IRISH GARDENING 



VOLUME V. 



No. 56 



A MONTHLY JOURNAL DEVOTED TO THE 



ADVANCEMENT OF HORTICULTURE AND 



ARBORICULTURE IN IRELAND 



OCTOBER 

 1910 



Bacteria in Relation to Crops 



II.— NITRIFICATION. 

 By Patrick Duffy, Associate of the Royal College of Science for Ireland. 



^01 L fertility depends 

 to a great extent 

 upon the activity 

 of certain races 

 of bacteria. As 

 shown in a pre- 

 \' i o u s article 

 (pag-e 81), the 

 amnion ification 

 changes that take 

 place in the soil 

 are entirely due to 

 bacterial action. Nitrification is another and 

 equally important factor in sustaining- tlie fer- 

 tility of the soil. 



Ammonification is closely allied to nitrification, 

 indeed the latter is the complement of the former 

 as we shall endeavour to show. As has been 

 explained in the article already referred to. 

 Ammonification is the breaking' down ot 

 complex nitrog-enous matter into ammonia. 

 Nitrification is, on the other hand, a build- 

 ing up process, whereby the ammonia is 

 converted into nitric acid and thence to a 

 nitrate. In a nitrate the nitrog-en is in a 

 form easily soluble and most readily available 

 as a food material for plants. Hence, any 

 process or agency that can chang-e the unavail- 

 able nitrog-en in the soil into a form that can be 

 made use of by plants, is deserving- of the 

 attention of the crop raiser. Such a process is 

 going on constantly in most soils, so that the 

 amount of nitrates in such soils will increase if 

 not removed by plants or washed away by 



drainage. When it is remembered that nitrogen 

 is the most costly element of artificial fertilisers, 

 and that in the form of a nitrate it is most readily 

 made use of by crop plants, the importance of this 

 process of nitrification may be realised. We 

 have next to consider how the process is 

 brought about. 



The building up of nitrates from ammonia is 

 a bacteriological process. It is effected by 

 minute organisms which are natural to the soil, 

 and are also found in large numbers in farmyard 

 manure. There are certain conditions of food 

 and environment which act advantageously — or 

 the reverse — on these organisms, and a know- 

 ledge of these conditions is essential to a proper 

 grasp of the many and complex problems of 

 soil fertility. Although these nitrifying bacteria 

 are present in most soils, their activity varies 

 greatly in different soils. They are active 

 where the conditions are favourable and inactive 

 or only feebly active where the conditions are 

 unsuitable Unlike the ammonifying bacteria, 

 they are prevented from carrying on their work 

 in the presence of soluble organic matter. 

 Farmyard manure when not well rotted contains 

 considerable soluble organic matter, so that 

 when added to the soil in quantity it checks 

 the formation of nitrates, the nitrifying 

 bacteria remaining inactive until tiic soluble 

 organic matter is decomposed by the ammoni- 

 fying and other bacteria which act on such 

 material. When the soluble organic matter 

 has almost all been decomposed the nitrifying 

 bacteria commence to use up the ammonia 



