Alfalfa,Medicago sativa L., in highly weathered,acid soils

Summary The effect of lime and P application on yield (top and root weigh), nodulation, intervally collected acetylene reduction (N₂-fixation), and N and Al uptake of young alfalfa (46 days growth) were investigated in greenhouse pots containing acid Bladen or Bradson topsoils. The effect on seed germination and seedling persistence under these greenhouse conditions was also recorded.Alfalfa yield and acetylene reduction increased with lime and P additions in both soils, but, predominately, with P. There was no advantage of increasing these two parameters with liming past pH 6.0 provided P was adequate. Positive relationships (R²) existed between yield and acetylene reduction, and with both factors and root weight, nodule weight, and N uptake. Increased uptake of Al by alfalfa seedlings depressed yield, but data indicate P may block Al uptake at high soil pH. There were no treatment effects on seed germination, but P application increased plant persistence in the Bladen soil.     

Plant Seeds as Mineral Nutrient Resource for Seedlings--A Comparison of Plants from Calcareous and Silicate Soils

Mineral nutrients of seeds constitute a significant source ofessential elements to seedlings and developing individuals ofvascular plants. In spite of their potential ecological significance,seed nutrient pools have attracted little attention with respectto calcifuge–calcicole behaviour of plants. The objectivesof this study were, therefore, to compare concentrations of13 macro- and micronutrients (K, Rb, Mg, Ca, Mn, Fe, Co, Cu,Zn, Mo, B, P and S) in seeds and leaves of 35 mainly herbaceousvascular plant species growing on both limestone (calcareous)and silicate (non-calcareous) soils. Concentrations of Rb andCo in seeds of plants originating from limestone soils were,on average, about half of those from silicate soils. Concentrationsof Mn, Mg, Zn and P of seeds were, or tended to be, lower orslightly lower in limestone-soil plants, whereas mean Ca andMo concentrations were higher. Comparing seed and leaf concentrationsof the same species from limestone and silicate soils generallydemonstrated a high P enrichment ratio, but a particularly lowK enrichment ratio in seeds, valid for both types of soil. Itwas also apparent that Fe and Mn, micronutrients which are lessreadily solubilized and taken up by plants on limestone soils,had significantly higher seed:leaf concentration ratios in plantsfrom limestone than from silicate soils, whereas the oppositewas true for Ca. This indicates a ‘strategy’ tosatisfy the demand of seedlings for elements which are lessreadily available in the soil.Copyright 1998 Annals of BotanyCompany Seed, leaf, plant, nutrient, content, calcareous, silicate, acid, soil.     

Response of Citrus Seedlings to Radopholus similis in Two Soils

Radopholus similis was less pathogenic to greenhouse-grown citrus seedlings in Leon loamy sand than in Lakeland fine sand. This was not affected by different watering regimes. Seedling growth reduction by the burrowing nematode in either soil, compared with noninfected controls, was significant at the 1% level.     

Acquisition of Cu, Zn, Mn and Fe by mycorrhizal maize (Zea mays L.) grown in soil at different P and micronutrient levels

Sustainability of soil-plant systems requires, among other things, good development and function of mycorrhizal symbioses. The effects of P and micronutrient levels on development of an arbuscular mycorrhizal fungus (AMF) and uptake of Zn, Cu, Mn and Fe by maize (Zea mays L.) were studied. A pot experiment with maize either inoculated or not with Glomus intraradices was conducted in a sand:soil (3 :1) mix (pH 6.5) in a greenhouse. Our goal was to evaluate the contribution of mycorrhizae to uptake of Cu, Zn, Mn and Fe by maize as influenced by soil P and micronutrient levels. Two levels of P (10 and 40 mg kg⁻¹ soil) and three levels of a micronutrient mixture: 0, 1X and 2X (1X contained, in mg kg⁻¹ soil, 4.2 Fe, 1.2 Mn, 0.24 Zn, 0.06 Cu, 0.78 B and 0.036 Mo), were applied to pots. There were more extraradical hyphae at the low P level than at the high P level when no micronutrients were added to the soil. Root inoculation with mycorrhiza and application of micronutrients increased shoot biomass. Total Zn content in shoots was higher in mycorrhizal than non-mycorrhizal plants grown in soils with low P and low or no micronutrient addition. Total Cu content in shoots was increased by mycorrhizal colonization when no micronutrients were added. Mycorrhizal plants had lower Mn contents than non-mycorrhizal plants only at the highest soil micronutrient level. AMF increased total shoot Fe content when no micronutrients were added, but decreased shoot Fe when plants were grown at the high level of micronutrient addition. The effects of G. intraradices on Zn, Cu, Mn, and Fe uptake varied with micronutrient and P levels added to soil. Accepted: 27 December 1999     

The effect of regeneration burns on the growth,nutrient acquisition and mycorrhizae of Eucalyptus regnans F. Muell. (mountain ash) seedlings

This study was conducted to compare the effects on the growth of Eucalyptus regnans seedlings of unheated soil and soil heated to different extents (as indicated by soil colour–bright red or black) in burnt logging coupes, and to separate the effects of heating of the soil on direct nutrient availability and on morphotypes and effectiveness of ectomycorrhizae. Burnt soils were collected from three logging coupes burnt 2, 14 and 25 months previously and unbumt soil from adjacent regrowth forests. Compared to unburnt soil, the early seedling growth was stimulated in black burnt soil from all coupes (burnt 2, 14 and 25 months previously). Seedling growth was generally poor in red burnt soil, especially in soil collected 2 months after burning. However, the concentration of extractable P was extremely high in red burnt soil, especially in soil collected 2 months after burning. In black burnt soil, extractable P was increased in soil 2 months after burning, but not in the soils collected 14 or 25 months after burning. However, both total P content and concentration in seedlings were increased in all collections of black burnt soil. Frequency of ectomycorrhizae was high in seedlings grown in all black burnt soils, but the mycorrhizal mantles were poorly developed in seedlings in black burnt soil collected 2 months after burning. Seedlings were also ectomycorrhizal in red burnt soil, except in soil collected 2 months after burning. Fine root inocula from seedlings grown in black burnt soils collected 14 and 25 months after burning significantly stimulated both seedling growth and P uptake compared with the uninoculated control, whereas the fine root inocula from the seedlings grown in all the other soils did not. These results suggest that, in black burnt soil, both direct nutritional changes and changes in the ectomycorrhizae may contribute to seedling growth promotion after regeneration burns. The generally poor seedling growth in red burnt soils is likely to have been due to N deficiency as the seedlings in these soils were yellow-green and the tissue concentrations of N were significantly lower than in other treatments. This revised version was published online in June 2006 with corrections to the Cover Date.     

The productivity of pine plantations in relation to previous land use

Summary Differences in the productivity of establishedP. radiata plantations on pasture and forest soils were found to be reproducible withP. radiata seedlings in a glasshouse environment. The growth of seedlings on pasture soil exceeded that of seedlings on native forest soil (the ‘primary pasture effect’). After a history of pine on both native and pasture soils a residual effect of pasture on seedling growth was evident (the ‘secondary pasture effect’). However, the effect of a history of pine plantation (the ‘pine effect’) was to decrease the productivity of both native and pasture soil as assessed by seedling growth. These effects were not related to changes due to land management in mycorrhizal infection or in soil structure. The analysis of seedling growth leads to the conclusion that soil fertility, particularly the availability of nitrogen and phosphorus, has changed.     

Amelioration of acid soil infertility by phosphogypsum

Amelioration of subsoil acidity requires an increase in Ca status along with a decrease in Al status in subsoil. In this study, effects of phosphogypsum (PG) on the amelioration of subsoil acidity have been evaluated, using cultivated and woodland subsoils representing Cecil, Wedowee (both Typic Hapludult) and Bladen (Typic Albaquult) series. Subsoil (0.6–0.8 m) samples were collected and treated with either PG (approximately 2 Mg ha^-1 rate), Ca(NO₃)₂ or Mg(NO₃)₂ along with an unamended control treatment. A fertile topsoil amended with NH₄NO₃ was placed on top of all treated subsoil. Top and root growth of alfalfa [Medicago sativa (L.) cv. Hunter River] and soybean [Glycine max (L.) Merr. cv. Lee] were significantly greater in PG-amended than in unamended pots of the Cecil and Wedowee soils, although most growth was observed with the Ca(NO₃)₂-amended treatment. In the Bladen soil, however, none of the amendments evoked a significant growth response in either alfalfa or soybean. The concentration of Ca in the displaced soil solution (in soils with no plants) as well as tissue levels of Ca suggest that the growth response was partly due to an improved Ca availability in both PG or Ca(NO₃)₂-treated soils. Exchangeable Al decreased in PG-amended soils. The self-liming effect of PG, which is a release of OH^- due to ligand exchange between SO₄ ^2- and OH^-, as well as a decrease in exchangeable Al in PG-amended soil is greater in predominantly kaolinitic Cecil and Wedowee soils than in smectitic Bladen soil. As a result, significant growth response to PG amendment was observed in the Cecil and Wedowee soils, but not in the Bladen soil.     

Effects of Nitrogen and Phosphorus on the Growth of Microorganisms Associated with Apple Replant Disease and on Apple Seedlings Grown in Soil Infested with these Microorganisms*

The growth of fungi causing apple replant disease (ARD) was inhibited by the addition of N and P to the growing medium. The population of bacteria antagonistic to ARD-causing fungi was significantly increased in the growing medium supplemented with N 400 P 400 mg/l or greater. The application of nitrogen alone or in combination with phosphorus to soil infested with fungi or bacteria that cause apple replant disease significantly increased seedling height. The addition of P alone to these infested soils did not have any effect on seedling height. Significant increases in seedling height occurred with N applications when seedlings were grown in soil to which bacteria that are antagonistic to fungi causing ARD had been added. These results suggest that the application of N, with or without P, to apple replant soils may suppress the growth of ARD-causing fungi or bacteria and promote the growth of antagonistic bacteria.     

Organic N and particulate organic matter fractions in organic and conventional farming systems with a history of manure application

Indicators of soil fertility are needed for the effective management of organic farming systems. Sustainable management hinges upon our gaining an improved understanding of C and N dynamics. The influence of cropping systems and amendments applied in the Lakeland Wisconsin Integrated Cropping Systems Trial on total hydrolyzable organic N (THN) fractions and particulate organic matter (POM) was investigated after a decade in a conventional cash grain system (Conv) of continuous maize amended with inorganic fertilizer, an organic cash-grain system (Org-CG) that relied on legume N, and an organic animal-based system (Org-AN) that included alfalfa and manure additions. Maize yields had consistently ranked Org-CG < Conv < Org-AN. The THN and amino acid-N (AA-N) contents were ranked Org-AN > Org-CG > Conv. Amino sugar-N (AS-N) contents, which reflect microbially derived N, did not differ among systems and concentrations were quite high (346.5 mg AS-N/kg soil in the 0–50 cm depth). This, and soil variability were attributed to the sites’ history of manure application. The amount (1.3 g POM-C/kg soil) and proportion (≈7.5% of total SOC) of POM-C were quite low and did not differ among systems. Failure to accumulate SOC or POM in these soils, even under organic management, is attributed to rapid C decay and/or limited root growth. An N rate study was added the fall before samples were taken and N addition did increase yield in the Conv and Org-CG systems despite evidence of soil N surplus. This suggests that either amino N is unavailable to plants or that root N acquisition is limited by other constraints. Low POM-C contents accompanied by high AS-N and AA-N levels reveal an imbalance in these soils which are likely to be C limited. Based on this, we conclude excess N has prevented use of organic practices from enhancing soil quality at this site.     

Effects of labile soil carbon on nutrient partitioning between an arctic graminoid and microbes

We measured partitioning of N and P uptake between soil microorganisms and potted Festuca vivipara in soil from a subarctic heath in response to factorial addition of three levels of labile carbon (glucose) combined with two levels of inorganic N and P. The glucose was added to either non-sterilized or sterilized (autoclaved) soils in quantities which were within the range of reported, naturally occurring amounts of C released periodically from the plant canopy. The aims were, firstly, to examine whether the glucose stimulated microbial nutrient uptake to the extent of reducing plant nutrient uptake. This is expected in nutrient-deficient soils if microbes and plants compete for the same nutrients. Secondly, we wanted to test our earlier␣interpretation that growth reduction observed in graminoids after addition of leaf extracts could be caused directly by labile carbon addition, rather than by phytotoxins in the extracts. Addition of high amounts of N did not affect the microbial N pool, whereas high amounts of added P significantly increased the microbial P pool, indicating a luxury P uptake in the microbes. Both plant N and in particular P uptake increased strongly in response to soil sterilization and to addition of extra N or P. The increased␣uptake led to enhanced plant growth when both elements were applied in high amounts, but only led to increased tissue concentrations without growth responses when the nutrients were added separately. Glucose had strong and contrasting effects on plant and microbial N and P uptake. Microbial N and P uptake increased, soil inorganic N and P concentrations were reduced and plant N and P uptake declined when glucose was added. The responses were dose-dependent within the range of 0–450 μg C g⁻¹ soil added to the non-sterilized soil. The opposite responses of plants and microbes showed that plant acquisition of limiting nutrients is dependent on release of nutrients from the soil microbes, which is under strong regulation by the availability and microbial uptake of labile C. Hence, we conclude, firstly, that the microbial populations can compete efficiently with plants for nutrients to an extent of affecting plant growth when the microbial access to labile carbon is high in nutrient deficient soils. We also conclude that reduced growth of plants after addition of leaf extracts to soil can be caused by carbon-induced shifts in nutrient partitioning between plants and microbes, and not necessarily by phytotoxins added with the extracts as suggested by some experiments. Received: 15 February 1997 / Accepted: 12 July 1997     

氮磷添加与不同栽植密度交互对樟树幼苗土壤化学性质的短期影响

研究氮磷添加对不同密度樟树(Cinnamomum camphora)幼苗土壤化学性质的影响,以期为全球化背景下樟树人工林生态系统的土壤养分管理提供依据。以1年生樟树幼苗为试验材料,选择氯化铵(NH4Cl)作为氮肥模拟大气氮沉降,以二水合磷酸二氢钠(NaH_2PO_4·2H_2O)模拟磷添加。氮磷处理设置CK、施N、施P和施N+P 4个水平,其中N、P和N+P施肥量分别为40 g m~(-2)a~(-1)(NH_4Cl)、20 g m-2a-1(NaH_2PO_4·2H_2O)和40g m~(-2)a~(-1)(NH_4Cl)+20 g m~(-2)a~(-1)(NaH_2PO_4·2H_2O)。种植密度设置4个水平:10、20、40和80株/m~2,试验时间为2017年6月至9月。研究结果表明,在各密度幼苗土壤中,N和N+P处理引起pH值的显著下降,N、P和N+P处理的土壤有机质和碱解N含量的变化规律不明显,P处理的幼苗土壤全P含量上升,P和N+P处理的土壤有效P含量增加,N+P处理的土壤全K含量以及N、P和N+P处理的土壤速效K含量均下降。在10、20和40株/m~2幼苗的土壤中,P处理的土壤全N含量高于N和N+P处理的,而80株/m~2幼苗的土壤全N含量低于其他密度幼苗。随着种植密度的增加,各施肥处理的土壤pH、全P、有效P、全K和速效K含量均呈现上升趋势,而施N和施P处理的土壤有机质呈现下降趋势,各施肥处理的土壤碱解N含量变化规律不明显。施肥和密度处理对樟树幼苗土壤有机质、碱解氮和速效钾含量有显著的交互作用。     

Distribution of ectomycorrhizal and pathogenic fungi in soil along a vegetational change from Japanese black pine (Pinus thunbergii) to black locust (Robinia pseudoacacia)

The nitrogen-fixing tree black locust (Robinia pseudoacacia L.) seems to affect ectomycorrhizal (ECM) colonization and disease severity of Japanese black pine (Pinus thunbergii Parl.) seedlings. We examined the effect of black locust on the distribution of ECM and pathogenic fungi in soil. DNA was extracted from soil at depths of 0–5 and 5–10 cm, collected from the border between a Japanese black pine- and a black locust-dominated forest, and the distribution of these fungi was investigated by denaturing gradient gel electrophoresis. The effect of soil nutrition and pH on fungal distribution was also examined. Tomentella sp. 1 and Tomentella sp. 2 were not detected from some subplots in the Japanese black pine-dominated forest. Ectomycorrhizas formed by Tomentella spp. were dominant in black locust-dominated subplots and very little in the Japanese black pine-dominated forest. Therefore, the distribution may be influenced by the distribution of inoculum potential, although we could not detect significant relationships between the distribution of Tomentella spp. on pine seedlings and in soils. The other ECM fungi were detected in soils in subplots where the ECM fungi was not detected on pine seedlings, and there was no significant correlation between the distribution of the ECM fungi on pine seedlings and in soils. Therefore, inoculum potential seemed to not always influence the ECM community on roots. The distribution of Lactarius quieticolor and Tomentella sp. 2 in soil at a depth of 0–5 cm positively correlated with soil phosphate (soil P) and that of Tomentella sp. 2 also positively correlated with soil nitrogen (soil N). These results suggest the possibility that the distribution of inoculum potential of the ECM fungi was affected by soil N and soil P. Although the mortality of the pine seedlings was higher in the black locust-dominated area than in the Japanese black pine-dominated area, a pathogenic fungus of pine seedlings, Cylindrocladium pacificum, was detected in soil at depths of 0–5 and 5–10 cm from both these areas. This indicates that the disease severity of pine seedlings in this study was influenced by environmental conditions rather than the distribution of inoculum potential.     

Reduced risk for positive soil-feedback on seedling regeneration by invasive trees on a very nutrient-poor soil in Seychelles

Invasive plants sometimes alter habitat conditions so as to promote further invasion, either by the same or by other non-native species. Such positive feedbacks often occur because the non-native species increases soil fertility, thereby favouring recruitment of non-native seedlings. This has been demonstrated in nitrogen-poor habitats invaded by nitrogen-fixing species, but it is unclear whether similar processes operate in habitats limited by phosphorus and other nutrients. I compared the growth of seedlings of Cinnamomum verum, an abundant invasive tree on phosphorus-poor soils in the Seychelles, in soils taken from beneath different tree species. I expected that soil phosphorus availability would be higher beneath stands of C. verum than beneath stands of either the native Northea hornei or the non-native nitrogen-fixing species, Falcataria moluccana. I therefore predicted that C. verum seedlings would grow faster in soil taken from beneath C. verum trees than in soil taken from beneath either of the other two species. To test this hypothesis, I performed a bioassay experiment with seedlings of C. verum grown in soils from stands of C. verum, F. moluccana and N. hornei. Different nutrient treatments (control, plus phosphorus (P), plus nitrogen (N), plus N and P, and plus complete fertilizer) were applied to investigate how nutrient availabilities modulate the effects of the trees. In the control treatment without added nutrients, there was a weak tendency for seedlings to perform better in the soils from beneath invasive than native trees. However, seedling growth in soils from beneath invasive species was markedly higher following the addition of phosphorus in the case of the F. moluccana soil, and complete fertilizer in the case of the C. verum soil. These results indicate that on very nutrient-poor soils, a low supply of nutrients other than N may reduce the risk of a soil-feedback by invasive trees on seedling regeneration.     

Belowground responses of <Emphasis Type="Italic">Picea asperata</Emphasis> seedlings to warming and nitrogen fertilization in the eastern Tibetan Plateau

The impacts of global climatic change on belowground ecological processes of terrestrial ecosystems are still not clear. We therefore conducted an experiment in the subalpine coniferous forest ecosystem of the eastern edges of the Tibetan Plateau to study roots of Picea asperata seedlings and rhizosphere soil responses to soil warming and nitrogen availability from April 2007 to December 2008. The seedlings were subjected to two levels of temperature (ambient; infrared heater warming) and two nitrogen levels (0 or 25 g m⁻²year⁻¹ N). We used a free air temperature increase from an overhead infrared heater to raise both air and soil temperature by 2.1 and 2.6°C, respectively. The results showed that warming alone significantly increased total biomass, coarse root biomass and fine root biomass of P. asperata seedlings. Both total biomass and fine root biomass were increased, but coarse root biomass was significantly decreased by nitrogen fertilization and warming combined with nitrogen fertilization. Warming induced a prominent increase in soil organic carbon (SOC) and NO₃ ⁻-N of rhizosphere soil, while nitrogen fertilization significantly decreased SOC and NH₄ ⁺-N of rhizosphere soil. The warming, fertilization and warming × N fertilization interaction decreased soil microbial C significantly, but substantially increased soil microbial N. These results suggest that nitrogen deposition combined with warmer temperatures under future climatic change possibly will have no effect on fine root production of P. asperata seedlings, but could enhance the nitrification process of their rhizosphere soils in subalpine coniferous forests.     

The productivity of pine plantations in relation to previous land use

Summary The improved growth of pine plantations on pasture soils compared with that on soils which previously supported native eucalypt forest is primarily explained in terms of soil phosphorus. Pasture development has resulted in a decrease in the P adsorption maximum of about 300 g g^–1 soil, a figure which agrees with the increase in total P due to the application of superphosphate. P adsorption isotherms were used to calculate additions of P to give comparable levels of soil solution P in eucalypt and pasture soils. The growth of pine seedlings in soils thus amended showed a strong N×P interaction. When P was non-limiting, addition of N raised productivity of the eucalypt soil above that of the pasture soil. It is postulated that the different nature of the N×P interaction in eucalypt and pasture soils results from differences in the nitrogen cycle in the two soils.     

北亚热带森林土壤有效微量元素状况研究

研究了北亚热带25a生栓皮栎林,杉木林,火炬松林,毛竹林和5年生2代杉木萌芽林土壤中B,Mo,Cu,Zn,Fe,Mn的有效含量,在土壤剖面中的分布规律,影响其有效性的土壤因子以及不同林分对土壤微量养分含量的影响。结果表明,在该地区的森林土壤中,有效B,Mo,Cu的平均含量均低于各自临界值,有效Zn平均含量接近临界值,Fe,Mn含量丰富;有效微量养分在土壤剖面中的分布园林分和元素种类而异影响微量元素有效性的主要土壤因子为有机质和有效磷含量;不同林分对土壤有效微量元素含量有显著影响,栓皮栎林土壤中有效微量养分含量最高,2代杉木萌芽林最低,其余林分居中且基本接近。     

Soil acidity and nutrient deficiency in central Amazonian heath forest soils

Experiments were carried out to test the effects of liming and nutrient additions on plant growth and soil processes such as C and N mineralisation in three contrasting forest types in central Amazonia: the stunted facies of heath forest (SHF), the tall facies of heath forest (THF) and the surrounding lowland evergreen rain forest (LERF). Calcium-carbonate additions increased soil respiration in the field plots in the SHF; in laboratory incubations, soil respiration was higher in the SHF when soils were fertilised with N, and in THF and LERF after S additions. The addition of N alone or in different combinations generally induced a net immobilisation of soil N. Net nitrification increased during the incubation in SHF and THF soils fertilised with N+P, and in LERF soils fertilised with either N, or P, or CaCO₃. In a field experiment using ingrowth bags, a higher fine root production was observed in all forest types when bags were fertilised with CaCl₂ or CaCO₃, suggesting that Ca may be a limiting nutrient in these soils. Calcium-carbonate addition in a glasshouse bioassay experiment with rice showed an overall positive effect on the survival and growth of the seedlings. In other treatments where soil pH was not raised, the rice showed acute toxicity symptoms, poor root and shoot growth and high mortality. Similar results were yielded in a field experiment, using naturally established seedlings in the field plots in SHF, THF and LERF. It is concluded that the acute H⁺ ion toxicity is a major growth-limiting factor for non-adapted plants in heath forest soils in central Amazonia.     

镁肥对马尾松幼苗生长与叶片元素积累的影响

为了探讨上杭种源马尾松Pinus massoniana叶营养与生长对不同镁肥水平的响应,以其优良种源1年生苗为材料,设置4个镁肥梯度(42 g·m-2、85 g·m-2、170 g·m-2、339 g·m-2),测定移栽1年后苗木生长指标及叶内营养含量。结果表明,施镁能够促进元素P、K、Ca、Fe、Cu、Zn积累,抑制N、Mg、Mn积累;镁施肥量为85 g·m-2时,对N、Mg、Mn积累的抑制作用不显著,对P、K、Ca、Fe、Cu、Zn积累的促进作用最大,苗木生长最好,为最佳施肥量。施镁并不能促进苗木对镁的吸收,而是改变了营养供应的土壤环境,从而改变植物对其他营养的吸收比例,进而影响植物的生长。苗木的生长与Fe、P、K的关系最为密切,其次是Mg、Mn、Ca、N、Cu、Zn。     

The inhibition of seedling growth by crop residues in soil inoculated withPenicillium urticae Bainer

Summary Laboratory experiments were conducted to determine the effects of crop residues, without and withPenicillium urticae Bainer inoculation, on growth of wheat seedlings in soil. Fifty grams of Sharpsburg silty clay loam soil, containing 1% by weight of incorporated alfalfa, sorghum and corn stover residue, were placed in petri dishes, autoclaved, wetted to 40% moisture, and incubated at 24°C. for periods of 2, 3, and 4 weeks. One-half of the petri dishes were inoculated withP. urticae. Germination and seedling-shoot measurements were taken after 7 days of growth.The results of this study showed that (1) inoculation of soil generally reduced seedling height regardless of the residue treatment; (2) inoculation of soil containing corn and sorghum residues resulted in greater tissue production but reduced height of seedlings as compared to non-inoculated soils; and (3) in the absence of residues, the inoculated control soils were a better growth medium for wheat seedlings than were the non-inoculated control soils. In addition, alfalfa residues, especially in the presence ofP. urticae, were strongly inhibitory to the wheat seedlings, causing curling and reduced wheat-seedling root growth.Joint contribution from University of Nebraska and Soil and Water Conservation Research Division, Agricultural Research Service, U.S. Department of Agriculture, and Nebraska Agricultural Experiment Station, Lincoln, Nebraska, cooperating. Published with the approval of the Director as Paper No. 1242, Journal Series, Nebraska Agricultural Experiment Station.     

Practical aspects of mycorrhizal technology in some tropical crops and pastures

Summary Greenhouse and field experiments were conducted on the effect of VA mycorrhiza (VAM) on the growth of cassava, various tropical grass and legume species, as well as beans, coffee and tea. A large number of VAM fungal species were evaluated for effectivity in increasing cassava growth and P uptake in acid low-P soils. The effectivity of VAM species and isolates was highly variable and dependent on soil pH and fertilizer applications, as well as on soil temperature and humidity. Two species,Glomus manihotis andEntrophospora colombiana were found to be most effective for a range of crops and pastures, at low pH and at a wide range of N, P, and K levels. At very low P levels nearly all crops and pasture species were highly mycorrhizal dependent, but at higher soil P levels cassava and several pasture legumes were more dependent than grass species. Mycorrhizal inoculation significantly increased cassava and bean yields in those soils with low or ineffective indigenous mycorrhizal populations. In these soils cassava root yields increased on the average 20–25% by VAM inoculation, both at the experiment station and in farmers’ fields. VAM inoculation of various pasture legumes and grasses, in combination with rock phosphate applications, increased their early growth and establishment. Agronomic practices such as fertilization, crop rotations, intercropping and pesticide applications were found to affect both the total VAM population as well as its species composition. While there is no doubt about the importance of VA mycorrhiza in enhancing P uptake and growth of many tropical crops and pastures grown on low-P soils, much more research is required to elucidate the complicated soil-plant-VAM interactions and to increase yields through improved mycorrhizal efficiency.