PDF《potassium fertilization》

Marques, 2011). In Brazil, pitaya cultivation is in the expansion phase, with the largest producing area located in the state of S?o Paulo, especially the region of Catanduva (Bastos et al., 2006). Although it is a small fruit compared to other commercialized fruits, it is becoming more popular in marketing centers due to its exotic appearance and organoleptic properties (Marques, Moreira, Ramos, Araújo, &

Silva, 2011;

Moreira et al., 2011). To expand the area of pitaya cultivation in this country, knowledge about crop management is necessary, especially in regard to fertilization. Although it is considered to be a hardy species due to its adaptation to different climatic and soil conditions, pitaya needs balanced fertilization to supply its nutritional demand, satisfactorily enabling Page

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9 Fernandes et al. Acta Scientiarum. Agronomy, v. 40, e35290,

2018 its growth and production (Corrêa, Almeida, Marques, Vale, &

Aquino, 2014). In Brazil, fertilization is performed as needed sporadically or based on doses recommended in other countries with different climatic and soil conditions (Cavalcante et al., 2011) because there is no information regarding plant nutrition for growth and satisfactory production. For accurate nutrient recommendations, knowledge about the nutritional state of the species is necessary, which takes into account the physiological ecology and the plant growth rate. Thus, the extrapolation of results that have been obtained in other cropping systems is not recommended (Souza, Pio, Coelho, Rodas, &

Silva, 2015). Among the essential nutrients for culture, potassium is highly required, participates in many biochemical processes, and, when properly applied, favors the quality of pitaya fruit (Then, 2013). Studies about potassium fertilization for pitaya in Brazil are still in the initial stages. In this sense, this study was performed with the aim to identify suitable doses of potassium in the production and fruit quality of two pitaya species. Material and methods The experiment was conducted in an orchard located

726 meters above sea level, 18° 04'

15 S latitude and 43° 28'

15 W longitude. The climate according to Koppen and Gleiger is AW, classified as tropical with a dry winter season, with an average temperature of 24°C in the hottest month and 18.4°C in the coldest month and an average annual temperature of 21.5°C. The average annual rainfall is 1,246 mm, with well-defined dry and rainy seasons. During the research period, the variation in temperature was recorded using a digital MT

240 MINIPA thermo hygrometer, and rainfall data were collected with the use of a rain gauge, both of which were installed in the experimental area (Figure1). Two species of pitaya, Hylocereus undatus (Haw.) Britton &

Rose and Hylocereus polyrhizus (Web.) Britton &

Rose, which were ten months old and established from

1 m long cuttings, were planted in January 2013. Before planting the pitayas, soil analyses of the experimental area at the depths of 0-

20 cm and 20-40 cm were performed (Table 1). Figure 1. Monthly average temperatures (°C), maximum temperatures (°C), minimum temperatures (°C) and precipitation (mm) from January

2013 to May 2016. Table 1. Chemical analysis of the soil in the experimental area before plantingat the depths of 0-20 and 20-40 cm. Depth (cm) pH P K Ca Mg Al3+ H + Al H2O ----mg dm-3 cmolc dm-3 0-20 5.1 1.8 40.7 1.0 0.3 0.5 3.7 20-40 4.9 5.09 40.7 0.6 0.3 0.7 4.2 Depth (cm) SB T T V M O.M cmolc dm-3 dag dm-3 0-20 1.4 1.9 5.1