Nutrient content of the moist tropical forest of Ghana

Summary The total weight of vegetation on an area of just over 1 acre of old secondary forest in the moist forest zone of Ghana has been determined, and found to be equivalent to roughly 150 tons per acre dry weight. The nutrient content of each component of the vegetation was also determined and showed that the amounts of the major nutrients immobilised in the vegetation were: N, 1,800 lb./acre; P, 120 lb./acre; K, 800 1b./acre; Ca, 2,400 lb./acre; Mg, 350 lb./acre. The corresponding amounts of nutrients in the top foot of soil supporting the vegetation were: total N, 4,100 lb./acre; available P, 11 lb./acre; exchangeable K, 580 lb./acre; exchangeable Ca, 2,300 lb./acre; exchangeable Mg, 330 lb./acre. About half the nutrients stored in the vegetation were contained in readily combustible material, and except for N would be released to the soil if the forest were cleared and burnt for cultivation. The quantity of roots and the amounts of nutrients contained in them were not sufficiently great to make an important addítion to the nutrient supply in the soil during subsequent cultivation. Of the total quantity of roots supporting the vegetation 85.5 per cent by weight were within 1 foot of the soil surface.     

THE CONTROL OF POTATO VIRUS DISEASES BY INSECTICIDES

Replicated trials were carried out in the years 1950, 1951, 1953 and 1954 to see if the spread of leaf-roll virus and virus Y in potato crops could be reduced by applying insecticides. The crops were disease-free, except for small numbers of deliberately introduced infected plants, and were sprayed at intervals of 10 or 14 days, according to the stage of growth of the plants, with a tractor-mounted spraying machine at 1OO gal./acre/application. Disease spread was estimated by growing tubers taken from the five plants on either side of each infector. DDT emulsion, DDT suspension, endrin, schradan, mipafox, malathion, parathion and Systox prevented the spread of leaf-roll virus and decreased the spread of virus Y, although DDT emulsion was the only insecticide used in all the trials. Dieldrin and toxaphene were ineffective. When virus control was successful, aphid control (estimated by counting apterae in the crops) was good.     

THE PRACTICAL CONTROL OF WIREWORM BY γ-BENZENE HEXACHLORIDE ('GAMMEXANE'): COMPARISONS WITH DICHLORODIPHENYLTRICHLORETHANE (D.D.T.)

Benzene hexachloride containing 13% of the insecticidally active gamma isomer known as 'Gammexane' has been used successfully in a considerable number of field trials in the control of wireworm. On heavily infested land the effective dosage rates associated with an appreciable reduction in wireworm population, and giving a marked improvement in plant establishment and substantial increases in yield, range between 1 and 6 lb./acre (2–12 oz./acre of Gammexane), on oats and wheat. The effective dosage rates vary and depend upon whether the insecticide is combine-drilled, broadcast, or applied as a seed dressing.
Although D.D.T. applied by similar methods was associated with similar reductions in wireworm population, the use of this insecticide resulted in smaller yield increases.     

The phytotoxicity of D.D.T. and of benzene hexachloride

Spraying with two preparations of D.D.T. had a negligible effect on the maturation of outdoor tomatoes and of summer cabbage. Spraying with a commercial D.D.T. suspension damaged cucurbits and treatment with the suspension base distorted glasshouse cucumbers during one season only.
Benzene hexachloride (B.H.C.) sprays did not affect the yield or flavour of tomatoes, but, at concentrations higher than those normally used, they severely scorched radish, turnip, swede, kale, spinach and beetroot seedlings. The application of B.H.C. dusts stunted seedlings of radish.
On one occasion young potato foliage was damaged by relatively high concentrations of two compounded B.H.C. sprays and by B.H.C. dust but late-season older foliage was unaffected. A spray compounded from B.H.C. dispersible powder caused tainting of potatoes, peas, carrots, beetroot, marrows, cauliflowers and lettuce. Apples and plums treated with B.H.C. spray preparations developed a taint after cooking.     

EFFECTS OF CULTURAL TREATMENTS ON WHEAT AND ON THE INCIDENCE OF EYESPOT, LODGING, TAKE-ALL AND WEEDS. Field Experiments 1945–8

An experiment was made on the fourth, fifth and sixth successive crops of winter wheat to determine the effects of various treatments on the troubles which result from close cereal cropping. Eyespot and lodging were prevalent in the first year (1946); weeds in the second; eyespot, lodging, take-all and weeds in the third.
Spraying with H₂SO₄ reduced the incidence of eyespot, lodging and weeds, and increased yield of grain on plots which received sulphate of ammonia (by 2.7, 2.2 and 10.0 cwt./acre in successive years).
Sulphate of ammonia increased the incidence at harvest of eyespot and lodging, reduced take-all and consistently increased yield of straw. Eyespot and lodging reduced the effect of the fertilizer on yield of grain, take-all increased it.
Increase in seed rate increased the incidence of severe eyespot and of take-all; it increased lodging except when plants were dwarfed by take-all.
Weight of straw and percentage straws with severe eyespot lesions independently affected lodging, together accounting for 51% of the variance in percentage area lodged at harvest and 64 % of that lodged 33 days earlier.
Mean yields of grain on untreated plots sown with 3.3 1/2 bushels seed/acre fell from 26.0 to 22.5 to 11.7 cwt./acre in successive years, whereas yields of 28.4, 29.9 and 29.1 cwt./acre were obtained on sprayed plots sown with 1 1/2.2 bushels seed/acre which received 4 cwt./acre sulphate of ammonia, showing that high yields were maintained when eyespot, lodging, take-all and weeds were controlled.
By 1948 yields of grain on unsprayed plots had fallen to the level of those on similarly manured plots on the continuous wheat experiment on Broadbalk field. Spraying increased grain by amounts similar to those resulting from one year's fallow on Broadbalk; but fallow had its greatest effects on plots with low nitrogen, spraying on those with high nitrogen.     

Wireworms and the sugar-beet crop; field trials and observations

Observations on wireworms in the sugar-beet crop during 1937–40 indicated the importance of alternative food, such as buried turf, weeds, excess seedlings and interdrilled wheat in determining the degree of injury to the crop.
In 1938, out of thirty-six recorded fields growing sugar beet after ploughed-up grass only one suffered severe wireworm damage. Six of these fields were selected for resowing with sugar beet in 1939, and all suffered moderate or severe attacks. Several other fields in their first year from grass showed only slight damage. These observations were supported by an analysis of the Norfolk War Agricultural Committee crop records for 1940.
Seven trials were carried out in 1939 to determine the effect of increasing the seed rate from normal (about 14–16 lb./acre) to 17–25 lb., and of interdrilling with wheat. In three trials, increasing the seed rate gave significantly higher plant populations before singling. It gave significant increases after singling in one out of two trials. However, in the one trial harvested the increase in 'washed beet' was only 7.6% and 'total sugar' 15%. Interdrilling with wheat at 40–70 lb./acre gave significant increases in the plant population before singling in three out of five trials, and after singling in three out of four trials. Increased plant populations both before and after singling were obtained in two other trials with alternating treatments. Increased seed rate and interdrilled wheat together gave greatly improved plant populations before singling in each of two trials and after singling in the one trial where such an observation was possible.     

Water and Nitrogen Uptake in Upland and Swamp Rice

The water uptake per unit dry matter and nitrogen uptake perunit water absorbed of swamp rice (Dima) and upland rice (Kindinga)at three nitrogen levels equivalent to 23.6, 70.8, and 118,kg./ha. (20, 60 and 100 lb./acre) respectively were studiedunder tropical green-house conditions in Trinidad. The water uptake per unit dry matter produced was significantlygreater in Kindinga than in Dima at the three nitrogen levels.Additional nitrogen increased the water requirement of Kindingabut decreased that of Dima, the greater increase in Kindingabeing attributed to increase in leaf area. The efficiency of nitrogen absorption in terms of water transpiredwas greater in Dima than in Kindinga at the three nitrogen levels.     

Laboratory and field tests in 1966-67 on chemical control of wireworms (Agriotes spp.)

Of sixteen compounds applied to soil in laboratory tests, azinphos-ethyl, P2188 (O,O-diethyl S-chloromethyl phosphorothiolothionate), ‘Dursban’ (O,O-diethyl O-3,5,6-trichloro-2-pyridyl phosphorothioate), P1973 (S-(N-methoxycarbonyl-N-methylcarbamoylmethyl) dimethyl phosphorothiolothionate), B77488 (O,O-diethylphosphorothioate O-esterwith phenylglyoxylonitrile oxime) and R42211 (O,O-diethyl O-(2-diethylamino-6-methyl-pyrimidin-4-yl) phosphorothioate) killed wireworms when first tested, but in second tests with the same soils only ‘Dursban’, P2188 and B77488 did so. Treating seeds with ‘Dyfonate’ (O-ethyl S-phenyl ethyl phosphonodithioate) or with ethion/γ-BHC mixtures killed few wireworms. Three field trials compared the organophosphorus insecticides ‘Dursban’, ‘Dyfonate’ and phorate with organochlorine standards. In trials with barley and potatoes the standard was 3 lb a.i./acre (3·36 kg/ha) of aldrin. The organophosphorus compounds increased plant stands of barley almost as much as aldrin, although they killed fewer wireworms; and they protected fewer potato tubers from wireworm damage. The third trial compared the organophosphorus compounds with 0·5 lb a.i./acre (0·56 kg/ha) γ-BHC sprayed on a site drilled with sugar beet seed dressed with dieldrin. The γ-BHC increased plant stands almost as much as did 3 lb a.i./acre of the organophosphorus insecticides, and killed as many wireworms.     

Effect of different soil types,pH and phosphorus levels on the wheat seedling and the incidence ofPythium graminicolum

Summary In the present study, the effect of different types of soil, pH and phosphorus levels on root, shoot development and browning extent on shoot of wheat seedlings growth in soil inoculated withPythium graminicolum; was studied. Out of the four soil types the development of root and shoot was better in Domatta soil where as the disease development was more in black clay soil. The pH values below 5.5 and above 8.0 are favourable for the root and shoot development whereas these values are unfavourable for the development of the Pythium and consequently for infection by it. The percentage of browning of the collar region was more in soils near neutral (pH 6.5–7.1) and it was less in acidic (pH 5.0) or alkaline (pH 8.6) soils. The development of wheat roots and shoot in soil with 30 lb/acre phosphorus was good as compared to that in soil with P₀, P_15,45 and P₆₀ lb/acre in inoculated soil. The percentage of extent of browning on collar region was less at 15 lb and 30 lb/acre P, due to less development of the disease.     

Further experiments on the control of white rot (Sclerotium cepivorum Berk;) in onions, shallots and leeks

Trials in 1945 confirmed earlier work on the efficacy of mercurous chloride (calomel) for the control of Sclerotium cepivorum in spring-sown onions. The application of 1 lb. 4% calomel dust to 50 yd. of seed drill at sowing time gave sufficiently good control of the disease in salad onions. Broadcast application of 1 oz. 4% calomel dust per sq.yd. before sowing was less effective but promising. Post-emergence application of the dust was useless. In autumn sowings, seed-drill treatment at 1 lb./so yd. controlled the disease in the following spring, but caused severe retardation and loss of crop.
Onion seedlings raised in heat and dipped in an aqueous paste of calomel dust before transplanting showed a high degree of resistance to a severe attack. Similar treatment of shallot bulbs was also effective. In both cases, the treatment substantially increased the yield and somewhat reduced storage losses.
Leek seedlings transplanted into dibber holes did not develop the disease.     

Field trials with D-D mixture against potato-root eelworm

A D-D mixture has been tested against Heterodera rostochiensis at seven 2-acre sites on sands, silts and blackland soils. Apart from a pilot trial where soil was injected in spring, injections were carried out in the autumn, and potatoes were grown the following year. Factors investigated were rate of application (0, 200, 400 and 800 lb. D-D/acre), depth of injection (4 or 8 in.) and the effect of rolling after injection. At the most responsive of the sites (Wainfleet), increases in yield, kill, and the post-crop eelworm population were all roughly proportional to the rate of application. Under favourable circumstances a 50% increase in yield and something like a 50% reduction in eelworm population 4 weeks after injection can be expected from 800 lb./acre, but the reduction is more than made good during the growth of the subsequent crop; accelerated multiplication of eelworm on the treated plots leads to their having a larger population than the untreated controls at lifting time. Of the sites tested, the blackland soils gave a lower eelworm kill and a much lower yield increase from D-D than silts or sands. After autumn injection the nematocidal, and probably the phytocidal, effects of D-D persist in the soil for many weeks. The hypochlorite method of 'hatching' eelworm larvae for counting has proved unreliable.     

The effects on soil fauna of insecticides tested against wireworms (Agriotes spp.) in wheat

The organophosphorus insecticides Bayer 38156 (O-ethyl S-p-tolyl ethyl phosphonodithioate), trichloronate, Stauffer N 2790 (O-ethyl S-phenyl ethyl phosphonodithioate), thionazin and fenitrothion were compared with aldrin, dieldrin and γ-BHC for their effects on soil fauna, particularly wire-worms, and on crop yields in 1964 and 1965. At 1·5 lb active ingredient/acre, none of the organophosphates had as great an effect on wireworms as an aldrin spray at 2·25 lb a.i./acre or a dieldrin seed dressing at 2·25 lb a.i./acre. Some treatments significantly increased and some significantly decreased numbers of mites and Collembola. Except for Allolobophora chlorotica in plots treated with Bayer 38156, earthworm numbers were greater in plots sprayed with Bayer 38156 or aldrin, or sown with dieldrin-dressed seeds, than in untreated plots. In May 1964, one month after sowing, untreated plots had significantly fewer plants than plots sprayed with aldrin, trichloronate or Bayer 38156, or sown with γ-BHC or dieldrin-dressed seeds, but yields from untreated plots at harvest were high for such a large wireworm population and did not differ significantly from yields of treated plots in either year. The persistence of thionazin and Bayer 38156 in treated plots was measured by a bioassay using Collembola. Bayer 38156 was detected in plots 1 month after spraying but not after 6 months. Thionazin left detectable residues 1 month after spraying in the two acid plots but not in the two alkaline plots. More frequent samples taken from thionazin-treated plots in 1965 showed a similar pattern of persistence, and laboratory tests, using soil mixed with various amounts of powdered calcium carbonate, confirmed that thionazin persisted longer in more acid soils.     

The action of some systemic aphicides on the nymphs of Anthocoris nemorum (L.) and A. confusus Reut

The aphicides phorate, dimethoate and menazon were compared to elucidate the different pathways by which they can affect Anthocoris nymphs and their aphid prey.
When nymphs were caged in contact with deposits on bean leaves phorate and dimethoate had contact LC 50s of 20 and 3 μg/cm² respectively to Anthocoris nemorum and 46 and 6 μg/cm² to A. confusus. When the nymphs were confined on treated leaves on the opposite surface to the deposits, neither phorate nor dimethoate killed them. Menazon did not kill anthocorids at any dosage. All three aphicides killed over 50% of Acyrthosiphon pisum (Kalt.) on bean leaves at 1.6 μg/cm² whether the aphids were on the treated or untreated surface.
Experiments with ³⁵S-labelled phorate showed that anthocorids confined on phorate-treated bean plants, with or without insect food, accumulated the insecticide or its labelled derivatives. In field experiments in which A. nemorum were caged on plants treated with phorate, many were killed on young newly treated plants but not on older plants. A. confusus was relatively unaffected.
Anthocorids were reared from 2nd-instar nymphs to adults on aphids killed systemically with phorate, dimethoate or menazon without ill effects, despite evidence that ³⁵S-labelled phorate was ingested from the aphids and excreted in the faeces.
In the field, fewer large A. nemorum nymphs were found in August in plots of tick beans treated with phorate granules at 6 lb/acre (6.7 kg/ha) when sown, than in plots treated at 1.5 lb/acre (1.7 kg/ha) with phorate or menazon or untreated plots.     

Fate of Bacillus sphaericus 1593 and 2362 spores used as larvicides in the aquatic environment.

Dry powders produced from insecticidal Bacillus sphaericus strains 1593 and 2362 were applied against Culex tarsalis and Anopheles franciscanus mosquito larvae in small-plot field trials. Good control of C. tarsalis, but not of A. franciscanus, was produced at 0.1 and 0.2 lb/acre [ca. 0.122 and 0.244 kg/ha]. B. sphaericus spores settled rapidly from upper water layers and accumulated in bottom muds. Control of third/fourth-instar C. tarsalis larvae was maintained through day 4 after testing and was related to the presence of at least 100 spores per ml in the upper water layer 2 days earlier. B. sphaericus was shown to recycle in dead larvae both in the laboratory and in the field, producing an increase of 100- to 1,000-fold in spore numbers. There was no evidence of recycling in treated water nor of significant spore persistence upon reflooding of ponds after a very hot, dry period.     

The production of a phytotoxin,nectrolide, by some root-surface isolates ofCylindrocarpon radicicola,Wr.

Summary A phytotoxic compound, for which the name nectrolide has been proposed, was isolated fromCylindrocarpon radicicola. Analysis of nectrolide and its physical and chemical properties show that the compound is identical with brefeldin A, an antibiotic produced byPenicillium brefeldianum.Twenty different isolates ofC. radicicola from plant roots were examined for their ability to produce nectrolide in liquid culture. Twelve of these yielded nectrolide at concentrations varying from 31 to 82 µg per ml when grown for 14 days on Czapek-Dox liquid medium. Eight isolates did not yield the metabolite in culture.At a concentration of 6 µg per ml nectrolide arrested the growth of germinated blackbutt seedlings, whilst at lower concentrations (2–4 µg per ml) the compound caused severe stunting and blackening of the roots of seedling plants. Nectrolide watered onto blackbutt seedlings growing in forest soils can be detected in the roots after 24 hrs. The compound has been crystallised from ether extracts of tomato roots supplied with pure nectrolide and can be detected in stem tissues within 24 hours of watering it onto the roots.As a result of the widespread association ofC. radicicola with unthrifty plants and the phytotoxic nature of nectrolide, it is suggested that this compound may function in a number of plant diseases, the causes of which have not been elucidated.     

The composition of the leachate through cropped and uncropped soils in lysimeters compared with that of the rain

Summary The composition of the leachate from undisturbed monolith lysimeters cropped with white clover or meadow fescue or maintained bare was compared with that of the rain falling on them. No nitrogen fertilizer was applied only an initial dressing of phosphorus and potassium. The grass received much more nitrogen from the rain than it lost by leaching whereas the clover lost more than it received. Most of the leached nitrogen was NO₃-N - 92 per cent on the bare soil and 90 per cent on the clover. About 27lb nitrogen per acre (30 kg/ha) per year was drained from the actively growing clover sward rising to about 117lb N/acre/year (131 kg/ha) when the clover died or was removed. Only 2.3lb/ac (2.5 kg/ha) was drained from the actively growing grass sward. It was estimated that the clover fixed at least 270lb N/ac/year (303 kg/ha/year. The rates of leaching of potassium from a grass sward was about 1.7lb/ac/year (1.9 kg/ha) and 0.8 lb (0.9 kg) phosphorus. The quantities were similar for clover. The grass received from the rain more phosphorus and potassium than was leached but only 60 per cent of the calcium and 13 per cent of the magnesium, similar results being obtained with white clover. During the year of establishment of the grass sward there was evidence of loss of gaseous nitrogen (elemental and/or compound) from the soil: subsequently the nitrogen content of the soil slowly increased. Calcium loss from the bare soil with an average rainfall of 26″ (650 mm) was about 100 lb Ca/ac/year (112 kg/ha).     

Thermal acclimation of photosynthesis in black spruce [Picea mariana (Mill.) B.S.P.

We investigated the thermal acclimation of photosynthesis and respiration in black spruce seedlings [ Picea mariana (Mill.) B.S.P.] grown at 22/14 °C [low temperature (LT)] or 30/22 °C [high temperature (HT)] day/night temperatures. Net CO₂ assimilation rates ( A _net) were greater in LT than in HT seedlings below 30 °C, but were greater in HT seedlings above 30 °C. Dark and day respiration rates were similar between treatments at the respective growth temperatures. When respiration was factored out of the photosynthesis response to temperature, the resulting gross CO₂ assimilation rates ( A _gross) was lower in HT than in LT seedlings below 30 °C, but was similar above 30 °C. The reduced A _gross of HT seedlings was associated with lower needle nitrogen content, lower ribulose 1·5-bisphosphate carboxylase/oxygenase (Rubisco) maximum carboxylation rates ( V _cmax) and lower maximum electron transport rates ( J _max). Growth treatment did not affect V _cmax :  J _max. Modelling of the CO₂ response of photosynthesis indicated that LT seedlings at 40 °C might have been limited by heat lability of Rubisco activase, but that in HT seedlings, Rubisco capacity was limiting. In sum, thermal acclimation of A _net was largely caused by reduced respiration and lower nitrogen investments in needles from HT seedlings. At 40 °C, photosynthesis in LT seedlings might be limited by Rubisco activase capacity, while in HT seedlings, acclimation removed this limitation.     

Isolation,Structures and Biological Activities of Colletotrichins,Phytotoxic Substances from Colletotrichum nicotianae

From the phytopathogenic fungus, Colletotrichum nicotianae, three phytotoxic substances have been isolated and named colletotrichin, colletotrichins B and C (1, 2 and 3). The structures of these compounds have been elucidated from the physical and chemical evidence. When applied on the tobacco leaves, colletotrichins induced the symptom similar to that of the tobacco anthracnose caused by C. nicotianae. The compounds were also toxic to the lettuce and rice seedlings.     

Importance of timing,spore concentrations,and levels of spore carrier in applications of Nosema locustae (Microsporida: Nosematidae) for control of grasshoppers

In a study of microbial control of grasshoppers, Nosema locustae was applied to 10-acre plots in 2 replications of 24 treatment combinations in which the factors were (1) times of applications: 4 applications spaced over 22 days; (2) concentrations of spores: 1, 30, and 900 spores/in²; and (3) levels of the spore carrier: 1 and 4 lb wheat bran/acre. The concentrations of spores had the most effect in reducing the densities of grasshoppers and the incidence of infection among the survivors at the last sampling (coincided with the initiation of oviposition), the average reduction in density attributed to application of 1 spore/in² was 21%, that attributed to 30 spores/in² was 46%, and that attributed to 900 spores/in² was 73%. The first and second applications caused the greatest reductions in density; the second, third, and fourth applications produced the highest incidence of infections. Also, a higher incidence of infection was observed among grasshoppers from plots treated with 30 spores/in² on 1 lb bran/acre than from plots treated with 30 spores/in² on 4 lb of bran/acre. Therefore, a ratio of about 0.63–0.94 billion spores/lb bran applied at a rate of 1–1.5 lb/acre (= 100–150 spores/in²) at the time when the principal early summer species are third-instar nymphs would have resulted in overall reductions in density of 50–60%, with 35–50% of the survivors sufficiently infected so that fecundity would probably be affected. The reductions and incidence of infections would be higher in species that readily accept and use wheat bran, among which are some of the more economically important species of grasshoppers.     

Internode length in Lathyrus odoratus. The involvement of gibberellins

Evidence was obtained by gas chromatography-mass spectrometry and gas chromatography-selected ion monitoring for the presence of gibberellin A₂₀), GA₁, GA₂₉, GA₈ and 2-epiGA₂₉ in vegetative shoots of tall sweet pea, Lathyrus odoratus L. Both tall (genotype L –) and dwarf (genotype II ) sweet peas elongated markedly in response to exogenous GA₁ attaining similar internode lengths at the highest dose levels. Likewise internode length in both genotypes was reduced by application of the GA biosynthesis inhibitor, PP333. The ratio of leaflet length to width was reduced by application of PP333 to tall plants and this effect was reversed by GA₁. When applied to plants previously treated with PP333, GA₂₀ promoted internode elongation of L – plants as effectively as GA₁, but GA₂₉ was not as effective as GA₁ when applied to II plants. In contrast, GA₂₀ and GA₁ were equally effective when applied to the semidwarf lb mutant but GA-treated lblb plants did not attain the same internode length as comparable GA-treated Lb – plants. The difference in stature between the tall and dwarf types persisted in dark-grown plants. It is concluded that GA₁ may be important for internode elongation and leaf growth in sweet pea. Mutant l may influence GA₁ synthesis by reducing 3β-hydroxylation of GA₂₀ whereas mutant lb appears to affect GA sensitivity.