Nov. 4, i9i8 Soil Factors Affecting the Toxicity of Alkali 319 



(4) Loam soils are more tolerant of alkali than either sand or clay. 

 The coarser loams are more tolerant than the finer at the same moisture 

 content, but if the heavier loams are maintained at an equivalent moisture 

 content they are more tolerant. 



(5) Organic matter increases the resistance to alkali when the soil 

 containing it is given sufficient moisture, but where present in large 

 quantities organic matter decreases the resistance if the moisture supply 

 is low. 



(6) Increasing the moisture content of a soil up to the maximum that 

 will produce good crops increases resistance to alkali. 



(7) The toxicity of sodium chlorid and sodium sulphate seems to 

 depend to quite an extent on the relation between concentration of salt 

 and percentage of moisture present, while the toxicity of sodium car- 

 bonate is more largely affected by the presence of organic matter. 



(8) Organic matter in the soil seems actually to remove sodium car- 

 bonate from the soil solution in large quantities. 



(9) This probably explains why in experiments where sodium carbonate 

 is added to a loam soil, it is less toxic than sodium chlorid, while in field 

 studies where the salt is determined by analyses, and in solution and 

 sand culture studies the sodium carbonate is more toxic. 



Practical conclusions that may be drawn from these experiments are: 

 (i) Loam soils and soils with a high water-holding capacity may be 

 successfully farmed at a higher alkali content than others. 



(2) Soils in which alkali reduces crop yields should be kept as moist 

 as is compatible with good plant growth. 



(3) Manure, or other organic matter, should be beneficial to alkali 

 soils, especially those high in carbonates. 



