Arizona republican., 1919-02-20
Plant Food Requirements
 Of The Salt Riper Valley
(By C. ]. King. BiophysieaI investiaa- tions. U. S. Department of Agricultural

(By C. j. King. Biophysieai investiaa- tions. U. s. Department of Agr'culture)
 Tho observing cotton growers of the valley have been quick to recognize that cotton has often been the object of abuse through the indiscriminate se- lection of soils on which to grow this crop. Many of the soils in their pres ent state of fertility are unfitted fol the production of substantial yields of cotton and even some of those which now produce fair yields will require some careful farming methods in or der to maintain their fertility during several years of continuous cropping 10 cotton.
 Tho cotton plant does not re-invest a large part Of its income of plant food into the treasury of the soil as do al- falfa and the other legumes which also add another five talents" received from the air. Instead. 1t makes heavy demands on the reserve store of plant food and unless the capital stock in the soil store house is large it Is not surprising that soil bankrutcy results after years of continuous cropping to the plant.
 Already considerable interest is be- ing taken in commercial fertilizers and intN-cropping methods as stimulants toward greater production. During the past few months a considerable num- Der Of growers have called into con- sultation soil analysists in the effort to secure data on their soils which might serve as a guide to their fertilizer needs for the greatest production of cotton. It is for the purpose of explaining the chemists' position in this matter that thts writing is presented.
 If any one element in a soil essential to plant growth is lacking in an avail able form. then that soil cannot pro- ducc good crop no matter how rich the soil may be in other essential e:e- ments. It Is natural for one to exclaim then Why not have a chemist analyze the soil and tell the farmer what ele- ments are lacking and which are abundant so that he will know how to fertlize-whether he ought to apply acid phosphate or cottonseed meal or potath or stable manure so as 10 get the best rcsults," This is a beautiful theory and in tho early days of agri- cultural science it was believed that through chemical analysis the key had been found by means of which the sec rcts of nature could be unlocked and all the problems of practical agricul- ture solved. It was found on trial. however. that this theory did not work out in practice. IL was discovered for instance that soil which was pro- ducing poor crops contained one-tenth Of one per cent phosphOric acid or about 1000 pounds per acre to one foot depth. and yet this soil was In need of phosphoric acid because when acid phosphate was used on 1t as a fertil- izer it responded with largely increased yields. It was evident that the phos phoric acid in this soil although abund ant in quantity, 400O pounds per acre was not in condition available to the plants SO that it could be absorbed by the roots.
 It was not difficult for the chemist 10 treat the soil with strong chemicals and to report that the soil contained 1000 pounds of phosphoric acid. 4,O0C pounds of nitrogen and 5000 pounds ol potash per acre, or ample plant food for producing good crops. but as a matter of fact the soil might be so pOoI as hardly to sprout peas. After many efforts to initiate the action of nature in the laboratory the conclusion was reached that it was not possible to tell by Q chemical analysis whether the soil was fertile or not, or what partic- ular element should be added to it for