Agriculture Reference
In-Depth Information
Dry Versus Liquid Fertilizers
Many of our fertilizers are dry, such as crushed or ground-up rock. Examples are rock
dust, calcitic lime and rock phosphate. They're applied in the garden with a spreader or
even by hand, or best of all, mixed thoroughly into the compost pile first. They're generally
broken down slowly by microbes throughout the year or over multiple years.
Along with organic matter and microbes, these dry fertilizers are often the basis of a soil
management program. I use them mostly for long-term soil building, although some of
them are available to microbes and plants in the short term, too. A fine ground product is
better than a coarse grind because it is more quickly available. Some consultants don't
mind a coarser product, but the fact is it can take decades for the nutrients to become avail-
able from it.
Liquid fertilizers can be fast and efficient at improving overall plant health and correct-
ing specific nutrient deficiencies when sprayed directly onto plants, called foliar fertilizing
or foliar feeding. One study found them to be 8 to 20 times more efficient. They can help a
plant deal with stress, give it some energy, and move it from vegetative growth to fruiting.
Sometimes they're sprayed directly on the soil, too.
They're especially important during the transition to a healthy organic garden, when the
plants can't yet get everything they need from the poor soil. Paradoxically, they work best
in a mineral-balanced and biologically active soil and don't work as well as a rescue spray.
You absolutely need sufficient calcium in your soil for them to work well.
When I think of liquid fertilizers, I tend to think of broad-spectrum biostimulants such as
liquid fish, kelp and sea minerals, all of which will be covered in the biostimulants chapter.
But more recently, liquids that provide just one mineral are being used more and more to
correct specific soil nutrient deficiencies. Liquid calcium is the main one that comes to
mind. Not only does this save money, but drastically curtails the environmental conse-
quences of mining and shipping large amounts of dry rock products such as lime.
Liquid products aren't a magic bullet to fix all nutrition problems, but they do give the
soil and plant a kick to get to work. Sometimes they're used to “untie” minerals such as
calcium or phosphorus in the soil. You may have enough calcium on a base saturation test,
for example, but a liquid calcium will often help make it available. A well-made liquid fer-
tilizer directly feeds microbes and stimulates their activity to start working.
Liquids can be applied through an inexpensive hose-end sprayer. A backpack or pump
sprayer is even better because you can use rainwater at a warmer temperature than cold, po-
tentially chlorinated, well or city water. The idea is to create a mist that thoroughly coats
both sides of all leaves, although if you're using microbial products, you need the openings
on the sprayer to be big enough to allow all of the microbes through, so the mist shouldn't
be too fine. Fungal mycelium can be broken up if the filter is too fine.
