A question came to me from a crop consultant. His alfalfa grower asked him how he could increase crude protein (CP) in his alfalfa. The buyer of the alfalfa, for the most part, is happy with the hay. For example, the buyer is happy with the total digestible nutrients (TDN), but he would like to see a little higher CP. The consultant said that the grower is generally on a 28-day cutting cycle and is generally cutting the hay pre-bloom. He wondered if nitrogen (N) fertilizer would help to improve CP.

The best way to improve CP is to: 1) cut early, 2) choose a more dormant variety (but give up yield), and 3) manage the harvest to retain the leaf fraction. Since this grower is already cutting pre-bloom, and since the grower is not yet replanting, that would leave option 3. Retaining the leaf fraction is important because the protein content of the leaves is higher than that in the stems. Trying not to rake the hay when it is especially dry might help to retain the leaves. 

Let's now focus on the consultant's question of whether N fertilizer could help to improve CP. The UC Irrigated Alfalfa Management production manual states that N fertilizer has resulted in higher CP in some instances but that an equal or higher number of trials showed no improvement to CP with N fertilizer. Dan Putnam, Rollie Meyer, Vern Marble, and other forage researchers have, for a long time, recommended against fertilizing alfalfa with N.  This is based upon field data, economics, and logic! 

1. Forage Quality. While N fertilizers can (in some cases) increase the apparent CP of the forage by a point or two, this "protein" is not actually well utilized by ruminants. N fertilizer usually results in a higher non-protein nitrogen content (NPN) which is NOT protein, but free N in various forms (e.g. nitrate or free amino acids), which is immediately released into the rumen upon ingestion and forms ammonia. The ammonia must be excreted by the animal at a metabolic cost (ATP), so it is actually costing feed energy.  It also results in excess urea in the manure. So, even though it looks like the protein is a little higher, it isn't actually. Remember, CP is measured N content (not just protein) multiplied by 6.25.

2. Economics. Small differences in yield are sometimes (not always) observed with applied N; however, those are rarely economically advantageous. Remember that the uptake levels of alfalfa are very high. A 10-ton Central Valley alfalfa crop will remove about 700 lbs of N, which with losses, one would need to apply close to 1,000 lbs N/year to meet the N needs of the crop.  One could never cost-effectively fertilize to satisfy this need.

3. Losing your free N.  N applications or high soil N have the tendency of suppressing N₂ fixation by making the Rhizobium lazy.  Fertilizers would mostly just replace fixed N. Atmospheric N contributions to alfalfa growth are a major environmental benefit, and it's a shame not to take advantage of it.

4. Weeds. N applications encourage weeds, especially grasses. This negatively impacts quality.

5. Trade-off with Energy.  Keep in mind that some alfalfa hay crops that have low N and low CP also have high TDN (energy values) such as the well-managed Intermountain spring cut hays grown under cool temperatures. This is due to dilution - if carbohydrates accumulate in the leaves, (e.g. 5-8 percentage points higher), then CP (and NDF/ADF) will be lower.  When something goes up, something else goes down. Since energy tends to be more valuable in the marketplace, however, this is a good thing!

Having said all of this, there are some rare situations where N fertilization may be helpful to get the crop going after the roots have been compromised, but even these are unusual.  Rachael Long detailed this in the blog When is N fertilization to alfalfa beneficial? Almost Never!   

Dan Putnam does have a lingering question about applying N fertilizer in alfalfa and that is whether very small amounts (e.g. via drip irrigation) might be effective at hastening regrowth after each cutting. Growers using drip have done this, and Dan thinks it could work with overhead sprinklers or with buried drip lines where the N can be 'spoon fed' and carefully managed. We need data, however, to prove whether or not this would be effective.  Dan suspects the differences would be minor.

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.

 

 

Here are a few announcements from UC Cooperative Extension. Please don't hesitate to reach out to me with any questions.

1. UC Cooperative Extension in San Joaquin and Stanislaus counties is partnering with the American Farmland Trust (AFT) to connect women landowners with resources, information, and a network. Women for the Land is an AFT program that began in the Midwest and Mid-Atlantic states, providing women landowners with information for land conservation. The meeting details are below, and documents are attached at the bottom of this post. Please share the flyer with interested women in our region!

• Tuesday, March 26, 2019. 1:00-4:00pm. Cabral Agricultural Center, 2101 E. Earhart Ave., Stockton, CA 95206. To register, visit: farmland.org/SanJoaquinCountyLearningCircle or call 916-448-1064.
• Wednesday, March 27, 2019. 1:00-4:00pm. Stanislaus County Agricultural Center, 3022 Service Rd., Modesto, CA 95358. To register, visit: farmland.org/StanislausCountyLearningCircle or call 916-448-1064.

 

2. UC Cooperative Extension is hosting two Weed Science field days in the San Joaquin Valley. Event details are below, and flyers are attached at the bottom of this post. The events are free, but space is limited, and registration is required by calling the UCCE Merced County office at 209-385-7403. Pesticide applicator continuing education credits are available at each event (3.5 units).

• Tuesday, April 2 2019. 8:00am-12:15pm. Kearney Agricultural Research and Extension Center, 9240 South Riverbend Road, Parlier CA 93648
• Thursday, April 11, 2019. 8:00am-12:15pm. Westside Research and Extension Center, 17353 West Oakland Avenue, Five Points, CA 93624

 

3. The UC Pest Management Guidelines for dry beans have been updated. The guidelines provide information on 19 insect pests, 18 diseases, 6 abiotic disorders, nematodes, and weeds, including a new table of registered herbicides and timings for dry beans.

Nitrogen (N) is part of a balanced, natural cycle in the environment among the atmosphere, soil, plants, animals, and water. Nitrogen is the most important element needed by crops, and we often add nitrogen fertilizer to optimize crop productivity. Nitrogen use in agricultural systems must be reported for regulatory compliance under the Irrigated Lands Regulatory Program and the Dairy Order to help ensure that a greater fraction of the applied N is recovered in the harvested crop and not lost to the environment. Nitrogen management gives consideration to the four R's:

• Right source: selecting the fertilizer source that matches the crop need and minimizes losses,
• Right rate: applying the right amount based on crop need and nutrient availability through other sources,
• Right time: applying the nutrient when the crop can use it,
• Right place: fertilizer placement that optimizes the crop's ability to use it.

The four R's address management considerations (e.g. fertilizer program, irrigation), but site characteristics (e.g. soil, cropping system, weather conditions) also influence N recovery in the crop. Also important to improving crop N recovery is understanding barriers to adopting best management practices, such as costs or risks to crop quality or yield.

While the four R's articulate four principles for N management, the N cycle in cropping systems is complicated. Nitrogen can be introduced and lost by various paths. We generally add N with organic matter amendments – such as crop residues, compost, or manure – or with fertilizer. While organic matter amendments must be mineralized before the N is available for plant uptake, fertilizer N is readily available for plants to use. That said, plants generally take up N at different stages during their life cycle, and there is a risk for N loss if the N is applied or becomes available when the plants do not need it.

Technologies have been developed to mitigate N losses from cropping systems. These technologies are collectively known as enhanced efficiency fertilizers (EFF) and include additives, physical barriers, and chemical formulations that stop, slow down, or decrease fertilizer losses. Nitrogen stabilizers are one example and are fertilizer additives intended to improve crop N use efficiency and reduce N losses to the environment by interrupting the microbial processes that change N to its plant-available forms. We developed a trial to evaluate two N stabilizer products with the objective of determining whether the treatments improved corn silage yield or plant N status compared to fertilizer alone. We did not attempt to measure N losses from the system (e.g. leaching, denitrification), as these are very challenging to quantify.

The trial took place in San Joaquin County on a DeVries sandy loam soil. A description of the methods can be found in the full report. Sidedress fertilizer application occurred on June 21, 2018 and provided approximately 105 lbs N per acre (UAN 32). Four treatments were applied at sidedress, when plants were at V3-4 stage of development (Figure 1). The N stabilizers were applied at the label rates, and the treatments were: 1) Vindicate (Corteva Agriscience) at 35 fluid ounces per acre, 2) Agrotain Plus (Koch Agronomic Services) at 3 pounds per acre, 3) combination of Vindicate and Agrotain Plus at aforementioned rates, and 4) fertilizer-only, no stabilizer product (“untreated”). Treatments were randomly applied in three replicate blocks. Aside from the treatments, the trial was managed by the grower in the same manner as the field.

We evaluated soil N status, plant N status, and silage yield. Soil results are available in the full report. There were no statistically significant differences in plant N status or yield (Table 1). Mid-season (i.e. silking, R1) leaf N averaged 2.88 percent across treatments, and aboveground biomass N at harvest averaged 1.12 percent. At mid-season, leaf N from 2.7 to 3.5 percent indicates that the plant had sufficient N to carry the crop to harvest, and at harvest, aboveground biomass N from 1.0 to 1.2 percent indicates that the N fertilization program was adequate for maximizing yield. Thus, it appears that the trial was not deficient in N. Calculated to 30 percent dry matter, average yield across treatments was 38.8 tons/acre, and dry matter was 35 percent. There was a trend for the two treatments with Vindicate to have higher N removed than the two treatments without it, but the difference was not statistically significant.

In summary, N is part of a balanced, natural cycle in the environment and is the most important nutrient in cropping systems. Giving consideration to N management will help ensure that a greater fraction of the applied N is recovered in the harvested crop and not lost to the environment, and keeps growers in regulatory compliance. Enhanced Efficiency Fertilizers, such as N stabilizers, have been shown to improve crop yield in regions like the Midwest and the Northeast, and may help to mitigate N losses to the environment. In our trial, we evaluated the efficacy of N stabilizer products for improvements in corn silage yield or plant N status compared to fertilizer alone. Under the management and environmental conditions of this trial, we found no differences in yield or plant N status; however, plant and soil tests indicated that N was not limiting in the trial. If N was lost from the system, the loss was not large enough to result in N limitation in the control. Future study should test these products using different N sources and N rates (e.g. grower rate versus grower rate minus 50 lbs N/acre). It may be possible to reduce the fertilizer N rate without sacrificing yield.

This trial was made possible with the generous cooperation of Hank Van Exel and Van Exel Farms; Carl Bannon and Steven Colbert (Corteva Agriscience); Brad Schrenk (Simplot); Eric Ellison (Koch Agronomic Services); Nick Clark and Daniel Geisseler (UCCE); and Shirley Alvarez, Cheryl Gartner, and Dan Rivers (UCCE technicians). An in-depth report is available from my website. Please don't hesitate to contact me with comments or questions.