Feb. II. 1918 Effect of Season and Crop Growth on Soil Extract 363 



container have given a better expression of the potential power of the 

 soil than has been obtained in the past. 



The study of the unpTanted soil is especially valuable because of the 

 definite information. which it furnishes in regard to the effect of fallowing 

 and cultivation. From the results of the present investigation it can 

 be stated that the changes occurring in water-soluble compounds, both 

 organic and inorganic, as the result of these practices, are great and far- 

 reaching in effect. They entirely justify the importance attached to 

 such treatment in the past. In biennial cropping, alternating with 

 fallowing, as practiced in California, it is probable that fully as much is 

 gained from the increase of water-soluble nutrients as from the moisture 

 stored up in the soil. 



In the preceding studies the data obtained have been considered solely 

 as a measure of the water-soluble nutrients obtained by a conventional 

 procedure of extraction. From the work performed by Hoagland in 

 collaboration the amounts extracted are definitely related to the actual 

 soil solution. Even though the figures so obtained do indicate a range 

 of concentrations higher than the actual truth, it has been previously 

 pointed out that this does not alter the relationships which have been 

 established. It is therefore believed, with this corroborative evidence, 

 that the changes observed in the water extract reflect actual changes in 

 the soil solution. 



SUMMARY 



(i) The water-soluble nutrients in 13 soils, of two different types, 

 have been periodically determined during two seasons. 



(2) Throughout the second season comparisons were made between 

 the planted soil and its uncropped duplicate. 



(3) Notable differences were observed between the nitrates, calcium, 

 potassium, and magnesium present in the water extracts from the 

 cropped and uncropped soils. 



(4) The phosphates did not exhibit corresponding differences. Great 

 dissimilarities were observed in the phosphate content of different soils, 

 but in any one soil the amount was practically constant in both the 

 cropped and uncropped plot. 



(5) Striking differences occurred between the soluble nutrients present 

 in the various uncropped soils. 



(6) While the crops were growing, the concentrations of nutrients in 

 8 of the 13 planted soils were practically the same. These 8 included 

 both good and poor soils, 



(7) The three poorest soils yielded the smallest amounts of water- 

 soluble nutrients and the smallest differences between the cropped and 

 uncropped duplicates. 



