**3. The apple tree**

The apple tree (*Malus domestica*) origin center is the Caucasus region, in the Asian montains and in the East of China. It is supposed that the development of the casual species have been initiated 20.000 years ago. It seems that the Greeks in the classical ancient times had cultivat‐ ed apple tree, in fact in the roman empire the apple tree culture was already widespread. In Brazil, the beginning of the apple tree culture occurred probably in Valinhos municipality, state of São Paulo in 1926 [21].

Apple is among the fourth most consumed fruits in the world. In Brazil it is commercialized during the twelve months of the year and distributed all over the country. Except its con‐ sumed *in natura* it is utilized in puree, jam, dry fruit, concentrated juice and fermented bev‐ erages. The apple tree fruit is rich in peptic substances and cellulose that together with lignin constitute fibers [21].

The apple orchards in Brazil initiated in the end of the 60's and beginning of the 70's. Since this date, Brazil depended on importation to supply the apple market. But trough the gov‐ ernment supporting, now a days, the evolution of the crops was fast, getting to 34 thousand of hectares and a production of about 850 thousand ton, concentrated in the Santa Catarina state. From 1988 Brazil started to export apples reaching self-sufficiency in 1998 when the exportations exceed the importations [21].

#### **3.1. Potassium fertilization in apple orchards**

Potassium (K) is the most extracted nutrients from the soil by apple fruits. Currently, with the use of new technologies, yield may reach values higher than 100 t ha-1 [22]. Which in‐ creases the nutrients demanded by the apple.

The effective fruiting of apple trees is influenced by N, which plays an important effect in floral bud formation and increases the period when the ovule can be fertilized [23]. K in‐ creases sugar translocation to sink tissues, promoting their growth [24]. Thus, fruits from Kdeficient plants have reduced size [25,26,27,28]. Which can reduce overall yield [22].

According with [29,30], an excess of K can affect the calcium (Ca) nutrition, increasing the intensity of physiological disorders related this nutrient, including the bitter pit, cork spot and lenticel blotch pit, among others. Increasing K as well as N rates can decrease flesh firm‐ ness, reducing the storage life of apples.

Fertilizer recommendations for apple in Santa Catarina (SC) and Rio Grande do Sul (RS) states Brazil are based on soil and leaves chemical analysis, shoot growth and orchard pro‐ ductivity [31]. The amount recommended for each year varies from 0 to 100 kg ha-1. These recomenadtion were obtained from results of research conducted in Fraiburgo/SC and Vaca‐ ria/RS, or adapted from other production regions around the world. Reginal fertilization test are quite important to São Joaquim/SC, considering that this region presents very stony and shallow Inceptisols and the mean temperatures are lower when in comparison to other pro‐ duction regions in Brazil.
