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To summarize the Beltsville results, instead of considering all mulch 

 materials as equally effective, vie need to take into account the nitrogen content 

 since that is directly related to the rate of decomposition and consequently the 

 release of nutrients. Hay from a very poor soil vdll necessarily be lacking in 

 nitrogen. It vdll therefore be of more value from a physical than from a chemical 

 standpoint. There is a common notion among grovrers that a "mulch is a mulch" and 

 that its main purpose is to conserve moisture. However important that may be, its 

 effect is limited unless it brings something of the response noted in those York 

 Imperial trees in Beltsville. 



On a cost basis, there is little difference in the cost per pound of nitrogen 

 applied as hay or as ammonium nitrate. Dr. C. P. Harley submits these figures: 



300 lbs. of ammonium nitrate per acre ^?15.00 



Labor (fertilize, mow, rake, haul, spread) .... 20.00 



Total cost per acre 335.00 



At 2f; N, 5 tons of hay contains 200 lbs. H. 

 Using 200 lbs. of hay per tree means h lbs. N, 

 Cost per tree is 700, or 17 i/2/!^per lb. of N. 



Ammonixom nitrate © ^0 per lb. means l5{i per lb. of N, 



labor 2^ 



17^ per lb. of N. 

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Savjdust or Straw I^ulch We are beginning to realize that 

 mulch materials vary considerably in their effect upon the 

 plant we are trying to benefit by mulching. Take, for 

 example, a material like savKiust or straw, both of vrhich are 

 high in carbon and very love in nitrogen. Before these 

 materials can decay, the organisms which bring about decay 

 must increase in numbers and complete their development. 

 This process requires nitrogen in available form, since 

 protein contains nitrogen. Thus they become competitors 

 of the plant for nitrates. So an apple tree on a poor soil 

 heavily mulched vdth sawdust v/ill, suffer a nitrogen 

 deficiency unless additional nitrogen is added to the 

 sawdust. Not so with a "high nitrogen" mulch material like 

 clover hay or even grass groi'm on a fertile soil. Here the 

 mulch material releases available nutrients as it decays. 

 It also helps to conserve moisturr- and smothers competing 

 vegetation. To make a long story short, any of the plant 

 residues have some value as a mulch material but those 

 containing a moderately high percentage of nitrogen cause 

 a more rapid response on a light soil. Blueberry plants 

 mulched with sawdust at the Beltsville Plant Industry Station 

 receive twice as much nitrogenous fertilizer as plants under 

 cultivation. 



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