Vegetable Waste Compost Used as Substrate in Soilless Culture

One of the main environmental impacts of forced systems in horticulture – such as plastic covers and soilless culture is the generation of organic plant residues and substrate waste. For example, the surface area of greenhouse cultivated crops in the province of Almeria, in southeastern Spain, exceeds 30,000 ha. These generate approximately 1,000,000 tons of solid plant waste per year. Greenhouse industry residues cause serious environmental and visual pollution, making it necessary to look for new ways to eliminate these plant residues. This mass not only acts as a host for pests, microorganisms, rats and insects; it also has other harmful environmental effects such as pollution of the soil by toxic elements, effluent runoff, and the emission of bad smells. Conway (1996) indicated that an important factor for sustainable agriculture in areas using protected systems is the need to eliminate the harvest residues of these crops. Controlled composting appears to be an effective method of eliminating residues by recycling them. For example, Ozores-Hampton et al. (1999) reported that in Florida 1.5 million tons of compost could be produced per year. The wastes generateed by intensive agriculture systems are very varied and frequently cannot be reused directly. Cara and Ribera (1998) indicated that greenhouses generate 29.1 tons of vegetable waste per ha and 6-10 tons of substrate remains per year in the province of Almeria (Spain). A less indiscriminate form of management of these residues, however, could turn them into usable products. This would also reduce their environmental impact. Callejon et al., 2010 indicated that the assessment of the environmental impact of a potential waste treatment plants showed that it would be better to recycle and compost waste than to try to obtain energy from it through combustion. This compost can be used as a soil conditioner or to improve the structure in degraded soils or those with low organic matter content. Another alternative is to reuse these residues, incorporating them as ecologically friendly substrates in soilless cultivation in the form of compost. Using waste materials, most of them locally produced, as soilless growing media has been the subject of an important number of studies, especially as an alternative to peat for ornamental potted plants (e.g., Ingelmo et al., 1997; Offord et al., 1998; Lao and Jimenez, 2004a,b), and less frequently for vegetable production (Shinohara et al., 1999; Ball et al., 2000) and even for tomato transplant production (Ozores-Hampton et al., 1999). However, it


Introduction
One of the main environmental impacts of forced systems in horticulture -such as plastic covers and soilless culture -is the generation of organic plant residues and substrate waste. For example, the surface area of greenhouse cultivated crops in the province of Almeria, in southeastern Spain, exceeds 30,000 ha. These generate approximately 1,000,000 tons of solid plant waste per year. Greenhouse industry residues cause serious environmental and visual pollution, making it necessary to look for new ways to eliminate these plant residues. This mass not only acts as a host for pests, microorganisms, rats and insects; it also has other harmful environmental effects such as pollution of the soil by toxic elements, effluent runoff, and the emission of bad smells. Conway (1996) indicated that an important factor for sustainable agriculture in areas using protected systems is the need to eliminate the harvest residues of these crops. Controlled composting appears to be an effective method of eliminating residues by recycling them. For example, Ozores-Hampton et al. (1999) reported that in Florida 1.5 million tons of compost could be produced per year. The wastes generateed by intensive agriculture systems are very varied and frequently cannot be reused directly. Cara and Ribera (1998) indicated that greenhouses generate 29.1 tons of vegetable waste per ha and 6-10 tons of substrate remains per year in the province of Almería (Spain). A less indiscriminate form of management of these residues, however, could turn them into usable products. This would also reduce their environmental impact. Callejón et al., 2010 indicated that the assessment of the environmental impact of a potential waste treatment plants showed that it would be better to recycle and compost waste than to try to obtain energy from it through combustion. This compost can be used as a soil conditioner or to improve the structure in degraded soils or those with low organic matter content. Another alternative is to reuse these residues, incorporating them as ecologically friendly substrates in soilless cultivation in the form of compost. Using waste materials, most of them locally produced, as soilless growing media has been the subject of an important number of studies, especially as an alternative to peat for ornamental potted plants (e.g., Ingelmo et al., 1997;Offord et al., 1998;Lao and Jiménez, 2004a,b), and less frequently for vegetable production (Shinohara et al., 1999;Ball et al., 2000) and even for tomato transplant production (Ozores-Hampton et al., 1999). However, it www.intechopen.com has been suggested that certain types of compost alone are unsuitable as growing media due to unacceptably high salt and pH content (Spiers and Fietje, 2000), in particular when immature, unstable compost is used (Ozores-Hampton et al., 1999). Another disadvantage of the use of compost as substrate is that it is a very heterogeneous material and therefore needs to be amended so that it can be used as substrate Urrestarazu et al., 2001;Urrestarazu et al., 2003;Sanchez-Monedero et al., 2004;Carrión et al., 2005;Mazuela et al., 2005;Mazuela et al., 2010)). Once physical-chemical properties were adjusted for soilless culture, yield trials proved the suitability of compost as an acceptable soilless growing media and as a viable and ecologically friendly alternative substrate.

Vegetable waste use as an alternative and friendly substrate
Many people are keen on the research and development of ecologically friendly substrates. Recently it has been demonstrated that these substrates are a perfectly viable alternative to other more traditional methods such as rockwool, perlite or hydroponic systems. However, in order to be competitive for vegetable production in the Mediterranean region, they must be used for at least one year. In recent years there has been an increase in soilless crop cultivation in southeast Spain (Almeria, Murcia and Granada) with a current surface area estimated at 5,000 ha, using substrates such as rockwool, perlite, sand, coconut fibre and other minor types (Urrestarazu and Salas, 2002   Alternative substrates have the advantage of being locally produced, renewable and contaminant and disease-free , and may be less expensive than any other traditional growing media used in soilless crop production. Abad et al. (2002) reported that coconut coir waste may be used for ornamental crops, and the decision on whether to use it as a peat substitute will depend primarily on economic and technical factors, and secondly on environmental issues.

Trace metals
The levels of trace metals in different composts are known to be much higher than in most agricultural soils (He et al., 1992), and depend on the origin of the compost. Pinamonti et al. (1997) reported that the use of compost from sewage sludge and poplar bark did not cause any significant increase in heavy metal levels in soil or plants in the short/medium term; by contrast, their experiments clearly demonstrated that the compost from municipal solid waste increased concentrations of Zn, Cu, Ni, Pb and Cr in soil, and in the case of Pb and Cd also in the vegetation and the fruits. In Spain, as in other European countries such as The Netherlands and Italy, the concentrations of some heavy metals are regulated in order to guarantee the safe use of compost. Heavy metal levels or potentially toxic microelements (   Mazuela and Urrestarazu (2009) determined the effect of leaching of compost for substrate preparation with two composting processes; C1 compost formed by mixing pepper, bean and cucumber waste; and C2, compost formed by melon plant waste. In both cases, sawdust was added (1:4 ratio v/v), as a C/N relation conditioner. The composting process was described by Suárez-Estrella et al. (2003), who indicated that piles of 2 m 3 were turned over and aerated periodically after the first 14 days of composting. Electrical conductivity (EC), anion content (NO 3 -, H 2 PO 4 -, SO 4 2-, Cl -) and cations (Ca 2+ , K + , Mg 2+ , Na + ) were determined by the saturation extract method (Warncke, 1986). Table 3 shows EC values above 21.38 and 11.84, in compost C1 and C2, respectively, likeness ratio indicated by McLachlan et al., 2004;Sanchez-Monedero et al., 2004;Mazuela et al., 2005. These values are higher than the recommended range of 0.75-1.99 reported by Abad et al. (1993) as optimum for soilless culture (Table 1). Amendment with leaching 1:6 volumes is sufficient to produce acceptable values of EC for horticultural purposes (Sanchez-Monedero et al., 2004;Mazuela et al., 2005). Soluble salts represent dissolved inorganic ions in the solution and are typically measured in terms of electrical conductivity. EC readings and mineral element concentrations of composts decreased sharply with leaching and eventually reached acceptable levels despite the high initial value of this parameter in the compost. This drop in the EC was parallel to that found in the concentrations of soluble mineral elements, mainly SO 4 2-, K + , Cl -, Mg 2+ , Ca 2+ and Na + , and showed significant differences for higher levels of elements at the end of the experiment independent of the initial values in the composts. Often, soluble salt measurements from different studies or laboratories cannot be cross-referenced or there is a lot of confusion when comparing the results. Dimambro et al. (2007) and Carrión et al. (2005) reported that total salts were higher in mixed waste composts, predominantly due to high concentrations of K + , Ca 2+ , SO 4 2-, and Na + . Nitrates and phosphates in leaching had low levels in both composts without significant differences. This suggests that the low levels of available nitrogen and the chemical binding or adsorption of phosphorus found in the composts studied will reduce N and P concentrations in leachates.  Table 3. Electrical conductivity (dS m -1 ), anion and cation contents (me L -1 ) in leaching experiments of compost from two horticultural crop residue mixtures (C1, mixing pepper, bean and cucumber waste; C2, melon plant waste ) using distilled water in different substrate volume: distilled water volume (sv:ws) Thus to avoid environmental pollution, special emphasis must be paid to the management and treatment of effluents produced when leaching saline composts under commercial conditions. The preparatory operation needs about six times the water volume of the substrate and should be done inside a composting station, where the lixiviated fertigation is controlled. It is recommended to saturate the substrate with the standard nutrient solution before draining the bags (Villegas, 2004).

Characteristics of compost used as growing media and effects on yield and quality in horticultural crops
Physical properties are the most important characteristics in a new alternative substrate, because they do not change when the substrate is in the container. These characteristics determine the time and frequency of irrigation. Table 4 shows the particle-size distribution of composts and a coarseness index, expressed as the percentage weight of particles with Ø > 1 mm (Richards et al., 1986).  Table 4. Texture and particle size distribution of compost originated from horticultural crop residues used as soilless growing media (% wt) and coarseness index (CI) Texture was very similar to those recommended by Jensen and Collin (1985) for soilless vegetable culture. The coarseness index was about 62 %, similar to peat (63 %) and much higher than coconut coir waste (35 %) values reported by Noguera et al. (2000). hese values easily explain the high wettability of compost (Table 1) according to Bunt (1988). Bulk densities were within the limits of the optimal range. Total pore space showed lower than optimum levels. The total water-holding capacity of composts did not stay within the optimum values (Abad et al., 1993). Shrinkage, wettability and organic matter content stayed within the optimum range. However, the deficient physical properties were not limiting for crop yield and quality ( Table 5, Table 6) probably because crops were irrigated according to the physical analysis (Table 7) of the substrate, a method tailored to the water transport capabilities of each individual substrate (Drzal et al., 1999). The criteria of Smith (1987) and the necessary local adjustments ) were adopted in the fertigation management.   Table 7. Daily mean fertigation parameters and water uptake of melon crops in coconut coir waste (CW) and compost (C) As part of a correct management procedure, previous acid rinsing and saturation with the standard nutrient solution are recommended in order to reduce the compost salinity and inadequate pH of the rhizosphere environment (Table 3). Once the physical-chemical properties were adjusted for soilless culture, yield trials proved the suitability of the compost as an acceptable soilless growing media and as a viable and ecologically-friendly alternative to rockwool and coconut coir waste (Table 8). In northern of Chile, Mazuela eta al., (2010) have similar results that shows in Table 9.   Table 9. Fertigation in drainage parameters, yield and quality in tomato (cherry) crop, in northern of Chile in Greenhouse (GH) and antiaphid mesh (AM)

Re-used substrate from waste materials
Recently, it has been demonstrated that the use of some ecologically friendly substrates are perfectly viable as alternatives to other more traditional media such as rockwool, perlite or hydroponic systems. Almond shell was found to be a viable culture substrate by Lao and Jiménez (2004a, b); these researchers used it as a peat substitute for an ornamental crop. Urrestarazu. (2008) reported that pure compost can be an acceptable substitute growing media for rockwool and coconut coir waste once it is leached and adjusted to physicalchemical proprieties. o limiting factors in comparison to rockwool were found for tomato and melon crops when alternative substrates were used as growing media. Rockwool slab, perlite and coconut bag culture are used in southeastern Spain for two or three years for vegetable production (García, 2004;Villegas, 2004); consequently, in order to be competitive in the market of soilless crops and to have similar commercial opportunity, the unit with an alternative substrate must be usable for this time. Urrestarazu et al. (2008) showed that re-used alternatives substrates as compost or almond shells did not affect yield in melon and tomato crops (  et al., 2004). The new substrates, before reutilization, were within the limit of optimal range (Urrestarazu et al., 2005b); in fact, this is the major disadvantage for transport in comparison to other more popular substrates such as rockwool and perlite Urrestarazu et al., 2005b).

Fertigation management and reference values for nutrient dissolution in organic substrates
Part of a correct management procedure for the use of compost as substrate in growing media is to saturate the bags with nutrient solution before draining the containers, in order to reduce the compost salinity in the rhizosphere environment. Once the electrical conductivity level was adjusted for soilless culture, yield trials proved the suitability of compost as an acceptable growing medim and this ecologically friendly alternative did not affect production, yield or fruit quality of melon and tomato crops. Thus the use of compost www.intechopen.com in soilless culture is a viable alternative to resolve the environmental problem of vegetable waste.
In the Mediterranean region, the control of soilless vegetable cultivation is commonly through measurement of some fertigation parameter ranges in the drainage; pH, electrical conductivity and volume percentage (e.g., Villegas, 2004;García, 2004;Urrestarazu et al., 2005b). Table 11 shows reference values of nutrient dissolution for horticultural crops for each substrate. They are measured almost daily and are easier and cheaper than other analyses or/and fertigation methods based on nutrient solution content in the substrate (Sonneveld and Straver, 1994), which in practice are only used one or two times during the crop cycle. Smith (1987) and Urrestarazu et al. (2005aUrrestarazu et al. ( , 2008 suggested that under adjusted management of the fertigation according to the different proprieties of the substrate, and within certain limits, it is possible to maintain the main parameters used as control for the fertigation method. Since in southeastern Spain rockwool (García, 2004) and perlite  are commonly used for similar lengths of time, it is suggested that alternative substrates are economically viable, since their cost is the same.   Sonneveld, 1980;2 García and Urrestarazu, 1999;3 Urrestarazu andMazuela, 2005: 4 Sonneveld andStraver, 1994;5 Escobar, 1993

Conclusion
Once of the main environmental impacts of forced systems in horticulture -such as plastic covered and soilless culture-is the generation of organic plant residues and substrate waste. Many people are keen on research and development of ecologically friendly substrates. The suitability of compost from horticultural residues as a growing medium in vegetable crop production is an acceptable substitute for rock wool and coconut coir waste. The unit of soilless crop: rockwool slab, perlite and coconut bag culture are used in South eastern Spain between two or three years by vegetable production, consequently in order to be competitive in the market of soilless crops and to have similar commercial opportunity the unit with the alternative substrate must be used during this time. Because the environmental care and economic profit to grower is of paramount importance, it was important to see if this reuse of alternative substrate would be viable in Mediterranean conditions.. Part of a correct management procedure for the use of compost as substrate in growing media is to saturate the bags with nutrient solution before draining the containers in order to reduce the compost salinity in the rhizosphere environment. Once the electrical conductivity level was adjusted for soilless culture, yield trials proved the suitability of the compost as an acceptable growing media and this ecologically friendly alternative does not affect production, yield and fruit quality of horticultural crops. In conclusion, the use of compost in soilless culture is a viable alternative to resolve the environmental problem of vegetable waste.