The Olive Its Culture in Theory and Practice/Chapter 5
Fertilization
CHAPTER V.
"Quite opposite to these are olives found,
No dressing they require and dread no wound;
No rakes nor harrows need, but fixed below,
Rejoice in open air, and unconcern'dly grow.
The soil itself due nourishment supplies;
Plough but the furrows and the fruits arise,
Content with small endeavors, till they spring,
Soft peace they figure and sweet plenty bring.
Men olives plant, and hymns to Pallas sing."
Virgil, Georgics II, 586.
So says Virgil, seemingly indicating that the soil of Italy at that time was richer and stronger than at present, for later experience has overwhelmingly demonstrated that fertilization is indispensable to the olive.
The analysis of the wood, leaves, and fruit of the olive, given in the preceding chapter, is equally applicable when considering the proper methods of fertilization. Lime for wood and leaves, and potash for the berry, seems to be the lesson it teaches.
It is no more possible in olive cultivation, than in the growing of any other vegetable, to year after year draw certain ingredients from the soil, without ever returning them again, and expect the trees to keep on giving fruit without receiving the nutriment they crave.
Fertilization is indispensable to maintain the olive in a prosperous and fruitful condition. In rich soils it may for a certain time be omitted, but a continued neglect will diminish the productiveness; and fructification will become infrequent and unremunerative, in places where the tree is seldom or never fertilized. The lack of manure, is one of the causes of the plant becoming weak and sickly, and bearing heavily only at long intervals. To fertilize an olive tree well, it is sufficient to restore to the ground the refuse from the oil making and the ashes of the branches from pruning. The most valuable fertilizer, is the water pressed from the olive. It is heavily charged with vegetable matter, black in color, and should be collected in a vat at the time of oil making. To this should be added the pomace, after all the oil is extracted. To increase the quantity, and at the same time add to the richness of this manure, grind into the mass marine plants for their potash, or in the absence of these, ferns, rushes, cornstalks, wheat and barley, straw, dregs of pressed grapes, vine twigs, or broom corn. Good, but in a lesser degree, because poorer in mineral properties, are husks of decayed olives, scrapings from threshing floors and refuse of whatever nature. These ingredients are very advantageously mixed during fermentation. As each, or any of these materials are thrown in, add a laver of earth. Keep this receptacle covered till the rains are well over, and then let the summer sun have access to it and the fermentation be thorough. The water will now have precipitated all valuable matter, and if it exists in too great quantities, let some run off; but enough should always be left in the vat, to allow the mass to take up moisture in place of that which is given off in fermentation. Care should be taken to locate this putrifying mass at a distance to leeward of the dwellings, or sickness might easily result from it. By September it can be cut out with a spade, like peat, and will make the very best of fertilizers for the olive orchard. But this is a powerful agent and should never be applied to the trees until thoroughly fermented in the manner described. If used as manure without fermentation, or mixing with other ingredients, the result would be the roots would be burned and the trees killed. The writer has seen the branches on young trees wither and die from coming in contact with pieces of sacking saturated with olive water and oil, and which had been used to protect the tree from rubbing against the stake to which it was tied.
The proper season to dress the olive, varies according to the climate, the soil, and yield of the plant. In a mild climate, however, the dressing may be applied in autumn and winter, whilst in more northern regions, it would be best given after all danger of freezing was past. The olive may be dressed in two ways—If the compost be plentiful, and the trees near together, it should be applied by scattering it about the orchard, and afterwards turning it under with a spade, a hoe, or plough; or, it should be done by digging holes about the tree, in a radius of from two and a half, to four and a half or six feet, according to the age and size of the tree. These holes should be from twelve, to sixteen inches deep, and should be dug some weeks before the dressing is applied, in order that the soil about the roots may be fully aired.
In localities where compost is scarce, it is well to alternate fertilization by plowing under lupins, beans or other vegetable matter of easy growth. If the dressing of the soil is done biennially, one half of the ground could be plowed under as stated. If triennially, the plowing under could follow, and a third of the plantation be plainly worked. If quadrennially, the surface should be divided in four sections, of which the first should be manured, the second worked, the third plowed under, and the fourth worked.
The nature of the fertilization that is necessary, cannot be exactly determined by the ashes of the wood alone, as the proportions of these may vary from a multiplicity of circumstances. The surest test for the fertilization, is the knowledge of the loss to which the tree has been subjected in fruit, leaves, and wood: and the object should be to restore to the soil that which has been taken from it in producing these. No manure should be applied till it is thoroughly fermented. To throw unfermented, or indeed any manure, close up against the trunk of the tree, is to do harm instead of good. With the rain fermentation starts again, and the heat generated is prejudicial to the tree as well as being a centre for the propagation of harmful insects. The suckers about the root are nourished to the detriment of the tree. The roots of the olive lie remarkably near the surface and these are the parts of the tree needing fertilization which should never be attempted nearer than a yard from the trunk. In cold regions, that is on the northern limit, sheep and goat dung is found to be an excellent manure; in temperate parts, stable ordure is good, and in hot regions cow dung is the best. It has been calculated that two hundred and twenty pounds of manure are equivalent to one gallon of oil. The foliage which falls naturally and decays under the trees every year, is eleven pounds per tree. The weight of these leaves is to the weight of the fruit as 71 is to 100.
The leaves taken off with the branches in pruning, supposing that operation is performed frugally and regularly, amount annually to a little more than a pound per tree. This foliage which is not restored to the soil, represents a weight of 5.50 per 100 and this is the 18th part of that which clothed the whole plant. The wood lost to the olive by meteorological accidents, and by pruning, may be estimated at seven pounds to the tree. The wood and leaves obtained by pruning are to each other as the number 78 and 22 are to 100. That is to say, in one hundred pounds of prunings there would be 22 pounds of leaves to 78 pounds of wood. With these data for a basis, the actual annual loss of the olive may be estimated as follows:
The olive consumes in fruit per tree, 15 lbs.
""""leaves ""115"
""""wood""7"
Manure is the dressing most commonly used for the cultivation of the olive, and is best administered when mixed with other fertilizers. Each year the amount of compost necessary to restore to the soil the principles essential to fertility, would be thirty-six pounds per tree, and that, a tree of medium size and one moderately pruned. To restore the same fertilizing principles with the foliage of the tree, alone, it would be necessary to yearly use at least fifty-two pounds.
Without manure the olive gives but a small crop of berries. Anything that can be used to enrich the soil is valuable; decayed vegetable matter, night soil, old rags, shoes, bones, hoofs, guano, fowl dung, are excellent manures. Green manure, in the dry summers of California, can be employed to great advantage.
During the early autumn rains, plants of rapid winter growth, such as beans, lupins, vetches, are sown in the orchard and turned under in the spring, thus giving a cheap manure without any cost for carriage. Whatever may be the nature of the manure, it is important not to place it at the foot of the trees, but to bury it at a slight depth from one to two yards distant from the trunk, digging a shallow trench for the purpose. It is a matter of absolute necessity to manure the olive, under penalty of losing all produce if abandoned to itself, and remembering also, that the produce will always be in proportion to the manure applied. In fact some writers say, that if the olive is not largely manured it had much better be pulled up altogether.
M. Riondet says: The expense of cultivating the olive varies greatly. If they are never manured, or pruned, the cost will not amount to more than eight dollars per annum, per acre, or sixteen dollars for two years, for this is the period that always enters into these calculations, since the tree ordinarily only gives a crop every second year. If it is desired to have regular and abundant crops, we should not fear to spend eighty dollars per acre every two years.
In the winter, after an abundant crop, it is necessary to manure the orchard heavily, at an expense of twenty-four dollars per acre, pruning, will cost sixteen dollars per acre, ploughing, sixteen more to which add for the expense of gathering and taking the crop to mill, another twenty-four dollars, and so we reach the sum of eighty dollars per acre for a period of two years. There will be a product of one thousand one hundred and thirty-two gallons of olives, per acre, every two years, which should be the equivalent of one hundred and fifty-four gallons of oil, per acre, for each period of two years. This will not come far from an annual average of one gallon per tree, and if the olive grower could assure himself of such a yield, he might well be satisfied.