172 



THE GAKDENEK'S ASSISTANT. 



expended upon it, the fertility must be main- 

 tained by a gradual development of the im- 

 mense store of plant-food which lies in a dormant 

 condition within the soil, assisted from some 

 external source in the form of manure. Ju- 

 diciously used special manures, such as guano, 

 nitrate of soda, sulphate of ammonia, potash 

 salts, superphosphate, &c, are the agents which 

 bring into useful activity the dormant resources 

 of the soil; they restore the proper balance 

 between the different constituents, and supply 

 the excessive demand for some particular ele- 

 ment. In addition to the special food-supply 

 contributed by these artificial manures, they 

 are, as a rule, more active, and give quicker 

 returns, than farmyard or stable manure. But 

 to the bulk of ordinary gardeners, farmyard 

 manure is the sheet-anchor, mainly because it 



is so easily applied, and most of the more im- 

 portant ingredients of plant-food are thus pro- 

 vided, although these may not always be in the 

 best proportions. 



Experiments with Potatoes. — At Eothamsted, 

 Hertfordshire, Sir J. B. Lawes and Sir J. H. 

 Gilbert have conducted a series of experiments 

 upon the growth of Potatoes grown year after 

 year upon the same land since the year 1876. 



The crop is grown without manure, with 

 farmyard manure, and with various descriptions 

 and combinations of artificial manure, in ten 

 plots. For the first four years the variety of 

 Potato planted was " The Eock ", for the next 

 eleven years "The Champion", and for the 

 next five years "Sutton's Abundance". The 

 following table gives a summary of the produce 

 up to the year 1895: — 



Yield of Potatoes per acre, at Rothamsted. 





Good. 



Small. 



Diseased. 



Total 

 Tubers. 



Per cent 

 Diseased 

 in Total. 





tons. 



cwts. 



tons. 



cwts. 



tons. 



cwts. 



tons. cwts. 



per cent. 



Unmanured, 



1 



13i 







5 







14 



1 19| 



3-15 



Superphosphate, 



3 



5 







5 f 







2| 



3 133 



3-66 



Mixed mineral manure, 



3 



1 



18? 







4^ 







2f 



3 15^ 



3-45 



Ammonium salts, 400 lbs., . 



1 







6* 







U 



2 5f 



4-06 



Nitrate of soda, 550 lbs., 



o 







H 







2f 



2 12i 



4-93 



Ammonium salts and minerals, 



D 







U 







8# 



6 14i 



6-26 



Nitrate of soda and minerals, 



5 



m 











9 i 

 3! 



6 13 



7'00 



Farmyard manure, 14 tons, ... 



3 



Vlh 







% 







4 2| 



4-56 



The general conclusions drawn from these 

 experiments is that, although the Potato crop 

 requires a full available supply of mineral con- 

 stituents within the soil, yet, these conditions 

 being provided, the amount of produce is largely 

 dependent on the available supply of nitrogenous 

 elements. In practice farmyard manure is mainly 

 relied upon to give this substance. It is used 

 in very large quantities per acre, and is some- 

 times supplemented by liberal dressings of arti- 

 ficial manures, both mineral and nitrogenous. 

 The crop removes, however, a less proportion 

 of the nitrogen of farmyard manure than any 

 other farm crop. This is the reason why culti- 

 vators of plants which do not like crude manure, 

 such as bulbs, prepare the ground for them by 

 first manuring and cropping it with Potatoes, 

 after which it is safe for the bulbs. 



It was found that the most characteristic 

 result of the increased growth of the Potato 

 under the influence of nitrogenous manures was 

 an increased production of the non-nitrogenous 

 constituent — starch. It was shown, however, 

 that for one of nitrogen supplied in manure, 



the increased amount of starch obtained in the 

 Potato was less than the increased amount of 

 sugar obtained in the Mangel Wurzel, and much 

 less than that yielded in the sugar Beet. It was 

 further found that although a larger proportion 

 of the total nitrogen of the Potato is in the 

 albuminoid condition than in the case of root- 

 crops, yet from 40 to 50 per cent of the total 

 nitrogen of the tuber may exist in the soluble 

 condition in the juice ; and it is obvious that in 

 the usual mode of cooking the Potato for the 

 table, most of this is lost as food. 



Next, the results show that Potato disease, 

 though largely dependent on season, developed 

 much more in tubers grown by highly nitro- 

 genous manures, and containing a juice rich 

 in nitrogen, than under contrary conditions. 

 Finally, it was shown that a result of the 

 disease is a destruction of starch, the formation 

 of sugar, the loss of organic substance, and the 

 growth of the fungus at the expense of the 

 substance of the tuber by the absorption of the 

 products of assimilation formed in the leaves 

 and intended to be stored up in the tuber. 



[j. J. w.] 



