Can managing soil health reduce disease pressure? By Bob Johnson
we have rotations for sclerotinia and verticillium, but not for pythium.” The article paid particular attention to pythium, a water mold that infects the roots of lettuce plants and produc- es spores that wait in the soil for the next lettuce crop. Incorporating vegetable crop residue provides a head start on getting more or- ganic matter into the soil. The residue from a 2.8- to 3.2-ton broc- coli crop leaves 2,200 to 2,700 pounds of carbon per acre in the ground, according to Smith. Lettuce residue can add 1,260 to 1,680 pounds of carbon an acre, while celery residue adds 1,090 to 2,300 pounds of carbon an acre. USDA research horticulturist Eric Brennan wrote a 2020 paper outlining the benefits cover crops can provide to subsequent vegetable crops. His re- port is available at www.ars.usda.gov/ pacific-west-area/salinas-ca/crop- improvement-and-protection- research/people/eric-b-brennan/ conf-proceedings-extension-pubs- tech-reports-and-blogs/. If a cover crop is grown, the contribu- tion to soil organic matter increases, as it is allowed to grow for a longer time before incorporation. A fall-grown cover crop adds 2,054 pounds of carbon when it is incorporat- ed in early October, but that rises to 3,471
Increase in crop losses from soil-borne pathogens have more Central Coast veg- etable growers interested in boosting soil health to reduce disease pressure. “The growers are thinking about whether there are things we can do to make the soil more suppressive of dis- eases,” said Richard Smith, University of California Cooperative Extension farm advisor emeritus. But researchers say it remains unclear if traditional practices used to manage soil health could also reduce soil-borne disease pressure. Smith, who retired after 37 years with UCCE, discussed challenges of building healthy soils during the 2023 Irrigation and Nutrient Management Meeting, sponsored by UCCE in Salinas earlier this year. Because growers can no longer use methyl bromide fumigation to eradicate diseases in the soil, they also have fewer opportunities to rotate into clean ground, and nonfumigant chemicals cannot al- ways reach pathogens. With fewer tools available, more conventional growers are interested in whether healthy soils can lead to reduced pathogens and production of quality veg- etable crops. Smith was part of a team of 13 research- ers from UCCE and the U.S. Department of Agriculture that contributed to a blog entry about suppressing pathogens by
Richard Smith, a University of California Cooperative Extension farm advisor emeritus, is a contributing author of a research blog about suppressing pathogens by improving soil health. Researchers say it remains unclear if traditional strategies used to manage soil health could suppress soil-borne diseases.
improving soil health. The researchers noted that “increasing carbon inputs is critical to increasing soil microbial ac- tivity, which may have an impact on sup- pressing soil-borne diseases.” Researchers said there are obstacles to overcome before growers can implement practices that would improve soil health by adding more organic matter. Expensive land leases make it diffi- cult to take ground out of production long enough to grow and incorporate a cover crop. The high cost of Salinas Valley farm- land makes rotations difficult, and for some diseases, effective rotations have not yet been discovered.
Use of compost also has dropped due to potential introduction of patho- gens in the compost that raises food safety concerns. Many soil labs do not offer all tests that would help growers evaluate their prog- ress in building healthier soil. “Because of the interest in soil health, I think labs will be doing more of these assays,” Smith said. Despite the obstacles, more Salinas Valley growers remain committed to us- ing practices that contribute to healthier soil as a way to manage nitrogen and to help combat soil-borne crop diseases. “Materials have to get down to treat a huge volume of soil,” Smith said. “And
See SOIL, Page 27
CIMIS REPORT | www.cimis.water.ca.gov
CALIFORNIA IRRIGATION MANAGEMENT INFORMATION SYSTEM
For the week of March 30 - April 5, 2023 ETO (INCHES/WEEK)
YEAR
3.0
THIS YEAR
2.5
LAST YEAR AVERAGE YEAR
2.0
1.5
1.0
0.5
0.0
MACDOEL II (236)
BIGGS (244)
DAVIS (06)
MANTECA (70)
FRESNO (80)
SALINAS-SOUTH (214)
FIVE POINTS (2)
SHAFTER (5)
TEMECULA (62)
IMPERIAL (87)
THIS YEAR LAST YEAR AVG. YEAR % FROM AVG.
.70 .96 .91 -23
1.03 .93 1.03 -1
1.02 1.29 1.25 -19
1.15 1.26 1.15 -1
1.04 1.24 1.03 -1
1.04 1.20 1.10 -5
1.09 1.19 1.09 0
1.10 1.14 1.04 8
N/A N/A N/A N/A
1.67 1.45 1.59 3
W eekly reference evapotranspiration (ETo) is the rate of water use (evapotranspiration—the sum of soil evaporation and crop transpiration) for healthy pasture grass. Multiplying ETo by the appropriate “crop coefficient” gives estimates of the ET for other crops. For example, assume ETo on June 15 is 0.267 inches and the crop coefficient for corn on that day is 1.1. Multiplying ETo by the coefficient (0.26 inches x 1.1) results in a corn ET of 0.29 inches. This
information is useful in determining the amount and timing of irriga- tion water. Contact Richard Snyder, UC Davis, for information on coefficients, 530-752-4628. The 10 graphs provide weekly ETo rates for selected areas for average year, last year and this year. The ETo information is provided by the California Irrigation Management Information System (CIMIS) of the California Department of Water Resources.
For information contact the DWR district office or DWR state headquarters:
SACRAMENTO HEADQUARTERS: 916-651-9679 • 916-651-7218
NORTHERN REGION: Red Bluff 530-529-7301
NORTH CENTRAL REGION: West Sacramento 916-376-9630
SOUTH CENTRAL REGION:
SOUTHERN REGION:
Fresno 559-230-3334
Glendale 818-500-1645 x247 or x243
22 Ag Alert April 12, 2023
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