- Author: Michelle Leinfelder-Miles
- Author: Radomir Schmidt
The term ‘soil health' has become a common term in agricultural research and management. While most of us are familiar with testing soil for chemical properties, like nutrients, salinity, and pH, soil health also considers soil physical characteristics – like compaction, aggregation, and water infiltration – and biological characteristics – like soil respiration, active carbon, and nitrogen mineralization.
These properties influence the soil's ability to function, and enhancing these properties can improve soil functioning to grow crops and produce ecosystem services. We often relate soil health to management practices like crop rotation, cover cropping, reducing tillage, and adding compost because these have been shown to increase soil functioning in agricultural landscapes. They are also some of the practices that are financially incentivized by the CA Department of Food and Agriculture Healthy Soils Program.
There is a regulatory framework for diverting green waste from landfills to make compost. In 2014, AB 1826 was passed in California, which required businesses to recycle organic wastes and jurisdictions to set up organic waste recycling programs to divert green waste from landfills. In 2016, AB 1383 established organic waste reduction targets (75% reduction by 2025, compared to 2014). The bill also required jurisdictions to do education and outreach. Green waste diversion is expected to reduce greenhouse gas emissions by 4 million metric tons per year and increase food recovery by 20 percent. Agricultural land could serve to receive green waste compost recovered by this regulatory framework.
Our project objectives were to learn whether green waste compost improves soil nutrient status or other soil health characteristics, whether it improves alfalfa yield or quality, or if its application affects greenhouse gas emissions from the system. Alfalfa was chosen for this study because it has a large footprint on the state's agricultural landscape and because it has a high phosphorus (P) and potassium (K) nutrient need which compost could help supply. Also, as a ‘high-traffic' crop, alfalfa soils can have poor physical traits (e.g. compaction, water infiltration), which could potentially be ameliorated with compost.
The study was conducted on commercial farms in Yolo and San Joaquin (SJ) counties. The Yolo site had a mineral soil with high clay content (approximately 50 percent clay), and the SJ soil was a mucky clay with high organic matter (approximately 8 percent). We are comparing two green waste compost rates (3 and 6 tons per acre) to the untreated control. Compost applications were annually (2020-2022) surface-applied in the fall/winter ahead of rain.
Our preliminary results indicate no statistically significant differences in total carbon and nitrogen among treatments (Fig. 2). There is a trend, however, for compost to increase carbon at the Yolo site, which is inherently low in organic matter. An interesting observation about the SJ site, where the soil is inherently low in K, is that the compost increased soil K (statistically significant, Fig. 3). The compost analysis showed that the product was roughly 1 percent K. Therefore, the 3-ton compost rate should have added approximately 50 lb of K per acre, and the 6-ton rate approximately 100 lb of K per acre. Based on the amount of change in soil K and the compost analysis, the compost was likely what contributed to the increase in soil K. This appears to be translating into higher tissue K (Fig. 3), and in turn, higher yields (though neither tissue K nor yield are statistically higher than the control, Fig. 4).
Greenhouse gas emissions have not differed among treatments (Fig. 5), indicating that the carbon that is added by the compost is not being respired from the system. There are higher CO2 emissions at the SJ compared to the Yolo site, which we attribute to the inherently higher carbon of the SJ soil. Additionally, we have observed that the soil acts as a methane sink. This is noteworthy because methane is a more potent greenhouse gas than CO2.
Based on our experiences working on this project, we have the following guidance for growers interested in applying green waste compost. While green waste compost is a relatively cheap input, transport cost can be high. In 2021, we estimated that material plus hauling cost was approximately $27/ton and spreading was an additional $10/ton. The highest demand for compost is in the fall. To ensure availability, growers should aim to purchase compost in the spring or summer and store it on-site until fall. Ordering the compost in spring or summer also tends to result in a higher quality product delivered (i.e. less trashy). Timing compost application can be a challenge (i.e. after all harvests but before soil gets too wet), so having the compost already on-site may help in getting it applied more readily. We still have more data to analyzed for this project, so more information will be forthcoming. We want to thank the growers in Yolo and San Joaquin counties for collaborating with us on this project.
Rice production in the Sacramento-San Joaquin Delta region has been steadily increasing in recent years. While Delta acreage is only a fraction of that in the Sacramento Valley, Delta yields are consistent with statewide averages. I estimate that in 2023, the Delta had around 10,000 acres of rice. In this seasonal recap, I'll overview UCCE research in Delta rice, as well as provide some observations about the 2023 season.
Armyworm Monitoring: I have been monitoring armyworm populations in the Delta since 2016, in collaboration with my UCCE colleague, Luis Espino. Monitoring involves scouting for damage and deployment of pheromone bucket traps that catch the moths. We can use trap counts and Growing Degree Day modelling (i.e. a temperature measure of time) to determine whether and when to treat fields. In 2023, we were thinking we might get away with minimal pressure because the population stayed low through early July. Then, the population spiked in mid-July, later than we had ever observed (Fig. 2). We surmise this was due to the cool, wet spring and later planting season. This year, Methoxyfenozide (Intrepid 2F) was available for use under full registration.
Disease Observations: We have identified diseases like stem rot, aggregate sheath spot, and rice blast on some Delta farms. It is important to scout for these diseases at late-tillering and early-heading because treatment timing is critical for management. Fungicide treatments are most effective when applied between late-boot and early-heading. Rice blast may be exacerbated by too much nitrogen, and stem rot and aggregate sheath spot by low potassium (K). K can be limiting in some Delta soils, especially where the straw is baled. There is a loss of approximately 28 lb K/ac for every ton of straw removed. Consider leaf tissue sampling for K between tillering and panicle initiation. The Y-leaf should have a K concentration of at least 1.5%. At heading, the flag leaf should have a K concentration of at least 1.2%. On-farm consultations are a service provided by UCCE. Please reach out if I can help identify pests and provide management guidelines.
Weedy Rice: We should continue to keep weedy rice on our radars because we have observed it in the Delta. In-season management includes rogueing or spot spraying before viable seed is produced. The organic herbicide Suppress is registered for spot spraying. Post-harvest management should include straw chopping, but not incorporation, and winter flooding. This will keep seed on the soil surface, where it can potentially deteriorate over the winter.
Variety Trial: UCCE collaborates with the California Rice Experiment Station to evaluate commercial varieties and advanced breeding lines. The San Joaquin County Delta location was one of ten locations in the 2023 statewide trial. The Delta is a test site for very-early maturing varieties because it has cooler growing conditions than other rice growing regions of the state. Variety trial results will be made available in the February 2024 newsletter.
Cover Cropping: With funding from the CDFA Healthy Soils Program and CA Rice Research Board, I am collaborating with Sara Rosenburg (UC Davis graduate student) and Whitney Brim-DeForest (UCCE rice advisor) to evaluate winter cover crops. We are interested to learn whether cover cropping improves soil carbon and nitrogen dynamics in the rice system. Since rice may be grown over multiple seasons without rotation, cover crops may provide an opportunity to introduce plant diversity, including nitrogen-fixing legumes. Trials will occur from 2022-2025, and the Delta site is one of three (also in Butte and Colusa counties). The 2022-2023 winter season presented several challenges for cover cropping. At the Delta location, seasonal rainfall exceeded 25 inches, and in the ten days after planting, the site received nearly 3.5 inches of rain. In addition to saturated soils, bird predation was severe. This fall, our aim is to plant earlier, if conditions allow.
Thank you to all the growers who collaborated with us on these projects. I wish everyone a good end to the year and a great 2024.
The UC Field Crops, Alfalfa, and Forage Field Day will take place on Friday, September 29, 2023. The field day will take place at the Kearney Research and Extension Center, 9240 S. Riverbend Ave., Parlier, CA 93648. Sign-in and morning refreshments begin at 7:00am, and the field tour tram leaves promptly at 8:00am. There is no registration fee, but please pre-register for the event to help us with our planning. Only preregistered attendees are guaranteed a lunch. CCA continuing education credits (1.0 SW; 1.0 PM; 1.5 CM) and CDFA INMP credits (1.5) have been approved. DPR continuing education credits (1.0) are still pending. The agenda is below and attached to the bottom of this post. We look forward to seeing you at the field day!
7:00 am Sign-in (refreshments provided)
8:00 am Depart for Field Tour
- Sorghum Variety Trials (Grain & Forage) – Jackie Atim, UC ANR
- Sorghum variety trial under deficit irrigation – Jackie Atim
- Dry beans variety selection – Bao Lam Huynh, UC Riverside
- Almond-Alfalfa Intercropping System – Sultan Begna and Lauren Hale, USDA ARS
10:00 am Return from Field Tour
10:10 am New Extension Advisors Introduction – Nick Clark, UC ANR
10:20 am Alfalfa Weed Management – Giuliano Galdi & Jorge Angeles UC ANR
10:40 am Cotton IPM – Ian Grettenberger & Buddhi Achhami, UC Davis
11:00 am Brief: Small Grain and Alfalfa Weed Management – Nick Clark
11:05 am Break
11:15 am Compost Application to Alfalfa – Michelle Leinfelder-Miles, UC ANR
11:35 am Byproducts Trends & Opportunities for the CA Dairy Industry – Jennifer Heguy, UC ANR
11:55 am Lima & Garbanzo Breeding and Dry Bean Heat Stress Testing– Christine Diepenbrock, UC Davis
12:15 pm Lunch/span>
We invite you to attend a Delta Rice Workshop on Wednesday, August 23rd from 10:00am to noon on Staten Island (23319 N. Staten Island Rd., Thornton). The workshop is collaboratively supported by Fish Friendly Farming, the Delta Conservancy, Conservation Farms and Ranches, the CA Land Stewardship Institute, the Regional Water Board, and UC Cooperative Extension. Organizers will demonstrate the use of a recirculation pump in rice production, with a discussion of potential financial support programs. Additionally, there will be a presentation on The Nature Conservancy's Bird Returns Program, and I will provide an update on UCCE research in Delta rice.
The agenda is below, and more information is available from the attached flyer. CDFA INMP (1.0) and CCA (1.0 SW, 0.5 CM) continuing education credits have been approved. We hope to see you at the meeting!
Fish Friendly Farming and Delta Conservancy/Regional Board funding - Laurel Marcus, FFF
Recirculation Pump System - Jerred Dixon, Conservation Farms and Ranches
Can funding programs such as SWEEP be used for recirculations pumps and pipelines - Laurel Marcus, FFF
Bird Returns Program - Julia Barfield, TNC
Research Activities in Delta Rice - Michelle Leinfelder-Miles, UCCE
UC Davis and UC Cooperative Extension will host the UC Dry Bean Field Day on Tuesday, August 15, 2023 from 9:30am to 11:30am. The field day will begin along Bee Biology Road on the UC Davis campus. The agenda is pasted below, and a downloadable version is attached to the bottom of this post. DPR (1.0) and CCA (1.0 Crop Management, 1.0 Pest Management) continuing education credits have been approved. Thanks for your interest, and we hope to see you at the field day!
9:30am Welcome and introductions: Christine Diepenbrock and Antonia Palkovic, UC Davis; Michelle Leinfelder-Miles, UC Cooperative Extension
9:35am How can we further improve lima bean? A project funded by the USDA to improve breeding resources: Paul Gepts, UC Davis
9:50am Walk through and discussion of lima breeding material: Antonia Palkovic and Christine Diepenbrock, UC Davis
10:00am Field diagnostics – bean pest identification and management: Sarah Light, Michelle Leinfelder-Miles, Nick Clark, UC Cooperative Extension
10:30am Travel to Veg Crops location (38.534222, -121.782222)
10:35am Blackeye varietal improvement - update on new pest-resistant varieties: Bao-Lam Huynh, UC Riverside
10:55am Results from round one of “speed breeding”, and testing nutritional alongside agronomic traits in limas: Christine Diepenbrock, UC Davis
11:00am From farm to (robot) stomach: what are the trait profiles of California beans after harvest?: Tayah Bolt, UC Davis
11:05am Screening for drought resilience in common and tepary beans: Matthew Gilbert, Tom Buckley, Troy Magney, Paul Gepts, Chris Wong, Antonia Palkovic, Travis Parker, UC Davis
11:20am Evaluating productivity and quality of cowpea and interspecific common/tepary bean in Davis and Parlier (contrasting temperatures): Sassoum Lo, Jonny Berlingeri, UC Davis
11:25am Developing low-cost phone apps/drone and rover platforms to measure agronomic traits: Earl Ranario, Heesup Yun, Vivian Vuong, UC Davis
11:30am Discussion and evaluation