NEWSLETTER ARTICLES

Strawberries, Soils and Water

FERTIGATION AND PLANT DEFICIENCIES

Nitrogen

Nitrogen fertilizers are the most commonly applied nutrients with fertigation. Effective use of nitrogen requires knowledge of how these fertilizers interact with water, and how they move through the soil. Nitrogen fertilizers should be grouped into 4 forms: Ammonia (NH₃). Ammonium (NH₄+), nitrate (NO₃-), and organic forms (ex. urea).

Nitrate nitrogen moves with the irrigation water. Nitrate nutrients generally result in faster adsorption and are translocated to the leaves once they are in the plant. Ammonium will remain in the roots and then change to nitrate as it is transported to the leaves.

Phosphorus

Phosphorus tends to remain near the place where it was applied. Most of the phosphorus fertilizers are applied as preplant fertilizers. Downward phosphorus movement is related to the soil texture. It moves farther in a sandy soil than in a clay soil.

Soil phosphorus is more available when the soil has high moisture. Also very young plants take up phosphorus faster than mature plants.

Potassium

Potassium fertilizer moves in the soil more than phosphorus, however, under sprinkler irrigation it only moves 2-4 inches. Under drip irrigation, potassium can move 1-2 feet in the area of saturated soil.

Crop potassium uptake is nearly equal to nitrogen. Similar amounts of potassium need to be supplied as nitrogen for adequate growth and fruit quality. Much of this potassium is available in the soil.

Plants grown on soils with excess potassium accumulate large amounts of potassium in the plant. The potassium is highly mobile in the phloem and is redistributed 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 potassium (K) and Calcium (Ca) and Magnesium (Mg) is well known. High K concentrations generally result in a Ca or Mg deficiency. In the Santa Maria area, because of the higher than normal Mg/Ca ratio, Ca deficiency is the major problem.

Calcium

Plants have a high calcium requirement. Calcium is used in plant cell walls. Calcium deficiency is associated with water balance in the plants. Higher than normal temperatures that cause higher plant transpiration or foggy overcast days with lower than normal transpiration can cause calcium deficiency in strawberries and vegetables.

A high level of Mg reduces the plant’s absorption of Ca and K. Magnesium excess is indicated when the exchangeable Mg is more than 40-60 percent of the cation exchange capacity.

Ca deficiency produces several characteristic symptoms. It is responsible for “tip burn,” hardening of fruit, root tip stunting, and growing point damage in strawberries, black heart of celery, brown head in broccoli, and blossom end rot in tomatoes and peppers. Calcium-deficient strawberry fruit shows a dense cover of seeds with smaller fruit size.