NUTRIENT DEMAND BY THE CARROT CROP IS INFLUENCED BY THE CULTIVAR Rosiane Filomena

Farmers must carefully choose the cultivar to be grown for a successful carrot crop. The yield potential of the cultivar may influence nutrient demand and should be known to plan for fertilization application. The aim of this study was to evaluate the cultivar effect on carrot yield and on the nutrient content and quantities allocated to leaves and roots. Three experiments were set up in two crop seasons in Rio Paranaíba, MG, Brazil. In the first season, typical summer, 10 summer cultivars were sown. In the second season, summer-winter (transition), two experiments were set up, one with summer cultivars and the other with winter cultivars. The treatments consisted of the carrot cultivars distributed in randomized blocks with four replications. Fresh and dry matter of the roots and leaves was quantified. Yield was calculated based on fresh matter of the roots. The nutrient content in leaves and roots was determined at the time of harvest. These contents and the dry matter production of roots and leaves were used to calculate nutrient uptake and export. The greatest average for total and commercial yield occurred in the crop under summer conditions. Extraction of N and K for most of the cultivars in the three experiments went beyond the amounts applied through fertilizers. Thus, there was contribution of nutrients from the soil to obtain the yields observed. However, the amount of P taken up was considerably less than that applied. This implies that soil P fertility will increase after cropping. The crop season and the cultivars influenced yield, nutrient content in the leaves and roots, and extraction and export of nutrients by the carrot crop.


INTRODUCTION
Worldwide production of carrot is more than 24 million tons (Singh et al., 2012), which may be consumed fresh or processed in forms such as mini carrots, grated carrots, baby food, and instant soups.
In Brazil, carrot is among the five main garden crops grown and 80 % of the total production supplies the Brazilian domestic market.The Southeast, Northeast, and South regions are the largest producers of this root crop.The State of Minas Gerais stands out in production of this vegetable crop and one of the main producing regions is São Gotardo, in the Alto Paranaíba region (Mesquita Filho et al., 2005).
Yield potential of the crop is from 100 to 120 t ha -1 ; however, the Brazilian average is much lower, at 33 t ha -1 (Embrapa, 2010).Success in growing this crop for high yields involves the integration of various factors, such as soil tillage, the cultivar chosen, and climatic conditions, among others.
Various cultivars are on the market that differ in relation to size, color, shape, sugar content, resistance to pests and diseases, and early maturity (Luz et al., 2009a).The correct choice of the cultivar for a certain crop season may define crop yield (Oliveira et al., 2008).
The cultivar × environment interaction exhibits different responses according to each cultivar (Nicolle et al., 2004).Plant spacing, fertilization levels, irrigation, soil tillage, and other factors may interact in diverse manners, depending on the cultivar.One of the environmental factors that strongly influences yield is soil fertility.Therefore, it is necessary to know the nutritional requirements for a cultivar to achieve its maximum yield potential.
High fertilization rates are common in carrot growing.Fertilization represents around 45 % of the production costs of this crop (CEPEA, 2010) and influences yield, the quality of the root crop (Luz et al., 2009b), and, therefore, the profitability of the crop.Nevertheless, the use of high rates of fertilization, though having a positive effect on yield, may compromise the economic viability and environmental sustainability of growing this crop (Smolen and Sady, 2009;Zumbado and Soto, 2010).
Knowing the nutritional demands of the crop in an accumulated manner and the nutrient uptake rate is highly important to achieve high yields (Singh et al., 2012).For each yield level and cultivar there is the respective nutritional demand; knowing this may assist the producer in applying amounts of nutrients that are not excessive, thus achieving reduction in production costs.
The nutrient content in the plant may be used in estimation of the amount of nutrients taken up and exported by the crop.These amounts are essential in establishing an effective fertilization system (Sharma et al., 2012).
To establish a more efficient method of fertilizer recommendation, based on nutritional balance, it is necessary to obtain the nutrient requirements of the different cultivars in accordance with the desired yield, as has been developed for the soybean crop (Santos et al., 2008).The aim of this study was to evaluate
the effect of cultivars on yield, and on the content, extraction, and export of nutrients by the carrot crop.

MATERIAL AND METHODS
Three experiments were set up in two crop seasons in the experimental area of the COOPADAP (Cooperativa Agropecuária do Alto Paranaíba) in the municipality of Rio Paranaíba, MG, in 2012.The geographic coordinates of the location are 19° 12' 21" S and 46° 10' 05" O, at an altitude of 1,140 m.The climate according to the Köppen international classification system is Aw, defined as tropical with a dry season.The soil was classified as a Latossolo Vermelho-Amarelo (Oxisol) with a very clayey texture.
Before planting, soil samples were taken from the crop areas and chemical characterization of the soils was carried out (Table 1).Planting density of the cultivars was 1.2 million seeds per hectare.For all the experiments, fertilization at planting was 1.0 t ha -1 of simple superphosphate and 1.5 t ha -1 of the fertilizer 04-30-16 (N-P 2 O 5 -K 2 O) broadcast and incorporated to 15 cm depth with a rotary hoe bed former.The fertilizer 21-00-21 was used for topdressing fertilization.Two applications were made at the rate of 200 kg ha -1 each, the first at 30 days after sowing (DAS) and the second at 70 DAS.Immediately after distribution of the topdressing fertilizer, the crop was irrigated for fertilizer incorporation.The fertilizer application rates, formulations, and periods were based on those adopted by producers in the Alto Paranaiba region of MG for the carrot crop.
The treatments in the three experiments consisted of carrot cultivars.A randomized block experimental design was used with four replications.In the first experiment, considered to be typical summer sowing (hot and rainy), the following cultivars were sown: AF 2031, AF 2335, Amanda, Bruna, Carandaí, Juliana, Marli, Poliana, Suprema, and Verano.Sowing of this experiment occurred on January 24, 2012 and harvest was on May 18, 2012.
Each plot consisted of a crop bed of 1.75 m width (distance between pathways), with 1.20 m width at the upper part and 6 m length.Four double rows were arranged in each crop bed.The useful part of the plots consisted of the four central meters of the bed.
Crop treatments such as thinning, irrigation, and weed, pest, and disease management were carried out according to practices usually adopted by carrot producers in the Alto Paranaiba region of Minas Gerais.
Carrots were harvested when most of the roots had achieved the most acceptable commercial standard, class 22.This class includes roots from 22 to 26 cm length, with diameter variation of less than 1 cm, without attack from pests or disease or the occurrence of green shoulder or cracking.
The roots were separated into commercial and non-commercial produce based on the classification criteria in effect for the carrot market.Based on commercial root production and total root production (commercial + non-commercial), commercial and total yield was calculated.In addition to roots, leaves were collected from the useful area, which were subsequently washed, and leaf fresh matter was quantified.Then a subsample of roots and another of leaves were weighed and placed to dry in an air circulation laboratory oven at 70 °C for 72 h.Based on the weight of the subsamples after drying, the dry matter content in the roots and leaves was determined.The dry matter yield was obtained by the product of the total yield and the dry matter content of each part harvested (roots or leaves).The dried and weighed subsamples were then ground to determine the nutrient content according to methods described by Malavolta et al. (1997).The ratio between the dry matter productions of roots and of leaves was calculated.
The nutrient extraction values were obtained by the sum of the amounts of nutrients allocated to the roots and to the leaves.These amounts were obtained by the product of the dry matter yield and the nutrient contents in the respective parts of the plants.Export was considered as the amount of nutrients allocated to the roots.
The data of each experiment were subjected to analysis of variance.When an effect of treatment was detected, the mean values were clustered by the Scott-Knott criterion at 5 %.The software Sisvar, version 5.3 was used for statistical analyses (Ferreira, 2011).

RESULTS AND DISCUSSION
The greatest overall mean of total and commercial yield occurred in cropping under summer conditions.In transition cropping (summer-winter), both the summer and the winter cultivars had lower total and commercial yields than in the first experiment (Table 2).This occurred due to the greater difficulty of adapting the best cultivar to a growing condition that has climate characteristics of winter and summer simultaneously, which may increase the incidence of diseases and physiological disturbances (Luz et al., 2009a).
In the three experiments, there were differences in the total and commercial yields of the cultivars (Table 2).The greatest total yield was not always associated with the greatest commercial yield.In the experiment in the summer crop (experiment 1), for example, the cultivar AF 2335 was in the group that had the greatest total yield; however, it exhibited less commercial yield than the cultivars Juliana, Marli, Poliana, and Verano.In the experiments set up in the summer -winter transition season (experiments 2 and 3), the number of cultivars that had greater total and commercial yield was less.Among the summer cultivars (experiment 2), the Nativa cultivar stands out, and among the winter cultivars (experiment 3), the cultivars Belgrado and Hana stand out.
The bigger difference between total and commercial yield of some cultivars may be explained by greater discard of roots due to defects such as cracks, the occurrence of galls, and green shoulder.Under high temperature conditions, these defects may occur to a greater degree and affect the commercial quality of carrot (Paulus et al., 2012).The smaller number of cultivars with greater commercial yield in the summer-winter transition crop (experiments 2 and 3) may be explained by the growing conditions, sometimes summer, sometimes winter, which impedes better adaptation of the cultivar to the environmental conditions of this growing season.
The mean dry matter content in the roots of the cultivars of the three experiments ranged from 8.6 to 10.3 % (Table 2).There was no effect of the cultivars on the dry matter contents in the roots only in the summer-winter transition crop with the summer cultivars (experiment 2).In the summer crop (experiment 1), the greatest dry matter contents in the roots were of the cultivars AF 2335, Bruna, Carandaí, and Juliana.In the summer-winter transitions crop season with winter cultivars (experiment 3), the greatest dry matter contents in the roots were in Maestro and Romance.The variation in dry matter contents in the roots is similar to that observed in other studies (Smolen and Sady, 2009;Figueiredo Neto et al., 2010).Knowledge of the dry matter content of the cultivar is used in estimation of dry matter yield based on total or commercial yield of the roots.This estimate is necessary for calculation of the amounts of nutrients accumulated and exported by the roots.
The mean value of the ratio between the dry matter of the roots and of the leaves ranged from 2.0 to 2.4, and in all the experiments exhibited differences among cultivars (Table 2).The greatest ratio was of the cultivar AF 2335 in the summer crop season (experiment 1), of the cultivars Juliana and Sigma (experiment 2), and of the cultivars Baltimore and Romance (experiment 3).The summer cultivars like Amanda, Bruna, Carandaí, Diana, Nativa, and Poliana exhibited the lowest ratios between root dry matter and shoot dry matter.In addition to the factor of the cultivar, this ratio is affected by climatic conditions, especially temperature.Greater temperatures reduce this ratio, i.e., there is greater allocation of photoassimilates in the leaves to the detriment of the roots (Hussain et al., 2008).
The ratio between root dry matter and leaf dry matter may be important in the estimate of nutrient uptake by carrot because, based on root dry matter production (more easily quantifiable), leaf yield may be estimated.The yields of roots and leaves, together with the respective nutrient contents, are determining factors for uptake and export of nutrients, which must be known for efficient fertilizer management (Oliveira et al., 2005;Santos et al., 2008).
For most of the nutrients, the cultivars differed in regard to the contents in the roots and leaves and the extraction and export of most of the The mean values followed by the same letter in the column do not differ among themselves by the Scott-Knott test at 5 %.** and *: significant at 1 and 5 %, respectively.ns : not significant.
nutrients (Tables 3 at 8).In general, the cultivars Juliana, Marli, Poliana, and Verano in the summer and transition crops had lower nutrient contents in the leaves and in the roots (Tables 3  and 5).The lower content is an indication that these cultivars accumulated more dry matter per nutrient unit taken up.This behavior is interesting for yield and, in fact, in the summer crop, these cultivars were highest yielding.In a similar manner, the winter cultivars in the transitions crop that had the lowest nutrient contents in leaves and in roots, Belgrado and Hana, were the highest yielding (Table 7).An exception was the K content in the leaves of the Belgrado cultivar, which was among the highest values found.The contents of Ca, Mg, K, and Zn are similar to those obtained by Nicolle et al. (2004) in various carrot cultivars with orangish colored roots in the south of France.
The contrasting nutrient contents among the cultivars associated with the different yields resulted in differences between the cultivars in regard to extraction and export of most of the nutrients (Tables 4, 6, and 8).Thus, it is necessary to consider the particular aspects of cultivars and of cropping systems on nutrient contents so as to obtain a better estimate of their extractions and exports for a balance between the applied and required amounts of nutrients.The amounts of K exported by the cultivars Juliana, Marli, and Verano in the summer crop (Table 4) and by the Nativa cultivar in the transition crop (Table 6) stand out, which went beyond 300 kg ha -1 of K.In the experiment with winter cultivars in the The mean values followed by the same letter in the column do not differ among themselves by the Scott-Knott test at 5 %.** and *: significant at 1 and 5 %, respectively.ns : not significant.
transition crop, the extractions and exports were less than in the other crops (Table 8).The lower extractions and exports of most of the nutrients by the cultivars Concerto, Forto, and Invicta stand out.The lower extractions of these cultivars are associated both with the lower contents in the leaves and in the roots (Table 7), as well as with the lower yields (Table 2).
The extraction of N and K for most of the cultivars in the three experiments went beyond the amounts applied through fertilizers.Thus, there was the contribution of soil nutrients to obtain the yields observed, without which there would have been nutritional limitation to yield.Nevertheless, exports were less than the amounts applied through fertilizer.In the nutrient balance, it is necessary to consider   The mean values followed by the same letter in the column do not differ among themselves by the Scott-Knott test at 5 %.** and *: significant at 1 and 5 %, respectively.ns : not significant.
both the total amounts taken up (roots and leaves), as well as exports (roots).Meeting the requirements of uptake allows the effect of nutritional limitation on yield to be minimized, while the application of at least the exports allows maintenance of soil fertility.
In the case of N, low levels of this nutrient in the soil may lead to reduction in organic matter in the soil.Costa et al. (2008) observed that the lowest contents of organic matter were observed in the soil under pasture without N fertilization.A suitable N The mean values followed by the same letter in the column do not differ among themselves by the Scott-Knott test at 5 %.** and *: significant at 1 and 5 %, respectively.ns : not significant.
supply may contribute to reducing degradation of organic matter or even increase it and, that way, maintain or improve the physical, chemical, and biological properties of the soil that interact with organic matter.
Mean extraction of P in the experiments ranged from 20.7 to 37.3 kg ha -1 and, in all cases, was influenced by the cultivar (Table 4,6,and 8).This is equivalent to extraction of 47 to 85 kg ha -1 of P 2 O 5 .The amount taken up is considerably less than that The mean values followed by the same letter in the column do not differ among themselves by the Scott-Knott test at 5 %.** and *: significant at 1 and 5 %, respectively.ns : not significant.
applied.This suggests that soil fertility in terms of P will increase after cropping.
Regardless of the crop season and the cultivar, the nutrient most taken up and exported was K, followed by N. It should be noted that Ca is the third element most taken up and only the fourth or sixth most exported, according to the cultivar.In contrast, Mg is the sixth most taken up and, nevertheless, for many cultivars, more exported than Ca.The cultivars Juliana, Marli, and Verano in the summer crop and Nativa and Conserto in the transition crop were those that showed the greatest exports of Mg.Thus, the correct choice of limestone or the use of additional sources of Mg is necessary for maintenance of the Ca:Mg ratio in the soil.Peixoto (2011) also found greater relative export of Mg in relation to Ca in the carrot cultivar Forto under cropping conditions in the Alto Paranaiba region (MG).The mean values followed by the same letter in the column do not differ among themselves by the Scott-Knott test at 5 %.** and *: significant at 1 and 5 %, respectively.ns : not significant.
The micronutrients most taken up and exported were Fe and B, and the least taken up and exported was Cu.The magnitudes of uptake and export of Zn and Mn varied with the crop and the cultivars.It should be noted that Fe has content and uptake similar to that of some macronutrients.This must be observed with caution because it may be linked to contamination of the samples with Fe from the soil.

CONCLUSIONS
The crop season and the cultivars influence the yield and the nutrient contents in the leaves and roots of the carrot crop, and the extraction and export of nutrients by the carrot crop.
Studies are necessary to quantify the efficiency of nutrient recovery by carrot cultivars, which,

Table 1 . Chemical characterization of the soil in the carrot cropping areas Property 1 st experiment 2 nd and 3 rd experiments 0-20 cm 20-40 cm 0-20 cm 20-40 cm
E x t r a c t o r s : P a n d K : M e h l i c h -1 ; C a 2+ , M g 2+ , a n d Al 3+ : KCl 1 mol L -1 ; H+Al: extracted by 0.5 mol L -1 calcium acetate at pH 7.0; B: hot water; Cu, Fe, Mn, and Zn: DTPA pH 7.3.

Table 8 . Nutrient extraction and export by winter carrot cultivars sown in the summer-winter transition crop season (Experiment 3)
Nutrient extraction (accumulation of nutrients in the leaves + roots) with nutrient uptake and soil fertility, allow estimation of the need for fertilizers. associated