Citrus row middle management to improve soil and root health

Citrus row middle management to improve soil and root health

Report Date: 05/14/2021
Project: 18-059C   Year: 2021
Category: Plant Improvement
Author: Sarah Strauss
Sponsor: Citrus Research and Development Foundation

1. Please state project objectives and what work was done this quarter to address them:
Objective 1: Determine how different cover crop mixtures impact soil and root health and weed cover in established commercial citrus groves.
Cover crops were last planted at the end of Nov 2020 and included sunnhemp, Austrian winter pea, daikon radish, oats, and winter rye. While the harvest in March did terminate some of the cover crops, there is still growth in the row middles. Further analysis of the soil nutrient and microbial samples collected in August 2020 found that the types of microbes performing denitrification (part of the nitrogen cycle) are completely different under the legume+non-legume cover crops compared to the other treatments. Soil organic matter has also significantly increased under cover crop treatments. Analysis of the weed data indicates cover crop planting impacts will have a significantly longer-term effect on weed suppression, which could be potentially attributed to the substantial reduction in the addition of weed seeds to the soil seed bank in the cover-cropped areas. The germination and establishment of cover crops in the second location appear to be improving over time, as noted from the comparisons of cover crop density in planted row-middles between 2019 and 2020.

Objective 2: Examine the impact of eco-mowing in conjunction with cover crops on soil and root health and weed cover in established commercial citrus groves.
Eco-mowing occurred at the end of November 2020 with the planting of the next round of cover crops. Data from Year 2 (collected in Aug 2020) is still being analyzed. Visual root growth assessments show continued root growth under cover cropping and eco-mowing, but analysis is ongoing. Soil moisture appears to be similar across all treatments, possibly due to the presence of a high water table at both sites. Quantitative data on root growth (volume, length and area), root dieback, and recent soil moisture dynamics by treatments will be presented in the next quarter and is being finalized now. Preliminary evaluation shows that conducting eco-mowing in the row-middles has unremarkable effects on weed emergence and coverage in the tree-rows.

Objective 3: Quantify the effect of cover crops and eco-mowing on tree growth and production.
Yield data for the second year of cover crops was collected in March 2021. Preliminary analysis of yield data indicates little change in with treatments in one location, and a slight increase with cover crops at the second site. Analysis of fruit quality, canopy volume, and trunk size is ongoing. Canopy and trunk size measurements, and leaf nutrient status will continue, and quantitative differences will be reported in the next quarter. However, the marginal changes are not unexpected, as trees of this age could take at least three years to show responses to treatments. We will continue to assess canopy volume and trunk size.

Objective 4: Identify the economic benefits of using cover crops
The cover crop survey is being administered via Qualtrics. Low response rates in Florida necessitated including other citrus producing states (Texas and California). To date, we identified about 60 usable surveys with respondents from each state. We attended the Citrus Show in May 2021 to encourage more Florida citrus growers to take the survey. Preliminary responses suggest that cover crops are more widely used by CA citrus growers than FL growers.

Objective 5: Communicate results to growers using field days and extension materials
Preliminary results are being presented at the Soil Science Society of America/American Society of Agronomy meeting in November. Observations on the impacts of cover cropping on weed control were presented at Weed Science Society meetings during Feb/March 2021. Information on cover crops was provided as a Tip of the Weed for the Citrus Industry magazine in May 2021. Cover crop information and preliminary data were also presented at two regional grower extension talks in March and April 2021. Discussions are underway about how to host a field day, or a virtual field day, in the summer or fall of 2021.

2. Please state what work is anticipated for next quarter:
Analysis of soil inorganic N fractions (ammonium and nitrate) for samples collected in August 2020 continues and updates on other soil/leaf nutrient variables will be provided in the next quarter. Half-yearly weed data analysis will be scheduled in the upcoming quarter. Canopy and trunk size measurements and leaf nutrient status along with root image collections and soil moisture monitoring will continue. Some soil moisture data loggers were disconnected due to wild animals and/or field equipment and data will be recovered this month and reported in the next quarter. The next set of cover crops are scheduled to be planted in June 2021. The annual soil sample collection will occur in August 2021. The composition of the mixes is still being discussed. The economics team will begin survey data analysis. They will also construct the framework for partial budgeting and assessing the cost of cover crop use and continue to collect data. Partial budgeting analysis will continue, and a report will be drafted.

3. Please state budget status (underspend or overspend, and why):
We are mostly on track with our planned budget spending, however delays in hiring and limited travel resulted in the economics team underspending.

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