Role of Calcium in Melon Production

It is also involved in cell wall division and elongation. Calcium also has a direct influence on the salt balance within plant cells and activates potassium to regulate the opening and closing of  stomata to allow water movement from the plant.

Calcium & fruit quality - firmness and cracks

Poor calcium nutrition results in a wide range of fruit quality problems, such as lack of firmness (cv. Galia - Muskmelon, South Africa). High levels of calcium thicken cell walls and firm the fruit. However, calcium needs to be balanced with adequate supplies of boron to prevent cracking.

Calcium and blossom end rot

Low calcium levels in the fruits can result in blossom end rot with a significant loss in marketable yield (Watermelon, Italy). One of the most common inducing factors for BER is water stress either due to a deficiency or excess.   Under high humidity conditions, transpiration slows and uptake of calcium – which is solely transported within the transpiration stream – is limited.

Calcium and glassiness

Low calcium supply can induce an early softening, or glassiness appearance of fruits, while the fruit is still immature (cv. Cantaloupe, France). As with all other calcium related fruit disorders, it is important to ensure calcium is available in the fruit right from fruit-set and particularly during early fruit-fill.

Calcium and fruit quality - net and chilling injury

By increasing calcium in the fruit growers can ensure better net development and reduced chilling damage (cv. Galia - Muskmelon, South Africa).

Calcium and nitrogen type

Fertilizer formulation also has a significant effect on quality characteristics and fruit disorders. Trials confirm that calcium nitrate is particularly effective at ensuring good fruit quality (cv. Congo - Watermelon, USA). This is largely because ammonium based fertilizers are antagonistic to calcium uptake. They also reduce soil pH and slow water uptake.

Calcium fruit sprays and quality

Calcium fruit sprays can be used to influence quality (Honeydew and Netted Melon, USA). However, these are less effective in certain types – e.g. netted melon and need to be applied early during fruit development.

See more on Melon Growth Stages.

General guidelines for Calcium application

The vast majority of calcium is held within the leaf and stems, so high rates are needed to provide the relatively low amounts found in the fruit that influence quality. Calcium is required for root and shoot development especially pre-flowering. High concentrations in plant cell walls at transplanting will reduce the incidence of fusarium wilt, damping-off and anthracnose.

Calcium availability is also critical during early fruit fill, in order to ensure good supplies find their way into the flesh and rind of the fruit. It is common practice to use applications throughout the growing season right through to early fruit maturation to build-up levels in crop tissue, maximizing quality potential and storability.

Calcium deficiencies in melon

Leaves take on a shell-like appearance with stunted, poorly developed veins. Growing points and roots die-off. Stems can crack due to the low cell strength. Crops suffer from BER and hollow heart. Fruits can also take on a glassy appearance with the internal flesh turning brown and breaking down to become watery. Problems may not be seen until after harvest, during transport or on the shelves. Thus it is important to be pro-active and maintain good calcium nutrition throughout periods of active growth. Deficiencies in the fruit can occur without the expression of any visible symptoms on the leaves.