PLANT NUTRITION 275 



impioxcinciil in sliiulinc laxois root dcNclopnunt and ])l;uU giowlli 

 and decreases soil erosion. Apjilications ol \\ciI-dc(()nij)osetI manure 

 improve light sandy soils by increasing their moisture-holding capacity. 



The greater humus content lollowing manurial treatment darkens 

 the soil and increases heat absorption from the sun. The higher tem- 

 perature o[ the soil is advantageous where early development or 

 growth is desired. 



BIOLOGICAL EFFECTS. The biological effects of a manure treatment 

 may be more important than the physical and chemical effects. An 

 application of manure supplies numerous bacteria and other or- 

 ganisms, a number of which will continue to thrive and to multiply. 

 Such an addition stimulates the multiplication of many native soil 

 organisms as well. The metabolism of soil organisms produces cement- 

 ing substances called "bacterial cement," which causes aggregation of 

 soil particles. 



The fact that small applications of manure exert a much more 

 favorable influence on plant growth than can result from the nutrient 

 content alone has been attributed to the inoculation of the soil with 

 desirable organisms and to the increased development of similar or- 

 ganisms peculiar to the soil. This increased bacterial activity is 

 thought to result in the production of plant stimulants analogous to 

 vitamins and hormones. 



REFERENCES 



Mineral Nutrition and the Balance of Life. F. A. Gilbert. University of Oklahoma 



Press, Norman, Okla., 1957. 

 Mineral Nutrition of Plants and Animals. F. A. Gilbert. University of Oklahoma 



Press, Norman, Okla., 1948. 

 Trace Elements in Plants and Animals. VV. Stiles. Cambridge University Press, 



Cambridge, England, 1951. 



