Nutrition: General Recommendations

A basic fertilizer program will vary according to the varieties, the soil types and fertility and the production/market strategy of the grower. Hence the following recommendations are quite generalized and should be modified according to the experience that you gain over time.

Nitrogen

Commercial varieties from California such as Camarosa have a high demand for nitrogen. Varieties from other breeding programs have their own distinct requirements.  You should calculate an uptake of about 250 - 275 kgs of elemental N per hectare over the course of a single production season. More important than the total amount of N is the form of application and the timing of the applications. The goal is to maintain a constant amount of N in the plant tissue during the period of flowering and fruiting. Please keep in mind the following recommendations:

• Do not utilize animal manure as a source of nitrogen. Plow down green manure crops or crop residues to add organic matter to the soil but avoid animal manure at all costs.
• On the basis of soil analysis, calculate the residual amount of N in the soil at time of planting. The difference between this residual and the total uptake is the amount of N that you will have to apply in order to maximize yields. For example, if your analysis shows a residual of 100 kgs of elemental N per hectare in the soil prior to planting, you will have to apply between 150 and 175 kgs of N to reach the goal of the 250 - 275 kgs that the plantation requires during the production season.
• Apply 20 percent of the additional N between the time of transplant and the formation of the flower buds in the crown of the plant (about 6 weeks prior to flowering). Apply 80 percent of the additional N in bi-weekly applications from the onset of bud formation to the end of the production season. Please note that the Sweet Charlie variety from the University of Florida requires only 50 percent of the nitrogen of the California varieties noted above. See the attached annex for an example of nitrogen management in a hypothetical production case utilizing California varieties.

Phosphorus and Potassium (P and K)

Unlike nitrogen, P and K are generally insoluble and do not move with the water through the soil profile. For this reason, the producer can make a single application of P and K to the soil prior to forming the beds. Note the exceptions below. Commercial strawberry varieties will take up between 180 and 220 kgs of elemental P and K per hectare during the course of a single production cycle. An application of 500 kgs of Superphosphate (36%) prior to bed formation supplies sufficient P for strawberry production. The farmer should disk in the fertilizer at least three times to make sure that it is well mixed into the soils.

The key variable in calculating the utilization of P and K is the amount of the nutrients that are actually available to the plant in comparison to the amount that is available in the soil. Some soils have a high fixation rate. The analysis may show a high P content but the fixation may be such that only a very low portion is available to the plants. In this case, the plants will be deficient in P or K even though the elements are in the soil. It is important to utilize the "available P/K" analysis rather than the "total P/K" analysis when planning the nutrient program. An analysis that shows a range of 60 - 120 ppm of available P and K is an indication of adequate nutrients for sustained production.

Where fixation is a problem, the farmer may have to make applications of P and K in the bed. In this case, the fertilizers are placed in bands that are 2 cm. below the root level and 2 cm. to the side of the line of plants. Precision application shoes or injecting knives are important for this type of application. Concentrating the fertilizers in bands partially overcomes the tendency of the soils to fix and immobilize the elements.

Calcium

Strawberry plants utilize as much calcium as phosphorus and potassium. Where soil pH is 7.2 or higher, I recommend yearly applications of 1,000 - 1,500 kgs of gypsum (calcium magnesium sulfate) per hectare as part of the regular soil preparation practice. If the soils are acidic, then similar quantities of agricultural lime will raise the pH and supply the needed Ca to the plants. Calcium deficiencies will show up in a deterioration of fruit quality and reduced yields.

Example of a Fertilization Scheme for California Strawberry Varieties

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