Mulches for yacon cultivation

In Brazil, studies on commercial exploitation of yacon are still scarce. A growing interest in this vegetable has demanded some researches on this crop cultivation management, though. Considering that yacon has a long cycle, which exposes the soil, studies on mulch management will be of great value. We used a randomized complete block design, with five replicates, under different soil mulches for yacon cultivation: two plastic film covers (black and double-sided), four mulches (corn husk, coffee husk in three levels), and the control (bare soil). Plastic mulch can be used for yacon cultivation, considering that the double sided plastic provides greater production of total roots; however, the same yield of the most valued roots was obtained using black plastic. The second highest total productivity and the highest commercial yield in the most valued root classes were obtained using 50 L m-2 of coffee husk as mulch, representing a good alternative for farmers.


Scientific communication
Hortic.bras., Brasília, v.36, n.3, July -September 2018 F ast paced life has caused serious harm to human health; that is why people have been seeking healthier lifestyles.Changing eating habit is one of the main goals to achieve, related to health benefits, targeting both sensory and nutritional quality (Barcellos et al., 2009).In this context, some functional foods, which present both nutritional and nutraceutical values, had appeared on the market (Zeraik et al., 2010).
A functional food that has attracted the interest of population is yacon root (Smallanthus sonchifolius), due to presence of bioactive elements in its composition, such as inulin-type fructose and fructo-oligosaccharides which provides several benefits to health (Gusso et al., 2015).
Its consumption has provided well-known benefits such as immune stimulatory effect (Tostes et al., 2014), prebiotics (Campos et al., 2012) and protection against colon cancer (Moura et al., 2012), besides acting in reduction of serum lipids (Habib et al., 2011), in intestinal regularization (Lobo et al., 2011), and in modulation of fasting insulin (Genta et al., 2010), and it also has provided control of chronic diseases like diabetes (Oliveira et al., 2013b).
Recent studies have further stimulated the consumption of yacon, increasing interest on this crop, especially food and pharmaceutical industries.In Brazil, the earliest cultivation took place in the countryside of São Paulo State, in the late 1990s.Yacon has been grown recently on the mountainsides of Rio de Janeiro, Santa Catarina and Espírito Santo States (Oliveira et al., 2013a).Nevertheless, to guarantee success of commercial production of yacon, technological knowledge on this management is necessary.This information is still scarce, though, mainly in Brazil.
Appropriate soil management is crucial to explore yacon as vegetable, considering that this crop presents a slow initial growing, it is able to take up to 60 days to emerge, and a long cycle, from 7 to 11 months (Silva, 2015), which allows soil exposure.
One good alternative to protect soil would be the use of mulch, which is already popular for growing vegetables,

Received on February 15, 2017; accepted on February 13, 2018
since it also contributes to improve production and quality of products.Some studies report the advantages of using mulch in growing onions (Santos et al., 2012), carrot (Resende et al., 2005) and beet (Sediyama et al., 2011), crops that, such as yacon, accumulate reserves in underground organs.
Several materials can be used in order to provide soil cover.For vegetable production, plastic films are more commonly used, as well as plantorigin materials, such as wood chips, bark and straw in general (Sediyama et al., 2011;Santos et al., 2012), including living mulches (Silva et al., 2013).
Nevertheless, the success with the use of mulch depends on information about appropriated management in each environment and about the growing crop.Thus, with an increase and recent commercial exploitation of yacon, studying soil mulch management is pretty important for its cultivation.
The aim of this study was to evaluate growing and production of yacon, cultivated under different mulch types.
The experimental design was randomized blocks, with five replicates and seven treatments: two plastic film covers, one black and another double sided (black/white); one covered with corn straw (30 L m -²); three covered with coffee husk under different levels (25, 50 and 75 L m -², considered levels 1, 2 and 3, respectively); and one under bare soil (control).
Each experimental plot consisted of 4 planting rows with 7 plants, spaced 1.0 between rows and 0.5 between plants.
The authors used two central rows as useful area, except the border plants of each row.
Soil was covered with mulching polypropylene (MPP), 25 micrometers thickness, [ElectroPlastic SA, MPP-P (black) and MPP-P&B (black/white)]; MPP-P&B film offers a black and a white side, the black side was in direct contact with soil.Soil was plowed at 30 cm followed by harrowing.After this soil preparation, the film was stretched over planting lines, covering 80 cmband of soil and then, pits were opened to plant seedlings.
Corn straw mulch was obtained from what was left of mechanical treshing (spike straw and ground corncob), which was performed 50 days before.During this period, straw was exposed to weather conditions.Coffee husk was obtained from Arabica coffee processing, done 270 days before its use, and was also exposed to weather conditions.
Yacon seedlings were formed through herbaceous stakes, measuring approximately 10-15 cm from adult plants.The stakes were put in 600-mL volume plastic bags (traditionally used for coffee seedling production), being irrigated daily.After 60 days, seedlings were ready to be planted, being selected the uniform sized.
Top-dressing fertilization was performed 50 days after transplanting, using 180 g of tanned bovine manure per plant.Bovine manure showed the following nutrients: 10.1 g kg -1 N; 3.96 g kg -1 P; 7.59 g kg -1 K; 4.54 g kg -1 Ca and 2.14 g kg -1 Mg.Additional irrigation was not done in the area.
Data were submitted to analysis of variance using ASSISTAT program (Silva & Azevedo, 2006).Average of original data related to height, number of leaves and number of stems were adjusted, based on simple linear regression, to different models, considering time as an independent variable.The authors chosed 2 nd degree polynomial model since it represents higher coefficient of determination (R 2 ) and significance of all regression coefficients (Table 1).The other data were submitted to Scott-Knott tests at 5% probability.

RESULTS AND DISCUSSION
Yacon vegetative development was influenced by soil covers.For all the evaluated variables (plant height, number of stems and number of leaves), the authors noticed practically no difference among treatments up to days after transplanting.From days on some difference in plants was noticed; this difference became clearer from 180 days on, mainly for coffee straw mulch, at levels 2 and 3 (50 and 75 L m -²) and two plastic mulches (black and double sided), considering that, using these covers, higher heights, larger number of stems and leaves were observed (Figure 1).
Overall, the authors observed that yacon plants showed a small difference in number of leaves from 60 up to 150 days, probably due to strong dry weather in this period (from June to September, 2015).Average rainfall was 22.3 mm/ month, considering that during July, the rainfall was only 5 mm and in August no rain at all.From this date up to the end of the cycle, the authors observed an increase in number of leaves, and that soil covers, mainly the coffee straw mulch at levels 2 and 3 and the two plastic mulches (black and double sided), promoted larger numbers (Figure 1).
Yacon plants grown using coffee straw mulches (levels 2 and 3) and two plastic covers (black and double sided) showed higher plants with greater number of stems (on average 100%), as well as with greater number of leaves (45%), compared to the ones which were grown in bare soil.This can be a result of water storage in covered soil, since according to Fernández et al. (2006), water availability is determinant for growth and productivity yield of yacon.Thus, all agricultural practice which benefits this availability may result in gains in this crop.
Generally, heights observed in plants with higher growth, were a little shorter, 110 to 130 cm, than the ones observed by Silva (2015), which measured around 170 cm, at 270 days after planting, being planted at the same time and in the same region.The same situation was observed for number of stems, from 2.5 to 3.5, from plants with higher growth, whereas Silva (2015) reported from 6 to 10 stems per plant.
This behavior may be related to propagation material, since in this study, seedlings from herbaceous stakes were used, whereas Silva (2015) used seedlings from rhizophores.According to Robles (2002), plants obtained from rhizophores showed better growth, mainly in initial phase, since they take advantage of the reserves accumulated in these reproductive structures, when compared with plants from axillary buds, resulting in higher plants, which can improve harvesting rates.
Vegetative growth gains, with number of stems and leaves, and higher plants, can reflect greater lightintercepting capacity, consequently an increase in photosynthetic rates, which reflects in greater dry matter accumulation in plants, which was noticed in plants grown under plastic covers (double sided and black) and with coffee husk (at levels 2 and 3) (Table 2).
The authors noticed that plants grown under coffee husk mulch at levels 2 and 3, besides showing greater total accumulation, also showed greater mass accumulation in rhizophores and roots, considering that the mass accumulation in roots was the same obtained under both plastic mulches (Table 2).
Higher production of rhizophores was presented with coffee husk mulches at levels 2 and 3, given that these materials show better potential for yacon propagation (Robles, 2002).Thus, their higher production could allow not only increase farmers' autonomy for future plantations, but also increase their commercial value, both as propagation material and as source of FOS, considering that rhizophores have large amounts of this oligosaccharide (Vilhena et al., 2000).
The results show that the use of a good mulch benefits yacon development.This behavior has been observed in several crops, being related to a greater water and nutrient conservation in soil, protection against erosion, increase in microbial activity and photosynthesis, lower thermal amplitude and greater control of spontaneous vegetation (Resende et al., 2005;Santos et al., 2011).
The best development of yacon observed with the use of soil covers resulted in higher fresh root productivities.The authors highlighted that higher total productivity was observed using double-sided plastic film, followed by coffee husk mulch level 2 and then coffee husk cover level 3 and with black plastic film, considering these last ones statistically Volume of 25 L m -2 ; 2 Volume of 50 L m -2 ; 3 Volume of 75 L m -2 .
Mulches for yacon cultivation 1 Volume of 25 L m -2 ; 2 Volume of 50 L m -2 ; 3 Volume of 75 L m -2 .Averages followed by same letter in the column did not differ significantly from each other, Scott-Knott, p<0.05.
Productivities observed were lower when compared with the ones obtained by Silva (2015), who also planted in October in the same region (average of 97.5 t ha -1 ).This difference is associated, mainly, to the water deficit from June to November, 2015.The exception within these 6 months was October, registering 145.8 mm and to propagative material used, herbaceous stakes, which showed lower growth, when compared with the plants from rhizophores, resulting in lower harvest index, as cited by Robles (2002).
Overall, yacon productivity is very varied.Some authors report that this is due to the influence of the propagative material, as well as to fertilization, spacing, soil and climatic conditions and different planting times (Robles, 2002;Kruger, 2003;Silva, 2015).
Mulches also influenced yacon fresh root classes.The authors noticed that mulching with coffee husk level 2 was the one which showed higher productivity of roots class 3A, followed by the mulch with two types of plastic films and then by the mulch with coffee husk level 3.For class 2A, the authors observed that these four mulches showed the same productivity, statistically.For class 1A, higher productivity was noticed using mulch with double-sided plastic film (Table 3).
H o w e v e r, g r e a t e r e c o n o m i c profitability, related to best prices on the market, is obtained producing classes 3A and 2A, and considering this fact, the mulch with coffee husk level 2 stood out since it presented higher volume even considering the sum of these two classes (20.93 t ha -1 ), which represented a yield of 73.8% of roots.
That means that great part of roots did not meet market needs, which represents economic losses.
Besides gains in root quantity, mulches also provided a small change in soluble solid contents (ºBrix) in roots.
The mulches with double-sided plastic film, corn straw and coffee husk level 3 showed higher ºBrix values (Table 3).
Higher soluble solid contents promoted by these mulches are interesting to yacon roots, since this index is expected to be used to verify the quality of roots, mainly due to the habit of eating raw roots; considering that, the higher the soluble solids content the greater the sweetness and the quality, and, therefore, consumers' greater interest (Gusso et al., 2015).
Other chemico-physical variable analyses did not show significant differences related to the use of different mulches, considering that pH values ranged from 5.94 to 6.29, corroborating  2015) from 0.17 to 0.48%.Given the above, the authors concluded that yacon plants are benefited by mulches, showing better vegetative and productive development, standing out the possibility of using soil cover technology.The double-sided mulch is the one which promotes higher total production volumes, showing the same yields when using the black plastic, for production of roots in the most valued classes, though.
Among the mulches which provided better performance of this vegetable, the coffee husk mulch stands out, mainly the one with 50 L m -², besides being lower volume (comparing with 75 L m -²), making handling easier, promoted the second best total productivity and higher yield of roots in the most valued classes.
This fact allows the use of this mulch in several productive systems, including organics, resulting in a good return with lower investment, mainly in regions where coffee is produced, and its husk is an abundant and available resource.
In short, soil cover for yacon cultivation can be done using plastic, considering that the double-sided plastic provides higher total production volumes of roots and higher gains in soluble solids, with the same yields the black plastic provides for roots in the most valued classes.
Mulch using 50 L m -² of coffee husk promotes the second best total productivity and better yields for roots in the most valued classes, representing a good alternative to the farmer who does not want to use agricultural plastics.for Scientific and Technological Development) and FAPES (Research Support Foundation) for financial support to this research.To FAPES for capixaba researcher scholarship to the first authors.

Table 1 .
Coefficients of the second degree polynomial model [Y = a+bt+ct 2 ] adjusted to height, number of stems and leaves of yacon plants grown under different soil mulches.Ibatiba, UFES, 2015.

Table 3 .
Total productivity and productivity per class, and soluble solids content of yacon roots grown under different mulches.Ibatiba, UFES, 2015.