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Growing Alfalfa crop nutrition advice
Growing Alfalfa crop nutrition advice
Everything you need to know about alfalfa fertilization, agronomic best practices, suitable ICL 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 a perennial crop, normally extending its productive period over at least 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 considered 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. The deep root system (long tap root) of alfalfa allows exploration and nutrient cycling of deeper layers of soil into the upper soil profile. Also, alfalfa fixes atmospheric nitrogen through its symbiotic relationship with Rhizobium bacteria.
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The fertilization plan and management should not only consider nutrient uptake and removal by the alfalfa crop, but also the nutrition required to promote optimal N fixation as a result of Rhizobia. Calcium improves nodulation of Rhizobium and sulfur supply is essential for effective N fixation.
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Lime amendments in acidic soil should be considered as preparation before sowing alfalfa.
Nutrient requirements
Estimated nutrient uptake (lbs/ton):
| N | P2O5 | K2O | Mg | S | Ca | |
|---|---|---|---|---|---|---|
| Aboveground | 50-70 | 8-16 | 48-72 | 5-8 | 4-6 | 28-35 |
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 | Mg | S | C |
|---|---|---|---|---|---|---|
| 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 just mowed, drying out in the field before collection
Alfalfa few days after mowing, drying out in the field before collection
Alfalfa Trials
Guides & Articles
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 parameters like crude protein and digestibility. In particular, supplying adequate amounts of nutrition to optimize N fixation, along with S to balance N, are important factors for increasing protein content.
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Alfalfa has the benefit of not requiring N fertilizer applications, but other nutrients including potassium, calcium, and sulfur should be considered due to their high removal rates by alfalfa or their importance to feed quality. Polysulphate is an excellent option for supplying K, Ca, Mg, and Swith the approval as an input for organic farming by most of the certification agencies.
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Sulfur deficiency in alfalfa can occur under many environmental conditions and over different soils types. Sulfur is essential for the functioning of the crop, but in this case, also for symbiotic N fixation, to fulfill crop protein requirements.
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The potential productivity of alfalfa on your farm will depend on the annual environmental 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 season. 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 precision agriculture approaches like variable rate application.
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Quite simply, it is a good option to rotate with your corn, wheat and other field crops. Alfalfa will allow exploration and nutrient transport from deeper layers of the soil, while also adding N from symbiotic. Special attention needs to be given to the management of fertilization over the growing period of alfalfa to balance the removal of nutrients (for example, potassium), with those in the soil amendment and fertilizer applications. This will help maintain soil fertility level for subsequent crops in the rotation.
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