Incorporating hedgerows in rice could provide growers with an alternative method for managing field margins without relying on pesticide applications to control the pests along the edges of rice fields. They may potentially improve soil health and lower costs for maintaining field edges and permanent levees. They may also increase beneficial insects found in rice fields. This study is the first of its kind in California rice, and provides the opportunity to learn about potential benefits to installing hedgerows along rice fields. In 2024, we established a hedgerow and collected data on soil health, weed control, insect populations, and success rates of hedgerow plants. The study is funded by the California Department of Food and Agriculture's Healthy Soil Program, and will continue to through 2027
The study site is located on a permanent levee next to a rice field in Arbuckle, in Colusa County. The field is rotated with annual crops, with rice being the main crop. The hedgerow area and the unplanted control area are adjacent and share the same soil type. Both the hedgerow and control areas measure 275 feet in length and 20 feet in width (Fig. 1).
Figure 1: Demonstration setup and area. The yellow squares between the hedgerow plants represent the areas seeded with California poppies (Eschscholzia californica).
In April 2024, we established a hedgerow of native plant species suited to Colusa County, including:
1. Arroyo willow (Salix lasiolepis)
2. Coffeeberry (Rahmnus californica = Frangula californica)
3. Deer grass (Muhlenbergia rigens)
4. California poppy (Eschscholzia californica).
The species are adapted to the soil and climate conditions of the study site and are also recommended by Rachael Long (2010) (https://ucfoodsafety.ucdavis.edu/sites/g/files/dgvnsk7366/files/inline-files/26499.pdf).
All plants were purchased from a local nursery in Butte County, and were transplanted from pots. The arroyo willows were spaced 15 feet apart, the coffeeberry 7.5 feet apart, and the deer grass 5 feet apart. Since the optimal seedling time for California poppy is late winter or early spring, we delayed seeding until November 2024. California poppy seeds were hand-sown in the spaces between the hedgerow plants at a seeding rate of 15–20 pounds per acre. In November 2024, we replaced the dead hedgerow plants to ensure the hedgerow's continued effectiveness.
Irrigation is recommended during the first three years to ensure the survival of hedgerow species during California's dry season. Since the experiment began in April 2024, we irrigated the field twice weekly for approximately 4–6 hours through October 2024. When temperatures reached 110°F, we increased irrigation to three times per week. Additionally, we hand-irrigated individual plants that required extra water. In addition to irrigation, we fertilized the hedgerow species after transplantation in April 2024 to promote establishment and improve survivability. Urea was applied at a rate of 15 g to the deergrass and coffeeberry, and 30 g to the arroyo willow.
We studied the effects of implementing hedgerows in annual cropping systems across four key aspects: (1) soil health, (2) weed pressure, (3) insects' population, and (4) establishment success rate for hedgerows.
Soil Health
To evaluate the benefits of hedgerows on soil health, we conducted baseline soil sampling on April 4th, 2024, in both the hedgerow and the unplanted control areas. Samples were sent to the lab and analyzed for carbon, nitrogen, organic matter, and micronutrients. We collected bulk density data on April 10th, 2024 and conducted soil water infiltration data collection on November 8th, 2024.
As this study only began last year, data collection on soil health is still ongoing, and analysis has not yet been completed.
Weed Pressure
To evaluate the benefits of hedgerows on weed control, we made a pre-emergent spray to control the weeds in the hedgerow area on April 2nd, 2024, before the experiment began. We used a tank mix of glyphosate + glufosinate + 2,4- D at their highest label rates and applied using a 10 ft handheld boom at 20 gallons of spray per acre. We assessed weed pressure in the hedgerow area and the unplanted control area monthly from May to September in 2024. Data collection included the percent cover of hedgerow plant species, weeds (grasses and broadleaf species), bare soil, and straw.
The first-year species composition data (Fig. 2) indicates significant differences between hedgerow plots and unplanted control areas. Specifically, we observed an increase in broadleaf weeds in the hedgerow plots over the summer, likely due to irrigation. The hedgerows also appeared to have much less residual straw, suggesting that irrigation may accelerate straw decomposition.
Figure 2: Percent cover in the hedgerow and untreated control of broadleaves, grasses, soil, straw, and hedgerow plants. Measurements were taken in 15 random 1 m x 1 m quadrants monthly per area starting at 1 month after planting.
Insect populations
To evaluate the benefits of hedgerows on insect populations, we used pit traps (in the ground) to collect the crawling insects and sticky traps to collect flying insects. We set up three pit traps and three sticky traps from the east, center, and west sections of the hedgerow area and unplanted control area and collected data monthly from May to September in 2024. In addition to traps, we used insect nets to sample insects from the tops of hedgerow plants, unplanted control areas, and adjacent rice fields. We conducted sweeps once each from the east, center, and west sections of both the hedgerow and unplanted control areas. We also conducted three sweeps at 40, 80, and 120 feet from the edge of both the hedgerow and unplanted control areas. Like the traps, insect sweeps were performed monthly from May to September in 2024.
As this study only began last year, data collection on insect population is still ongoing, and analysis has not yet been completed. However, we noticed an increased presence of praying mantises in the hedgerow areas, suggesting potential benefits in attracting more beneficial insects.
Establishment success rate for hedgerows
To evaluate the establishment success rate for hedgerow plants, we evaluated which plants survived the planting and established well. In May, July, and September 2024, we collected survivability data by counting the number of alive and dead plants for each hedgerow species. The survivability percentage = (the number of living plants/the total number of plants initially planted) * 100.
The first-year survivability data (Fig. 3) indicates coffeeberry appears less suitable as a hedgerow species in this particular location, potentially due to its intolerance to flooding. Willow and deer grass, however, may be better options. The hedgerow species' survival rate can be affected by the transplanting, so it is important to ensure the correct transplanting methods are used. Improper transplanting can lead to transplant shock, which may decrease plant survival. Hedgerow species could also be significantly affected by pesticide drift, particularly if pesticides are applied by air. This applies to both organic or conventional pesticides. To minimize pesticide exposure, it is important to maintain buffer zones between spray fields and hedgerows. Additionally, using larger spray droplets, applying pesticides during calm weather, and adjusting nozzle settings can help reduce drift. At this site, we collected phytotoxicity data, and found no phytotoxicity present after the adjacent rice field had an herbicide application.
Figure 3: Percent survival of the transplanted coffeeberry, deergrass, and willow at 1 month, 3 months, and 5 months after planting.