Showing papers in "Plant and Soil in 1970"

Nodulation ofMedicago sativa in solution culture

Abstract: Calcium and hydrogen ions interacted on nodulation. Increasing acidity from pH 5.6 to pH 4.8 increased the calcium concentration required to nodulate 50% of the plants, from 0.1 mM to 6 mM. Calcium concentration below 0.2 mM or pH below 4.8 inhibited nodulation at all tested levels of the other variable. Root extension and root-hair production were insufficiently affected by calcium or pH to explain reductions in nodule numbers.

The effect of nutrient deficiencies on phosynthesis and respiration in spinach

Abstract: Spinach plants were grown in nutrient-culture solutions containing reduced levels of all the macro- and micro-nutrient elements except cobalt and chlorine. The rates of photosynthesis (carbon dioxide fixation in the light expressed on a per unit chlorophyll or per unit fresh-weight basis) and respiration (carbon dioxide evolution in the dark expressed on a per unit nitrogen or per unit fresh-weight basis) for whole plants were measured using infra-red gas analysis techniques. Measurements were made when the plants displayed clear symptoms of deficiency relative to control plants. All nutrient deficiencies except iron and molybdenum depressed photosynthesis when chlorophyll was the basis of calculation; manganese-, copper-, phosphorus- and potassium-deficient plants showed the greatest depression. Alternatively when photosynthesis was calculated on a fresh weight basis calcium was the only deficiency which had no affect. Similarly when respiration was calculated on a nitrogen basis all deficiencies except iron, molybdenum and nitrogen result in depressed rates but when respiration was expressed on a fresh-weight basis potassium deficiency resulted in enhanced respiration rates and nitrogen, phosphorus, sulphur, manganese, zinc and molybdenum deficiencies resulted in reduced respiration rates.

Root hairs and phycomycetous mycorrhizas in phosphorus-deficient soil.

Abstract: Coprosma robusta formed phycomycetous mycorrhizas in unsteamed forest soil and grew equally well with or without added phosphate. In steamed soil it did not grow unless phosphate was added. Of the other species tested (Leptospermum scoparium, Solanum nigrum, Lolium perenne, Hakea enkiantha, Histiopteris incisa, Marchantia berteroana) most formed mycorrhizas in unsteamed soil, but all grew better in steamed soil. The dry matter of the mycorrhizal Coprosma seedlings contained the highest concentration of phosphorus, but the relatively large plants that the other species produced in steamed soil contained a greater total quantity. It is suggested that this entered mainly through their extensive root hairs (or rhizoids), and that lack of root hairs in Coprosma and other woody species explains their need for added phosphate when mycorrhizas are not formed.

The preparation and use of legume seed inoculants

Abstract: p a ge 1. I n t r o d u c t i o n . . . . . . . . . . . . . . . . . . . . . . . 675 2. P r e p a r a t i o n of the peat carrier . . . . . . . . . . . . . . . . 676 3. P r e p a r a t i o n of broth cultures . . . . . . . . . . . . . . . . . 681 4. C o n d i t i o n s of g r o w f h in the fermenter . . . . . . . . . . . . 682 5. M i x i n g of the broth culture with peat . . . . . . . . . . . . 683 6. Factors affecting survival and g r o w t h in p e a t d u r i n g s f o r a g e . . . 685 7. Quality control . . . . . . . . . . . . . . . . . . . . . . 687 8. S t r a i n selection and testing . . . . . . . . . . . . . . . . . 688 9. S u m l n a r y of the stages in the produetion of peat-based legume inoculants . . . . . . . . . . . . . . . . . . . . . . . . . 695 10. Seed inoculation . . . . . . . . . . . . . . . . . . . . . . 696 11. M e t h o d of p e l l e t i n g s e e d . . . . . . . . . . . . . . . . . . 697 12. General conclusions . . . . . . . . . . . . . . . . . . . . 699 13. A e k n o w l e d g e m e n t s . . . . . . . . . . . . . . . . . . . . . 700 14. R e f e r e n c e s . . . . . . . . . . . . . . . . . . . . . . . . 700

Plant-endophyte symbiosis in non-leguminous plants

Abstract: A wide taxonomic range of non-leguminous dicotyledonous plants bear root nodules and are able to fix atmospheric nitrogen. These plants belong to the orders Casuarinales, Myricales, Fagales, Rhamnales, Coriariales, and Rosales. Actinomycetes are involved in the root-nodule symbiosis.

Evaluation of effectiveness in mutant strains of Rhizobium by acetylene reduction relative to other criteria of N2 fixation.

Abstract: The feasibility of the acetylene reduction technique for evaluation of comparative effectiveness inRhizobium was tested inR. leguminosarum, R. trifolii, andR. meliloti with strains which were closely related but differed widely in effectiveness. Several variables in sampling and handling of nodules were found to introduce significant error into this sensitive assay. Freezing of nodules destroyed all reducing activity. Removal of nodules from the roots, storage of detached nodules for several hours before assay, and the dry-wet condition of nodules during assay contributed to lowered ethylene production. The time pattern of appearance, increase, and decline of acetylene reducing activity paralleled that of leghemoglobin content in effective pea nodules assayed at different stages of development. In a comparison of strains from all 3 species, there was generally good agreement between the rate of acetylene reduction (assayed at a stage of peak activity for effective nodules only) and plant dry weight, plant nitrogen, or visual ratings of effectiveness. Several exceptional mutants which were rated as partly effective on the basis of nodule type or leghemoglobin content showed little acetylene reduction or N2 fixation. Suitability of the acetylene assay for strain comparison and the question of units of comparison with other criteria of N2 fixation are considered.

The supply of nutrient ions by diffusion to plant roots in soil III. Uptake of phosphate by roots of onion, leek, and rye-grass.

Abstract: SummaryMeasurements were made of the diffusion of P32-labelled phosphate to single roots of onion, leek and rye-grass growing in an Upper Greensand sandy loam (UGS) and a Coral Rag Clay (CRC) to which different amounts of phosphate had been added. Concentration-dependent diffusion coefficients for phosphate ions in the soils were calculated from phosphate desorption isotherms in calcium chloride. The experimental uptake by roots of known dimensions was compared with supply expected by diffusion to a cylindrical model root of the same dimensions. Allowance was made for absorption by the root hairs on rye-grass roots.Phosphate absorption by a cm length of intact root was found to continue for at least 16 days for onion, 10 days for leek and 5 days for rye-grass. Over a wide range of conditions (phosphate concentrations, soils, plant species), experimental uptake was close to the maximum calculated to be possible for the diffusion model except on one soil at a high level of phosphate. Although the concentration of phosphate in the soil solution at the root boundary appeared to be reduced to a small fraction of the initial concentration, because of the extreme non-linear form of the desorption isotherm less than 1/2 of the P32 exchangeable pool of P was considered to contribute to diffusion.Phosphate uptake by rye grass could only be accounted for if the root hairs were active. Although only a small fraction of the uptake is derived from inside the root hair cylinder, this increases the efficiency of the central root 2.3 fold by providing a zone close to the central root through which phosphate moves very readily.

The uptake of applied selenium by agricultural plants. 2. The utilization of various selenium compounds.

Abstract: SummaryElemental selenium and a series of selenites and selenates were applied in pot and field experiments. With the elemental selenium a small increase in concentration in the plants was found in both kinds of experiments with red clover, lucerne, mustard, andsugar beet as test plants, but not with barley. In the second year an increase in the concentration in the plants was found in lucerne only (field experiment). In a pot experiment eight successive cuts of clover all had nearly the same content.All the selenites had the same effect on the concentration in the plants, and the concentration in the eight cuts of clover decreased with time at the same rate for all six selenites irrespective of solubility. The decrease was about a factor of six. In the field the effect of K2SeO3 in the second year was reduced by 50 to 80 per cent.Also the selenates gave the same concentration in plants independently of the solubility. But the concentration was 20–50 times that obtained with selenites, and the decrease in the effect with time was greater. In the eight clover cuts the effect of selenate decreased four times as much as the effect of selenite. In the field the effect of K2SeO4 decreased more from the first to the second year than the effect of BaSeO4.During a two years field experiment with mustard the total uptake as a percentage of the added selenium was 0.01% of Se°, 4% of K2SeO3 and 30% of K2SeO4 and BaSeO4. With lucerne, barley and sugar beet the uptake was one third of this or less.Determinations of water-extractable selenium in profiles from the field in the autumn showed no increase succeeding the addition of K2SeO4 in the spring while the addition of BaSeO4 increased the extractable amount in both autumns. Addition of five times more selenite increased the water-extractable as well as the total soil selenium in the upper 25 cm, and the increase in total Se was also present in the second autumn.

Microbiological problems in the inoculation and nodulation of legumes

Abstract: page 1. I n t r o d u c t i o n . . . . . . . . . . . . . . . . . . . . . . . . 703 (a) T h e role of legumes in pastures . . . . . . . . . . . . . . 703 (b) N o d u l e formation and effectiveness . . . . . . . . . . . . 704 2. Factors affecting the success of the app l i ed i n o c u l u m . . . . . . 709 (a) I m p o r t a n c e of numbers per seed and inoculant q u a l i t y . . . . 709 (b) F o r m of t h e i n o e u l u m . . . . . . . . . . . . . . . . . . 709 (c) Contact with fertilizers . . . . . . . . . . . . . . . . . . 710 (d) S u r v i v a l on pe l l e ted seed . . . . . . . . . . . . . . . . . 712 3. L ike ly problems in legume establishment . . . . . . . . . . . 714 4. E x a m p l e s of a p p l i c a t i o n of l e g u m e Rhizobium studies . . . . . . 717 (a) Legume inoculant quality control . . . . . . . . . . . . . 7 t 7 (b) The use of l ime-pe l l e t ed seed for aerially sown legumes . . . . 722 (c) Legume inoculant production . . . . . . . . . . . . . . ~ 723 5. R e f e r e n e e s . . . . . . . . . . . . . . . . . . . . . . . . . 724

Non-exchangeable binding of ammonium and amino nitrogen by Norway Spruce raw humus.

Abstract: The capacity of an originally acid Norway spruce raw humus to fix isotopically labelled ammonium and amino nitrogen in a form resistant to cold 1N HCl treatment was studied. The amount fixed was determined after a reaction period of 24 hours (the humus pretreated with propylene oxide), using the amount of labelled N in the HCl-leached humus residue as a basis for calculating the amount of added N fixed. The nitrogen sources used were ammonium chloride, glycine and cyanamide. It was found that the fixation of added ammonium and glycine N was exceedingly low in the H+-saturated raw humus (pH 3.3–3.4), but the fixation rate was rapidly increased by increasing the pH during the aerobic incubation. Maximum fixation was obtained at a final pH of 10–11. Within the acid range the fixation was constantly higher for added glycine-N than ammonium-N. On the alkaline side of the neutral point the amount of fixation tended to be similar for ammonium and glycine. In treatments with N15-labelled ammonium, it was shown that small but fully detectable amount of added N were present in the soluble organic N fraction of the HCl extract, the quantities increasing with increasing soil pH during the incubation. The fixation was increased by increasing temperature and decreased by oxidative pretreatment of the humus before the addition of N. In the nitrogen gas atmosphere the fixation figures were 40 to 50 per cent lower than for corresponding treatments in air atmosphere. When various N compounds were added in equimolar concentrations the highest fixation was recorded for cyanamide. In studying the stability of fixed N to acid hydrolysis, it was found that 54 per cent of the fixed N resisted eight hours' refluxing with 6N HCl, the corresponding figure for the native raw humus N being 19 per cent. About one third of the fixed N was liberated as ammonia during the acid hydrolysis.

Forest tree mycorrhiza — The conditions for its formation and the significance for tree growth and afforestation

Abstract: page 1. Di f fe ren t t ypes of m y c o r r h i z a . . . . . . . . . . . . . . . . . 590 2. Signif icance of m yco r r h i za l assoc ia t ions for t he t rees . . . . . . . 591 3. The s ignif icance of m yco r r h i za l assoc ia t ions for t h e fungi . . . . . 595 4. Cond i t ions for t h e f o r m a t i o n of e c t o t r oph i c m y c o r r h i z a in fores t t r ees 595 5. P r a c t i c a l app l i ca t i ons a n d ef fec t ive ly of d i f fe ren t species of mycor rh iza l fungi . . . . . . . . . . . . . . . . . . . . . . . . . 603 6. Refe rences . . . . . . . . . . . . . . . . . . . . . . . . . 606

Gel formation on nodal root surfaces of Zea mays. 1. Investigation of the gel's composition.

Abstract: A gel forms profusely on the surface of nodal roots of corn. The nature and properties of the material was investigated with the purpose of understanding the mucilaginous layer which exists at the root-soil interface. Acid hydrolysis of the material revealed that it contained uronic acids, galactose, arabinose, xylose, and frucose in an approximate molecular ratio of (3:7:5:11). In addition to these sugars glucose and fructose were also present in the exudate of first or second stage nodal roots. The enzymes acid phosphatase and ATPase were present in the gel. ATPase was only slightly stimulated by K. The gel showed phosphatase activity over a broad range in pH.

Soil water potential as a factor in the ecology of Fusarium roseum f. sp. cerealis 'culmorum'

Abstract: The soil water potential (inferred from vapor pressure measurements by thermocouple psychrometry) influenced both chlamydospore germination and continuing growth of germlings ofFusarium roseum f. sp.cerealis ‘Culmorum’ the same way in two different soils. Chlamydospore germination in both Ritzville silt loam (RSL) and Palouse silt loam (PSL) amended with about 2,500 ppm C (as glucose) and 250 ppm N (as ammonium sulfate) was 40–50 per cent in 24 hours at water potentials down to −50 to −60 bars. Some germination occurred by 72 hours at −80 to −85 bars in both soils but not at lower potentials.

Chromatographic transport through soils

Abstract: A simulation model, written in CSMP, is described permitting the calculation of chromatographic transport in heterogeneous systems like soils. Breakthrough curves of tritiated water were determined on undisturbed, water-unsaturated soil columns (100 cm length, 12 cm o). With the model, tortuosity and dispersion factors were calculated for three soils — a sand, a clay and a loess. The mean values for the tortuosity were 0.3, 0.2, and 0.2 and for the dispersion 0.7, 0.8, and 6 cm, for the three soils respectively. From these values it appears that usually dispersion is the main factor in forming the distribution pattern in soil, the contribution of ionic diffusion being rather small. In many cases good approximative values of the dispersion coefficient may be obtained with an analytical solution of the chromatography equation assuming an averaged homogeneous system.

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

Abstract: 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.

Nitrogen fixation in submerged soilsand-energy material media and the aerobic-anaerobic interface

Abstract: Flooded soils usually consist of a surface aerobic phase a few millimeters thick (in contact with the atmosphere or oxygenated solution) underlain by an anaerobic phase. The objective of this research was to study nitrogen fixation in the aerobic-anaerobic interfacial area in flooded, cellulose enriched media and the utilization of the products of anaerobic decomposition of cellulose by nitrogen-fixing organisms when these products are brought under aerobic conditions by processes such as diffusion, mixing, and drying. The medium used for these studies was basically a sand matrix supplemented with a small amount of soil and mineral nutrients. When columns of medium enriched with cellulose were sectioned after incubation in the dark under flooded conditions, the increase in content of nitrogen per gram medium in the top 2 to 3 mm of the column was as much as 10 to 15 times the increase in nitrogen content of the lower portions of the column. Periodic mixing of flooded media, alternation of shaking in nitrogen and air atmospheres, and alternate flooding and drying all enhanced fixation relative to undisturbed, continuously flooded media incubated in air. Fixation during incubation under a nitrogen atmosphere was less than fixation under air atmospheres. The results of numerous experiments are consistent with the hypothesis that nitrogen fixation is enhanced when the products of anaerobic decomposition of cellulose are brought under aerobic conditions by any of several processes.

Root distribution and the cause of its spatial variability in Pseudotsuga taxifolia (Poir.) Britt.

Abstract: The roots of 36-year-old Douglas firs were sampled in a stratified random fashion with a Veihmeyer-type auger. The lengths of root were very variable as was the proportion of fine roots which were dead. From consideration of the possible causes of spatial variability, it was concluded that it was not due primarily to environmental variation; nor to position relative to the tree trunks and crowns except for concentrations adjacent to the trunks where stem flow is considerable. Cyclical initiation, extension and death of fine roots in a spatial pattern with cells perhaps as small as 30 cm diameter could explain the observations. A drought period might have caused more extensive death of fine roots on one of the three plots examined.

The influence of Acacia senegal on the fertility of a Sand Sheet ('goz') soil in the central Sudan.

Abstract: Acacia senegal increased total nitrogen and organic carbon while it had no effect on the soil texture, pH, available phosphorus and available potassium of a Sand Sheet soil. The higher nitrogen content in the topsoil may have been partly caused by symbiotic fixation. To minimise soil variability when conducting field trials in areas cleared fromA. senegal trees the uprooted tree patches must be avoided in plot layout and liberal amounts of nitrogen fertiliser and farmyard manure must be applied over the whole trial area when possible.

Some factors affecting growth and survival ofRhizobium spp. in soil-peat cultures

Abstract: The growth and survival of rhizobium were studied in neutralized and sterilized soil-peat cultures containing alder bog peat, old moss peat, young reed peat, or young moss peat enriched with lucerne meal and sucrose. Although all these media proved to be excellent carriers for rhizobium, old moss peat from the 0–20 cm layer was less favourable than old moss peat from the 20–40 and 40–60 cm layer, while young moss peat proved to be the least satisfactory type of peat.

Relationship between cation exchange capacity of roots and mineral composition of plant tops as influenced by age.

Abstract: Maize (Hy-Ganga-101) and french bean (Waghya) were grown in pots using soil collected from Agricultural College Farm, Poona. Plant tops and roots were collected periodically. Plant tops were analysed for calcium, magnesium and potassium, and the cation-exchange capacity of the roots was determined. The object was to study the relationship between root CEC and mineral composition of plant tops as influenced by age. The results can be summarised as follows: (i) Age of plant influenced root CEC of maize and french bean. In maize, root CEC increased upto the 30th day and gradually decreased till maturity, whereas root CEC of french bean increased upto flowering stage and decreased thereafter till maturity. (ii) The cation content of the tops of maize and french bean did not show definite significant relationships with root CEC according to Donnan distribution of monovalent and divalent cations when the entire life period of the plants was considered. The probable reasons for this non-significant relationships are discussed.

Algal fixation of atmospheric nitrogen.

Abstract: page 1, The p r e p a r a t i o n of un ia lga l bac te r i a f ree cu l tu res of b lue -green algae 556 2. Tes t ing a n algal cu l tu re for a capac i ty to fix N~ . . . . . . . . . 558 (a) Measur ing gains in t o t a l n i t r o g e n b y K j e l d a h l ana lys i s . . . . . 558 (b) T h e use of n i t r ogen isotopes in m e a s u r i n g for N2-f ixa t ion . . . . 558 (c) The use of ace ty l ene reduct ior t as a n i ndex of n i t r o g e n f i x a t i o n . 559 3. Growth , Ne-I ixa t ion , a n d t he p r o d u c t i o n of ex t ra -ce l lu la r n i t r ogen . 562 4. The m e c h a n i s m oI Nef ixa t ion . . . . . . . . . . . . . . . . . 566 5. The role of N2-f ixing algae in r~atural ecosysterns . . . . . . . . 568 (a) N i t r o g e n f ixa t ion in soils . . . . . . . . . . . . . . . . . 568 (b) N i t r o g e n f ixa t ion in a q u a t i c h a b i t a t s . . . . . . . . . . . . 573 6. Associa t ions of b lue-green algae w i t h o t h e r plart ts . . . . . . . . 578 7. Refe rences . . . . . . . . . . . . . . . . . . . . . . . . . 580

Volatilization of ammonia from submerged tropical soils.

Abstract: A laboratory study was made of the losses of nitrogen through ammonia volatilization from four flooded, tropical soils. The soils used varied considerably in pH, organic matter content, and cation exchange capacity. Losses were measured from the unamended soils, and from ammonium sulphate and urea-treated soils. Two rates of nitrogen application (approximately 50 and 200 kg/ha N) and two methods of application (simulated field broadcast and fertilizer incorporation) of the nitrogen were used. Losses of ammonia were detected for each of the unamended soils, including an acid sulphate soil of pH 3.6. Increased application of both ammonium sulphate and urea resulted in increased losses of ammonia through volatilization. Incorporation of the nitrogen into the mud of the flooded soils significantly decreased losses due to volatilization. It was concluded that the initial or ‘aerobic’ pH of the soils was the soil characteristic most closely related to the magnitude of losses due to volatilization.

Haemoglobin determination and its value as an early indication of peanut rhizobium efficiency.

Abstract: A modified procedure based on the cyanmethaemoglobin method for haemoglobin (Hb) determination in peanut nodules is described. It gave reliable results when tested on peanuts at all stages of vegetative growth, including when the green pigment was present in the nodules. It was shown that early (32–34 days after planting) determination of Hb in nodules of peanuts grown in a greenhouse under bacteriologically controlled conditions can be taken as a measure of the nitrogen-fixing ability of peanut Rhizobia and thus much of the time and greenhouse facilities usually required for strain screening may be conserved. Early determination of nitrogen concentration in leaflets of peanuts proved to be also a useful measure of Rhizobium efficiency, but less sensitive than the early determination of nodule haemoglobin.

Effect of certain soil conditions on nodulation of Acacia spp.

Abstract: Growth and nodulation ofAcacia spp. in sand increased with increase in soil moisture to an optimum at 15 per cent soil moisture and this agreed with the occurrence of these species in the more moist sites reported by other workers.

Competition between soil- and seed-borne Rhizobium trifolii in nodulation of introduced Trifolium subterraneum

Abstract: Native rhizobia associated withTrifolium albopurpureum, T. bifidum, T. ciliolatum, T. depauperatum, T. dichotomum, T. flavulum, T. melanthum, T. microcephalum, T. microdon, T. oliganthum andT. tridentatum were found in Northern California range soils. These rhizobia nodulate subterranean clover but are ineffective in nitrogen fixation with this host. Native rhizobia compet with those in commercial inoculants to form nodules. To ensure effective nodulation by nitrogen fixing rhizobia, commercial inoculants should be applied at rates greater than those recommended by the manufacturerse Effective nodulation was achieved by an application of 7.5×104 rhizobia per seed, four times the recommended rate.

Contribution of organic carbon and clay to cation exchange capacity in a chronosequence of sandy soils

Abstract: CEC and oxidisable carbon content were highly correlated (r=0.96) whereas a lower coefficient was obtained for a correlation of CEC and clay content (r=0.57) in a chronosequence of sandy soils from New Zealand.

Effect of several herbicides on bacterial populations and activity and the persistence of these herbicides in soil.

Abstract: Samples of a sandy loam soil were supplied with normal, 10-fold and 100-fold rates of ioxynil, dalapon, mecoprop, dichlorprop, MCPA + dichlorprop, picloram, and amitrole-T and incubated at 29°C at 65 per cent of the waterholding capacity. Treated soil samples were compared with untreated samples. Samples supplied with (NH4)2SO4 and herbicides were used to investigate the effect of the herbicides on the rate of nitrification and the production of nitrite. In several cases higher numbers of bacteria were found for a longer or shorter period in soil treated with herbicides. There was some evidence that certain groups of bacteria had adapted to ioxynil in a soil sample supplied with the 100-fold rate of this chemical. After 2 or 4 weeks lower numbers ofAzotobacter chroococcum were found at the normal rate of ioxynil, dalapon, mecoprop, and dichlorprop. At the 100-fold rate of application the numbers of Azotobacter were unfavourably affected by all herbicides. The production of mineral nitrogen was hardly affected by the normal and 10-fold rates of application. In the first week the rate of nitrification was slightly depressed in soil samples treated with the normal rates of dichlorprop and amitrole-T and with the 10-fold rates of dalapon, mecoprop, and MCPA + dichlorprop. Strong inhibition of the nitrification for at least 7 weeks was shown by the 10-fold rate of amitrole-T. At the 100-fold rate all herbicides, with the exception of picloram, depressed the rate of nitrification for a longer or shorter period. During the second week a very small increase of nitrite was found in the samples treated with the normal and 10-fold rates of dalapon, mecoprop, dichlorprop, and amitrole-T. A small increase of nitrite was noted for 26 weeks in samples treated with the 100-fold rates of amitrole-T. A highly significant depression of CO2 evolution was found in the first week in samples treated with the normal rates of ioxynil, dalapon, mecroprop, dichlorprop, and amitrole-T, also in samples treated with the 10-fold rates of dalapon, mecoprop, dichlorprop, MCPA + dichlorprop, picloram, and amitrole-T. A highly significant depression of CO2 production was found after 8 weeks in all the samples treated with herbicides at the 100-fold rate with the exception of the sample treated with picloram. The decomposition of the herbicides was studied in soil samples treated with the 100-fold rates of herbicides. Only traces of dalapon and mecoprop were found after 9 months, but 7.2% ioxynil, 29.8% dichlorprop, 39% (MCPA + dichlorprop), 52.1% picloram and 52.2% amitrole-T were still present in active form.

Some Australian studies relating to the long-term effects of the inoculation of legume seeds

Abstract: The work outlined in this paper is only a small part of the legume inoculation work being undertaken in Australia and it deals only with temperate pasture problems. It has been presented as an example of certain principles related to the production of legumes, which have very general applications. These may be summarized as follows: 1. Successful inoculation is frequently an essential part of obtaining maximum seedling establishment. 2. Inoculated strains ofRhizobium may not persist and responses may be transitory. 3. If the natural population which develops is inferior in terms of nitrogen fixation, it will be necessary to further select for persistent strains of high nitrogen fixing capacity.

Total soil nitrogen and nitrogen mineralization

Abstract: The mineralization capacity of 24 different soils was determined from incubation experiments. Relatively rapid mineralization and nitrification was found with soils from cultivated land, and pastures, but soils under natural vegetative covers of conifers and hardwoods were mostly ammonifying. A close relationship could be established between the total nitrogen content of the soil and the amount of mineral nitrogen formed during incubation. Important connections could also be shown between the available nitrogen contents at different times during the incubation period; these suggest that the incubation period can be considerably shortened.