Restoring Degraded Land: Growing Crops on Bedrock

Elephant grass for soil building
Elephant grass for soil building

This blog post is part of an ongoing series on how to restore degraded land. Good land is hard to come by and often not affordable unless you’re rich. The facts presented here are from the video Building Soil with Clive. His farm in Hawaii was scraped bare with a bulldozer down to bedrock not once, not twice, but three times before he started leasing it. The thought of farming land like this seems hopeless, right? But over the last 18 years Clive has built up 3”- 4” of topsoil on bedrock using the techniques he describes in his video, which are summarized here. He feels his main job is creating good habitat and taking care of the organisms in the soil using primarily mulch and cover crops. It’s interesting to note that he never seems to find time to make IMOs (indigenous microorganisms). Instead, his focus is on creating massive quantities of organic matter to build soil. The results speak for themselves.

Virtually 100% of all food in Hawaii is imported if you take into account what is grown locally is almost always grown with imported fertilizer. That’s shocking. Much of the land in Hawaii is bulldozed down to rock and crops are grown with chemical fertilizers. How crazy can you get? Clive has 18 acres under cultivation. He grows 9 acres in elephant grass and 9 acres of crops with elephant grass mulch. The crops are rotated every year. Since 1997, 3”- 4” of topsoil has accumulated from this process. He uses no imports other than a little fish waste for organic matter.

Elephant grass grows 16’ in one year. Clive drives a brush hog through it with his tractor which pulls a forage harvester with a grinder that blows it into a 13 yd. dump trailer. Soil is built when the elephant grass roots die. This is called ‘root recycling’. So when you cut the grass, graze it down or roll it with machinery the roots die and turn into soil. A small rhizome type thing remains to grow new grass. The same thing happens on tall grass prairies. Clive dumps the grass cuttings into a pile where it gets hot to kill off the nodes so they can’t grow. He grows crops like ginger, turmeric, pineapple and large taro 5x/year with mulch and sprinkling of fish waste. (Crops are rotated to avoid diseases.)

Clive’s goal is to demonstrate how marginal soil can be rebuilt. The process is very efficient. He only spends one day per year cutting the grass. In 10 years you can have 3” of soil. Much of the soil comes from dead insect bodies and insect poop. The shells of insects provide calcium. He uses the mulch for temperature control, moisture retention, protecting soil organisms by keeping the sun off, adding carbon to the soil, lessening force of rain, and weed suppression. The depth of mulch is critical. Only 2”-3” of mulch would hold moisture but to suppress weeds you have to add about 8” of mulch. He calls this system grass culture.

Clive also teaches tree culture where trees are grown for building soil. The trees create organic matter, mulch and fodder. This method lends itself to goats. He recommends melokia, secropia, albezia, glucidia (spelling?) – whatever is easy to cut with a machete and grows well in your area. He’s experimented for years with using 20’ poles from these trees to build up 3’ thick mulch layer of sticks. Rain and air can penetrate much like a forest floor. Wild vines grow up through the wood mulch and create a canopy to foster the soil food web by keeping it dark and cool. One key advantage of his tree culture method is it introduces a lot of lignin. Most fungi will not break down lignin but the ones that do are ideal for agriculture. (Hmm… this could be one reason wood chip gardening is so effective.) Again, the best fungi needs lignin. Without lignin as a food source the most beneficial fungus won’t be there.

He advises clients to devote at least 50% of the land to growing organic matter (60-70% is better) or otherwise they would have to import materials. Plant trees and cover the soil with the stick mulch. The soil food web will go crazy and the trees will produce 2,000-4,000 lbs. of citrus/year. That’s without adding any fertilizer. The stick mulch has to be replaced once a year in the tropics. The main key to success is sustaining habitat for microorganisms by adding lots of organic matter regularly.

Image credit: University of Florida

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