ALFALFA ROOT STUDIES. 3 



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 Redfield 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 

 fwater 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. No 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 

 i where these are not already present in the soil also results in a larger 

 iroot system. That root development is affected by close grazing or 

 frequent cuttings was indicated by a test conducted at Redfield in 

 jl916. 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 



