The overall goal of the project was to provide a detailed assessment of cover crop impacts on soil nutrient cycling and microbial communities, weed growth, tree performance, and economic considerations. Treatments in this trial included two different mixtures of cover crops planted in the row middles: legumes + non-legumes (LG + NL) and non-legumes only (NL). These were compared to a grower standard control (GSC) that primarily consisted of weeds. Cover crops were planted twice during the year: June and late October/early November to correspond with the rainy season. Trials were conducted in two different locations in Southwest Florida (labeled North and South groves).
We found cover crops had a significant impact on components of soil health for this project. Both cover crop mixtures increased soil organic matter, though this increase was only found at the North grove location. The increase in soil organic matter was linked with increased nitrogen availability in the row middle soils where cover crops were planted and significant changes to the soil microbial community. The mixtures of cover crops planted (LG + NL compared to NL only) also significantly impacted the abundance and types of microbes in the soil, and their roles in soil nitrogen availability. For example, there were more bacteria capable of fixing nitrogen in soils under LG + NL, as well as completely different types of bacteria involved in other aspects of the nitrogen cycle. While these changes in soil organic matter, microbial communities, and nitrogen availability in the row middles did not translate to changes in root or tree growth or production, they do indicate changes to soil health are possible. The trees in both locations of this study were 25+ years old, and therefore more time may be necessary to observe changes in production. Based on a survey of citrus growers about the use of cover crops conducted as part of this project, growers were on average willing to wait 4.4 years for cover crops to benefit citrus production. It is possible that changes in production due improved soil health from cover crops may also be evident more quickly in younger trees.
In addition to changes to soil parameters, cover crops also significantly suppressed weed growth. In particular, the cover crop mixtures in this study substantially suppressed the germination and growth of grasses and sedges. Based on the economic analysis conducted in this project, there is an estimated short-term savings of $75.47 per acre due to not frequently mowing the row middles where cover crops are planted. The overall net cost of adopting cover crops was estimated to be $144.32 per acre, on average.
Based on the results from this project, cover crops can significantly impact components of soil health, reduce costs related to weed suppression, and have the potential to provide greater impacts to soil nutrient availability. There have been nine publications from this project to date, with at least five more in preparation. Publications include both articles for the Citrus Industry magazine and peer-reviewed scientific journals. In addition, PIs on this project have presented results at multiple grower meetings. A grower/extension seminar with presentations of the results of this project by all PIs is scheduled to be held at the UF/IFAS SWFREC on June 23.