48.
Importance Of Humus In Soil Preservation
And Role Of Farmyard Dung In Humus creation
Humus is a word that was invented before the days of Liebig to cover up a large number of complexities that could not be simplified, and the word remains because the situation also remains. We are still very much in the dark about the precise composition of humus and exactly why it is so important.
However, evidence that comes from observing effects must not be rated lower in value than evidence that can explain the effects. To take up again the analogy of the trial for murder; if a witness is produced who saw the accused stick a knife into the victim, that evidence—provided the witness is reliable—outweighs all the circumstantial evidence that tries to show why the accused had reason to commit the murder or how he had the opportunity and so on.
Humus is the dark brown or black decomposed organic matter invariably noticeable in what are called rich soils. Farmyard manure, stable manure, vegetable waste matter, these in their fresh forms are not humus but rather the raw materials that can be turned into humus.
However, evidence that comes from observing effects must not be rated lower in value than evidence that can explain the effects. To take up again the analogy of the trial for murder; if a witness is produced who saw the accused stick a knife into the victim, that evidence—provided the witness is reliable—outweighs all the circumstantial evidence that tries to show why the accused had reason to commit the murder or how he had the opportunity and so on.
Humus is the dark brown or black decomposed organic matter invariably noticeable in what are called rich soils. Farmyard manure, stable manure, vegetable waste matter, these in their fresh forms are not humus but rather the raw materials that can be turned into humus.
Its Properties
By far the simplest way to interpret humus is to list the things it can do. Its properties—from the point of view of soil fertility—can be divided into three classes; mechanical or physical, biological, and chemical.
The physical or mechanical effects are as follows. It can bind together a light, crumbling soil; but it can also make a sticky, heavy soil more friable.
The erosion disasters in the United States, in which thousands of crop-producing acres became a desert or 'dust-bowl', are now generally admitted to have been caused by humus deficiency. The soils were originally very rich; they were farmed without attention to humus replacement—the top-soils became more and more friable, crumbled into dry dust; then, once a certain level in deterioration was reached, nothing could save the soils from being swept away by rough weather.
Humus keeps the soil particles apart and so keeps air moving through the soil. It holds water better than soil so that plants in a humus-rich soil are less affected by drought conditions.
Sir John Russell has reported that plots at Rothamsted regularly treated with farmyard manures contain 3 to 4 per cent more water than plots under similar cropping conditions but which receive non-humus containing manures. And, of course, every gardener knows how much better are his moisture-needing summer crops like beans, peas, tomatoes, marrows, etc., if rotted organic matter is trenched in underneath them.
A minor physical effect comes from its colour, for by tending to darken the soil it increases the absorption capacity of the soil for warm sun rays and thus can keep the soil temperature a little higher.
Its biological properties are vital. It increases the activities of so many organisms whose work is a favourable factor to soil fertility. From the earthworm to the invisible earth bacteria, the life of the soil population is stimulated by the presence of humus. This is an important matter that we shall have to consider in much more detail later—for the moment let it be left at that.
Chemically, humus—or at any rate the manures that contain humus—will contain supplies of the elements of plant-growth. This is obvious for the manures have been produced by the 'rotting' of plant material-—whether a cow has eaten, digested, and expelled grass or mangolds or whether waste green material has been directly composted in a heap.
At this preliminary and general stage, we need not go into the question of how much of the original minerals etc. taken from the soil by the plants will still remain in the humus type manures which are later put back into the soil; but clearly the manures will have some definite value of this kind.
Also, in this plant food department of soil fertility, humus plays an indirect role; for it can increase the soil's capacity for retaining soluble (and therefore active) kinds of these plant-foods. As we shall see later, there is always a tendency for immediate fertility in soils to be lost through the soil's inability to hold all its active plant-food supply indefinitely. So that the help of humus in compensating for this adverse factor is important.
The physical or mechanical effects are as follows. It can bind together a light, crumbling soil; but it can also make a sticky, heavy soil more friable.
The erosion disasters in the United States, in which thousands of crop-producing acres became a desert or 'dust-bowl', are now generally admitted to have been caused by humus deficiency. The soils were originally very rich; they were farmed without attention to humus replacement—the top-soils became more and more friable, crumbled into dry dust; then, once a certain level in deterioration was reached, nothing could save the soils from being swept away by rough weather.
Humus keeps the soil particles apart and so keeps air moving through the soil. It holds water better than soil so that plants in a humus-rich soil are less affected by drought conditions.
Sir John Russell has reported that plots at Rothamsted regularly treated with farmyard manures contain 3 to 4 per cent more water than plots under similar cropping conditions but which receive non-humus containing manures. And, of course, every gardener knows how much better are his moisture-needing summer crops like beans, peas, tomatoes, marrows, etc., if rotted organic matter is trenched in underneath them.
A minor physical effect comes from its colour, for by tending to darken the soil it increases the absorption capacity of the soil for warm sun rays and thus can keep the soil temperature a little higher.
Its biological properties are vital. It increases the activities of so many organisms whose work is a favourable factor to soil fertility. From the earthworm to the invisible earth bacteria, the life of the soil population is stimulated by the presence of humus. This is an important matter that we shall have to consider in much more detail later—for the moment let it be left at that.
Chemically, humus—or at any rate the manures that contain humus—will contain supplies of the elements of plant-growth. This is obvious for the manures have been produced by the 'rotting' of plant material-—whether a cow has eaten, digested, and expelled grass or mangolds or whether waste green material has been directly composted in a heap.
At this preliminary and general stage, we need not go into the question of how much of the original minerals etc. taken from the soil by the plants will still remain in the humus type manures which are later put back into the soil; but clearly the manures will have some definite value of this kind.
Also, in this plant food department of soil fertility, humus plays an indirect role; for it can increase the soil's capacity for retaining soluble (and therefore active) kinds of these plant-foods. As we shall see later, there is always a tendency for immediate fertility in soils to be lost through the soil's inability to hold all its active plant-food supply indefinitely. So that the help of humus in compensating for this adverse factor is important.
'Humus is a natural body; it is a composite entity, just as are plant, animal, and microbial substances; it is even more complex chemically, since all these materials contribute to its formation.'
~ S. A. Waksman
Humus Creation
How can the humus content of the soil be kept up? By the digging or ploughing in of animal manures—farmyard, stable, or sewage manures. By composting all organic wastes. By the deliberate growing of what are called 'green manure' crops, e.g. mustard, for digging in.
And by the digging in of all crop wastes left after harvesting, e.g. stubble, mangold tops, and so on. When grassland is converted to arable land, as has happened so widely in wartime, the turned-in turf provides valuable humus as it slowly rots down in the soil.
It will be noted that the application of fertilizers has not been given as a direct method of providing humus, but the application of bulky organic manures is. This is a fundamental distinction.
Larger crops mean bigger residues for ploughing-back, and also bigger root systems left in the soil to rot down into humus. The extent to which the below-ground parts of crops provide humus is much under-estimated. When a ley is ploughed in, we realize obviously enough that its green stem and foliage matter must make a big contribution to the soil's humus; but the thick mass of root systems underneath may well make an even bigger one.
And by the digging in of all crop wastes left after harvesting, e.g. stubble, mangold tops, and so on. When grassland is converted to arable land, as has happened so widely in wartime, the turned-in turf provides valuable humus as it slowly rots down in the soil.
It will be noted that the application of fertilizers has not been given as a direct method of providing humus, but the application of bulky organic manures is. This is a fundamental distinction.
Larger crops mean bigger residues for ploughing-back, and also bigger root systems left in the soil to rot down into humus. The extent to which the below-ground parts of crops provide humus is much under-estimated. When a ley is ploughed in, we realize obviously enough that its green stem and foliage matter must make a big contribution to the soil's humus; but the thick mass of root systems underneath may well make an even bigger one.
Farmyard Manure Vs Fertilizer
The difference between farmyard manures and fertilizers is confused by the fact that the manures contain not only humus but also supplies of the fertility elements. In this latter sense, therefore, they overlap the function of fertilizers. We must neither exaggerate the value of this overlap, nor underestimate it.
Important questions affecting the whole argument about fertilizers are: (1) how much 'chemical' plant-food do these natural manures provide; (2) how much natural manure of all kinds is, or can be made, available; (3) how much plant-food must be added to the soil to maintain fertility at the level necessary for our requirements?
It is the chemical plant-foods with which fertilizers are more concerned. Liebig made the point that any element found by analysis in the composition of a healthy plant was ipso facto an element necessary to its proper growth. (It is not so true in a quantitative sense, for an element that is present in large quantities in a plant may not be any more important than one present only in very much smaller quantities. The different elements have different functions. One element may function as a direct food; another may be needed only in traces in order to allow the plant to digest the first element.)
Important questions affecting the whole argument about fertilizers are: (1) how much 'chemical' plant-food do these natural manures provide; (2) how much natural manure of all kinds is, or can be made, available; (3) how much plant-food must be added to the soil to maintain fertility at the level necessary for our requirements?
It is the chemical plant-foods with which fertilizers are more concerned. Liebig made the point that any element found by analysis in the composition of a healthy plant was ipso facto an element necessary to its proper growth. (It is not so true in a quantitative sense, for an element that is present in large quantities in a plant may not be any more important than one present only in very much smaller quantities. The different elements have different functions. One element may function as a direct food; another may be needed only in traces in order to allow the plant to digest the first element.)
If your energy is all engaged in manufacturing tires and wheels, then who will go to the farm...So gradually farming will be reduced, and the city residents, they are satisfied if they can eat meat. And the farmer means keeping the, raising the cattle and killing them, send to the city, and they will think that “We are eating. What is the use of going to...” But these rascals have no brain that “If there is no food grain or grass, how these cattle will be...?” Actually it is happening. They are eating swiftly.
-Srila Prabhupada (Room Conversation with Dr. Theodore Kneupper
— November 6, 1976, Vrndavana)
The elements found in plants generally are: carbon, nitrogen, hydrogen, oxygen, phosphorus, potassium, calcium, magnesium, sulphur, iron, manganese, chlorine, boron. Even this is not a complete list but it contains the main ones and some minor ones.
Now of these elements there are three important ones that the soil itself does not seem able to supply sufficiently for our cropping needs—nitrogen, phosphorus, and potassium. Each harvested crop takes away supplies of these elements that have come from the soil and, after a time, these losses reduce the soil's ability to go on feeding crops.
By sampling and analysis it is a simple matter for a chemist to measure just how much of these elements is removed, say, per acre by a crop.
Thus, a good crop of potatoes might take from the soil about 150 pounds of potash (oxide of potassium) per acre. What happens to this 150 pounds? The potatoes are eaten, digested, expelled from the human system into the sewage system.
In a modern city this usually means that the sewage is treated and then conducted into a river or sea as quietly and unobtrusively as possible. That part of the potash in the discarded peelings may go on to a compost heap or be fed to pigs or poultry in which case a fraction of the potash will eventually find its way back to the soil. But, in sewage disposal, most of the potash is lost completely.
Admitted, there is some sewage reclamation carried on, but it must be remembered that sewage in modern sanitation is heavily diluted with water and this means that the active plant-food—the kind that can dissolve in water-must pass into the liquid fraction of sewage. And it is this liquid fraction that is discarded in most systems—the sludges that are reclaimed at some works are composed of the solid, insoluble parts of sewage. There is, therefore, continuous loss. In less civilized countries—or perhaps it is fairer to say less industrialized countries— the sewage is disposed of by putting it directly back on to and into the soil.
In cattle farming, the nitrogen, phosphorus, and potash consumed when the cattle eat grass or fodder crops returns to the farm as manure. That is why the farmyard manures have been valued so much in traditional farming.
Now of these elements there are three important ones that the soil itself does not seem able to supply sufficiently for our cropping needs—nitrogen, phosphorus, and potassium. Each harvested crop takes away supplies of these elements that have come from the soil and, after a time, these losses reduce the soil's ability to go on feeding crops.
By sampling and analysis it is a simple matter for a chemist to measure just how much of these elements is removed, say, per acre by a crop.
Thus, a good crop of potatoes might take from the soil about 150 pounds of potash (oxide of potassium) per acre. What happens to this 150 pounds? The potatoes are eaten, digested, expelled from the human system into the sewage system.
In a modern city this usually means that the sewage is treated and then conducted into a river or sea as quietly and unobtrusively as possible. That part of the potash in the discarded peelings may go on to a compost heap or be fed to pigs or poultry in which case a fraction of the potash will eventually find its way back to the soil. But, in sewage disposal, most of the potash is lost completely.
Admitted, there is some sewage reclamation carried on, but it must be remembered that sewage in modern sanitation is heavily diluted with water and this means that the active plant-food—the kind that can dissolve in water-must pass into the liquid fraction of sewage. And it is this liquid fraction that is discarded in most systems—the sludges that are reclaimed at some works are composed of the solid, insoluble parts of sewage. There is, therefore, continuous loss. In less civilized countries—or perhaps it is fairer to say less industrialized countries— the sewage is disposed of by putting it directly back on to and into the soil.
In cattle farming, the nitrogen, phosphorus, and potash consumed when the cattle eat grass or fodder crops returns to the farm as manure. That is why the farmyard manures have been valued so much in traditional farming.
'The fixation of nitrogen is vital to the progress of civilized humanity, and unless we can class it among the certainties to come, the great Caucasian race will cease to be foremost in the world, and will be squeezed out of existence by the races to whom wheaten bread is not the staff of life.'
~ Sir William Crookes, 1898.
