Tillage and dicyandiamide influence on nitrogen fertilizer immobilization,remineralization, and utilization by maize (Zea mays L.)

Summary Both tillage and nitrification inhibitors such as dicyandiamide (DCD) have the potential to influence N availability and thus plant N uptake. A field experiment was conducted to investigate the impact of DCD and tillage (rototillage and no-tillage) on N immobilization and the subsequent impact of residual and fertilizer N on N availability to maize (Zea mays L.) ¹⁵N-labeled urea and urea-DCD were surface applied at the rate of 16 g N m^-2, in either 1987 or 1988, to small plots which had been planted to maize (Zea mays L.). Soil samples were collected four times during the 1988 growing season and analyzed for the ¹⁵N and ¹⁴N components of inorganic N, organic N, and hydrolyzable (6 M HCl) amino acid N, hydrolyzable NH _inf4 ^sup+ -N, and non-hydrolyzable N. Plant samples were collected three times during the 1988 growing season, and analyzed for the ¹⁵N and ¹⁴N components of total N. The total amount of NO _inf3 ^sup- percolating through the profile was less than 15 kg N ha^-1 in 1987 and 1988. N uptake by maize was reduced under notillage and when the urea was treated with DCD. The tillage treatments had no effect on the uptake of N fertilizer applied in 1988 or on N immobilization. However, no-till-age reduced the uptake of residual N fertilizer. The reduced use of N fertilizer was attributed to a reduction in the actual mineralization rates of immobilized residual N. DCD reduced the uptake of N fertilizer applied in 1988. The reduced uptake was attributed to increased N immobilization or to organic matter fixation.     

Kinetics of zinc uptake by mycorrhizal (VAM) and non-mycorrhizal corn (Zea mays L.) roots

Summary The kinetics of Zn absorption were studied in mycorrhizal (Glomus macrocarpum) and non-mycorrhizal roots of corn (Zea mays L.) at pH 6.0 at Zn concentrations of 75 mol to 1.07 mol m^-3. Five concentration-dependent phases of Zn absorption were recognized; phase 0 (1.5–4.0 mmol m^-3) was linear but the other four phases (4.0 mmol to 1.07 mol m^-3) obeyed Michaelis-Menten kinetics. At low concentrations (less than 4 mmol m^-3), sigmoidal kinetics of Zn absorption were observed. The absorption of Zn by mycorrhizal maize was greater at low concentrations but decreased at higher levels. This appeared to be a result of a higher maximal uptake rate in phase 1 and lower K _m values in the subsequent phases. Kinetic models yielding continuous isotherms could not account for the observed multiphasic pattern.Research paper no. 6820 through the Director, Experiment Station, G.B. Pant University of Agriculture and Technology, Pantnagar 263 145, UP, India     

Relative significance of soil and nitrogenous fertilizer in nitrogen nutrition and growth of wetland rice (Oryza sativa L.)

Summary A pot experiment was conducted to compare the yields from five commercially cultivated varieties (Bas-198, Bas-370, Bas-Pak, Bas-385, and IR-6) of rice (Oryza sativa L.) and to establish the relative significance of soil N and fertilizer N (¹⁵N-labelled ammonium sulphate) in affecting crop performance. Another aim was to study the interaction of fertilizer N and soil N as influenced by different rice varieties. Among the five varieties tested, Bas-Pak gave the maximum dry matter and N yield. The N-use efficiency (percentage of applied N taken up by the plants) of different varieties ranged between 33.7 and 43.7%, Bas-Pak being the most efficient. Significant losses of fertilizer N occurred from the soil-plant system. The maximum N loss (52.1% of applied N) was observed with IR-6 and the minimum loss (39.2%) with Bas-Pak. A substantial increase in the uptake of soil N following the application of fertilizer and an interaction between the two N sources were observed with all varieties except Bas-385. The interaction was attributed to greater root proliferation following the application of fertilizer. It was concluded that a varietey with greater potential to use soil N is likely to give a better yield and that, of the two N sources, the availability of soil N was more important in determining the yield performance of different varieties of rice.     

Effect of pre-incubated sawdust-based cowdung on growth and nutrient uptake of Zea mays (L.) and on soil chemical properties

Summary A greenhouse soil culture experiment was set up to evaluate the effect of pre-incubation time (0, 2, 4, 6 weeks) of sawdust-based cowdung, prior to use, on the growth, dry-matter yield, and uptake of nutrients by Zea mays (L). The chemical properties of the soil (an Alfisol) were examined after the various treatments. The results indicated that incubation of cowdung for 4 weeks before planting time enhanced the growth and dry-matter yields of maize. Soil pH increased with the length of incubation while organic-C contents and cation exchange capacity remained unaffected. The length of pre-incubation enhanced the uptake of N and P but did not affect the uptake of K, Ca, Mg, and Na.     

Variability Among Maize (Zea mays L.) Inbred Lines for Seed Longevity

Genotypes conserved in active collections may suffer genetic erosion and modifications. The objective of this work was to investigate changes in germination and vigour in maize (Zea mays L.) inbred lines during cold storage in an active collection. Seeds of 16 maize inbreds produced along 16 years were evaluated for emergence and seedling vigour in a growth chamber. Linear and quadratic regressions of vigour and viability-related traits over seed age were calculated and tested for homogeneity. The seed of five production years of five inbreds that behaved differently in the regression analysis was multiplied in 1998, and original and renewed seed were evaluated in a growth chamber in 1999. Viability and vigour decreased linearly with age for most inbreds, particularly for B84 and EP10, varied at random for a few inbreds, and remained high for EP56 and A295. Aging caused reduction of vigour and loss of viability in most inbreds. There was variability for seed longevity among inbred lines; longevity was highest for inbred EP56. During storage, some seeds of each inbred died, while enduring seeds, when multiplied, produced new seed with enhanced viability and vigour compared to the average seed of the inbred, suggesting natural selection for viability and vigour during storage within inbred lines.     

15N-labelled fertiliser recovery by maize (Zea mays L.) and leaching of nutrients as influenced by oil palm empty fruit bunch biochar in a mini-lysimeter under controlled tropical environment

Converting oil palm empty fruit bunches into biochar is an alternative waste management method and has strong potential to improve N fertiliser use efficiency in agriculture. The aim of this study was to determine the effectiveness of oil palm empty fruit bunch biochar (EFBB) in improving recovery of ¹⁵N-labelled nitrogen fertiliser by maize (Zea mays L.) and leaching of mineral N and K. An experiment was conducted in a mini-lysimeter system with randomised complete block design layout and six replications under controlled environment in a rain shelter. Each mini-lysimeter was filled with 20 kg of sandy loam soil before adding EFBB (0, 5, 10 and 20 Mg ha^?1). The N source used was (¹⁵NH₄)₂SO₄ at 80 kg N ha^?1 (2 at% ¹⁵N excess). Maize was irrigated to induce leaching every 4 days. Maize plant and soils were sampled 58 days after sowing (tasselling stage). Application of EFBB significantly reduced cumulative leachate volume and mineral N leaching. Soils applied with EFBB significantly improved ¹⁵N fertiliser recovery in maize and dry matter weight. This study shows that EFBB has the potential to be applied on highly weathered acidic soil as an amendment to improve fertiliser efficiency and crop growth.     

Ammonia volatilization from nitrogen fertilizers surface-applied to corn (Zea mays) and grass pasture (Dactylis glomerata)

Summary The major agronomic concern with NH₃ loss from urea-containing fertilizers is the effect of these losses on crop yields and N fertilizer efficiency. In this 2-year study, NH₃ volatilization from surface-applied N fertilizers was measured in the field, and the effects of the NH₃ losses detected on corn (Zea mays L.) and orchardgrass (Dactylis glomerata L.) yield and N uptake were determined. For corn, NH₄NO₃ (AN), a urea-AN solution (UAN), or urea, were surface-broadcast at rates of 0, 56 and 112 kg N ha^–1 on a Plano silt loam (Typic Argiudoll) and on a Fayette silt loam (Typic Hapludalf). Urea and AN (0 and 67 kg N ha^–1) were surface-applied to grass pasture on the Fayette silt loam. Significant NH₃ losses from urea-containing N sources were detected in one of four corn experiments (12%–16% of applied N) and in both experiments with grass pasture (9%–19% of applied N). When these losses occurred, corn grain yields with UAN and urea were 1.0 and 1.5 Mg ha^–1, respectively, lower than yields with AN, and orchardgrass dry matter yields with urea were 0.27 to 0.74 Mg ha^–1 lower than with AN. Significant differences in crop N uptake between N sources were detected, but apparent NH₃ loss based on N uptake differences was not equal to field measurements of NH₃ loss. Rainfall following N application markedly influenced NH₃ volatilization. In corn experiments, NH₃ loss was low and yields with all N sources were similar when at least 2.5 mm of rainfall occurred within 4 days after N application. Rainfall within 3 days after N application did not prevent significant yield reductions due to NH₃ loss from urea in grass pasture experiments.     

Availability of soil and fertilizer nitrogen to wheat (Triticum aestivum L.) following rice-straw amendment

Summary A pot experiment was conducted to study the N availability to wheat and the loss of ¹⁵N-labelled fertilizer N as affected by the rate of rice-straw applied. The availability of soil N was also studied. The straw was incorporated in the soil 2 or 4 weeks before a sowing of wheat and allowed to decompose at a moisture content of 60% or 200% of the water-holding capacity. The wheat plants were harvested at maturity and the roots, straw, and grains were analysed for total N and ¹⁵N. The soil was analysed for total N and ¹⁵N after the harvest to determine the recovery of fertilizer N in the soil-plant system and assess its loss. The dry matter and N yields of wheat were significantly retarded in the soil amended with rice straw. The availability of soil N to wheat was significantly reduced due to the straw application, particularly at high moisture levels during pre-incubation, and was assumed to cause a reduction in the dry matter and N yields of wheat. A significant correlation (r=0.89) was observed between the uptake of soil N and the dry matter yield of wheat with different treatments. In unamended soil 31.44% of the fertilizer N was taken up by the wheat plants while 41.08% of fertilizer N was lost. The plant recovery of fertilizer N from the amended soil averaged 30.78% and the losses averaged 45.55%     

氮施用量对夏玉米土壤水氮动态及水肥利用效率的影响

采用田间小区试验,监测夏玉米不同生长期土壤水分和硝态氮剖面含量变化,研究不同施氮量对其时空变化及籽粒产量、水肥利用效率的影响,探讨氮肥对水肥资源高效利用的调节作用。结果表明：不同施氮处理,土壤剖面水分和硝态氮随土壤深度的变化趋势基本一致,即表层50 cm土壤水分和硝态氮含量较高且呈降低态,50-110 cm相对较低且波动较小,灌浆期二者均达到最低值;各生长期表层50 cm土壤含水量呈不施氮处理均高于施氮处理,50-110 cm土层则相反;施氮能提高土壤硝态氮含量,土壤硝态氮运移受土壤水分状况和含量的影响,含量越高,向下移动越深;施氮能显著提高水分利用效率及籽粒产量,增产效果明显（增产28.52%-37.86%）,二者均以施氮240 kg/hm^2处理最高;随施氮量的增加籽粒产量及籽粒吸氮量和水分利用效率增幅均表现为先升高后降低之趋势,当施氮量超过240 kg/hm^2后,籽粒产量和水分利用效率提高并不显著;不施氮与施氮处理氮素生产力、氮肥利用率之间均存在极显著差异。在本试验条件下,从控制土壤硝态氮积累及取得较高的产量和氮素利用率综合考虑,夏玉米的适宜施氮量范围应控制在120-240 kg/hm^2较好。     

Biological nitrogen fixation in maize (<Emphasis Type="Italic">Zea mays</Emphasis> L.) by <Superscript>15</Superscript>N isotope-dilution and identification of associated culturable diazotrophs

The nitrogen-fixing capacity of a range of commercial cultivars of maize (Zea mays L.) was evaluated by the ¹⁵N isotope-dilution method. Biological nitrogen fixation (BNF) expressed as percent nitrogen derived from air (Ndfa) ranged from 12 to 33 regardless of nitrogen fertilization. BNF was not affected by mineral nitrogen fertilization except on cultivar Topacio and PAU-871 cultivars. Subsequently, culturable bacterial diazotrophs were isolated from endophytic tissue of maize: seed, root, stem, and leaf. All isolates were able to grow on N-free semisolid medium. Eleven bacteria isolates showed nitrogen-fixing capacity by the reduction of acetylene to ethylene and confirmed by PCR the presence of nifH gene in their genome. Identification of the 11 isolates was performed by bacteriological methods, 16S rRNA gene sequences, and phylogenetic analysis, which indicated that the bacteria isolated were closely related to Pantoea, Pseudomonas, Rhanella, Herbaspirillum, Azospirillum, Rhizobium (Agrobacterium), and Brevundimonas. This study demonstrated that maize cultivars obtain significant nitrogen from BNF, varying by maize cultivar and nitrogen fertilization level. The endophytic diazotrophic bacteria isolated from root, stem, and leaf tissues of maize cultivars may contribute to BNF in these plants.     

Effects of 15N-labelled ammonium nitrate and urea on soil nitrogen during growth of wheat (Triticum aestivum L.) under field conditions

We studied the effects of ¹⁵N-labelled ammonium nitrate and urea on the yield and uptake of labelled and unlabelled N by wheat (Triticum aestivum L., cv. Mexi-Pak-65) in a field experiment. The dry matter and N yields were significantly increased with fertilizer N application compared to those from unfertilized soil. The wheat crop used 33.6–51.5 and 30.5–40.9% of the N from ammonium nitrate and urea, respectively. Splitting the fertilizer N application had a significant effect on the uptake of fertilizer N by the wheat. The fertilizer N uptake showed that ammonium nitrate was a more available source of N for wheat than urea. The effective use of fertilizer N (ratio of fertilizer N in grain to fertilizer N in whole plant) was statistically similar for the two N fertilizers. The application of fertilizer N increased the uptake of unlabelled soil N by wheat, a result attributed to a positive added N interaction, which varied according to the fertilizer N split; six split applications gave the highest added N interaction compared to a single application or two split applications for both fertilizers. Ammonium nitrate gave 90.5, 33.5, and 48.5% more added N interaction than urea with one, two, and six split N applications. A values were not significantly correlated with the added N interaction (r=0.557). The observed added N interaction may have been the result of pool substitution, whereby added labelled fertilizer N replaced unlabelled soil N.     

The effect of Azospirillum brasilense Sp7 and Azotobacter chroococcum on nitrogen balance in soil under cropping with oats (Avena sativa L.)

Summary Pot experiments with oats were carried out to study the effect of Azospirillum brasilense Sp 7 and Azotobacter chroococcum 94K on the yield of plants, the N content of soil and the ¹⁴N balance. The plants were grown on gray forest soil under irrigation with deionized water and application of ¹⁵N-labelled fertilizer at a rate of 4 mg N 100 g^-1 soil. Inoculation of plants with Azospirillum spp. and Azotobacter spp. failed to increase the plant yield. However, the increase in total N in the soil at the end of the experiment and the positive ¹⁴N balance in the soil-plant system due to increased nitrogenase activity in the rhizosphere were statistically significant. The amount of N accumulated in the soil was comparable with the rate of N applied as fertilizer.     

Interaction of 15N-labelled ammonium nitrate,urea and ammonium sulphate with soil N during growth of wheat (Triticum aestivum L.) under field conditions

The effects of ¹⁵N-labelled ammonium nitrate, urea and ammonium sulphate on yield and uptake of labelled and unlabelled N by wheat (Triticum aestivum L. cv. Mexi-Pak-65) were studied in a field experiment. The dry matter and N yields were significantly increased with fertilizer N application compared to those from unfertilized soil. The wheat crop used 64.0–74.8%, 61.5–64.7% and 61.7–63.4% of the N from ammonium nitrate, urea and ammonium sulphate, respectively. The fertilizer N uptake showed that ammonium nitrate was a more available source of N for wheat than urea and ammonium sulphate. The effective use of fertilizer N (ratio of fertilizer N in grain to fertilizer N in whole plant) was statistically similar for the three N fertilizers. The application of fertilizer N increased the uptake of unlabelled soil N by wheat, a result attributed to a positive added N interaction, which varied with the method of application of fertilizer N. Ammonium nitrate, urea and ammonium sulphate gave 59.3%, 42.8% and 26.3% more added N interaction, respectively, when applied by the broadcast/worked-in method than with band placement. A highly significant correlation between soil N and grain yield, dry matter and added N interaction showed that soil N was more important than fertilizer N in wheat production. A values were not significantly correlated with added N interaction (r=0.719). The observed added N interaction may have been the result of pool substitution, whereby added labelled fertilizer N stood proxy for unlabelled soil N.     

Kinetics of 15N-labelled nitrate uptake by maize (Zea mays L.) root segments

Abstract

Isotherms and kinetic constants of nitrate uptake by excised root segments from the apical root zone of 6-d-old maize seedlings pretreated with nitrate were investigated using ¹⁵N-labelled nitrate. The isotherms were resolved into two systems namely a multiphasic saturable system at substrate concentrations lower than 2 mol m^?-3 and a linear system at higher concentrations. The detailed analysis of the multiphasic saturable system suggested the existence of at least three phases, which followed the Michaelis-Menten kinetics. The I _max and K _m of each phase increase from the lower phase to the upper phase. The distance from the root tip and the presence of stele affected considerably the linear system but only slightly the saturable system.     

Shoot,root, soil and microbial nitrogen dynamics in two contrasting soils cropped to barley (Hordeum vulgare L.)

Summary Dynamics of barley N, mineral N, and organic N were compared at Ellerslie (Black Chernozem, Typic Cryoboroll) and Breton (Gray Luvisol, Typic Cryoboralf) in central Alberta, using ¹⁵N-urea. On average, shoot N and shoot ¹⁵N recoveries at Ellerslie (14.1 g m^–2, 36%) were greater than at Breton (4.5 g m^–2, 17%). Root N (g m^–2) did not significantly differ between sites (0–30 cm) but root ¹⁵N recovery was greater at Breton (3.4%) than Ellerslie (1.8%). Low levels of shoot N and shoot ¹⁵N at Breton were partly due to very wet soil conditions in July, which resulted in premature shoot senescence and low plant N uptake. Although the total ¹⁵N recoveries from the system (to 30 cm depth) at Ellerslie (63%) and Breton (56%) were similar, soil ¹⁵N was greater at Breton (35%) than at Ellerslie (26%). There were no differences in mineral N between sites but the average ¹⁵N recovery in the mineral-N pool was significantly greater at Ellerslie (3.3%) than at Breton (1.6%). There was no difference in ¹⁵N recovery in the microbial biomass (3%) between sites, although non-microbial organic ¹⁵N was greater at Breton (31 %) than at Ellerslie (20%). The two soils showed differences in the relative size of kinetically active N pools and in relative mineralization rates. Microbial N (0–30 cm) was greater at Ellerslie (13.3 g m^–2) than at Breton (9.9 g m^–2), but total microbial N made up a larger proportion of total soil N at Breton (1.6%) than at Ellerslie (0.9%). In the 0–10 cm interval, microbial N was 1.7-fold greater and non-microbial active N was 3-fold greater at Breton compared to Ellerslie, when expressed as a proportion of total soil N. Net N mineralization in a 10-day laboratory incubation was 1.4-fold greater in the Black Chernozem (0–10 cm interval) from Ellerslie, compared to the Gray Luvisol from Breton, when expressed per gram of soil. Net N mineralization in the soil from Breton was double that of the soil from Ellerslie, when expressed as a proportion of soil N. Although soil N (g m^–2) was 2.5-fold greater at Ellerslie compared to Breton, it was cycled more rapidly at Breton.     

Natural N abundances of inorganic nitrogen in soil treated with fertilizer and compost under changing soil moisture regimes

This study was conducted to examine whether the applications of N-inputs (compost and fertilizer) having different N isotopic compositions (δ¹⁵N) produce isotopically different inorganic-N and to investigate the effect of soil moisture regimes on the temporal variations in the δ¹⁵N of inorganic-N in soils. To do so, the temporal variations in the concentrations and the δ¹⁵N of NH₄⁺ and NO₃⁻ in soils treated with two levels (0 and 150 mg N kg⁻¹) of ammonium sulfate (δ¹⁵N=−2.3‰) and compost (+13.9‰) during a 10-week incubation were compared by changing soil moisture regime after 6 weeks either from saturated to unsaturated conditions or vice versa. Another incubation study using ¹⁵N-labeled ammonium sulfate (3.05 ¹⁵N atom%) was conducted to estimate the rates of nitrification and denitrification with a numerical model FLUAZ. The δ¹⁵N values of NH₄⁺ and NO₃⁻ were greatly affected by the availability of substrate for each of the nitrification and denitrification processes and the soil moisture status that affects the relative predominance between the two processes. Under saturated conditions for 6 weeks, the δ¹⁵N of NH₄⁺ in soils treated with fertilizer progressively increased from +2.9‰ at 0.5 week to +18.9‰ at 6 weeks due to nitrification. During the same period, NO₃⁻ concentrations were consistently low and the corresponding δ¹⁵N increased from +16.3 to +39.2‰ through denitrification. Under subsequent water-unsaturated conditions, the NO₃⁻ concentrations increased through nitrification, which resulted in the decrease in the δ¹⁵N of NO₃⁻. In soils, which were unsaturated for the first 6-weeks incubation, the δ¹⁵N of NH₄⁺ increased sharply at 0.5 week due to fast nitrification. On the other hand, the δ¹⁵N of NO₃⁻ showed the lowest value at 0.5 week due to incomplete nitrification, but after a subsequence increase, they remained stable while nitrification and denitrification were negligible between 1 and 6 weeks. Changing to saturated conditions after the initial 6-weeks incubation, however, increased the δ¹⁵N of NO₃⁻ progressively with a concurrent decrease in NO₃⁻ concentration through denitrification. The differences in δ¹⁵N of NO⁻₃ between compost and fertilizer treatments were consistent throughout the incubation period. The δ¹⁵N of NO₃⁻ increased with the addition of compost (range: +13.0 to +35.4‰), but decreased with the addition of fertilizer (−10.8 to +11.4‰), thus resulting in intermediate values in soils receiving both fertilizer and compost (−3.5 to +20.3‰). Therefore, such differences in δ¹⁵N of NO₃⁻ observed in this study suggest a possibility that the δ¹⁵N of upland-grown plants receiving compost would be higher than those treated with fertilizer because NO₃⁻ is the most abundant N for plant uptake in upland soils.     

Ammonium-excreting Azospirillum sp. become intracellularly established in maize (Zea mays) para-nodules

Maize seedlings develop nodule-like tumour knots (para-nodules) along primary roots when treated with the auxin 2,4-dichlor-phenoxy-acetic acid (2,4-D). Inoculated NH ₄ ⁺ -excreting Azospirillum brasilense cells were shown to colonize these tumours, mostly intracellularly, promoting a high level of N₂ fixation when microaerophilic conditions were imposed. The nitrogenase activity inside the para-nodules was less sensitive to free O₂ than in non-para-nodulating roots. Both light and electron microscopy showed a dense bacterial population inside intact tumour cells, with the major part of the cell infection along a central tumour tissue. The bacteria colonized the cytoplasm with a close attachment to inner cell membranes. In an auxin-free growth medium, young 2,4-D-induced para-nodules grew further to become mature differentiated root organs in which introduced bacteria survived with a stable population. These results provide evidence that gramineous plants are potentially able to create a symbiosis with diazotrophic bacteria in which the NH ₄ ⁺ -excreting symbiont will colonize para-nodule tissue intracellularly, thus becoming well protected.     

Grain yield response of Zea mays (hybrid AE 703) to Azotobacter chroococcum H23

Summary Field experiments were conducted during 1985 and 1986 to examine the effect of Azotobacter chroococcum on the grain yield of maize. Application of 40 kg N ha^–1 plus A. chroococcum caused a significant increase in maize yield. Azotobacter inoculation was more efficient at lower doses (40 kg N ha^–1) than at high doses (80 kg N ha^–1) of urea.     

Diversity of diazotroph populations in the rhizosphere of maize (Zea mays L.) growing on different French soils

Summary We studied the dominant diazotrophs associated with maize roots and rhizosphere soil originating from three different locations in France. An aseptically grown maize plantlet, the spermosphere model, was used to isolate N₂-fixing (acetylene-reducing) bacteria. Bacillus circulans was the dominant N₂-fixing bacterium in the rhizosphere of maize-growing soils from Ramonville and Trogny, but was not found in maize-growing sandy soil from Pissos. In the latter soil, Enterobacter cloacae, Klebsiella terrigena, and Pseudomonas sp. were the most abundant diazotrophs. Azospirillum sp., which has been frequently reported as an important diazotroph accociated with the maize rhizosphere, was not isolated from any of these soils. The strains were compared for their acetylene-reducing activity in the spermosphere model. The Bacillus circulans strains, which were more frequently isolated, also exhibited significantly greater acetylene-reducing activity (3100 nmol ethylene day^-1 plant^-1) than the Enterobacteriaceae strains (180 nmol ethylene day^-1 plant^-1). This work indicates for the first time that Bacillus circulans is an important maizerhizosphere-associated bacterium and a potential plant growth-promoting rhizobacterium.     

Effects of Selected Surfactants on Nutrient Uptake in Corn (Zea mays L.)

Surfactants in herbicide formulations eventually enter soil and may disrupt various processes. Research examined effects on nutrient uptake in corn caused by surfactants, herbicides, and surfactant-herbicide combinations applied to silt loam and silty clay loam soils in the greenhouse. Surfactants evaluated were Activator 90, Agri-Dex, and Thrust; herbicides were glyphosate, atrazine, and bentazon. Corn was planted in fertilized soils with moisture content maintained for optimum growth. Foliage (V8 growth stage) was collected for elemental analyses. Nutrient uptake differed with soil texture. Nutrient uptake from silty clay loam was more affected by surfactants and/or herbicides than in silt loam. Potassium uptake was significantly (P = 0.05) decreased in silt loam only by Thrust but uptake of phosphorus (P), potassium (K) calcium (Ca), sulfur (S), copper (Cu), and zinc (Zn) decreased by ≤30% in silty clay loam treated with surfactants. Surfactants and/or herbicides may interact with soil texture to affect nutrient uptake. Long-term field studies to validate changes in nutrient uptake and grain yields after annual applications of surfactants plus herbicides are needed.