I probably should have started with this way back in July, when I started this blog, as it is the fundamentally most important thing you have to learn about gardening. But as it is the first day of the New Year we should probably start with some line-dancing scarecrows just to keep us in the festive mood?
Fact: Tropical soils are not necessarily fertile. We see the rainforests and the incredible mass of vegetation that they they support and think wow! -just think what I could grow on that. The trouble is, the fertility is all in the canopy. Once you remove the natural vegetation and inherent recycling of nutrients, the soils quickly become depleted and acidic because of their high rainfall and leaching – the good stuff is simple washed away.
Fact: The alkaline elements in the soil are more soluble in water than the acid ones (think about how stalagmites are formed (alkaline calcium carbonate in solution slowly being deposited on the floor of a cave)) that is why tropical soils quickly acidify.
The Amazon story – it’s a sorry one. Hectare after hectare was cleared to run beef cattle (mostly for the American hamburger market) thinking they had found Bonanza! Very quickly they discovered that that the soils, that had previously supported a verdant and incredibly diverse rainforest, couldn’t even grow grass without a massive chemical input.
Fact: Most volcanic tropical soils look wonderful, but they are so old, especially in Australia, that if the vegetation is cleared above them they quickly become very acid and infertile. The exception is Indonesia where the volcanic activity is recent – in fact currently very active. Try flying over Java and seeing 45 active volcanoes puffing away above the cloud-line – a sight to behold and you see what I mean. The trouble is Indonesians today are trying to grow food crops on what were once rice fields/or cleared rainforest and you have the same inherent problems – within a couple os seasons acidity from water leaching. We are all in the same boat. So how do we fix it?
Understanding pH will help you be a better gardener. So buy a kit and test your soil. Getting the soil chemistry right is fundamental to growing a healthy garden and remember that food is only as good as the soil it is grown in.
Slightly acidic or neutral soils, with a pH of 6.5-7, is the aim as this is when most minerals in the soil become chemically available to plants.. If the chemistry isn’t right, merely adding extra fertilizer won’t improve plant health, it just wastes money.
Think of the nutrients in your soil as being like the treasures locked away in a bank vault and the right pH being the combination that unlocks them. They are mostly there all the time but unavailable except to the person with the knowledge and the right numbers (and a handy little pH testing kit!)
|Testing soil pH. A first for Balinese farmers|
This is where the organic gardener has the upper hand over ‘conventional’ gardeners. Invariably, the continual use of organic mulches and fertilizers will, over time, rectify pH problems without having to do just about anything else. But, what do you do if you want to fix the soil quickly without harming it?
Soils too acid- below 5. Add lime or dolomite at a rate of one handful per square metre and rake it in. Add mushroom compost – it contains composted chalk (alkaline) and will help to neutralize the soil while adding vital organic matter.
Soils too alkaline – above 9. Add blood and bone/chicken manure and lots of compost. For a quick fix add iron chelates.
FACT: The continual addition of organic matter to soil in the tropics will do more, in the long term, to keeping your plants healthy than just about anything else. DON’T WASTE IT – RECYCLE IT: composted kitchen scraps, grass clipping, animal manures, aquatic weeds, shredded garden waste, green weeds/straw/tree chippings/mushroom compost/seaweed etc. WHY?
1. They add vital nutrients to the soil that are needed by plants in a regular supply – nitrogen, phosphorus, potassium and calcium.
2. Enrich the roil with beneficial micro-organisms.
3. Increases the ‘sponginess’ of the soil i.e. air spaces
4. Hold all those valuable nutrients in the soil and stop them from washing away in heavy rains.
The old bracelet test. How to tell what type of soil you have and whether it has sufficient organic matter.
Get a handful of soil and moisten it.
- Try to form it into a ball. If it won’t do that it is SAND.
- Try forming it into a long strip. If you can make a short one but then it begins to crack as you bend it – this is a LOAM (usually has plenty of organic matter and will be fertile)
- If you can make it into a long strip and bend it around your wrist – this is CLAY. Good for making pots, but not much else.
Fifteen years ago I bought a property in the sub-tropics of northern NSW and swooned at the sight of the 2m deep red earth that looked like chocolate. I then begun to wonder why nothing really thrived. A pH showed the soil to be 4! – way too acid. The vegetation had been removed many years before with no soil improvement and it needs continual love and care for it to be productive – even today.
‘The answer lies in the soil’
NOTE: see previous posts “In Praise of the Humble Earthworm”, “Composting“, “Hot Composting” and “No-Dig Garden Beds”