APPENDIX No. 15

Report on the Occurrence of Soluble Salts in the Lands of the Esperance District.

By JOHN W. PATERSON, BSc., Ph.D., Professor of Agriculture in the University of Western Australia.

To the Chairman of the Royal Commission on the Mallee Belt and Esperance Lands.

Sir, I have now the honour to report on the occurrence of soluble salts in the lands lying northwards from Esperance, near the line of the railway survey.

I arrived at Norseman on 23rd October, and spent the next fifteen days chiefly driving over the lands between Norseman and Esperance, in the company of the Commissioners. My object was to make notes of the probable occurrence of salts on cultivated and bush lands, and to take samples of soils and waters for chemical examination. In all, 60 samples of soils and subsoils, and nine samples of waters were taken in the locality. Curing the return journey to Perth visits were paid to Kellerberrin, Meckering, and York, in company with two of the Commissioners, to study the salt problem in those districts for purposes of comparison, and 11 samples of soils and subsoils and one of water were taken in those districts. Altogether 71 samples of soils and 10 waters have been submitted for analysis in connection with this inquiry, and the discussion of those analyses, together with notes made from personal observation, forms the basis of this report.

I had previously inspected the Esperance lands, more particularly from Salmon Gums to Esperance, during a lecturing tour to settlers in February, 1914.

Before going on to consider the results of my investigations of the Esperance lands in particular, it will be useful to review, in some little detail, the general question of salt in agricultural lands.

A. GENERAL CONSIDERATIONS AFFECTING THE OCCURRENCE OF SOLUBLE SALTS IN SOILS.

Nature of the Soluble Salts.

The main bulk of a soil is insoluble in water; but a soils always contains a certain quantity of soluble salts: this is essential to its fertility. At times, however, a soil may contain an excess of soluble salts, and such excess in injurious to vegetation. A garden path may be cleared from weeds, by applying a heavy sprinkling of common salt.

The soluble salts present in soils may be of different kinds. A mixture is always present. The principal salts include chlorides, sulphates, nitrates, and sometimes carbonates of soda, potash, magnesia, and lime. The proportion in which the various salts are present in the mixture depends chiefly upon the chemical character of the soil minerals, the supply of soil moisture, and the nature of the drainage.

                                                                                              Origin of the Soluble Salts.

The soluble salts present in soils have two sources of origin. One of these is the soil itself. The insoluble mineral constituent of the soil, also the humus bodies, slowly undergo chemical change as the result of weathering agencies. Some of those changes yield soluble salts. The food materials taken from the soil by crops are soluble salts, and without the production of soluble salts in soils plant growth would be impossible.

Soluble salts are also added to the soil by rain. Thus at Rothamsted (England) 24lbs. of common salt (sodium chloride) and 31lbs. of sodium sulphate were obtained annually per acre through rain; at Canterbury (New Zealand) the respective figures were 89 and 26. At Gibson's Soak hotel the rain-tank water gave, on analysis, 6•7 grains of common salt per gallon, showing that rain here may be a considerable source of salt. Observations at other places* show that rain always supplies soluble salts, and at maritime stations the amounts are naturally greater than further inland.

                                                                                 How the Salts may accumulate.

From the soil itself, therefore, and from rain the soluble salts receive constant additions. Whether in any particular soil the amount of soluble salts will increase depends upon whether or not the annual gains exceed the annual losses. With good drainage (natural or otherwise), and sufficient rainfall, any harmful excess of soluble salts is soon washed away. In districts with a small rainfall or bad natural drainage, all the soluble salts produced or received by the soils tend to accumulate. Generally speaking, excess of soluble salts in an evil which is confined to arid and semi-arid districts.

In a humid region the best soils produce soluble salts freely, including those required for plant growth. That is why they are good, and any excess of the salts is soon washed out by the drainage. In drier districts the best soils also develop soluble salts freely, and here the excess may not be washed away. As a result we find, therefore, that excess of soluble salts is not only characteristic of arid and semi-arid districts, but also that where it occurs in such districts it occurs most commonly on the better classes of land.

The salts of the sea represent soluble salts which have been washed from the soils of districts with a sufficient rainfall. In drier districts the salts may not travel further than the first depression in the land.

                                                                          Relation of Vegetation to the Salts.

In districts with a limited rainfall the growth of trees or forest scrub notably influences the behaviour of the soluble salts in the land. Growing vegetation takes much water from the soil. Data are not available for the water requirements of bush vegetation, but a 20 bushel crop of wheat draws in our climate about 700 tons of water from the soil. That trees also take much water from the ground may be inferred from the influence of isolated trees standing in a crop in restricting growth; as one would expect, this influence is particularly felt during a dry season.

The soluble salts present in a soil form a solution with the soil water. Where the land is devoid of vegetation the water which had been received during winter rises to the surface by capillarity in the dry weather, and is evaporated into the air. When it rises by capillarity in the soil it brings the dissolved salts up with it. If a solution of salt be evaporated down in a kettle the salt will remain behind as white solid salt, and when the soil water containing soluble slats is evaporated at the surface of the ground the salts will be left there as solid salts. If in sufficient amount, they will be apparent to the eye as a white efflorescence or crust upon the surface of the ground.

• Jour. Agric. Science, Vol. I., Part 3.