Commercial above-ground bench worm farms collect and recycle liquid feed, and they produce large quantities of solid humus/fertiliser.
A particularly effective system utilises a bench system for the worm beds. Above it is mounted a micro sprinkler system, which sprays water over the beds to the point where it leaches through and drains into a holding tank. The worm leachate is aerated in this tank using an oxygenating device designed for aquariums; it is then pumped back to the worm beds and recirculated until it has attained sufficient nutrient concentration to be optimal for liquid feeding plants. An electrical conductivity meter is used to monitor the concentration of nutrient salts in the worm leachate, and a filter is utilised to ensure that organic-matter particles do not clog up the irrigation system. The solid worm castings are also harvested every year or so and applied directly to the soil (after the worms have been separated and returned to the worm farm) when the worm beds are renovated to ensure efficient operation.
In-ground worm farms
These units involve either trench composting (which is part composting, part worm farming) or some sort of structure, such as a large-diameter PVC drainpipe, which is partially buried in the soil and has slots or holes in the below-ground portion to allow the worms to move in and out of the surrounding soil. A section of the pipe is above ground level and should ideally have an aerated lid to allow the system to breathe. To add food to the top of the system for the worms to feed on, simply remove the above-ground lid.
Although an in-ground worm farm is usually a small-scale system, it still has several advantages:
It is very low maintenance. Simply dig it in once, and add food scraps for 3–6 months before moving it to the next spot.
The nutrients produced by the worms go straight into the soil to feed the surrounding plants up to a metre away.
The worms can move away from unfavourable extremes of temperature or moisture (in other words, they self-regulate).
The only major disadvantage we have found with in-ground worm farms is that they do not allow you to distribute fertiliser around the garden. However, this issue can be overcome to some extent by regularly moving your in-ground worm farm to a different position in the garden. When you move the unit, it is desirable to lift the castings out and separate the worms from the castings – at least enough to ‘seed’ the next spot with some worms.
An in-ground worm farm starts fertilising your plants as soon as the worms get to work. The liquid from the unit carries nutrients and beneficial microbes into the soil, while the worms cultivate and aerate the soil whenever they travel out of the unit and tunnel beneath the soil surface. Indeed, a network of in-ground worm farms will save you the trouble of having to dig your soil to prepare it for future crops.
QUALITY OF VERMICAST AND WORM ‘WEE’
We have said previously that the quality of compost you get out of worm-farm systems, in terms of its fertiliser value at least, will be dependent on what you put in. In Melbourne, the city council has encouraged the use of the worm-bin vermicomposting system in various institutions, including restaurants and blocks of flats. This has given us the opportunity to use laboratory analysis to compare the nutritional value of restaurant vermicast (vermicompost) with that of Angus’ household vermicompost. The restaurant feedstock contained mixed vegetables and eggshells but no added water, while Angus’ household feedstock featured mixed whole kitchen scraps, including eggshells and bones, with extra water added (so he can extract soluble nutrients as worm ‘wee’ compost). The results of the comparison are shown in the Nutritional Value of Various Worm Composts table.
The council-sponsored systems do not permit the use of meat scraps, but Angus does, which is one reason why Angus’ worm compost has much higher phosphorus, iron and possibly zinc and copper levels. The restaurant worm compost – with its very high fruit and vegetable content – has high potassium levels, whereas Angus’ is leached to generate liquid feed, so much of the soluble potassium content has been removed and is now in the liquid feed.
Angus’ compost is very mature, as it is taken from the lowest shelf of his layered system. This also explains why the insoluble nutrients phosphorus, calcium, iron, zinc and copper become so concentrated. As the compost gets older, the carbon content drops and the insoluble mineral matter increases in proportion. The restaurant worm compost, on the other hand, is fresher and hence shows a higher nitrogen content but a lower iron level.
A small in-ground worm farm is a very simple and labour-saving system for the recycling of kitchen scraps.
An in-ground worm farm starts fertilising your plants as soon as the worms get to work.
Angus’ worm ‘wee’
Angus likes worm farming and often raves about the response he gets from using a ‘juice’ or ‘wee’ that he makes from his worm farm. All he does is pour the water from a full watering-can through the worm farm every time he needs some liquid feed. The excess water drains out, and the worms don’t get too wet. He sent a sample of both the ‘wee’ and the solid worm compost to Simon’s lab. The nutrients in the ‘wee’ are given in the Nutritional Value of Angus’ Worm ‘Wee’ table on the opposite page.
The results are remarkable. Look at the ‘ideal’ levels for the different nutrients in a middle-of-the-road liquid or hydroponic feed compared with Angus’ worm ‘wee’. The ‘wee’ represents a very close approximation to the perfect liquid feed, as the ratios of the major and minor plant nutrients are all close to ideal for the average plant. This is not really surprising, since Angus uses all his kitchen scraps – which represent a cross-section of plants he grows on his urban farm – in the compost. He also adds some meat, bones and eggshells. Notice how high the potassium level is – this is higher than necessary for most plants, but perfect for fruit and flowering crops that need plenty of potassium.
The levels of nitrogen, calcium, phosphorus and iron are much higher in Angus’ household vermicompost than in the worm ‘wee’, while the potassium level is much lower. This is not so surprising if you remember that the first four elements are not very soluble. Potassium, being very soluble, is quickly leached away into the ‘wee’, leaving the other elements behind. The very high calcium and phosphorus is no doubt the result of adding bones and eggshells to the mixture.
NUTRITIONAL VALUE OF VARIOUS WORM COMPOSTS
ELEMENT RESTAURANT* ANGUS’ HOUSEHOLD*
Nitrogen 2.62 per cent 2.24 per cent
Potassium 1.36 per cent 0.58 per cent
Calcium 6.21 per cent 5.57 per cent
Phosphorus 0.32 per cent 1.32 per cent
Magnesium 0.68 per cent 0.52 per cent
Sulphur 0.31 per cent 0.44 per cent
Iron 5235 mg/kg 18,900 mg/kg
Manganese 238 mg/kg 290 mg/kg
Zinc 70 mg/kg 268 mg/kg
Copper 49 mg/kg 127 mg/kg
Boron 19.7 mg/kg 45.2 mg/kg
*Note: We usually measure macronutrients as a percentage by dry weight. Micronutrients are present in much lower amounts, however, so we express these as milligrams per kilogram, which is a more sensitive unit of measurement.
Nitrogen is a bit more complicated, as it forms very soluble minerals (nitrate and ammonium) but also remains as an integral part of the organic-matter matrix (seen as proteins and other insoluble living components). As it ‘mineralises’ during the process of decomposition, it releases slowly into the soluble nitrate (NO₃) and ammonium (NH₄) that we see in the liquid component.
The result: a perfect fertiliser combination. Use the solids as a pre-plant fertiliser for the beds before planting the seedlings or sowing the seeds. When they start to grow, use the liquid ‘wee’ maybe twice a week – depending on how the plants look – as a well-balanced and readily available feed to encourage rapid and healthy growth.
The only problem with worm farming the Angus way is that, depending on the size of your garden, you are more than likely going to run out of sufficient ‘wee’ and castings. You are left with trying to source alternati
ve forms of organic waste for your worms to eat. However, this may not be an issue – friends and neighbours usually welcome the chance to join in this environmentally friendly (and productive) exercise.
A highly concentrated dark-coloured worm juice or compost tea needs to be diluted in a watering-can before use.
NUTRITIONAL VALUE OF ANGUS’ WORM ‘WEE’
ELEMENT WORM ‘WEE’ (MG/L) ‘IDEAL’ LIQUID FEED (MG/L)
Nitrogen 200 150–250
Potassium 410 200–300
Calcium 89 50–100
Phosphorus 39 30–60
Magnesium 23 20–50
Sulphur 50 30–60
Iron 4.6 2–5
Manganese 0.24 0.2–1
Zinc 0.28 0.3–0.8
Boron 0.1 0.05–0.1
Sodium 59 < 100
Chloride 89 < 100
BEWARE OF THE BALANCE
The important thing to know about Angus’ vermicomposting method is that he uses a cross-section of normal plant material. Do what you can to source natural plant material that worms like. Vegetable waste from the local greengrocer, spoiled lucerne hay and animal manures from pasture-fed horses or poultry are all perfect for the process.
Unfortunately, other kinds of easily available organic material are not so well balanced. Many of the commercially available animal manures are from stall-fed chickens, cows and ducks. The diets of such animals and birds are very high in protein (nitrogen), calcium and phosphorus for rapid bone and egg growth. Some manures, such as those from feedlot cows, have extremely high zinc levels. This is because farmers feed these cattle a diet with excessive amounts of zinc, in the mistaken belief that it aids growth rates. The zinc level in the manure can actually make it dangerous to use on the garden for any length of time (see here in the Soils and Soil Fertility Chapter). None of the commercially available animal manures are very good sources of potassium, one of the most important elements for vegetable and fruit production.
Because additional water is not poured through the worm farm … the salinity of the restaurant’s worm juice is … concentrated.
Melbourne Council worm juice
The Melbourne Council worm farms produce a different kind of liquid extract. They have a lot of moist vegetable and fruit waste, which actually results in excess water slowly but continuously dripping out of the bottom without the need to add any extra water. This liquid exudate is collected and bottled for use as a fertiliser, just like Angus’ worm ‘wee’. We analysed the liquid from the Melbourne restaurant worm farm mentioned earlier in this chapter, and the results are shown in the Nutritional Value of Restaurant Worm Juice table on the opposite page.
These results tell a very interesting story. The liquid that slowly drips out of the worm beds in the restaurant worm farm as the various vegetable components decay is highly condensed. Because additional water is not poured through the worm farm, unlike in Angus’ system, the salinity of the restaurant’s worm juice is much more concentrated. In fact, it is far too concentrated to be put straight onto many plants. The electrical conductivity (EC), a measure of the salt content of liquid, is 12.6 for the restaurant’s worm juice, but only 1.9 for Angus’ worm ‘wee’. Liquid feeds for plants should be between 1.5 and 3 EC units, so a 1 to 5 dilution of the restaurant’s worm juice (in other words, 2 litres of this worm juice into a 10-litre bucket) would be about right and bring it very close to the concentration of Angus’ worm ‘wee’.
In the worm juice, potassium is the outstanding component and needs to be diluted. Sodium is also quite high, maybe due to the use of salt in the restaurant. Both sodium and potassium are, of course, very soluble, so they obviously become highly concentrated in worm farms that are not flushed out with extra water.
The worm juice is not very well balanced, so diluting it may make the potassium level acceptable but the other nutrients will then be too low. This is not a great concern, as both the liquid and the castings are applied to urban plots in the city, with the one offsetting the other. Using both together provides the perfect balance of nutrients.
This large-scale set-up for dealing with organic restaurant waste in Melbourne produces highly concentrated worm juice and solid compost.
NUTRITIONAL VALUE OF RESTAURANT WORM JUICE
ELEMENT RESTAURANT (MG/L) ANGUS’ WORM ‘WEE’ (MG/L)
Nitrogen 395 200
Potassium 3900 410
Calcium 125 89
Phosphorus 68 39
Magnesium 148 23
Sulphur 223 50
Iron 10 4.6
Manganese 0.9 0.24
Zinc 0.48 0.28
Copper 0.55 0.30
Boron 0.44 0.1
Sodium 788 59
Organic carbon 2700 —
BOKASHI COMPOSTING
Developed in Japan, this radically different form of composting may be of interest to the urban farmer because it can be done in very confined spaces and it generates significant quantities of liquid fertiliser that is rich in nutrients and beneficial microbes. It is perfectly feasible to set up this system in a home unit or high-rise flat, because it uses a bucket with a snap-on airtight lid that excludes vermin, vinegar flies and other insects, unlike most other composting systems.
However, there is a distinct downside to this system – compared to the other composting methods that we have looked at, it is relatively complicated. It requires a regular input every few days of the particular microbes required to make the system work efficiently. Nevertheless, in our opinion, the benefit of producing a rich liquid organic fertiliser in confined spaces makes this system well worth investigating.
The Bokashi system is rather unique among urban composting structures in that it is based on fermentation of the ingredients, usually kitchen scraps. A particular group of beneficial microorganisms that thrive with little or no oxygen is used. Normally, anaerobic microbes produce a negative result; however, these ones have been carefully selected to produce a positive result. The microbes can be either cultured at home or purchased from a commercial enterprise, and they are added to the mix every time a deposit of organic material is made into the system.
Unlike other composting methods, the Bokashi system does not produce mature compost. The microbes break down the internal contents of the composted material until there is just a shell left behind, in the process creating a liquid brimming with a large proportion of the nutrients from the raw ingredients, as well as a range of organisms that are beneficial to soil biology. Any material remaining in the system can be buried in soil, placed in a compost heap or added to a regular worm farm to complete the breakdown process.
The Bokashi system, in our experience, works best for high-nutrient organic material, such as kitchen scraps. However, there is no reason it could not be used for other organic material, such as wastepaper or animal manure. It is certainly worth considering using this system if you are in a confined space that does not have room for alternative composting systems.
UTILISING ‘WASTE’ ORGANIC MATERIAL
We mentioned earlier that compost is used in several ways on the urban farm, for example as mulch, soil conditioner or fertiliser. So let us explore these ideas further.
Compost as mulch If you have a lot of woody materials (such as sticks, twigs, bark or woodchips), it will take a lot of extra nutrients to break down these materials into fully mature compost that will not draw extra nutrients from the soil when it is mixed in. However, compost that is partially broken down and still full of coarse, woody materials can still be readily used as mulch. In this case, it is spread over the top of the soil to act as an insulating blanket that keeps moisture in the soil, eliminates temperature extremes and suppresses weed growth. It is better for mulch to be coarse and open, as this allows it to admit rainfall or irrigation water but also provide excellent insulation.
TO PEE OR NOT TO PEE
An obvious source of nitrogen and other nutrients is animal urine. Most of us have a diet that is particularly rich in all sorts of goodies that
plants and other organisms can use to fuel growth. The tragedy of modern society is that we have not focused more on ways to capture and use this nutrient stream in a sustainable way.
One time-honoured method of utilising the nutrients in urine is to add the liquid to composts, where the breakdown process destroys or denatures any health issues that may arise. We realise that it may not always be feasible to urinate on your compost heap in heavily populated urban environments; however, we can both attest to the great benefits of adding urine to compost if you can somehow make it happen!
The Bokashi system is … based on fermentation of the ingredients, usually kitchen scraps.
Compost as soil conditioner If you have compost that is ‘mature’ (in other words, it has fully broken down), then it is ready to be dug into the soil. Some composts in this category may have lower nutrient value, as the nutrients have all been used up during the composting process, while others may have quite a lot of nutrients. It all depends on the feedstock, with high-carbon materials having a lower nutrient value. If there is very little in the way of extra nutrients in the compost, then it should be considered as a soil conditioner and used to boost the soil’s physical fertility. It can help with the water- and nutrient-holding capacity of the soil, as well as improve soil structure (which in turn improves drainage and aeration within the soil).
Compost as fertiliser If the raw materials for your compost are high in nutrients (such as animal manures or kitchen scraps), then the ‘mature’ compost will not only act as a soil conditioner, but it will also be a source of plant nutrients. The nutritional value of compost diminishes over time, as nutrients can be lost via escaping gases (such as ammonia), by leaching (as water passes through the pile) or if the pile is exposed to rainfall for long periods. Understanding these processes can help you to minimise the losses – for instance, you can collect the nutrients that are being leached out and use them as a liquid fertiliser.
Grow Your Own Page 21