NEWSLETTER ARTICLES

Strawberries, Soils and Water

HIGH SOIL PHOSPORUS AND POTASSIUM

Soil testing can help by identifying fields low in plant nutrients and soils with excessive amounts.

Excess phosphorus (P) and potassium (K) have been applied to fields without testing the soil or evaluating the need of additional fertilizers. As a result, some fields have soil test levels of P and K so high that additional applications of fertilizer will not boost crop yields and may interfere with the absorption of other needed nutrients.

Lack of economic crop returns, and in some cases even a negative economic return, is not the only problem associated with excess applications of P and K.

Although these two nutrients will not leach from the soil, they can be removed from the field through erosion.

Plants grown on soils with excess potassium accumulate large amounts of potassium in the plant. The potassium is highly mobile in the phloem and redistributes the K from older leaves to young leaves or growing organs.

When this "luxury consumption" of potassium occurs due to high concentrations in the soil, the absorption and translocation of other nutrients may be depressed.

The relationship between K and Magnesium (Mg) is well known, as is the relationship between K and calcium (Ca). High K concentrations generally result in an Mg deficiency. When the K is in greater imbalance, Ca deficiency occurs. In the Santa Maria area, because of the higher than normal Mg/Ca ratio, Ca deficiency is the major problem.

An excess of Phosphorus (P) can cause an iron (Fe) or zinc (Zn) deficiency.

Soils should be routinely tested in order to monitor the levels of nutrients for either an increase or decrease in the P or K status of the field. Once you have established the soil P or K concentrations, and the incline or decline rates, fertilizer programs can be adjusted to fit the cropping pattern.