Soil Improvement with Organic Mulch

Tacy CalliesSoil Improvement

By Jim Hoffman

This article is about my experiences with incorporating organic mulched materials into select areas of groves at Estes Citrus in the Indian River region.

Our citrus groves consist of bedded, 40-acre blocks where it is common to have three or four distinct soil types in each block. Unfortunately, we have several sand-pond areas that have a history of low production and diminished tree growth.

Our local water control district recently started to mechanically remove the vegetation that was accumulating in the canals and reservoirs. Prior to that, a helicopter and herbicides were used for weed control. As workers were piling the organic material along the ditch banks so it could be hauled away, we quickly noticed that the surrounding grasses turned a dark green and grew at twice the rate of the nonadjacent grass.


Trees treated with organic mulch resulted in a denser canopy of leaves, better color and more fruit than untreated trees.


Untreated trees had a thinner canopy of leaves and shorter height than treated trees.

I approached our local water control district and asked if I could get a couple of loads of organic mulch material dropped off at the corner of one of our nearby groves. Since the district was incurring the expense of trucking it several miles away to a disposal area, delivering it to my local grove amounted to a significant savings for the district in both labor and transportation costs. The district became a valuable partner as I started to address our low-production areas.

We tried two different application methods. Our first attempt involved letting the organic mulch pile decompose to a fraction of its original size and then using a side-chute manure spreader to apply it onto the bed tops. This proved ineffective, as there was constant clogging of the chute, and despite several trips down the same bed tops, we were never able to get enough material out. It only took a tree branch or a clump of grass to stop the operation.

Instead, we opted to use a front-end loader to drop multiple loads of fresh mulch material down the bed tops. We were trying to lay down a 12- to 15-inch-thick layer of the organic material down the bed tops of our worst sand-pond areas. We then followed up by discing the material to chop it up and smooth it out. Lastly, we changed the pitch of our disc blades to gently roll some of the material up under the skirt of the trees, to get it into the maximum root-zone area. Ultimately, we ended up with about a 3-inch layer of finely chopped material that was lightly incorporated into the top layer of sand.

As a parallel comparison, we applied a timed-release fertilizer on an entire adjacent row of citrus trees in the same sand-pond area. While we saw improvement in this row of trees, the cost of the slow-release fertilizer was very high, and it never fully addressed the underlying issue of the poor sandy soil.

To validate what we were doing, samples of the decomposed mulch material were sent out to quantify the effectiveness of our effort. To our surprise, test results came back very high in almost all nutrient values, including potassium, magnesium, calcium, sulfur, boron, zinc and copper. Equally as important, we changed the cation exchange capacity of the soil, which has given us value over a long period of time.

The citrus trees have shown a remarkable turnaround. Since our mulch application, all of our irrigation, fertigation and dry fertilizer applications now have a better chance to hang out in the root zone, instead of just leaching right through the sandy soil profile. Another positive is that by utilizing this organic material that was removed from our local waterways, we have been able to recapture nutrient loads that could contribute to poor water quality in the region.

Probably the only drawback that we encountered was that when we used the organic mulched material, we introduced a lot of undesirable weed species into the sand-pond area. It took almost an entire growing season before we were able to restore our original Bahia and Bermuda grass.

In summary, we were very pleased with our results. The cost came out to approximately $200 per bed top, which would make it prohibitive on a large scale of acres. Most of that cost was the expense of physically moving the large volume of material with repeated trips down the bed tops.

We were fortunate to have access to a good supply of free material. If you have an opportunity to partner with your local water control district, contractor working in your area, or even if you are doing routine canal cleaning within your properties, there is an opportunity to enrich your soils. For our small sand-pond areas, this proved to be a good solution that has given us long-term benefits versus having to constantly reapply slow-release fertilizers like we did on the adjacent trial area.

Jim Hoffman is the production manager for Estes Citrus Inc. in Vero Beach, Florida.

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