PLANT FOOD. 3895 
EXPERIMENTS BY LAWES AND GILBERT, OF ROTHAMSTED, ENGLAND 
WITH VARIOUS KINDS OF FERTILIZERS UPON POTATOES. 
Average yield per acre for twelve years when each of the |Composition of 100 
following manures were used. Ibs. of fresh tubers. 
Good. | Small.| Dise’sd; Total. 4 « d 
- a 1o 
o a ro Alen - sels = 4 2 50 
rs| + a S28 | = 1 =o t= (rs A 4 ea a= 
elolalolal|ola|o || & a*)_< |4 
— |————S§ $| ————_ | | | | | 2 | Fi St ae 
Unmanured..........0...6.ceeeee 1 [13%] ...| 5 114) 1 |1934) ee 84) 334 
Superphosphate................ | 3] 5. |....| 594|--..] 234] 3 [13% bea aae 1,07) 249 
Mixed Minerals.................| 3 | 734]....| 4%|....| 256] 3 [15% basen ts 1.11) .236 
Ammonium Salts.............5. 1 |1734| ...| 6%|....] 17%] 2 | 534]] 73-08,26.2) .77) 384 
Sodium Nitrate.. ............... 2 | 456]....| 544] ...] 256] 2 [iarg|| 79-05/28.5) © 75) 382 
- Ammonium Salts & Minerals] 5 |18%). 7 83g] 6 |144% pean 8s : 1.02) .319 
ee pnd peed t 5 173% 6% 94| 6 |13 cain 8} 1.00} .341 
Damanured 6 years .2. 5) 3 p2|----| 64]----] 3] 4 | 284] 72.09.27.1) 98) 298 
7yts.Parm Manures and Su- } : | 
perphosphates.......... .... -| 4 | 74g]....| 636]....] 476] 4 11836] 74.07 25.9) 1.00) .292 
_ years Poon eure alone. ) | 
years Farm Manures alone. =3/ , / 7 iS 
Gycars Superphosphates (| 4 |!5%|----| 6%)----| 9%] 5 L134) 74.0925.1]  .93) .339 
Sodium Nitrate.............. \ ! | | | 
3. Can the use of commercial fertilizers be put off or possibly 
avoided? 
Yes, by putting something back in the soil for everything that is 
taken away. Wecannot expect to continually borrow from nature 
and never pay anything back. The fact should be kept in mind that 
the four elements, nitrogen, phosphoric acid, potash and lime, are 
the ones which are drawn upon to the greatest extent by plants. 
lime is present in nearly allof our soils in sufficient amounts so 
as not to cause any present or future trouble. 
By a judicious use of farm manures, the working supply of nitro- 
gen and phosphates can be kept up. Manures rich in phosphates 
and nitrogen can be produced by looking carefully after the food 
stuffs which are fed on the farm. Beans, shorts and barley all pro- 
duce manure which is more valuable than manure from animals fed 
on corn or oats. As long asthe organic matter in the soil is kept 
up, the want of available phosphates will not be severely felt. The 
humus in the soil formed from the decaying organic matter unites 
with the complex and insoluble phosphates in the soil and converts 
them into forms which are available as plant food. It is cheaper to 
work over the insoluble phosphates in the soil, and, by means of the 
humus, get the phosphates into an available form, than it is to pur- 
chase available plant food in the form of commercial fertilizers. 
There is a good stock of unavailable phosphates in the soil which 
should be worked over before resorting to commercial fertilizers. 
The question of keeping up the working supply of potash in the 
soil is a more difficult and serious one than that of the phosphates. 
A judicious and liberal use of all of the available supplies of wood 
ashes will do a great deal towards solving a part of the problem. 
There is a great difference in the value of ashes from various 
sources. No doubt a few who have made a trial of the ashes from 
A aes, 
4 
