PRUNING ORCHARDS. 



335 



est sense fertility is a word used to desigf- 

 nate the productive power of the soil. This 

 productive power may be due in larg-e mea- 

 sure to the physical condition of the soil 

 rather than to a liberal supply of the chemi- 

 cal constituents necessary for great produc- 

 tivity. Or on the other hand a soil may be 

 wholly unproductive yet contain excessive 

 quantities of plant food, because of the poor 

 physical condition of the soil. All this 

 means that the plant food within the soil 

 counts for nothing- if the plant can not get 

 it. We have already emphasized the im- 

 portance of thorough tillage for making 

 available what plant food there is within the 

 soil. Yet as above stated, even with the 

 best management of the soil in this particu- 

 lar, it may still lose so much plant food that 

 it is necessar}' to supply commercial fertili- 

 zers or other manures. 



Of the thirteen elements which the soil 

 may contain and which may be used by 

 plants, only three are ever lost in such quan- 

 tities as to make their restoration necessar\'. 

 These are nitrogen, potassium, and phos- 

 phorus. Of these three the one most readily 

 lost is nitrogen. This element, which com- 

 prises four-fifths of the air, combined with 

 other elements becomes available to the 

 plant. It is the element which is responsi- 

 ble for the rapid development and early for- 

 mation of our apple trees and other plants. 

 Phosphorus, in the form of phosphoric acid, 

 is necessary in order to give strength and 

 firmness to plants and, next to nitrogen, is, 

 all things considered, the most important 

 element of plant food. While needed only 

 in relatively small quantities by plants it is 

 lacking in many soils. Potash comes next 

 to phosphorus in importance and is the most 

 important constituent for fruiting plants, at 

 least those that are expending their energies 

 in that direction. 



Nitrogen. — The yellowing of the foliage 

 and stunted appearance of the tree is a pretty 

 sure indication that the soil is deficient in 



nitrogen. An insufficient supply of nitrogen 

 tends to dwarf plants. Good stable manure, 

 if well taken care of, that is, not allowed to 

 leach by rains, will supply to the soil liberal 

 quantities of plant food. 



Other sources- of nitrogen for plant com- 

 pounds. — Sodium nitrate is the most im- 

 portant commercial fertilizer containing 

 nitrogen. A hundred and twenty - five 

 pounds of this salt would probably be 

 the minimum amount per acre. But its 

 use is advisable only after other means 

 have failed. This might also be said of 

 barn-yard manure. By all means the cheap- 

 est way of securing nitrogen is by thorough 

 tillage, which increases or hastens nitrifica- 

 tion, and by green manuring. If these two 

 latter methods are practiced there will rarely 

 ever be occasion to resort to commercial 

 fertilizers. 



By green manuring is meant the growing 

 of some crop in the orchard, especially those 

 leguminous or nitrogen forming plants, 

 which, when turned under and decomposed, 

 add nitrogen and other food material to the 

 soil. The greatest good, however, derived 

 from this operation is the addition to the 

 soil of large quantities of humus or decay- 

 ing vegetable matter which greatly improves 

 the physical condition of the soil, thereby 

 increasing its power to hold plant food and 

 moisture. What crops are most advisable 

 for this purpose depends almost entirely 

 upon soil and climatic conditions. They 

 are usually confined to some of the clovers, 

 peas, beans, vetches, or lupines. Wherever 

 clovers or vetches succeed well they should 

 be used. 



These leguminous plants are enabled to 

 take up the free nitrogen of the air by vir- 

 tue of small nodules or tubercles formed on 

 their roots as a result of the activity of mi- 

 croscopic forms of life known as bacteria. 

 It is now clearly known that if these organ- 

 isms are not present in the soil the legumin- 

 ous plants are unable to use the nitrogen of 



