Identification and validation of QTLs conferring resistance to sorghum downy mildew (Peronosclerospora sorghi) and Rajasthan downy mildew (P. heteropogoni) in maize

We have mapped the quantitative trait loci (QTLs) conferring resistance to sorghum downy mildew (Peronosclerospora sorghi; SDM) and Rajasthan downy mildew (P. heteropogoni; RDM), two species of DM prevalent throughout India. QTL mapping was carried out on a backcross population of 151 individuals derived from a cross between CM139 (susceptible parent) and NAI116 (highly resistant to both SDM and RDM). Heritability estimates were 0.74 for SDM and 0.67 for RDM. Composite interval mapping combined with a linkage map constructed with 80 simple sequence repeat (SSR) markers resulted in the identification of three QTLs (one each on chromosomes 2, 3 and 6) for SDM resistance and two QTLs (one each on chromosomes 3 and 6) for RDM resistance, all of which were contributed by NAI116. The significance of the major QTL on chromosome 6 (bin 6.05) that confers resistance to diverse DMs in tropical Asia, including SDM and RDM in India, was also verified. The results confirmed that some common QTLs contribute to both SDM and RDM resistance, while additional loci might specifically govern resistance to SDM. The QTL information generated in this study provide information that will aid in undertaking an integrated breeding strategy for the transfer of resistance to SDM and RDM in maize lines using marker-assisted selection.     

Indirect monitoring of root activity in soybean cultivars under contrasting moisture regimes by measuring electrical capacitance

The applicability of root electrical capacitance (EC) measurement for in situ investigation of root activity and drought tolerance was tested in soybean cultivars. Well-watered and drought-stressed plants were grown in pots with repeated EC measurements, followed terminally by harvest to determine root dry mass (RDM), shoot dry mass (SDM), root/shoot ratio (RSR) and leaf area (LA). EC measurement showed the cultivar differences in root growth and biomass production. EC increased till the beginning of flowering, then became nearly constant. Terminal EC was highly correlated with RDM for non-stressed (R ² = 0.844) and stressed plants (R ² = 0.936). Drought reduced the EC of cultivars by 28.8–50.5 %, consistently with the corresponding changes of SDM (25.5–49.1 %) and LA (23.6–51.5 %), but considerably exceeded the loss of RDM (12.6–47.3 %) in some cultivars. The reason is drought increased the RSR (by 3.9–21.9 %), leading to decreased water uptake, and thus EC per unit of RDM. This was confirmed by the significantly decreased slope of EC–RDM regression line from 0.437 to 0.317 nF g^?1 RDM calculated for well-watered and drought-stressed plants, respectively. As EC referred to root uptake activity, it was better indicator of the actual root status than RDM. EC measurement was adequate for monitoring the cultivar-specific differences in root growth and for estimation of biomass loss caused by drought. By supplementing the conventional methods, this in situ technique could be useful for various fields of agriculture, including cultivar selection or stress tolerance studies.     

The effect of the presence of a forage legume on nitrogen and carbon levels in soils under Brachiaria pastures in the Atlantic forest region of the South of Bahia,Brazil

The impact of forest clearance, and its replacement by Brachiaria pastures, on soil carbon reserves has been studied at many sites in the Brazilian Amazonia, but to date there appear to be no reports of similar studies undertaken in the Atlantic forest region of Brazil. In this study performed in the extreme south of Bahia, the changes in C and N content of the soil were evaluated from the time of establishment of grass-only B. humidicola and mixed B. humidicola/Desmodium ovalifolium pastures through 9 years of grazing in comparison with the C and N contents of the adjacent secondary forest. The decline in the content of soil C derived from the forest (C3) vegetation and the accumulation of that derived from the Brachiaria (C4) were followed by determining the ¹³C natural abundance of the soil organic matter (SOM). The pastures were established in 1987, 10 years after deforestation, and it was estimated that until 1994 there was a loss in forest-derived C in the top 30 cm of soil of approximately 20% (9.1 Mg C ha^–1). After the establishment of the pastures, C derived from Brachiaria accumulated steadily such that at the final sampling (1997) it was estimated 13.9 Mg ha^–1 was derived from this source under the grass-only pasture (0–30 cm). Samples taken from all pastures and the forest in 1997 to a depth of 100 cm showed that below 40 cm depth there was no significant contribution of the Brachiaria-derived C and that total C reserves under the grass/legume and the grass-only pastures were slightly higher than under the forest (not significant at P=0.05). The more detailed sampling under the pastures showed that to a depth of 30 cm there was significantly (P<0.05) more C under the mixed pasture than the grass-only pasture. It was estimated that from the time of establishment the apparent rate of C accumulation (0–100 cm depth) under the grass/legume pastures (1.17 Mg ha^–1 yr^–1) was almost double that under the grass-only pastures (0.66 Mg ha^–1 yr^–1). The data indicated that newly incorporated SOM derived from the Brachiaria had a considerably higher C:N ratio than that present under the forest.     

Potential of Crotalaria species as green manure crops for the management of pathogenic nematodes and beneficial mycorrhizal fungi

On the basis of preliminary experiments, some Crotalaria species from Senegal were investigated to determine (1) their susceptibility to Meloidogyne javanica and M. incognita compared to a sensitive host (tomato), (2) their mycorrhizal and rhizobial responses, and (3) the effect of their cultivation on the mycorrhizal soil infectivity. The nematode invasion rates on Crotalaria spp. ranked from 0.17 to 7.17% and from 0.58 to 5.25%, respectively, for M. incognita and M. javanica, vs. 97% and 77% on tomato. Moreover, the inoculated J2 which invaded tomatoes developed into adult females, while those on Crotalaria spp. rarely developed beyond the third stage, confirming that all Crotalaria spp. evaluated are non hosts or poor hosts. In two other experiments, Crotalaria spp. were inoculated with an arbuscular mycorrhizal fungus (Glomus intraradices). Mycorrhization was generally well developed among Crotalaria species, and mycorrhizal colonization enhanced mainly phosphorus content of shoot tissues and always significant plant growth. Inoculation with both rhizobial isolates and Glomus intraradices enhanced growth and nodule formation on some Crotalaria species. The data recorded in both experiments showed, for the first time, that Crotalaria spp. are highly mycorrhiza dependent, some of them reaching more than 90% mycorrhizal dependency. Among Crotalaria species, twelve were used in two different experiments. A significant correlation was obtained between their mycorrhizal dependencies calculated on the shoot dry mass recorded in each experiment. Crotalaria spp. could be used as pre-crops for providing green manure while at the same time decreasing the level of detrimental nematodes and increasing the level of beneficial mycorrhizal fungi.     

Diary

Abstract

The use of organic amendments is a common practice in Pakistan to improve soil fertility. Organic amendments affect the chemical speciation and thus the bioavailability of heavy metals and their uptake and toxicity to plants. The present study evaluates the influence of organic amendments viz. farm yard manure (FM), poultry manure (PM), press mud (PrM) and activated carbon (AC) on nickel (Ni) bioavailability in soil, as well as its uptake into, and growth responses of, Trifolium alexandrinum. Pot experiments were conducted where T. alexandrinum was exposed to three different concentrations of Ni i.e., 30, 60 and 90 mg kg^?1 in the form of NiCl₂ solution in the presence and absence of organic amendments each applied at 15 g kg^?1 soil. The results showed that the effect of organic amendments on Ni bioavailability and uptake by T. alexandrinum depended on the Ni concentration in the soil and the amendment type. Application of organic amendments generally increased Ni phytoavailability in soil and Ni uptake by plants at low Ni levels (Ni-0 and Ni-30) but decreased at higher levels (Ni-60 and Ni-90).     

Iron deficiency in pasture species on coralline rubble soils

Summary Iron deficiency was diagnosed in some pasture species growing on a coralline rubble soil (Troporthent) of high pH in the Solomon Islands. A comparative study of the response of a selection of pasture species to additions of iron indicated differential species tolerance to iron deficiency particularly among legumes.Macroptilium atropurpureum andM. lathyroides produced good yields on this soil without additions of iron while other legume species,Centrosema pubescens, Pueraria phaseoloides andStylosanthes guianensis either grew poorly or failed to survive.     

Response of Stylosanthes guianensis to endomycorrhizal fungi inoculation as affected by lime and phosphorus applications

The effect of 3 different species of vesicular-arbuscular mycorrhizal fungi on the growth of Stylosanthes guianensis (Aubl.) Sw. cultivated in a sterilized acid and dystrophic soil (Quartzipsament), with 4 levels of lime (0; 0.27; 0.63 and 1.10 meq Ca²⁺/100 g air-dried soil, as Ca(OH)₂) and 2 P levels (0 and 20 mg P/kg soil, as KH₂PO₄) was evaluated under greenhouse conditions. Plants were harvested 40, 60, and 80 days after planting. Stylosanthes guianensis was highly mycotrophic, especially in soil without P fertilization. Mycotrophism was highest in plants inoculated with Acaulospora scrobiculata in soil receiving no P fertilizer and with 0.63 meq Ca²⁺/100 g air-dried soil. Shoot growth increment was as high as 5129% at the third harvest. Inoculation with Glomus macrocarpum presented intermediate results, whereas inoculation with Gigaspora margarita had no significant effect on plant growth. Root per cent colonization and shoot dry weight, as well as root percent colonization and shoot to root ratio were significantly correlated. The occurrence of S. guianensis in very acid and dystropic soils, containing toxic levels of Al³⁺, requires the association with VAM fungi for the plant tolerate such conditions.     

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 Zeolite-Containing Material and Ammonium Nitrate on Biodegradation of n-Tridecane in Heavy Clay-Loam Leached Chernozem with High Organic Matter Content

Biostimulation based on usage of soil amendments is growing due to their efficiency in removing different petroleum hydrocarbons (PHC) from contaminated sand or loam-sand soils. However, the research on clay-rich soils with higher organic carbon content, in which PHC biodegradation may proceed differently and which are more difficult to clean up, has been less extensive. In a pot experiment, we studied and compared the effects of two soil amendments, natural zeolite-containing material (ZCM, 50 g kg^?1) as a bulking agent and ammonium nitrate (0.3 g N kg^?1) as a nitrogen fertilizer, on biodegradation of n-tridecane (1 wt.%) in a weakly acidic heavy clay loam leached chernozem with fairly high organic carbon content (3.71%). After 48 days, the nitrogen-amended contaminated soil showed enhancement of both respiratory activity (basal and substrate-induced respiration rates) and the number of n-tridecane- degraders. As a consequence, the extent of n-tridecane biodegradation (86.5%) was essentially higher in the presence of added nitrogen than that in the non-amended soil (73.7%). In contrast, due to the partial retention of n-tridecane molecules in its pores, ZCM retarded biodegradation to 56.0%, showed no significant effect on the number of n-tridecane-degraders and, moreover, enhanced the decomposition of the soil intrinsic organic matter. The obtained data indicate that more precautions should be considered when using porous sorbents such as ZCM for remedial arrangements in PHC-contaminated soils.     

Absorption, tissue distribution, metabolism and excretion of ormetoprim and sulphadimethoxine in cod (Gadus morhua) after oral administration of Romet30

Uptake, tissue distribution, metabolism and elimination of sulphadimethoxine (SDM) and ormetoprim (OMP) were examined in Atlantic cod (Gadus morhua) following oral administration of Romet³⁰ at a dose of 5 mg OMP and 25 mg SDM per kilogram fish. Absorption and elimination was rapid for OMP and slow for SDM characterized by peak plasma concentrations (C_max) of 1.44 and 20.93 μg ml^?1 after 7 and 59 h, respectively, and plasma elimination halflives (t_1/2β) of 7 h for OMP and 56 h for SDM. High concentrations of SDM were found in the bile indicating high biliary excretion of this drug whereas moderate concentrations of N‐acetylated SDM were found in tissues and bile indicating N‐acetylation to be a less important metabolic pathway for SDM in cod. The biliary concentration of OMP was low.     

Direct Effects of Soil Amendments on Field Emergence and Growth of the Invasive Annual Grass Bromus tectorum L. and the Native Perennial Grass Hilaria jamesii (Torr.) Benth

Bromus tectorum L. is a non-native, annual grass that has invaded western North America. In SE Utah, B. tectorum generally occurs in grasslands dominated by the native perennial grass, Hilaria jamesii (Torr.) Benth. and rarely where the natives Stipa hymenoides Roem. and Schult. and S. comata Trin. & Rupr. are dominant. This patchy invasion is likely due to differences in soil chemistry. Previous laboratory experiments investigated using soil amendments that would allow B. tectorum to germinate but would reduce B. tectorum emergence without affecting H. jamesii. For this study we selected the most successful treatments (CaCl₂, MgCl₂, NaCl and zeolite) from a previous laboratory study and applied them in the field in two different years at B. tectorum-dominated field sites. All amendments except the lowest level of CaCl₂ and zeolite negatively affected B. tectorum emergence and/or biomass. No amendments negatively affected the biomass of H. jamesii but NaCl reduced emergence. Amendment effectiveness depended on year of application and the length of time since application. The medium concentration of zeolite had the strongest negative effect on B. tectorum with little effect on H. jamesii. We conducted a laboratory experiment to determine why zeolite was effective and found it released large amounts of Na⁺, adsorbed Ca²⁺, and increased Zn²⁺, Fe²⁺, Mn²⁺, Cu²⁺, exchangeable Mg²⁺, exchangeable K, and NH₄⁺ in the soil. Our results suggest several possible amendments to control B. tectorum. However, variability in effectiveness due to abiotic factors such as precipitation and soil type must be accounted for when establishing management plans.     

Investigating the biochar effects on C‐mineralization and sequestration of carbon in soil compared with conventional amendments using the stable isotope (δ13C) approach

Biomass‐derived black carbon (biochar) is considered to be an effective tool to mitigate global warming by long‐term C‐sequestration in soil and to influence C‐mineralization via priming effects. However, the underlying mechanism of biochar (BC) priming relative to conventional biowaste (BW) amendments remains uncertain. Here, we used a stable carbon isotope (δ¹³C) approach to estimate the possible biochar effects on native soil C‐mineralization compared with various BW additions and potential carbon sequestration. The results show that immediately after application, BC suppresses and then increases C‐mineralization, causing a loss of 0.14–7.17 mg‐CO₂–C g^?1‐C compared to the control (0.24–1.86 mg‐CO₂–C g^?1‐C) over 1–120 days. Negative priming was observed for BC compared to various BW amendments (?10.22 to ?23.56 mg‐CO₂–C g^?1‐soil‐C); however, it was trivially positive relative to that of the control (8.64 mg‐CO₂–C g^?1‐soil‐C). Furthermore, according to the residual carbon and δ¹³C signature of postexperimental soil carbon, BC‐C significantly increased (P < 0.05) the soil carbon stock by carbon sequestration in soil compared with various biowaste amendments. The results of cumulative CO₂–C emissions, relative priming effects, and carbon storage indicate that BC reduces C‐mineralization, resulting in greater C‐sequestration compared with other BW amendments, and the magnitude of this effect initially increases and then decreases and stabilizes over time, possibly due to the presence of recalcitrant‐C (4.92 mg‐C g^?1‐soil) in BC, the reduced microbial activity, and the sorption of labile organic carbon (OC) onto BC particles.     

Short-term impact of dry olive mill residue addition to soil on the resident microbiota

The short-term response of the resident soil bacterial and fungal communities to the addition of 5% (w/w) of either dry olive mill residue (DOR), DOR treated with Phlebia sp. (PTDOR) or DOR previously extracted with water (WEDOR) was investigated. As opposed to bacteria, the diversity of fungi increased upon the amendments as assessed by denaturing gradient gel electrophoresis of 18S rDNA. Over the first 30 days, phospholipid fatty acids analyses indicated a gradual decrease in the relative abundances of Gram⁺ bacteria (from 44.8% to 37.9%) and a concomitant increase of Gram⁻ bacteria (from 37.3% to 51.2%) in DOR-amended soil. A considerable increase in the fungal/bacterial ratio was observed after 7 days in DOR, WEDOR and PTDOR-amended soils with respect to the control (0.316, 0.165 and 0.265, respectively, vs. 0.011). The overall microbial activity was stimulated by the amendments as indicated by the higher activity levels of both dehydrogenase and fluorescein diacetate hydrolase. These results indicate that DOR at the application level examined is not toxic on soil microorganisms.     

Evaluation of Organic and Inorganic Amendments on Maize Growth and Uptake of Cd and Zn from Contaminated Paddy Soils

Pot and field experiments were conducted to investigate the effects of soil amendments (cow manure, rice straw, zeolite, dicalcium phosphate) on the growth and metal uptake (Cd, Zn) of maize (Zea mays) grown in Cd/Zn contaminated soil. The addition of cow manure and rice straw significantly increased the dry biomass, shoot and root length, and grain yield of maize when compared with the control. In pot study, cow manure, rice straw, and dicalcium phosphate all proved effective in reducing Cd and Zn concentrations in shoots and roots. Cd and Zn concentrations in the grains of maize grown in field study plots with cow manure and dicalcium phosphate amendments to highly contaminated soil (Cd 36.5 mg kg^?1 and Zn 1520.8 mg kg^?1) conformed to acceptable standards for animal feed. Additionally both cow manure and dicalcium phosphate amendments resulted in the significant decrease of Cd and Zn concentrations in shoots of maize.     

Organic Amendments to Enhance Atrazine and Metamitron Degradation in Two Contaminated Soils with Contrasting Textures

Among all types of xenobiotics, pesticides such as herbicides play a significant role in soil and water pollution due to their wide usage all over the world. This study addresses the ability of organic amendments to enhance atrazine and metamitron degradation in two herbicide-contaminated soils with contrasting textures under laboratory conditions. Soil samples were collected from surface soils with textures of sandy loam and silty clay, from northeastern Iran. Initial concentration of herbicides was 50 mg · kg^{? 1} soil. Contaminated soil samples were treated with manure, compost and vermicompost at rates of 0, 0.5, and 2% (w/w). Residual concentrations of atrazine and metamitron were determined by HPLC at the end of incubation periods of 20, 40, and 60 days. Residual concentrations of atrazine were 46.5, 38.9, and 36.2 mg · kg^{? 1} after 20, 40, and 60 days incubation, respectively. Residual metamitron concentrations were clearly lower than atrazine. After 20, 40, and 60 days, concentrations of metamitron were 2.9, 1.0, and 0.6 mg · kg^{? 1}, respectively. Organic amendments at the rates of 0.5 and 2% showed similar effects on the enhancement of herbicide degradation in soils. However, no statistically significant effect was observed among types of organic amendments (α = 0.05). Degradation was affected by soil textures. Residual concentrations of herbicides were higher in sandy loam than in silty clay soil.     

The response of denitrifiers in a sandy loam soil affected by a long-term fertilization to organic carbon and nitrate

The response of denitrifiers to carbon in the form of glucose (Glc-C) and nitrate (NO ₃ ⁻ -N) amendments was studied in four differently fertilized plots of sandy-loam soil. Two basically different characteristics of denitrification activity were determined: (1) potential denitrification measured as nitrous oxide production during 1-d incubation in the presence of acetylene, and (2) denitrifying enzyme activity determined in soil slurries as a N₂O production in the presence of acetylene and chloramphenicol during 1 h of incubation. Potential denitrification was strongly influenced by both Glc-C and NO ₃ ⁻ -N amendments in their various combinations, but was also affected by the fertilization practice. The response of denitrifiers to Glc-C and NO ₃ ⁻ -N was generally lower in unfertilized and surprisingly also in highly fertilized soils than in organically and moderately fertilized soils. Denitrifying enzyme activity was stimulated by the fertilization and was, in contrast to potential denitrification, the highest in highly fertilized soil. The results indicate that although active denitrifiers were present in a highly fertilized soil, their ability to develop under optimal conditions was decreased (being similar to that of denitrifiers in unfertilized soil). This suggests long-term changes in soil microbial community in a highly fertilized soil, presumably connected to changes in soil chemistry caused by fertilization.     

The effects of carbon sources and micronutrients in fermented whey on the biodegradation of n-hexadecane in diesel fuel contaminated soil

Fermented whey has previously been shown to stimulate biodegradation of n-hexadecane in diesel contaminated soils. The proposed explanation for the stimulatory effect is that fermented whey provides easily accessible carbon and micronutrients, which give rise to an increased degrading biomass.The objective of this work has been to investigate the role of the different carbon sources and vitamins in fermented whey on the microbial degradation of n-hexadecane in soil.The effects of lactose, lactate, vitamins and free amino acids were tested in combinations according to a full factorial design experiment, at concentrations corresponding to those present in fermented whey. The target substance was ¹⁴C-labeled n-hexadecane in nutrient amended soil microcosms contaminated with 5000 mg diesel fuel kg⁻¹ dw. Biodegradation was monitored by determination of evolved ¹⁴CO₂.Significant effects on the biodegradation of n-hexadecane were observed for lactate and amino acids additions in a sandy soil. Lactate showed both an inhibitory effect in the early phase of the experiment and a stimulatory effect in the later phase. The effect of amino acids was slightly stimulatory, mainly evident as a shortening of the lag time.The degree of n-hexadecane degradation at the end of the experiment was correlated with the total concentration of organic compounds added to the soil.

Scientific relevance

There are a handful papers describing the potential of using organic amendments (often industrial by-products) with a content of both easily accessible carbon and micronutrients, to enhance the bioremediation of polluted soils. Enhanced biodegradation is often reported and the proposed explanations are that the combination of easily accessible carbon and micronutrients increases the degrading biomass.In this paper, we examine the effect of fermented whey on the degradation of n-hexadecane and correlate the observed effects on the biodegradation with the main components lactate, amino acids, lactose and B-vitamins. This has to our knowledge never been done before.     

炉渣与生物炭施加对稻田土壤产甲烷菌群落结构的影响

为了了解废弃物施加处理影响稻田甲烷排放通量的微生物学机制,对稻田分别进行炉渣、生物炭单一施加和混合施加处理,分析施加处理条件下早、晚稻拔节期稻田土壤的理化性质,并采用PCR-RFLP技术及克隆测序对稻田土壤中的产甲烷菌群落组成多样性及其结构进行分析。研究结果表明:早稻拔节期,混施处理显著提高土壤盐度和pH;晚稻拔节期,混施处理显著提高土壤盐度,炉渣和混施处理显著提高pH。香农-威纳指数(H')和辛普森指数(D)显示:炉渣、生物炭和混施处理提高了稻田土壤产甲烷菌的多样性。群落组成分析结果表明:稻田土壤产甲烷菌主要含有甲烷微菌目(Methanomicrobiales)、甲烷杆菌目(Methanobacteriales)、甲烷八叠球菌目(Methanosarcinales)、甲烷球菌目(Methanococcales)、甲烷胞菌目(Methanocellales)和Methanomassiliicoccales等6大类群,其中甲烷微菌目(Methanomicrobiales)为优势类群。从属水平的群落结构来看,与对照相比,3种施加处理均降低了早稻土壤Methanomassiliicoccus相对丰度;生物炭处理还降低了Methanosarcina相对丰度。初步认为Methanomassiliicoccus和Methanosarcina这2个菌属与CH_4排放量减少密切相关。     

Calcium sulfate or coal combustion by-product spread on the soil surface to reduce evaporation, mitigate subsoil acidity and improve plant growth

Removal of sulfur dioxide from flue gas produced by coal-burning power plants has increased the availability of by-products that may be useful as soil amendments for agriculture. We studied the effects of surface layers (caps) of fluidized bed combustion residue-fly ash mixture (FBCR-FA) or calcium sulfate on reduction of evaporative water losses and improvements in subsurface acid soil chemical characteristics. Caps 3.8 cm thick of porous FBCR-FA, hydrated commercial calcium sulfate (CCS), or soil (check) were placed on columns of coarse-loamy, mixed, mesic Umbric Dystrochrept soil of pH 4.2. After the addition of 40 cm of water during a 16-week period, mean daily water loss from the column with the FBCR-FA cap was 0.51 mm compared to 0.98 mm in the check. Mean increase in soil exchangeable Ca in the 5- to 40-cm depth for the CCS treatment was 0.83 cmol_c kg^–1 and mean pH (H₂O) increase was 0.21 units. Mean KCl-extractable Al decreased from 6.08 to 5.52 cmol_c kg^–1. Roots of sudangrass (Sorghum bicolor (L.) Moench) planted in the columns after removal of the caps reached 2 cm depth in the control, 18 cm in the FBCR-FA and 38 cm in the CCS treated columns after 47 days of growth. The gypsum cap was effective in improving deep rooting in acid soils and the FBCR-FA cap reduced evaporative water losses.Abbreviations FBCR-FA fluidized bed combustion residue-fly ash mixture - CCS hydrated commercial calcium sulfate - ICP inductively coupled plasma - GLM general linear models.     

Effect of Crinipellis perniciosa Infection on Abscission of Cacao Cotyledons, Reserve Mobilization and Dry Matter Partitioning

Infection by Crinipellis perniciosa on cacao seedlings prevented the abscission of cotyledons which normally abscise within 32–61 days from seed sowing. The early growth and development of control and artificially inoculated seedlings was investigated for root dry mass (RDM), shoot dry mass (SDM), shoot‐to‐root ratio (SRR), total dry mass (TDM), cotyledonary dry mass (CDM) and cotyledonary water content (CWC). Cotyledonary reserve mobilization was estimated at 69 and 56% at 5 weeks and 79 and 64% at 8 weeks in control and infected seedlings, respectively. Infection induced the enlargement of tissues but was not accompanied by an increase in dry mass. Infection both delayed and reduced the utilization of cotyledonary food reserves resulting in slower accumulation of RDM, SDM and TDM culminating in a reduction of growth by a factor of 1.6 at 8 weeks. However, the SRR of inoculated plants was similar to that of control plants, suggesting that the balance between the root and shoot systems exists which is unchanged by the effect of the pathogen. CWC was decreased upon senescence to an average of 65% at abscission. The prevention of cotyledonary abscission in infected seedlings is suggested to be due in part to the CDM remaining above a critical level of 20% of the initial CDM. The implication of this response in relation to the infection biology of the pathogen is discussed.