Citrus row middle management to improve soil and root health

Citrus row middle management to improve soil and root health

Report Date: 08/13/2021
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 last planted in June and July 2021 and included sunnhemp, cowpeas, buckwheat, millet, and Egyptian wheat. Based on data collected in previous years, we have found 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. Statistical analyses suggest that the differentiation of these type of microbes is not only attributed to the soil properties of soil moisture and soil organic matter but also the different CC mixtures, and thus was to some extent controlled by the plants. Soil organic matter has also significantly increased under cover crop treatments. The negative correlation between the growth and coverage of cover crops and weeds observed in the previous measurements has continued based on the analysis performed on data collected from the recent quarter. The density of monocot weeds (e.g., grasses and sedges) is 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 will occur 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. 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. 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, and quantitative differences will be reported in the next quarter. 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 began and estimates where used as a benchmark for cover crop costs in the survey. The economics team began data collection via the survey instrument. The survey solicited information on growerÂ’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). This effort resulted in 308 responses of which 90 surveys are usable: 43 from Florida and Georgia and others from Texas and California. These responses do not constitute a representative sample, so data collection efforts continue. For Florida and Georgia, the preliminary sample includes 99,874 acres and the average farm has 2,323 acres of citrus. Surprisingly, 49% of FL/GA citrus growers (59% of acres) in our sample say they used cover crops in their citrus groves. Seventy percent of growers (99% of acres) indicated they are aware of cover crop use in citrus production. Respondents have almost 11 years of farming experience and are willing to wait 4.9 years to see benefits from cover crops. 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. The student on the team has successfully completed his MS and a postdoc was hired in August to complete project objectives.

Objective 5: Communicate results to growers using field days and extension materials
Preliminary results were recently presented at the Educational Session hosted by CRDF and Florida Citrus Mutual. In addition, results will be presented at the Soil Science Society of America/American Society of Agronomy meeting in November and the American Geophysical Union meeting in December. 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:
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 more recent data could not be recovered due to severe damage to the data loggers. The loggers have been repaired and will be re-installed to collect any data during the remaining duration of the project and reported in the next quarter. The next annual soil sampling and half-yearly canopy measurements will occur at the end of August 2021 and the next set of cover crops will be planted at the end of October 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 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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