NATIONAL COUNCIL OF HORTICULTURE 11 



mous amounts of plant food elements present in the root zone of field 

 crops are no more to be regarded as plant food for those crops than 

 they are food for the animals feeding upon pasture grass. 



The food of plants, derived from the soil, is only certain substances 

 which are dissolved in the soil moisture or which are carried in the 

 soil in a form which may be readily so taken up ; and the amounts 

 of these, present in the root zone of field crops at any one time, is 

 relatively very small when compared with the amounts of plant food 

 elements from which they are derived. Much more is a soil like a 

 pasture where plant food grows than like a bank or granary where 

 it is stored, and just as a rich pasture may produce sufficient grass 

 to carry a large herd so may a fertile soil produce, from day to day, 

 plant food sufficient for good crops. Just as pastures differ in the 

 amounts of herbage on the ground and in the amounts they are able to 

 add to this as it is fed away, so do fields differ, both in the amounts 

 of plant food present in the root zone at any one time and in the 

 amounts they are able to add as this is withdrawn. Our own observa- 

 tions, published by the Bureau of Soils, have demonstrated that four 

 good soils, observed to produce two and a half times the yield per 

 acre of corn and potatoes that four poorer soils did under identical 

 treatment, also gave up, when washed three minutes in five times 

 their weight of pure water, 2.58 times as much plant food. Not 

 only was there this difference in the amounts of plant food car- 

 ried in water-soluble form in the best and in the poorer soils, but the 

 amounts of this same plant food taken out of like areas of field by 

 like numbers and kinds of plants during the same time was 3.2 times 

 as great in the sap of the plants which gave the highest yields. Such 

 observations would appear to fully justify the general conviction that 

 increased yields should be directly attributed to better feeding and 

 that better feeding is a direct result of larger amounts of plant food 

 available to the crop. It is taught, however, by the Bureau of Soils, 

 that all soil solutions are sensibly identical in composition and in 

 concentration ; that they are strong enough for large yields and that 

 this strength will be indefinitely maintained. From these conclusions 

 the Bureau further teaches that mineral fertilizers, green and stable 

 manures and a good rotation of crops owe their efficiency to the 

 power they have of neutralizing toxic principles which tend to accumu- 

 late in cultivated soils, rather than to any power of increasing avail- 

 able plant food, an abundance of which, at all times and in all soils, 

 is held to be present. 



While it is true that good soils may yield to pure water two, 

 three and more times the amounts of plant food that poorer soils 

 will, and while the absolute differences may be as 3,200 pounds per 

 acre-four-feet to 1,200 pounds, yet these quantities are so small in pro- 

 portion to the total water present in the soil that one may in truth 

 say, from the standpoint of the chemical balance, as Professor Whit- 

 ney does, that the composition and concentration of all soil solutions 

 are sensibly the same. Nevertheless it is undoubtedly true that soil 

 solutions are measurably different, both in composition and con- 



