Growth of Potato Plants of the ‘Asterix’ Cultivar and Accumulation of Nutrients

The objective of this research work was to quantify both the development of potato plants of the ‘Asterix’ cultivar and the accumulation of nutrients by the plants. The experiment was carried out at Perdizes, state of Minas Gerais, Brazil, in a randomized complete block design with seven treatments (sampling moments) and three replications. The spatial arrangement of the plants in the field was of 0.80 m between rows and 0.35 m between plants in the row. Plant samples were taken 30, 42, 54, 66, 78, 90, and 114 days after planting (DAP) for the determinations of plant dry matter and accumulated nutrients. The potato plant was slow to grow up to 42 DAP and the highest rate of dry matter accumulation was observed between 51 and 90 DAP. Plant cycle was of 97 days and total productivity of 44 t ha. Total macro nutrients accumulated by the plants up to 90 DAP were of 369.3, 184.0, 42.7, 18.0, 16.2, and 13.8 kg ha of K, N, Ca, P, Mg, and S, respectively. The micronutrients Fe, Mn, Zn, B, and Cu were found to have reached values of 1,225, 525, 439, 164, and 96 g ha, respectively.


Introduction
Potato (Solanum tuberosum) tubers are the fourth more important source of food for mankind only surpassed by rice, wheat, and corn (Filgueira, 2003).World production of potatoes is of 329 556 911 tons harvested from an area of 18 326 242 hectares, this meaning a mean productivity of 18 t ha -1 .The biggest potato producers in the world are China, Russia, Ukraine, and the United States (Food and Agriculture Organization of the United Nations [FAO], 2011).
Potatoes are one of the most important vegetables in Brazil with a total production of 3 443 737 tons cultivated in an area of 140 987 hectares, this meaning a mean productivity of 24 t ha -1 .If compared to yields verified in developed countries such as the United States, the Netherlands, Germany, and France (between 44 and 46 t ha -1 ), the Brazilian productivity is considered low (FAO, 2011; Instituto Brasileiro de Geografia e Estatística [IBGE], 2011).
Factors such as plant mineral nutrition and soil fertilization help to explain such low productivity.Plant nutrition affects tubers productivity and quality, which is in turn influenced by soil fertilization whose efficiency is dependent on fertilizers doses and time of application.
Research works concerned with the quantification of plant growth and the march of absorption or accumulation of nutrients are basic to improve the efficiency of soil fertilization, optimize production, and reduce environmental impacts by the excess of fertilizers.Several research works (Alvarez-Sánchez et al., 1999;Aguilar et al., 2001;Alva et al., 2002;Yorinori, 2003;Heard, 2004;Cabalceta et al., 2005;Favoretto, 2005;Mora-Aguilar et al., 2005;Sharifi et al., 2005;Geremew et al., 2007;Horneck & Rosen, 2008;Coraspe-León et al., 2009;Ñústez et al., 2009;Fernandes, 2010) viewing to evaluate potato plant growth and accumulation of nutrients have shown that the amounts of extracted nutrients vary according to cultivation conditions.
Potato plant metabolism and cycle were different under different climatic conditions.Mainly temperature, photoperiod, and precipitation have been reported to significantly influence potato plant growth and the accumulation of dry matter this leading to differences in nutrients absorption and accumulation (Sancho, 1999;Bertsch, 2003).Thus the evaluation of potato plant cultivars demand for nutrients is necessary to be carried out under the local conditions where they are cultivated.
With these considerations in mind, the present research work viewed to quantify the growth and the accumulation of macro and micronutrients by potato plants of the 'Asterix' cultivar and simultaneously obtain the equations which best represent them.

Materials and Methods
The experiment was set and carried out in a private rural property located at the municipality of Perdizes (19°21′10″ S and 47°17′34″ W), state of Minas Gerais, Brazil, from July 5 to October 27 of 2009 in a soil classified by Empresa Brasileira de Pesquisa Agropecuária [EMBRAPA] (2006) as a Red Yellow Argisol.The dominant climatic condition in the region is that of tropical altitude with yearly mean temperature and pluvial precipitation of 20.4 °C and 1,574.7 mm.
A chemical analysis carried out in soil samples of the region taken at depths between 0 and 20 cm showed the following results: pH (CaCl2) = 5.4; organic matter = 35 g•dm -3 ; P (Mehlich-1) and K = 2.7 and 96 mg•dm -3 , respectively; Ca, Mg, H + Al, and Al = 35, 17, 31, and 0 mmol c •dm -3 , respectively, and soil bases saturation of 64%.The physical analysis of the soil showed the contents of sand, silt, and clay to be, respectively, of 391, 232, and 377 g kg -1 .
Seed tubers of the cultivar 'Asterix' were planted in rows so that the distance between plants would be of 0.35 m and between rows of 0.80 m.Soil liming was not made for, according to Fontes (1999), it is not necessary when soil bases saturation is higher than 60%.At planting, 40, 420, and 30 kg ha -1 of N, P 2 O 5 , and K 2 O, respectively, were placed at the bottom of the row.At 27 days after planting (DAP) 150 and 120 kg ha -1 of, respectively, N and K 2 O were applied to complement soil fertilization.
In the field, the experiment was set according to a randomized complete block design with three repetitions and seven treatments (sampling times).Potato plants started to be collected 30 DAP and then at each 12 days, with the exception of the last one which was collected 24 days after the penultimate.Plants for sampling purpose took place at 30,42,54,66,78,90,and 114 DAP.At each collecting moment, three plants per repetition were taken.At 114 DAP the samples were formed just by tubers since the plant aerial part had already died.
Brought to a laboratory, the plants were divided in leaves, stems, and tubers.The vegetative materials were washed in running water and then in deionized water.That was followed by the drying of the materials in an oven of forced ventilation at a temperature of 65 °C till constant weight.After that, the materials had their weight determined in a digital scale with a precision of 0.01 g.These materials were ground and their contents of macro and micronutrients determined according to procedures described in Bataglia, Furlani, Teixeira, Furlani, and Gallo (1983).Based on the results, the accumulated amounts of each nutrient in the stem, leaves, and tubers were calculated.Polynomial and logistic [Y = A/1 + e -K(X -Xc) , where Y = mean value of the evaluated characteristic; A = asymptotic maximum (maximum quantity); K = mean increment rate of the accumulated quantity; X = time (days); Xc = time necessary for half the maximum quantity to be reached] functions were used to represent growth and nutrients accumulation data with the help of the software ORIGIN 6.0.

Potato Growth
Potato plant growth expressed in terms of dry matter accumulation was slow up to 42 DAP (Figure 1a).Tuber formation was started 37 DAP, that is after 32% of the plant cycle had elapsed and when the dry masses of leaves and stems were, respectively, of 9.0 and 7.0 g plant -1 , corresponding to 25 and 63% of their maximum.
The dry matter partition favored stems and leaves up to 44 and 50 DAP, respectively.After those periods, dry matter started to be allocated essentially for tubers (Figure 1a).1a) wi 9 g plant -1 , co after the senesc 8 kg ha -1 day -1 crucial inform e it permits th tion is econom eaves -the am t -1 , respectively t aerial part (st nt -1 ) correspond al research wo es (Y 2 ), and tu ith a mean incr orresponding t cence of the pl according to th mation for the he farmer to an mically compen mounts of dry m y (Figure 1a).dry matter allocated to the tubers vary between 69 and 90% of the plant total (Alvarez-Sánchez et al., 1999;Aguilar et al., 2001;Alva et al., 2002;Yorinori, 2003;Mora-Aguilar et al., 2005;Sharifi et al., 2005;Geremew et al., 2007;Horneck & Rosen, 2008;Ñústez et al., 2009;Fernandes, 2010).This variation may be explained by genotype effect, cultivation time, environmental factors specially temperature and photoperiod, soil fertilization and the level of senescence of the plant aerial part at the moment the sample was taken.
Between the penultimate and the last harvest, tubers dry matter had an increment of 5% (13.4 g plant -1 ), the equivalent to 478 kg ha -1 .Plant cycle was 97 days, when a productivity reached at 44 t ha -1 , a value close to that (40 t ha -1 ) reported by Fernandes (2010) in a research work with potato plants of the same cultivar.

Macronutrients
Starting with the first evaluation, it was possible to verify decrements in the accumulation of N in the stems up to the end of the plant cycle in comparison with leaves and tubers.At 30 DAP there were 303.7 mg plant -1 of N whereas at 90 DAP that amount had dropped to 184.2 g plant -1 (Figure 1b).
Up to 61 DAP, N accumulation occurred more in leaves than in the tubers, reaching 1101 mg plant -1 .Starting at that point, N accumulation in the leaves began to decelerate probably due to the drain power of the tubers.N accumulation in the leaves is important since this element takes part of the growth and cell differentiation processes (Malavolta, 2006).Consequently leaves grow more vigorously, radiation, water, and nutrients are absorbed more efficiently this leading to the production of larger amounts of dry matter to be accumulated by the tubers.
Accumulation of N in the tubers was verified to undergo a sharp increase from 42 to 90 DAP.In that interval of 48 days, tubers accumulated 3565.4 mg plant -1 , this representing 85.2% of the total accumulated by that plant part (Figure 1b).Between 42 and 90 DAP, Fernandes (2010) also verified higher N accumulated in tubers of the 'Asterix' cultivar (2251.5 mg plant -1 ), representing 84.3% of the total accumulated in this organ.
At 90 DAP, the amounts of N accumulated in tubers (3736.5 mg plant -1 ), stems (184.2 mg plant -1 ), and in leaves (1255 mg plant -1 ) corresponded to 67, 3, and 22% of the total accumulation (5596 mg plant -1 ).At 114 DAP when there were only tubers, the total N accumulated was of 4187 mg plant -1 .Alva et al. (2002), working with the cultivar 'Hilite Russet', found a total (leaves, stem, and tubers) of accumulated N of 5504.4 mg plant -1 , a value quite close to the amount found in this work.Fernandes (2010) verified values of accumulated N between 2464 and 3276 mg plant -1 in the cultivars 'Ágata', 'Asterix', 'Atlantic', 'Markies', and 'Mondial'.In a similar work, Yorinori (2003) found a total of accumulated N in plants of the 'Atlantis' cultivar was 3362 mg plant -1 in the rainy season and 2861 mg plant -1 in the dry season.Heard (2004) reported total accumulated N was 7562 mg plant -1 in the cultivar 'Ranger Russet'.
Up to 50 and 43 DAP, P accumulated mainly in leaves and stems, respectively.From 51 DAP onwards, P accumulated essentially in tubers.At 90 DAP, the total amount of P accumulated in tubers was of 430 mg plant -1 , a value larger than that of the leaves (62.2 mg plant -1 ) and of the stems (12.0 mg plant -1 ), as shown in Figure 1c.These results corroborate those reported by Alvarez-Sánchez et al. (1999).In stems, the accumulation of P started to decrease from 30 DAP onwards (36.4 mg plant -1 ) up to 90 DAP (12.0 mg plant -1 ) whereas in the leaves a slight increase was observed between 30 and 54 DAP (26 mg plant -1 ).After that moment, up to 90 DAP, P content in leaves became constant (Figure 1c).
Between 42 and 90 DAP, P content in tubers grew vigorously (Figure 1c) reaching a total of 403 mg plant -1 , which corresponded to 70% of the total accumulated in the plant (576 mg plant -1 ).Yorinori (2003) showed that the total P accumulated in the plants (leaves, stems, and tubers) of the 'Atlantis' cultivar were 422.9 mg plant -1 during the rainy season and 366.3 mg plant -1 during the dry season these values being lower than the one found in this work (504.2mg plant -1 ) at 90 DAP when leaves and stems had not dried up.Data published by Fernandes (2010) show that, at 97 DAP, plants of the 'Agata', 'Atlantic', and 'Markies' cultivars had accumulated a total of 392 mg plant -1 and those of the cultivars 'Asterix' and 'Mondial' of 504 mg plant -1 , a value close to the one we found in this investigation (504.2 mg plant -1 ) at 90 DAP.The P value reported by Heard (2004), such as was the case of N, is larger (1277 mg plant -1 ) than the one found in this work.Of all nutrients, K was the most absorbed by the potato plant corroborating data published by Cabalceta et al. (2005), Horneck andRosen (2008), andFernandes (2010).Yorinori (2003) verified K to be more absorbed than N during the rainy season and the opposite during the dry season.Potassium plays a very important role in the elaboration of carbohydrates and their mobilization to the tubers (Bertsch, 2003).
Potassium accumulation in tubers was observed to occur from 42 to 90 DAP.The highest amount of K in the tubers was observed 114 DAP: 6600 mg plant -1 .In the leaves and stems the maxima, respectively, of 2981.74 and 978.91 mg plant -1 were reached 90 DAP (Figure 1d).Larger amounts of K in the tubers than in other plant parts were also reported by Yorinori (2003) in plants of cultivar 'Atlantic' and Fernandes (2010) in cultivars 'Agata', 'Asterix', 'Atlantic', 'Markies', and 'Mondial' in which the total amount of accumulated K was between 3210 and 7168 mg plant -1 .These values are less than the one found in this research 90 DAP (penultimate sample), that is, 10 302 mg plant -1 .The highest amount (more than 11 640 mg plant -1 ) of K was reported by Heard (2004).
The potato leaves showed a strong increment in Ca accumulation from 42 to 78 DAP, reaching, in that period, a total of 647.3 mg plant -1 which represents 72% of the total Ca accumulated by leaves up to 90 DAP.In the stems, the highest amounts of accumulated Ca were observed between 30 and 59 DAP.The amount accumulated during that period of 29 days was of 153 mg plant -1 , which corresponded to 70% of the total accumulated by stems up to 90 DAP.The accumulation of Ca in tubers was kept practically constant with a slightly higher accumulation starting at 66 DAP.Between 90 and 114 DAP, the amount of Ca in tubers went from 73.7 to 100.5 mg plant -1 (Figure 2e).
The results showed that Ca, differently from the other nutrients, accumulated more in the stem and leaves.At 90 DAP, the leaves had 902 mg plant -1 , the stem, 217.2 mg plant -1 , and the tubers just 73.7 mg plant -1 .The amount in the tubers was of 6% of the total accumulated by the plant (1219 mg plant -1 ) whereas leaves and stem had, at 90 DAP, 74 and 18% of the total Ca accumulated by the plant.Fernandes (2010), with the cultivar 'Asterix', and Heard (2004), with cultivar 'Ranger Russet' found totals of 1400 and 2258 mg plant -1 of Ca.Yorinori (2003) reported values of 521.5 mg plant -1 during the rainy season and 350.2 mg plant -1 during the dry season.
The intense transpiration taking place in the leaves in comparison with the other parts of the plant causes Ca to be transported predominantly to the leaves.Since Ca is practically immovable in the plant, most of it will be found in the leaves in the mature plant and only a small proportion in the tubers, this being the opposite of what was verified with N, P, and K.The small proportions with which Ca occurs in tubers were confirmed by results reported by Yorinori (2003), Heard (2004), Coraspe-León et al. (2009), andFernandes (2010).
Stem and leaves showed different amounts of Mg but the period of the largest demand was the same for both plant parts when they reached their maximum concentration between 30 and 66 DAP, with 29.2 mg plant -1 in the stem and 81.9 mg plant -1 in the leaves, these values representing, respectively, 60 and 74% of the total accumulated by these plant parts at 90 DAP.In the tubers, most of the Mg accumulated between 48 and 96 DAP with a value of 291 mg plant -1 , this amount representing 90% of the total accumulated by the tubers at 114 DAP (Figure 2f).At 90 DAP, the largest amount of S was verified in tubers (295.3 mg plant -1 ), followed by the leaves (82.8 mg plant -1 ) and stems (8.7 mg plant -1 ), as shown in Figure 2c.Similar data were reported by Yorinori (2003), Heard (2004), andCabalceta et al. (2005).Data published by Coraspe-León et al. (2009) though pointed the leaves and stems the plant parts where most of the S accumulated.
Total accumulated S was of 419.2 mg plant -1 , a value larger than the one found by Yorinori (2003), that is, 260.6 mg plant -1 in plants of the 'Atlantic' cultivar grown during the rainy season and 161.4 mg plant -1 in those grown during the dry season.Heard (2004), on the other hand, reported to have found 988 mg plant -1 of S.

Micronutrients
The largest amounts of B accumulated in leaves (1.3 mg plant -1 ) and stems (0.3 mg plant -1 ) took place up to 64 and 52 DAP, corresponding to 87 and 76% of the total accumulated in those plant parts, respectively.In tubers the great increment in B content took place between 54 and 90 DAP with 2.3 mg plant -1 , which corresponded to 56% of the total B accumulated in that plant part at 114 DAP (Figure 2h).
The maximum amount of B in tubers was found at 114 DAP and was of 2.9 mg plant -1 .Yorinori (2003), in tubers of the cultivar 'Atlantic', found 1.8 and 1.6 mg plant -1 in plants grown, respectively, during the rainy and the dry seasons.Working with potato plants of the cultivar 'Asterix', Fernandes (2010) found the highest amount (1.0 mg plant -1 ) of B in the tubers at the end of the plant cycle.
Copper accumulation in stems practically did not increase from the plant cycle beginning to 90 DAP, a moment when it was of 0.13 mg plant -1 .In that period, leaves accumulated 1.2 mg plant -1 and tubers 1.3 mg plant -1 (Figure 3i) thus totalizing 2.6 mg plant -1 .In leaves, the highest accumulation of Cu took place between 42 and 78 DAP when a total of 1.1 mg plant -1 was reached.At 114 DAP, the total amount of Cu in tubers was of only 1.5 mg plant -1 .Yorinori ( 2003) also found the tubers to be the plant part with most of the accumulated Cu (0.7 and 0.9 mg•plant -1 ) followed by the leaves (0.3 and 0.3 mg plant -1 ), and stems (0.1 and 0.1 mg plant -1 ) in plants growing, respectively, in the rainy and the dry seasons.Similar results were reported by Fernandes (2010) in plants of the cultivar 'Asterix': 3.9, 0.4, and 0.1 mg plant -1 in, respectively, tubers, leaves, and stems.
The largest amount of Cu in tubers took place from 45 to 90 DAP with a total accumulated in that period of 1.2 mg plant -1 , this representing 80% of 1.5 mg plant -1 which was the total at 114 DAP (Figure 3i).
The highest demand of Fe was verified between 42 and 78 DAP, when 17.8 mg plant -1 were accumulated which represented 88% of the total accumulated by the leaves.Fe accumulation in the stem showed a slight decrement from 30 (2.7 mg plant -1 ) to 90 DAP, when it was of 2.3 mg plant -1 (Figure 3j).
The largest amount of Fe at 90 DAP was observed in tubers (22.1 mg plant -1 ), followed by the leaves (20.2 mg plant -1 ) and stems (2.3 mg plant -1 ), as shown in Figure 3j.Yorinori (2003) and Fernandes (2010), in, respectively, plants of the 'Atlantic' and 'Asterix' cultivars, reported the tubers and the leaves to be the plant parts in which Fe accumulated most.

Figure 1
Figure 1.D ems and leave ding to 11.2 (le orks show that ubers (Y 3 ) of p rement rate of o 89% of the lant aerial part he plant popul decision as to nalyze whethe nsated by the p matter accumu At that mome es) was rather s eaves), 3.5 (ste the total Figure 2.

Figure
Figure 3. C Tubers showed the highest accumulation of S between 44 and 93 DAP with 290.9 mg plant -1 , this representing 89% of the total accumulated in that tissue up to 114 DAP.