It saddens me to admit that the prevalence of seriously problematic soils appears to have increased dramatically over the previous few decades. Despite the proximity of international tensions, the world seemed a considerably safer and altogether more stable environment when I started gardening in my teens and early twenties. Perhaps this misrepresents the reality. It might be more accurate to suggest that certain issues were once described in concrete terms, without the numerous complexities and differences of opinion which are routinely encountered in the popular media of today. Like everyone else, I’m confused and disturbed by the reports on global warming, climate change, and species decline. When I look at my original notes for this section, I’m aware that I intended to separate problem soils into two distinct categories. Problem soils determined by geographic and environmental factors versus those which are distinctly caused by situations of adverse human influence. If it is true that we have irreversibly upset the stability of our global weather patterns, my attempt to differentiate these two categories should perhaps be revised.
In most cases, problem soils will be characterised by the influence of extreme geographic or climatic conditions. They may also be contributed to by human impacts such as structural erosion, overly intensive agricultural practices, and industrial contamination. Newly released land developments are often criticised for their soils which seem incapable of supporting a garden. Modern subdivisions may include unstable tracts of wetland and those which have been inappropriately reclaimed using cheap and readily accessible fill materials. As modern urban regions expand toward and beyond their planned boundaries, another relatively common practice involves the rezoning of previously agricultural and industrial land into residential allotments.
The soils of reclaimed agricultural lands may suffer from a range of problems such as erosion, salinity, severe nutrient deficiencies, and toxicity related to agricultural chemicals and other treatments. Depending on its previous use, reclaimed industrial land may contain soils contaminated with unacceptable levels of toxic metals, hydrocarbons like diesel oil, and chemical substances which remain potentially harmful for many years. Such irresponsible land practices can result in entire neighbourhoods without gardens. Several years ago I happened to visit one of these reclaimed suburbs and was astonished to learn of the thriving local trade in plastic and artificial plants. I was driving on a wide road with a pink sunset behind me. Everything seemed surreal and unfamiliar. I tried to imagine what it would be like for the parents who built plastic gardens for their children to play in.
Local knowledge is invaluable
The likelihood of correcting specific soil problems is greatly increased by gathering sufficient knowledge concerning local geography and the human interventions which might have disrupted the site’s natural composition and structure. Many suburban soils, for example, are seriously degraded by the erosive influence of their climates. This is particularly apparent in regions where a hot, dry season alternates with one of high rainfall.
Accelerated erosion can also occur on alluvial plains supported by river systems which are diverted for cropping irrigation. Over time, the slow drying of river tributaries can severely reduce trees, native grasses and groundcover, leaving the uppermost layers of humus exposed. The topsoil is then vulnerable to being blown or washed away, leaving subsoil deficient in organic material and plant nutrients. Because the subsoil remains permeable to subterranean water, mineral salts may be deposited in quantities sufficient to cause further destruction to soil organisms and plants. In many cases of erosion, the short-term remedy involves incorporating organic material and securing the remaining nutrients with a suitable groundcover. Hardy native grasses and low growing shrubs with complex root systems are often ideal for this purpose.
Chemical and industrial contamination
In my opinion, it is imperative to obtain professional advice in those cases where a garden or property is likely to be affected by chemical or industrial agents. Given the current rate of land reclamation within major cities, it would be helpful for prospective purchasers to include soil analysis as a component of their property inspection and valuation reports. In the United States alone, there are numerous litigations involving the sale of contaminated residential properties. The problem may widen considerably as industrially exposed land is increasingly exchanged and developed within economically emerging nations like China, India, and Vietnam.
The effective treatment of seriously contaminated soils can be extremely expensive and time consuming. When the contamination is restricted within a manageable surface area the usual treatment is a combination of soil replacement and the application of activated charcoal. This can be purchased from organic garden centres and should be spread over affected areas in quantities specific to the manufacturer’s recommendation. Over time, the charcoal will neutralise and absorb a wide spectrum of chemical residues. As a bonus, any excess charcoal will provide useful minerals and plant nutrients while improving soil drainage.