58 



SCIENCE. 



[Vol. IV., No. 76. 



als in phosphoric acid, and root-crops in potash) 

 has frequently led to the compounding of so-called 

 special fertilizers or manures, intended to be particu- 

 larly adapted to the growth of certain crops. The 

 starting-point in the preparation of such fertilizers 

 has usually been Liebig's 'restitution theory' (ersatz- 

 lehre), according to which the soil must be manured 

 with the same quantities of fertilizing materials as 

 are removed by the crops produced. On this theory, 

 a special manure for beans would contain much 

 nitrogen, and one for corn or wheat much phosphoric 

 acid. Such special manures were first brought prom- 

 inently into notice in this country by Professor Stock- 

 bridge of the Massachusetts agricultural college, and, 

 for the last few years, have enjoyed great popularity, 

 almost every prominent fertilizer-manufacturer pro- 

 ducing fertilizers for all conceivable crops, even to 

 orange-trees. These fertilizers have seldom had the 

 same composition in two successive years ; and those 

 of each maker have differed from those of every 

 other, thus affording to consumers an abundant 

 variety from which to choose. 



It is not proposed here to enter into a consideration 

 of all the numerous fallacies involved in the use of 

 special manures, but only to present the results of 

 some recent experiments, which have an important 

 bearing upon the fundamental idea of such fertilizers. 

 This idea is, in brief, that crops must be manured 

 most abundantly with those elements which they 

 contain most abundantly. There are not wanting, 

 however, indications that this is not altogether true. 

 For example: wheat contains, on the average, about 

 half as much nitrogen as clover; yet experience has 

 shown that wheat is greatly benefited by nitrogenous 

 manures, while clover is comparatively indifferent to 

 them. Indeed, it is a common practice to grow wheat 

 after clover, using the latter crop to gather nitrogen 

 for the former. Many other similar cases might be 

 cited ; and it is a noteworthy fact that many special 

 manures, while professing to be compounded on the 

 theory stated above, are, in fact, modified to corre- 

 spond with these teachings of experience. 



All this suggests that one important factor in deter- 

 mining the most suitable manuring for any crop is 

 the power which that crop has of gathering its sup- 

 plies from natural sources. Paul Wagner has recently 

 published 1 some investigations upon this subject, 

 which are interesting, both in themselves and in their 

 suggestions for future work. He compared peas and 

 barley, growing them in zinc vessels twenty-five centi- 

 metres high and twenty-five centimetres in diameter. 

 These vessels were uniformly filled with carefully 

 mixed and sifted soil, were provided with a constant 

 water-supply, and, in short, differed only in the 

 manuring which they received. 



The following manurings were given in each 

 series: No. 1, nothing; No. 2, nitrogen; No. 3, pot- 

 ash; No. 4, phosphoric acid; No. 5, phosphoric acid 

 and nitrogen; No. 6, nitrogen and potash; No. 7, 

 potash and phosphoric acid; No. 8, potash, nitrogen, 

 and phosphoric acid. Each manuring was duplicated, 



1 Landic. jahrbiicher, xii. 717. 



so that thirty-two vessels were used in all. Nitrogen 

 was given in every case at the rate of 40 kilos per 

 hectare, in the form of nitrate of soda; potash, at the 

 rate of 80 kilos per hectare, in the form of chloride; 

 phosphoric acid, at the rate of 100 kilos per hectare, 

 in the form of superphosphate. The duplicate manur- 

 ings gave reasonably accordant results, and the 

 author estimates the limits of error at 3 % of the total 

 yield. The following table shows the relative yield 

 of total air-dry matter (grain and straw), that of the 

 unmanured vessels being taken as 100. 



No. 



Manuring. 



Nothing 



Nitrogen 



Potash 



Phosphoric acid 



Phosphoric acid and nitrogen .... 



Nitrogen and potash 



Potash and phosphoric acid .... 

 Potash, phosphoric acid, and nitrogen, 



Crop. 



Peas. 



Barley. 



100 



100 



104 



113 



100 



107 



126 



113 



132 



146 



102 



121 



147 



126 



151 



181 



A study of these figures, remembering that differences 

 of three or four per cent have no significance, leads 

 to the following conclusions: — 



The nitrogen had as good as no effect upon the 

 peas (compare 1 with 2, 3 with 6, 4 with 5, and 7 with 

 8: the greatest difference is 6%). The same com- 

 parison for the barley shows that the nitrogen here 

 had a very beneficial effect, the increase in the crop 

 amounting to from 13% (nitrogen alone) to 55% 

 (nitrogen in combination with potash and phosphoric 

 acid). Interesting differences in the effect of potash 

 and of phosphoric acid upon the two plants are also 

 evident, but we pass over these for the present. 



The nitrogen of the unmanured soil amounted to 

 13.77 grams in each vessel; that of the manuring, to 

 0.2 of a gram. The nitrogen of the unmanured soil 

 was fully sufficient to supply the needs of the peas, 

 as the following considerations show. There were 

 produced — 



Without manure 



With nitrogen 



With potash and phosphoric acid, 



With potash, phosphoric acid, and 



nitrogen 



Containing 

 nitrogen. 



0.91 grams. 

 0.95 " 

 1.34 " 



1.37 " 



That is to say, manuring with potash and phosphoric 

 acid enabled the peas to produce 47% more dry mat- 

 ter, the 0.43 of a gram of nitrogen necessary for this 

 increase being obtained as readily from the compara- 

 tively insoluble nitrogen of the soil as from the solu- 

 ble nitrogen added as manure. 



For the production of barley, the figures stand as 

 follows : — 



