114 



Agricultural Gazette of N.S.W. 



[Feb. 2, 1920. 



by field tests to be absolutely wrong. The crop must have in an easily 

 soluble form all the plant food it needs ; otherwise the size of the crop is 

 limited by the amount of plant food which is easily available. Some reganl 

 must therefore be paid to the plant food removed by the crop from the soil. 

 This is now considered to be of more importance than the total amount of 

 plant food (much of which is insoluble to the plant) present in the soil. In 

 other words, chemical analysis of the soil is no guide to fertiliser requirements, 

 but in a study of the plant food removed by different crops from the soil and 

 actual field tests with different fertiliseis, there is bright hope for the correct 

 and profitable use of fertilisers to ensure the permanent fertility of the soil. 

 The two following tables show (1) the amount of plant food removed by 

 an average maize crop and (2) the amount supplied by artificial fertilisers : — 



Table showing Plant Food removed from one acre by an 

 average Maize crop. 



Crop. 



Nitrogen. 



Phosi^horic 

 Acid. 



Potash. 



If the stalks aie returned to the soil, whether by feeding off or by 

 ploughing under, it may be reckoned that only 50 lb. nitrogen is removed 

 instead of 75 lb., and that the bulk of the phosphoric acid and pota.sh in the 

 stalks is also xeturned to the soil thereby. AVhen the stalks are burnt, 

 however, the whole 75 lb. of nitrogen is removed from the soil, and some of 

 the potash (now largely in a water-soluble form in the ash) will also be 

 lost from a sandy soil by leaching. The loss could be minimised by growing 

 a cover crop during the winter, provided the rainfall is high during this 

 period. It ma}'^ be reckoned that ten shillings worth of fertility is destroye.d 

 from an acre by burning the stalks from a 50-bushel maize crop. 



Tahle showing Plant Food supplied ))er acre by different Artificial Fertilisers 

 commoidy applied (alone or in mixtures) to Maize in New .South Wales. 



P7 mixture consists of equal parts of superphosphate and bonedust ; P8 of equal parts 

 of superphosphate and blood and bone ; and P5 of 4 pans superphosphate to one part 

 sulphate of potash. 



