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IX. Magnesium Deficiency in Humans

IX. Magnesium Deficiency in Humans

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GRASS TETANY OF RUMINANTS



369



cated the positive effects of Mg supplements in the treatment of Nigerian

children suffering from protein-calorie malnutrition.

Gardner et al. (1950) reported that tetany in newborn children fed

entirely on cow’s milk in a Massachusetts hospital, responded to Mg

therapy. In a recent review, Krehl (1967) indicated that dietary Mg

deficiency is one of the most common nutritional deficiencies in clinical

medicine. He indicated that clinicians are becoming more aware of it, as

hospital laboratories become more proficient in making Mg determinations. Workers interested in Mg deficiency in humans are also referred to

the reviews by Aikawa (1963) and Wacker and Parisi ( 1 968). A collection

of articles dealing with recent Mg research is contained in Flink and

Jones ( 1969).

X.



Summary



Grass tetany occurs when cattle or sheep graze grass or small grains

forages in cool weather. Pregnant or lactating animals are most susceptible. The primary cause of the disease is low Mg in the forage, but high

concentrations of N and K in the forage can be contributing factors. Other

factors that may be involved are low concentrations of carbohydrates

and high concentrations of trans-aconitic acid, citric acid, and certain

higher fatty acids.

The disease may be prevented by Mg fertilization of acid, coarsetextured soils. However, because of higher adsorption capacities of finetextured soils, and lower solubilities of MgC03 in soils of high pH,

higher rates of Mg fertilizer would generally be required in these cases.

This is more expensive, and in these cases it may be better to supply Mg

by oral supplementation by legumes, adding Mg to feed or salt blocks, or

by foliar applications of MgO to the forage. Another possible solution is

the use of Mg bullets in the rumen of cattle and sheep, but more research

is needed concerning the effectiveness of this method. A long-term solution may be the breeding and selection of legumes that grow as early in

the season as cool-season grasses, and the breeding of grasses containing

high concentrations of Mg.

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THE MICROFLORA OF GRASSLAND



Francis E. Clark and Eldor A. Paul

U. S. Department of Agriculture, Fort Collins, Colorado,

and the University of Saskatchewan, Sarkatoon, Canada



I.



111.



IV.



V.



VI.



VII.



Page

375

376

A. Phyllosphere .................... ....................... .......................

376

B. Rhizosphere ....................................................

38 1

The Microflora of Grassland Litter ...._.....

.............. 385

A. Quantitative Considerations ..

...............................

386

B. The Microflora of Aboveground Litter ............................................

388

C. The Microflora of Belowground Litter ........................................

390

D. Rate of Litter Decomposition ...................................................

39 I

The Microflora of Grassland Soils ...........................................

395

A. Bacteria and Actinomycetes .....................................

3 96

.............................................

B. Fungi

398

............... 402

s ....................................

C. Algae

Biomass and Bioactivity Measurements .....

....................

40 3

A. Magnitude of the Biomass .......

.................................

403

y .................. ...................... 405

B. Biomass in Relation to Microbia

C. Measurement of Bioactivity in Soil .................................................

406

The Humic Component of Grassland Soil ..............................................

409

A. Characteristics of the Humic Component .............................

409

B. The Biodegradability of Soil Humus ...................................

410

C. Microbial Utilization of Humic Materials ..........

414

Nitrogen Transformations in Grassland Soils ........

416

A. Nitrogen Fixation ........................................

416

B. Nitrification ...................... ............

....................

422

C. Denitrification and Volatilization ...

.......................

424

References ..................... ..........

........................................

426



Introduction



..........................................................



1. Introduction



The role of microscopically small organisms in numerous soil processes, particularly those affecting plant productivity, is well recognized.

Less well known is a quantity of recently gathered information concerning

microorganisms as components of major plant communities and the

extent to which they participate in the total energy flow therein. Macfadyan ( 1963) has calculated that, of ecosystem gross productivity, rough375



376



FRANCIS E. CLARK A N D ELDOR A. PAUL



ly 14% is respired by higher plants, 28% is consumed by herbivores, and

56% is metabolized by the decomposer organisms, namely, the soil and

plant microflora and fauna. Similarly, Golley (1 960) has estimated that

the decomposers as a group use 70%of net production.

Although the soil microflora is the single most important group in the

annual turnover of energy trapped by photosynthesis, to the authors’

knowledge no broad general review of the microflora of grassland has

heretofore been compiled. Indeed this review itself achieves little more

than fragmentary coverage of the existing literature on the microflora

present in grassland soils or associated with either the living or dead

vegetation thereon. It makes no attempt to discuss those influences on

the ecosystem that the bacteria and hngi may exert in their role as causative agents of plant or animal disease. In several instances in which review

discussions do exist on specific aspects of the grassland microflora, citation of such literature is used in lieu of duplicate discussion. In other

instances, data are cited for nongrassland soils or communities. This

may be either for comparison with similar data for grassland or, if comparable data are not available for grassland, to point up the need for such

data. In the context of this review, grassland denotes any landscape which

supports mainly grasses as its native vegetation or if exploited by man,

is used mainly for graminous plants.

II. The Microflora of the Living Plant



There is a rich microflora associated with the surfaces of living plants

that is either nonpathogenic or at most functioning at an extremely marginal level of pathogenicity. This microflora feeds primarily on exudates

and sloughed cellular material. It commonly is divided into two categories: (a) the aboveground, shoot-associated microflora, or broadly the

phyllosphere; and (b) the belowground, root-associated microflora, broadly, the rhizophere.

A. PHYLLOSPHERE

Although earlier workers (Beijerinck, 1888; Winkler, 1899) had isolated bacteria from plant leaves, Burri ( 1903) first showed that a variety

of plants support an abundant leaf-surface microflora. Bacterial populations of from several millions to more than a hundred million per gram of

fresh leaf material were observed. Legumes and vegetable crops carried

appreciably higher phyllosphere populations than did grass leaves. A

year later Duggeli (1 904) reported essentially similar observations. Both

Burri and Duggeli, as well as other workers of the era (Huss, 1907; Gru-



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