Wednesday, July 31, 2013

Myth : Tropical Soil is Fertile

When I moved here I had plenty of people tell me that everything would grow great here. Lush. Tropical soils were fertile. I was actually believing this until I tried growing flowers and veggies. Yes, I had been sucked in by the myth of fertile tropical soils. I thought gardening would be easy and take care of itself! 

Grasses grow great on my farm. Ohia, eucalyptus, and guava trees thrive. Things are always green. But when I started growing flowers and veggies I learned something very significant. Those grasses and trees don't need very fertile or moist soil.
My mother's grass. It was mowed too short when it was first started.
Now it never grows thick nor tall. I could improve this but she is not
interested in having to mow the grass more than once a month. 

The fertility of soil on my farm crashes as soon as the sun can reach the soil surface. So wherever I mow the grass short, the soil dries out, the sun kills the micro-organisms, the grass growth is stunted. Whenever I tilled or flipped over the soil, things didn't want to grow well in that spot. Thus the soil itself appears to have rather poor fertility, with it's fertility highly dependent upon the ecology of surface micro-organisms and surface moisture. A thick grass mat keeps the soil surface shaded and moist. Remove that, and the soil's toast.

In my first few years of gardening, I really crashed the soil ecology. In order to get harvestable vegetables, I needed to rely on commercial fertilizer. I knew that I needed to change my gardening methods, but I was so busy clearing land, building the house, and caring for my parents that I resorted to commercial methods for the quick fix. That meant lots of irrigation, fertilizer, herbacides, pesticides, fungicides.

Now after many seasons of adding compost, manures, trace minerals, inoculated biochar, and constant mulches, my soil is producing great veggies. So many people look at the garden and think, "Tropical soil is so fertile!" The same exact thing happens when people look at the community garden here. I always hear, "Well of course, you're starting out with good tropical soil." FALSE! These gardens are thriving because of the work that has gone into improving soil fertility. It didn't happen by chance.

I'm still experimenting and learning about how to handle the soil on my farms and at the community garden to make them fertile. Some tricks that I find work:
...keep the soil surface covered with mulch.
...if I don't have enough mulch, then let the weeds grow and shade the soil surface. This is a better alternative than letting the sun bake the soil surface.
...add compost with each new crop being planted. Plus till in the old mulch.
...use inoculated biochar in the compost, rather than plain dry biochar. I use urine, manure tea, or compost tea to inoculate the biochar.
...use manures in the compost.
...never let the soil bake dry.
...use a little ocean water in the compost for trace minerals. Or use fermented fish waste when I have it.

As I said, I'm still experimenting. I've been using ocean coral, burnt animal bones, and wood ashes. I'm switching to low-till in the improved areas so that the soil surface is only disturbed in a narrow bed where the seeds will be sowed. I'd like to install drip irrigation, but that will have to wait for now.

Ah, so much to learn, so many experiments to try!


  1. Are you able to get soil tests done for a decent price by the Ag Extension folks? I have started making a plot map of my garden/pasture/orchard areas, with the idea of doing bi-annual tests to guide me on what amendments are needed to keep the pH and such in good balance. Sorta like charting progress through the unknown.

  2. U of H will do basic soil testing : pH, P and K, at a reasonable cost. For more analysis, one needs to send soil to a mainland lab. My problem is that U of H is 2 hours away. And since I test my soil frequently, I looked for a better option. I purchased a professional soil test kit so that I can test P, K, and pH at home. I don't bother testing for N because it's availability and quantity is dependent upon microbial action in the soil plus the types of additives in the compost and mulch. Significant variable factors affecting N include the amount and stage of decomposition of compost, manure, biochar. Since these items are constantly being replenished and I take care to maintain very active surface microbial conditions, while at the same time not digging in excess amounts of organic material, I do not think I have to worry about low nitrogen levels.

    Once a year, sometimes more in areas that are being developed, I send a sample to the mainland for an in depth analysis, with supplemental recommendations. I find this helps with such elements as magnesium, boron, iron, copper, etc. It also helps me control the amount of sulfur and aluminum.

    Soil science is real complex. And what I see, in my opinion, is that it is a science in its infancy. The experts still have a whole lot to learn! So it's fun to experiment here in my garden, using the information from the soil guys then tweeking it with permaculture ideas. Much of the time I'm fairly successful. Where I'm a bit slow getting great results is where I start out with very depleted, worn out, or grossly unbalanced soil. Seems to take a couple of years to get things going well.

  3. Oh by the way, soil testing is one area where I am willing to spend some money. I'm pretty frugal about other things, but I need to know what my soil is doing as it is being developed. Some areas I've cut back on the soil testing other than pH, but all areas in development get tested.