626 EXPEBIMEirr station BECOED. [Vol. 87 



with lime gives best returns where phosphoric acid alone is used, no increase 

 Is secured. Alamance silt loam near Momvse, Durham sandy loam near Oxford, 

 and Norfollt coarse sand near Hoffman all show nitrogen to be the most needed 

 element of plant food, with phosphoric acid and potash, giving good yields 

 when used with phosphoric acid and nitrogen. For large crops a good supply 

 of all of the plant food constituents with lime is needed, as well as an increased 

 supply of vegetable matter. On the Cecil clay soils potash either gives no gain 

 or depresses the yields. On other phases of the Cecil series of soils experi- 

 ments show that nitrogen Is the chief limiting element of plant food for large 

 yields of crops, with additions of phosphoric acid needed for best crops. Potash 

 is of least Importance. 



Field tests ^vith coastal plain soils show that " with the exception of muck, 

 nitrogen is the limiting clement of plant food, . . . with potash and phosphoric 

 acid needed to produce good gains In crop yields. The results on Norfolk 

 sandy loam at Elizabeth City have shown that phosphoric acid comes before 

 potash in importance. ... On the muck soil, lime seems to be of first impor- 

 tance, [followed in order by] . . . phosphoric add, potash, and nitrogen. 

 . . . Nitrogen, potash, and phosphoric acid give best returns when used In 

 connection with lime. Norfolk sand at Greenville gives evidence of needing 

 humus-forming material before any fertilizer can be used with profit. With 

 peaty soils, the addition of potash and phosphoric acid seems to have a de- 

 pressing effect so far when used alone or In combinations without lime." 



Thirty-five years' results with fertilizers, F. D. GxVkdneb, C. F. Noll, and 

 P. S. Bakxk (Pcnnsylvanin Sta. Bui. 146 (1917), pp. S-29, figt. il).— This is a 

 summary of tlie results of oxperimenLs begun In 1881 and pre\'iously noted 

 (E. S. R., 84, p. 128) on the use of commercial fertilizers, barnyard manure, 

 lime and land piaster In a rotation of corn, oats, wheat, and mixed clover and 

 timothy grown on residual limestone soil varying from clay to silt loam in 

 character. 



It was found that In the absence of manure or fertilzers of any kind the 

 fertility of this soil showed a marked decline. The average yield of all crops 

 In the rotation for all of tlie untreated plats during the last five years was only 

 61 per cent as much as the yield for the same plats and crops during the first 

 five years. The reduction in yield was most pronounced in case of hay and corn. 

 Wheat started wltli a comparatively low yield and showed the smallest decline 

 in yield. The average yield of both wheat and wheat straw during the last 

 five years equaled 94 per cent of the yield during the first five years. 



" Phosphoric acid is the limiting factor in crop production on this soil. The 

 average yield on the plats treated with phosphoric acid alone is 18 per cent more 

 than the average of tlie check plats and 41 per cent more than the average of 

 check plats which are nearest to tlie phosphoric acid treated plat. Ground bone 

 as a source of phosphoric acid appears to be slightly more efficient than dls- 

 •solved bone black." 



Potash alone had no appreciable effect on the yield of crops, but potash ap- 

 plied 'With phosphoric acid gave a very marked increase In yield over phosphoric 

 acid alone, and very materially increased the profits on the fertilizer applied. 

 The use of iOO lbs. of muriate of potash per acre In alternate years Is believed 

 to be sufficient to meet tlie needs for the crops gro\vn on this soil. Potash and 

 phosphoric acid In combination proved to be the most profitable mixture u.'jod. 

 This combination in tliis rotation, In which clover occurs once every four years, 

 practically maintained the fertility of the soil for a period of 35 years. 



Nitrogen alone and a combination of nitrogen and potash had no appreciable 

 effect on these crops. Nitrogen In addition to phosphoric add and potash pro- 

 duced a considerable increase in yield of crops. Of the three forma of nitrogen. 



