Effect of inoculation with Azotobacter chroococcum on nitrogenase activity of Zea mays roots grown in agricultural soils under aseptic and non-sterile conditions

Summary Inoculated and non-inoculated seedlings of Zea mays were grown in agricultural soils under aseptic and non-sterile conditions. Acetylene reduction activity and microbial counts were determined after 7 and 30 days of growth. Irrespective of the soil type Azotobacter spp. were commonly isolated under maize cultivation. Inoculation of agricultural soils with a suspension of A. chroococcum led to an increase in Azotobacter numbers, although this effect diminished with time. Nitrogenase activity was detected on maize roots and increased in response to the inoculation with A. chroococcum, showing that this associative growth could be of primary importance for the plant. The results of assays for acetylene reduction activity indicated that the nitrogenase activity was associated only with the root systems.     

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.     

Effect of nitrogen on the yield response of Pennisetum americanum,Triticum aestivum and Zea mays to inoculation with Azospirillum brasilense under temperate conditions

Summary A nitrate-respiring strain, a denitrifying strain, and a non-nitrogen-fixing strain of Azospirillum brasilense were compared for their effect on the growth of pearl millet (Pennisetum americanum), wheat (Triticum aestivum) and maize (Zea mays) under temperate conditions in nitrogen-limited pot cultures. Increases in yield of Z. mays shoots occurred with all three strains when inoculation coincided with the addition of low levels of combined nitrogen. The inoculation of A. brasilense did not show any effect on the yield of P. americanum and T. aestivum. Increased numbers of A. brasilense became associated with Z. mays roots following the addition of low levels of combined nitrogen. Low and very variable rates of acetylene reduction activity were observed from excised roots of inoculated Z. mays plants without preincubation. Results indicate that inoculation of cereals with A. brasilense under temperate conditions has only a limited effect on plant growth.     

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.     

Response of maize (Zea mays) to Azotobacter inoculation under fertilized and unfertilized conditions

Summary Inoculated seeds of maize (Zea mays) with 11 Azotobacter strains, sown in the fields receiving no fertilizer and fertilizers (N and P at the rate of 125 and 40 kg ha^–1 respectively) increased the grain yield by 19.63% and 15.89% respectively over the corresponding control. The effect was greater in unfertilized than in fertilized soil. The increase in yield due to fertilizers was 21.2% without inoculation and 37.09% with inoculation. The correlations between total yield, and N, P and K uptake were highly significant and comparable among themselves. This indicated that increase in yield due to inoculation was not due to N₂ fixation but that some other mechanisms like production of growth hormones by this bacterium may be responsible.     

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     

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。     

Growth and nitrogen nutrition of maize (Zea mays L.) in soil treated with the nitrification-inhibiting insecticide Baythroid

A pot experiment was conducted to compare the uptake and dry matter production potential of NH _inf4 ^sup+ and NO _inf3 ^sup- and to study the effect of Baythroid, a contact poison for several insect pests of agricultural crops, on growth and N uptake of maize (Zea mays L.). Nitrogen was applied as (¹⁵NH₄)₂SO₄, K¹⁵NO₃, or ¹⁵NH₄NO₃ and in one treatment Baythroid was combined with ¹⁵NH₄NO₃. Source of N had, in general, a nonsignificant effect on dry matter and N yield, but uptake of NO _inf3 ^sup- was significantly higher than that of NH _inf4 ^sup+ when both N sources were applied together. Substantial loss of N occurred from both the sources, with NH _inf4 ^sup+ showing greater losses. Baythroid was found to have a significant positive effect on dry matter yield of both root and shoot; N yield also increased significantly. Uptake of N from both the applied and native sources increased significantly in the presence of Baythroid and a substantial added nitrogen interaction (ANI) was determined. The positive effect of Baythroid was attributed to: (1) a prolonged availability of NH _inf4 ^sup+ due to inhibition of nitrification, (2) an increased availability of native soil N through enhanced mineralization, and (3) an enhanced root proliferation.     

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.     

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.     

Characterization of a flint maize (Zea mays var. indurata) Italian landrace, II. Genetic diversity and relatedness assessed by SSR and Inter-SSR molecular markers

A comparative characterization of 10 field populations of the maize (Zea mays var. indurata) landrace Nostrano di Storo was carried out using different types of PCR-based markers. The inbred line B73 and three synthetics (VA143, VA154 and VA157) selected from as many landraces were also used. Genetic diversity and relatedness were evaluated over 84 SSR and 53 I-SSR marker alleles using a total of 253 individual DNAs. Up to 23 alleles per SSR locus were scored while the average effective number of alleles per population was 6.99. Nei's total genetic diversity as assessed with SSR markers was H_T = 0.851 while the average diversity within populations was H_S = 0.795. The overall Wright's fixation index F_ST was as low as 0.066. Thus, more than 93% of the total variation was within population. Unique alleles over all SSR loci were found for six populations. An average of 17.7 marker alleles per I-SSR primer were scored with an effective number of marker alleles per locus of 1.34. The Shannon's diversity information index over all populations and I-SSR loci was 0.332, varying from 0.286 to 0.391. The extent of differentiation between populations was as low as G_ST = 0.091. Dice's genetic similarity matrices were estimated for both SSR and I-SSR markers. The mean genetic similarity coefficients within and between populations were respectively 0.269 and 0.217, for SSR markers, and 0.591 and 0.564, for I-SSR markers. UPGMA dendrograms displayed all field populations but one clustered into a distinct group, in which the synthetic VA154, selected from the Marano Vicentino landrace, was also included. One field population and the other two synthetics were clustered separately as well B73. The matrix correlation assayed by the Mantel's correspondence test was as high as 0.908. Findings suggest that, although a high variability can be found among plants, most plant genotypes belong to the same landrace called Nostrano di Storo. Although gene flow from commercial hybrids might have occurred, the large number of polymorphisms and the presence of both unique alleles and alleles unshared with B73 and synthetics are the main factors underlying the value of this flint maize landrace as a source of genetic variation and peculiar germplasm traits. Because of its exclusive utilization for human consumption, such a molecular marker characterization will be a key step for obtaining the IGP mark and so promote the in situ conservation and protection of the landrace Nostrano di Storo.     

Salt tolerance in <Emphasis Type="Italic">Zea mays</Emphasis> (L). following inoculation with <Emphasis Type="Italic">Rhizobium</Emphasis> and <Emphasis Type="Italic">Pseudomonas</Emphasis>

This study aimed to investigate the effect of inoculation with plant growth-promoting Rhizobium and Pseudomonas species on NaCl-affected maize. Two cultivars of maize (cv. Agaiti 2002 and cv. Av 4001) selected on the basis of their yield potential were grown in pots outdoors under natural conditions during July. Microorganisms were applied at seedling stage and salt stress was induced 21 days after sowing and maintained up to 50% flowering after 120 days of stress. The salt treatment caused a detrimental effect on growth and development of plants. Co-inoculation resulted in some positive adaptative responses of maize plants under salinity. The salt tolerance from inoculation was generally mediated by decreases in electrolyte leakage and in osmotic potential, an increase in osmoregulant (proline) production, maintenance of relative water content of leaves, and selective uptake of K ions. Generally, the microbial strain acted synergistically. However, under unstressed conditions, Rhizobium was more effective than Pseudomonas but under salt stress the favorable effect was observed even if some exceptions were also observed. The maize cv. Agaiti 2002 appeared to be more responsive to inoculation and was relatively less tolerant to salt compared to that of cv. Av 4001.     

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.     

Effect of seed inoculation with the rhizopseudomonad strain 7NSK2 on the root microbiota of maize (Zea mays) and barley (Hordeum vulgare)

Summary The addition of sugars or amino acids to the soil gave rise to the development of different groups of microorganisms. The increase in the number of different groups of microorganisms in the soil had an influence on the microbiota in the rhizoplane and endorhizosphere of maize and barley grown in that soil. Furthermore, growth of maize and barley decreased with increasing microbial activity and density in soil. This effect could be counteracted effectively by the rhizopseudomonad strain 7NSK2. The beneficial effect of the strain 7NSK2 correlated inversely with the microbial activity, as measured by soil respiration, in the bulk-pretreated soil.The effect of seed inoculation with the rhizopseudomonad strain 7NSK2 on the root microbiota of maize and barley was evaluated. The strain 7NSK2 was capable of colonizing the rhizoplane and endorhizosphere of the maize cultivar Beaupré and barley cultivar Than very effectively and of considerably altering their composition. The number of total bacteria, fungi, pseudomonads and coliform bacteria in the rhizoplane and endorhizosphere of both plants was strongly reduced by inoculating the seeds with the strain 7NSK2.     

Corn response to potassium placement in conservation tillage

Improvements in the yield potential of corn (Zea mays L.) grown using conservation-tillage may depend, in part, on K fertility management. Field research was conducted in 1997 and 1998 on a field which had been in continuous no-tillage (NT) for the previous 12 years near Paris, Ont., Canada to evaluate potassium (KCl) placement effects on corn growth and yields in NT, spring zone-tillage (ZT) and spring mulch-tillage (MT) systems. Soils were classified as moderately well drained and had low soil-test K levels. Potassium was spring-applied (1 day prior to corn planting) at either 0 or 100 kg K ha⁻¹. Potassium was either broadcast applied, deep in-row banded (15 cm deep), or half broadcast applied and half shallow-banded (5 cm beside the row, 5 cm below seeding depth). Early season and mid-season corn ear-leaf K concentrations indicated that spring-applied K fertilizer was available for uptake by corn in conservation-tillage systems. Potassium application sometimes significantly increased corn yields compared to the zero K control in the NT and ZT systems. However, MT corn yields did not show any response to K fertilization in either season despite the low soil-test K levels. There were no significant corn yield increases with deep banding of K fertilizer relative to shallow placement in any tillage system. This study suggests that, for similar low-testing K soils, alternate K placements will have greater impacts on corn plant nutritional status than on final yields. Surface broadcasting of K fertilizer is appropriate for continuous NT corn despite evident K stratification present after long-term NT. MT may improve corn K nutrition after long-term NT.     

半干旱区模拟降雨下沟垄集雨种植对夏玉米生产影响

在人工模拟降雨条件下研究了不同降雨量沟垄集雨种植对夏玉米(Zea Mays L.)个体发育、生物量积累及产量的影响。结果表明，沟垄集雨种植处理后，夏玉米生育期提前，株高和叶面积显著增加(p<0.05)，在230、340和440 mm降雨量下玉米总生物量比平作分别提高44.71％、28.51％和7.58％；230 mm和340 mm降雨量下，单株籽粒产量比平作分别提高了75.40％和36.70％，穗长分别增加了25.30％和16.00％，穗粒数分别增加了59.30％和29.20％，230 mm降雨量下，玉米穗粗和千粒重比平作分别增加了11.40％和10.30％；440 mm降雨量下籽粒产量与平作相比差异不明显。     

Collecting maize (<Emphasis Type="Italic">Zea mays</Emphasis> L. convar. <Emphasis Type="Italic">mays</Emphasis>) with potential technological ability for bread making in Portugal

The Portuguese maize bread (“broa”) manufactured from traditional maize landraces still plays an important economic and social role on Central and Northern rural communities of the country. However the traditional maize landraces agricultural systems are changing. Local maize landraces are in risk of disappearing because of the progressive adoption of hybrid varieties not suitable for bread production. These changes are contributing to a major loss of genetic diversity. An expedition took place in the Central region of Portugal (Beira Interior and Beira Litoral) with the purpose of collecting enduring maize landraces with technological ability for bread production and to access the possibility of establishing a participatory plant breeding and conservation program. A total of 51 different maize landraces and 175 other varieties of associated crops were collected. Maize landraces showed to maintain high diversity and potential for improvement. The production relayed on small farms with polycrop, quality oriented, sustainable systems. A participatory plant breeding and conservation program would be possible on this region with the proviso that local authorities would be involved. This program would allow a higher valuation of these maize populations, contributing to halt the current loss of these unique Portuguese maize landraces.     

Nitrogen contribution by leucaena (Leucaena leucocephala) prunings to maize in an alley cropping system

Summary The N uptake of maize was assessed on an Alfisol in a sole crop and in an alley cropping system in southwestern Nigeria. Although the application of prunings increased the maize N content in both sole and alley-cropped maize, the N contributed to the maize by the prunings was low, ranging between 4.4 and 23.8 kg ha^–1. This was equivalent to 3.2% and 9.407% of the N released during decomposition of the prunings. Application of the prunings increased the grain yields of the sole maize by 38% and the maize yield in the alley-cropped plots by 104%, compared with yields in the corresponding plots where prunings were not applied. The results indicate that part of the N from the prunings was retained in the soil organic-N pool. Maize N, dry weights and grain yields were lowest in the alley-cropped plots where prunings were removed, probably because of competition between the maize and the hedgerow trees.