Assessing Tools for Citrus Soil Health

Soil microbiologist Sarah Strauss on Jan. 28 discussed the benefits, challenges and unknowns of cover crops, compost and humic acid for citrus soil health. Strauss is a University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) associate professor at the Southwest Florida Research and Education Center.

She pointed out that Florida’s citrus soils are problematic because they are 98% sand, low in organic matter and nutrient deficient.

COVER CROPS

Cover crops provide nitrogen; reduce weeds, soil erosion and soil compaction; and increase soil moisture and soil organic matter, Strauss stated.

She named several citrus cover crops, singling out the legume sunn hemp as one that has offered good benefits for citrus.

Soil organic matter increased after one year of cover crops, she reported. Other take-home messages about cover crops included:

• Cover crops can change soil microbiome composition and functions.
• The magnitude of change depends on the cover crop mix and timing.
• Cover crops can impact the citrus rhizosphere.
• Remaining questions about cover crops include their long-term impacts on trees, nutrient release/availability and carbon sequestration.

COMPOST

Strauss said compost benefits include being readily available and a nutrient source.

Difficulties with compost include high cost, availability, variability and being a potential source of weed seed.

The researcher’s take-home messages stated that compost impacts on the rhizosphere differ based on rootstock, and that compost can change the rhizosphere related to specific root nutrients.

Questions remaining about compost include:

• Long-term impacts on trees
• Nutrient release/availability
• Difference in compost types and application rates

HUMIC ACIDS

Strauss said humic acids, which have extremely high carbon content, are often recommended to growers to increase soil nutrients, build soil organic matter and promote crop growth. However, she reported that humic acids did not:

• Change soil physiochemical properties
• Significantly change the active soil microbial community
• Improve tree growth or yield

Remaining questions about humic acids include the wide range of application rates that are recommended.

SUMMARY POINTS

Strauss concluded with several overall summary points about citrus soil health, including:

• Microbes are critical components of soil health through their contributions to soil organic matter, nutrient recycling and plant defenses.
• Cover crops and compost can impact soil microbes and soil health in groves, but impacts might be rootstock and tree-age dependent.
• Humic acids appear to have little impact on soil physiochemical properties or microbes, and no impact on tree growth.
• Altering soil health in citrus trees is a long-term investment, and changes to the trees may take several years.

UF/IFAS multi-county citrus Extension agent Mongi Zekri hosted Strauss’ virtual presentation.

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