Hyphal density as a measure of suppression of Gaeumannomyces graminis var. tritici on wheat roots

Runner hyphae of Gaeumannomyces graminis (Sacc.) Arx & Olivier var. tritici Walker on seminal roots of wheat seedlings were photographed and their length measured. As well, their length was estimated using the line-intercept method. The correlation of 0.904 between measured and estimated lengths of hyphae was highly significant. This line intercept method was used to estimate the density (length/unit area) of hyphae on roots of plants growing in the presence and absence of a soil suppressive to G. graminis var. tritici. Estimations were made eight times during 28 days growth at 15°C. In fumigated soil (non-suppressive) inoculated with 0.1% ground oat grain infested with G. graminis var. tritici, the density of hyphae on roots started to increase at five days compared with 15 days when soil there was a 10.8% cover of the root surface after 15 days when the hyphae had reached maximum density. Suppression to G. graminis var. tritici is normally detected by a difference in disease rating of roots at 28 days but this study has shown that suppression can be demonstrated by the difference in the density of hyphae if roots are examined between seven and 19 days.     

A device to study metabolic gases in the rice rhizosphere

A simple apparatus was developed to study metabolic gases in the rice rhizosphere. With this device, a positive rhizosphere effect of rice was demonstrated on three soil microbial activities: N₂ fixation, CH₄ formation and denitrification.     

Acetylene inhibition of nitrous oxide reduction and measurement of denitrification and nitrogen fixation in soil

Reduction of N₂O in moist soil was inhibited completely by 10^?2 atm C₂H₂ and partially by 10^?5 atm C₂H₂. The effect of C₂H₄ was 10⁴ times less than that of C₂H₂. Denitrification of NO^?₃ occurred in anaerobically or aerobically incubated waterlogged soil and in anaerobic but not in aerobic moist soil. In the absence of C₂H₂ there was transient accumulation of N₂O. In the presence of C₂H₂ there was stoichiometric conversion of NO^?₃ to N₂O. Some kinetics of the reduction of N₂O and of NO^?₃ to N₂O are presented. Denitrification of 1 μg added NO^?₃-N.g^? could be measured within 1 h. Stoichiometries of production of N₂O from NO^?₂ and NO^?₃, respectively, and production of CO₂ attributable to denitrification were consistent with reported energy yields. Reduction of C₂H₂ to C₂H₄ occurred immediately following complete denitrification of added NO^?₃. The incubation of soil in the presence and in the absence of C₂H₂ thus permits assay of both denitrification and N₂ fixation and provides information on the mole fraction of N₂O in the products of denitrification.     

Patterns of energy use and the critical choices ahead

Patterns of energy use in the U.S. by industry, commerce, residential and agriculture with comparisons of Northern and Central California energy use in the same sectors are presented. End-use applications are also covered.     

The spread and development of Rhododendron ponticum L. on dunes at Winterton,Norfolk, in comparison with invasion by Hippophaë rhamnoides L. at Saltfleetby,Lincolnshire

A survey was made in 1972, of the status of Rhododendron pronticum L. at Winterton, Norfolk, and aerial photographs were used to assess its spread in recent years. The ecological implications of the continuing presence of this invsive alien shrub on the dunes are discussed. Comparisons with the highly successfull dune shrub Hippophaë rhamnoides L. help put into perspective the present and likely future role of Rhododendron at Winterton. The implications of controls are discussed together with methods by which this may be achieved.     

Zur pedochemie des berylliums — untersuchungen einer bodengesellschaft im gebiet des bärhaldegranits (südschwarzwald)

The profile distribution of Be is given for a toposequence of podzols, brown earths, stagnogley, forest bog and “Ockererde” (slope gley with infiltrated Al, Mn and Fe). Analysed were the parent rock, fine earth, four fractions of mineral soil (fine skeleton, sand, silt, clay) and the needles of spruce trees.Beryllium is involved in selective weathering processes of elements. Accordingly, the Be-content increases from the fine skeleton to sand, rock, silt and clay, progressively. Through pedogenetic enrichment, Be accumulates in the mica-rich silt fraction.Uptake of Be by spruce is very low even from these acid soils. The accumulation in the needles becomes greater with increasing age.The pedochemical behaviour of Be is very similar to that of Al.Be is incorporated very little in the organic matter cycle, and is therefore not enriched in the soil humus.The brown earth has lost Be, especially in the A_h-horizon.In the A_e-horizon of the podzol, loss of Be is even greater; the loss is partly offset by Be-enrichment in the B-horizon.In the profiles of depressions, the Be-content is high and is ascribed to lateral flow from the slopes. Be-enrichment is especially high in horizons with a pH of about 5.The Be-balance of the watershed indicates an export of about 10% of the original amount.     

Survival of sclerotia of Macrophomina phaseolina and Sclerotium cepivorum after drying and wetting treatments

Exposure of sclerotia of Macrophomina phaseolina to 0 and 33% relative humidity (r.h.) for 12 weeks and of Sclerotium cepivorum to 0, 33 and 55% r.h. for 20 weeks did not reduce their germinability on agar. Exposure to 78% r.h. caused high loss of germinability in M. phaseolina and complete loss in S. cepivorum. After 7-day exposures respective moisture contents of sclerotia of M. phaseolina and S. cepivorum were 1 and 2% at 0% r.h.; and 10 and 14% at 78% r.h. M. phaseolina sclerotia held at 0% and 33% r.h. in desiccators for several times up to 12 days did not decrease in subsequent survivability in moist soil, unlike sclerotia held at 78% r.h. for 4 days.More sclerotia of M. phaseolina were colonized by fungi and Streptomyces spp. on alkaline soil than on acid soil. On alkaline soil twice as many sclerotia were colonized after exposure to 0% r.h. as after exposure to 33, 55 and 78% r.h. Colonization of S. cepivorum sclerotia was as high on acid as on alkaline soil and 3 times as high on sclerotia treated at 0% r.h. as on those treated at higher r.h. Attempts to ascertain the effects of colonization on sclerotial viability were unsuccessful. Incubation of sclerotia of M. phaseolina in moist Rumsford sandy loam (50% m.h.c.) for 20 weeks reduced survivability by 43%. At room temperature, alternate drying and wetting of soil containing sclerotia did not appreciably affect survivability of either pathogen. Survivability of S. cepivorum sclerotia was highest when the sclerotia were incubated in air-dried soil (2–3% m.h.c.) for 20 weeks.Incidence of white rot on onion seedlings transplanted to S. cepivorum-infested soil was higher in soil that had been air-dried for 20 weeks than in soil that had been alternately wetted and dried. Sclerotia that were exposed to 0% r.h. for 7 days before soil incubation produced little white rot.     

The effect of urea on the voluntary intake by calves of silages preserved with formaldehyde and formic acid

Perennial ryegrass cv. S23 was preserved by fermentation (C), or with the addition of 8.7 1 formalin (35% w/w formaldehyde) per t fresh herbage (F) or of 9.0 1 equal mixture (by vol.) of formalin and formic acid (85% w/w solution) per t fresh herbage (FF). These three silages comprised the treatments in a three-period, crossover design in which urea (u) was given at the rate of 20 g per kg dietary DM to half the animals. Twelve calves were allocated to the treatment sequences when they were approximately 12 weeks of age from within groups which had previously received diets with or without urea. Calves ate significantly (P< 0.001) less of silages F or FF than of silage C when each was offered alone, but when urea was given, intakes of silages F and FF were significantly (P < 0.001) increased such that the intakes of all three silages with urea were similar (23.6, 19.6, 19.3, 24.2, 24.2, 24.7 ± 0.51 g DM per kg LW for C, F, FF, Cu, Fu and FFu, respectively). Significantly (P<0.01) more of the DM in silage C was digested than in F or FF and the addition of urea significantly (P<0.05) increased the digestibility of DM from silage FF only (73.8, 71.3, 69.8, 74.6, 70.7, 72.5 ± 0.72% for C, F, FF, Cu, Fu and FFu, respectively). When the silages were given alone, calves spent longer eating and ruminating per kg DM ingested with F or FF than with C. The time spent on F and FF was significantly (P<0.01) reduced by the addition of urea (303, 388, 411, 297, 299, 290 ± 18.9 min per kg DM ingested for C, F, FF, Cu and Fu and FFu, respectively). The results presented suggest that urea partially alleviated the reduction in voluntary intake by calves given herbage preserved using formalin, but the mode of action was not clear.     

Nitrogen fixation by white clover in hill pasture

An experiment is described in which the amount of nitrogen fixed by the white clover component of a surface-sown hill sward was determined using small quantities of ¹⁵N-labelled ammonium sulphate. Between 11 July and 22 August 1974 25 kg ha^?1 N was fixed. No evidence of a transfer of N from clover to the associated perennial ryegrass was detectable over this period although the N content of the grass growing with the clover was higher. The relative advantages of the isotope technique and the acetylene reduction assay are discussed.