October 



SCIENTIFIC AGRICULTURE 



45 



tes would probably result in increased 

 vegetative growth of the tree, and if the 

 supply of nitrates continued to be abun- 

 dant or in excess as compared "with the car- 

 bohydrate content of the tree, late veget- 

 ative growth witli resultant winter injury 

 may take plat-e. It is not unusual to see 

 trees injured by the application of ni- 

 trates, not that tlie nitrates have a toxic or 

 deliterious effect upon the plant, but be- 

 cause of the presence of too much avail- 

 able nitrogen late in the season causing 

 the tree to enter the winter with uniipen- 

 ed wood, with subsequent wi£iter injury 

 showing up the following year. 



Where nitrates have not been used and 

 trees in spring present considerable yellow 

 leaf and an unthrifty appearance, recover- 

 ing later in the season, an application of 

 five pounds per tiee the first year is not 

 out of place. But to continue this amount 

 annually might result in over-stimulation 

 so that the grower must, by intimate study 

 of his tree, decide upon the frequency and 

 quantity of these applications. 



Later when discussing fruit bud forma- 

 tion it will be seen how these early applica- 

 tions of nitrogen may materially assist in 

 maintaining annual bearing by establishing 

 a correct balance between carbohydrates 

 and nitrogen supply. 



In orchards grown on sod where little 

 nitrogen has been supplied we often find a 

 condition where an application of nitrates 

 will work wonders in productiveness. In 

 such instances the trees already have an 

 abundant supply of reserve carbohydrates, 

 but lacking nitrogen are unable to fully 

 utilize these reserves for vegetative exten- 

 sion and fruitfulness. 



It might be well to point out here that 

 this balance could at least be temporarily 

 obtained by severe pruning for by such a 

 practice the leaf area is reduced with a eon- 

 sequent reduction in available carbohydra- 

 tes, thus relatively increasing the nitrogen 

 carbohydrates ratio. Probably in the case 

 of older trees which are barren a moderate 

 heading back under such circumstances ac- 

 companied by a light application of ni- 

 trates would be a better means of estab- 

 lishing the proper balance. 



All this tends to illustrate that nitrogen 

 is not onh^ essential for vegetative exten- 



sion but for fruitfulness as well, that there 

 is close relationship between vegetative ex- 

 tension and fruitfulness and that the two 

 are not diametrieally opposed as has too 

 often been thought. 



At this juncture reference should again 

 be made to tlie abandoned practice of 

 yearly heading back. What is the expla- 

 nation of the poor vigor and delayed fruit- 

 fulness of trees groAvn uiider this system? 

 tSimply that in removing such large quan- 

 tities of wood a consideiable amount of 

 carbohydrates as well as the future means 

 for its manufacture were removed and a 

 condition of relatively low carbohydrates 

 content and abundant nitrogen supply re- 

 sulted with necessarily reduced vegetative 

 vigor and delayed fruitfulness. 



We have seen then that there must exist 

 a correct balance between the nitrates and 

 carbohydrates: that this may be re-estab- 

 lished by the addition of nitrate to the soil 

 in early spring, and by early cultivation; 

 or that by reducing the top of the tree, thus 

 lowering relatively the carbohydrate ni- 

 trogen ratio, we can arrive at the same end 

 at least temporarily. Thus is established 

 the close relationship between fertilization 

 and pruning. 



Before leaving tlie question of fertilizers, 

 reference must be made to potash and 

 phosphorous. 



Although nitrogen seems to be the one 

 fertilizer which is giving the most univer- 

 sal results, it does not necessarily mean 

 that we have in the past been wrong in as- 

 suming that potassium and phosphorous 

 have a part in the chemistry of the plant. 



Indeed potassium appears to be very es- 

 sential to fruit production. Hooker in his 

 chemical .studies of the apple buds found 

 that bearing spurs had a high potassium 

 content in the spring whereas non-bearing* 

 and barren spurs exhibited no such condi- 

 tion. The inference is that potassium is 

 quite as necessary as any element for plant 

 life and reproduction. 



Results from practical fertilizer testsr 

 give contradictory results with reference 

 to potash. 



Alderman in Virginia in working with 

 peaches found that muriate of potash used 

 alone checked growth when used at the 

 rate of one pound per tree and exhibited a 

 distinct toxic effect at two pounds, with 



