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Optimize seed-to-soil contact for high alfalfa yields

Tim Clark Published on 27 February 2015
alfalfa stand

A thick, healthy stand is every alfalfa grower’s goal. Mother Nature throws plenty of curve balls, but using good management practices can help you come out the winner.

To successfully establish a crop of alfalfa, you must optimize seed-to-soil contact; it is the key to optimal yield. But how do we optimize that?

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Soil (and air) temperature

The first step to optimum seed germination is to plant with the proper soil temperature. Soil must be at least 3ºC and ideally 18ºC. Since sandy soils warm up faster than clay soils, lighter soils can be seeded earlier.

Soil condition, aggregate size and moisture also play an integral role in the rate at which the temperature of the soil can warm. Use a soil thermometer for accuracy.

Proper air temperature is also essential when seeding; an air temperature holding at -3ºC or less for more than four hours will kill an alfalfa plant.

Soil moisture levels

The next management tool to ensure a bountiful crop is appropriate soil moisture levels. It’s essential that soil is dry enough to establish a good, firm seed bed regardless of tillage practice. If it’s too wet, the soil aggregates in clumps, which will not allow you to maximize your seed-to-soil contact. Don’t waste your time seeding when it’s too wet.

Proper soil moisture, on the other hand, aids quick germination. Determining appropriate moisture is trial and error. Take a shovel and dig a small hole. If the soil you turn over is cloddy and clumpy, it’s too wet.

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Another good way to tell is to stand in your field: When you take a step, you should only sink a quarter-inch to a half-inch at the most. If you feel comfortable standing there, your plant will, too.

Can the soil be too dry? Yes, if it’s too dry the seed will lay dormant and won’t germinate. Seeds need solid moisture around the seed bed to start germinating. In addition, the seed may germinate and die if there is not enough moisture for the plant to continue to develop a root system.

Many growers who have light, loamy soils find that it helps to press in or lock moisture around the seedbed. This is a great practice but comes at the expense of additional equipment, time and compaction from another pass across the field.

Soil pH

Although soil temperature and moisture are at the top of the list for soil management, the next important management tool is soil pH. The pH for alfalfa needs to be between 6.7 and 6.9. I advocate using lime to keep the pH in balance.

Most alfalfa growers already know that lime improves the soil structure. It helps develop the nitrogen-fixing bacteria Rhizobium and adds calcium and magnesium to increase the phosphorus availability.

There are soil pH test kits available from public universities and retailers. If your soil has a high salt content causing adverse pH levels, there are varieties of alfalfa bred to grow in high-salinity soils.

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Soil fertility

The last soil element to consider is fertility. Nitrogen, potassium, phosphorus and sulfur are essential to healthy alfalfa plant growth. The best fertilizer? Manure.

It’s readily available on farms and is part of a sustainable farming system. Test your manure and soil, see what nutrients you have, then match with a supplemental fertility program.

Make sure to manage fertility within your nutrient management plan. No one type fits all and certainly not all manure is equal, but it is the best fertilizer you can get when it comes to alfalfa.

To review, the whole management strategy is to optimize seed-to-soil contact. Proper soil management will give you the foundation to establish and maintain optimal yields. Next, we must take particular consideration of the seed.

Seed variety yield

Look for seed that has the highest-yielding genetics. Data is available from universities, independent testing organizations and industry-provided data. Be mindful of the source and check multiple sources to lessen the potential for bias.

The majority of alfalfa seed companies can provide you with data relative to the product you are going to purchase. One company goes the extra step to test their products in an on-farm alfalfa strip-trial network and provide growers with that data as well.

Seed variety persistence

Besides striving for a high yield, you need a variety that has persistence to endure your cutting and crop rotation schedule. Persistence is the seed’s durability over time. How long do you want to have that stand? How does that seed tolerate normal stress elements such as drought or cutting schedule?

How many cuttings are you planning? Each alfalfa product has varying features and benefits that can “play” better to your persistence expectations. Some seed can perform well for three, four, even five years – but others simply will not.

Seed variety disease and pest tolerance

Disease tolerance is another factor to consider. Every product is rated on the industry-accepted disease rating index (DRI). There are seven primary alfalfa diseases, and each is given a performance rating from one to five against each challenge. A higher rating means better disease tolerance.

Relating this back to soil, more adverse soil conditions foster more disease pressure. Heavy-saturated soils, high pH, high salt and other soil challenges lead to the onset of more diseases and pest pressures.

In these environments, more consideration for the DRI score is needed because alfalfa faces more pressure while growing.

Other threats to the alfalfa crop include pests. Nematodes, potato leafhoppers, aphids and many other pests challenge alfalfa and inhibit high yields. Look for varieties with a strong tolerance to insects or seed treatments to aid in the suppression of alfalfa pests.

Germination and seed coating

Keep in mind you’re not only planting a seed variety but a seed product. When you buy seed, check the seed bag tag. Bags may have a nice design, but the packaging doesn’t indicate the product contents. Seed germination, coating material, date tested and origin of seed are just a few items on the tag.

The most important part of growing alfalfa is seed germination, and the industry standard for the germination rate of that seed should be 90 percent.

That means out of 100 seeds planted, 90 will germinate. Look closely at the tag, as some seed will have a poor germination rate – sometimes as low as 65 percent.

Seed coating is another factor to consider. You can buy seed from uncoated to 34 percent coating material. This can have a huge impact on the price per pound of actual seed you are buying. Consider two products priced at $200 per bag.

The uncoated seed is $4 per pound; however, the 34 percent coated seed is $6.06 per pound because 17 pounds of the product is inert coating material.

There is no conclusive scientific data to prove that coating seed improves germination. Check seed tags and make sure you match what is in that bag with your targeted seeding rate.  PD

PHOTO
By paying attention to soil and air temperature, moisture levels, pH and soil fertility, growers can set the stage for a high-yielding crop. Optimize seed-to-soil contact and do some thorough research on alfalfa seed yield, variety persistence over time, tolerance to diseases and pests, and seed bag tag data. Integrating these management practices from the start will bring growers closer to a beautiful, healthy, high-yielding alfalfa crop. Photo by PD staff.

Tim Clark
  • Tim Clark
  • Forage Product Manager
  • Dairyland Seed

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