36 MISCELLANEOUS PUBLICATION 952. U.S. DEPT. OF AGRICULTURE 



subsoil may have been depleted to 

 the extent that it limited production. 

 The regression lines calculated 

 from annual yields of treated and 

 untreated wheat, corn, and alfalfa 

 when grown continuously on the 

 same land are shown in figure 2. 



Legumes Versus Inorganic Nitrogen 

 Sources 



Bray and Schnittker (4) studied 

 the economics of crop rotations in 

 eastern and central Kansas. Part 

 of then studies were based on 

 Hobbs' data {32). If prices for 

 alfalfa hay are favorable, they con- 

 cluded that up to 25 percent of the 

 cropland in eastern Kansas could 

 profitably be cropped to alfalfa. 

 However, the data showed that 

 fertilizers were good substitutes 

 for legumes in rotation unless there 

 were soil structure or erosion prob- 

 lems. 



Soil Moisture Use by Legumes and 

 Grasses 



In 1929. Duley {15) reported the 

 effect of alfalfa on soil moisture at 

 Manhattan on Geary silt loam. 

 Alfalfa reduced the moisture con- 

 tent of the deep subsoil to a low 

 level, which then remained con- 

 stant as long as alfalfa was on the 

 land. TThen alfalfa land in a 16- 

 year rotation was broken and 

 planted to corn and wheat for 10 

 years, the deep subsoil failed to 

 gain significant moisture. Similar 

 results were obtained in Nebraska 

 (39,. 



In 1936, Grandfield and Metzger 

 (23) found that alfalfa depleted 

 the available moisture to a depth of 

 25 feet in 2 years at Manhattan. 

 Clean fallow restored moisture in 2 

 years. These results are at vari- 

 ance with Nebraska results (39), 

 where 5 years of fallow failed to 

 restore moisture below the 11-foot 

 level. The difference in rate of 

 restoration of subsoil moisture un- 



der fallow in the Kansas and 

 Nebraska experiments emphasizes 

 the importance of soil and climatic 

 variability. Apparently the soil at 

 Manhattan was more permeable 

 than the soil at Lincoln. Annual 

 precipitation averaged 31.9 inches 

 at Manhattan and 27.5 inches 

 at Lincoln. 



In 1953. Hobbs (31) reported on 

 replenishment of soil moisture sup- 

 plies after the growth of alfalfa 

 and bromegrass at Manhattan for 

 193S-49. The land was plowed out 

 of alfalfa and bromegrass in 1937 

 and cropped to cereals for 12 years. 

 Twelve years of cereal cropping 

 resulted in water being stored to a 

 depth of at least 22 feet. This 

 deep moisture reserve vas available 

 to alfalfa but not to cereals. If 

 not used by deep-rooted crops such 

 as legumes, this water would even- 

 tually move to the water table. 

 Annual precipitation for the 12 

 years averaged 0.62 inch above 

 normal. From October 1941 to 

 October 1945 annual precipitation 

 exceeded longtime averages bv 13.4. 

 1.3. 11.3. and 10.6 inches. 'Mois- 

 ture samples were not taken during 

 this period, but it seems probable 

 that most of the deep moisture 

 storage may have occurred in this 

 4-year period. 



The disagreement between Hobbs' 

 {31) and Duley's (Id) data are 

 believed to be due to exceptionally 

 wet years that occurred during 

 Hobbs" study. Hobbs found that 

 bromegrass did not seriously deplete 

 soil moisture below 4 feet. 



Lnder favorable rainfall condi- 

 tions. Hobbs concluded that it was 

 unnecessary to iallow for planting 

 alfalfa on land previously sown to 

 this crop, provided a sufficient num- 

 ber of cereal crops had been pro- 

 duced between alfalfa crops. 



Myers (58) found that sweet- 

 clover grown for two seasons 

 reduced the subsoil moisture to a 

 maximum depth of 14 feet at Man- 



