The Olive Its Culture in Theory and Practice/Chapter 4
Soil
CHAPTER IV.
"Cet arbre vient sur tous les terraius."
Gasparin.
"And first for heath and barren hilly ground,
Where meagre clay and flinty stones abound;
Where the poor soil all succor seems to want,
Yet this suffices the Palladian plant.
Undoubted signs of such a soil are found,
For here wild olive shoots o'erspread the ground
And heaps of berries strew the fields around."
VIRGIL GEORGICS II. 249.
The olive will live in almost any soil except a dry and compact, or a humid one. An analysis of the ashes of the wood, leaves, and fruit of this tree give the following result:
| WOOD. | LEAVES. | FRUIT. | |
| Potash | 20.60 | 24.81 | 53.03 |
| Lime | 63.02 | 56.18 | 15.72 |
| Magnesia | 2.31 | 5.18 | 4.38 |
| Sulphuric Acid | 3.09 | 3.01 | 1.19 |
| Silicate | 3.82 | 3.75 | 5.58 |
| Phosphoric Acid | 4.77 | 3.24 | 7.30 |
| Phosphate of Iron | 1.39 | 1.07 | 2.24 |
| Chloride of Potassum | 1.00 | 2.76 | 9.56 |
| 100.00 | 100.00 | 100.00 |
The berry, and especially the meaty part, contains a very large proportion of potash, while the wood and the leaves abound in lime. This is an important fact. The deduction from it is that a soil, rich in these ingredients, possesses all the conditions necessary for the complete development of the plant, and the abundant production of the best quality of fruit. Hence, it is safe to assume, that the olive prefers a soft, friable, moderately cool soil, and one rich in lime and potash; a permeable soil, such as a limey clay of medium consistency, not inclined to either dryness or humidity. The roots would then encounter no obstacle in extending themselves, and the air and moisture could circulate sufficently. Lime, abounding phosphates, magnesia, with an abundance of silicates of alum and mercury, and a sufficiency of potash and soda, are the chemical and physical requisites which this tree will find most advantageous to its development, and cause it to produce abundantly, and, provided other circumstances are equal, give the very best oil. It is seen that the olive will flourish wherever its roots will penetrate easily, and there is no deficiency of lime and alkali, such as a loose soil of rocky clay, or sand of volcanic or granite formation. But, while the olive will subsist on many different soils, and prosper in several, it is not to be concluded that it may be condemned to bare, sterile, impoverished ground, where not even a forest tree would be nourished.
The latitude must largely guide one in selecting the kind of soil for an olive orchard.
In Andalucia and Valencia, in southern Spain, the mean summer temperature is as high as eighty-two degrees. There, they hold red soils in very low estimation, and prefer the light colored or white; considering that the red attracts too much heat, and requires too much fertilization and irrigation, without which the tree gives no fruit in that latitude. There, a very porous soil, giving free passage to moisture, and evaporating freely, requires repeated fertilizing and watering. Going north in central Spain, the light red soil with a porous tendency to carry off the frequent rains, is preferred, and the white is altogether condemned. Still further north, the dark red and very porous soils are exclusively used. The calcareous soils, through their action on the natural and artificial fertilizers, quickly put into circulation the elements of nutrition of the olive, and so promote its growth; but for this very reason require that the trees should be frequently manured in order to obtain an annual product. It is the want of nourishment in the ground, that causes the olive to fruit only every other year, or every third year.
An irrigated soil loses its fertility quicker than one that is not watered; so, where irrigation is practiced, it is necessary to frequently manure. In general, it may be said that the olive requires the same kind of soil as the vine, and in proof of that we often see them grown together. Excessive moisture is prejudicial, and also in a dry, hard soil the tree contracts, splits, and leaves the roots gorged with sap. The most favorable soil is an open, loose and fairly fertile one, and should be of at least a yard in depth to give the roots opportunity to extend themselves.
The olive is fond of a chalky soil, that is, one largely made up of lime carbonates. The carbonate of lime is indispensable to vegetable life; and it is noticed, that the oil from olives grown on a calcareous soil, is better than that from a soil lacking in this element. Chalky soils are cold, because they do not easily absorb the heat of the sun. For the same reason red soils are warm, absorbing and retaining a great degree of heat. The best soil for the olive is that in which lime predominates; and where silica exists, and there is no lack of clay. Such a soil would give passage to moisture, and offers no obstacle to the extension of the roots, and at the same time has consistency enough to sustain the tree and preserve the elements of nutrition. The oxide of iron exists in all soils, but where it abounds, the red color declares it. It is favorable to the growth of the olive, particularly in cold regions.
Suppose two adjacent pieces of ground in such a locality; on the red soil the olives will ripen, whereas on a light colored one they will not.
Liebig says, that when at the time of flowering of any vegetable, the soil abounds in phosphates, the fruit sets well, and is started on its road with every advantage; and on the contrary, if these are lacking, the flowers fall off and the tree gives its strength to wood.
The hygroscopicity of a soil, or the property of retaining moisture, is of great value in a hot and dry country. It is well known that the more a soil is manured and cultivated, the more moisture it retains. The following table will show the percentage of water contained in different soils.
| Silicious sand | .25 |
| Gypsum | .27 |
| Calcareous sand | .29 |
| Dry chalk | .40 |
| Chalk, somewhat more fertile | .50 |
| Clay soil | .60 |
| Clay, pure | .70 |
| Calcareous soil | .85 |
| Manure | 1.90 |
| Garden soil | .89 |
| Arable land | .52 |
The capacity to absorb humidity from the atmosphere varies with different soils. The following are the results of experiments.
| Silicious sand | .0 of water |
| Calcareous sand | 1.5 " " |
| Gypsum | 0.5 " " |
| Dry chalk | 13.0 " " |
| Chalky earth | 15.0 " " |
| Clayey earth | 18.0 " " |
| Clay | 21.0 " " |
| Fine calcareous earth | 15.5 " " |
| Magnesia | 38.0 " " |
| Manure | 48.5 " " |
| Garden earth | 22.5 " " |
| Ordinary earth | 11.0 " " |
Absorbtion is greater by night than by day. and recently cultivated ground is the most receptive, as it exposes the greater number of particles to the action of the air.
As the earth grows dry. its capacity to absorb moisture diminishes. So we observe that ground frequently and thoroughly cultivated retains moisture the longest.
THE DRYING QUALITY OF SOILS.
| Silicious sand in four hours evaporates | 88.4 |
| Calcareous | 75.9 |
| Gypsum | 71.7 |
| Dry chalk | 52.0 |
| Earthy | 45.7 |
| Clayey soil | 34.6 |
| Clay | 31.9 |
| Carbonate of lime in four hours evaporates | 28.9 |
| Manure | 20.5 |
| Magnesia | 10.8 |
| Garden earth | 24.3 |
| Arable hand | 32.0 |
These figures indicate what we see in practice, that the more sandy the soil, the sooner it dries. Some soils when they dry, actually diminish in volume, and through splits and cracks expose the roots of the tree. Sandy, limey and gypsum soils do not have this drawback; the others vary in the following degrees.
| Carbonate of lime soils loses | 50 |
| Dry chalk | 60 |
| Earthy | 89 |
| Clayey soil | 114 |
| Clay | 183 |
| Magnesia | 154 |
| Manure | 200 |
| Garden earth | 149 |
| Arable land | 95 |
Different soils retain heat in proportion to their weight; a pebbly soil retains heat longer than one of fine sand. Chalky and clay soils quickly lose heat; and, on this account, the former is called an early soil, and the latter a late one. The color of the soil has much to do with the absorbtion of heat. In any given earth there is a difference of fourteen degrees, Fahrenheit, between the extremes of color.
The ancients thought that the olive would not grow unless it had the sea air, and laid down the rule, that it should not be planted more than ninety miles inland. The Arabic and Latin authors follow the same recommendation; but it has been well established, that the olive can be grown at any distance inland, provided the soil and climate are agreeable to it. Pliny remarks, the olive of the low land is more liable to disease, than that grown on high ground.