Effect of organic matter on the growth,nodulation, and nitrogen fixation of soybean grown under acid and saline conditions

Abstract

A field experiment was conducted to examine the effects of two organic materials (Bark and Tenporon composts) on the growth, nodulation and nitrogen fixation (measured as acetylene-reducing activity) of soybean plants (Glycine max L.) under acid and saline conditions. These organic materials were incorporated into acid and saline (induced by irrigating the soil with a NaCl solution) soils at 4% rate of application.

These composts tended to improve nodule formation in soybean under acid and saline conditions, especially in the plants treated with Bark compost. Acetylene-reducing activity was significantly (P<0.05) increased by these composts under acid condition.

These composts also tended to improve shoot growth under acid and saline conditions, presumably due to the improvement of the soil moisture status of the soils and nutrient uptake. These results suggest that the growth of soybean could be improved by the application of organic matter under acid and saline conditions.     

Comparison of water stress effects on growth,leaf water status,and nitrogen fixation activity in tropical pasture legumes siratro and desmodium with soybean

Siratro (Macroptilium atropurpureum), desmodium (Desmodium intortum), and soybean (Glycine max) were grown in pots with or without irrigation for 20 d at the vegetative growth stage in order to examine the effects of water stress on the leaf water potential, stomatal conductance, biomass production, biological nitrogen fixation, and nitrogen accumulation. Whole plant weight decreased under water stress conditions and the decrease was less pronounced in siratro than in desmodium and soybean. Decrease in total leaf area was the largest and dry matter partition to stem and petioles was the highest in siratro. Decrease in leaf water potential was lower in desmodium and soybean than in siratro. Although water stress decreased biological nitrogen fixation in all the species, the decrease was relatively less pronounced in siratro than in desmodium and soybean. Whole plant nitrogen concentration was higher in siratro than in soybean and desmodium. The results indicated that siratro is more tolerant to water stress than soybean and desmodium. This could be partially attributed to the maintenance of a higher water potential and higher biological nitrogen fixation by siratro under water stress conditions.     

Copper,nitrogen, and Rhizobium japonicum relationships in determinate soybean

A relationship among Cu, N, and Rhizobium japonicum was hypothesized because previous research had shown that (a) 35% or more legumes in the Atlantic Coastal Plain have Cu concentrations of 6 mg kg^‐1 or less, (b) Cu influences N fixation in some legumes, and (c) irrigated soybean (Glycine max L. Merr.) can accumulate most of its N through fixation. Soybean were grown on a Cu‐deficient Norfolk (fine‐loamy, siliceous, thermic Typic Paleudult) loamy sand with 3 fertilizer sources of Cu, 2 strains of R. japonicum, and with or without 336 kg ha^‐1 of N fertilizer. Application of Cu significantly increased the number of pods plant^‐1 suggesting pod abortion in determinate soybean may be caused by low Cu, but seed yield was not increased. Fertilization with N increased vegetative growth, but not total biomass or seed yield. Inoculation with R. japonicum strain 110 significantly increased seed yield by 0.3 Mg ha^‐1 compared to strain 587. The yield increase was similar with or without fertilizer N application indicating strain response was not totally caused by improved N efficiency. There was no relationship between seed yield and nodule occupancy as measured by the ELISA technique.     

Effects of changes in applied nitrogen concentrations on nodulation,nitrogen fixation and nitrogen accumulation during the soybean growth period

ABSTRACT

The specific mechanism by which nitrogen application affects nodulation and nitrogen fixation in legume crops remains uncertain. To further study the effects of nitrogen application on soybean nodulation and nitrogen accumulation, three consecutive tests were performed during the VC-V4, V4-R1 (10 days), and R1-R2 (10 days) growth periods of soybean. In a dual-root soybean system, seedlings on one side were watered with a nutrient solution containing NH₄⁺ or NO₃^? as the N source (N+ side), and those on the other side were watered with a nitrogen-free nutrient solution (N- side). During the VC-R2 period, on the N+ side, high nitrogen treatment inhibited nodule growth and nitrogenase activity (EC 1.18.6.1), and the inhibition was significantly increased with increasing high nitrogen supply time (10 days, 20 days). When the high nitrogen treatment time reached 20 days, the specific nitrogenase activity (C₂H₄ μmol^?1 g^?1 nodule dry mass h^?1) was similar to that in the low nitrogen treatment, indicating that the nitrogen fixation capacity per gram of dry mass nodules was almost the same. Therefore, it is assumed that long-term high nitrogen treatment mainly reduces nitrogen fixation by reducing the nodule number. The effect of nitrogen concentration on the roots on the N+ side was greater than that on the N- side. Taken together, these results indicate that nitrogen application affects a contact-dependent local inhibition of root nodule growth, nitrogenase activity, and nitrogen accumulation. The whole plant systematically regulates specific nitrogenase activity, and high nitrogen inhibition is recoverable.     

Effect of elevated carbon dioxide on growth,nutrient partitioning,and uptake of major nutrients by soybean under varied nitrogen application levels

Rising carbon dioxide (CO₂) concentration causes fertilization effects resulting in enhanced crop biomass and yields and thus likely enhances nutrient demand of plants. Hence, this field study was carried out to investigate the effects of elevated CO₂ and N on biomass yield, nutrient partitioning, and uptake of major nutrients by soybean (Glycine max L.) using open‐top chambers (OTCs) of 4 m × 4 m size. Soybean was grown in OTCs under two CO₂ [ambient and elevated (535 ± 36.9 mg L^?1)] and four N levels during July to October 2016. The four N levels were N₀, N₅₀, N₁₀₀, and N₁₅₀ referring to 0, 50, 100, and 150% recommended dose of N. Both CO₂ and N significantly affected biomass and grain yield, though the interaction was non‐significant. CO₂ enrichment produced 30–65% higher biomass and 26–59% higher grain yield under various N levels. As compared to the optimum N application (N₁₀₀), the CO₂‐mediated increment in biomass yield decreased with either lower or higher N application, with the response being lowest at N₁₅₀. As compared to ambient concentration, elevated CO₂ resulted in significant reduction of seed P concentration at all N application levels but at N₁₅₀, an opposite trend was observed. The decrease in seed P was maximum at N₀ and N₅₀ (7–9%) and by 3% at N₁₀₀, whereas there was a gain of 7.5% at N₁₅₀. The seed N and K concentrations were not affected either by CO₂ or N application. Total N, P, and K uptake at harvest were significantly affected by CO₂ and N, but not by CO₂ × N interaction. Elevated CO₂ resulted higher uptake of N by 18–61%, P by 23–62%, and K by 22–62% under various N treatments.     

壳聚糖对NaCl胁迫下菜用大豆结瘤固氮的影响

【目的】研究壳聚糖对盐胁迫抑制菜用大豆结瘤固氮的缓解效应,为进一步探讨壳聚糖抗逆机理提供新的线索。【方法】以蛭石为基质,以菜用大豆‘特早王’–根瘤菌共生体系为研究对象,采用人工气候箱培养,研究NaCl胁迫下壳聚糖对菜用大豆根瘤形成、生物固氮的影响。菌种为与‘特早王’共生匹配性较好的快生根瘤菌N18。接种后的植株进行如下4个处理:1)叶面喷施清水,根部浇灌无氮营养液(CK);2)叶面喷施壳聚糖水溶液,根部浇灌无氮营养液(CTS);3)叶面喷施清水,根部浇灌溶有NaCl的无氮营养液(Cl);4)叶面喷施壳聚糖水溶液,根部浇灌溶有NaCl的无氮营养液(CTS+Cl)。上述各处理施用的水或水溶液均为无菌水配制,NaCl处理的浓度为50 mol/L,CTS处理的适宜浓度为200 mg/L。接种30天后,将大豆植株取出,用清水将根部蛭石冲洗干净后,立即测定根瘤固氮酶活性、根瘤数及根瘤鲜重,然后测定根瘤豆血红蛋白含量和根系活力,最后测植株干重和全氮量。【结果】氯化钠胁迫下,植株干重显著下降,与CK相比降幅达49%,喷施壳聚糖后(CTS+Cl),降低幅度显著减小,但依然显著低于CK (P <0.05)。无盐条件下,与CK相比,壳聚糖处理(CTS)增加植株干重的效果不明显。喷施壳聚糖显著增加了菜用大豆的根瘤数、根瘤鲜重、植株含氮量、根系活力、豆血红蛋白含量及固氮酶活性(P <0.05)。NaCl胁迫显著抑制了菜用大豆的结瘤固氮作用,其中根瘤数、根瘤鲜重分别较CK下降了79%、90%,而壳聚糖处理(CTS+Cl)使菜用大豆在盐逆境下的结瘤数、根瘤鲜重、植株全氮含量、根系活力、豆血红蛋白含量及固氮酶活性等均显著回升,增幅分别达对照的29%、20%、17%、48%、19%、21%,但均显著低于CK。【结论】非NaCl胁迫下,喷施壳聚糖可以显著促进菜用大豆结瘤,提高豆血红蛋白含量及固氮酶活性,最终增加植株含氮量。在NaCl胁迫下,外源壳聚糖可以显著缓解氯化钠胁迫导致的对根系活力和结瘤固氮的影响。因此,叶面喷施壳聚糖是促进菜用大豆结瘤固氮和生长的有效措施。     

Glyphosate effects on photosynthesis,nutrient accumulation,and nodulation in glyphosate‐resistant soybean

Previous greenhouse studies have demonstrated that photosynthesis in some cultivars of first‐ (GR1) and second‐generation (GR2) glyphosate‐resistant soybean was reduced by glyphosate. The reduction in photosynthesis that resulted from glyphosate might affect nutrient uptake and lead to lower plant biomass production and ultimately reduced grain yield. Therefore, a field study was conducted to determine if glyphosate‐induced damage to soybean (Glycine max L. Merr. cv. Asgrow AG3539) plants observed under controlled greenhouse conditions might occur in the field environment. The present study evaluated photosynthetic rate, nutrient accumulation, nodulation, and biomass production of GR2 soybean receiving different rates of glyphosate (0, 800, 1200, 2400 g a.e. ha^–1) applied at V2, V4, and V6 growth stages. In general, plant damage observed in the field study was similar to that in previous greenhouse studies. Increasing glyphosate rates and applications at later growth stages decreased nutrient accumulation, nodulation, leaf area, and shoot biomass production. Thus, to reduce potential undesirable effects of glyphosate on plant growth, application of the lowest glyphosate rate for weed‐control efficacy at early growth stages (V2 to V4) is suggested as an advantageous practice within current weed control in GR soybean for optimal crop productivity.     

Effect of Mn on growth,modulation, and nitrogen fixation by soybeans grown in the greenhouse

Abstract

Soybean (Glycine max (L.) Merr. cv Bragg) plants were grown in the greenhouse using a low‐Mn Leefield sand amended with 0, 2.5, 5, 20 and 50 yg Mn/g. The plants were inoculated and were primarily dependent on symbiotically fixed N. Measurements of DTPA‐extractable soil Mn, soil pH, leaf tissue Mn, top weight, top N content, and nodule weight, volume and number were made at 27, 42, 56, 63 and 69 days after planting. The DTPA extrac‐tant was a good predictor of leaf tissue Mn giving a highly significant (P = 0.01) overall correlation coefficient of 0.704 for this comparison. Because of an unexpected decline in soil pH from 6.8 to 6.0 and an associated increase in DTPA‐extractable Mn from 0.14 to 0.24 yg/g during preparation and handling prior to the first harvest time, Mn in the leaf tissue of the controls was never less than 21 yg/g. Since this concentration of Mn is above the deficient level, no significant responses in top growth, nitrogen fixation or nodule measurements were obtained from the addition of low rates of Mn. The highest Mn rate was only mildly toxic in terms of top growth and top N content, producing leaf tissue having Mn concentrations ranging from 171 to 180 yg/g at the last three harvest periods.     

大豆生物固氮模型研究进展

定量描述大豆生物固氮量对于施肥管理以及农业非点源污染控制具有十分重要的意义。生物固氮模型作为一种重要工具,在定量预测大豆生物固氮速率方面具有不可替代的作用。国内研究者对不同环境因子对固氮的影响开展了一些工作,但多未从定量角度出发。国外的生物固氮模型按构建方式大致可以分为经验模型和机理模型两类。其中机理模型研究较多,也是目前生物固氮模型的主要发展方向。本文简述了这两类模型的研究现状,并着重介绍了5种目前国外使用较为广泛的田间尺度下的大豆生物固氮机理模型,比较了不同模型中采用的环境因子响应函数的差异,并对进一步的研究作了展望,以期为国内大豆生物固氮定量研究工作的开展提供借鉴。     

Effect of water stress on growth,photosynthesis, and photoassimilate translocation in soybean and tropical pasture legume siratro

Siratro (Macroptilium atropurpureum) and soybean (Glycine max) were grown in pots with or without irrigation for 3 weeks at the vegetative stage to examine the effect of water stress on plant biomass production, biological N₂ fixation, CO₂ assimilation rate, stomatal conductance, leaf water potential, and the partition of ¹⁴CO₂ to plant parts. Biomass production decreased by water stress and the decrease was less conspicuous in siratro, mainly due to the maintenance of a relatively higher growth rate in stem plus petioles and roots. Siratro maintained a higher stomatal conductance and CO₂ assimilation rate at a lower leaf water potential compared to soybean. Water stress decreased the biological N₂ fixation in both species, and the decrease was more appreciable in siratro than in soybean under stress conditions. Water stress affected the export of photoassimilates from leaves in both species. The translocation of ¹⁴CO₂ photoassimilates to nodules and roots was less substantial in siratro than in soybean under water stress conditions. Translocation of photoassimilates from leaves to stem plus petioles in siratro enables the maintenance of growth of stem and petioles under water stress conditions.     

Concomitant inhibition of nitrogen fixation and N-Phenyl-1-Naphthylamine uptake activity of bacteroids of a Bradyrhizohium japonicum strain by nitrate

Abstract

Effect of the treatment of soybean nodules with nitrate on the permeability of the outer membrane of bacteroids of Bradyrhizobium japonicurn strain 138NR was examined using the hydrophobic fluorescent probe N-phenyl-1-naphthylamine (NPN). The incorporation of NPN into the outer and inner membranes of the bacteroid cells isolated from nodules of soybean (Glycine max L. Merro cv. Tamahomare) was followed by the measurement of fluorescence at 30°C. The NPN-uptake activity of the bacteroids was expressed by two parameters, the initial rate of NPN-uptake, k, and the final fluorescence intensity, F _max. Acetylene reduction activity (ARA) of nodules, k, and F _max decreased exponentially during three weeks following the 20 d period after planting (DAP), resulting in high correlations between logarithmic transforms of k-values or F _max per bacteroid and those of ARA per bacteroid. Application of 20 mM KNO₃ to the nodulated roots at 24 DAP inhibited ARA of the roots by 85% of the control after 4 d of treatment. There were concomitant decreases in k and F _max by 75% and 65% of the control, respectively. These results suggest that treatment of soybean nodules with nitrate results in some changes in the permeability of the outer membrane of bacteroids with a concomitant decline of N₂-fixing activity of bacteroids.     

Effects of co-inoculation of Bradyrhizobium japonicum SAY3-7 and Streptomyces griseoflavus P4 on plant growth,nodulation, nitrogen fixation,nutrient uptake,and yield of soybean in a field condition

ABSTRACT

Co-inoculation of nitrogen-fixing bacteria with plant growth-promoting bacteria has become more popular than single inoculation of rhizobia or plant-growth-promoting bacteria because of the synergy of these bacteria in increasing soybean yield and nitrogen fixation. This study was conducted to investigate the effects of Bradyrhizobium japonicum SAY3-7 and Streptomyces griseoflavus P4 co-inoculation on plant growth, nodulation, nitrogen fixation, nutrient uptake, and seed yield of the ‘Yezin-6’ soybean cultivar. Nitrogen fixation was measured using the acetylene reduction assay and ureide methods. Uptake of major nutrients [nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg)] was also measured. This study showed that single inoculation of SAY3-7 significantly increased shoot biomass; nodulation; Relative Ureide Index (RUI %), percent nitrogen derived from N fixation (% Ndfa); N, P, K, Ca, and Mg uptakes; during the later growth stages (R3.5 and R5.5), compared with control. These observations indicate that SAY3-7 is an effective N-fixing bacterium for the plant growth, nodulation, and nitrogen fixation with an ability to compete with native bradyrhizobia. Co-inoculation of SAY3-7 and P4 significantly improved nodule number; nodule dry weight; shoot and root biomass; N fixation; N, P, K, Ca, and Mg uptake; at various growth stages and seed yield in ‘Yezin-6’ soybean cultivar compared with the control, but not the single inoculation treatments. Significant differences in plant growth, nodulation, N fixation, nutrient uptake, and yield between co-inoculation and control, not between single inoculation and control, suggest that there is a synergetic effect due to co-inoculation of SAY3-7 and P4. Therefore, we conclude that Myanmar Bradyrhizobium strain SAY3-7 and P4 will be useful as effective inoculants in biofertilizer production in the future.     

15N study on the partitioning of the nitrogen taken by soybeans from atmospheric dinitrogen,medium nitrate or ammonium

Abstract

Soybean plants (Glycine max, cv. Akisengoku) were water-grown in a greenhouse with a low concentration of nitrate in the culture solution. Under these conditions root nodulation mostly on primary roots was profuse. At the vegetative and pod-filling stages, plants were fed ¹⁵N-labeled dinitrogen, nitrate, or ammonium for 7 to 8 hr in the daytime.

Partitioning of the ¹⁵N from the three nitrogen sources showed distinct characteristics. The nitrogen (N) from dinitrogen preferentially distributed to the developing organs, young leaves, and developing pods, in comparison with N from nitrate. N from ammonium showed distribution pattern similar to that of N from dinitrogen.

The nodule N was supplied by both directly fixed-N and transferred nitrogen, and fixedN was inferred to play a major role in this process. The pro tein N in the roots could be furnished by the recycled N of dinitrogen and nitrate through the shoots along with direct incorporation of amino acids produced in the roots from nitrate     

Interaction of Glyphosate with Zinc for the Yield,Photosynthesis, Soil Fertility and Nutritional Status of Soybean

Application of glyphosate herbicide in genetically modified (GM) soybean [Glycine max (L.) Merrill] in soils with low zinc (Zn) concentration may interfere in the uptake of this and other nutrients, with negative impact on productivity. Thus, an experiment was conducted in greenhouse conditions on Ustoxix Quatzipsamment soil to investigate the effects of the interaction of glyphosate with Zn for the yield, photosynthesis, soil fertility and nutritional status of soybean. The treatments consisted of two soybean varieties [BRS 133 (conventional—NGM) and its essentially derived transgenic line BRS 245RR (GM) with and without glyphosate application] and five Zn rates (0, 5, 10, 20 and 40 mg kg^?1, source zinc sulfate (ZnSO₄)), with four replicates. Except for the copper (Cu) and iron (Fe) concentrations, the introduction of the herbicide-resistant gene is the predominant factor reducing nutrient uptake, photosynthetic (A) rate, stomatal conductance (Gs), leaf chlorophyll and ureide concentrations. The administration of Zn rates lowered the leaf phosphorus (P) concentration, and there was significant increase in Zn concentration in the soil and in the plant. Except for the 20 mg kg^?1 of Zn rate, the use of the herbicide did not affect the shoot dry weight (SDW) and seed yield, and on average, the maximum seed yield was obtained with Zn concentrations of 26.4 and 18.7 mg kg^?1 extracted by Mehlich 1 and diethylenetriaminepentaacetic acid-triethanolamine (DTPA-TEA), respectively.     

Effect of nitrogen fertilization on yield component distribution and assimilate translocation of determinate and indeterminate soybean lines

Studies were conducted to compare the main‐stem and branch yield component distribution of two soybean [Glycine max (L.) Merr.] lines differing in architecture and growth habit, and to relate the partitioning of carbon assimilates during pod filling and seed filling stages. An indeterminate line (MI) and a determinate line (MD) were planted in early May on a fine, mixed mesic Udic Haplustalf soil in southwestern France. For the N treatment, N fertigation was applied at the end of the vegetative phase and the early stages of reproductive growth. Pod production on branches was stimulated in response to N application for the determinate line, and N also enhanced the weight of seeds located on branches for both lines. At different stages during pod setting and seed filling, mid‐canopy‐level leaves were allowed to assimilate ¹⁴CO₂ and 24 h after exposure, radioactivity was measured in different organs and levels of the whole plant. ¹⁴C‐assimilates appeared to be preferentially transferred to the lower level of the main‐stem in MI and to the lower level and branches in the MD line. For N‐treated plants, radiocarbon accumulation was particularly marked in pods located on the lower level and on branches; this was consistent with the yield component distribution patterns seen at harvest.     

Variability of nodulation and dinitrogen fixation capacity among soybean cultivars

 In order to identify soybean cultivars with higher biological N₂ fixation capacities, North American and Brazilian soybean [Glycine max (L.) Merrill] cultivars, belonging to maturity groups VI–VIII, were evaluated for nodulation parameters and N₂ fixation rates. The symbiotic performance of 152 cultivars was evaluated in pots containing 4 kg soil with an established population of the three Bradyrhizobium elkanii strains [29w (SEMIA 5019):SEMIA 566 : SEMIA 587, 22%:36%:34%] which are established in most Brazilian soils cultivated with soybean. Differences were verified among cultivars, with some accumulating up to twice as much nodule dry weight and N in tissues as others. The variability among cultivars was also confirmed when six of them were used in a field experiment, resulting in differences in nodulation, yield and total N accumulated in grains. The analysis of nodule occupancy in 12 cultivars grown either under sterile conditions and receiving a double inoculum and N-free nutrient solution, or in pots containing soil with an established population of bradyrhizobia, showed the preference of cultivars for specific strains. Received: 7 December 1998     

Effects of foliar fertilization on yield,protein, oil and elemental composition of two soybean varieties

Abstract

The effects of foliar fertilization on the yield and seed composition of two soybean (Glycine max L. Merrill) varieties were investigated under mid‐Missouri conditions over a 2‐year period. The foliar fertilizer treatments consisted of (i) 80–8–24–4 (NPKS) kg/ha, (ii) 40–4–12–2 (NPKS) kg/ha, and (in) control (no foliar treatment) with the optimum proportion of N:P:K:S in the solution 10:1:3:0.5 respectively. Nutrient sources were urea, potassium polyphosphate, and potassium sulfate. Water solutions of fertilizers (pH 6.9) containing 0.1% Tween 80 (v/v) were sprayed on the plants using a CO₂ ‐ pressurized back‐pack sprayer. Foliar fertilizer was split between four equal applications during the seed filling period. The variety Mitchell at the higher rate and the variety Williams at the lower fertilizer application rate produced slight, though statistically insignificant, yield increases. At the higher rate of application, the seed protein contents of both varieties increased, while the oil contents decreased. The concentrations of P and K in the seeds were not affected by foliar fertilization, but at the higher rate, there was a small decrease in S content of Williams variety.     

Soybean nodulation and nitrogen fixation on soil previously amended with sewage sludge

Summary A greenhouse study was conducted to examine the residual effects of sewage sludge on soybean Glycine max (L.) Merr., nodulation, and N fixation. Nodulating and nonnodulating isolines of Clark soybean were grown to the R2 stage in soils (Typic Paleudults) obtained from plots where heat-treated sludge had been applied in 1976 at rates equal to 0, 56,112, and 224 Mg ha^–1 high (7.0) and low (6.2) soil pH regimes were established by CaCO₃ additions. Sludge and soil pH treatments resulted in clearly defined differences in metal uptake by soybean shoots. Plant Zn, Cd, and Ni concentrations were greater on pH 6.2, sludge-amended soil than on the pH 7.0, amended soil. At low soil pH, soybean Zn and Cd concentrations, respectively, increased from 41 and 0.19 mg kg^–1 (control) to 120 and 0.58 mg kg^–1 at the 224 Mg hat sludge rate. At the high soil pH and 224 hg hat sludge rate, Zn and Cd concentrations were 45 and 0.15 mg kg^–1, respectively.Symbiotic N fixation provided 90% of the total N accumulation. Total N accumulation, shoot N concentration, dry matter, and N fixation by nodulating soybeans exhibited a significant linear increase with sludge rate. Total N accumulation, dry matter, and N fixation were significantly greater at high soil pH. For high and low soil pH, respectively, N fixation increased from 422 and 382 mg N per plant (control) to 614 and 518 mg N per plant at the 224 Mg ha^–1 sludge rate. While soybean nodulation also increased linearly on sludge-amended soil, a significant rate times pH interaction for nodule number indicated that nodulation was less strongly enhanced by sludge at low soil pH.     

长期施肥对土壤微生物生物量碳、氮及矿质态氮含量动态变化的影响

利用位于陕西杨凌的17年长期定位试验研究了长期不施肥(CK)、单施化肥(F)、化肥配施有机肥(F+M)和化肥加秸秆还田(F+S)处理对小麦-玉米轮作体系中作物不同生长时期土壤微生物生物量碳、氮(SMBC、SMBN)和矿质态氮含量的影响。结果表明,0—10 cm土层土壤SMBC、SMBN和矿质态氮含量的变化范围分别为264.8~752.2、37.51~14.8和3.83~8.5 mg/kg。不同处理相比,F+M处理中各采样时期(小麦苗期、拔节期、灌浆期及玉米播种期、大喇叭口期、灌浆期和收获后)土壤SMBC和SMBN含量均为最高,分别为不施肥对照的1.382~.65和1.892~.50倍;F+S处理矿质态氮含量最高,SMBC和SMBN也高于F和CK处理,大部分采样时期的差异达显著水平(P0.05);与CK相比,长期单施化肥也使各时期SMBC和SMBN含量提高。在小麦拔节期到灌浆期的旺盛生长阶段各施肥处理土壤SMBN含量均下降,而矿质态氮含量变化不大,处于较低水平;在玉米大喇叭口期到灌浆期的旺盛生长阶段,F+M、F+S和F处理土壤矿质态氮含量显著下降,而SMBN含量均有所升高。表明在土壤矿质态氮含量较高时,作物首先利用矿质态氮,而在土壤矿质态氮含量处于较低水平时,微生物固持的氮素可能会释放出来供作物吸收利用。     

Boron fertilization enhances photosynthesis and water use efficiency in soybean at vegetative growth stage

Abstract

Influence of boron (B) on photosynthesis and water use has not sufficiently been evaluated in soybean despite its worldwide importance as a crop. The objective of this work was to evaluate the effects of B application on photosynthesis and water use in soybean at vegetative growth stage. A pot experiment was carried out in a greenhouse. Soybean [Glycine max (L.) Merrill cv. M8644 IPRO] was grown in a clayey Oxisol previously fertilized with 4 B rates (0, 1.5, 3.0, and 6.0?mg dm^?3). Net photosynthesis rate (P_n), intercellular CO₂ concentration (C_i), transpiration rate (E), stomatal conductance (g_s) were measured in the second trifoliate leaf of plants at the V4 growth stage. Instantaneous water use efficiency (WUEis = P_n/E) and intrinsic water use efficiency (WUEic = P_n/g_s) were calculated. B application to soil increased all these variables. The most consistent increases were in P_n, WUEis, and WUEic. The critical level of hot water extractable B in soil that maximized photosynthesis and optimized water use by soybean at vegetative growth stage was calculated to be 0.38?mg dm^?3.