.

Experimental application of eight acidifying, neutral, or alkalizer compounds (range: –16 to 16 kmol ha^–1 of acid‐neutralizing capacity [ANC]) was realized in two northern hardwood stands having significantly different soil base saturation (BS) (a “poor” and a “rich” site) to assess responses of soil physico‐chemical properties, and nutrition, growth, and health of sugar maple (Acer saccharum Marsh.) trees in the short (3 y) and longer term (10 y). The treatments influenced the main indicators of acidity in the forest floor (soil exchangeable‐Ca saturation [S_Ca], BS, exchangeable‐acidity saturation [S_H+Al], and the S_Ca/S_H+Al ratio) at both sites, their values increasing (decreasing for S_H+Al) along the ANC treatment gradient in both the short and longer term, except for pH. Base saturation of the upper 15 cm of the mineral B horizons of soils was influenced at the two sites 10 y after treatment application. Although ANC treatments affected nutrient concentrations of tree foliage in the short term, their effect was no longer detectable after 10 y at the two sites. Growth, however, was strongly related to ANC treatments after 10 y, but only at the poor site. From 1990 to 2000, the basal‐area growth rate of trees at the poor site was (mean ± SE) –0.62 ± 0.28 cm² y^–2 tree^–1 for the most negative ANC treatment to +0.90 ± 0.20 cm² y^–2 tree^–1 for the most positive ANC treatment. A climatic‐stress episode occurring in 1995/96 appeared to accentuate the growth decline of trees subjected to the most negative ANC treatment at the poor site. The experimental results support the hypothesis that atmospheric acid deposition load can cause forest soil base‐cation depletion, acidification, and predispose sugar maple to health and growth decline in the longer term in base‐cation‐poor soils, and that the phenomenon may be reversible by adding alkalizers.     

Formation and remobilisation of soil microbial residue. Effect of clay content and repeated additions of cellulose and sucrose

In two studies, we assessed the mass balance of added ¹⁴C-labelled sucrose and ¹⁵NH₄¹⁵NO₃ by measuring ¹⁴CO₂, ¹⁴C and ¹⁵N in soil microbial biomass (SMB) and ¹⁴C and ¹⁵N in soil solution. Specifically, we assessed the potential of recently added ¹⁴C to be re-mobilised by cryptic growth using subsequent additions of sucrose and cellulose and the effect of physical protection on the stabilisation of the labelled substrate. We used both a constructed soil with low soil organic matter content and varied the clay content as well as a natural soil. We observed a substantial initial as well as a later stage transfer of ¹⁴C into unidentifiable form, hypothesised to be microbial residues. When using a standard k _EC value of 0.45, only roughly 50% of the added labelled substrates were accountable and therefore we explored the full range of reported k _EC values to assess the mass balance. Subsequent application of unlabelled sucrose and cellulose did not substantially increase turnover ¹⁴C and ¹⁵N. Contrary to our expectation, there was no effect of clay content on the amount of unidentified ¹⁴C and ¹⁵N. The unidentified ¹⁴C and ¹⁵N is ascribed to formation of soil microbial residue. The low recovery of added isotope suggests that our mechanistic models are missing a large and important pool in order to realistically simulate organic matter turnover in soil.     

Rate of nitrapyrin and soil ph effects on nitrification of ammonium fertilizer and growth and composition of burley tobacco

Abstract

Laboratory and greenhouse experiments were conducted to determine the effects of rate of nitrapyrin and soil pH on nitrification of NH₄ ⁺ fertilizer in soil, and growth and chemical composition of burley tobacco (Nicotiana tabacum L. cv. ‘KY ‐14'). Such experiments were needed to develop information for increasing efficiency of N fertilizer use and to lessen the fertilizer‐induced soil acidity and salt effects on tobacco plants.

Results for laboratory and greenhouse incubations indicated that nitrification proceeeded slowly below pH 5.0 and the nitrapyrin necessary to delay nitrification increased with both increasing soil pH and length of incubation time. Generally, nitrification could be delayed 30 days by nitrapyrin rates of 0.25 or 0.5 μg g^‐1 regardless of soil pH. but rates of 1 μg g^‐1 nitrapyrin or higher were required for 60 days and longer incubation times, particularly at higher soil pH.

Growth and morphology of tobacco plants were either unaffected, or affected positively, by low rates of nitrapyrin (up to 2 μg g^‐1). However, rates of 4 μg g^‐1 and above reduced total plant dry weight, reducing sugars and contents of mineral elements. Concentrations and content of plant NO₃ ^‐ N and Mn were greatly decreased by application of nitrapyrin. Values for most parameters measured increased with increasing soil pH. The data show that low rates of nitrapyrin may be used to alter the ratio of NO₃ ^‐ to NH₄ ⁺ N absorbed by tobacco and possibly improve growth and safety of tobacco.     

嫁接黄瓜果实表面蜡粉形成与砧木的相关性及其硅吸收分配特性

黄瓜果实表面蜡粉的多少影响其商品品质,蜡粉多少在一定条件下取决于植株对硅的吸收特性。本试验选择4个果实表面具蜡粉的南瓜自交系（Z1、 Z2、 Z3和Z4）和4个果实表面没有蜡粉的南瓜自交系（Z5、 Z6、 Z7 和Z8）为砧木,嫁接津优1号黄瓜,以自根黄瓜为对照,研究了嫁接和自根黄瓜果面蜡粉形成与硅吸收分配的关系。结果表明, 采用果面具蜡粉砧木Z1、 Z2嫁接的黄瓜果实表面鲜亮、 光滑,几乎无蜡粉;果面具蜡粉的砧木Z3、 Z4以及不具蜡粉的4个砧木嫁接的黄瓜果面蜡粉量多,色灰暗,与自根黄瓜之间差异显著或不显著。果面没有蜡粉的黄瓜植株各器官中硅含量显著低于果面有蜡粉的黄瓜;果实果皮中硅含量高于果肉。嫁接黄瓜果面是否具蜡粉与砧木果面有无蜡粉没有必然联系,采用去蜡粉砧木嫁接的黄瓜硅吸收量明显减少。     

Effects of Organic and Inorganic Fertilizers on Soil and Plant Nutrients and Yields of Pearl Millet and Wheat under Semi-arid Inceptisols in India

A study was conducted to assess fertilizer effect on pearl millet–wheat yield and plant-soil nutrients with the following treatments: T₁, control; T₂, 100% nitrogen (N); T₃, 100% nitrogen and phosphorus (NP); T₄, 100% nitrogen, phosphorus and potassium (NPK); T₅, 100% NPK + zinc sulfate (ZnSO₄) at 25 kg ha^?1; T₆, 100% NPK + farmyard manure (FYM) at 10 t ha^?1; T₇, 100% NPK+ verimcompost (VC) at 2.5 tha^?1; T₈, 100% NPK + sulfur (S) at 25 kg ha^?1; T₉, FYM at 10 t ha^?1; T₁₀, VC at 2.5 t ha^?1; T₁₁, 100% NPK + FYM at 10 t ha^?1 + 25 kg S ha^?1 + ZnSO₄ at 25 kg ha^?1; and T₁₂, 150% NPK treatments. Treatments differed significantly in influencing soil-plant nutrients and grain and straw yields of both crops. Grain yield had significant correlation with soil-plant N, P, K, S, and zinc (Zn) nutrients. The study indicated superiority of T₁₁ for attaining maximum pearl millet grain yield (2885 kg ha^?1) and straw yield (7185 kg ha^?1); amounts of N (48.9 kg ha^?1), P (8.8 kg ha^?1), K (26.3 kg ha^?1), S (20.6 kg ha^?1), and Zn (0.09 kg ha^?1) taken up; and amounts of soil N (187.7 kg ha^?1), P (13.7 kg ha^?1), K (242.5 kg ha^?1), S (10.1 kg ha^?1), and Zn (0.70 kg ha^?1). It was superior for wheat with grain yield (5215 kg ha^?1) and straw yield (7220 kg ha^?1); amounts of N (120.7 kg ha^?1), P (13.8 kg ha^?1), K (30 kg ha^?1), S (14.6 kg ha^?1), and Zn (0.18 kg ha^?1) taken up; and maintaining soil N (185.7 kg ha^?1), P (14.5 kg ha^?1), K (250.5 kg ha^?1), S (10.6 kg ha^?1), and Zn (0.73 kg ha^?1). Based on the study, 100% NPK + FYM at 10 tha^?1 + Zn at 25 kg ha^?1 + S at 25 kg ha^?1 could be recommended for attaining maximum returns of pearl millet–wheat under semi-arid Inceptisols.     

Release of C and N from roots of peas and oats and their availability to soil microorganisms

Nutrient mobilisation in the rhizosphere is driven by soil microorganisms and controlled by the release of available C compounds from roots. It is not known how the quality of release influences this process in situ. Therefore, the present study was conducted to investigate the amount and turnover of rhizodeposition, in this study defined as root-derived C or N present in the soil after removal of roots and root fragments, released at different growth stages of peas (Pisum sativum L.) and oats (Avena sativa L.). Plants were grown in soil columns placed in a raised bed under outdoor conditions and simultaneously pulse labelled in situ with a ¹³C-glucose-¹⁵N-urea solution using a stem feeding method. After harvest, ¹³C and ¹⁵N was recovered in plant parts and soil pools, including the microbial biomass. Net rhizodeposition of C and N as a percentage of total plant C and N was higher in peas than in oats. Moreover, the C-to-N ratio of the rhizodeposits was lower in peas, and a higher proportion of the microbial biomass and inorganic N was derived from rhizodeposition. These results suggest a positive plant-soil feedback shaping nutrient mobilisation. This process is driven by the C and N supply of roots, which has a higher availability in peas than in oats.     

Evaluation of yield and some physiological changes in corn and sorghum under irrigation regimes and application of barley residue,zeolite and superabsorbent polymer

In order to investigate the changes in chlorophyll fluorescence, chlorophyll, relative water content (RWC) and forage yield of corn and sorghum under various irrigation regimes and combination treatments of barley residue, zeolite and superabsorbent polymer, an experiment was conducted over 2 years in Kerman, Iran. A randomized complete block design arranged in a factorial split was used with three replications. Two irrigation regimes of normal and drought stress based on 70 and 140 mm cumulative pan evaporation, respectively, and two plant species (corn and sorghum) as factorial combinations were compared in the main plots. Five treatments, (1) 10 t ha^?1 zeolite + 4.5 t ha^?1 residue, (2) 60 kg ha^?1 superabsorbent + 4.5 t ha^?1 residue, (3) 5 t ha^?1 zeolite + 30 kg ha^?1 superabsorbent + 4.5 t ha^?1 residue, (4) 4.5 t ha^?1 residue and (5) – control, were compared in subplots. In both plants, forage yield, potential quantum yield (Fv/Fm), chlorophyll a, total chlorophyll and carotenoid contents decreased significantly under drought stress. Chlorophyll a content, SPAD index and Fv/Fm were higher in corn than in sorghum, but RWC was higher in sorghum. Corn produced higher forage yield (62.8 t ha^?1) than sorghum (49.3 t ha^?1). The application of 10 t ha^?1 zeolite with 4.5 t ha^?1 residue increased most traits more than any of the other treatments, but the superabsorbent had no significant effect on the studied traits.     

Efficiency and response of sunflower to rate and timing of banded nitrogen

Abstract

Nitrogen use efficiency and response of sunflower (Helianthus annuus L.) to timing and rate of surface banded N was characterized in a split‐plot 4x2 factorial experiment. Nitrogen rates (main plots) were 0, 34, 67, and 134 kg ha^‐1 at Mississippi State and 0, 45, 90 and 180 kg ha^‐1 at Brooksville, MS. Nitrogen, applied as NH₄NO₃, was surface banded either at planting or at the four leaf stage (subplot). Seed yield was significantly influenced by rate of N application at both locations. Seed yield showed a quadratic response at Mississippi State and a Mitscherlich‐type response at Brooksville. Maximum seed yields of 2606 and 2380 kg ha^‐1 were obtained at the respective sites. Sunflower responded to N fertilizer application when inorganic N content of the soil to 60 cm depth at planting was less than 50 kg ha^‐1. Nitrogen efficiency was influenced by rate and timing of application, exhibiting exponential declines with increasing N rates. Fertilizer losses at the highest rates of applied N were 19 and 52% at Mississippi State and Brooksville, respectively. Clay‐fixed NH^⁺ accounted for 26% of the applied N fertilizer loss at Brooksville. Nitrogen fertilizer efficiency and recommendations for sunflower could be improved if initial soil inorganic N is taken into account.     

Influence of level and source of Fe on growth and nutrient content of Euglena gracilis

Abstract

Growth parameters and Fe, Cu, Mn and N status of Euglena gracilis cells were determined as a function of level and source of Fe supply in the nutrient environment. Use of FeEDDHA promoted cell division while FeSO₄·lb7H₂O promoted cell enlargement after 7 days. Greatest N content was present in rapidly dividing as compared to enlarging cells. Copper content was directly related to cell size with larger cells containing more Cu than smaller cells. Manganese uptake was inversely related to Fe supply with FeSO₄·lb7H₂O inhibiting Mn uptake to a greater extent than chelated Fe. Iron uptake increased significantly with the addition of iorganic or chelated Fe. The Fe uptake was comparable from both sources at the 1 ppm Fe level of supply, but much greater amounts of Fe were accumulated from inorganic supply at the 10 ppm Fe level.     

Comparison of Arsenic and Phosphate Uptake and Distribution in Arsenic Hyperaccumulating and Nonhyperaccumulating Fern

Abstract

Uptake of arsenic (As) and its distribution in Chinese Brake fern (Pteris vittata L.), an As hyperaccumulator, and Boston fern (Nephrolepis exaltata L.), a nonhyperaccumulator, in the presence of phosphorus (P), were characterized by employing a hydroponic experiment with a complete three-factorial design. Two levels of As (100 and 1000 µM) and four levels of P (0, 100, 500, and 1000 µM) were used in this study. Arsenic uptake rates on the basis of root fresh weight for the two ferns were similar at low As concentration (100 µM). At high As concentration (1000 µM), however, As uptake rates (373–987 nmol g^?1 f wt h^?1) of P. vittata were significantly greater than those of N. exaltata (164–459 nmol g^?1 f wt h^?1). In both ferns, addition of P reduced their As uptake rate as well as accumulation. Pteris vittata had a greater As TF (Translocation factor = concentration ratio of fronds to roots) than N. exaltata. On the contrary, N. exaltata displayed a greater P TF than P. vittata. As a result, high P/As ratio was observed in the roots of P. vittata, whereas high P/As ratio was observed in the fronds of N. exaltata. The study illustrated that As hyperaccumulation by P. vittata may be facilitated by its high As influx rate and its high molar P/As ratio in the roots resulting from both high As TF and low P TF.     

Phytoavailability and toxicity of beryllium and vanadium

Greenhouse and laboratory studies were conducted to evaluate the toxic effects of Be and V on collards (Brassica oleracea, var. acephala L.). In the laboratory germination study, incremental increases in the Be concentrations of the growing medium induced a steady decline in the radicle length of seven-day-old collard seedling. Beryllium concentrations greater than or equal to 8 mg Be L^?1 totally inhibited seed germination. The presence of V in the growing medium had no effect on collard germination; however, it had a profound effect on subsequent radicle elongation. Concentrations of V less than 1 mg V L^?1 stimulated radicle elongation, while concentrations greater than or equal to 3 mg V L^?1 caused severe toxicity. In the greenhouse study, Be toxicity was observed in collards grown in a Blanton sand (Grossarenic Paleudult) received treatments greater than or equal to 150 mg Be kg ^?1 (as BeSO₄). Irrespective of treatment level, 97% of the Be taken up by the plants remained in the roots while only 3% was translocated to aboveground plant parts. Vanadium tissue concentrations and toxicity to collards varied with soil type. Additions as low as 80 mg V kg^?1 to the Blanton sand significantly reduced collard biomass while additions as high as 100 mg V kg^?1 to an Orangebury loamy sand (Typic Paleudult) had no effect on plant biomass. The differential response was attributed to greater accumulation of V by plants grown in the Blanton soil.     

Identification and characterization of salt- and thermo-tolerant Leucaena-nodulating Rhizobium strains

 Rhizobium-legume symbioses are important for their nitrogen input, but salinity and elevated temperature in arid and semi-arid areas limit their effectiveness, and therefore plant growth and productivity. Sixteen Rhizobium strains isolated from root nodules of Leucaena trees grown in different geographical areas of Egypt varied in their degree of tolerance to salinity and in their symbiotic effectiveness with Leucaena leucocephala under saline conditions. Three strains were tolerant to >3% NaCl. L. leucocephala grown in the greenhouse at concentrations of NaCl up to 1.0% and inoculated either with strain DS 78 or strain DS 158 displayed significantly better growth than those plants grown at the same levels of salinity and inoculated with reference strain TAL 583. Although nine of the Rhizobium strains grew at 42  °C, their mean generation times were lengthened two- to fourfold. When daylight growth temperatures were elevated from 30  °C to 42  °C, nodule number and mass, nitrogenase activities and shoot top dry weight of plants inoculated with strains DS 78, DS 157 and DS 158 significantly increased, whereas these parameters decreased in plants inoculated with strain TAL 583. Rhizobium strains that effectively nodulate Leucaena under adverse saline conditions and at high temperatures were thus isolated, identified and characterized. Received: 12 September 1997     

Effect of Graded Levels of Nitrogen and Sulfur and Their Interaction on Yields and Quality of Aromatic Rice

ABSTRACT

In a greenhouse experiment, involving factorial combinations of nitrogen (N) (0, 15, 30, 45, and 60 mg kg^{? 1} soil) and sulfur (S) (0, 7.5, 15.0, 22.5, 30.0 mg kg^{? 1}soil), application of all levels of N and S 15 mg kg^{? 1} and above increased the grain yield of aromatic rice (Basmati cv. ‘Taraori’) significantly. The highest grain yield of aromatic rice was recorded from the treatment combinations of 60 mg N + 15 mg S kg^{? 1} or 45 mg N + 30 mg S kg^{? 1}. The interaction of N and S influenced the N and S content in rice grain, N content in straw, N: S ratio both in grain and straw, milling (%), and other quality parameters significantly. Milling (%) and hulling (%), thousand grain weight, L: B ratio, cooked grain breadth, and aroma score were found to be significantly and positively correlated with the N: S ratio of rice grain while grain breadth had a significant inverse relationship with N: S ratio in grain.