786 IOWA DEPARTMENT OF AGRICULTURE. 



annual rainfall. In the southern portion of the United States more than 

 this is necessary, and in the north, on account of the cooler climate, a 

 less amount may be sufficient. Much also depends upon the distribu- 

 tion of the rainfall, the water-holding capacity of the soil, the depth to 

 permanent moisture, the presence of seepage water from neighboring 

 slopes, and other local or climate conditions which affect the evaporation 

 of the available water supply through the growing season, so that it is 

 impossible to state the necessary rainfall in other than an approximate 

 manner. 



SOIL. 



Favorable Conditions. — Alfalfa grows best in a well-drained, loamy 

 soil with a subsoil sufficiently open to allow the roots to penetrate to a 

 considerable depth; yet an examination of the soil in the various alfalfa 

 districts shows that there is a much wider variation in the soil condi- 

 tions than has generally been supposed. 



Acidity of soils and other unfavorable conditions. — The Missouri Ex- 

 periment Station has shown that an acid soil is unfavorable to this crop, 

 a fact which has been corroborated by the experience of growers in the 

 East. This unfavorable condition can be corrected by the application of 

 lime, the amount depending upon the degree of acidity. It may be in 

 any given case that the unfavorable factor is not the acidity of the soil, 

 but compact texture, lack of aeration, or some other condition which is 

 corrected by the incorporation of lime or the accompanying tillage. 



Excess of loater. — An excess of water in the soil is a very unfavorable 

 condition for alfalfa. Where the water level is near the surface, or 

 where the surface wat^r from heavy rains is unable to drain off rapidly, 

 alTalfa usually fails. For this reason an alfalfa field is injured by being 

 submerged from an overflow, or even killed if the water remains over 

 the surface for too long a period. Experience has shown that when cov- 

 ered by clear running water the injury is much less than when a sedi- 

 ment is deposited or the water is stagnant. Ordinarily alfalfa will not 

 withstand an overflow of more than a f^v days. Flooding in the winter 

 is less injurious than during the growing season. 



Nature of subsoil. — It is generally stated that alfalfa requires a porous 

 subsoil, but this statement must be modified. If the subsoil is near the 

 surface and is of such a nature as to prevent the entrance of the alfalfa 

 roots, alfalfa will probably fail; but many of the so-called imprevious 

 subsoils allow the roots to penetrate. The effect of the subsoil seems to 

 depend on how its effects drainage and upon the texture and fertility of 

 the surface soil. The reports of successful alfalfa fields upon subsoils 

 of gumbo, hardpan, and stiff clay are too numerous to disregard. Near 

 Syracuse, N. Y., there is an alfalfa field growing upon a rocky hill where 

 the coating of the soil is only 2 to 4 inches in depth. The success under 

 such apparently adverse conditions is due to the fact that the roots are 

 able to penetrate the numerous vertical cracks in the rock. 



Need of fertility. — An important condition and one which is likely to 

 be lacking in many of the worn-out eastern soils is fertility. It is very 



