The Law of the Minimum is an ecological principle that considers the proper balance among factors required for the
growth of a living organism Justus von Liebig (1803-1873), Agricultural Chemist
centred on building soil humus with an emphasis on a “living bridge” between soil life, such as mycorrhizae and bacteria, and how this chain of life from the soil supported the health of crops, livestock and mankind. To illustrate the Law of Return concept, Howard wrote about how, in a forest, all dead plant and animal residues are added to the soil and how they serve to enrich the soil in humus. Minerals contained in the dead plant and animal residues are also recycled by this natural process, which occurs in all native forests and grasslands. Building soil humus is vital to maintaining soil quality and healthy soil biological activity. When land is used for growing and harvesting crops and livestock, mineral nutrients are removed from the soil. The failure to effectively return the waste products of agriculture back to the land results in mineral depletion of soil and represents a lost opportunity to build soil humus. This was of great concern to Albert Howard, who strongly advocated the Law of Return as a key principle of soil fertility management. While Howard recognised the significance of Liebig’s writings on agricultural chemistry, he was no Leibig devotee. Howard thought that Liebig was “a sinner” for vigorously combating the so-called humus theory and instituting the so-called “NPK mentality,” that is, the practice of fertilising only, or principally, with nitrogen, phosphorus and potassium. One of Howard’s main criticisms was that Liebig focused attention on soil chemistry to the neglect of soil biology and physics. As a result of this single- minded focus on chemistry, the once- great appreciation for soil organic matter fell to a position of low esteem. In recent decades, however, there has been a renewed appreciation for soil organic matter.
Hardened Attitudes
Although Howard knew that certain nutrients could be severely limiting in some soils, he opposed using chemical fertilisers, even though they could more easily correct specific nutrient limitations than could the use of compost. Thus, Howard’s extreme position against any use of chemical fertilisers created a challenging situation for organic farmers attempting to balance nutrient supply, for example, to effectively deal with the Law of the Minimum. Howard's hard-line position against the use of
chemical fertilisers, however, was not shared by some of his contemporary supporters who felt that the use of artificial fertilisers could sometimes be justified. Howard was, however, open to the use of some naturally occurring mineral sources such as pulverized rocks.
Liebig’s absolute concept of “only”
inorganic nutrient uptake by plants has been disproved and yet it persists in modern soils literature. This represents a case of mechanistic rigidity in the history of science that illustrates a lack of a functional understanding of natural systems. Likewise, the hard-line position of Howard against the use of any chemical fertilisers may represent a case of extremism. Moreover, Howard’s extreme position contributed to the common, but mistaken, impression that organic is simply defined as farming without the use of synthetic fertilisers. Current literature, however, provides evidence that some plants can uptake and utilise limited amounts of organic forms of nitrogen such as amino acids and peptides. Not only were those early arguments incorrect, but they also misrepresented the principles of organic farming as if it were defined by carbon (organic) chemistry rather than a philosophy of living systems. Another implied argument is that the biological processes occurring in the soil, and responsible for mineralisation, are of no value to soil quality. Recently, however, there has been an increasing appreciation for the biological processes associated with the soil food web.
Current Thinking
Most turfgrass agronomists have been trained in the concept of plant nutrition on the philosophy of Lieberg. The giant mineral fertiliser industry was developed on the assumption that specific levels of mineral nutrients in plants are directly related to nutrient availability and impact plant performance. Many modern turfgrass agronomists have been involved in research concerning the impact of mineral fertilisation on turfgrass. Results from studies dealing with various sources of nitrogen applied to turfgrasses are readily available, as are the ratios of major fertiliser elements on plant growth. However, the correlation between the rate which grass leaves grow because of fertility and turfgrass quality is poor. Often heavy fertilised turfgrass that grows rapidly is more susceptible to environmental stresses than less fertilised, slow growing grass.
Recently, interest has developed in the concept that suppression or enhancement of plant growth represents the effect of hormonal balance. Frankenberger and Arshad,1995, reviewed reports of the effect of organic amendments on plant growth. They concluded that plant stimulation associated with applications of organic materials cannot be substituted by equivalent application of mineral nutrients. They also pointed out that research has shown that hormones were also important in influencing plant growth. Work at Virginia Tech, USA, with various materials applied in small quantities to turfgrass, have shown to stimulate growth that cannot be attributed to traditional plant nutrients. These are referred to as biostimulants or metabolic enhancers, and include seaweed extract, humic acids, amino acids, benzyladenine, trinexapace-ethyl, propiconazole, salicylic acid and silicates. When treated with these substances, turf grasses are better able to tolerate environmental stresses such as low soil moisture, salinity, heat, cold, dollar spot disease, high UV light intensity, herbicides, and nematodes. Pre- treatment with biostimulants changes the hormonal balance to favour cytokinins and auxin production so that antioxidant production can continue when stress occurs. Increased antioxidant content is a common factor associated with increased stress tolerance of biostimulant treated turfgrasses. Treatment with biostimulants trigger the enhancement of antioxidants for protection against environmental conditions.
Conclusions
Growing turfgrasses for the preparation of playing surfaces will probably always necessitate the input of inorganic fertilisers. However, to solely rely on synthetic sources produces a reliance on other petrochemical products, e.g. pesticides, to counteract the effects of parasitic fungi and insect attack and environmental stresses.
Using materials that enhance the
microbial population of the soil and the hormonal balance within plants, has resulted in reduced fertiliser and pesticide requirements. Some argue that to be anti-chemical goes against all the benefits we have developed in health care and hygiene, saving the lives of millions of people. This is undoubtedly true and we must be
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