EFFECT OF VARIOUS CROPS UPON THE WATER EX- 

 TRACT OF A TYPICAL SILTY CLAY LOAM SOIL 



By G. R. Stewart, Chemist, Hawaiian Sugar Planters' Association, and J. C. Martin, 

 Assistant Chemist, California Agricultural Experiment Station 



The senior author has previously reported a series of investigations 

 carried on at the California Agricultural Experiment Station upon the 

 changes which took place in the water extracts from a group of selected 

 soils. These consisted of six silty clay loams and seven fine sandy loams. 

 All were typical soils brought from various places in California and repre- 

 sent a considerable range of past treatments and some variations in 

 known productive capacity. A large quantity of each soil was brought 

 to the Experiment Station at Berkeley, where it was sifted, mixed, 

 placed in two uniform containers, and afterwards kept under controlled 

 conditions. A crop of barley was raised upon all the soils during the 

 first year of the experiment in order to bring them into a somewhat 

 comparable state of tilth. During the second season one container of 

 each soil was cropped and the other was maintained as an uncropped 

 duplicate. Notable differences were found in the amounts of water- 

 extractable constituents from the cropped and the uncropped soils. 

 The water-soluble nitrates, calcium, potassium, and magnesium were 

 generally higher in the uncropped soils. Considerable differences were 

 also observed in the amounts of water-soluble constituents extracted 

 from the different uncropped soils. Further details of the experimental 

 methods and of the results obtained may be found in the original pub- 

 lication. 1 



The conclusion from our previous work, that barley reduces the nitrates 

 of soils to a low and fairly uniform magnitude independently of the soils' 

 crop-producing power and also tends to reduce the amounts of other 

 water-extractable constituents, seemed to require that the observations 

 be extended to include the effects of other crops. It was also deemed 

 desirable to study the effect of varying numbers of plants in accelerating 

 the changes observed and if possible to ascertain the rate of movement 

 of water-extractable substances through the soil. 



The experimental work consists of two separate studies, one to cover 

 the specific effect of different types and numbers of plants, the other to 

 shed light on the movement of solutes through the soil. 



1 Stewart, Guy R. effect of season and crop growth in modifying the son, extract. In 

 Jour. Agr. Research, v. 12, no. 6, p. 311-368, 24 fig., pi. 14. 191S. Literature cited, p. 364-368. 



Journal of Agricultural Research, Vol. XX, No. 8 



Waslnagton. D. C Jan. 15, 1921 



vz Key No. Calif. -2 7 



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