FERTILIZERS, OTHER THAN NITROGENOUS 223 



fertilizer amounts to over twice that taking place when nitrate of soda 

 is appHed. The change in soil reaction occasioned by one or two succes- 

 sive applications of the same material would seldom be large enough 

 to have great practical importance in the orchard, but since the effects 

 are cumulative repeated applications for many years might conceivably 

 result in injury to the trees. The remedy for this situation is the use first 

 of the nitrate of soda and then of the sulphate of ammonia, keeping the 

 soil reaction about as it is at the outset. 



Attention should be called to the inconsequential difference obtained 

 in actual field trials from the use of these nitrogen-carrying fertilizers 

 when nitrogen is the limiting factor and when amounts are used carrying 

 approximately the same quantities of nitrogen. Nitrate of calcium 

 has been emploj^ed occasionally as a fertilizer in an experimental way and 

 the response has not differed materially from that to nitrate of soda. 



The diiferent influences of these nitrogenous fertilizers on the inter- 

 cultures in the orchard may be of greater significance than the differences 

 in their direct influence on the trees. The acidic influence of the sulphate 

 of ammonia is likely to increase gradually the growth of certain species 

 like bluegrass, timothy, redtop and orchard grass and to decrease the 

 growth of the clovers and certain other legumes. The basic influence of 

 the nitrate of soda has the opposite effect. This is brought out strik- 

 ingly by work at the Rothamstead Experimental Station'^o extending 

 over a period of 30 years. Therefore if certain leguminous cover crops 

 are to be grown or more especially if it is desired to keep the orchard in a 

 permanent clover or alfalfa sod, some caution should be exercised in the 

 use of sulphate of ammonia. Sodium, calcium or potassium nitrates could 

 be used more safely. 



The results of many investigations^"" with field crops indicate that a 

 given quantity of nitrogen in the form of nitrate of soda has a greater 

 influence than the same amount carried in many other fertilizers. That 

 is, it has more crop producing power when held in one form than in 

 another. Furthermoi'e this relative efficiency varies with many factors, 

 such as the kind of crop plant and the character of the soil. Presumably 

 this varying crop producing power is associated with secondary or indirect 

 effects that the fertilizer or its disintegration products may have on the 

 plant through their influence on soil reaction, the availability of other soil 

 constituents and many other soil conditions and processes. Very little 

 is known regarding the varying crop-producing value of nitrogen qarried 

 in different fertilizers when they are used on fruits. 



Nitrogen from Organic Sources. — A word should be said regarding the 

 use of certain nitrogen-carrying organic fertilizers. Barnyard compost 

 and green manuring crops have been recommended often as the best 

 sources of nitrogen for the orchard. There can be no doubt but that 

 they are effective fertilizers when nitrogen is a limiting factor, often 



