October, 1909,] 



327 



Scientific Agriculture, 



shown equally satisfactory results. A 

 publication of the U. S, Department of 

 Agriculture mentions that in a very 

 large number of experiments with 

 various legume crops carried on in 

 sixteen States, a gain of 122 lb. of 

 nitiogen per acre was indicated. At 

 the Delaware Experimental Station, 

 a crop of crimson clover was found to 

 have added as much as 200 lb. of nitro- 

 gen per acre to the soil in one season. 

 Cowpeas are not infrequently grown in 

 rotation with cotton in some of the 

 cotton-growing districts of the Southern 

 States of America. An instance report- 

 ed by the Alabama Experiment Station 

 indicates the beneficial influence of the 

 legume crop on the succeeding crop of 

 cotton. In this case there was noted an 

 increase of 6961b. in the yield of seed- 

 cotton to the acre, or 83 per cent., as the 

 result of ploughing under a crop of cow- 

 pea vines on land which had been in 

 cotton in the previous season. 



The annals of the Rothamsted Experi- 

 ment Station contain many illustrations 

 in point. Thus an experiment is 

 recorded in which a piece of laud, 

 which in the previous five years had 

 grown cereal crops without nitrogenous 

 manure, was divided into two parts in 

 1872, one being sown with barley and 

 the second with clover. Barley was 

 again grown on the first plot in 1873, but 

 the clover was allowed to stand, three 

 cuttings being made for fodder purposes 

 during the season. The quantities of 

 nitrogen in the crops from the two plots 

 were 37*3 lb. in the barley yield, and L51*3 

 in the clover. An analysis of the soil 

 was made after the crops had been re- 

 moved, which showed a content of , 1566 

 per cent, of nitrogen in the first 9 inches 

 from the surface in the plot where clover 

 had been grown for two seasons, as com- 

 pared with a nitrogen content of 0"1416 

 per cent, on the other portion. In 1874, 

 barley was once more grown on both 

 plots, the quantity of nitrogen removed 

 in the barley following barley being 

 39-1 lb., while in the barley following 

 clover 69'4 lb. were r emoved 



Another experiment was carried out 

 on land which at the start contained 

 2,657 lb. of nitrogen per acre in the first 

 9 inches from the surface. Barley and 

 clover were grown in 1883, and clover 

 only in 1884 and 1885. It was estimated 

 that 319'5 lb. of nitrogen was removed 

 in the crops cut during the three years, 

 but a soil analysis made at the end 

 showed that nitrogen equal to 2,832 lb. 

 was present in the top 9 inches, or a 

 gain of 175 lb. per acre in the three 

 years, making a total, with the crop 

 removed, of nearly 500 lb. of nitrogen per 

 acre to be accounted for. The work, 



therefore, done by this partnership be- 

 tween leguminous plants and the nodule- 

 producing bacteria is of the utmost im- 

 portance, and must annually add to 

 the wealth of the world many hundreds 

 of thousands of pounds sterling. 



With the facts already enumerated 

 before them, it was natural that workers 

 in agricultural science should begin to 

 debate the question whether the majo- 

 rity of cultivated soils were sufficiently 

 well stocked with nitrogen-gathering 

 bacteria to give the best results when a 

 leguminous crop was grown, or whether, 

 by the introduction into soils of the 

 suitable organisms, and the more extend- 

 ed growth of legumes, considerable in- 

 crease in crop yields could not be obtain- 

 ed. A great deal of experimental work 

 in relation to this subject has been done 

 in the past twenty-three years. 



Iu work of the nature referred to, it is 

 obvious that the main point is to ensure 

 the presence of the assimilating bacteria 

 in the soil under experiment. This can 

 be done by distributing: over the land, 

 and slightly harrowing; in, a supply of 

 soil taken from a field which has just 

 previously yielded a flourishing crop of 

 the legume to be grown. As early as 

 1887 soil inoculation experiments of this 

 kind were undertaken by Salfeld at 

 the Moor Culture Experiment Station, 

 Bremen, Germany. The trials were made 

 with such legumes as lupins, serradella, 

 clover and beans, on reclaimed peaty 

 and sandy soils, on which, without 

 inoculation, such crops made but little 

 growth, and developed no root nodules. 

 About 3| cwt. of suitable soil were dis- 

 tributed per acre over the land, and 

 harrowed in before sowing the seed. The 

 results of Salfeld's work were strikingly 

 successful. As the season advanced, the 

 effect of the inoculation was markedly 

 evident in the dark-green colour and 

 luxuriant growth of the plants, on the 

 land which had been treated as described, 

 as compared with the land where no soil 

 had been scattered, which bore very 

 small yellow plants that ultimately died 

 of nitrogen hunger. 



Salfeld's results were received with 

 great interest, and the example thus 

 set was shortly followed by a number 

 of investigators working with many 

 different kinds of soils. A satisfactory 

 measure of success was achieved in some 

 instances, but many cases were recorded 

 iu which the results were negative, and 

 the opinions entertained as to the 

 practical value of soil Inoculation were 

 of a very contradictory nature. On 

 sandy heath soils, on moorland recently 

 placed under cultivation, and on raw 

 soils brought up from deeper layers by 

 the plough, the operations had uudoubt- 



