the amount of calcium and phosphorus in the 
soil and the amount in prairie grasses growing 
on the soil. They concluded that plants nor- 
mally low in calcium and phosphorus remain 
low even when grown in fertile soils, and that 
plants normally high in these elements remain 
high even when grown in poor soils. 
Parent Material and Texture of Soil 
Parent material can affect the chemical com- 
position of plants only indirectly through the 
derived soils. Acidity, nutrient status, texture, 
and water-holding capacity of soil may be dif- 
ferent in soils developed from different parent 
materials. Few studies have been made of the 
effect of parent material on plant composition. 
In Massachusetts, Archibald and Bennett 
(1933) found that limestone soils produced 
plants with higher calcium content than other 
parent materials. In South Dakota, McEwen 
and Dietz (1965) found that plants growing on 
limestone soils had higher ash, moisture, and 
protein content during vegetative growth than 
similar plants growing on soils derived from 
metamorphic rocks. However, factors besides 
parent material and soil influenced these dif- 
ferences; the limestone sites were at higher el- 
evations and had higher precipitation. Conse- 
quently, the stage of plant maturity was re- 
tarded and soil moisture was higher than on 
the metamorphic sites. No difference between 
parent materials was found for nitrogen-free 
extract, crude fiber, crude fat, calcium, and 
phosphorus content of plants. 
Texture of soil can influence chemical com- 
position of plants—mainly through its effect 
on water-holding characteristics and nutrient 
status. Finer soils have a higher nutrient ex- 
change capacity and can hold more water 
(Midgely 1937). However, little agreement 
has been found during studies comparing 
chemical composition of plants on soils of dif- 
ferent textures. Archibald and Bennett (1933) 
reported that loams and sandy loams with a 
compact substratum had good water-holding 
capacities and produced herbage higher in pro- 
tein and calcium and lower in crude fiber than 
excessively drained sandy loam soils. Grizzard 
(1935) found that alfalfa plants grown in fine 
soils such as clay loams had a higher nitrogen 
content than plants grown in coarse, sandier 
soils. Clarke and Tisdale (1945) found that 
plants grown in sand were lower in phospho- 
rus content than those grown in loam, but that 
the content of other constituents was not af- 
fected by texture. Thus, the differences in re- 
sults of these studies were probably caused by 
factors other than soil texture. 
Compaction of soil can also affect the nutri- 
ent status of plants, but little research on this 
has been reported. VanDiest (1962) found that 
the nitrogen content of corn grown in com- 
pacted soil was significantly less than that of 
plants grown in less compacted soil. Content of 
phosphorus and potassium in plants was not 
affected by soil compaction. 
ALTITUDE 
Altitude affects plant composition through 
the interrelation of light intensity, carbon 
dioxide concentration, temperature, precipita- 
tion, and length of growing season (Oelberg 
1956). Development of plants is often delayed 
and precipitation is often greater at higher ele- 
vation (McEwen and Dietz 1965). Therefore, 
plants at different elevations compared at a 
given time reflect composition differences due 
to variations in development and in soil mois- 
ture as well as the other factors mentioned 
above. In Wyoming, Roberts (1926) and 
McCreary (1927) found that crude protein, 
phosphorus, and nitrogen-free extract in- 
creased with altitude whereas crude fiber de- 
creased. 
GRAZING 
Grazing can affect the chemical composition 
of individual plants by altering the form of 
growth or the progress of development of ex- 
isting plants. The chemical composition of 
available forage as a whole is affected when 
grazing changes the composition of the plant 
community. Plants of different species, growth 
forms, or stages of development often have 
markedly different nutritive content and di- 
gestibility. 
In discussing grazing effects, we will be con- 
sidering both the specific nutrient content of a 
plant or species and the actual diet or effective 
nutrition of the grazing animal, as determined 
by grazing habits and the nature of the forage. 
Effect of Herbage Removal on Plant 
Production and Nutrient Content 
Many studies have shown that removal of 
herbage, if too severe or too prolonged, will re- 
duce dry-matter yield of forage. However, such 
clipping treatments may increase the nutritive 
value of forage. Protein, phosphorus, and other 
desirable nutrients decrease as plants mature, 
and lignin and other nondigestible components 
increase. Herbage removal by grazing or clip- 
ping interrupts development of plants, prevents 
maturity, and prolongs growth or initiates 
regrowth. The composition of clipped plants is 
similar to that of plants in an early growth 
stage; the percentages of protein, phosphorus, 
and carotene are high, and the percentages of 
crude fiber or lignin are low (Fudge and Fraps 
1944; Jameson 1963; and Stoddart 1946). Di- 
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