Managing Calcium Demand in Citrus

Relying on the unpredictability of available calcium from the soil could lead to slowed growth during key growth periods and poor fruit quality. Nitrogen is also a key nutrient for establishing new growth and is usually the driving factor behind new growth. For citrus, nitrate nitrogen is the preferred form of nitrogen for plant uptake. Nitrate nitrogen and calcium are both key factors in plant health pre-bloom through fruit fill, YaraLiva® CN-9® calcium nitrate provides both of these nutrients in soluble and preferred forms.

The amount of nitrogen needed for a citrus crop varies by species and location; however most citrus growing areas have established some range of standard practices as far as nitrogen rates are concerned. Calcium fertilization, on the other hand, varies widely across regions. Some areas fertilze with calcium and some areas rely on soil test calcium levels to support the plant’s growth. Although most soils do contain high soil test calcium levels in the soil structure, most of that calcium is highly insoluble. This can be seen in comparing a water soluble soil test with a standard soil test method like Mehlich 1 or 3. Predicting when soil test calcium will become available is very difficult, so fertilizing with calcium at key growth stages is critical to ensure soluble calcium is available when the plant needs it. To determine how much calcium might be needed during fertilization, we can look at crop uptake and removal and calculate total calcium demand based on how much calcium is in the plant and how much is removed in the fruit.

Grapefruit removes about 0.82 pounds of Ca per ton of fruit harvested (ref 1). With a yield of 400 boxes to the acre (85#/box), that is only about 14 pounds of Ca removed per acre from harvested fruit. However, most of the calcium in a citrus tree is not in the fruit, approximately 90% of the calcium taken up by a citrus tree is put into the tree itself, leaves, branches, trunk, and roots (ref 2, figure 1). A 400-box yield per acre of grapefruit means that acre needs about 140 pounds of soluble Ca per acre per year. Outside of peak demand, some of this calcium is available from the soil, but during peak demand soluble calcium like YaraLiva CN-9 calcium nitrate should be applied for maximum tree health and yield.

Calcium is the nutrient in highest demand for citrus production (figure 1, figure 2). Demand and uptake can vary by tree species and even cultivar. In figure 2, we see that for a 40,000 pound/acre (45 mt/ha) orange yield, the trees need 200 pounds (225 kg/ha) of calcium per acre per year.

Figure 1

Figure 2

Citrus trees have peak calcium demand during the stages of bloom, fruit set (cell division), and fruit enlargement (cell expansion). To meet this need, calcium fertilization should occur just prior to each of these stages. Since peak calcium and peak nitrogen demand occur at similar times (figure 2), calcium fertilization timing can occur at the same time as nitrogen fertilization.

YaraLiva CN-9 liquid calcium nitrate provides a soluble source of calcium and nitrogen in the form of nitrate. Use YaraLiva CN-9 at peak demand to meet all of your calcium needs and most of your nitrogen needs. YaraLiva CN-9 is 9% nitrogen and 11% calcium by weight.

References:
Ref 1: Koo, 1958; Chapman, 1968; Malavolta, 1989. IFA Manual
Ref 2: Boaretto Et Al., 2007.

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