PLANT NUTItlKNTS AND TIIEIli AHSOIil'T ION 1]:^ 



on in inany scMrtioiis where seasonal and soil conditions an; iriat(!i'ially 

 dilferent from thoso of Illinois and Indiana antl it is concoivabh; lliat 

 under Certain environinontal conditions nitrate production, evcni under 

 sod, inif2;ht keep pace; wilh the tn^e's requirements for nitrog(!n. 



Losses of Nitrogen from the Soil. — Nitrates are very soluble in 

 \vat(M- ajid unlike most of the mineral nutrients, are not adsorbed or 

 otherwise; fixed in the soil to any considerable degree. Heavy rains or 

 heavy irrigation washes them out and carries them away in the drainage 

 water. In one Florida experiment this loss from leaching was found to 

 ('(pial the nitrate content of over 800 pounds of nitrate of soda per acre 

 during a 10-month period/ Not the least important function of cover 

 crops is to take up the nitrates that are being formed in late summer and 

 autumn, to store their nitrogen in organic form during the winter and to 

 return it to the soil — thence to the trees — the following growing season, 

 thus preventing a large loss through drainage. The advantage of a 

 soil, and of orchard management methods, permitting deep rooting and the 

 storage of large quantities of capillary water minimizing seepage losses, 

 is evident. 



Maintaining the Nitrogen Supply of the Soil. — Despite the means 

 that may be taken to prevent undue loss of soil nitrates, crop production 

 alone removes considerable quantities and unless the supply of nitro- 

 genous coinpounds from which they arc derived is maintained the time 

 will come when they cannot be formed in quantities sufficient for maxi- 

 mum crop production. The organic matter of the soil is the storehouse 

 of these nitrogenous compounds and with its gradual depletion the 

 nitrogen problem becomes acute. It is well known that constant tillage 

 is one of the most effective means of reducing or "burning out" humus 

 supply. Consequently the cultural methods in the orchard that make 

 nitrogen available most rapidly, deplete the total supply most rapidly. 

 Indeed it may be questioned if, over a long period, the orchard under a 

 strictly clean-culture method of management will not need heavier 

 nitrogen fertilization than the one in sod. 



Some measure of the cumulative effect of tillage as compared with a sod 

 covering on total nitrogen supply is contained in the following statement: 

 "Analysis of soil taken from this land at the time the experimental work was 

 started indicated a nitrogen content of 5,000 pounds per acre. After this soil 

 had been cropped and cultivated for 20 years, the nitrogen content was approxi- 

 mately 4,000 pounds per acre. Adjacent soil which was in grass during the 20- 

 year period contained 5,600 pounds of nitrogen."^ It is significant that, though 

 there was a loss of 20 per cent, of the total nitrogen supply of the soil during the 20 

 years in the cultivated land, there was an actual increase of 12 per cent, in the 

 sod land during the same period. This can be attributed to nitrogen fixation, 

 particularly by leguminous plants in the sod, in addition to the nitric acid 

 contributed by rain water. 



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