PDF《potassium fertilization》

28 26 0.4 20-40 1.0 1.7 5.2

19 40 0.1 pH(H2O): soil-water relation 1:2.5;

P and K: Mehlich-1 extractor;

Ca, Mg and Al: KCl

1 mol L-1 extractor;

T: cation exchange capacity at pH 7.0;

m: aluminum saturation;

V: base saturation;

OM: organic matter, determined by multiplying the result of organic carbon by 1.724 based on the Walkey-Black method;

sand, silt and clay: pipette method.

0 50

100 150

200 250

300 10

15 20

25 30

35 40 precipitation mean temperature maximum temperatures minimum temperatures Temperature (°C)

2013 2014

2015 Experimentalperiod

2016 Precipitation (mm) K fertilization for pitayas Page

3 of

9 Acta Scientiarum. Agronomy, v. 40, e35290,

2018 The holes in which the pitayas were transplanted were 0.5 * 0.5 * 0.5 m, prepared with

200 g of dolomite lime (PRNT = 87%),

20 L of manure, and

300 g of single superphosphate (P2O5 = 18.0%, Ca = 18.0%, and S = 20.0%). The pitayas were attached to eucalyptus fence posts at 1.80 m in height at a spacing of

3 *

3 m. A

1 m long beam was positioned at the end of each fence post, forming a T -shaped structure. The plants were attached by a single cladode to reach the desired height;

they were later pruned to form the productive shoots. The experimental design was randomized blocks, with a

2 *

4 factorial design. The factors were two pitaya species and four doses of K2O: 0, 50, 100, and

200 g per plant, with four blocks and three plants per plot. The source of K used was potassium chloride (58% of K2O). The tested doses were split in three months (November, January, and April of each year). In these months,

100 g of N per plant was also applied using ammonium sulfate (20% of N and 22% of S). One hundred and twenty grams of Yoorin Master? was applied, split between January and April of

2014 and between January and April of 2015, and

5 L of manure was applied in June of

2014 and in June of 2015. Yoorin Master? contains 17.5% P2O5, 18.0% Ca, 7.0% Mg, 0.1% B, 0.08% Cu, 0.3% Mn, 10% Si, and 0.55% Zn. Irrigation was performed weekly, and weed control was conducted by hand up to

40 cm from the plant. The rest of the area was mowed. The production per plant (kg and number of fruits) was evaluated in the production cycles 2013/2014, 2014/2015, and 2015/2016. Fruit quality was analyzed using representative samples collected on each fertilization treatment. Ten fruits per plot were collected when they presented a peel with red coloration. The following parameters were evaluated: longitudinal diameter (mm), transverse diameter (mm), mass (g), soluble solids content (°Bx), titratable acidity (% of malic acid) and soluble solids/titratable acidity ratio. In June

2014 and June

2015 soil samples were collected after harvesting the fruits for the analysis of the nutrient content in the soil. Cladode samples were collected in September

2014 and September 2015. For the evaluation of soil fertility, samples were taken with a Dutch auger at a distance of 0.2 m from the main cladode and at a depth of

0 - 0.2 m for each plant, forming a sample composed of each experimental plot. The cladodes that were removed to compose the sample were one year old, with an average size of 0.4 m and a healthy appearance. Each sample was composed of five cladodes per plot. The data were submitted to analysis of variance, and the K2O doses were submitted to polynomial regression analysis (p <

0.05). The species of pitaya were compared by the F test (p <

0.05). Results In the 2013/2014 productive cycle, differences were observed among the K2O doses in terms of the number of fruits and production per plant (Figure 2A and B). Increases of 20.7% in the number of fruits per plant of H. undatus occurred with an estimated dose of 106g of K2O per plant. H. polyrhizus showed an increase of 24.4% in the plants that received