Research and Development
Plant Needs: What? How Much?
Since India has no lack of sunlight, it has the porous, humus-covered soils that absorb and hold more air and moisture, which are most productive in giving a sustained, high yield of biomass. This is ancient knowledge, though less understood these days.
Through the digestive processes of soil-dwelling creatures, including earthworms, the organic matter added to soil gets decomposed into a progressively more inorganic or mineral form. The mineral rich excreta of these creatures must then dissolve in moisture, before being absorbed by the roots of plants.
However, more serious yet is the misconception about how much of minerals or water is needed by plants. Dispelling this common misunderstanding, Bhaskar Save, the ‘Gandhi of Natural Farming’, an educator, entrepreneur, farmer and activist, clarifies that the organic matter we add to soil is not the ‘food’ of a plant, at least in any direct sense. Rather, it is food for innumerable soil-dwelling creatures and micro-organisms, which function ceaselessly to maintain the fertility of land. And there are more micro-organisms in half a cup of good soil than there are humans on earth!
Scientific analysis confirms that approximately 88 percent of the weight of a plant – or any organic matter – consists of just carbon and oxygen, with roughly equal contributions of about 44 percent each. Much of these two elements are drawn by the plant from atmospheric carbon dioxide, absorbed through minute pores or stomata in the underside of leaves.
Hydrogen, drawn from moisture, is third on the list and contributes about six percent of the plant’s weight. The moisture also provides some of the oxygen, as does the air contained in the pores of soil.
Three main elements – carbon, oxygen and hydrogen – obtained from air and moisture, together form about 94 percent of the entire weight of a plant. They are combined together into living matter in the presence of sunlight by a process called photosynthesis.
It is important to understand that though the principal needs of plants are originally derived from air and moisture, a considerable part of these may be drawn via soil and root system. Hence, the physical condition and absorptive quality of the soil is far more vital than its chemical or mineral composition typically over-emphasised by modern agriculture.
Where the porosity, or internal pore space of soil is high – as in all good, living soils characterised by a granular, ‘crumb structure’ – this enables it to hold enormous reserves of both air and moisture. Such a condition – known to local farmers as waafsa – where dampness and air (also warmth) are simultaneously present in the soil, is ideal for plant growth.
This was recognized by outstanding agricultural scientists like Sir Albert Howard. His book, ‘An Agricultural Testament’ (1940), is hailed as a classic, but its contents were too inconvenient for the agribusiness interests of his time to acknowledge. While today, many in western countries look upon Howard as a ‘pioneer’ in sustainable, organic farming. However, he himself confessed that he learnt it all from simple, peasant farmers in India.
Continuing with the list of ‘building-blocks’ required by a plant, nitrogen comes a distant fourth, contributing between 1-2 percent of its weight. This element, abundant in air, is made available in soil through the action of billions of rhizobia – the micro organisms that dwell in the root nodules of leguminous plants. Nitrogen is also supplied when dead organic matter is broken down in soil, under the action of even larger numbers of decomposer bacteria.
Less than five percent of the weight of a plant originates in various other mineral nutrients provided by soil itself. These are elements like phosphorous, potassium, calcium, silicon, magnesium; and a number of trace elements or micronutrients required in very minute quantities, such as iron, copper, zinc, boron, cobalt, manganese, etc.
The earthworm castings in a mixed natural farm or forest provide an abundant supply of these minerals and trace elements. Myriad other animals, birds, insects and micro organisms (bacteria, fungi, molds etc) add their contribution in recycling nutrients to the soil. In fact, every creature – in excretion and in death – is an integral part of the continuous fertility cycle of nature.
Additionally, deep-rooted trees draw up fresh supplies of minerals dissolved over time from the underlying parent rock or sub-soil. Thus, a farmer, who is mindful of the natural, biological processes of fertility regeneration, scarcely needs to bother about the chemical analysis of his soil. The important thing is to religiously return all crop residues and bio-wastes to the earth. Any pronounced ‘nutrient deficiency’ in the topsoil – often caused by cash-cropping monocultures – then becomes largely corrected in a few years by reverting to mixed cropping. Of course, checking soil erosion and shunning agro-chemicals is also essential.
Unfortunately, in present times, much of our bio-wastes are literally wasted, instead of being returned to farmlands. And all plants grown in monocultures – year after year, in the same plot – draw the same mineral nutrients from the same level of soil, depleting these. Most problems of ‘nutrient or micro-nutrient deficiency’ in soil today, unimaginable in most parts of the world as compared to a hundred years ago, are a direct result of these two factors. And we must remember that farmers in India, China, Japan, Korea, have been growing their crops for well over 40 centuries. India, according to some, has a 10,000-year-old history of sustainable agriculture.
In tropical and sub-tropical regions, rate of decomposition of organic matter is much faster than in the temperate climates of Europe or most of USA. In particular, the hot, humid conditions in wet tropics cause high bacterial activity in breaking down the bio-residues that come in contact with soil. Thus, an abundance of mineral nutrients is recurrently available for the plants. However, during tropical monsoons, the newly recycled nutrients near the surface of the topsoil are also prone to rapid erosion and leaching under strong rain or wind. This makes it all the more imperative to have a protective ground cover of vegetation, and to constantly replenish the organic matter (leaf litter, crop residues, etc) on the surface to bind the soil under a carpet of humus.
In contrast, the problems caused by agro-chemicals are less severe and show up more slowly in the temperate conditions of Europe or USA. Not only are there fewer decomposer bacteria in soil, but also the snowfall in winter conserves organic material underneath, further retarding its break-down into inorganic minerals. This is why the organic matter status of soils in temperate countries is much higher. Because of this extra cushion of carbonaceous material, soils have a larger capacity to absorb artificial nitrogen.
While chemical inputs hasten the decomposition process in temperate lands as well, they do not deplete soil of its organic content as rapidly as they do in the tropics and sub-tropics, where the natural rate of decomposition is already high. Nor are there torrential monsoon downpours, as in many parts of India. Consequently, both the eroding and polluting effects of chemical fertilisers are much slower and less visible in temperate climates.
Caution was recommended even in temperate countries through the combined use of considerable quantities of organic manure along with the chemicals. The farmers were moreover taught to exercise precision in the dosages and ratios of their inputs. Nonetheless, the West seems to be witnessing a significant turn-around from chemical methods. The movement towards organic farming is picking up faster than one would have imagined a few decades ago.