- 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.
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>
The annual UC Davis Alfalfa and Small Grains Field Day will take place on Thursday, May 11, 2023 at the Department of Plant Sciences Field Facility (2400 Hutchison Drive, Davis, CA 95616). Registration opens at 7:30am, and the wagons leave for the field at 8am. The event is free and open to the public, but registration is requested. Lunch is sponsored by the CA Crop Improvement Association, and continuing education credits will be available. Directions are as follows:
The field day is located on Hutchison Drive, just west of Davis. Take the Hwy. 113 exit north from I-80, or Hwy. 113 south from Woodland. Exit west on Hutchison Drive. Take a right at the first roundabout, a left at the second roundabout, and the field headquarters is about ¼ mile down in a clump of trees and buildings on the left.
The agenda is as follows:
8:10 Alfalfa Breeding Efforts at UC Davis - Charlie Brummer
8:20 Choosing Varieties for Pest Resistance - Dan Putnam
8:30 IPM and Importance of Management of Insect Resistance in Alfalfa - Ian Grettenberger
8:40 Test your Weed IQ - Identification of Weeds - Brad Hanson
8:55 Use of Compost to Improve Soils in Alfalfa - Michelle Leinfelder-Miles
9:05 Sorghum Projects for Forage and Biofuels - Jackie Atim
9:15 Improving Agronomic and Grain Quality Traits in Sorghum under Well-watered and Drought Conditions - Christine Diepenbrock
9:35 Flood or Drought? Alfalfa Strategies for Coping with California's Future - Dan Putnam
9:45 Teff as an Alternative Summer Forage Crop - Dan Putnam
9:50 Overhead Irrigation Technologies for Improved Efficiency - Isaya Kisekka
10:05 Updates from UC Davis Small Grains Breeding Program - Jorge Dubcovsky
10:20 Effects of Genotype and Environment on Productivity and Quality in California Malting Barley - Maany Ramanan
10:30 California Grain Foundation and Research on Food Use of Triticale - George Fohner
10:40 Small Grain Research Update from Tulelake - Rob Wilson
10:55 Evaluating Digestate and Hydrolysate as Alternative N Sources in Small Grains - Valentina Roel
11:05 Biosolids as a N Fertilizer Source in California Small Grains - Konrad Mathesius
11:15 Helping Farms in the Central Coast get N Scavenging Credits for Cereal Cover Crops - Eric Brennan
11:25 DIY In-field Plant Tissue Tests to Determine N Sufficiency in Wheat - Karla Estrada
11:30 Updates on Small Grain Research and Production in the Central Valley - Mark Lundy
11:45 Tour Small Grain Variety Trials
1:20 Small Grain Breeding Field Day
The UC Alfalfa and Forage Field Day will take place on Thursday, September 29, 2022. 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. We have applied for DPR, CCA, and N management (ILRP program) continuing education credits, and the agenda is below. We look forward to seeing you at the field day!
7:00 AM Sign-in and morning refreshment
8:00 TRAM LEAVES FOR FIELD TOUR
- Choosing Alfalfa Varieties for Pest Management and Adjustments to Water Situations – Dan Putnam, UC Davis
- Sorghum Drought Research – Bob Hutmacher, UC West Side Research and Extension Center
- Sorghum Varieties – Bob Hutmacher, UC West Side Research and Extension Center
- Winter Flooding and Summer Deficit Irrigation of Alfalfa – Khaled Bali, UC Kearney Research and Extension Center
- Compost Trials in Alfalfa – Michelle Leinfelder-Miles, UCCE San Joaquin
10:00 TRAM RETURNS
10:10 Alfalfa Weevil Resistance Management – Ian Grettenberger, UC Davis
10:25 Pesticide Regulations – Drift Prevention and New Laws – Shawn Atayasay, Fresno County Ag Commissioner's Office
10:40 ALS Herbicide Resistance Screening of Common Chickweed in Small Grains – Nick Clark, UCCE Kings
11:20 Introduction of UC Cooperative Extension Specialist for Abiotic Stress – Jackie Atim, UC Merced
11:35 Small Grains Drought Resiliency – Mark Lundy, UC Davis
11:50 Alfalfa Cutting Schedule Impacts Yields, Quality, and Weeds – Dan Putnam, UC Davis
- Author: Michelle Leinfelder-Miles
- Author: Rachael Long
- Author: Radomir Schmidt
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.