Our approach to growing plants increasingly needs to be environmentally friendly and sustainable in a world where resources are being used faster than they are being replenished. Sustainable Horticulture encompases both careful planning to avoid over use of resources, as well as applying effective cultural techniques that will get maximum return with minimum depletion of resources.
Permaculture is a sustainable technique developed originally in Australia, but which has spread throughout the world.
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Organic Plant Culture
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WASTE DISPOSAL IN A PERMACULTURE SYSTEM
Waste can be water (eg. from the bath or toilet) or solid (eg. in the rubbish bin or compost heap).
There are two main types:
a/ Greywater -water from washing (eg. bath water, kitchen water, laundry water etc)
b/ Blackwater -waste water from the toilet.
Consider substances/chemicals which might be in this waste. Some chemicals affect plants (eg. poison them), or have other harmful affects if released into the environment; particularly if they are not biodegradable.
Large double compartment grease traps are necessary before water is transferred to the septic tank.
Grease will accumulate on the top, and clearer water is discharged from beneath. The use of kitchen strainers will help reduce the occurrence of fine particles that can be easily removed. The water can be pumped directly onto the garden (check with your local council health department), or you can use the greenbelt system.
apply directly to the soil - do not use in sprinkler or drip irrigation systems.
use on flat areas - not steep sloped land.
spread water over a large are not a small concentrated area.
rotate irrigation water with clean fresh water to aid in the leaching of the minerals and contaminants.
use thick mulch.
do not use near acid-loving plants, as greywater is alkaline.
do not use grey water for edible crops that produce leafy crops near the soil or underground root crops.
use greywater only on well established plants - not on fresh seedlings or houseplants.
There are various ways of treating toilet waste:
Septic Systems (Tanks) -can eventually pollute ground water
Long Drop (A toilet built over a very deep hole) -can pollute ground water
Composting Toilets -good ones are environmentally sound
Sewage systems -effectiveness depends on how the authority treats the waste
Biological Filtration Systems -series of ponds, reed beds etc. -can be very environmentally sound.
Extract of notes from Permaculture Design Course Handbook:
(reproduced with kind permission from the Permaculture Institute).
WASTE DISPOSAL AND RECYCLING
Water and plants as cleansers of system pollution
Fix excess nutrients: watercress, ruches (eg. Scirpus validus), water hyacinth.
Algae, eg. Spirulina, desalinates, cleanses, removes radioactives, builds protein from nitrates and nitrites, has a high BTU value, is 68% digestible protein, and has low cellulose.
Uses of Waste Water
Sewage lagoons: aeration, weeds, and water fowl -- then goes to fish, and finally discharged to non food forests, nut crop, essential oil crop, bamboos.
Types of Nitrogen
For purposes of this section, nitrogen may be considered as existing in three general forms.
Organic nitrogen is generally unavailable for plant use. An important exception is urea, which is organic but for all practical purposes acts like an inorganic form. (Urea and urea formaldehyde fertilizers may contain biuret, a by product toxic to many plants.
Unless labelled biuret free, these materials should be used only after thorough testing on each crop.) Organic nitrogen is linked to carbon and is not normally water soluble.
Certain organic forms such as the amino acids (structural components of the proteins) have been shown to be absorbed by plant roots, but their occurrence and importance in the nursery soil is minor.
Insoluble organic nitrogen might be considered as a storage form; available nitrogen will be produced from it by chemical or microorganism activity.
Sometimes, as in manures or leaf moulds, steaming will result in a chemical reaction which produces an available form.
The more stable organics will require action by microorganisms to produce this available nitrogen.
The first breakdown product of organic nitrogen which is of practical interest to the nurseryman is ammonium.
The ammonium nitrogen may also be provided as a commercial fertilizer, such as ammonium sulfate or dissolved ammonia. Urea is quickly hydrolyzed in the soil to produce the ammonium form.
Ammonium nitrogen is water soluble, can be absorbed readily by the roots, and can be utilized by the plant. In certain cases utilization may be so fast as to disrupt normal functioning of the plant. Although water soluble, the ammonium form of nitrogen is not as readily leached through the soil as is nitrate. Because of the positive charge of the ammonium ion it may be removed from solution by the negatively charged clay &
organic ingredients; this prevents its being leached from the soil.
Nitrate, which is negatively charged may be readily leached. This non-mobile status of ammonium is temporary, owing to its subsequent conversion to nitrate.
Also, the presence of other positively charged ions (for example, calcium, magnesium, sodium, and potassium) may cause the ammonium to be "unseated" and release into the soil solution, which makes it leachable.
It is evident from the foregoing that ammonium nitrogen applied to the soil surface may not reach the root zone with the first irrigation. For this reason it is sometimes referred to as being more slowly available than the nitrate form, whereas it is just as available as nitrate if it is in the vicinity of the root.
The conversion of ammonium nitrogen to nitrate nitrogen is also by microorganisms.
Nitrate is completely water soluble and, since it is negatively charged, it does not enter into any non mobile combinations with soil components. In a normal well aerated soil, nitrate is, from a practical viewpoint, the end product of nitrogen conversions. Under prolonged conditions of composting of organic products, most of the nitrogen will be converted to the nitrate form. In the field little ammonium normally exists except under very acid of waterlogged conditions the organic nitrogen being slowly converted to ammonium and then relatively rapidly to nitrate. Under the natural conditions where plants evolved, nitrate was, therefore, the principal form of nitrogen utilized. Perhaps some plants have lost their tolerance to ammonium as a result.
The cycle of nitrogen within the plant is the opposite of that in the soil.
Nitrate is slowly converted to ammonium, which is rapidly combined with certain organic compounds to form proteins, enzymes, pigments, and many other complex substances. Under natural conditions, ammonium nitrogen & its first reaction products will not be present within the plant in appreciable quantities. Under artificial conditions, if ammonium nitrogen is supplied directly, an abnormal accumulation of ammonium and initial reaction products may occur within the plant, resulting in possible "self poisoning." An important concern of this section is this ammonium toxicity and it prevention.
Factors Affecting Nitrogen Release From Organic Sources
In well aerated soils such as those obtained in the physical medium of the U.C. type mix, the following factors may affect the amount and rate of release of available organic nitrogen.
In natural soils the population of microorganisms will be much higher in the surface 6 to 12 inches than at greater depths.
Subsoils are frequently low in organism population. This is to be expected since the moisture, air, and organic matter necessary for most organism activity are more available in surface soils.
The difference in the effect on rate of nitrogen release by untreated surface and subsoils may be substantial. Where heat or chemical treatment is practiced, the difference between surface and subsoils is reduced, since all nitrifying bacteria are killed and the population of those which produce ammonium is initially reduced.
Heat and chemical treatment
As suggested in the preceding paragraph, the procedure of treating the soil to rid it of pathogens necessarily affects the whole microorganism population.
Nitrifying bacteria will be eradicated where treatment is effective.
Ammonium production may be reduced but not entirely eliminated.
Furthermore ammonifiers will more rapidly repopulate the soil.
Thus ammonium may be produced, but not converted to nitrate, until the soil becomes reinoculated with nitrifiers.
Under normal conditions, inoculation will occur within a period of several days to several weeks.
This is an uncertainty which in the future may be eliminated by the use of inovulation cultures.
Soil reaction (pH)
Highly acid media generally have little effect on the activity of ammonium producers, while inhibiting the activity of nitrifiers. This was shown in a nursery test in which azaleas were grown in beds of pure peat plus organic nitrogen.
Hydrated lime was worked into a test bed before planting.
After several months, plants in the limed area were noted to be darker in colour than the remainder. Tests of the growing medium showed the differences in acidity and nitrogen concentration.
It has been demonstrated by Tierdjens and Robbins (1931) that some crop plants are unable to utilize the ammonium form of nitrogen when the pH is low, but do so readily when the pH is in the neutral to alkaline range. The use of lime in recommended mixes should decrease difficulties of this nature.
In general, the warmer the soil, the greater will be the activity of microorganisms into it.
There is an upper limit, of course, beyond which an increase in temperature will reduce and even kill them. When temperatures are low, activity is reduced. The nitrifiers are more critically affected than are the ammonifiers.
Thus during cool weather there will be a reduced rate of ammonium production, and an even greater reduction in the rate of nitrification. When soil temperatures are below 40 deg. F, applications of blood meal or other organic sources may be quite ineffective and the rate of release of nitrogen too slow to meet the plant requirements.
Under these conditions the grower should use soluble materials such as calcium nitrate.
Concentration and source of organic nitrogen
As already shown, an increase in amount of organic nitrogen added to a soil mix will increase the rate of release as well as the total amount of available nitrogen. Therefore, the higher rate of addition does not necessarily mean that the period of release will be lengthened.
The sources of organic nitrogen are quite varied in chemical composition.
Some organic sources of nitrogen seem to be more readily assimilated by organisms which decompose them than do others.
Urea formaldehyde, hoof and horn meal, and blood meal are among the slowly decomposable forms of organic nitrogen. Cottonseed meal, castor pomace, and fish meal are quite rapidly decomposed. Since the primary objective in adding an organic nitrogen source to the mix is one of prolonging the period of release of available nitrogen, it is most reasonable to add those sources which are slowest in rate of breakdown.
As explained below, there are substantial differences in rate of release of available nitrogen when organic materials are broadcast over the surface of the soil as compared with being mixed into it. Presumably the more finely divided and more "palatable" materials would result in more rapid release of available nitrogen with surface application.
Moisture and aeration
A soil that is dry will not support plant growth and as might be expected, will retard microorganism activity.
It is, however, unsafe to assume that a stored soil mix is dry enough to prevent the release of available nitrogen from organic sources. In some cases oven dried and stored samples have been found to produce available nitrogen.
Lack of adequate moisture would probably be more damaging to the growing plant than any side effect it might have on nitrogen relations.