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.

Wet winter and spring. The rain keeps falling! According to the California Irrigation Management Information System (CIMIS), Manteca has received approximately 11 inches of rain this year (as of April 2^nd), and Staten Island has received approximately 19 inches, just to name a couple sites in the region. With that rain has come associated cool, possibly anoxic (lack of oxygen) soil conditions. While the amount of standing water has probably been less than what we saw in the winter of 2016-17, it still might be wise to keep an eye on fields in the coming growing season. In this article, Dan Putnam (UC Alfalfa and Forage Specialist) describes things to look for in alfalfa fields where there has been standing water over the winter. Of note, one of the issues that can result from saturated conditions is damage to root nodules where nitrogen fixation occurs (Fig. 1). This can cause lower nitrogen availability for the crop and reduced growth. While we generally never recommend applying nitrogen to alfalfa fields, there are a few rare situations where it may be beneficial, as noted in this article by Farm Advisor Rachael Long. A field with poor nodulation may be one situation where starter N (11-52-0) can help to regrow roots and reestablish nodulation.

Roland Meyer, UC Soils Specialist Emeritus, provided this information regarding water-run inoculum: it does not work well because the inoculum is not water soluble and floats to the surface. Rather, better success with re-inoculating fields comes with applying additional alfalfa seed coated with inoculant. The field needs to be irrigated soon after broadcasting the seed to get the inoculant into the soil.

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.

Stem Nematode. There are areas of San Joaquin County where stem nematode is a perennial problem, particularly in the northwest part of the county. Stem nematode reduces alfalfa growth in the spring (Fig. 2), and unfortunately, there isn't much that can be done to manage it, aside from variety selection. In areas prone to stem nematode, it is essential to pick varieties that are highly-resistant (HR). The National Alfalfa and Forage Association produces this leaflet with the resistance ratings of alfalfa varieties. I have also heard from the seed industry that selecting a lower dormancy rating (4 or 5) might help in the battle against stem nematode because alfalfa plants will delay “waking up” when the stem nematodes are most active. Remember, once conditions warm up, stem nematodes recede deeper into the soil and have less impact on alfalfa growth. So, in addition to HR varieties, consider lower dormancy varieties where stem nematodes are present.

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.

For the rest of this discussion, let's focus on K. While we generally recommend applying fertilizer in the fall, K fertilizer can be applied anytime, so it's not too late! (Keep in mind that in-season applications may not produce immediate results.) Alfalfa K deficiency is distinct (Fig. 3), but some varieties may not show these symptoms as readily. Either soil or plant tissue tests can help determine whether to apply K fertilizer. If a soil test (ammonium acetate extract) has a K value less than 40 ppm, then the soil is deficient, and a fertilizer application would likely improve plant growth. A value between 40-80 ppm is considered marginal, and applying fertilizer may improve yield. A value between 80-125 ppm is considered adequate. Muriate of potash (0-0-52) applied to the soil surface will be the most economical choice, but potassium sulfate (0-0-52, 18% sulfur) is another option if sulfur is also deficient. For soil K in the deficient range, correct it by applying 300-400 lbs K₂O/acre (if yield was around 8 tons/acre) or 400-600 lbs K₂O/acre (if yield was around 12 tons/acre). For soils that test in the marginal range, apply a rate of 150-200 K₂O/acre (if yield was around 8 tons/acre) and at a rate of 200-300 lbs K₂O/acre (if yield was around 12 tons/acre). Single applications of K should not exceed 200-300 lbs K₂O. If tests indicate that higher rates are needed, then split the 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

Registration is required. Visit http://ucanr.edu/rice2018 to register, or see this post for more information.)

 

2. USDA-NRCS Warm Season Cover Crops Field Day

Wednesday, August 22, 2018

10:00am-12:00pm

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

10:00am-12:00pm

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.

I presented the following information at the UC Davis Alfalfa Field Day last Thursday. Don't forget that UC Cooperative Extension will host a Small Grains and Soil Health Field Meeting on June 5th.

 

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 1^st because crop water use exceeded precipitation, so the crop drew upon soil moisture. On December 1^st, 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 11^th 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 20^th 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 20^th, 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 20^th.) 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. 

Agenda

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

10:40               Break

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 neclark@ucanr.edu.