Effectiveness of rehabilitation treatments on a slowly revegetating hillslope in a recently burned coastal forest,Republic of Korea

In April 2000, a large forest fire burned through the largest mountain range in the eastern coastal area of the Republic of Korea. Although various measures are applied to restore vegetation cover and minimize surface soil erosion after forest fires, few studies have quantified their effectiveness in the Republic of Korea. The goal of this study was to evaluate the effectiveness of rehabilitation treatments on a slowly revegetating hillslope after burning. In 2002, we installed six treatments (ground seeding, hydroseeding, tree planting, sodding, vegetation sacks, log erosion barriers), examined the vegetation coverage and sediment yield in these treated sites, and compared these results to those in an untreated site. The results showed that our study hillslope, which features a high-severity fire regime, erodible silty sands, steep slopes, and frequent high-intensity rainfall, required at least 4 years to achieve surface soil stability through the recovery of native plant species. However, the rehabilitation treatments achieved surface soil stability more quickly. In particular, despite frequent high-intensity rainfall, the hydroseeding and vegetation sack treatments were highly effective in early recovery because they provided seed stability and a high growth rate. The log erosion barrier treatment was critically effective in reducing the sediment yield because it provided storage spaces.     

Altered N,P and C dynamics with absence of fire in Eucalyptus forests affected by premature decline

Absence of fire is increasingly recognized as an important driver of soil nutrient budgets in Eucalyptus forest, especially in forests affected by premature Eucalyptus decline, due to the effects of soil nutrient accumulation on nutrient balances and forest community dynamics. In this study, we present a dataset of soil and foliar nutrient analyses, and vegetation measurements from a fire chronosequence survey in native E. delegatensis forest. Measured indices include total soil and extractable soil nitrogen (N), or phosphorus (P), soil organic carbon (C), soil acid‐phosphatase (PME) activity, foliar N and foliar P, and understorey and overstorey vegetation canopy height. We show that in some cases indices are strongly linked to time since fire (2–46 years). Time since fire correlated positively with foliar N, total and extractable soil N, soil organic C, and also soil PME activity; the latter an indicator of biotic P demand. Differences in the strength of these relationships were apparent between two geology types, with stronger relationships on the potentially less‐fertile geology. The strong positive correlation with time since fire and understorey canopy height reflected increasing shrub biomass and thickening of the shrub layer. The strong positive correlation for soil or foliar N, but not P, with time since fire, indicates that P does not increase relative to N over time. P may, therefore, become limiting to growth in this plant community. Similarly, the significantly higher concentrations of soil N but not P, also found in both older and long‐unburnt forest stands (>100 years since management), may exacerbate a situation of soil nutrient limitation over several decades. A characteristic feature of long unmanaged stands is a developing tea tree (Leptospermum sp.) understorey, which may benefit from elevated soil N availability and increasing organic C accumulation with prolonged fire absence. This increased shrub biomass would outcompete Eucalyptus for resources, including soil nutrients and water.     

Effects of fire frequency on survival,growth and fecundity of Paspalum quadrifarium (Lam.) in a grassland of the Flooding Pampa (Argentina)

Abstract Fire and grazing are important factors in the regulation of the grassland structure of the Flooding Pampa (Buenos Aires Province, Argentina dominated by Paspalum quadrifarium plants (henceforth ‘pajonal’)). Winter burning of pajonal is a practice that increases P. quadrifarium growth and its nutritious value for cattle. The objective of this work was to determine the responses of different demographic variables of P. quadrifarium growing in a grassland managed with different fire frequencies. The work was carried out in a pajonal situated in San Ignacio (Ayacucho county, Buenos Aires Province, Argentina). The treatments were: high fire frequency (0.8 fires per year) and low fire frequency (0.4 fires per year). The population of P. quadrifarium was affected by fire frequency. Biomass, number of tillers, and the relative production of tillers per plant did not change with fire frequency. Plant height was negatively affected by fire frequency. Whereas no plant mortality was observed in high fire frequency, 30% of the mature plants died at the end of the experiment in low fire frequency. In both treatments, plant mortality was size‐dependent and juvenile plants were more affected than mature ones. Burning had an immediate negative effect on mature and juvenile plants in terms of fecundity, survival of tillers and basal cover. Tiller survival and fecundity were significantly lower in burned plants than in unburned ones. In the high fire frequency treatment the number of ramets and/or genets and basal cover were greater than in the low fire frequency treatment.     

Fire and soil-plant nutrient relations in a pine-wiregrass savanna on the coastal plain of North Carolina

Summary Changes in soil and plant nutrient conditions were evaluated following various burn and clip treatments in a longleaf pine-wiregrass savanna in Bladen Co., N.C., USA. Ground fires were found to add substantial quantities of N, P, K, Ca, and Mg to the soil, though not necessarily in forms immediately available to plants. Less than 1% of the total nitrogen in the charred residue (ash) is present as nitrate or ammonium. Considerable quantities of all nutrients examined were lost to the atmosphere during burning. Green leaf tissue in recently burned areas was consistently higher in N, P, K, Ca, and Mg compared to unburned areas. Howerver, when compared to similar tissues from clipped plots, burned area tissues were significantly higher in N, Ca, and Mg only. Data presented here suggest that tissue age significantly affects nutrient content and must be considered in any analysis of tissue nutrient content following burning. Within 4–6 months following fire, burned-area tissue nutrient content decreases to concentrations found in the unburned area. Burning resulted in initial enrichment of available soil nutrients including PO₄, K⁺, Ca⁺⁺, and Mg⁺⁺, however, NO₃ ^-, and NH₄ ⁺ concentrations in burned soil were not significantly different from unbruned soil. Soil and plant nutrient changes in an area burned two years in succession indicate that repeated burning may diminish nutrient availability. Plant response to various nutrient enrichment treatments of the soil indicated that nitrogen is limiting growth in both burned and unburned soils and that burning may alter some factors other than nutrients which may retard plant growth in unburned areas.     

火干扰强度对亚热带四种森林类型土壤理化性质的影响

火干扰是通过改变土壤理化性质而影响土壤生态系统功能的重要因素之一。探讨火干扰强度对不同森林类型下土壤理化性质的影响,为利用火干扰促进林分更新及经营提供理论指导。2014年在湖南省株洲市和湘潭市4种次生林(枫香次生林、马尾松-木荷混交林、杉木-木荷混交林及檫木-杉木混交林)内设置16块20 m×20 m样地进行试验,研究了火干扰强度(对照、低强度、中强度、高强度火烧)和林分类型对土壤容重(BD)、土壤斥水性(SWR)、有机质(SOM)、pH、全氮(TN)、全磷(TP)和全钾(TK)的影响。通过描述性统计分析、单因素方差分析和Fisher LSD检验研究各土壤性质在同一林分不同火干扰间,以及同一火干扰下不同林分间的显著性差异和变化趋势(P<0.05)。研究发现BD、SWR、pH、TK都随火强度的增大呈上升的趋势,而SOM、TP随火强度增大而减少,TN则随火强度增大没有规律性变化。在同一林分内与对照组相比,低强度火烧对BD、SWR、pH和SOM的影响不显著,中强度有一定影响,而高强度火烧影响显著;而TN、TP、TK在火烧前后均无显著性差异。火干扰后,TN和TP在同一火强度下不同林分间均...     

The effects of pruning,fertilizers, and organic amendments on lowbush blueberry production

A four-year field study was conducted on a Hebert gravelly sandy loam (pH 4.5) in Nova Scotia to assess the effects of pruning management and seven fertility amendments on lowbush blueberry (Vaccinium augustifolium Ait) production (yield, above ground and root tissue composition) and soil fertility. Pruning by oil burning produced higher fruit yields than flail mowing but burning had the opposite effect on the plant N content (with a lesser influence on above ground Mn and Zn). None of the fertility treatments (chicken manure, dairy manure, swine manure, urea, sawdust, NPK, NPK+S+Lime+Micronutrients) produced fruit yields significantly greater than the control. Treatments provided the equivalent of 50kg total N/ha/2-yr cycle. Treatments influenced tissue N, P, K, Ca, Mg, B, Mn, Cu, Zn and Mo levels. In general, the three manure treatments produced the highest levels of plant macronutrients; the urea treatment produced the lowest levels of plant nutrients. In most cases, extractable levels of soil P, K, Ca and Mg were highly correlated with the plant tissue content of these elements. Overall, the dairy manure treated soils were the highest in soil fertility.     

Effects of forest fire ash on germination and early growth of four pinus species

Fire modifies the germination of seeds of numerous species. One of the fire factors that cause these modifications is the ash. This study analysed the germination of seeds of Pinus sylvestris L., Pinus nigra Arn. Pinus radiata D. Don and Pinus pinaster Aiton, subjected to different ash treatments, and the development of seedlings that grew in these conditions for 14 weeks. We obtained the ash by completely burning leaves and small twigs from the most abundant woody species in populations of pines. The ash treatments applied were as follows: Control (without ash), Low (half of the amount registered in a fire), Medium (equal to the amount registered in a fire) and High (double the amount registered in a fire). Germination took place on paper inside Petri dishes and in soil, and growth was only analysed for the plants that grew in the soil. For all species, and especially P. nigra, germination rate decreased as the amount of ash applied increased. The negative effects of the ash were more apparent following treatments in Petri dishes than in the soil. In the dishes, the average germination time varies little between the four species of pine. In soil, the average germination time is more prolonged, and only some differences were observed between treatments in P. sylvestris and P. nigra. In these species the high treatment significantly increased the average germination time. We found a greater sensitivity of P. sylvestris and P. nigra to the addition of ash, showing a higher seedling mortality rate. However, it appears that seedling development (length and weight) was not affected in any of the species through the addition of ash. These tests allow us to deduce that, in P. sylvestris, P. nigra, P. radiata and P. pinaster, the ash produced by forest fires has an inhibiting effect on germination and little effect on the development of seedlings in the first months of life. This revised version was published online in June 2006 with corrections to the Cover Date.     

The response of seedlings of two dipterocarp species to nutrient additions and ectomycorrhizal infection

An experiment was conducted to investigate the effect of ectomycorrhizal infection on growth and nutrient uptake, especially of P and K of dipterocarp seedlings.Hopea helferi (Dyer) Blanco andHopea odorata Roxb. seedlings were grown in a sandy loam soil given a basal dressing. Nutrient treatments were unamended soil (NIL), amended soil with the addition of P and K (F), amended soil without P but with K (-P), amended soil without K but with P (-K), amended soil without P or K addition (-PK). Seedlings grown in the amended soil treatments showed foliar symptoms suggestive of calcium deficiency. Ectomycorrhizal infection appeared to improve shoot Ca concentration and relieved the foliar symptoms. Ectomycorrhizal infection inH. odorata plants increased shoot P concentration and increased shoot and total dry weight to the same or greater extent than those of uninfected plants growing on P amended soil.H. helferi showed a positive response to ectomycorrhizal infection in shoot, root and total dry weight in all nutrient treatments but no response to the nutrient treatments themselves.     

Plant species diversity affects plant nutrient pools by affecting plant biomass and nutrient concentrations in high-nitrogen ecosystems

Plant species diversity affects plant nutrient pools, however, previous studies have not considered plant nutrient concentrations and biomass simultaneously. In this study, we conducted an experimental system with 90 microcosms simulating constructed wetlands (CWs). Four species were selected to set up a plant species richness gradient (1, 2, 3, 4 species) and fifteen species compositions. The plant biomass, plant N, phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg) concentrations and pools were analyzed. Results showed that, (1) plant species richness increased plant biomass, and the presence of Oenanthe javanicae increased while the presence of Reineckia carnea decreased plant biomass; (2) plant species richness only increased plant K and Mg concentrations of the communities and plant Mg concentration of the species, and the presence of O. Javanica increased while the presence of R. Japonicus decreased plant N and P concentrations of the communities; (3) plant species richness increased plant N, P, K, Ca, and Mg pools, and the presence of O. Javanica increased while the presence of R. Carnea decreased plant N, P, K, Ca and Mg pools; (4) the four-species mixture produced more biomass and nutrient pools than the corresponding highest specific species monocultures. In case the plant uptake can remove nutrients from CWs through harvesting, the results suggest that both nutrient concentrations and biomass must be considered when evaluating the accumulation of nutrients. Assembling plant communities with high species richness (four species) or certain species (such as O. Javanica) is recommended to remove more nutrients from CWs through harvesting.     

On ecology of post-fire soil fungi: assessing impact of disturbance using species-abundance models as measure of community organization

Mediterranean ecosystems are among those most significantly modified by fires. Such fires lead to evident disturbance of the above- and below-ground ecosystem components, at various spatial and temporal scales, including soil microfungi. The ecological parameters used to measure the effects of disturbance on soil fungal communities include species-abundance distribution patterns, which reflect changes in the relationships between species numbers and their relative abundance, and serve as a critical measure of community organization. Species-abundance distribution patterns were used to assess the disturbance impact of experimental fires on soil fungal communities in Mediterranean maquis (southern Italy) in the short- to mid-term. The trend in the distribution patterns of heat-stimulated and xerotolerant soil fungi over time, their varying responses to low- and high-intensity fire, the efficiency of the soil germplasm bank, and the pivotal role of Neosartorya spp. in post-fire community structure in Mediterranean burned soils may all be used as tools to accurately assess the effects of fire on soil mycobiota.     

Effects of erosion on ecto- and VA-mycorrhizal inoculum potential of soil following forest fire in southwest Oregon

The Longwood Complex wildfire in the Siskiyou Mountains of southern Oregon in August 1987 created an opportunity to study erosion and its effects on mycorrhizal fungus inoculum potential of a forest soil on steep slopes. As measured by the erosion-bridge method, most erosion occurred in a single, intense storm in December after the fire and amounted to an estimated 2 to 4 cm of surface soil. Captured eroded soil had a higher pH and P and Mg levels than residual soil. Seedlings ofLibocedrus decurrens andPseudotsuga menziesii were planted on eroded plots with additions of captured eroded soil (ET) or pasteurized eroded soil (PET) transferred to the planting holes. After one growing season,Libocedrus seedlings formed nearly 4 times the vesicular-arbuscular mycorrhizae in ET treatments and more than twice as much in PET treatments than in controls. Survival and basal area growth were significantly better in ET than in the other treatments, and both ET and PET produced more seedling shoot growth than did controls.Pseudotsuga seedlings did not differ in measured characteristics between treatments; ectomycorrhiza formation was slight, evidently the result of reduced inoculum potential resulting from the fire.     

Effects of fire recurrence in Quercus coccifera L. shrublands of the Valencia Region (Spain): II. plant and soil nutrients

The consequences of fire recurrence (1, 2 and 3 fires in 16 years) on plant and soil C, N, P and K from Quercus coccifera garrigues were analysed in the Valencia Region (E Spain). Plant and forest floor (L horizon) nutrient concentrations either changed weakly or showed no change with fire recurrence. At the soil surface (0-2.5 cm), soil potential mineralisable nitrogen increased and available P decreased after an initial increase, whereas exchangeable K was not affected by successive fires. However, the significance of those observed trends for N and P was site-dependent. Despite the rapid formation of the L soil horizon, fire recurrence did not permit the development of the whole forest floor profile observed in the unburned garrigues. These organic layers contained a great proportion of the total nutrient pool, especially for N. Forest-floor and aboveground plant combustion by fire may produce significant losses of N and P compared with those available in mineral soil, whereas soil exchangeable K is large enough to replace these losses. Belowground nutrient reserves may account for the quick recovery of the Quercus coccifera aboveground biomass although successive fires could deplete these reserves and produce a loss of biomass and productivity in this species.     

Nutrient stocks in managed and natural humid tropical fallows

Managed fallows which recover nutrients more rapidly than natural secondary vegetation may improve the performance of shifting agriculture systems operating under inadequately long fallow cycles. Our objective was to construct nutrient balances for the soil, vegetation, and litter compartments of six planted leguminous fallows and natural secondary vegetation during 53 months. The fallows were planted on a previously cultivated Ultisol (Acrisol) in the Peruvian Amazon and included:Centrosema macrocarpum (Centrosema),Pueraria phaseoloides (Pueraria),Stylosanthes guianensis (Stylosanthes),Desmodium ovalifolium (Desmodium),Cajanus cajan (Cajanus), andInga edulis (Inga). In addition, in the natural fallow treatment secondary vegetation was allowed to establish and grow naturally. Quantities of extractable P, K, Ca, and Mg, total N, and organic C in soil to a 45 cm depth, and macrouttrients in aboveground biomass, roots, and litter were estimated at fallow planting, at 8, 17, and 29 months afterward, and at fallow clearing (53 months). Total N stocks increased by 10% in the Stylosanthes, Desmodium, Pueraria, and Inga treatments, but changed little in the Cajanus, Centrosema and natural fallows. This difference was largely due to greater net increases in both soil and vegetation compartments in the former group of treatments. In the Inga, Desmodium, and natural fallows, total stocks of P and K at 53 months were about 40% to 80% greater and 12% greater, respectively, than initial values, but Ca and Mg stocks were reduced by 25% to 40%. In the other treatments, there was generally little change in P stocks, but large (30% to 60%) reductions in K, Ca, and Mg during the course of the fallow. Although there were net decreases of stocks of P, K, Ca, and Mg in soil in all treatments during the fallow, storage of P and K in vegetation and litter in the Inga, Desmodium, and natural fallows offset losses of these nutrients from soil. These treatments also tended to accumulate more Ca and Mg in biomass and litter than the other treatments. These results suggest that leguminous fallow vegetation that accumulates large amounts of biomass may increase N, P, and K stocks, but that incomplete recuperation of Ca and Mg may limit the sustainability of short-rotation fallow-based systems on acidic, infertile soils. ei]Section editor: G R Stewart     

Fire and Grazing Change Herbaceous Species Composition and Reduce Beta Diversity in the Kalahari Sand System

After rainfall and soils, fire and herbivory are two of the main determinants of savanna ecosystems. Although the interactive effects of fire and herbivores on soil and vegetation are widely acknowledged few studies have addressed these two factors in concert, and none of the studies has focused on the Kalahari sand system. We experimentally studied how annual late dry season fires and grazing affect herbaceous plant species composition, above- and belowground biomass, and soil and grass nutrient concentrations in the nutrient-poor semi-arid Kalahari system in northern Botswana. Four treatments (fire, grazing, fire + grazing, and no-fire–no-grazing) were applied for two consecutive years in the late dry season. Plant species composition was affected by treatment and year. The no-fire–no-grazing treatment was distinctly different from all the other treatments in terms of species composition. Beta diversity was lower on the fire treatment and grazing treatment, but not where fire and grazing were combined. Fire and grazing alone or in combination did not have a substantial effect on biomass, soil and plant nutrients or plant species alpha diversity. Plant nitrogen was the only element that differed between treatments, with high concentrations on all the grazed treatments in the first year and low levels on the fire-alone treatment during the second year. The results show that fire and grazing mainly affect species composition and large-scale biodiversity patterns as indicated by the no-fire–no-grazing treatment being distinctly different from other treatments, suggesting the evolutionary adaptation of this dystrophic Kalahari sand system to herbivory and fire.     

长期培肥黑土微生物量磷动态变化及影响因素

长期采用两种不同量有机肥(M2、M4)、化肥(NPK)方式培肥黑土,研究微生物量P在作物生长季动态变化．结果表明。施用有机肥微生物量P显著高于施用化肥(NPK)和不施肥(CK),微生物量P分别为M48．75～47．68mg·kg^-1,M2 3．02～37．16mg·kg^-1,NPK1．59～10．62mg·kg^-1,CK0．76～6．74mg·kg^-1之间,波动性较大．M4、M2处理微生物量P最大值出现在抽雄吐丝期,NPK、CK处理最大值出现在大喇叭口期;施肥数量和种类不同所引起的黑土微生物量P的差异并未因季节变化及玉米生育时期影响而明显改变．微生物量P的动态变化与绝大多数黑土生物、理化特性指标的动态变化没有显著的相关性;微生物量P与黑土生物、理化特性(除全钾外),植物氮、磷、钾含量有极显著的正相关关系,与黑土含水量呈显著正相关关系．     

Nutrient changes in surface soils after an intense fire in jarrah (Eucalyptus marginata Donn ex Sm.) forest

The effects of an intense fire on the nutrient status of jarrah(Eucalyptus marginata Donn ex Sm.) forest soils were investigated. At seven experimental sites, representing a range of soil and vegetation types, surface soils were sampled to a maximum depth of 20 cm before, immediately after, and 1 year after the fire. Immediately after the fire, concentrations of total and extracted nutrients in surface (0–3 cm) soils increased markedly. One year later, concentrations of extracted nutrients in surface soils had returned to levels close to pre-burn concentrations. During this period, some properties of sub-surface (3–20 cm) soils also changed: Bray-extractable phosphorus and electrolytic conductivity decreased, whereas ex-tractable potassium and pH increased relative to pre-burn concentrations. Initial increases in concentrations of extractable forms of nutrients were determined largely by the amounts of nutrients deposited in fine ash, whereas the changes after 1 year depended more on the leaching of ions and their reactions with the mineral soil. Increases in total amounts of major nutrients in surface soils arising from additions of fine ash were generally well correlated with amounts in pre-burn litter and with amounts in the components of organic matter likely to be consumed in the fire. Significant quantities of all nutrients are redistributed from aboveground sources to the soil surface during intense fires, including nutrients which are most susceptible to losses through volatilization. This redistribution of nutrients is discussed in relation to short-term and long-term effects on plant growth and functioning of the jarrah ecosystem.     

Growth and elemental content of several sagebrush-steppe species in unburned and post-wildfire soil and plant effects on soil attributes

Fire is the principal means of stand renewal in big sagebrush-steppe communities of western North America. Plant growth following fire may be influenced by heat-induced changes in the nutrient status of the soil. Moreover, post-wildfire pioneer plant species may alter soil properties, and thereby, impact subsequent plant recruitment. Our study compared the growth and elemental content of big sagebrush (Artemisia tridentata), squirreltail (Elymus elymoides), cheatgrass (Bromus tectorum), and Indian ricegrass (Achnatherum hymenoides), grown under greenhouse conditions in post-wildfire and similar unburned soil. We also examined soil attributes following plant growth. Cheatgrass and squirreltail, grown in post-wildfire soil, had significantly (p≤0.05) greater aboveground mass than plants grown in unburned soil. As compared with unburned soil, post-wildfire soil engendered the following significant (p≤0.05) differences in leaf elemental content: 1) big sagebrush had higher levels of P and lower levels of Mn; 2) squirreltail accumulated more P and N; and 3) all grass species had higher SiO₂ content. Following harvest of plants, post-wildfire soil generally contained significantly (p≤0.05) more KCl-extractable ortho-P, NH _inf4 ⁺ , and SO ₄ ⁻ , than unburned soil. Plant growth in both burned and unburned soils fostered a significant (p≤0.05) increase in the bicarbonate-extractable pool of P as compared with unplanted controls. Soil Kjeldahl-N was significantly (p≤0.05) greater after plant growth in burned treatments as compared with the control. This study demonstrates that post-wildfire soil can have a stimulatory effect on plant growth for some species. Squirreltail deserves consideration as a post-wildfire revegetation species. Furthermore, pioneer plant growth following wildfires can attenuate soil properties and therefore influence plant succession.     

围封对不同退化程度荒漠草原植物群落和土壤的影响

围封是退化草原生态系统恢复的有效措施之一,已在中国北方草原地区实施多年并取得良好的效果。由于不同退化草原生态系统具有完全不同的植被和土壤条件,围封对不同退化草原植物群落和土壤的恢复是否具有一致的影响,目前仍不清楚。对内蒙古地区轻度、中度和重度退化荒漠草原分别设置6年围封后,对植物群落特征和土壤理化性质进行了调查和测定。研究结果发现,围封显著提高了3种退化荒漠草原短花针茅（Stipa breviflora）和无芒隐子草（Cleistogenes songorica）种群以及群落的高度、盖度和地上生物量（P<0.05）,表明围封从多组织层次使退化草原植物群落得到有效的恢复。围封总体提高了轻度和中度退化荒漠草原植物多样性,但降低重度退化荒漠草原的植物多样性。重度退化荒漠草原在围封后群落高度、盖度和地上生物量恢复效率显著高于轻度和中度退化的（P<0.05）,表明围封对重度退化荒漠草原植被恢复更加有效。除轻度退化外,围封显著降低中度和重度退化荒漠草原土壤全碳、全氮、全磷、有效氮和速效磷含量（P<0.05）,但对3种退化荒漠草原的土壤水分含量无显著影响,表明围封对不同退化荒漠草原土壤的影响具有滞后性。研究为荒漠草原围封成效评估提供理论指导和退化荒漠草原生态系统科学合理实施围封政策提供科学依据。     

Analysis of acid-soil stress in sorghum genotypes with emphasis on aluminium and magnesium interactions

Acid-soil stress in 12 sorghum (Sorghum bicolor (L.) Moench) genotypes was attributed mainly to aluminium (Al) toxicity. Root damage and magnesium (Mg) deficiency are two independent aspects of plant sensitivity to Al, either in acid soil or in nutrient solution. At moderate soil acidity, Mg deficiency dominantly limited growth whilst at high acidity root damage overruled the effect of Mg deficiency on the growth response. In nutrient solutions containing Al, increased Mg supply improved both root development and Mg nutrition of plants, whereas increased calcium (Ca) supply, or nutrition with ammonium (NH₄) instead of nitrate (NO₃), alleviated root damage but amplified Mg deficiency. At lowered pH the syndrome of Al toxicity was more profound. The implications of Mg-Al interactions, root damage, Mg supply and genotype selection are elucidated.     

Effect of heating on properties of some soils from Southern Nigeria and growth of rice

Summary The effect of heating on the properties of Apomu (Psammentic Usthorthent), Egbeda (Oxic Paleustalf) and Gambari (Typic Plinthustalf) surface soils were studied under laboratory conditions. Heating at low temperatures (100°C) have no detrimental effects on soil properties, on the contrary it increased the soil extractable P, Mg, Fe, Mn and Zn levels. Pronounced reductions in total N, Org. C, Org. P and extractable Ca and Mg levels and marked increases in extractable P, Zn, Mn and Fe were observed by heating to 200°C. Heating to 500° had an adverse effect on soil chemical and physical properties.Plant height and dry matter yeild of rice plants were higher when grown on Egbeda soil previously heated to 100°C. With addition of N, P and K there was no observed beneficial effect of the heating treatment. Rice plants grown on Egbeda soil previously heated to 200°C showed high uptake of Mn. Plants grew badly in soil previously heated to 500°C.