Citrus row middle management to improve soil and root health

Citrus row middle management to improve soil and root health

Report Date: 05/15/2020
Project: 18-059C   Year: 2020
Category: Plant Improvement
Author: Sarah Strauss
Sponsor: Citrus Research and Development Foundation

The fall cover crop mix planted in early November at both locations had some of the best growth we have seen so far, and crops from the planting in November continue to grow. This mix included daikon radish, coker, Wrens grain rye, and dove millet. Sunnhemp, alyce clover, sesbania, dixie crimson clover, and yellow sweet blossom clover were included in the mixes for the nitrogen-fixation treatments (1/2 of the rows). Germination counts and biomass samples have been collected and are currently being analyzed.

Yield and juice quality data were collected for the North grove location in mid-March. Unfortunately, due to COVID-19, we were not able to collect yield and juice quality data for the South grove location. However, preliminary analysis of the North grove yield data found trends of increased yield under the Cover Crop Mix#1 with eco-mowing.

After 1-year treatment in the North grove, the content of soil organic matter significantly increased in the row middles treated with cover crops (with values in the range of 3.6-4.2%) compared to the grower-standard control (3.3%). Under the tree canopy, we observed a greater, but not significant, increase in soil organic matter in treatments under eco-mowing (with values in the range of 4.1-4.8%) compared to those without in both cover crop mixes (values in the range of 3.8-4.3%) and the grower-standard control (4.1%). Canopy size measurements in all treatments continue every six months though significant differences and trends have not been detected. However, changes in these parameters could take up to 2 to 3 years in mature citrus trees following changes in practices. Preliminary measurements and analysis of changes in soil organic matter for the South grove are in progress. Measurements are in progress to determine the abundance of nitrogen-fixing genes (important with legumes since they are related to changes in the content of ammonium in soils) and denitrification genes (often linked to changes in soil organic carbon, organic matter, and nitrogen losses from the soils). Multivariate statistical analyses are also in progress to evaluate the influence of abiotic (soil properties) on biotic (microbial gene abundance) variables in treatments with and without cover crops.

Dataloggers and soil moisture probes continue to record soil moisture every hour. Root growth measurements using the mini-rhizotron tubes installed in both groves were performed in March and July 2019 and Feb 2020. Data on these measurements are currently being analyzed and will continue in Fall 2020. Additional nutrient measurements are still in progress.

The next measurements of weed density, soil and tree nutrients, and microbial communities will occur in August 2020.

The next set of cover crops will be planted in both groves are being planted on May 15 and May 19, 2020. The mixes will include sunn hemp, cow pea, several millet species, and buckwheat.

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