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Growing Alfalfa
crop nutrition advice
Everything you need to know about alfalfa fertilization, best practice, suitable products, field trials and more.
Advice for growing Alfalfa (Medicago sativa)
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Alfalfa is grown across the world, in rain-fed and irrigated farming systems, in all types of soils, from tropical acidic soils with pH levels around 5-6, to calcareous soils with pH up to 8.5.
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Alfalfa is an all-year round crop, normally extending its crop cycle over 3 or 4 growing seasons.
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Good soil drainage is essential to grow alfalfa. Farm management, especially mowing and other machinery operations, need to be wisely planned to reduce soil compaction.
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Alfalfa is a key part of crop rotation, especially in organic farming systems, as it helps to improve soil fertility. On the one hand, deep rooting system (long tap root) of alfalfa allows exploration and nutrient cycling of deeper layers of soil into the farming system; and the other hand, through N fixation, occurring by the symbiosis with Rhizobium, at the root zone.
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The fertilization plan and management need to take into account Rhizobium’s physiology and nutrient requirements.
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Calcium improves nodulation of Rhizobium and sulphur supply is essential for effective N fixation.
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Lime amendments in acidic soil should be considered as preparation before sowing alfalfa.
Alfalfa just mowed, drying out in the field before collection
Alfalfa few days after mowing, drying out in the field before collection
Nutrient requirements
Estimated nutrient uptake (kg/t):
| N | P2O5 | K2O | MgO | SO3 | CaO | |
|---|---|---|---|---|---|---|
| Aboveground | 26 | 6 | 25 | 3.8 | 6.5 | 14 |
Source: IPNI
Dynamic of nutrient uptake over a crop season in alfalfa
Crop nutrient requirements and the dynamics need to be considered when setting up the fertilization plan. Nutrient uptake in alfalfa occurs during the growing season, in several waves during between cuts. Fertilizers with prolonged availability such as Polysulphate, are of high value in this case.
N uptake does not need to be considered in the fertilization, plan, as alfalfa uptakes its N from the atmosphere, through the symbiosis with Rhizobium at the root zone. However, nutrient availability will determine the effective nodulation and N fixation by the Rhizobium and, hence, it needs to be considered. Depending on the environmental and soil conditions, nutrients may be limited at different moments of the growing season. For example, sulphur may be limited early in the season, due to leaching of sulphate beyond the rooting zone during the winter period.
Other nutrients, such as potassium, may be more limiting later in the season as the crop uptakes the soil reserves.
The total quantity of nutrient taken up by the crop depends on the number of cuts that the farming system allows and its productivity. Productivity is higher during the second and third year, with over 20 tons of dry matter in irrigated alfalfa of southern locations.
Role of nutrients
| Key parameter | N | P2O5 | K2O | MgO | SO3 | CaO |
|---|---|---|---|---|---|---|
| Rhizobacteria nodulation | ++ | ++ | + | + | ++ | |
| N fixation | ++ | ++ | + | ++ | + | |
| Growth and branching | ++ | + | + | ++ | + | |
| Plant development (flowering) | ++ | + | + | + | + | |
| Drought resistance | + | ++ | ++ | + | + | |
| Dry matter production, and protein content | + | + | ++ | + | + | |
| Digestibility | + | +/- | +/- | ++ | + | |
| Winter resilience and stand longevity | ++ | + | + | ++ | + |
+ = improving; – = decreasing; +/- = different results, depending on the rate of nutrient applied
Source: Different sources and references in the literature
Nutrient deficiencies
Alfalfa plant on the right shows shorter leaves and reduced branching due to phosphorous deficient in comparison to a well-nourished plant. Source, Lissbrant et al., Purdue University Extension
Alfalfa crop showing some early symptoms of combined nutrient deficiencies, of potassium, sulphur and magnesium (irrigated alfalfa in north-east Spain)
Alfalfa Trials
Q&A
Here are some frequently asked questions we received from farmers regarding alfalfa.
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Soil fertility and nutrient availability to alfalfa, significantly affects quality of alfalfa. If look at the differences of alfalfa in different areas, with different soil types, we can get a good idea of its importance. At the same time, fertilization management can help us in getting the best quality in our farm. Soil analyses, and crop analyes, can give a precise picture, and a crop advisor can help us in setting up the right fertilizaiton plan for improved quality.
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Any organic materials adjustments in the soil before establishing an alfalfa feed, will bring a good portion of nutrients into the following seasons that need to be considered (limitations may apply, so follow local recommendations regarding application rates). Additionally, there are a good set of mineral fertilizers, coming from crude natural salts, which may be used for organic farming systems (the fertilizer producer will need to get the specific certification of inputs for organic farming and regional regulation may apply). Polysulphate fertilizer, is an excellent option, with proved results in organic for conventional alfalfa production, with the approval as an input for organic farming by most of the certification agencies.
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Sulphur deffiency in alfalfa can occur under many environmental conditions and over different soils types. Sulphur is essential for the functioning of the crop, but in this case, also for Rhizobium symbiosis within the crop and the effective N fixation, to fullfill crop requirements.
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The potential productivity of alfalfa on your farm will depend on the annual enviromental conditions and the quality of your soil. In most areas, if we achieved a good crop stand and keep weeds under control, the potential will be higher during second growing period. Depending on topography, soil types, past management, and others; productivity potentials in your farm may differ in different areas. Therefore it may be good to evaluate variability and consider the identification of management zones to evaluate the suitability of precission agriculture.
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Quite simply, it is a good option to rotate with your maize, wheat and other field crops. Alfalfa will allow exploration and nutrient transportation within deeper layers of the soil, adding N fixation through the symbioses of the crop with Rhizobium, at the root zone. Alfalfa roots remaining in the soil after 2 or 3 years of alfalfa will bring into the soil a good portion of nutrients for your crops later in the rotation. Special attention needs to be taken into the management of fertilization over the growing period of alfalfa to balance the exportation of nutrients (in particular potassium), with those in the soil amendment and fertilizer applications. This will help maintain soil fertility level for later crops in the rotation.
