How to Measure Alfalfa Quality

Dr. Harold Willis

But how is the quality of animal feed measured? There are many ways of measuring, or attempting to measure feed quality, and we do not need to go into detail about them here. Briefly, some methods attempt to measure the total energy value of feeds, based on actual feeding trials with animals or by measuring the number of calories contained in the food. Other methods measure only the protein content of the feed as an index of quality. In one such method, one of the most commonly used, only the nitrogen content of the feed is measured and the result is multiplied by 6.25 to give an estimate of protein content. This quantity, called crude protein, is a very inadequate and often misleading protein measure, for in poor quality sick plants, there is often an excess of nitrates and other non-protein forms of nitrogen. A better measure of protein quality would be an analysis of the amino acid content, since a certain balance of amino acids is needed for high quality protein, but such tests are very expensive.

Now that you have seen the importance of high quality feeds, how do you go about growing them yourself?

Balanced fertility

The most important factor that determines the quality and yield of a crop is the soil. We have already covered the importance of loose, well aerated soil with plenty of humus and beneficial microorganisms. The other aspect of good soil is to have the right fertility—the proper amounts and balance of soil nutrients—what the plants need, when they need them.

The actively growing forage plants need those plus the others that crop plants need. According to a typical study (which may not have been made with balanced fertility), 10 tons of alfalfa removes from the soil 500 lb./acre of nitrogen, 50 pounds of phosphorus (120 pounds of P2O5), 500 pounds of potassium (600 pounds of K2O), 350 pounds of calcium, 60 pounds of magnesium, and 50 pounds of sulfur. Also needed are 11 oz./acre of boron, 10 oz. of zinc, 1.1 lb. of manganese, 1.5 lb. of iron, and 3 oz. of copper. The iron and copper are also needed by nitrogen-fixing bacteria inside root nodules, plus they also need molybdenum and cobalt in very small amounts.



Nitrogen is definitely needed by legumes, but if things are working right, they can get most of their needs from nitrogen taken from the air (which is 78% nitrogen) by bacteria in root nodules. However, if soil conditions do not allow the nodules to form or if they are not functioning well, legumes will take nitrogen from the soil, just as any other plant that has no nodules. Healthy, active nodules will be pink or red inside due to a red pigment, leghemoglobin; a greenish color inside indicates a sick or dying nodule. Nodule bacteria also require oxygen and freedom from toxic chemicals. Many alfalfa fields in this country have few or no nodules, mainly from poorly aerated soil and toxic substances.

Effective nodules can fix from 75 to 240 pounds of nitrogen per acre per year, which isn’t bad for free fertilizer! If your alfalfa doesn’t have nodules, you had better find out what’s wrong.


Legumes are large consumers of calcium, and to obtain high quality forage that promotes animal health and productivity, large amounts of calcium are essential. Calcium serves so many important roles in the soil medium that it seems extremely doubtful that alfalfa culture can be very successful without it. Calcium is vital for cell division and healthy cell walls, for root growth and root hair formation, for enzyme activation, and protein production. A deficiency of calcium has been found to decrease resistance to insect pests. Calcium also stimulates growth of beneficial soil microorganisms, including nitrogen-fixing bacteria, and helps counteract toxins in the soil and in the plant.

If your soil needs it, calcium should be applied even though the pH test results show no need for lime to “correct” soil acidity, because the plants need the calcium no matter what the pH. High pH can be caused by other elements than calcium.


Phosphorus is the major element most often overlooked in crop fertilization programs. Even though the soil has large amounts of phosphorus in its minerals, it is nearly all chemically locked up and unavailable to the plant at any one time. If soil conditions are favorable, the beneficial soil microorganisms will slowly break down mineral phosphorus and make it available, but unfortunately, most of today’s soils are in such poor shape that plants cannot obtain their phosphorous needs.

Phosphorus is essential for quality crops.

Phosphorus is needed for all cell activities by transferring energy within the cell, it is part of the cell’s genes and membranes, and is important in growing roots and stem tips. Phosphorus is especially needed by young plants; as much as 75% of a plant’s supply of phosphorus may be absorbed by the time it has produced 25% of its dry weight. Phosphorus also directly or indirectly increases drought and disease resistance and nitrogen fixation, and decreases maturity time, especially in cool temperatures.


The main problem with growing alfalfa today is that traditional recommendations are for too much potassium in proportion to the other elements, and you cannot grow really top quality forage when the soil’s available potassium exceeds available phosphorus or calcium. Now don’t get me wrong, you can grow lots of alfalfa with high potassium—and pretty good looking alfalfa, too. Scores of research experiments prove that. But it is not the highest quality animal food. It is what is called carbonaceous—too much cellulose. What animals need is proteinaceous feed, with an increased proportion of high quality protein, and that kind of forage can only be grown when the soil has plenty of calcium and phosphorus and not too much potassium.


No single element is more important than another for optimal plant growth; all are necessary, but in different amounts or proportions. Therefore, the proper balance of nutrients is the important thing. And that means the nutrients available to the plant, not the total present (but tied up) in the soil. That’s the only way to grow top quality crops.

One of the keys to keeping the right balance of nutrients is to have well aerated soil with plenty of humus, for humus and its associated microorganisms tend to provide balanced nutrition to plants. But that’s not all. They also provide many other valuable pluses. They produce growth-stimulating substances, improve the general vigor and health of the plant, and combat plant diseases and pests. Properly fertilized alfalfa stands can live 30 or 40 years.

Experiments have shown that unbalanced fertility may result in increased yields (bulk), but also give crops of lower nutritional value to animals. For example, alfalfa was fed to Guinea pigs. Moderately fertilized alfalfa increased the animals’ weight gain, while alfalfa fertilized with too much phosphorus and potassium decreased weight gains.

Source: How to Grow Great Alfalfa