Posts Tagged ‘composts’

Solid fertilisers should be easier to measure out but often aren’t. Some manufacturers put a handy measuring container in the packet but most don’t. Statements such as a handful to the square metre aren’t that useful when you consider the variation in the size of hands! Filling an everyday container, such as a cup, with your fertiliser and weighing it can be a useful guide.

• A teaspoon holds about 4g of fertiliser;
• A tablespoon holds about 16g;
• A match box holds about 25g;
• A cup holds about 250g.

It can be useful to have a rough guide to what your crop needs (see my post on “Crop removal or how do you know how much fertiliser to apply?”. Commercial lettuce crops generally get 2-300 kg/ha nitrogen. Things like cabbages which are much slower but also much bulkier get 5-700 kg/ha. Tomatoes are also in that ballpark. Then you have native plants which only use a fraction of that – say 80 kg/ha nitrogen for an adult Geraldton wax bush which is being picked heavily for its flowers and foliage.

Evaluating the nutrient value of a solid fertiliser is done in the same way as for liquid fertilisers. For example, something like CSPB’s garden fertiliser is 13.5% nitrogen (N), 1.9% phosphorus (P) and 8.0% potassium (K) with a range of other nutrients including trace elements. That means in every kilogram of the product there is 135g (13.5/100) x 1000 (g) = 135g of N. Using the same system we come up with 19g P and 8g K.

It does pay to check the bag to compare fertiliser products. If you are paying twice as much for a product with 5% N then its not as good value for money.

Products from many other countries are sold here. You may find American products that have analyses like 10-10-10 – that is because they express formulae as the oxide form . The N is OK, it’s the same but the P need to be multiplied by 0.44 and the K by 0.83 to be equivalent to the base element.

Always be wary of any product that has a really high figure in the middle (ie for P) check the label and the origin and its probably American.

These days fertilisers aren’t registered. That means almost anything can be packaged up and sold as fertiliser. Ideally it shouldn’t because there is an industry code of practice (which isn’t law yet) but I do see a constant flow of new products coming onto the market (coming and going). And the buzz these days is microbes and humates (humic acid). So companies will try and sell you something with almost no nutritional value but lots of other buzz words for a hugely inflated price!

Just bear in mind that for microbes to prevail in soil they need a food source which is carbon (organic matter). Put them in your sand and they won’t last 5 minutes! And if you put them into and environment that is already highly organic and has its own microbe population they may well get out-competed by those already in residence!

So is a high nutritional analysis everything? Not necessarily. If the fertiliser is a quick release one the higher the analysis the more likely you are to come to grief if you overdo it. Quick release fertilisers are designed to be applied every couple of weeks or monthly.

You can of course use slow release fertiliser like Osmocote™, Nutracote™, Macracote™ and so on. They are expensive, you pay for convenience but you only need to apply them every few months. And you may waste a lot less – the danger with quick release fertilisers is that you irrigate them away in the next few days. We monitor growers who fertigate (fertilise through the irrigation) and we see soil nitrate levels (nitrogen is highly mobile) plummet between fertiliser applications – going from 80 mg to 20 within, say 3-4 days.

Some cheap fertilisers may also contain things like muriate of potash – potassium chloride. Chloride is salty and you probably don’t want it. Better to go for potassium nitrate or even potassium sulphate for your potassium. Potassium sulphate will make your soil more acidic but the sulphur can be useful.

Fertilisers imported from overseas can also contain nasties like heavy metals (cadmium, lead, nickel). These are particular risks from China or India. There is random sampling of fertilisers on entry for these sorts of things so it shouldn’t be an issue but things can slip through occasionally. You also need to be aware that manures and composts can also contain toxic levels of heavy metals, microbes like E coli or even amoeba and they are largely unregulated unless you buy bagged product made to the Australian Standard. There are plenty of places where you can back up a trailer and buy – who knows what! Not exactly what you want if you are trying to produce healthy food on your block.

When to apply fertilisers?

Most people assume you should fertilise when you see activity but we only see what’s happening above ground. It’s the roots that take up fertiliser and its root activity you need. Its widely said that you shouldn’t fertilise in winter. But many natives have their active root growth in winter and are largely dormant in summer. Other deciduous species also take up nutrients during that time and store them in the plant frame for later redistribution and use in the plant. But when its really cold, nutrients ARE taken up more slowly and of course rain leaches fertiliser away from the root zone and it is wasted. So for this reason fertilising in autumn can be a good thing. Just remember that however you fertilise, plants need it to be dissolved in water to take up. No point in spreading fertiliser around the canopy of a plant that is watered from one dripper in one spot! If its watered using overhead retic or mini-sprinklers and the soil is uniformly wet all around – then fine.

Foliar fertilisers

Foliar feeding is largely a very expensive way of doing things. More often than not what you apply to the leaves gets washed off into the soil and feeds through the roots anyway. Only in very special cases is it worthwhile and that is mostly for commercial growers who can’t afford crop failures. Calcium is often fed in this way because its immobile in the plant and bouts of high humidity can prevent its uptake by halting the transpiration stream that carries it around. Immobile trace elements such as iron can also be foliar fed.

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If you’re in the business of trying to grow anything, the weather we’re having isn’t making it easy! And even if you’re not a commercial grower, the twists and turns of the weather lately makes it really hard to get the best from your plants.

I downloaded the weather data from Medina Research station for last December to today. The daily evaporation for that period ranged from 1.5 mm for the day up to 11.4 mm! That’s a ten fold difference. And I bet the settings on your irrigation controller haven’t changed in that whole time! When you sum up the evaporation over a week it doesn’t look quite as variable – 44.1 mm, 44.2, 57.9, 63.4, 54.2, 66.2 and 58.4 – which is only about a 50 % variation. Actually last week would have been less because I haven’t subtracted off the rain we had, which at home was 42 mm but for Medina was about 30mm. So you really need to take that off the weekly evaporation. Incidentally, from a commercial point of view we don’t regaard anything under 4 mm as being effective ie its not regarded as beng enoguh to do any good.

Anyway, what I’m trying to say is that unless you vary your irrigation you are either going to run into trouble with plants drying out, or you are overwatering like mad to cater for the worst case scenario, wasting water and probably washing away most of the fertiliser you put on into the bargain.

Commercial growers vary their water on a daily basis if they are doing their job properly. And at this time of year, depending on their crop they may be watering anything up to four times a day in amounts that will add up to the total daily evaporation – plus or minus depending on crop and stage of growth. Now, no home gardener can be bothered with that, plus if you have to abide by the two or three time a week watering edict, you simply can’t water every day unless you hand water. And in sand that’s a problem because it does not hold water and actively growing plants will dry the root zone out in well under a day and get stressed or even die – particularly if they are small seedlings.

What can you do to help this? Amend your soil with clay and organic matter. Be wary of the source – you get what you pay for! Don’t run the risk of getting dieback with your clay and remember that compost has quite a lot of phosphorus in it relative to nitrogen. Much of this is explained in previous posts.

The other thing you can do is mulch. But remember to use coarse chunky and COMPOSTED material (again to prevent importing disease and weed seeds) so any applied water runs straight through or you will end up with wet mulch and dry plants. Keep mulch away from the collar of the plants. Mulch does a good job of moderating soil temperatures and the trials we have been running at Murdoch TAFE show that if you start with a nice wet soil profile, mulch can do quite a good job of helping to maintain the soil moisture. Don’t layer the mulch on too thick though, keep it in proportion to the size of the plants it is around. And don’t add the same amount to it each year, just maintain the thickness you need.

Still though, if you are having trouble with plants not thriving in the garden, the best thing you can do is get out with a spade and dig. You may be surprised. I have been. Beds I thought should have been well wet have shown dry patches and even been dry about 25 cm down – well within the root zone of any plants.

Always beware of newly planted plants. Inferior potting mixes (you get what you pay for) and simply the type of mix, may mean the root ball of your plant dries out before the soil around it.

In my experience many plant problems come down to the basics and on our sands its odds on its watering or lack of nitrogen and those two are inextricably tied together. Too much watering means you wash all your nitrogen away. Assuming you had enough in the first place – nitrogen is the one nutrient always in short supply on our sands, and manures and composts never have enough of it while at the same time they are overloaded with phosphorus.

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