creased soil moisture and to a delay in matur- 
ity rather than to temperature. In New Mex- 
ico, Watkins (1943) found that in mild winters 
with above-normal precipitation, range grasses 
had higher carotene content than in colder, 
drier winters. Presumably, this content was 
higher because the basal leaves and stems of the 
grasses remained green as a result of favorable 
temperature and moisture. 
LIGHT INTENSITY 
Lack of adequate light has definite effects on 
plants; some effects are direct, but most are in- 
direct. Plants growing in the shade usually 
have the following characteristics compared to 
those of the same species growing in the sun: 
1. Less herbage production (Cooper 1960; 
McConnell and Smith 1965; Pace 1958; and 
VanDyne and Heady 1965a). 
2. Lower percentage of nitrogen-free ex- 
tract (McEwen and Dietz 1965) or total car- 
bohydrates including reducing sugars, invert 
sugars, and easily hydrolyzable carbohydrates 
(Watkins 1940; Welton and Morris 1928). 
3. Higher percentage of lignin (Anonymous 
1959; VanDyne and Heady 1965b). 
4. Higher percentage of protein (McEwen 
and Dietz 1965; Roberts 1926). 
Most of these differences are only indirectly 
caused by shade. Stage of development is often 
retarded in shaded areas (McEwen and Dietz 
1965), and soil moisture is higher in shaded 
areas (Cook and Harris 1950); therefore, 
shaded plants remain succulent longer during 
the summer.’ Since protein and moisture con- 
tent have a high positive correlation (Camp- 
bell and Cassady 1954), higher moisture con- 
tent of plants is probably responsible for the 
presence of more protein in shaded plants. Re- 
duced leaching because of intercept of rain by 
overstory species might also be a factor. 
_ Even the effect of shade on total production 
is not clear in all studies. Welton and Morris 
(1928) found that artificial shading had the 
same effect as tree cover in reducing carbohy- 
drate content of grasses, but artificial shading 
did not reduce total yield because there was no 
competition for soil moisture from the tree 
species. However, in other studies under con- 
trolled conditions, reduced light levels have de- 
creased production of some species (Leopold 
1964). However, shade-tolerant species may be 
affected very little by low light intensities. 
* Krueger, William C. Lignin, protein, and sugar 
relationships of plants on different soils of California’s 
Aue coast. M.S. thesis, Humboldt State Coll., Arcata, 
alif. 
SOIL 
A great many studies have shown that 
plants of the same species grown in different 
soils often differ in chemical composition and, 
consequently, in palatability (Heady 1964). 
Even when the causes of differences in soil 
were defined, other influences may have been 
acting in conjunction with those defined, or 
were confounded with them. Beeson (1941) 
stated this very clearly: 
“While plants are dependent upon the 
soil for their mineral nutrients, cli- 
matic conditions so affect . . . physio- 
logical processes that the composition 
of both the mineral and the organic 
matter of crops may be greatly modi- 
fied even though the crops are grown 
upon identical soils. . . . Plant com- 
position is modified by both the cli- 
mate and the soil in which it is grow- 
ing, and both these factors are closely 
interrelated, often modifying the ef- 
fect of the other. Thus the assimila- 
tion of phosphorus growing in calcar- 
eous soils may be less in dry than in 
wet years, whereas entirely contrary 
results may be obtained in plants 
growing in siliceous soil. . . . Crops 
growing in the same soil type sepa- 
rated by sufficient distance so as to 
not receive the same amount of rain- 
fall at the same time in any one year 
may be quite different in their chemi- 
cal composition.” 
Various soil factors that affect chemical 
composition are discussed below. 
Soil Moisture 
The amount of soil moisture available for 
plant growth affects both the yield and chemi- 
cal composition of plants. However, in most 
studies of plant composition, effects of soil 
moisture are confounded with temperature, 
stage of plant maturity, and many other fac- 
tors. Early in the growing season soil moisture 
is often abundant and most herbaceous plants 
are green and growing rapidly; the moisture, 
protein, phosphorus, and carotene content of 
such plants generally is high, whereas the 
fiber, lignin, and nitrogen-free extract content 
is low. During the middle and latter part of 
the growing season in temperate regions with 
a continental climate, precipitation and soil 
moisture decrease, temperature increases, and 
herbaceous plants grow to maturity and be- 
come dry. As these events occur, the following 
changes take place in most herbaceous plants: 
1. Percentages of protein and phosphorus 
39 
