ALFALFA ROOT STUDIES. 6 
While alfalfa roots are ordinarily able to penetrate compact soil 
strata, their ability to do so is modified to a considerable degree by 
moisture conditions. A soil layer may become so hardened by 
drought that the roots are unable to go through it, but such a con- 
dition may be alleviated by the presence of only a small quantity 
of moisture as a result of opportune rainfall. Compact soil appears 
to cause greater branching and less pronounced taproots, while the 
open or porous soils tend to produce long, slender taproots with few 
branches. The varied development of root systems due to differ- 
ences in soil texture was noted in seedlings in similar kinds of alfalfa 
examined at Redfield. S. Dak., and Arlington Farm, Va.. in 1916. 
The seedlings at Jledfield showed pronounced taproots and few 
branches, while those examined at Arlington showed indistinct tap- 
roots and a mass of fibrous roots. Roots often terminate or else are 
deflected from their natural course by very hard material, such as 
hardpan or stone. On land where the water table is near the sur- 
face, the water will act as a barrier to deeper root growth. On irri- 
gated lands root growth is influenced by the time and quantity of 
water applied. 
CLIMATIC CONDITIONS. 
The form and development of the root system is doubtless influ- 
enced, to some extent, by the weather conditions that immediately 
follow seeding. It has been found that alfalfa roots make very rapid 
early growth, especially at two to three months of age, and it is 
probably true that the form of the root system is most influenced 
within this period. Under north-temperate dry-land conditions, 
young plants from sowings made in early spring or late summer, are 
generally subject to a long period of cool and moist weather, while 
late-spring or early-summer sowings have a long period of relatively 
warm and dry weather in which to make their early growth. Xo data 
are available showing the exact effect of these conditions on the 
growth of the young plant, but they are doubtless of considerable 
importance. 
CULTURAL FACTORS. 
The application of stable manure or commercial fertilizers usually 
increases root growth. Inoculation with nitrogen-fixing bacteria 
Avhere these are not already present in the soil also results in a larger 
root system. That roojt development is affected by close grazing or 
frequent cuttings was indicated by a test conducted at Redfield in 
1916. A broadcast plat of alfalfa that was seeded August 12, 1915, 
was selected to determine the influence of frequency of clipping on 
root growth. This plat had an almost perfect stand, was free from 
weeds, and had not previously been harvested either for hay or 
