Wood Fiber as Growing Medium in Hydroponic Crop J. Muro, I. Irigoyen and P. Samitier Dpto. Producción Agraria Universidad Pública de Navarra. 31006 Pamplona Spain

P. Mazuela Facultad de Agronomía Universidad de Tarapacá Chile

M.C. Salas, J. Soler and M. Urrestarazu Dpto. Producción Vegetal Universidad de Almería Spain

Keywords: coir, perlite, tomato, melon Abstract Fibralur  is a growing medium that comes from sawmill residues. The substrat has neither resins nor other phytotoxic compounds, and is an organic, stable and sterilized product. In this paper, three trials are showed in order to compare different growing media under hydroponic conditions, in two different crop production areas of Spain. Compared growing media were: wood fibre (Fibralur), coir and perlite. The first trial was developed in a greenhouse in Northern Spain with tomato crop (cv. Jack). The trial was designed to develop 4 successive cycles in the same bags. Yield, fruit quality, irrigation and drainages solution composition, were evaluated. At the beginning and at the end of the trial, physical characteristics of growing media was also analysed. The experiment started in July 2001 and finished in July 2003 (4 cycles). The results show that during first three crop cycles, there was no differences in commercial yield between growing media. In the last cycle, coir yield was lower than in perlite and wood fibre cases. The second trial was carried out in a greenhouse in Southern Spain, wood fibre and coir were tested in melon (cv. Yucatán) during one crop cycle (March – June 2002). This trial shows that yield and quality fruit are the same in the two treatments, without significant differences. The third trial was carried out in South, in the same place. In this case growing media were compared in tomato (cv. Pitanza). The study took one cycle (30 August 2002–January 2003). Growing media do not show yield significant differences, however, yield wood fibre slightly tends to come early. These results confirm the validity of Fibralur  as hydroponic growing medium, in the tested crop production areas, being a alternative, with environmental advantages, compared with other non bio-degradable growing media used nowadays. INTRODUCTION Nowadays, the increasing expansion of soilless production systems, the overexploited non-renewable natural resources, as in the case of peat, and the concern for the environment leads to the search of new substrates that fit as best a series of criteria: durability, minimum environmental impact in its obtainment, processing and use, and absence of problems in its elimination after its use as a substrate. The pine fibre substrate presents great expectations for application not only in a soilless production system, but also because it concerns a resource that is generated within our country, so it can be used with major economic and environmental profitability. In this paper the results are shown of the agricultural evaluation experiments with pine fibre being used as a substrate in a soilless production system with vegetables in contrast with other currently used substrates. MATERIAL AND METHODS The first experiment was carried out in a heated greenhouse, situated in San Sebastian (Northern Spain) in which three different substrates were compared: perlite, coir and wood fiber (Fibralur) during four consecutive production cycles of tomato, cv. Jack. The experiments were initiated in July 2001 and ended in July 2003, alternating two crop cycles summer-autumn with two crop cycles winter-spring. The first cycle (July-December 2001) started with bags filled with Fibralur (FI), perlite (PI) and coir (CI). In the second production cycle, three new treatments were added to the experiment. On the one hand new bags with perlite and coir, identical to the aforementioned but with one production cycle less (PN and CN). On the other hand, bags Proc. IS on Soilless Cult. and Hydroponics Ed: M. Urrestarazu Gavilán Acta Hort. 697 ISHS 2005

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were incorporated with Fibralur submitted to a less intensive fibrillation treatment than the one used in the first cycle and which we name Fibralur improved (FM). This way, from the second crop cycle on, the treatments in experiments make six, with the last three treatments having one production cycle less than the first three. The second and third experiments were carried out in two greenhouses belonging to the University of Almería. The second experiment was carried out between 1st of March and 27th of June 2002, evaluating the production of melon (cv. Yucatán) on Fibralur substrate in relation to the production obtained on coir. The third experiment was done between 30th of August 2002 and 15th of January 2003 evaluating the production of tomato (cv. Pitanza) on the same type of substrates. The irrigation system that was used in the crop in every experiment was drip irrigation, which was regulated by a controller. The supplied nutrient solution, drainage, pH and electric conductivity were measured during the cultivation period in one bag of every treatment in the first experiment, and in two bags, for the second and third experiment. During the harvest, regarding the first experiment, two times a week were determined the number of ripe fruits, their total weight and sorted according to the commercial classes (extra, first, second) and waste (damaged and small). To evaluate the possible influence of the substrate on the quality of the fruit the acidity, refractive index and pH of the juice of 8 ripe tomatoes were determined. Also was determined the composition of the ripe fruits concerning Ca, K and P, by means of ICP equipment, on samples of tomato triturated, dried, grinded and burned: the N-organic content was determined according to Kjeldahl (Hilrich, 1990). At the end of the first and last production cycle the water retention curves, porosity and density of each substrate were determined, according to the method described by Ansorena (1994). In the second experiment, the harvest of the melon started the 28th of May till the 25th of June harvesting once a week, in total five times. The weight and number of fruits were determined. The parameters to determine the quality of the fruits were: total soluble solids, firmness of the pulp and dry matter. And in the third and last experiment, the harvest of the tomatoes was done between the 29th of November and the 15th of January, taking care it was done each week. The weight and number of bunches were determined and the same quality parameters were measured as in the previous experiment. RESULTS AND DISCUSSION Production To assess correctly the results of the first experiment, it has to be emphasized that the first and third crop cycle pertain to the autumn crop cycle and the second and fourth correspond to the spring. Giving the better light and temperature conditions of the crop cycles during spring, in the 2nd and 4th cycle higher yields are obtained than in the 1st and 3rd crop cycle (Table 1). The quantitative production (total production, commercial, number of fruits) of the first three crop cycles was, in all cases, no significant differences was obtained, not being affected by the type of substrate, nor by the difference in age of the bags, indicating that the degradation suffered by the substrate did not affect the production. Only the commercial production of the tomatoes produced on coir reduced significantly, CN as much as CI during the fourth crop cycle (spring). Although this reduction is small, it represents a downturn of 14% in respect to the average of the other substrates (Table 1). Concerning wood fiber, it can be observed that FI in regard to FM does not show any significant differences in the commercial production. In spite of that, FI has obtained in all crop cycles better results than FM although without significant difference, as a result of which the improvements realized in aforementioned substrate have to be reconsidered. In the second experiment, the wood fiber reached a commercial production of 6.19 kg.m-2, for coir this value is 6.55 kg.m-2 (Table 2). One can observe a slight difference, but not significant, in favour of the coir. The pine fibre is able to produce at the same level in comparison to the control substrate. Concerning the number of fruits, no significant differences were found, neither in the total, nor in the weekly production. 180

And in regard to the third experiment, the wood fiber reached a commercial production of 9.47 kg.m-2, being the value for coir 7.67 kg.m-2 (Table 3). A difference of 1.8 kg.m-2 in favour of the wood fiber is observed, in contrast with the previous experiment, although without significant difference. Analysing the data per fortnight (data not shown), it can be observed that there is an advance in production during the first fortnight for the pine fibre in respect to the coir. Fruit Quality Analysing the parameters, examined in the first experiment, the amount of citric acid as well as the refractive index increase in all treatments during the course of the crop cycles, but always are maintained within the optimum level proposed by Segura (1995) (Table 1). As for N and P (Table 4), the maximum values were obtained in the treatments of the fourth crop cycle. In spite of that, all fruits presented the correct concentrations for tomato (Roorda van Eysinga and Smilde, 1981). On the other hand, regarding K, the first crop cycles have the highest concentrations, being in general low values. Finally, the Ca maintains the same amounts in all crop cycles apart from the coir, which contains major amounts in the fourth crop cycle and less in the third. Concerning the second and third experiment, for the measured parameters of the quality of the fruit: firmness of the pulp, percentage dry matter and total soluble solids (Table 2 and 3), no statistical differences exist between the treatments, neither in the average of the crop cycle nor in its evolution. Drain Analysis The results obtained in the control of the pH of the drain (data not shown) did not present differences between the various substrates in none of the experiments, maintaining satisfactory intervals for a good root development. In turn, no different response was measured because of the aging of the same. It can be highlighted in the first experiment the tendency, not significative, of the acidification of the drain from perlite. The natural tendency of cultivation media to acidify, due to the absorption of cations by the crop, can be neutralized in the case of organic substrates, coir and wood fiber (Loomis and Conor, 2002). Also can be observed that only a few times the pH differed one unit between the irrigation solution and drain, so in this case it also meets the interval proposed by Kläring (1998). The percentage of drain reflects the different behaviours of the various substrates in regard to the absorption of water. In general, all treatments present the same behaviour. The percentage of volume of drain that was considered suitable to obtain good results was comprised between 20-30% (Nuez, 1995). In most of the cases, it exceeded this range, apart from the second experiment, where the drain kept in between these limits. The coir showed in general a major absorption of water, which is not surprising, yet it has a major capacity to retain water than the other substrates. Physical Characteristics of the Substrates Used The analyses of the physical characteristics were only done after the first experiment, at the end of the fourth crop cycle. These analyses show the decomposing experienced in all treatments. Comparing the results between the first and the last season one can observe that the typical decomposing reaction of the substrate FI as well as FM (Fig. 1) due to its repeated use, is the reduction of air volume, particularly at a pressure of -10 cm water column. This is caused by the breaking-up of the fibres provoking a loss of structure, reducing the number of macro-pores and increasing the number of pores with a reduced size. The two versions of Fibralur had lost their capacity to retain air, being FM the one that had the major aeration capacity of the two. With respect to perlite (Fig. 2), and like Fibralur, with repeated use, bit-by-bit it was loosing the aeration capacity. Perlite has a good air capacity at a pressure of -10 cm of water column, also in the 4th cycle. Concerning coir (Fig. 3), it offers less aeration at a pressure of -10 cm of water column than perlite and Fibralur. This is shown clearly with its use, as just like the other substrates, the decomposition reduces the air capacity of the said substrate even more. So, one can affirm that Fibralur improved acts satisfactory with regard to its repeated 181

re-use in successive crops, being the substrate with major aeration capacity of all. As well as Fibralur like perlite in the last crop cycle, maintain a suitable aeration capacity. Coir has initially less aeration capacity than the two previous, and at the same time presents also major decomposition during the experiment. CONCLUSIONS The quantitative and qualitative production of tomato and melon in hydroponic culture using bags with wood fiber does not differ in respect to the obtained with other substrates, improving even the one obtained with coir, in the fourth repetition of the cropping cycle. No significant differences were observed between the initial Fibralur and the Fibralur improved (trial 1), although the initial Fibralur always obtained better results. Therefore, the improvements made in this substrate should be reconsidered in future experiments. Concerning its behaviour in relation to the physical decomposition, initial Fibralur and Fibralur improved show a good performance, maintaining an adequate % of aeration including during its use in the last crop cycle. Coir is the substrate with initially less aeration, provoking a slight reduction in production when it is re-used during four cycles. Fibralur, still from organic origin, doesn’t show problems in its reiterative use, being sufficiently stable to guarantee during at least four crop cycles the appropriate conditions for cultivation in hydroponics, and it can be used as an alternative substrate with the same results in production and quality as the substrates used nowadays. Literature Cited Ansorena, J. 1994. Substratos: Propiedades y caracterización. Mundi-Prensa. Madrid. Kläring, H.P. and Cierpinski, W. 1998. Control of nutrient solution concentration depending of greenhouse climate in sweet pepper crop. Proc. IS Water Quality & Quantily in Greenhouse Horticulture. Acta Hort. 458: 141-146 Hilrich, K. 1990. Oficial Methods of analysis of the AOAC. Pp: 127-129. AOAC. International Washington. USA. Loomis, R.S. and Connor, D.J. 2002. Ecología de cultivos. In: Productividad y manejo en sistemas agrarios. Mundi-Prensa. Madrid. Muro, J., Irigoyen, I. and Salazar, R. 2004. Estudio comparado de un substrato de fibra de madera como substrato de cultivos hidropónicos, en condiciones de clima atlántico. Proc. VII Jornadas de Substratos. Marzo 2004. Madrid. (in press). Nuez, F. 1995. El cultivo del tomate. Mundi-Prensa. Madrid. Roorda Van Eysinga, J.P.N.L and Smilde, K.W. 1981. Nutritional disorders in glasshouse tomatoes, cucumbers and lettuce. Centre of Agricultural Publishing and Documentation. Wageningen. Netherlands. Segura, 1995. Fisiología de la planta del tomate. In: El cultivo del tomate. Mundi-Prensa. Madrid. Urrestarazu, M., Soler, J. and Salas, M.C. 2002. Evaluación agronómica de la fibra de pino como substrato para uso en hortícolas. Proc. VII Jornadas de Substratos. Marzo 2004. Madrid. (in press)

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Tables

Table 1. Commercial production, number of fruits, acidity and refractive index, for various substrates: initial Fibralur (FI), Fibralur improved (FM), initial perlite (PI), new perlite (PN), initial coir (CI) and new coir (CN) in trial 1. FI Commercial prod. (kg/m2) 1er ciclo

FM

PI

PN

CI

CN

2º ciclo 3er ciclo 4º ciclo

8.53 a(*) 15.77 a 10.22 a 14.74 a

15.77 a 9.54 a 13.87 ab

16.25 a 9.94 a 14.54 a

13.96 a 9.32 a 11.54 b

Fruits/m2 1er ciclo 2º ciclo 3er ciclo 4º ciclo

9.26 a 16.5 a 10.49 a 14.04 ab

9.49 a 15.53 a 9.89 a 13.07 b

57.2 a 74.8 a 116 a 63.45 a

74.3 a 110 a 60.6 a

76 a 113 a 64.15 a

58 a 74.4 a 114 a 60.35 a

69.3 a 105 a 54.4 a

62 a 73.9 a 127 a 59.3 a

Citric Acid (g/l) 1er ciclo 2º ciclo 3er ciclo 4º ciclo

4.49 3.53 5.68

3.44 6.43

4.47 3.53 5.68

3.64 5.56

4.84 3.89 5.92

3.65 5.66

4.12 5.51 6.2

4.23 6.1

4.31 4.6 5.8

4.42 6.1

4.18 4.29 6.1

4.45 4.8

°Brix

1er ciclo 2º ciclo 3er ciclo 4º ciclo

(*) Horizontally, the average with the same character do not differ significantly (p< 0.05) according to the S-NK test.

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Table 2. Commercial production, number of fruits, acidity, total soluble solids, firmness of the pulp and percentage dry matter in melon crop (trial 2) for the substrates coir (C) and pine fibre (F). Variable Commercial prod. (kg/m2) Fruits/m2 Total soluble solids (ºBrix) firmness of the pulp (kg) Dry matter (%)

C 6,55 a(*) 5,08 a 12,30 a 1,72 a 10,14 a

F 6,19 a 5,12 a 11,78 a 1,64 a 9,89 a

sig. n.s. n.s. n.s. n.s. n.s.

(*) Horizontally, the average with the same character do not differ significantly (p< 0.05) according to the S-NK test.

Table 3. Commercial production, number of fruits, acidity, total soluble solids, firmness of the pulp and percentage dry matter in tomato crop (trial 3) for the substrates coir (C) and pine fibre (F). Variable

C

Commercial prod. (kg/m2) bunchs/m2 Total soluble solids (ºBrix) firmness of the pulp (kg) Dry matter (%)

7,67 a(*) 14,10 a 4,6 a 3,4 a 5,4 a

F

sig.

9,47 a 16,52 a 4,7 a 3,7 a 5,2 a

n.s. n.s. n.s. n.s. n.s.

(*) Horizontally, the average with the same character do not differ significantly (p< 0.05) according to the SN-K test.

Table 4. N, P, K and Ca (%) content of the ripe tomatoes obtained in the 1st, 3rd and 4th cycle of trial 1. (1C, 3C, 4C). %N

%P

%K

%Ca

Substrate 1C

3C 4C

1C

3C

4C

1C

3C

4C

1C

FI

1.8

-

2.5

0.42

-

0.47

5.1

-

4.5

0.12

FM

-

-

2.6

-

-

0.50

-

-

3.9

-

-

Perlite

1.9

2.2

2.3

0.46

0.44

0.50

5.2

3.7

4.0

0.11

0.12 0.11

Coir

1.9

2.0

2.1

0.46

0.45

0.48

5.0

3.9 3.2

0.12

0.09 0.17

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3C 4C -

0.13 0.13

Figures 100

water AGUA % volum en

80 60 40

AIRE air

20 0 0

50 Tensión Pressure (cm )

100

Fibralur inicial Fibralur (FI)tras after1 1ciclo cycle

Fibralur tras 1 ciclo Fibralurmejorado (FM) after 1 cycle

Fibralur inicial Fibralur (FI) tras after44ciclos cycles

Fibralur tras 3 ciclos Fibralurmejorado (FM) after 3 cycles

Fig. 1. Water retaining curves of initial Fibralur (FI) and Fibralur improved (FM) in trial 1. 100

water AGUA

% volum en

80 60 40

AIRE air

20 0 0

50 Tensión (cm ) Perlita tras 1ciclo

100 Perlita tras 3 ciclos

Perlita tras 4 ciclos

Fig. 2. Water retention curves of perlite in various cycles of experiment 1. 100

AGUA water % volum en

80 60

AIRE air 40 20 0 0 Fibra 1 ciclo Coir coco after 1tras cycle

50 Tensión Pressure (cm )

100 Fibraafter coco 3 ciclos Coir 3 tras cycles

Fibra 4 ciclos Coir coco after 4tras cycles

Fig. 3. Water retention curves of coir in various cycles of experiment 1.

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