THE SUPPLEMENT TO THE 



Tropical Agriculturist and Magazine of the C. A. 8. 



Compiled and Edited by A. M. & J. FERGUSON. 



No. 4.] APRIL, 1910. [Vol. VI. 



OBSCURE CAUSES OF UNPRODUC- 

 TIVENESS IN LAND. 



The occurrence of bare or unthrifty patches 

 in cultivated land often proves as much a source 

 of vexation as a cause for speculation, and it is 

 seldom that any satisfactory explanation of them 

 can be given. This matter has received the at- 

 tention of the Chemical Branch of the New 

 South Wales Department of Agriculture and the 

 contribution by Mr. Lionel Cohen to the "Agri- 

 cultural Gazette " of that Colony is full of interest 

 and instruction. A fact that tends to make the 

 study of the question more confusing than 

 otherwise is that the soil of these patches is 

 generally found by the chemist to be as well 

 supplied with plant food as the rest of the land. 

 It is to be inferred, therefore, that the unpro- 

 ductiveness of the soil in the areas referred to 

 must be due to the presence of some deleterious 

 substance inimical to plant life. Such substances 

 as carbonate of soda, sulphate of soda and com- 

 mon salt are well known to render land, parti- 

 cularly in arid areas, unfertile ; but these fami- 

 liar causes of barrenness can in most cases be 

 removed by judicious treatment, e.g., drainage, 

 irrigation and cropping. Other substances 

 which have a similar action are the lower oxides 

 and the sulphides of iron, as well as an excess 

 of magnesia over lime. Still other factors of 

 infertility are the toxic compounds of organic 

 origin, which have of late received consider- 

 able attention both in America and England. 

 Mr. Cohen has in his experience come across 

 patches of soil with a large percentage of 

 manganese, while only the merest traces were 

 found in the rest of the land ; and yet the 

 soil on the patches was richer in plant 

 food than the surrounding land, Mr. W. 

 P. Kelly, of the Hawaii Experiment Station, 

 records the failure of a soil to grow pine- 

 46 



apples owing to an excess of manganese, though 

 sugarcane grew luxuriantly on the same soil. 

 It would appear that certain plants are pecu- 

 liarly sensitive to the presence of certain sub- 

 stances in the soil : for instance, Barley to man- 

 ganese, while others, such as oats, sorghum and 

 maize, are not so sensitive. Here then are 

 further considerations for the agriculturist to 

 ponder over, and for the chemist to weigh, for 

 it would appear that not only must we know the 

 proportions of plant food in the soil, but also 

 ascertain to what extent undesirable compounds 

 (according to the idiosyncrasies of plants) are 

 present in it. They also point to the necessity 

 for carefully selecting crops suitable to parti- 

 cular conditions of soil. The occurrence of un- 

 productive tracts have also been traced to too 

 large a percentage of calcium chloride and 

 potassium chloride. In this connection might 

 be quoted Dr. Aikman's recommendation that 

 sulphate of potash is preferable to chloride of 

 potash as a manure, for the reason that the 

 chloride is liable to give rise to calcium chlo- 

 ride " a compound distinctly harmful to many 

 plants.'' According to Kuhn when ammon- 

 ium chloride is applied to a soil the ten- 

 dency is for the ammonia to be assimilated 

 and the chloride to form hydro-chloric acid 

 to such an extent as to prove fatal to plants. 

 At the Woburn Experimental Farm (England) 

 the continued use of ammonium. salts (sulphate 

 and chloride) has brought about an acid condi- 

 tion resulting in complete sterility, which, how- 

 ever, could be neutralised by the application of 

 time. It may thus happen that manuring nth 

 chemical manures may actually result in harm 

 if their action and reaction are not fully under- 

 stood. All this shows how complex is the science 

 of agriculture and how much iight can be thrown 

 upon the subject by the labours of the working 

 scientist. 



