Effects of Plant-Growth-Promoting Rhizobacteria on Yield,Growth, and Some Physiological Characteristics of Wheat and Barley Plants

In 2009 a greenhouse experiment was conducted to determine the effects of boron (B) and plant growth-promoting rhizobacteria (PGPR) treatments, applied either alone or in combination, on yield, plant growth, leaf total chlorophyll content, stomatal conductance, membrane leakage, and leaf relative water content of wheat (Triticum aestivum L. cv. Bezostiya) and barley (Hordeum vulgare L. cv. Tokak) plants. Results showed that alone or combined B (0, 1, 3, 6, 9 kg ha^?1) and PGPR (Bacillus megaterium M3, Bacillus subtilis OSU142, Azospirillum brasilense Sp245, and Raoultella terrigena) treatments positively affected dry weight and physiological parameters searched in both species. Statistically significant differences were observed between bacterial inoculation and B fertilizer on root and shoot dry weight under non-cold-stress (NCS) and cold-stress (CS) conditions. Leaf total chlorophyll content (LTCC), stomatal conductance (SC), leaf relative water content (LRWC), and membrane leakage (ML) were negatively affected by CS conditions and decreased with reduced temperatures of media, but B and PGPR application alleviate the low-temperature deleterious effect in both species. The greatest SC and LRWC, and the lowest ML, were obtained by 6 kg B ha^?1 combined with R. terrigena treatment. The greatest LTCC in both NCS and CS conditions was observed with B. megaterium M3 application alone.     

Silicon Increases Tolerance to Boron Toxicity and Reduces Oxidative Damage in Barley

ABSTRACT

Silicon (Si) protects plants from multiple abiotic and biotic stresses The effect of exogenous Si levels (50, 75, and 100 mg kg^?1) on the growth, boron (B) and Si uptake, lipid peroxidation (MDA), lipoxygenase activity (LOX; EC 1.13.11.12), proline, and H₂O₂ accumulation, non-enzymatic antioxidant activity (AA) and the activities of major antioxidant enzymes (superoxide dismutase, SOD, EC 1.15.1.1; catalase, CAT, EC 1.11.1.6 and ascorbate peroxidase, APX, EC 1.11.1.11) of barley (Hordeum vulgare L.) were investigated under glasshouse conditions. Increasing levels of Si supplied to the soil with 20 mg kg^?1 B counteracted the deleterious effects of B on shoot growth. Application of B significantly increased the B concentration in barley plants. However, Si application decreased B concentrations. Increasing application of Si increased the Si concentration in barley plants. The concentration of H₂O₂ was increased by B toxicity but decreased by Si supply. Boron toxicity decreased proline concentrations and increased lipid peroxidation (MDA content) and LOX activity of barley. Compared with control plants, the activities of AA, SOD, CAT, and APX in B stressed plants grown without Si decreased, and application of Si increased their activities under toxic B conditions. The LOX activity was decreased by Si. Based on the present work, it can be concluded that Si alleviates B toxicity by possibly preventing oxidative membrane damage, both through lowering the uptake of B and by increasing tolerance to excess B within the tissues.     

Boron and Amino Acid Foliar Application on Wheat-Soybean Intercropping in a Non-Tillage System

Micronutrient and amino acid (AA) foliar fertilization has generally been sprayed onto plants to increase the crop yield. The experiment had the aim of evaluating the foliar boron (B) and AA application on grain yield (GY), physiological characteristics, nutritional status, and yield components in wheat (Triticum aestivum L.) and soybean [Glycine max (L.) Merrill] intercropping in a non-tillage system (NTS). The experiment was set up as a randomized block design with eight treatments and four replicates. The treatments had the following boron (B) rates: [0, 1, 2, 4, and 8 kg ha^?1, source: boric acid (H₃BO₃)] + AAs (2 L ha^?1) applied by foliar spraying and the additional treatments [(Control - without B and AAs), 2 kg ha^?1 B, 2 L ha^?1 AAs and 2 kg ha^?1 B + 1 L ha^?1 AAs] applied at the end of the elongation and spike beginning of wheat plants and development growth stage (V5) of soybean for two growing seasons. Boron and AAs had no influence on the physiological and yield components and had no increases in the foliar and grain B content in wheat and soybean. No matter the dose, the foliar B + AAs (2 L ha^?1) application did not increase the GY in wheat-soybean under a rotational NTS in loamy soil with suitable available B.     

CELL WALL URONIC ACID CONCENTRATIONS OF RESISTANT AND SENSITIVE CULTIVARS OF WHEAT AND BARLEY UNDER BORON TOXICITY

In this study, changes in cell wall uronic acid concentrations of boron (B)-tolerant and B-sensitive cultivars of wheat and barley were analyzed in control (plants that were grown on water and received no B) and B-treated plants. Ten-day-old seedlings of wheat (Triticum aestivum L. ‘Atay’ (B-sensitive) and ‘Bolal’ (B-tolerant)) and barley (Hordeum vulgare L. ‘Hamidiye’ (B-sensitive) and ‘Anadolu’ (B-tolerant)) were grown in H₃BO₃ solution (10 mM final concentration) or water for 3, 5, or 7 days. For determination of changes in cell wall uronic acid concentrations of wheat and barley cultivars, cell walls were extracted from root and leaf tissues of control and B-treated plants. Cell wall uronic acid concentrations of root and leaf tissues of each cultivar were statistically analyzed. Various reciprocal analyses were performed. These analyses were high-B-tolerant versus B-sensitive cultivars and control versus B-treated plants. In all reciprocal analyses, no significant changes were observed. These data, thus, suggest that cell wall uronic acid content does not contribute to detoxification of excess B in wheat and barley.     

Plant Growth-Promoting Rhizobacteria (PGPR) and Phosphorus Fertilizer-Assisted Phytoextraction of Toxic Heavy Metals from Contaminated Soils

Phytoremediation is a remediation technique that involves the use of plants to extract, sequester, and/or detoxify pollutants through physical, chemical, and biological processes. The use of phytoremediation is expanding due to its cost-effectiveness compared with conventional methods. This study was conducted to investigate the effects of autumn and spring application of plant growth-promoting rhizobacteria (PGPR, 10⁸ cfu mL^?1 Bacillus megaterium var. phosphaticum sprayed at 250 mL plot^?1) and phosphorus (P) fertilizer (0, 11, 22, 33, 44 kg P ha^?1) on dry matter yield and heavy metal uptake by plants in soils contaminated with heavy metals. Field experiments were conducted using a randomized complete block design with four replications between 2004 and 2007. The results of the study indicated that P fertilization, but not PGPR application, significantly affected dry matter yield. Application of PGPR increased heavy metal availability in soils and the heavy metal uptake of meadow plants. The heavy metal content of the meadow plants resulting from PGPR application was 4–6 times higher for the spring application than the autumn application. Approximately 16, 30, 10, 10, and 3 growing seasons without PGPR are necessary to remove all lead (Pb), nickel (Ni), boron (B), manganese (Mn), and zinc (Zn), respectively, from polluted soil. The time required for Pb, Ni, B, Mn, and Zn removal could be further decreased to approximately 4, 6, 3, 3, and 1 growing seasons, respectively, with 33 kg phosphorus pentoxide (P₂O₅) ha^?1 and 10⁸ cfu mL^?1 PGPR applications at rates of 250 mL plot^?1 in the spring season.     

Effects of zinc fertilization and irrigation on grain yield and zinc concentration of various cereals grown in zinc‐deficient calcareous soils

Effects of varied irrigation and zinc (Zn) fertilization (0, 7, 14, 21 kg Zn ha^‐1 as ZnSO₄7.H₂O) on grain yield and concentration and content of Zn were studied in two bread wheat (Triticum aestivum), two durum wheat (Triticum durum), two barley (Hordeum vulgare), two triticale (xTriticosecale Wittmark), one rye (Secale cereale), and one oat (Avena sativa) cultivars grown in a Zn‐deficient soil (DTPA‐extractable Zn: 0.09 mg kg^‐1) under rainfed and irrigated field conditions. Only minor or no yield reduction occurred in rye as a result of Zn deficiency. The highest reduction in plant growth and grain yield due to Zn deficiency was observed in durum wheats, followed by oat, barley, bread wheat and triticale. These decreases in yield due to Zn deficiency became more pronounced under rainfed conditions. Although highly significant differences in grain yield were found between treatments with and without Zn, no significant difference was obtained between the Zn doses applied (7–21 kg ha^‐1), indicating that 7 kg Zn ha^‐1 would be sufficient to overcome Zn deficiency. Increasing doses of Zn application resulted in significant increases in concentration and content of Zn in shoot and grain. The sensitivity of various cereals to Zn deficiency was different and closely related to Zn content in the shoot but not to Zn amount per unit dry weight. Irrigation was effective in increasing both shoot Zn content and Zn efficiency of cultivars. The results demonstrate the existence of a large genotypic variation in Zn efficiency among and within cereals and suggest that plants become more sensitive to Zn deficiency under rainfed than irrigated conditions.     

Determining critical limit of boron in soil for wheat (Triticum aestivum L.)

Abstract

Critical values of boron (B) for wheat nutrition in soil and plant were determined through a pot experiment with twenty-one surface soils of Alluvial flood plain and Red-latertic belt comprising three major soil orders (Entisols, Alfisols, Inceptisols) with four levels of boron. Application of boron significantly increased the dry matter yield as well as uptake of B by plants. Critical concentration of hot calcium chloride (CaCl₂) extractable B in soil for wheat was found to be 0.53?mg?kg^?1. The critical plant B concentration varied with growth stages and values were 7.4?mg?kg^?1 at panicle initiation and 4.18?mg?kg^?1 at maturity, respectively. The findings of this investigation also recommend the application of 2?kg?B^?1?ha^?1 for ensuring B sufficiency to wheat in Indo-gangetic alluvial and Red-Lateritic soils.     

Phosphorus amendment decreased cadmium (Cd) uptake and ameliorates chlorophyll contents,gas exchange attributes,antioxidants, and mineral nutrients in wheat (Triticum aestivum L.) under Cd stress

A 28-day pot (sand culture) experiment was carried to evaluate the effects of phosphorus (P) application in alleviating Cd phytotoxicity in wheat plants. Different levels of P (0, 10, and 20 kg ha^?1) were applied without and with 100 µM Cd. The results showed that 100 µM Cd concentration decreased plant biomass, chlorophyll contents, gas exchange attributes, and mineral nutrients in wheat plants. Cadmium stress increased tissue Cd and H₂O₂ concentrations. The activities of superoxide dismutases (SOD), peroxidase (POD) enzymes, increased while the activities of catalase (CAT), ascorbic acid (AsA), α-tocopherol, and phenolics decreased under Cd stress. Phosphorus supply increased shoot biomass, leaf area, photosynthetic pigments, and mineral nutrients and decreased Cd and H₂O₂ concentrations in shoots. Phosphorus application improved antioxidant enzyme activities and gas exchange attributes which emerged as an important mechanism of Cd tolerance in wheat. We conclude that P application contributes to decreased Cd concentrations in wheat shoots and increased gas exchange attributes and antioxidant enzymes and could be implemented in a general scheme aiming at controlling Cd concentrations in wheat for sustained production of this important grain crop.     

MITIGATION EFFECTS OF SILICON ON TOMATO PLANTS BEARING FRUIT GROWN AT HIGH BORON LEVELS

Interactive effects of silicon (Si) and high boron (B) on growth and yield of tomato (Lycopercison esculentum cv. ‘191 F1’) plants were studied. Treatments were: 1) control (B1), normal nutrient solution including 0.5 mg L^?1 B (boron), 2) B1 +Si treatment: 0.5 mg L^?1 boron plus 2 mM Si, 3) B2 treatment: 3.5 mg L^?1 B, 4) B2 +Si treatment: 3.5 mg L^?1 B plus 2 mM Si, 5) B3 treatment: 6.5 mg L^?1 B, and 6) B3 +Si: 6.5 mg L^?1 B plus 2 mM Si. High B reduced dry matter, fruit yield and chlorophyll (Chl) in tomato plants compared to the control treatment, but increased the proline accumulation. Supplementary Si overcame the deleterious effects of high B on plant dry matter, fruit yield and chlorophyll concentrations. High B treatments increased the activities of superoxide dismutase (SOD; EC 1.15.1.1), peroxidase (POD; EC. 1.11.1.7) and polyphenol oxidase (PPO; EC 1.10.3.1). However, supplementary Si in the nutrient solution containing high B reduced SOD and PPO activities in leaves, but POD activity remained unchanged. These data suggest that excess B-induced oxidative stress and alterations in the antioxidant enzymes. Boron (B) concentrations increased in leaves and roots in the elevated B treatment as compared to the control treatment. Concentrations of calcium (Ca) and potassium (K) were significantly lower in the leaves of plants grown at high B than those in the control plants. Supplementing the nutrient solution containing high B with 2 mM Si increased both nutrients in the leaves. These results indicate that supplementary Si can mitigate the adverse effects of high B on fruit yield and whole plant biomass in tomato plants.     

Soil chemical attributes,nutrient uptake and yield of no-till crops as affected by phosphogypsum doses and parceling in southern Brazil

This study evaluated soil chemical attributes, leaf nutrient concentrations and grain yield of corn (Zea mays), barley (Hordeum vulgare), common bean (Phaseolus vulgaris) and wheat (Triticum aestivum) as affected by phosphogypsum (PG) rates and split application to a Typic Hapludox under no-till from Southern Brazil. A Randomized complete block design was used, with factorial treatment structure (5 x 2) consisting of increasing PG rates (0, 3, 6, 9 and 12 Mg ha^?1) either in single or split (half dose, two consecutive years) application. PG rates have reduced concentrations of Al³⁺, increasing Ca²⁺, SO₄^2- and pH values in soil layers up to 0.8 m. Leaf concentrations of Ca (between 28 and 42%) and S (between 6% and to 50%) increased in all crops, while leaf levels of Mg decreased on corn (?16%), bean (?22%) and wheat (?14%) by PG rates. Compared to the control, PG rates between 4.0 and 6.1 Mg ha^?1 promoted increases of 11%, 10% and 10% on corn, barley and wheat yields, respectively. There was no effect of PG on common bean’s yield. Phosphogypsum was effective for improving soil fertility, plant nutrition and crop yields. Applying the PG annually at one-half rate gave best overall results.     

Yield enhancement and phosphorus economy in lentil (Lens culinaris Medikus) with integrated use of phosphorus,Rhizobium and plant growth promoting rhizobacteria

The study evaluated the effects of phosphorus (0, 20, 30, and 40 kg P₂O₅ ha^?1) and biofertilizers [Rhizobium (Rhizobium leguminosarum bv viciae), plant growth promoting rhizobacteria (PGPR) (Pseudomonas fluorescens), Rhizobium + PGPR, and uninoculated control] in lentil. Application of 40 kg P₂O₅ ha^?1 resulted in the highest number of nodules, nodule dry weight, leghemoglobin content in nodules, chlorophyll content, yield attributes, and grain yield. Coinoculated treatment performed better than uninoculated control, and individual inoculations of Rhizobium and PGPR in terms of all above mentioned parameters. Application of 20 kg P₂O₅ ha^?1 + Rhizobium inoculation gave statistically similar and 20 kg P₂O₅ ha^?1 + Rhizobium + PGPR inoculation gave significantly higher grain yield than that by 40 kg P₂O₅ ha^?1 alone. The use of Rhizobium alone and Rhizobium + PGPR consortium can save not only 20 kg P₂O₅ ha^?1 but also increase the grain yield of lentil.     

Determination of Residual and Cumulative Boron Requirements for Cotton and Wheat Crops Grown Under Calcareous Soil Conditions

A two-year field experiment was conducted to elucidate the residual and cumulative boron (B) requirements for cotton and wheat crops. For the first time, cotton was sown in randomized complete blocks those received 0.0, 1.0, 1.5, 2.0, 2.5 and 3.0 kg B ha^?1 as borax (Na₂B₄O₇.10H₂0). Later, each plot was divided into two subplots for successive wheat and cotton crops and half of the pots received B at similar rates. Our results revealed that direct application of B at the rate of 2 and 2.5 kg ha^?1 produced optimum cotton yield during 2005. The same rates of B were consistent in residual plots but not in cumulative plots for both of the crops in successive years. It was thus concluded that soil applied B at the rate of 2.0 and 2.5 kg ha^?1 had significant residual effects on cotton and wheat yields.     

Residual Effect of Copper and Zinc from Fertilizers on Plant Concentration,Phytotoxicity, and Crop Yield Response

Abstract

To avoid toxicity resulting in reduced crop yields and/or phytotoxic symptoms on the foliage, information on the residual effect of micronutrient fertilization after periods of application is desirable. This article includes discussion on the micronutrients copper (Cu) and zinc (Zn), because they are essential and are of concern from plant and animal standpoints. In general, no detrimental effects in yield reduction or phytotoxicity were noted from Cu applications of up to 50 kg Cu ha^?1 to barley (Hordeum vulgare L.) and wheat (Triticum aestivum L.). Barley was an exception where 50 kg Cu ha^?1 decreased yield by about 12% in the first‐year crop. The Cu levels in plants did not exceed 9 mg kg^?1. Studies showed that Zn applications of 50 kg ha^?1 for 2 years in succession and the resulting crop tissue Zn levels as high as 105 mg kg^?1 did not cause any phytotoxicity in cereals. The results of this study suggest that cereals can tolerate high levels of Cu and Zn.     

Crop stand density enhances competitive ability of spring barley (Hordeum vulgare L.)

Abstract

The aim of the research was to establish weediness, competitive ability and productivity of the crop. The experimental object was agrophytocenoses of spring barley – Hordeum vulgare L. – crop of spring barley ‘Aura’ and unsown soil, and weeds growing in them. The crop was formed sowing 0, 120, 200 and 280 kg ha^?1 (0, 2.7, 4.5 and 6.2 million seeds per ha^?1 respectively) seeds of spring barley ‘Aura’. Spring barley crop was not harrowed and herbicides were not applied. In the field experiment estimates were made of changes of weeds and spring barley inter- and within- species competition optimizing crop density. During three years of field experiment in the crop of spring barley annual weeds prevailed at 88–99%, such as Chenopodium album, Stellaria media, Erysimum cheiranthoides. Perennial weeds formed 1–12% of the crop weeds, such as Sonchus arvensis, Cirsium arvense, Equisetum arvense. General number of weed species in spring barley crops varied from 13 to 21. Weed abundance proportionally declined in the crops of higher density, hence, higher seed rate should be recommended for organic agriculture where weeds are controlled in non-chemical ways. Consistently increasing barley stand density, the competition between species (spring barley with weeds) gradually turned into competition within species (between barley plants) when a higher number of weaker and non-productive stems started forming. Spring barley yield did not significantly depend on the stand density. Increasing stand density enhanced cultivated crop yield to a certain level (200 kg ha^?1), since an increase in spring barley plant number resulted in the reduction in weight per plant and 1000 grain weight, which was compensated by an increase in the number of spring barley plants. Different spring barley density had an essential influence on the chemical composition of weeds which was similar to that of spring barley. Weeds accumulated the greatest amount of crude proteins, crude fat and crude fibre growing without spring barley.     

Evaluation of the NH4HCO3‐DTPA soil test for assessing boron availability to wheat

Abstract

The NH₄HCO₃‐DTPA (AB‐DTPA), 1 MNH₄HCO₃, 0.005 M DTPA, pH=7.6, was proposed as a multi‐element extractant, for evaluating macro and micronutrients availability to plants. AB‐DTPA was also evaluated as a soil test, for assessing boron availability and toxicity to alfalfa. In a pot experiment, ten soils of Northern Greece were used to assess AB‐DTPA as an extractant of available boron to wheat (Triticum aestivum L., cv. Yecora), in comparison with hot water and saturation extract. Boron (B) was added as borax (Na₂B₄O₇*10H₂O) to the ten soils, at rates equal to 0, 3, and 5 mg B kg^‐1. Wheat was grown in pots containing the boron amended soils to the stage of tillering, and dry aboveground biomass, B concentration and B uptake by wheat were determined. AB‐DTPA extractable B was significantly greater than saturation extract and similar to hot water at each B application rate, and was correlated significantly with hot water (r=0.84), or with saturation extract (r=0.48). Extractable boron by all extractants, boron concentration in wheat and boron uptake were significantly affected by the soil x B application rate interaction. In assessing B availability to wheat using AB‐DTPA as a soil test, CEC should be included in the regression equation for B concentration, or pH for B uptake. However, the corresponding adjusted coefficients of determination for B concentration (adjusted R²=0.46) and B uptake (adjusted R²=0.48) were similar or lower to those of hot water (adjusted R²=0.45 and 0.60, respectively) and the saturation extract (adjusted R²=0.70 and 0.49, respectively), when the latter two soil tests were used in the regression equations without the inclusion of any soil property.     

CO2激光与外源NO对低温胁迫小麦的防护效应

以冬小麦‘小堰22号’为试验材料,研究了CO2激光与外源一氧化氮(NO)复合作用对低温胁迫(4℃)下小麦幼苗自由基双氧水(H2O2)、超氧阴离子(O2?)浓度,超氧化物歧化酶(SOD)、过氧化氢酶(CAT)、过氧化物酶(POD)、抗坏血酸过氧化物酶(APX)和谷胱甘肽还原酶(GR)、一氧化氮合成酶(NOS)活性,一氧化氮(NO)及蛋白质含量,及幼苗生长发育的影响。结果表明:与单独低温胁迫相比,外源NO处理后低温胁迫和CO2激光处理后低温胁迫都显著降低了H2O2和O2?浓度,提高了SOD、CAT、POD、APX、NOS活性,NO和蛋白质含量,促进幼苗生长发育。外源NO处理后再进行CO2激光辐射,虽然可以降低低温胁迫下幼苗H2O2和O2?浓度,提高SOD、CAT、POD、APX、NOS活性及NO和蛋白质浓度,促进幼苗生长发育,但其保护效应明显低于外源NO处理后低温胁迫和CO2激光处理后低温胁迫的效果。上述结果说明,NO对低温胁迫的防护效应优于NO和CO2激光复合处理。因此,建议在农业生产中单独采用NO处理或者CO2激光处理,可以促进农作物对低温胁迫的抗性。     

RELATIONSHIP OF SOIL EXTRACTABLE AND FERTILIZER BORON TO SOME SOIL PROPERTIES,CROP YIELDS,AND TOTAL BORON IN COTTON AND WHEAT PLANTS ON SELECTED SOILS OF PUNJAB,PAKISTAN

Boron (B) is an essential microelement, which is necessary for reproductive organs including pollen tube formation in wheat (Triticum aestivum L.), and flowering and boll formation in cotton (Gossypium hirsutum L.) The study was associated with wheat-cotton rotation in 80 farm fields, belonging to different soil series, in four districts of cotton belt of Punjab, Pakistan to assess concentrations of extractable B in soils [0.05 M hydrochloric acid (HCl) extractable B], and added fertilizer B and their relationship to some soil physico-chemical properties [pH, organic matter (OM), calcium carbonate (CaCO₃) and clay content], yields and total B concentrations in wheat and cotton plants. All soils had alkaline pH (7.45 to 8.55), high CaCO₃ content (2.14 to 8.65%), less than 1.0% OM (0.33 to 0.99%), low plant available-P (Olsen P less than 8 mg kg^?1 soil) and medium ammonium acetate extractable potassium (K) (< 200 mg K kg^?1 soil). Of the 80 soil samples, 65 samples (81%) were low in available B (<0.45 mg B kg^?1, ranging from 0.11 to 0.43 mg B kg^?1) Of the corresponding 80 plant samples, leaves B concentrations were below critical levels (<10 mg B kg^?1 for wheat; <30 mg B kg^?1 for cotton) for all the tested samples for wheat and cotton. The regression analysis between plant total B concentrations and soil extractable B concentrations showed strong linear positive relationships for both wheat (R² = 0.509***, significant at P <0.001) and cotton (R² = 0.525***, significant at P <0.001). Further regression analysis between extractable soil B and wheat grain yield as well as between wheat leaves total B and wheat grain yield also depicted strong linear relationships (R² = 0.76 and 0.42, respectively). Boron fertilizer demonstration plots laid out at farmers’ fields low in extractable B, in each district not only enhanced grain yields of wheat crop but also contributed a significant increase towards seed cotton yield of succeeding cotton crop through residual B effect. In conclusion, the findings suggest that many soils in the cotton belt of Punjab may be low in extractable B for wheat and cotton, especially when these crops are grown on low OM soils with high CaCO₃ content.     

NITROGEN ACCUMULATION IN SHOOTS AS A FUNCTION OF GROWTH STAGE OF CORN AND WINTER WHEAT

Midseason fertilizer nitrogen (N) rates based on predicted yields can be projected if the quantity of N accumulated in winter wheat (Triticum aestivum L.) and corn (Zea mays L.) is known especially early in the growing season. This study was conducted in 2006 and 2007 to establish the amount of N accumulated in corn and winter wheat over the entire growing season. Plots representing three N fertilization rates 0, 45, and 90 kg ha^?1 at Stillwater and 0, 67, and 112 kg ha^?1 at Lahoma were selected from two long-term wheat experiments located at research stations in Stillwater and Lahoma, Oklahoma. For corn, three N fertilization rates 0, 112 and 224 kg ha^?1 at Lake Carl Blackwell and 0, 56 and 112 kg ha^?1 at Perkins were selected from N studies, located at research stations near Lake Carl Blackwell and Perkins, Oklahoma. Sequential aboveground biomass samples were collected from 1 m² area of wheat and 1.5 m long row (0.76 cm spacing) for corn throughout their respective growing seasons. In general, this work showed that more than 45% of the maximum total N accumulated could be found in corn plants by growth stage V8 (8th leaf collar fully unfolded). For winter wheat, more than 61% of the maximum total N accumulated at later stages of growth could be accounted for by Feekes growth stage 5 (F5, leaf strongly erected). Our findings are consistent with those of others showing that yield potential can be predicted at mid-season since such a large percentage of the total N accumulated was accounted for early on in the growing cycle of either wheat or corn.     

Nitrogen (total and 15N) uptake by barley and wheat under two irrigation regimes’

Nitrogen (total and ¹⁵N) uptake by barley (Hordeum vulgare L., cv. ‘Walfajr') and wheat (Triticum aestivum L., cv. ‘Karaj I') plants subjected to water stress were studied at the College of Agriculture, University of Tehran Experimental Farm located in the city of Karaj, Iran. The treatments consisted of two irrigation intervals, 7 days (control) and 14 days (stress). The plants were at the reproductive stage of growth at the start of the ¹⁵N treatment. Nitrogen (¹⁵N) was applied to 1m x 1m plots selected at the center of the 2.5m x 2.5m main plots. The ¹⁵N was provided to plants by adding 250 mg ¹³N as (NH₄)₂SO₄ (5.1 Atom % ¹⁵N) dissolved in water to each plot. The ¹⁵N treatment period continued for 48 hours. The plants were harvested at 6‐hour intervals during the ¹⁵N treatment period. After each harvest, the straw and the grains were separated, oven dried at 65°C and dry weights were recorded. Plant materials were ground in a Wiley Mill to pass through a 2mm sieve for chemical analysis. Total N was measured by an Auto‐Analyzer after Kjeldahl digestion, and ¹⁵N was measured using a mass spectrometer.

Nitrogen (total‐N and ¹⁵N) content of both plant species decreased under stress, with wheat appearing more severely affected than barley. However, nitrogen concentration was slightly higher for the stressed plants as compared with the controls. This pattern was essentially similar for both plants.     

Effectiveness of an elemental sulfur fertilizer in an oilseed‐cereal‐legume rotation on the Canadian prairies

Adequate sulfur (S) nutrition is critical for sustaining yields in crop rotation systems. Because of slow oxidation of elemental S (S°), research on S° fertilizers has emphasized improving the short‐term availability, while the long‐term effects of S° have been overlooked. The effectiveness of a dispersible granule S° fertilizer (SF: Sulfer95), consisting of S° particles smaller than any S° fertilizer reported in literature (< 44 μm in diameter), was compared to gypsum (CS: CaSO₄) and ammonium sulfate [AS: (NH₄)₂SO₄] in a three‐year experiment (1997—1999) on a moderately S deficient Black Chernozem soil (Typic Cryoboroll). The three S fertilizers were applied to canola (Brassica rapa L.) at 20, 40, and 80 kg S ha^‐1, supplemented with corresponding rates of nitrogen (N) fertilizer in the first year. The control treatment (CT) received N only. Barley (Hordeum vulgare L.) and peas (Pisum sativum L.) were grown in the second and third years to test the availability of residual S. Although the yield of canola in SF fertilized treatments was only slightly higher than in CT, available S provided by SF produced a higher physiological S efficiency (PSE). Superior yields with residual SF were obtained in the second and third years by barley and peas at the rate of 80 kg S ha^‐1 applied in the first year, indicating that slow oxidation of SF was beneficial to the crops subsequently grown. Over three years, the total crop S uptake was 21, 4.0, and 15% higher with SF than with CT, CS, and AS, respectively.