EFFECT OF POTASH SALTS ON CROP YIKLIXS 49 



A word of warning may be necessary to guard against attaching undue 

 significance to dift'erences in crop yields of perennials. The initial error 

 which may have been caused by unconscious selection of plants is perpetu- 

 ated through the years. Ileiieated takings of the product of a single 

 planting do not in such case constitute effective replication of the ex- 

 periment. 



The results as a whole show significant differences in yield arising from 

 the comparative use of these two salts only in the case of the winter- 

 tender cane fruits, raspberries and blackberries. There were, however, 

 certain other differences c\ident from time to time. In some years potato 

 tops on the muriate plots "went down" a week or ten days earlier than 

 did those on the sulfate. Raspberries and blackberries showed great 

 differences in yield following those seasons in which winter-killing was 

 serious. Whether this was a protecti\e influence of the sulfate of potash, 

 or a reverse influence of the muriate, is not evident, and is now a matter 

 ()!' study. Growth of cIo\'er on sulfate of jiotash was often better than 

 on the muriate, but with differences seldom shown in yield owing to the 

 fact that increased weed growth made up for weight of crop lost when 

 clover failed. In certain years, also, there was betterment in the table 

 quality of j)otatoes from sulfate of potash. A number of analyses of 

 starch were made in an endea^()r to correlate the presence of this carbo- 

 hydrate and the potash salt used. Dift'erences in starch content were 

 found to be of little significance and not correlated with the quality of the 

 tuber. 



These relatively minor although sometimes important differential 

 effects of the several potash salts are difficult to measure. Plates I and 11, 

 however, show these in a visual way for grass and clover and for potatoes. 



Effect of Sulfur 



In view of the fact that sulfur is occasionally deficient in soil and when 

 so deficient ranks as an "essential" plant food, comparison of average 

 yields under sulfur versus no sulfur treatments is of value. As calculated 

 from average analyses, there were applied on the sulfate of potash plots 

 184 pounds per acre of sulfur trioxide annually from 1894 through 1899, 

 115 pounds annually from 1900 through 1916, 69 pounds annually begin- 

 ning in 1917. On the muriate of potash plots, however, no sulfur was 

 u.sed save the very small c^mount contained in the bone, which is estimated 

 at 1-10 of 1 per cent, or slightly more than half a pound of sulfur trioxide 

 yearly. We do not know the amount which comes down annually with 

 precipitation. In any case, this amount must be similar on the plots under 

 discussion. Average yields of most of these crops as secured during the 

 course of the experiment have already been given. Owing to lack of 

 definite cropping system, it is impracticable to measure tendencies by com- 

 paring crops grown in recent years with those produced at an earlier date, 

 presumably before sulfur shortage, if any, had become serious. The yields 

 in the last five-year period prior to changing the concept of the experiment, 

 representing as they do the influence of twenty to twenty-five years of 

 sulfur versus no sulfur differential fertilization, do, however, throw light 

 on the question. There is no evidence that shortage of sulfur has been 

 reducing yields; nor that the sulfur in sulfate of potash was of significant 

 value to the crop. The yields follow: 



