864 ANNUAL REPORT OF THE Off. Doc. 



A comparison of the different sources of insoluble phosphoric acid 

 as given by the tigures in Table 19, page G2, shows slag phosphate 

 to have produced the larger total yield (also a larger yield of both 

 grain and fodder) than either soluble or reverted phosphoric acid. 

 Bone meal produced a little more grain than any other form of in- 

 soluble phosphoric acid, but the cost per pound of plant food was 

 about 50 per cent, more than that in the slag and three times as 

 much as that in the South Carolina rock and Florida phosphates. 

 The insoluble phosphate of lime, as furnished by the South Caro- 

 lina rock, gave better results than the insoluble phosphate of iron 

 and alumina as furnished h\ the Florida soft phosphate. 



GREEN CROPS FOR TURNING UNDER WITH INSOLUBLE PHOSPHATES. 



In order to test the value of green crops, or vegetable matter, 

 for rendering insoluble phosphates available, four plots had crimson 

 clover seeded in corn for turning under; four plots had rye in the 

 same manner, while four others had no green crop turned under and 

 were allowed to remain bare during the winter. These plots showed 

 the average results to be considerably in favor of the crimson clover 

 for this purpose. Part of the advantage of the clover no doubt ex- 

 isted in the nitrogen w^hich it furnished and also in the available 

 plant food which it brought from the sub-soil. The clover decom- 

 poses rapidly and aids the physical condition of the soil. The rye 

 used seems to have been a disadvantage and did not give as good 

 yields as when no green crop was used. This was particularly the 

 case with the corn crop. The disadvantage rested, probably, in the 

 rye decomposing slowly and thus producing a bad physical state at 

 times and making the corn crop suffer from dry weather. 



There is one fact worthy of note, though not directly concerning 

 the experiment under discussion, and that is that by turning under 

 a large amount of leguminous crop like crimson clover, corn can 

 be successfully grown for a number of years in succession with in- 

 creasing yields. 



CONCLUSIONS FROM THE MARYLAND STATION EXPERIMENTS. 



In the matter of drawing conclusions it is always well to be 

 cautious and to err, if at all, on the side of conservatism. This 

 policy is particularly w^ell adapted with reference to the applica- 

 tion of the results which have been obtained in the experiments 

 under consideration and in using the conclusions that may be 

 drawn. 



There is no doubt that the results, as shown by the total product 

 of the crops for five years (last column, Table 19, page 62), are, at 



