302 



Journal of Agricultural Research 



Vol. XII. No. 6 



CONCENTRATION AND RATE OF FORMATION OF SOLUTES 



Since even our poor soils appear to be able to furnish adequate amounts 

 of all solutes at the most critical periods, we can only ascribe nutritive 

 difficulties of soils to inability on the part of the plant to absorb this po- 

 tentially soluble supply. The rate of absorption by any plant may be 

 limited by the possible supply and by the concentration of that supply, 

 but we have seen that in all cases which have come under our observation 

 the supply is adequate at all times. We should therefore either measure 

 the concentration of the soil solution itself or evolve some other means 

 of estimating the relative power of soils to maintain an optimum concen- 

 tration. Our data do not permit us, unfortunately, to estimate the 

 concentration of individual ions in the soil solution, but we may per- 

 haps get an idea of the relative power of soils to maintain or restore a 

 proper concentration by consideration of the data on soils with and 

 without crop. We present in Table IV the seasonal averages of the 

 water-extractable substances in cropped and uncropped soils. 



Table IV. — Water-extractable matters in cropped and uncropped soils. 



averages 



[Results expressed as parts per million of soil] 



Seasonal 



Constituent. 



Yield in bushels per acre . 

 Soil No 



Nitrate : 



Uncropped. 

 Cropped .... 

 Difference. . 



Phosphate: 



Uncropped . 

 Cropped . . . . 

 Difference. . 



Potassium: 



Uncropped. 

 Cropped . . . . 

 Difference. . 



Calcitiin: 



Uncropped. 

 Cropped. .. . 

 Difference. , 



Magnesium : 

 Uncropped. 

 Cropped . . . . 

 Difference. 



Productivity. 



131 

 36 



95 



40 



31 



9 



34 

 24 

 10 



23 

 13 

 10 



120 

 87 



55 



50 



5 



37 

 19 

 18 



15 



7 



146 



30 

 116 



18 



17 



47 

 14 



91 



58 

 Z2> 



24 

 17 



7 



Good. 



8s- 9 



141 



43 



Z3 



27 



6 



47 

 28 



19 



87.0 



180 



28 



152 



17 

 12 



5 



49 

 31 

 18 



66 

 34 

 32 



15 

 10 



5 



154 



27 



127 



30 

 26 



67 



19 



51 

 29 

 22 



13 

 7 

 6 



96 

 23 

 73 



13 



Aver- 

 age all. 



S4. 7 



137 



30 



107 



14 



52 

 40 

 12 



51 

 30 

 21 



17 

 10 



7 



