Humanity will reach the organic (biological)
age or cease to exist
– H.P. Rusch
There are several competing philosophies today that underwrite one or another form of agricultural practice. Although it is relatively easy to describe goals for a more sus- tainable agriculture, things become much more problematic when it comes to attempts to define sustainability: Everyone assumes that agriculture must be sustainable. But we differ in the interpretations of conditions and assumptions under which this can be made to occur. As Andrew Campbell right- ly puts it ‘attempts to define sustainability miss the point that, like beauty, sustainability is in the eyes of the beholder… it is inevitable that assessments of relative sustainability are socially constructed, which is why there are so many defini- tions.
None the less, when specific parameters or criteria or selected it is possible to say whether certain trends are steady, going up or going down. For example, practices causing soil
to erode can be considered to be unsustainable relative to those that conserve soil. Practices that remove the habitats of insect predators or kill them directly are unsustain- able compared with those that do not. Planting trees is clear- ly more sustainable for a community than just cutting them down. Forming a local group as a forum for more effective collective action is likely to be more sustainable than individ- uals trying to act alone.
At the farm or community level, it is possible for actors to weigh up, trade off and agree on these criteria for measur- ing trends in sustainability. But as we move to higher levels of hierarchy, to districts, states and countries, it becomes increasingly difficult to do this in any meaningful way. It is, therefore, critical that sustainable agriculture does not pre- scribe a concretely defined set of technologies, practices or policies at these levels. The definitions of sustainability are time and location specific. As situations and conditions change, so must our constructions of sustainability also change. Sustainable agriculture is therefore not a simple model or package to be imposed. It is more a process of learning, a way of looking and a way of thinking.
Broadly, sustainable agriculture involves the integrated use of a variety of seed, pest, nutrient, soil and water man- agement technologies and practices. These are usually combined on the farms to give practices finely tuned to the local biophysical and socioeconomic conditions of individual farmers. Most represent low-external input options. Natural processes are favored over external inputs and by-products or wastes from one component of the farm become inputs to another. In this way, farms remain productive as well as reducing the impact on the environment.
Sustaining soil fertility
Little or no consideration is paid in the literature of agri- culture to the means by which Nature manages land and con- ducts her water culture. Nevertheless, these natural meth- ods of soil management must form the basis of all our stud- ies of soil fertility.
In plants “Protein production” is a bio-synthesis, a syn- thesis by life itself requiring interaction of all the essen- tial elements including trace elements.
For the nutritive value of the crops and the health of the plants, we must first look to the soil- to the geological, the chemical, the biochemical and the biological perform- ances by which the numerous streams of life take off from the soil and continue to flow through the many species of plants and animals.
Protein producing plants demand a long list of ele- ments from the soil: nitrogen, sulphur, and phosphorus are required to make part of the protein molecule; calcium and lime also required; and magnesium, manganese, boron, copper, zinc, molybdenum and other elements are needed in connection with protein construction, even if only in such amounts as are called “trace”. If the soil is not properly fer- tile, not teeming with microorganisms, the whole process grinds to halt. To keep the micro-organisms alive great quantities of decaying organic matter needed to be added to the earth.
People call the soil… mineral matter, but some one hun- dred million bacteria, yeasts, molds, diatoms, and other mi- crobes live in just one gram of ordinary top soil. Far from be- ing dead and inanimate, the soil is teeming with life. These microorganisms do not exist without reason. Each lives for a purpose, struggling, cooperating, and carrying on the cycles
of nature. Into this soil, man throws powerful chemical fertil- izers.
The seminal principle is that instead of trying to feed the plant directly, the objective should be to nourish the soil. The objective of sustainable agriculture is not mere non- chemical agriculture. It is depending on the local resources, it is making best use of natures’ products and processes, it is replacing the external chemicals with farmers’ knowledge, management skills and labor. One important thing which many scientists often underplay or do not realize is the basic difference between the temperate and the tropical climate conditions. It is neces- sary to understand this difference to know why the USA, Eu- rope and Japan, which are all in tem- perate climates, have escaped rapid destruction despite chemicalised farming and why the destruction caused by this method of farming is far more rapid in tropics. In temperate climates, the rainfall is evenly distributed throughout the year. There is neither torren- tial downpour, nor any prolonged dry spell. As against this, in the humid tropical zones, there is tor- rential rainfall for three or four months, during which there is a heavy run-off of the topsoil unless there is protective cover. This is followed by a prolonged dry spell, during which the soil is baked hard and much of it cracks. Hence, when the rains next come, this cracked soil washes away at an even greater rate. On the other hand, in the dry tropics, the rain fall is scanty, the particles of scorched soil disintegrate rapid- ly and the bits are blown off by the wind. Thus, the prone- ness for soil erosion is much higher in both wet and dry trop- ics. Besides, high humidity and high temperature cause high bacterial activity in the wet tropics, leading to quick decompo- sition of soil organic mat- ter and making the soil yet more prone to erosion unless there is continuing replenishment of organic matter. If nitrogenous
fertilizer is applied under these conditions, it leads to further oxidation of soil organic matter.
In temperate climates, the soil remains moist through- out the year. Snowfall in winter conserves organic material under- neath. The soft flow of molten snow in summer, too, is benefi- cial to soil; it does scour. This is why the organic mat- ter sta- tus of soils in temperate countries is very much higher. These have a larger cushion, with a high carbon-to-nitrogen ratio, and hence with a higher capacity for absorption of arti- ficial nitro- gen. This is the reason why both the eroding and the polluting effects of chemical fertilizers are much slower and much less visible in temperate countries.
What plants really need?
The plants feed themselves in two distinct ways, from the atmosphere and from the soil. Elements taken from the atmo- sphere are; carbon (44 %), oxygen (44 %), hydrogen (6 %) and nitrogen (via the microbial world 2 or 3 %). Thus bulks (95-98 %) of the nutrients are taken from atmosphere and are available in plenty.
The balance, a mere 5 % of a plant’s diet, comes from the soil. This consists of small quantities of various minerals. Thus plants feed quantitatively from atmosphere and qualitatively from soil. To feed the plants quantitatively from the soil as be- ing done in conventional agriculture is thus going against their physiology.
The elements taken from the soil are of two kinds, con- stitutive and non-constitutive of plant matter. The constitutive elements are absorbed by plants either in an oxidized or che- lated way. These transformations are brought about by the microorganisms in the soil.
Elements from the atmosphere (represent 95-98 % of a plant’s dry weight) vital elements all constitutive: carbon, oxygen, hydrogen, nitrogen
- Elements from the soil (represent 2-5 % of a plant’s dry weight)
- Twelve vital elements
- Two non-constitutive: potassium and chlorine
- Ten constitutive: phosphorus, boron, calcium, magne- sium, sulphur, iron, manganese, molybde- num, copper, zinc
- Eighteen trace elements
- Four non-constitutive: lithium, sodium, rubidium, cae- sium, and
- Fourteen constitutive: fluorine, silicon, selenium, co- balt, iodine, strontium, barium, aluminium, vana- dium, tin, nickel, chromium, beryllium, bromine
The non-constitutive elements (e.g. potassium, lithium, etc) simply provide the electric charges needed for their var- ious growth processes. These elements are returned to the soil at the maturity stage. Only green plants and other living parts such as seeds, contain minute quantities of these ele- ments.
The soil contains most of the nutrients needed by the plants. There are exceptional cases wherein soils may be naturally deficient in one mineral or other but this is a rare phenomenon. These deficiencies are usually brought about either by wrong fertilization or wrong cultivating methods like mono-cropping or by using hard chemicals that kill the micro- organisms. In no way does it mean that this or that element is, as such, lacking in the soil but that there are no soluble forms
of it available. In fact the core of the question of farm- ing is to find out how to stimulate and enlarge the microbial population in our soils.
For the plant it is more difficult to get the 5% (plus the nitrogen fixed by the microbes) elements from soil than to take the 95% of the elements from the atmosphere. It is obliged to produce a lot of roots to feed in the soil. If we take a wheat plant, the area that is exposed to the sun-the area of the stem and leaves would be about 5 sq. mt but if you meas- ure the area of roots, it would be about 1000 sq. mt! The problem plants face in feeding from the soil is that they can only take elements in a solution. This is actually the big source of problems for plants. They can absorb elements in a solution of water.
The soil maintains the moisture so as to bring nutrients into soil solution. Several factors are in place that works together for maintenance of moisture in the rhizosphere. Organic matter, in this scenario takes up various responsibil- ities. It acts as a wet sponge, as a surface layer that insulates from dry winds apart from itself being nutrient source. It further mediates the aggregation of soil particles. All these con- ditions are existent in a natural forest, which puts into the pic- ture the best use of scarce rain water. It assures the fact that plants need moisture but not water. Plants perform well in conditions resulting continuous availability of moisture. This is not the picture in case of a field consuming chemicals for plant requirements. The high salt concentration, heat of dis- solution, moisture depletion of inorganic fertilizers badly dam- aged the soils chemically and physically. These ‘sick’ soils are unable to hold moisture and hence acquainted with high volumes of irrigation water.
So the way out…
The manufacturing of chemical fertilizers involves unnatural combinations of minerals forced together in factory processes. These combinations are highly water soluble and many are so concentrated that soil organisms cannot live in it. These chemicals are intended for direct utilization by the plant roots, nullifying the role of soil organisms.
On the other hand, organic plant nutrition aims to (i) work within natural systems and cycles, (ii) maintain or increase long- term soil fertility, (iii) use renewable resources as much as possible, and (iv) produce food that is safe, wholesome, and nutritious.
The dependency on soil organisms for nutrient contri- bution to the plants involves a constructive way adding organic matter to the soil leading to diverse advantages to the soil health. Incorporating organic residues like farmyard manure, pressmud compost, wheat straw, sugarcane extract effects the physical properties of soil by lowering bulk density, reducing volume of soil cracks and increasing hydraulic conductivity. The increased availability of the major nutrients for longer periods coincides with the use of organic residues.
Organic amendments like vermicompost, cowdung slurry, soil conditioners, organic boosters effect physico- chemical properties. It was observed that a moderately deep black, calcareous, typic haplustertic soil significantly showed lowering of pH to near neutral, lowering in EC and increase in organic carbon content.
Another important property of organic manures is the residual effect that is by and large beneficial. This points the long-term advantages in nutrient availability, enhanced mois- ture retention, loamy structure etc. a significant yield in the dry
pod yield in any crop with the residual effect contributed by various organic sources like farmyard manure, vermicom- post, neem seed cake, pressmud cake, glyricidia, cowdung urine slurry and also with the combination of biofertilizers like azotobacter and phospho bacteria.
The sustainable properties of organic farming have long been recognized and practiced. But the blanket recom- mendations of a few chemical fertilizers took over and claimed a heavy toll in Indian agriculture. Any crop when well nourished in natural way and when the metabolism is com- plete, resists pests. Many studies reveal that the pests can easily take over a malnourished crop. Popular argument is that why to fight over the source of nutrients as the plant can- not distinguish a nutrient from inorganic or organic source. But, one need to remember that plant may not distinguish but they have a differential impact on soil, therefore it distinguish- es. Another argument is that even from a nutritiously poor soil, the plant will absorb the required nutrients in required quantities. This cannot be true as any plant cannot absorb a nutrient that is not available.
Soil protection
Much of the top fertile soil is lost through different agen- cies of erosion. The importance of protecting the soil surface from rainfall to preserve beneficial soil properties and there- by reduce erosion has long been recognized. Numerous works have been reported on effectiveness of surface mulch in both increasing infiltration and reducing erosion. The effect of mulch is two fold. First, mulch on soil surface intercepts the falling raindrops and dissipates their energy, thus preventing detachment of soil particles and sealing of the soil surface. As there will be no surface sealing or crusting, water moves into
the profile instead of moving off as runoff. Secondly, the mulch rate of 14 and 1/2 ton per acre are effective in reducing flow velocity of water and reduced particle detachment and carrying capacity of the runoff. In addition, the temperature of the soil under mulching is congenial for the development of soil organisms and the mulch being the source for organic matter is an added advantage.
The soil under live cover of plants is an ideal environ- ment for the aggregation of soil particles. By definition, aggre- gation is the ‘naturally occurring cluster of group of soil parti- cles in which the forces holding the particles together are much stronger than the forces between the adjacent aggre- gates. A well-aggregated soil has a good structure and tilth and lowers the extent of soil erosion. Presence of plants on soil exerts the beneficial effects on aggregation in the follow- ing ways:
- protect the soil surface from rain drop splash and other weathering effects.
- the mass of fine roots ramify throughout the topsoil exert pressures that help to form aggregates 33000
- Continual removal of water wherever the root hairs are in contact or near contact with the soil grains lead to local drying effect producing stresses and strains. tion
- Furnish food to the rhizosphere microorganisms that may directly or indirectly through polysaccharide formation play a vital role in aggregation.
In addition, the best aggregated soils are possible in those conditions that have been continually in grass for many years. Even a poor aggregated soil when under sod crops for a few years will show remarkable improvement in aggrega- tion. Such phenomenon is not restricted in case of sod crops alone but reaches its maximum.
All this calls for a paradigm shift in thinking about the sus- taining soil fertility, making it productive over longer years. It is not only nutrient management; it is not only inputs to be ap- plied to the soil; it is not only replacing one product with an- other like replacing chemical fertilizers with organic sources, it is making best use of natures products and processes, it is replacing the external input with knowledge, management skills and labor of the farmers. As some one said, we have not in- herited this environment from our forefa- thers but borrowed it from our future generations, lets give them back in a more productive form.
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