PRESS BULLETIN 144
florida Agricullural Experiment Stalion
FERTILIZING VALUE OF OLD PINEAPPLE PLANTS
By A. W. Blair
As the pineapple fields on the East Coast become old and give way
to new plantings, the grower is confronted with the problem of disposing
of the old plants. In the past they have usually been disposed of in the
way that seemed easiest, without much thought of their value. Some have
hauled them out to the river bank or other out-of-the-way place; some have
burned them; a few have dug trenches and buried them at a depth of 12
inches or more; while others have put them in piles to decay, and then
spread the residue over their fields.
Amount of Dry Material
To know the value of the old plants we must know the amount of ma-
terial per acre and its plant-food content. The average green weight of
several whole plants from a four-year-old field, was found to be 12% pounds.
There would be about 14,000 such plants to the acre, since this is the
average number that is usually set. This will give 87% tons of green plants.
Since about 15% per cent. of this is dry matter, there would be approxi-
mately 13% tons of water-free material to the acre. From the average of
many analyses we find that this water-free material contains the following
amounts of fertilizing constituents: nitrogen 0.74 per cent., (equivalent to
0.9 per cent. ammonia), phosphoric acid 0.83 per cent., and potash 2.4 per
Amounts of Fertilizing Constituents
From these figures we find that 13% tons of dry material will contain
200 pounds of nitrogen (243 pounds of ammonia) equivalent to 1428 pounds
of high-grade dried blood, 224 pounds of phosphoric acid equivalent to 1224
pounds of slag phosphate, and 648 pounds of potash equivalent to 1296
pounds of high-grade sulphate of potash. At the present price of fertilizers,
these materials would be worth $81.59 (93% cents per ton for the green
material, $6.04 per ton for the dry material). If the plants from an acre
of ground are thrown on the river bank or in some other waste place, all of
this is lost. If they are burned, the nitrogen (ammonia) is lost, the value
of which would be $40.70. In either case the land is deprived of its rightful
heritage, the humus.
February 28, 1910
How to Utilize the Material
It would certainly be better to bury the plants than to throw them
away or burn them; but to bury them completely requires the digging of
trenches at least twelve inches deep, and in doing this, much of the surface
soil, which is the richest (analyses have shown that there is much more
nitrogen just at the surface in the pineapple fields than there is at a depth
of 12 inches or more) is placed entirely out of the reach of the roots of the
young plants that are to follow. In coarse sandy soils like the pineapple
soils, the plant-food tends to leach away, especially when it is once beyond
the network of roots, and on this account it does not seem wise to cover up
the rich surface soil deeply.
The method of piling the plants into heaps like compost heaps has been
successful, and would seem to be the least wasteful of any. One grower
who dispose of his old plants in this way cuts off the tops and grubs
them into the soil to the depth of four to six inches, and also digs up the
stubs with the lower leaves and puts them in large piles to rot. In about
two years they are in the condition of well-rotted stable manure, and when
spread over the ground are grubbed in to the depth of two or three inches.
If this should seem an expensive method, we need only remind ourselves
that the old plants must be disposed of in some way, and in throwing them
away or burning them *e lose much plant-food, and in addition, have to
bear the expense of moving them.
Improvement of the Condition of the Soil
In addition to furnishing nitrogen, phosphoric acid, and potash, the
decayed plants furnish the humus which is greatly needed. This is
especially the case on the East Coast where the climatic conditions favor
the rapid disappearance of humus. The humus furnishes food for the bac-
teria which are at work converting inert nitrogen into available nitrogen,
it acts as a sponge to hold moisture and plant-food, and it causes better
circulation of the air through the soil.
This decaying organic matter will gradually bring about an acid condi-
tion of the soil, which can readily be corrected by the use of slag phos-
phate, finely ground limestone, or ashes. Only when the plants are dis-
eased should they be burnt, and this should be done in such a way that
the ashes can be returned to the soil.
State papers please copy.