Citrus row middle management to improve soil and root health

Citrus row middle management to improve soil and root health

Report Date: 11/15/2021
Project: 18-059C   Year: 2021
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 planted in November 2021 and included sunnhemp, daikon radish, rye, and oats. Preliminary data from an additional assessment of the influence of cover crops on the soil microbial communities at deeper soil depths (down to 30 cm) indicates that the changes to the soil microbial community due to cover crops extend down to at least a depth of 20 cm. Both cover crop mixtures are increasing carbon availability and mineralization. Based on data from August 2021, soil organic matter remains greater under cover crops compared to the grower standard controls. The negative correlation between the growth and coverage of cover crops and weeds observed in the previous measurements has continued, with the density of monocot weeds (e.g., grasses and sedges) being significantly low in cover cropped row middles compared to the non-cover cropped control. 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 primarily occurs prior to planting the winter season cover crops, as the movement of harvest equipment in the spring has eliminated the need for mowing to terminate cover crops prior to planting. The next eco-mowing occured in October/November 2021. We have not seen any significant impact of eco-mowing on the soil microbial communities. Data from Year 2 (collected in Aug 2020) has been analyzed, but analysis of Aug 2021 data continues. Visual and quantitative root growth assessments show continued root growth under cover cropping and eco-mowing, but we observed no differences between treatments and no consistent trends over time. Soil moisture appears to be similar across all treatments, possibly due to the presence of a high water table at both sites. 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, and the final yield collection will occur in March 2022. Initial analysis of yield data indicates little change 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 also showed no significant differences between treatments. Canopy and trunk size measurements and leaf nutrient status will continue this fall. However, the marginal changes are not unexpected, as trees of this age could take several 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
Partial budget analysis is ongoing and estimates where used as a benchmark for cover crop costs in the survey. The economics team is currently analyzing data collected via the survey instrument. The survey solicited information on grower’s use of cover crops, willingness to pay to for cover crops, and ranked how they valued different soil and pest attributes. The instrument was administered online only by Qualtrics as well as emailed by extension agents to their mailing lists, to the Indian River Citrus League members, and to growers who attended the 2021 Citrus show (whose email address were collected by the student on the team). These responses do not constitute a representative sample, so data collection efforts continue. Preliminary results indicate that FL/GA growers are willing to pay $484 to implement cover crops, on average. Willingness to pay estimates are similar to the benchmark calculated using partial budgets. Survey results also indicate the FL/GA growers rank nutrition, soil erosion, soil moisture, soil organic matter, pests, and weeds in order of highest to lowest concern, respectively

Objective 5: Communicate results to growers using field days and extension materials
Preliminary results were presented at the Citrus Expo in August 2021 and at the Soil Science Society of America/American Society of Agronomy meeting in November. Preliminary results will also be presented at the UF/IFAS Citrus Health Forum in February at the North Florida REC. Discussions are underway about how to host a field day, or a virtual field day, in the fall of 2021.

2. Please state what work is anticipated for next quarter:
Soil and leaf samples were collected in August 2021 and analysis of the soil inorganic N fractions (ammonium and nitrate) and microbial communities is underway. Microbial DNA was extracted from soil samples, and this has been sent for amplicon sequencing analysis. In addition, analyses of the nitrogen-cycling gene abundances are currently in progress. Canopy and trunk size measurements along with root image are currently being collected in November 2021. Analysis and interpretation of the weed data will be conducted in the next quarter. Also, data collection on weed density and biomass will be planned. The final harvest data will be collected in March 2022. The economics team will continue data collection and analysis. As noted above, the data shows severe selection bias which likely affects the results. Auxiliary data will be collected to improve the richness of the survey data. The postdoc will explore ways to reduce selection bias and complete partial budgeting analysis. A journal article will be drafted once data collection is complete.

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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