Lately, I have been corresponding with growers and consultants about slow spring growth in their alfalfa fields. There are several reasons why growth may resume slowly this spring. I describe them below and discuss some way we may be able to manage for them.
Dormancy. I think we have a tendency to look over the figurative fence at neighboring fields and make comparisons. Keep in mind that the dormancy rating of a variety will have an influence on whether the field “wakes up” early in the season or tends to start growing a little bit later.
Nutrients. Nutrient management involves complex decision making and an understanding of agronomy, soils, and economics! When commodity prices are low, it can be hard to justify input expenses, but keep in mind that alfalfa is a perennial crop with perennial nutrient needs for maintaining yield and quality. Fall is the best season for addressing alfalfa fertilizer needs, particularly phosphorus (P) and potassium (K). There are soils in this region, especially in the Delta, that are low in K. We suggest soil sampling in the fall to gain an understanding for nutrient availability and then, as needed, applying fertilizer between October and February because it could take 60-90 days for the crop to fully respond to fertilizer application.
A couple other considerations for K nutrient management:
1) In new stands where the taproots may not yet be deep, soil sample in the top 12 inches to determine K availability. I have heard that some folks may be sampling down to 24 inches in alfalfa fields because they know alfalfa grows long taproots. While a mature stand will have developed taproots and may be able to scavenge for nutrients that deep, a younger stand probably cannot, and sampling too deep may give a false impression for nutrient availability.
2) Even when the soil test indicates adequate K, some K fertilizer may be needed in high-yielding crops. Alfalfa has a long growing season, and therefore, a long season of nutrient demand. Each cutting removes large amounts of nutrients with the plant tissue.
Use these rates to guide your K fertilizer applications – remembering that soil type, climate, and yield will influence fertilizer needs – and keep good records of all laboratory results, fertilizer applications, and crop observations. These records will be helpful in developing a long-term, economical fertilization program that maintains alfalfa yield and quality year after year.
Sending everyone best wishes for the season, and don't hesitate to reach out if you have questions or comments.
Mark your calendar with these upcoming meetings brought to you by UC Cooperative Extension, USDA-NRCS, and the California Rice Experiment Station. See the links or attached flyer for more information.
1. UCCE Rice Production Workshop
Tuesday, August 7, 2018
8:30am - 3:00pm (lunch included with registration)
5311 Midway, Richvale, CA 95974
2. USDA-NRCS Warm Season Cover Crops Field Day
Wednesday, August 22, 2018
Lockeford Plant Materials Center, 21001 N. Elliott Rd., Lockeford, CA 95237
No registration required. See agenda in the attachment (below).
3. UC Davis Dry Bean Field Day
Thursday, August 23, 2018
UC Davis Agronomy Farm: Take Hutchison Dr. approximately 1.5 miles west from Hwy 113, in Davis. Turn south on Hopkins Lane, and then take the first left turn (heading east) onto a gravel/broken pavement road with a row of olive trees; park along the fence. The field is located north of the Bee Biology Center.
4. Rice Experiment Station Annual Field Day
Wednesday, August 29, 2018
7:30am-12pm (lunch included)
Rice Experiment Station, 955 Butte City Hwy, Biggs, CA 95917
No registration required. For more information, visit http://www.crrf.org/.
4. UCCE Alfalfa and Forage Field Day
Wednesday, September 19, 2018
7:30am-12:30pm (lunch included)
Kearney Agricultural Research and Extension Center, 9240 S. Riverbend Ave., Parlier, CA 93648
More information will be forthcoming.
The 2012-2016 drought was one of the worst droughts in California history, not solely for the lack of precipitation, but also for its length, high temperatures, low snowpack, and water demand. It's probably safe to say that it won't be our last drought – or even our worst – as we look into the future. That said, what can we do in the California alfalfa industry to better manage for drought and the likely salinity impacts from a lack of water?
Water Management during the Growing Season: Dan Putnam wrote a blog article, “Why Alfalfa is the Best Crop to Have in a Drought” (http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=17721), which describes the water use of alfalfa compared to other crops, its adaptations to water-stressed conditions (like being deep-rooted), and ways we can adapt our management in low-water years. In particular, during the growing season, we can optimize water use and alfalfa growth during the early part of the season when yield and quality are highest, and dry down in the later part of the season. Dan's research has shown that the alfalfa will survive and resume growth when moisture conditions become favorable.
Water Management during the Winter Season: In 2013 through 2015, I cooperated with alfalfa growers in the Delta region to understand soil salinity conditions and leaching fractions in fully irrigated fields. I then modelled soil moisture and salinity conditions to understand these conditions during the winter season to help inform our management during the off-season.
Figure 1 (below) shows the daily water balance (precipitation minus crop evapotranspiration, ETc) and the change in soil moisture from field capacity (i.e. soil moisture after free drainage has ceased) at seven alfalfa fields during Winter 2013-14. This figure helps us to visualize why precipitation, particularly in a drought year, is not contributing more to soil moisture for early spring growth or to leaching salts. Total rainfall was approximately 8.2 inches, and for only a few storms (shown as peaks) was there enough precipitation to exceed crop water use (ETc).
The other lines on the graph (labelled Sites 1-7) illustrate the soil moisture deficit from field capacity. Soil moisture is expressed relative to field capacity because a primary interest in this modelling was to understand how much water is available for leaching salts. Until a soil reaches field capacity, we assume the water is held in the soil and not available for leaching. For all sites, the soil was drier than field capacity in the fall after the last cutting and before the first rain event. The lines decrease (i.e. become more negative) until December 1st because crop water use exceeded precipitation, so the crop drew upon soil moisture. On December 1st, there was a rain event that was enough to exceed ETc, so the soil moisture deficit decreased, but soil moisture was still less than field capacity. This trend continued for the remainder of the winter. If there had been enough precipitation to increase soil moisture above field capacity, then water would have been available for leaching, but this did not happen in Winter 2013-14. Precipitation rarely exceeded ETc, and each alfalfa site remained at a soil moisture deficit over the entire winter. In other words, precipitation was never high enough to fill the soil profiles, exceed the soils' field capacity, and leach salts.
Figure 2 (below) represents conditions for water year 2014-15. Total rainfall was approximately 11.8 inches, and precipitation exceeded ETc more frequently than in water year 2013-14. There was a period starting on December 11th where soil moisture exceeded field capacity (for all but Site 5), providing water for leaching. The highest peak on each site's line represents the total water available for leaching after accounting for ETc and filling the soil profile to field capacity. This peak occurred on December 20th and was 0.8, 3.3, 1.1, 1.8, 0, 1.4, and 1.2 inches, for Sites 1-7, respectively. (Site 5 was 0 inches because the soil moisture deficit remained the entire year; thus, zero water was available for leaching.) As this water was available for leaching, we assume that this water drained from the profile, and the lines drop to zero, or field capacity. Beyond December 20th, the daily water balance was never enough to exceed field capacity for any of the sites. (Note: the lines for all sites, except Site 5, overlap after December 20th.) So, no other water was available for leaching over the remainder of the winter season.
Conclusions: The 2012-2016 drought provided limited ability to manage salts with winter rainfall. For seven Delta alfalfa sites, we modelled 0 inches of rainfall available for leaching in Winter 2013-14. We modelled a range of about 0 to 3 inches of rainfall available for leaching in Winter 2014-15, depending on location. As a result, root zone soil salinity decreased in Spring 2015 (data not shown). When winter rainfall is not adequate for effective leaching, however, we need to be creative in our leaching strategies. Leaching during the season may not be advisable for crop health and nutrient management reasons, but we may be able to leverage winter rainfall with irrigation by wetting the soil profile before a rain event. A soil profile that is brought to field capacity with irrigation would likely result in rain water passing through the profile and leaching salts, rather than just soaking into a dry soil. We should also consider field modifications that improve irrigation efficiency prior to planting alfalfa, like increasing on-flow rate, narrowing border checks, or shortening field length, where possible. While drip irrigation in alfalfa is still not widely employed, in those fields that have it, it might be wise to also maintain a surface irrigation system for leaching. Our options are not many, but they could provide some relief when water is scarce.
Figure 1. The daily water balance (i.e. precipitation minus ETc) and the change in soil moisture from field capacity for Winter 2013-14 at seven Delta alfalfa sites. This model shows that there was no water available for leaching. All rainfall was soaked up and held by the soil.
Figure 2. The daily water balance (i.e. precipitation minus ETc) and the change in soil moisture from field capacity for Winter 2014-15 at seven Delta alfalfa sites. This model shows that there was some water available for leaching in mid-December, ranging from about 0-3 inches, depending on location.
The annual Alfalfa and Forage Field Day at the UC Kearney Agricultural Research and Extension Center (9240 S. Riverbend Ave., Parlier, CA 93648) will take place on Wednesday, September 20, 2017. Registration begins at 7:30am, and lunch is offered at the end of event. The event is free, and no registration is required.
7:30 AM Registration
8:00 Tram leaves for field tour
- Alfalfa Varieties for Pest and Disease Management – Shannon Mueller, Agronomy Advisor and County Director, UCCE Fresno
- Remote Sensing in Sorghum to Phenotype Drought Stress – Jeffery Dahlberg, Director, Kearney Agriculture Research & Extension Center
- Sub-Surface Drip Irrigation Alfalfa Management – Daniel Putnam, CE Agronomy & Forage Specialist, UC Davis
9:15 Tram Returns
9:20 Managing Weeds in Agronomic Crop Rotations – Kurt Hembree, Weed Management Advisor, UCCE Fresno
9:40 Alfalfa Weevil Management – Rachael Long, Agronomy & Pest Management Advisor, UCCE Sacramento, Solano, & Yolo Counties
10:00 Managing Sugarcane Aphid in Forage Sorghum – Nicholas Clark, Agronomic Cropping Systems & Nutrient Management Advisor, UCCE Kings, Tulare, & Fresno Counties
10:20 Irrigation & Nitrogen Fertility Management in Forage Sorghum & Corn – Robert Hutmacher,CE Specialist, UC Davis, & Director of West Side Research & ExtensionCenter
11:00 Irrigation Systems and Salinity Management in Forage Production– Daniel Munk, Agronomy & Irrigation Advisor, UCCE Fresno
11:20 Low Lignin Alfalfa & GMO vs. Conventional Varieties for Export – Dan Putnam, UC Davis
11:40 Optimizing Surface Irrigation in High Flow Systems – Marsha Campbell-Matthews, Agronomy Advisor Emeritus, UCCE Stanislaus
12:00 PM Lunch
Continuing Education Requested: DPR 1.5 hours of Other
For more information, contact Nicholas Clark at (559) 852-2788 or firstname.lastname@example.org.
Common purslane is a summer, annual weed that thrives under warm, moist soil conditions. It has succulent stems and leaves, grows prostrate, and is a prolific seeder. Under the right conditions, fleshy stems that break away can re-root and increase infestation. Common purslane is edible and does not present any toxicity problems for livestock. There are cultural, biological, and chemical approaches to controlling common purslane. In agricultural systems, cultivation will help manage this weed when the plants are in the seedling stage, and both pre-emergence and post-emergence herbicides are effective. More information on the biology and management of common purslane is available from UC IPM.
The moisture content of common purslane stems and leaves presents a problem when it is raked into alfalfa hay and baled. With moisture in the stems, the stems are still respiring. The process of respiration produces heat. If the heat cannot dissipate, there is the potential for the hay to catch fire. Dan Putnam, UC Alfalfa and Forage Specialist, describes this in a blog post. He explains how it is critical to monitor the hay curing process and stem moisture, and he provides some guidelines for bale moisture content. This situation with common purslane is a variation on the same theme. Moisture within the bales from the purslane presents the potential for trapped heat, so it is important to control this weed, monitor bale moisture, and stack bales so that heat can dissipate.
Glyphosate tolerance, or Roundup Ready technology, is available in alfalfa. Weed control in Roundup Ready alfalfa has been reported by UC Cooperative Extension weed scientists. In stand establishment studies, Roundup controlled common purslane in the seedling stage, but efficacy was reduced on mature plants. Additionally, there is the potential for this broad-spectrum herbicide to have reduced efficacy when used repeatedly. Under conditions of repeated use, a shift in weed species populations may occur to favor weeds like common purslane.
So now, let's go back to the present situation and this PCA's consideration to control common purslane with Shark. Shark is a PPO inhibitor, also classified as a contact herbicide. These herbicides will burn leaves and stems and are most effective on broadleaf weeds. Shark was approved for use in California alfalfa in 2014 and can be used in the winter when the alfalfa is dormant or in-season between cuttings. It can also be tank-mixed with other products, like glyphosate. (Note: always consult the label before making applications.) Another herbicide of the same chemistry class, Sharpen (saflufenacil), was approved in 2016 but only for winter-dormant alfalfa. Growers should be aware, however, that contact herbicides will burn alfalfa, and the best weed control will occur on smaller weeds and with thorough coverage of the herbicide. Alfalfa regrowth could potentially be reduced in the next cutting by the equivalent of 1-2 weeks of growth, but the crop should resume regular growth, and yield should recover. See this presentation for information on weed control in established alfalfa fields.