Amanda Charles comes to us from Petaluma, CA as a new member of the Community Education Specialist team. She represents the Sonoma County region at the UCCE Sonoma office in assisting growers with the application and implementation processes of CDFA's Climate Smart Ag Funding Programs – AMMP, HSP, SWEEP. Charles earned her bachelor's degree in Agricultural Business at Cal Poly San Luis Obispo where she took a special interest in Dairy Science courses, furthering her love and knowledge for the industry. Upon returning home, she began working for a sustainable grass-fed beef company where she educated consumers about the positive impact farming practices can have in sequestering carbon and mitigating the issues of climate change. 

Charles' involvement in local agriculture began as a child, exhibiting dairy cattle and market lambs in 4-H. She knew she wanted to return to Sonoma County to expand on her passion for sustainable agriculture in her community. “Helping farmers understand how switching up their farming practices can better their soil and our atmosphere, and then letting them know that there is funding available for these new practices is the best of both worlds” said Charles. She is looking forward to collaborating with more local coalitions to support farmers and ranchers in the fight against climate change. 

Cover crops can provide many soil and ecosystem benefits, like improving water infiltration and providing resources for pollinators. However, we don't yet know which cover crop species are best suited for specific cash crops. 

To answer this, I planted potatoes into the residue of 5 cover crop mixes in Shafter (Kern County). Here are the mixes I planted: 

1. Soil health mix: Merced rye, common vetch, berseem clover, and daikon radish 

2. Soil builder mix: triticale, Dundale peas, common vetch, yellow mustard, and radish 

3. Brassica pollinator mix: yellow mustard, daikon radish, Nemfix mustard, “Bracco” white mustard, and canola 

4. Simple mix 1: Merced rye and Dundale peas 

5. Simple mix 2: barley and common vetch 

I wanted to see if the cover crops would reduce disease incidence or improve yield. Here's what I did in this trial:

	5 different cover crop mixes were terminated in Shafter on March 18, 2021 using a disc harrow.
	To encourage further decomposition, the cover crops were disked multiple times and irrigated once in March and April.
	These yellow potatoes were planted at 1' spacing in 30” beds on April 22, 2021. The beds were 60' long. The potatoes received adequate moisture from solid set sprinklers.  We applied nitrogen fertilizer once, at the beginning of the growing period.

Potatoes were harvested on August 3, 2021.

So, what did we see? We had a few challenges:

Southern blight and other soil borne pathogens

By June 9, all of the rows had some potato plants, but it was very patchy.

The plants were dying because they were infected with southern blight and other soil borne pathogens (right photo).

Results

So, did we find anything interesting? 

There was too much variability and not enough replication to see meaningful differences in the yields associated with the different cover crop mixes. 

Further research is needed to identify the best cover crop species for each cash crop in Kern County. 

Key takeaways

Southern blight thrives under the conditions of the trial field in Shafter. It has historically only been a major problem in Kern County, but other areas of California are now reporting cases due to warming temperatures. 

It grows best under these conditions:

-       Warm temperatures 

-       Acidic soil – the soil pH in the top 6 inches of soil was between 5.8 and 6.3 

-       Decaying organic matter – in this case, the decomposing cover crops

-       High soil moisture – we used sprinkler irrigation

Unfortunately, southern blight doesn't just attack potatoes. It has a wide range of hosts and can decimate other vegetable crops like tomatoes, cucumbers, and chard.  

Should I not plant cover crops because of southern blight?

The potato trial in the neighboring field was also decimated by southern blight. That field was fallow before the potatoes were planted, with no cover crops.  

If you plan to grow a crop that is susceptible to southern blight and you are in Kern County, you should focus on the cultural practices and chemical products that will reduce your risk of crop loss. 

If you plant cover crops, make sure that the crop residue has completely decomposed before planting your cash crop. This might require terminating your cover crops early, so that there is enough time for complete decomposition. 

In this trial, there was an incredible amount of biomass left over from the cover crops. They were irrigated and planted at 1.8X the recommended seeding rate. There was also plenty of nitrogen and warm weather to fuel their growth. If your cover crops do not produce as much biomass, especially ligneous biomass, then they should not take as long to break down as the ones in this study did. 

More information about southern blight 

-       https://content.ces.ncsu.edu/southern-blight-of-vegetable-crops

-       http://ccvegcrops.ucanr.edu/newsletters/Tomato_Info_Newsletters72607.pdf

For more information about the trial, contact Shulamit Shroder at sashroder@ucanr.edu or 661-903-9442. 

Many thanks to Jed Dubose, Jaspreet Sidhu, Jennifer Fernberg, Cristal Hernandez, Brian Marsh, Rick Ramirez, Caddie Bergren, and Samikshya Budhathoki for their help. 

Unruh walnut orchard and cover crops in March, 2021

Daniel Unruh, and his family, farm just under 200 acres of walnuts alongside the Sacramento River, just outside of Princeton, CA. The walnut orchard is irrigated with solid set sprinklers and is only irrigated when needed, or if there is not enough rain during the season. Daniel started cover cropping in 2013 with the main goal of nematode suppression, and soon after, he and his wife took over the orchard operations. The cover crops that show up now between rows is voluntary, as he has not spread seed in years, but still sees a successful cover. He also practices reduced till on his farm to encourage the cover crop growth and help increase biomass production.

Daniel has not received money from any grants, or other outside funding sources to establish cover crops, this was just something he saw benefit in after the first few years of nematode reduction. His passion for cover cropping has grown to encompass more than just nematode suppression however, and he is now seeing plenty of benefits elsewhere around his orchard.  

Beneficials of all kinds consider his orchard a home, less water is running off of his property during storms and irrigation, and he has cut his input and commercial fertilizer bill down by close to 75%. The soil organic matter for his orchard has also increased from around 1.7-1.9% to 3.0% when tested in 2020. When Daniel and his wife first took over in 2014, the orchard was sprayed for husk fly, coddling moth and blight, but now only blight has been addressed in recent years. In fact, he has not used any fertilizer at all the past few years, but has seen a slight reduction in yield as a result. Daniel also has seen changes in his irrigation cycle in what used to be a rotation of every 7-10 days, has been extended to every 12-14 days due to moisture retention. 

Roller crimper, that Daniel designed, used in his walnut orchard to terminate the cover crops

Like many other farmers, his main concerns with cover cropping in an orchard system was termination, and the learning curve that comes along with it. Daniel was even able to design a roller crimper, with chevron crimps, specifically for his operation and the type of cover crops he uses for termination. His cover crop stand consists of brassicas, grasses and legumes and can easily grow to over 6 feet tall. When he originally planted, Daniel spread seed 17 feet across for almost 90% coverage.  His roller crimper helps lay plant material down to protect the soil from the sun, improve water retention and creates an environment beneficial to microorganisms. 

Daniel in his walnut orchard - dug up a sample of his soil after years of cover cropping

Daniel is so passionate about improving his soil microbiology and reducing his inputs, he even serves as a Mentor Farmer at the Chico State Center for Regenerative Agriculture. Daniel has presented at numerous events and has hosted workshops at his orchard to educate and encourage other growers to give soil management practices a try. Daniel says he is never done learning, and attends many workshops throughout the year as well.

 Finally, Daniel encourages a holistic outlook, and motivates others to keep trying various approaches if it doesn't work the first time until you find a system that does work for your operation. He goes on to say you should try alternatives first before going straight to spraying fertilizer as eventually plants will rely on this synthetic ‘health' and it will not last.More on Daniel and how he has contributed to this research can be found at https://www.csuchico.edu/regenerativeagriculture/demos/daniel-unruh.shtml