Vegetative Development and Nutrient Absorption March of Sorrel ( Rumex acetosa L . )

Sorrel (Rumex acetosa L.) is an unconventional food plant. It is a perennial herbaceous plant that forms thickets. There are studies related to the accumulation of nutrients in sorrel, but there is no information on its absorption march and vegetative development. The objective of this study is to determine macronutrient absorption and biometric parameters of sorrel during 60 days after seedling transplantation (DAT) of seedlings. The experiment was completely randomized with eight treatments and four replications. It was conducted in a greenhouse. The treatments consisted of plant collection times, performed at 15, 20, 25, 30, 35, 40, 50 and 60 DAT. Plants’ biometric parameters (leaf blade length, relative leaf area, and shoot fresh and dry matter) and macronutrient absorption march were evaluated. Biomass, leaf blade length and relative leaf area of sorrel plants increased over time and, more markedly, after 35 DAT. The maximum levels of macronutrients accumulated in sorrel shoots, in descending order, were K > N > Ca > Mg > P > S. There was no significant difference in Ca and S contents among collection times, that is, the absorption and accumulation of these nutrients by sorrel did not vary throughout the evaluation time.


Introduction
The agroindustry and markets have neglected some plants.They are currently considered weeds or grasses (Viana et al., 2015).Their ecological importance and their economic and food potential are neglected.This is mainly due to the modernization of agriculture and globalization, as well as the life style of contemporary society (Kinupp & Barros, 2004).Such species, known as unconventional food plants (PANCs), have been kept and grown in small gardens, backyards and farms.According to Madeira and Kinupp (2016), the term PANC began to be disseminated in 2008 through the documentary "PANCs Project: food sovereignty and palpable biodiversity", and the definition also includes food plants of non-organized productive chains.The recovery and valuing of such plants in food represent extraordinary gains.Traditionally, they are present in typical regional dishes relevant to cultural expression (Pedrosa et al., 2012).Encouraged mainly by rural tourism, these dishes have been rescued and reinvented, which has fostered the market of these dishes.
Sorrel (Rumex acetosa L.) is a perennial herbaceous plant of the family Polygonaceae.It reaches 25-55 cm in height and forms thickets with dozens of propagules (Kinupp & Lorenzi, 2014).It has a low nutritional requirement and adapts to medium to low fertility soils (Gaweda, 2008).Sorrel is considered an unconventional food plant because it was at one time widely consumed by the population and, due to changes in dietary behavior, its economic and social expressions decreased, losing space and market for other vegetables (Pedrosa et al., 2012).This species occurs in wild regions of Europe, Asia and North America.In Brazil, it is cultivated in mild climate regions from Rio Grande do Sul to Minas Gerais (South-Southwest region).Its leaves can be consumed in natura or cooked.However, they present a high content of antinutricional factor, calcium oxalato, which limits the consumption by people with renal problems (MAPA, 2010).However, Redzic (2006) reported that this species has some therapeutic properties such as anti-scurvy, anti-diarrhea, anti-inflammatory and anticancer activity.It contains other substances, such as tannins, anthraquinones and flavonoids (Viana et al., 2015).The roots have an antioxidant activity and a mixture of polysaccharides revealed antitumor action in mice (Lee et al., 2005).Despite its importance, there is a lack of information on sorrel.Therefore, further studies on production, cultivation and nutritional properties are needed.
Knowledge on the nutrient absorption march, which is related to the plants' development stage, is of great importance for a rational fertilization strategy.Such knowledge avoids nutrient losses due to volatilization and leaching, and the possibility of contamination of water blade and watercourses.Such studies would allow understanding the moment when each element is more intensely absorbed, indicating the appropriate time for its supply (Fernandes et al., 1975).Absorption and nutrient requirements vary according to the plant's development stage.Nutrient requirements intensify at flowering and fruiting (Kano et al., 2011).In relation to sorrel, there are studies on nutrient accumulation (Silva et al., 2013;Torres, 2014;Viana et al., 2015;Silva et al., 2018).However, there is no information on the absorption march.
Thus, the objective of this study is to determine macronutrient absorption and biometric parameters of sorrel during 60 days after transplantation (DAT) of seedlings grown from seeds.

Method
The experiment was conducted in a greenhouse at the Agricultural Sciences Center of the Federal University of São Carlos (UFSCar) in the municipality of Araras, SP (22º18′00″ S, 47º23′03″ W, 611 m altitude), from August to November 2014.
The substratum was Alic Red Latosol (Oxisol) with a clayey texture (LV) (EMBRAPA, 2013).After sieved, the soil was placed in polyethylene pots with a capacity of 4.5 dm 3 .According to manuals of cultivation of unconventional vegetables (Silveira et al., 2010;Pedrosa et al., 2012), the recommended fertilization for sorrel cultivation should be similar to that used for lettuce.Lettuce fertilization was used as reference in this study.In March 2014 (180 days before transplantation of seedlings to pots), 5.7 g of dolomitic limestone (PRNT = 85%) were added to each pot to raise base saturation to 70% according to the recommendation for lettuce (Raij et al., 1997).The soil chemical analysis for fertility purposes was performed after liming following methods described by Raij et al. (2001).The results are pH = 5.2, P (resin) = 2.40 mg dm -3 , K = 2.9 mmol c dm -3 , Ca = 27 mmol c dm -3 , Mg = 12 mmol c dm -3 , H + Al: 29 mmol c dm -3 , base saturation: 41.4 mmol c dm -3 , cation exchange capacity: 70.4 mmol c dm -3 , and SOM = 9.5 g kg -1 .
In order to standardize the development of all sorrel seedlings, the planting was done using seeds rather than division of thickets, as this species is commonly propagated.By using division by thickets, there is hardly any standardization in the development of seedlings due to a greater variability in the energy reserve of each propagule.Seeds, obtained from Botanical Interests, Inc. (lot # 3), were sown in 128-cell expanded polystyrene trays using commercial substrate for the production of vegetable seedlings.After five days, seedlings emerged.The results of the chemical analysis of the substrate (Nogueira & Souza, 2005) were pH (CaCl 2 ) = 5.5, presine = 102.0mg dm -3 , OM = 175.0g dm -3 , K = 7.7 mmol c dm -3 , Ca = 72.0mmol c dm -3 , Mg = 24.0mmol c dm -3 , H + Al = 25.0 mmol c dm -3 , BS = 104.0mmol c dm -3 , total CEC = 129.0 mmol c dm -3 , and V% = 81.
In September 2014, twenty-five days after plant emergence in trays, the seedlings were transplanted to the pots.Each pot received one plant.At that time, planting fertilization was carried out following the recommendation for lettuce (Raij et al., 1997): 0.5 g of ammonium sulphate per pot (40 kg ha -1 of N), 5.6 g of simple superphosphate per pot (400 kg ha -1 of P 2 O 5 ), and 0.4 g of potassium chloride per pot (100 kg ha -1 of K 2 O).Cover fertilizations were carried out at 10, 20 and 30 days after transplantation by applying 0.30 g of ammonium sulfate (75 kg ha -1 of N) per pot at a time.After seedling transplantation, the pots were kept at a humidity of 70% of field capacity, verified daily by weighing.

The analy parameters
Normally, indicate a absorption leaf area) p 0.98 and s days after matter (Fig Figure 1      absorption (Marenco & Lopes, 2009).It may explain the small variation in the absorption of Ca by sorrel plants over time.
The maximum levels of macronutrients accumulated in sorrel shoots, in descending order and in g kg -1 , were 58.22 (K) > 45.94 (N) > 10.1 (Ca) > 7.09 (Mg) > 5.95 (P) > 3.9 (S).The result is similar to that obtained by Silva et al. (2013) and Torres (2014) in their studies on sorrel.However, these results differed from the decreasing order of macronutrients accumulated in different lettuce cultivars obtained by Granjeiro et al. (2006), which was K > N > P > Mg > Ca.
The use of nutrient content curves as a parameter for fertilization recommendation is a good indication of the nutrient needs at each stage of plant development.The amounts absorbed were optimal to achieve a certain productivity, thus helping to establish a fertilization for the crop and mainly facilitating the fractionation of fertilization.However, they should not be used in isolation since other factors are involved and should be taken into account, such as soil type, climatic conditions, crop management and fertilizers (Grangeiro et al., 2006).
Concentrating a fertilizer that provides macronutrients at the beginning of transplantation of sorrel plants whose seedlings were obtained from seeds seems to be an way to promote the best use of nutrients for plant development, especially before the estimated commercial harvest interval (between 20 and 35 DAT).A good strategy would be to increase the amount of N in planting fertilization and to perform only one cover fertilization at 15 DAT.The maximum biomass accumulation point did not occur within the estimated harvest interval.These results probably do not apply to seedlings obtained from seeds.Further studies on this topic are needed.According to Torres (2014), it is important to consider the amount of nutrients exported by the crop since it represents a constant and increasing loss of system elements because sorrel is a plant that re-sprouts and allows successive cuts.

Conclusion
Biomass and relative leaf area of sorrel plants increased over the days after transplanting and, more markedly, within the estimated commercial harvest time (20-35 DAT), when the leaves would have 10.2 and 20.13 cm in length, respectively.
The maximum absorption of N, P, K and Mg occurred after the estimated commercial harvest interval.The Mg absorption peaked near the maximum biomass accumulation point.
Figure 2. A