10 JAMESTOWN CONGRESS. OF HORTICULTURE 



SOILS. 



THEIR PRODUCTIVITY AS INFLUENCED BY COMPOSITION AND STRUCTURE. 



F. H. KING, MADISON, Wis. 



Soils are an aggregation of rock and mineral fragments carrying 

 an admixture of organic debris, together with substances in soluble 

 and colloidal condition. The productivity of soils is determined by 

 their composition, by their structure, by their climate, and by the life 

 activities within them. By composition we refer to their mineral and 

 chemical nature ; by their structure we refer to the size of the soil 

 grains and the segregation of them; by their climate we refer to 

 their water content, their temperature, their aeration, their drainage; 

 by life activities we refer to the interaction of the roots of plants 

 and micro-organisms upon one another, upon the soil grains, upon the 

 organic matter, upon substances in solution and upon colloids. 



COMPOSITION. 



The composition of soils, and their structure so far as it influences 

 weight, determines the absolute amount of plant food elements per 

 unit volume, per cubic foot, per acre-foot or per acre-four-feet, which 

 is the depth to which most crops are able to feed, to which they send 

 their roots if all the factors of productivity are at their best. Com- 

 position, therefore, determines the endurance of a field, the outermost 

 limit of its productive capacity. This statement is not in accord with 

 the teaching of our national Department of Agriculture where it 

 affirms : 



"That practically all soils contain sufficient plant food for good 

 crop yields, that the supply will be indefinitely maintained and that 

 this actual yield of plants adapted to the soil depends mainly, under 

 favorable climatic conditions, upon cultural methods and suitable crop 

 rotations." 



It is safe to say that no statement in recent years, designed to 

 direct agricultural practice and issued by high authority, is further 

 from the truth than thist Few statements could be more misleading 

 and land agents are using it, both in good faith and unscrupu- 

 lously, to sell at high price low grade lands. Much nearer the truth 

 is the statement : No soils contain sufficient plant food for maximum 

 yields when all other factors are at their best; and the best cultural 

 methods, with rotation of crops, only hasten the exhaustion of soils. 



The Department's teaching has resulted from confusing plant food 

 elements with plant food. Analysis has demonstrated that primary 

 rock, crushed to the fineness of soil, may carry per acre-four-feet 78 

 tons of potassium, 250 tons of calcium, 133 tons of magnesium and 

 even 8 tons of phosphorus. So, too, an acre-four-feet of good soil 

 may carry as much as 100 tons of potassium, 45 tons of calcium, 35 

 tons of magnesium and even 12 tons of phosphorus, and there is this 

 much foundation in fact for the statement criticized. But these enor- 



