JtTtffl 1908,] 



555 



Scientific Agriculture- 



Insofar as the increase of combined 

 nitrogen in the soil is concerned, the 

 amounts brought down in the rain and 

 snow, or absorbed as ammonia from the 

 humus, are of minor importance. They 

 do not exceed a few pounds per acre 

 annually. On the contrary, the gain of 

 nitrogen compounds in the soil through 

 the agency of bacteria is very important. 

 It was largely through the work of these 

 microscopic beings that our soils have 

 been enabled to accumulate their store 

 of nitrogen, and their work in the 

 present is no less important than it was 

 in the past. A better knowledge of these 

 bacteria must prove of great benefit to 

 every farmer, since such knowledge will 

 enable him to utilize them to the best 

 advantage in providing nitrogeon for his 

 crops. 



Among the conditions which must be 

 metin order to render the soil a suitable 

 medium for the rapid and vigorous 

 growth of nitrogen-gathering bacteria 

 are those of moisture, humus and miueral 

 salts. Bacterial life soon comes to a 

 standstill in soils deficient in moisture. 

 Similarly, bacteria as living things must 

 have food, and this they find in the 

 humus. Hence humus is important not 

 only as a source of food to bacteria, but 

 also in creating conditions favorable for 

 their development, since the greater the 

 amount of hum as the greater theamount 

 of moisture in the soil, and the greater 

 the amount of moisture, the more 

 rapid the growth of the bacteria. 

 We should remember likewise that 

 bacteria are after all only minute plants, 

 and as such they need a supply of avail- 

 able lime, phosphoric acid and potash. 

 Soils poor in these constituents are un- 

 sifted for the intense growth of bacteria 

 and therefore are unsuited for the 

 vigorous growth of crops. The need of 

 large quantities of mineral plant food is 

 particularly prominent in the case of 

 leguminous crop-, crops which form a 

 partnership with bacteria in their roots 

 and become enabled thereby to draw 

 lavishly on the vast store of nitrogen gas 

 in the air. The clovers, lupines, alfalfa, 

 the vetches, etc. thus create a supply of 

 nitrogen not only for themselves but 

 also for the non-leguminous crops which 

 feed on their decaying remains. It 

 should be remembered, however, that in 

 this process of nitrogen-accumulation by 

 legumes, large amounts of lime, phos- 

 phoric acid and potash are used up ; hence 

 the best results in the utilization of 

 atmospheric nitrogen by leguminous 

 crops can be secured only Avhere ample 

 provision is made for the supply of the 

 mineral iugredients of plant food. 

 Repeated experiments have demonstrat- 

 ed that under favourable conditions 

 70 



leguminous crops may contain 100 to 200 

 pounds of nitrogen per acre, most of it 

 derived from the air. It is evident thus 

 that with an abundance of lime, phos- 

 phoric acid and potash, the accumulation 

 cf atmospheric nitrogen by legumes is 

 only governed by climatic conditions, 

 and by the numbers and vigor of the 

 bacteria in the root nodules. If is for 

 this reason that soil inoculation, that is, 

 the introduction into the soil of large 

 numbers of the desired bacteria, may 

 under suitable conditions prove of great 

 advantage to the farmer who would 

 make use of atmospheric nitrogen by 

 means of leguminous crops. 



The different methods of soil-treatment 

 largely aim either to conserve the 

 nitrogen compounds already in the soil, 

 or to add to their amount by applications 

 of nitrogeneus material. We may note 

 among these methods of treatment 

 fallowing, green-manuring, the appli- 

 cation of barnyard manure and the 

 application of nitrogen salts or of other 

 commercial forms of combined nitrogen. 



Fallowing was once an essential part 

 of farm practice, for it was believed that 

 soils need rest, and practical experience 

 had really demonstrated that larger 

 crops could be raised after bare 

 fallows than could be secured in the con- 

 tinuous growing of crops. With the 

 introduction of hood crops the practice 

 of fallowing lost ground, for it was re 

 cognized that it was, on the whole, a 

 wasteful system. More recently fallow- 

 ing has been made the subject of much 

 discussion. The discovery of nitrogen- 

 gathering bacteria living by themselves 

 in the soil, and likewise of the fact that 

 they grow abundantly in bare fallows 

 has led to the belief that they may be- 

 come an important means for the utiliza- 

 tion of atmospheric nitrogen. The ex- 

 perimental evidence available, however, 

 fails to support this view, aud we must 

 regard fallowing as a method extremely 

 wasteful of plant food. 



Whatever the value of fallowing as a 

 means of increasing the nitrogen con- 

 tent of the soil, the efficiency of green- 

 manuring for this purpose has been 

 effectively demonstrated. Green manur- 

 ing has proved most successful on light 

 soils, not only because such soils compel 

 the leguminous crops to utilize exten- 

 sively the nitrogen of the air, but also 

 because these crops decay rapidly when 

 incorporated into sandy laud, and furnish 

 thus an abundant supply of available 

 nitrogen food to sunceedine: non-legu- 

 minous crops. A brilliant demonstration 

 of the significance of leguminous green 

 manures on sandy soils is furnished by 

 the classical work of Schulz-Lupiz. lie 



