Salting the Earth: Intentional Application of Common Salt to Australian Farmland during the Nineteenth Century

: During the nineteenth century, common salt (NaCl) was liberally applied to Australian farmland as a manure to improve productivity and as a fungicide to prevent, or at least reduce, the impact of rust in wheat. In an age where salinity control is paramount for biodiversity and agricultural productivity alike, it is worth reﬂecting that during the nineteenth century salt was intentionally applied as a manure to improve soil productivity. This paper traces the origin and extent of this practice in Australia.


Introduction
Dryland salinity has become one of the main drivers for changes in Australian landmanagement practices during the late twentieth and early twenty-first centuries. The problems this phenomenon poses for the environment and farm productivity are likely to continue for at least another fifty years. Rising water tables lead to the dissolution of the existing salts in the lower parts of the soil profile and their concentration (caused by evaporation of the moisture) at the upper part of the column. Where the groundwater table is close to the surface, the vegetation has been impacted, and many plants have been replaced by more salt-tolerant species. As the salt concentrations increased further, fewer plants survived, leading to exposed ground and scalding, which set in train erosion processes. Irresponsible water management practices, such as over-irrigation and the clearing of tree cover in rainfall recharge areas, have been identified as the major contributors [1,2]. In many areas of the world, rising groundwater tables and the concomitant dry-land and farmland salinity have become the scourge of the agricultural community; this is certainly the case in much of the Riverina, north-eastern Victoria, and Western Australia [3][4][5][6]. The impacts are not confined to agricultural production land but also affect public infrastructure, such as roads and water supply systems [7], as well as heritage buildings and streetscapes [8][9][10][11].
In an age of GPS-aided precision farming where farmland and urban salinity are one of the major causes of modern land degradation, it is somewhat ironic, as this paper will discuss, that during the eighteenth and nineteenth centuries farmers purposefully applied liberal quantities of common salt (NaCl) to improve the productivity of the land.
Historical research has the capacity to inform policy responses to current environmental concerns. Historical ecology and environmental history in particular consider the trajectories and impact of past human practices on current environmental conditions, such as historic resource exploitation [12], including species extirpation [13] and introduction [14] and diseases [15], as well as land [16] and river management practices [17]. The paper presented here is concerned with the historic influences on the management of arable soils.
While there is an abundance of research into the colonial settler society of Australia and its impact on Indigenous Australian communities and their land use [18][19][20][21][22][23], as well as the expansion of the pastoral and agricultural industry on the continent [24][25][26][27] and the introduction of plant and animal species [28][29][30], there has been comparatively little work (xxxi, 33) [64], as well as Cato and Virgil, commented on this [65,66]. Given the renewed interest in Greek and Roman texts during the Renaissance, such knowledge found a revival among educated circles; these sources, albeit centuries old, were still deemed valid knowledge. The first mention of salt as a manure in more recent times dates to the end of the sixteenth century [67]. During the seventeenth century, farmers' lore held that salt could be used as a manure to improve barren soils and fatty loams [66,68,69]. By the early part of the eighteenth century, the use of salt as a manure, both as a phytocide and a (selective) manure, had become well-established [70][71][72] and continued to be advocated [73]. The significance of salt as a fertilizer was such that in 1768 King George III assented to an act that reduced the duty on the salt unfit for human consumption and destined for use as a fertilizer. The use of salt as a manure was not limited to the United Kingdom but also practiced on the continent [74][75][76].
The concepts soon crossed the Atlantic, and agricultural guides and newspapers published in the USA advocated the application of salt as a manure [90][91][92][93][94], especially to cleanse and strengthen the plant and to improve growth [95,96], to improve yield, to speed up ripening, and to prevent rust and smut [97]. Likewise, the ability of salt to reduce the freezing point of water was seen as beneficial. In the USA, the application of salt to flax and wheat crops was advocated as a means of reducing the impact of frosts [95]. In addition, the application of salt was assumed to improve the productivity of some fruit trees, such as apple, pear, and cherry [95].
Not surprisingly then, these concepts were also brought to Australia as a part of farmers' lore. In addition, throughout the early and mid-nineteenth century, Australian papers frequently reprinted items from the British Press, uncritically accepting the opinions of the motherland as gospel, e.g., [98,99]. Thus, a contribution to the Brighton Gazette was reprinted in Adelaide [100] and Launceston [101]. In some cases, that chain of evidence had a long trajectory. For example, an item on "Salt as a preventative of rust" and also mildew, published in the Perth Gazette of 4 December 1868, cites Johnson's Farmer's Encyclopedia of 1842 [102], which in turn cites an 1818 communication by a Revd. Edmund Cartwright [87].
More often than not, major contributions were reprinted throughout the Australian colonies. An example of this is an item written by a 'J.B.' of Wandin Yalloak, carried by the Melbourne paper, The Leader. In this, the author reported some experiments he had conducted (see below and Table 1). The newspaper item was widely reprinted and appeared in Launceston (Tas) [103], Adelaide (SA) [104], Port Elliott (SA) [105], Armidale (NSW) [106], and Sydney [107], as well as in a Sydney weekly with a colony-wide circulation [108]. Three years later it was picked up again, this time reprinted in Maitland (NSW) [109], Boorowa (NSW) [110], and Toowoomba (Qld) [111], as well as by the same Sydney weekly [112]. By the 1880s the qualities of salt were still extolled by the authorities. According to the application of salt to common farm crops increased the weight of the grain per bushel, while mixing salt with a top dressing would improve the strength of the straw. Experiments in the United States seemed to confirm this [113].
Johnston [114], however, cautioned that "some chemists . . . doubt that salt or soda is essential to plants" Indeed, it is worth noting that Justus von Liebig, one of the eminent researchers of fertilizers and manures in the nineteenth century, does not mention the use of salt in his Principles of agricultural chemistry even though in his research he draws heavily on British examples and findings [115]. The failure of salt to have any demonstrable positive manurial effect was already well-publicized in England and Australia in 1852 [116] and again in 1862 [117,118]-but it proved to be quite difficult for science to overcome the deeply ingrained farmers' lore [119].
In addition, purchasing salt as manure was not cheap. With the exception of the period of the mid-1850s, the price of a pound of table salt in New South Wales was at or below 1 d ( Figure 1) [120]. The costs of table salt were thus 8 s 4 d per cwt. While we can assume that the price of common and untreated/cleaned salt would have been substantially less, the cost of salt manuring was not insubstantial-especially if the advice was to broadcast up to 5 cwt of salt per acre ( Table 2). The situation was somewhat different in Victoria. In 1865, the Victorian colonial government introduced an import duty on salt (£1/ton) to promote a local salt production industry [121,122]. This industry failed to take off as rapidly as hoped [121,[123][124][125][126][127][128][129].
In consequence, much of the salt was imported from the United Kingdom [130], Germany and India [121]. As a result of the tariff, the price of salt was high, even if the salt was unfit for human consumption [121]. Other colonies exempted non-purified ('rock') salt from the import duties [131].

Rust in Wheat and the Problem of Declining Yields
Australian wheat yields declined in the second part of the nineteenth century, partly due to an exhaustion of the fragile soils after years of tilling, and partly because the strains of wheat grown were not resistant to a variety of diseases, chiefly rust. In New South Wales, European crops were affected by rust within a decade from the start of their introduction, with rust outbreaks on record for 1799, 1803,1805, 1829, and 1832 [35]. Rust appeared in South Australia in 1853/54 [146], but the infestation did not reach catastrophic proportions until 1863/1864 in New South Wales and Victoria and 1867/1868 in South Australia. This is well illustrated by the coverage of the topic in Australian newspapers (Figures 2 and 3). In 1864, the Colony of Victoria established a committee to investigate rust in wheat, followed by a similar committee in South Australia in 1867 [34].
The stem rust fungus (Puccinia graminis tritici) produces millions of small, orangeto-red colored spores, which are blown by the wind onto various plants. Under moist conditions these spores germinate and enter the host plant through its stomata (breathing pores). It was assumed that a harder stem would be more resistant to the colonization by the fungus than the soft-straw wheat varieties [139]. The rust in wheat problem was so large that a number of diverse lines of enquiry were followed. In addition to the establishment of a scientific research direction to oversee the work and to approach the problem from a purely scientific perspective, a series of trials was instituted to assess the viability and effectiveness of a range of traditional remedies [119,147].
While the focus of the paper is on the Australian situation, we need to be aware that Australian agriculture in the mid-and late nineteenth century was in its comparative infancy. While established on traditional British techniques of farming, these had to be adjusted to the local situation, in particular to the soil fertility, the different manifestations of the seasons, and the climatic extremes of drought and excessive rainfall. Even if it had been solicited, Indigenous Australian land management experience was of little help when dealing with production agriculture using introduced grasses (primarily wheat). Consequently, Australian agriculture was open to suggestions and improvements that had been, or were being, trialed in other settler colonialist countries, namely the USA and Canada. For example, the Albury newspaper, Border Post, carried an item in 1890 that reported on Canadian research into rust in wheat and quoted extensive excerpts [143,148].
With Australian agricultural research in its infancy and riven with intercolonial rivalries, and in the absence of authoritative advice, many farmers resorted to traditional remedies, either drawn from old and often-reprinted agricultural publications or sourced from 'folk wisdom', which made the recipients more susceptible to misinformation.

Salt as a 'Home Remedy' to Increase Wheat Yield
From the early days of agricultural production in Australia, salt, seawater, and urine were advocated and used as a steep to pickle seed wheat with the hope of overcoming the wheat's susceptibility to smut, blight, and rust [98,149,150]. This technique had been based on age-old recipes, en vogue in England since the early seventeenth century [70,151] and recommended in the United States as early as the 1780s [95]. In the 1860s, salt and seawater were still in widespread use as seed steeps in Australia [137,[152][153][154]. In the 1880s, the salt or brine pickle, often with lime added, was reported as being extensively used in America and thus formally recommended for Australia [146]. The brine, in which the seed was to be pickled for 5 min, was to be "sufficiently strong to float an egg" [59,155].
Even though it had been established by the Queensland government chemist Karl that salt steeping did not work against rust, the 1890 Intercolonial Conference on Rust in Wheat recommended experiments to assess the effectiveness of the salt pickling of wheat seed, indicating the popularity that the 'remedy' still held [138]. This recommendation was based on observations that wheat grown close to the ocean and/or under the influence of sea breezes appeared less susceptible to rust [156]. The results confirmed that salt steeping did not work against rust. Salt-based seed steeps to combat rust were once more tried in Europe during the 1910s, again without much success [157]. Salt steeps, however, are effective in separating wheat seed from other admixtures. For example, nematode eggs float up in the brine, which can then be removed. This process is still recommended for developing countries as a simple means of purifying the seed material.
The amount of salt introduced into the ground through seed steeps was likely to be very small, even if the technique was applied in several successive crops. The same principle, however, was also applied on a larger scale.

Broadcasting Salt as a General Fertilizer
MacIvor [155], in his lectures on agriculture in Victoria, commented that: "the application of salt to mangolds must be beneficial . . . Beans, cabbages, onions, and turnips, are also much benefited by the presence of salt in the soil." William Story submitted a prize-winning essay in 1860 that collated all the known information on agricultural chemistry. His essay, published in 1861 as a pamphlet, found wide distribution and reception. Story noted that while salting was carried out in the United Kingdom, specifically in Cheshire, the application of too much salt was injurious to the crop. He made it quite clear that in his view there was no need to apply salt as a manure in southern Victoria [158].
The range of popular beliefs regarding the beneficial characteristics of broadcasting salt on the land is quite staggering. Story [158], for example, quotes an authority stating that the application of salt to the amount of six bushels per acre was "recommended . . . on meadows after hay was got in, particularly in dry and hot summers". The theory that was advanced was that salt attracted moisture and thus would be beneficial. Its property of attracting moisture was still hailed to be of "a special value in a dry climate" in an article in the weekly newspaper, the Australasian [59].
Some farmers, as well as government staff, carried out experiments [146]. Some of these were quite scientific for their time, but not as rigorous as those carried out by Nathan Cobb in the 1890s [119,159]. In 1872, for example, the farmer "J.B." of Wandin Yalloak in Victoria, sowed wheat in six parallel strips and applied varied quantities of salt when the plants were about two inches high [105,109]. At first sight, the result seemed convincing (Table 1).
Not surprisingly, the salt producers then actively marketed the salt "as an admirable fertiliser of the soil." An article in the Border Post, quoted from a self-serving brochure of the "Salt Union Ltd." of Cheshire, UK, stated: "Salt is recommended as the most powerful substance known for breaking up the soil and setting its constituents free to nourish the roots of plants; it absorbs moisture from the atmosphere and retains it in the soil, it purifies and decomposes all inert matter, makes stubborn soils easier to work, destroys noxious vermin, renovates old pastures, makes sour grasses sweet and palatable, strengthens the straw in cereals, prevents disease in potatoes, dissolves manures, sweetens and preserves fodder, and generally in all agricultural operations is found to be a most efficient and reliable aid" [160].
By the first decade of the twentieth century, salt had gone out of fashion as a broadcast fertilizer. It was still being advocated for a range of root crops, as well as a means of strengthening the straw of cereal crops [136].

Salt as a Remedy to Rust in Wheat
Salt was also regarded as both a preventative of and a treatment against rust in wheat [109,134,153,[161][162][163][164][165]. Many farmers upheld that the application of salt strengthened the stalks and leaves [165,166] and yet affected the yield of wheat only very little [59,139]. From a physiological perspective this is correct as wheat plants growing in saline soils showed a thickening of the cuticle and a reduced size of the epidermal cells, thus leading to a perceived stiffness of the wheat [157], making it somewhat resistant to rust [136,146,165]. On the other hand, harder wheat was less favored by the millers [167,168]. The first Intercolonial Conference on Rusts in Wheat, held in March 1890 in Melbourne, recommended a number of fertilizer trials, among them the application of salt, to assess whether the rust problem could be overcome. The trial of "salt as a manurial application before the seed is sown [was indicated because it] . . . has a valuable effect in checking the growth, and making the straw more flinty and firmer, and therefore, better able to resist the encroachment of this fungus" [133]. The head of the Roseworthy Experimental Farm in South Australia, William Lowrie, also recommended a salt trial because, even if it failed, it was a cheap experiment [139]. These recommendations were derived from experimental work conducted in the USA and the UK. A letter sent by William Farrer to the first Intercolonial Rust in Wheat Conference drew attention to the work conducted in the 1880s by Prof. A.E. Blount of the Colorado Agricultural Experiment Station. Blount had stated in a letter to William Farrer that he had "used common salt as preventive, [which was] quite effectual. One to five bushels of refuse or any salt to the acre, sown broadcast upon a growing crop . . . will not only become a valuable fertilizer, but will give the straw a siliceous coating capable of in most cases resisting the attacks of the rust" [140].
The recommendation to add salt or saline water to the wheat crop to prevent rust, however, was not confined to Australia or the USA. In Europe, it included not only the use of salt, but also the spreading of herring and herring brine [157]. Russian experiments of the 1930s confirmed that NaCl application in spring reduced rust infection and thus increased yields, but also highlighted that on some soils wheat yields declined due to the salt application [169]. While wheat is moderately salt tolerant, it is affected by high concentrations in dry soils or by moderate concentrations in waterlogged soils [170][171][172].

Experiments with Salt
In 1890, the newspaper media reported that the NSW Department of Agriculture had recommended the trial of salt at concentrations of 2 cwt per acre, to pickle the seed wheat in brine, and to treat rust outbreaks with a spray of 1 lb of common salt per of gallon water [138].
The experiences of some farmers had shown that a broadcast application of salt at the time when rust had been detected did not yield results [173]. In late 1890, the results of the trials came in. Experiments in the Wollongong area had shown that a dressing with 1 cwt of salt per acre had produced "no difference in the rusts on the cereal plants, but the crops on the ground operated on with salt looked stronger than the others" [141].
In his discussion at the first Intercolonial Conference on Rusts in Wheat (Melbourne, March 1890), Lowrie advocated trialing concentrations of 80, 140, and 200 lbs per acre, which is equivalent to 9.0, 15.7, and 22.5 g/m 2 [139]. In response, the director of the NSW Department of Agriculture, H.C. Anderson, argued that each of Lowrie's test applications was only "a small manurial application. The dressing usually advocated varies from 300 to 400 lbs. to the acre when it is administered in a solid form before the crop starts its growth" [133]. In the event, the Agricultural Gazette of NSW of 1890, presenting the official view of the Rusts in Wheat committee, recommended that "2-5 bushels of common salt be broadcast, when the crop is four inches high" [142].
Experiments conducted by George Frederick Berthoud, a farmer at Corowa who had been proactive in the experimentation with wheat varieties [174], used 3 cwt of salt per acre, without tangible benefits [144]. These observations were confirmed by a Canadian study conducted from 1888-1890, which found that rust could be reduced if the overall rust infection was low, but that the salt treatment failed if the rust infection was universal [143].
Despite these negative findings, which were publicized in the local and regional press, the use of salt continued to be advocated as a general fertilizer, for example as a top dressing to accompany a sowing of oats [145]. Even beyond cereals, the 'curing action' of salt was advocated. Mangolds, beans, onions, turnips, and cabbages were deemed to especially benefit from salt applications [59]. A farmer from Cootamundra commented "on the sheep camp we generally put salt on the poorest place" [173]. A newspaper item on the treatment of apple scab, quoting the American Agriculturalist, recommended the spread of a pint of salt under a small tree, and a quart of salt under a large one [175].
By the late 1890s, however, agricultural science had begun to make inroads and salt was no longer en vogue as a fertilizer-notwithstanding the odd throw-back to previous concepts [136]. The development of rust-resistant wheat varieties better suited to Australian conditions, combined with an understanding of superphosphates as fertilizer, changed Australian wheat production for good [152]. By 1908 Thompson noted that the application of salt: "had not any direct manurial action, as is expected by some; its economic value lies in another direction. When applied in sufficient quantities at the proper time of the year, owing to its germicidal properties it not only destroys rank grasses and vegetable rubbish, but also the hosts of injurious insect pests and their embryos that lie lurking and undergoing transformation in their midst. Converting both into valuable fertilizers, and thus cleaning the land and sweetening the sour pastures" [65].
While the reputed value of salt was still discussed in the late 1930s [169], the direct application of salt was no longer recommended, and the salts contained in other fertilizers would have been deemed sufficient.
If we consider the timelines of this debate, then it took almost 50 years until these folk remedies had been disproven and supplanted by better methods and another 30 years until the last vestiges had been extinguished. In human terms, the 50 years equates to almost two generations of agriculturalists, showing the power of the persistence of long-standing remedial concepts.
How much salt has been applied onto the fields? Table 1 compiles the data that could be gleaned from a systematic search of digitized Australian newspapers as they were made accessible via 'Trove [176]. As can be expected, there is considerable variation in the recommendations. The application of salt on wheat ranged from 9 to 62 g/m 2 per planting season (Table 2), while it could be as high as 113 g/m 2 for root crops (Table 3). To put this into context: the European and North American practice of salting the urban and suburban roads to reduce the risk of black ice requires an application of 8-27 g/m 2 [177], with well-documented negative effects on the health of street trees [178][179][180].
The application of salt on wheat added to the saline content of the upper sections of the soil column, with near-surface transport to the lower sections of the slopes and some concentration in the lowlands above the floodplains. In the medium term, this would have increased the salinity levels at the root zone of residual trees in largely cleared farmland, as well as in adjacent remnant bushland. At the application were topics, i.e., on a field-by-field basis with a rotation fallow system; the total accumulation would not have been uniform across the landscape but would have manifested itself in patches. Given that clearing the land of native timber was considered as 'improving' the land [24,25], any vegetation impact would have gone unnoticed, or in fact been welcomed, but an attribution to the practice of spreading salt would have been unlikely.
Given that salt is soluble and readily mobilized in the soil matrix, it thus quickly migrates through the soil column, and all the salt applied during the nineteenth century would have long been washed out.  The main impact would have been the cost of this dubious practice to the nineteenthcentury farmers. During the period of 1861-1868, when rust in wheat had become a major problem, the higher salt price would have required an investment of 6s8d to £2/6/1 per acre (9 to 62 g/m 2 ), even if low quality table salt was used. During the period of 1869-1900, when salt was advocated as a general manure, that cost had been reduced to between 5s and £1/14/7 per acre depending on the quantity spread across the fields. That reduction in salt price was the effect of the introduction of evaporation techniques that increased the salt concentration in the brine and thus reduced the costs for fuel in the final evaporation stage [181].

Conclusions
Overall, the historic evidence shows that salt had been a popular-albeit unsuccessfulremedy to prevent the outbreak of rust in wheat. Beyond this, salt had a reputation as a general fertilizer and as such had been applied for a number of purposes. As with all agricultural practices and techniques, the belief in salt as a suitable remedy for rust in wheat and as a general fertilizer was imported by British settler colonialists from the United Kingdom to the Australian colonies. While the new environment, with its different soil and climatological conditions, challenged existing agricultural wisdom, leading to scientific examination of the underlying causes, folk remedies were deeply ingrained and persisted for at least two generations after rust in wheat had become a major trans-colonial problem.
In the absence of statistical data on (a) the extent of the salt production along Australia's eastern seaboard and (b) the volume of actual salt sales into the agricultural communities, we cannot estimate the positive economic impact the demand for salt may have had on the salt producers, nor do we know the impact when salt went out of broadscale agricultural use again.
Finally, even though the application of salt was of a long duration during the second half of the nineteenth and the early part of the twentieth century, its use in the landscape was comparatively patchy. Moreover, as surface-applied salt will enter a solution when wet and will gradually migrate downwards through the soil column, its effect was generally short-lived and little, if any, of the historically applied salt will remain in the soil today.
Funding: This research received no external funding.

Conflicts of Interest:
The author declares no conflict of interest.