60 FERTILIZERS 



IRRIGATION AND FERTILIZERS. 



94. Plants can take up food, only when it is pro- 

 vided in solution. The food may be dissolved by 

 water, or by direct root action, or by the process of 

 fermentation, which is almost constant in all soils. 

 In either case water is essential, and the common 

 carrier, and the way in which it is used, seriously 

 effects the results of fertilization. Especially is this 

 true because the top foot of soil contains the most 

 valuable fertilizing ingredients. 



There are three kinds of water in soils : free water 

 which moves by gravity ; hygroscopic water, detect- 

 able only by laboratory methods even in the dryest 

 earth, and capillary water, which moves by the 

 power of attraction between particles of matter. 

 This capillary water is what plants feed and depend 

 upon mainly. It travels up and down freely with 

 very little motion, sideways, carrying with it the 

 soluble fertilizers. 



95. It is useless to apply fertilizers on dry ground 

 that is not dampened by irrigating water, as for 

 instance ; far under very old trees or on the midway 

 spaces in young orchards where furrows are not 

 made. 



As moisture evaporates at the surface, it is con- 

 stantly supplied from below by the capillary move- 

 ment. The dissolved fertilizers contained, remain at 

 the surface from which the water evaporates ; hence 

 they accumulate so that top soils are always the 

 richest. The next rain or irrigation carries the plant 

 food down only to rise again as evaporation pro- 

 gresses at the surface. There is thus an oscillation 

 of water containing many kinds of plant food, up 

 and down many times a year. 



