Since Fall 2020, I have been evaluating the effects of applying green waste compost on established alfalfa. The three-year project includes two trials – one in the San Joaquin County Delta and the other in Yolo County – and is a collaboration with Rachael Long (UCCE) and Radomir Schmidt (UC Davis). The project is supported by a CA Department of Food and Agriculture Healthy Soils Program (CDFA HSP) demonstration grant. Our interests are in evaluating whether compost enhances soil carbon and nitrogen storage, improves soil physical characteristics (i.e. improved water infiltration, reduced compaction), reduces greenhouse gas emissions, and/or boosts alfalfa yield.

Compost is decomposed organic matter from plants or animals and may be classified by the carbon-to-nitrogen ratio (C:N). The C:N is the relative amount of carbon and nitrogen in the material. Plant-derived composts (like green waste compost) have a high C:N, and animal-derived composts (like composted manures) have a low C:N. A material with a ratio greater than 30:1 is considered a high C:N material. The ratio is important because it affects microbial metabolic functioning and plant-available nitrogen. Both high and low C:N composts promote soil functioning by increasing soil carbon that is in a form easily accessible to microbes. That, in turn, can improve soil biological activity and physical conditions. With a high C:N material, however, nitrogen may be immobilized (“tied up”), so soil nutrient monitoring is important in order to stave off impacts to crops.

The San Joaquin County trial is approximately 20 acres, and there is no history of compost application at the site. The soil is a Peltier mucky clay loam that is considered partially to poorly drained. Compost applications are surface-applied in the fall/winter to plots that are two border checks wide (120 ft) and approximately 1000 ft long. Two green waste compost rates – 3 tons/ac and 6 tons/ac – are being compared to the untreated (non-composted) control. The first compost application was made in Fall 2020 following the first cutting season of the alfalfa stand. The second application was made in Winter 2021, and the final will occur in fall/winter 2022. Baseline soil samples were collected at the beginning of the study (October 2020), and annual sampling is done every fall season before compost application. Alfalfa yield is assessed 3-4 times per year by taking quadrat samples from the grower's windrows. Greenhouse gas samples are collected on a monthly basis.

Preliminary results. Yield was measured from three cuttings in 2021, and so far, from two cuttings in 2022. (We anticipate measuring yield from two more cuttings in 2022.) Our preliminary results from these five cuttings indicate that compost can improve alfalfa yield over the untreated control but that a rate of 6 tons/ac does not improve yield over the 3 tons/ac rate (Fig. 1). We are also testing forage quality, and those results will be available in the fall.

I recently held a field day at the trial location. If you were not able to make it, please visit my website for the handouts. The handout “Compost for Soil Improvement in Alfalfa” shows other preliminary results from this trial, including soil carbon and nitrogen and greenhouse gas emissions. In addition, there are handouts describing other organic matter amendments in alfalfa and forages.

Figure 1. Preliminary yield results over five cuttings in 2021 and 2022. The compost rate of 3 tons/ac improved alfalfa yield over the untreated control.

Conclusions. Organic matter amendments, as from compost, can improve soil functioning, but changes take time to observe, let alone be realized financially. We estimate that compost (material plus hauling) costs approximately $27/ton, with an additional $10/ton for spreading (Fig. 2). To help offset the costs, the CDFA HSP provides incentives grants for farmers, and more funding may be available later this year. UC ANR Technical Service Providers Hope Zabronsky or Caddie Bergren are available to help growers with the application. And please don't hesitate to reach out to me if you would like more information on this trial or on the CDFA incentives programs.

Figure 2. Compost spreading at the San Joaquin County trial. Compost is not a small expense, but it may help improve soil functioning and alfalfa yield over the long-term.

UC Davis and UC Cooperative Extension will host the UC Dry Bean Field Day on Thursday, September 1, 2022 from 9:00am to 11:00am. The field day will begin at the Campbell Tract on the UC Davis campus, which is a different location from where it has been in recent years. The agenda is pasted below, and a downloadable version is attached to the bottom of this post. CCA continuing education credits have been requested (2.0 units of Crop Management). Thanks for your interest, and we hope to see you at the field day!

Agenda:

Attendees are invited to venture into the fields to look at the lima breeding materials, cooperative dry bean nursery, and heirloom-like dry beans at the student farm (38.541667, -121.767111), with Travis Parker, UC Davis

UC Cooperative Extension and UC Davis will host a Healthy Soils Program field meeting on compost. The meeting will take place on Thursday, July 28th from 10:00am to 11:30am. The meeting will take place off of S. Landi Road, on Roberts Island in the Delta. Presentation topics include how to acquire compost, different types of compost, how compost can improve soil health and mitigate greenhouse gas emissions, and how to apply for cost-share funding. The meeting location is where we are trialing different rates of green waste compost application for potential soil health and alfalfa yield benefits. Preliminary results will be described. Attendance is free, and registration is not required. Continuing education credits will be offered (CCA and N management applications pending). The agenda is pasted below, and a downloadable version is attached. Thanks for your interest in UC Cooperative Extension programming, and we hope to see you later this month!

Agenda

I have been trapping armyworms in Delta rice since 2016, after the industry experienced an outbreak in 2015. Monitoring involves scouting for damage and deployment of pheromone bucket traps that catch the moths (Figure 1). I have traps at three Delta locations, and at each location, there are three traps that span adjacent fields. 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. UC IPM provides treatment guidelines, and a Section 18 emergency exemption of methoxyfenozide (Intrepid 2F) has been approved for the 2022 season. (For more information, please contact your county Agricultural Commissioner's office.)

We have begun our 2022 monitoring, and trap counts are higher than they were at this same time last year (Figure 2). (Overall, 2021 was a low-pressure year.) The counts we are observing are not extreme but are on par with what we saw in 2020. It's hard to pinpoint why populations fluctuate from year to year, but it could relate to higher minimum winter temperatures (i.e. better winter survival), and/or migratory patterns from other western states and Canada.

The monitoring that I do in the Delta is part of a larger effort that is spearheaded by my colleague, Luis Espino, rice advisor in Butte and Glenn counties. Luis writes a weekly blog to provide real-time information on trap counts to help growers and consultants with scouting and decision-making. In his blog announcements, he will link to an interactive mapping tool called Ag Pest Monitoring, where you can view counts across trapping locations. Please consider subscribing to Luis Espino's blog, but don't hesitate to reach out to me if you'd like to discuss what is happening in the Delta.

Good luck this season, and I hope to see you in the field!

Figure 1. Bucket traps are placed along field edges. Nine traps are deployed across three Delta locations and are checked weekly. The traps include a pheromone lure that selectively traps true armyworm moths. (Photo by M. Leinfelder-Miles)

Figure 2. 2016-2022 Delta armyworm trap counts. The trap counts represent the number of moths caught per day, averaged across three Delta locations (9 total traps). The 2022 counts are still moderately low, averaging about thirteen moths per day during the week of June 13^th, but now is the time to intensify monitoring since peak populations tend to occur between now and early July.