286 Nutrients 



growth. In certain parts of Australia hardly any production of clover 

 could be obtained although general growth conditions and the supply 

 of common nutrients in the soil seemed to be adequate. After a long 

 study it was discovered that required trace amounts of molybdenum 

 were lacking in these areas. When the astonishingly small quantity 

 of 5g of molybdenum per hectare ( H 6 oz per acre ) was added to 

 the soil, a thick growth of clover more than 30 cm high was obtained. 



As a result of generations of study of the nutrient needs of agricul- 

 tural plants we have accumulated a considerable knowledge regarding 

 the use of commercial fertilizers for our common annual crop plants. 

 Bags of chemical fertilizers that we see being applied to farms bear 

 designations such as 6-8-4 or 5-10-5. These numbers refer to the per- 

 centages of total nitrogen, available phosphoric acid (P2O5), and 

 water-soluble potash (K2O) that are contained in the fertilizer. 

 Great success has been attained in supplying these commonly de- 

 ficient materials to agricultural lands by means of such chemical fer- 

 tilizers. However, we still know extremely little about deficiencies in 

 trace elements and in the more complicated organic compounds. 

 These materials also are leached from the soil by rain, and removed 

 from the area when crops are harvested. In the movement known 

 as "organic farming" the plowing-in of green manure and other types 

 of organic materials is especially recommended with the hope of re- 

 plenishing as many as possible of the trace elements and organic 

 constituents that are removed from the soil as the result of farming. 

 Crops grown with a full supply of all nutrients, minor and major, will 

 be more vigorous, more resistant to disease and provide more com- 

 plete nourishment for man and the domestic animals using them 

 as a source of food. 



We have much less information about the needs and deficiencies 

 of nutrients for natural vegetation in uncultivated areas. For forest 

 land the time scale is entirely different, and the critical nutrients may 

 also be different. When a crop of trees is harvested after 40 years' 

 growth, we do not know what loss of nutrients the soil has sustained 

 during this long period, nor do we know how to treat forest land to 

 maintain its productive capacity. 



Aquatic plants have the same general nutrient requirements as ter- 

 restrial plants, and, interestingly enough, two of the elements that 

 are critical on land, nitrogen and phosphorus, are also likely to be 

 seriously scarce in the water environment. Potassium is ordinarily 

 sufficiently abundant in fresh water, and reference to Table 3 will 

 indicate that it is one of the six most abundant ions in sea water. 

 Other materials occurring in small or trace quantities may sometimes 



