1. Introduction

Crop losses occur upon climatic conditions in greenhouses. The excessive use of synthetic chemicals in order to minimize yield losses are harmful to the environment and human health (1). The research has been introduced which adversely affects soil structure and may lead to pollute water recently (2) and the increasing consumer awareness of organic agriculture and creating pressure has increased the importance of organic agriculture in greenhouse.

At high yield greenhouse production monoculture farming of the species is common practice therefore the difficulty of rotation is important for soil fertility. Increasing the amount of organic matter in soil at long term is important (3, 4, 5). One of the ways that by enriching the chemical, biological characteristics of the soil in terms of its organic substance, to prevent erosion and soil moisture is "green manure" (6).

Green manures are plants which are grown to improve the structure and nutrient content of the soil (7, 8, 9, 10). Grains or legumes can be used as green manure. Green manures are usually dug into the soil when the plants are still young, before they produce any crop and often before they flower (3, 7, 9). If grain plants had been used as green manuring, the nitrogen in the soil becomes immobilized, so it can not be used by the plants (11). To prevent this, legumes should be planted mixed or banyard manure added (4, 12, 13). If the aim is to provide necessary nitrogen by organic ways lettuce green plant fertilizer must be used (10, 14). Legume family fixes 34 kg nitrogen per hectare/year (11). Approximately 20-60% of it are used by the next product depending on the climate and soil conditions (5, 11). As a result of symbiotic life, they fix significant amount of atmospheric nitrogen to the soil with Rhizobium bacteries (15, 16, 17). While green manure plants are using top soil nitrogen, the nitrogen in deeper is consumed by plants. However, subsequent mineralization enriches the soil above (4, 5, 10, 15, 18). Due to the effective roots of vegetables are different, an interaction comes out between vegetable types and green manure plants (18, 17).

Since the very early years, many researchers have been made about fertilizing on various field crops and vegetables (4, 5, 10, 19, 20, 21, 22, 23). In this study were(i) to compare summer green manure crops with organically grown head lettuce crop in term of yield, quality and (ii) to evaluate the effect of green manuring on soil fertility.

2. Material and Method

The experiment was conducted in a polyethylene (PE) covered double span greenhouse (12.5 × 25 m) with galvanized construction, Side and the roof of the greenhouse were covered with insect net from 2005 to 2007 in Bornova (38°27′16.5″N, 27°13′16.8″E), İzmir, Turkey. Side and the roof of the greenhouse was covered by insect net. Since 2000, the greenhouse was used for organic vegetable production, the soil was washed by spraying with water ponding before green manure. Some physical and chemical properties of soil before the green manure was given in Table 1.

Table 1. Some physical and chemical properties of the experimental soil

Soybean (Gylcine max. L. Merr.), (1), cowpea (Vigna sinensis L) (2), maize (Zea mays) (3) were used as green manure (GM). Without green manurlng parcel was used as control. 5 weeks after planting the first flowers were observed in soybean and cowpea. In this period, while soybeans and cowpeas stirring the soil, corn was stirred by breaking down when it reached 80-100 cm height. Before head lettuce cultivation, green manure parcels divided in two and in addition to green manure 0.75 kg m^-2 PM was applied. PM is organic origin in pellet form and provided by Org-E-Vit (ITM Turhol Company, Antalya, Turkey) (Table 2).

Table 2. Some physical and chemical characteristics of pultry manure

In winter, head lettuce (Lactuca sativa cv. Coolguard) was cultivated. Both cultivation periods, lettuce seeds were provided from Asgrow company. First year, seedling production was carried out in greenhouses of A.U.A F in the department of Horticulture, and second year in Ege Seedling company in Torbalı, İzmir. 10 seedlings used for each application with three replications according to pattern. Seedlings were planted 50x30x25 cm intervals. Production schedule of the experiment is given in Table 3. Plant maintenance works (25) were conducted.

In the study; total yield (g m^-2), head weight (g), marketable plant weight (g) were determined. Head length and wide were measured by ruler in three heads for each replication and leaf number of marketable head were counted.

Table 3. Production Schedule of the experiment

After 0,5 grams of leave sample was homogenized in water for vitamin C content, it was filtered and taken sample after filtering, the sample was stabilized wit oxalic acid for 1%. In the sample taken from this mixture 2-6 diklorofenlindefenol for 0,0012 % was added and absorbance values were read at a wavelength of 518 nm in spectrophotometer. The same readings were made at the standard ascorbic acid solution, and standard solutions prepared with stabilized substance, and standard curves were prepared; absorbance values reading at the samples converted into amounts C by the help of standard curve, and the results were given as mg in g fresh weight (26).

Nitrate content of leaves, the leaves of homogeneously received 95 ml of distilled water 5 g of homogenized and filtered white-band filter paper, filtering the sample mixture onto 5% salicylic acid + sulfuric acid and 4 N NaOH was added, with stirring at 410 nm spectrophotometer reading was taken Standards are also prepared by the same method Curve factor read out and nitrate contents in mg kg^-1 was calculated (27). Irrigation was performed by drip irrigation method. In order to determine the amount of water required was calculated according to the evaporation values of open water surface, and calculated with ET=Epan x kc x kpan x A (liter) equation

Before the procedures of green manure seed planting (1st Year: 23.7.2005; 2 Year: 19.07.2006), head lettuce planting (1st Year: 12/13/2005, 10/17/2006 2nd year), and head lettuce harvest (1 year: 3.9 .2006; 2nd year: 01/10/2007) the soil was taken from 0-30 depth of the experimental area and brought to the lab and it made wait by putting into cardboards boxes. Afterwards it was ready for analysis by sieving for 2mm diameter and organic substance (29) and total N (30) analysis were processed in these soil samples.

Weekly periodic observations were made so as to intervene the diseases and pests as soon as possible during the cultivation. The temperature and soil temperature in greenhouse was monitored by "hobo data recorder". During the cultivation period greenhouse internal temperature first year: min: 11.50; max: 31,87℃; second year: min: 12.21; max: 30.53℃ and soil temperature, first year: min: 13:94; max; 26:44℃; second year: min: 15.63; max: 25.57℃ values were determined.

According to the data obtained from the research, analysis of variance was carried out using a statistical analysis package program (ANOVA) and the least significant difference (LSD) test was conducted at 5% importance level in order to identify differences between means.

3. Results and Discussion

3.1. Yield Parameters

The effects of green manures on the yield of head lettuce are shown in Table 4. Green manures and PM did not effect the total yield in the first year, but total yield and marketable head weight is found significantly important in the second years. The highest total yield of maize +PM application (7431 g m^-2) and control +PM owned and controlled by the rate of 40.79 %, and 44.52 %, respectively, were higher (Table 4).

Table 4. The yield parameters of head lettuce

Head lettuce salad-yield varies depending on many factors such as climatic conditions, cultivation period, the number of plants per unit area , yield between 3-4 kg m^-2 is reported to be good (31). These values to yield values obtained in this study, as well as head lettuce produced in different studies in the same period is similar to the yield, even on some of the remains (32, 33). According to that, organic cultivation was realized without efficiency lost in this study. Having encountered any problems with diseases and pests played great important role. In the second year, the problem of nematod appeared in cowpea and soybean both decreased output of green manure plants and biomass that made mix in the soil and it was determined that efficiency values and total N amounts decreased.

3.2. Quality Parameters

In the first experiment, head height, head diameter and the total number of leaves did not affect applications (Table 5).

In the second experimental year, head height, head diameter, and total number of leaves and application effects were found important. When chicken manure and green manure were used together head height, head diameter and the total number of leaves increased compared to the control application (Table 5). The application effects in head lettuce on nitrate and vitamin C content is given in Table 6. Nitrate content was found higher in plant samples taken from parcels that having to be applied with poultry manure and green manure.

The quality values obtained in this study are similar to head lettuce produced in the same period and different studies (32, 33, 34, 35). High nitrate contents is undesirable in the vegetables for direct human consumption. For this reason, it was focused on nitrate between the parameters regarding to quality characteristics. High nitrate concentration leads to either dismantle of intestinal membrane or vasodilation. It also prevents the transport of oxygen in the blood in young children when transformed from nitrate to nitrite. It is essential to worry about consider high nitrate content of vegetables in abundance, especially in case of nitrate fertilization. It was observed that nitrate amount was higher in the applications of green manure that legume plants were used (7, 36) and also in the parcels with poultry manure as well as in soybean and cowpea applications.

Table 5. Effects of treatments on plant characteristics

Table 6. Effect of treatments on nitrate (mg kg-1) and vitamin C content (mg 100 g-1)

3.3. Soil Characteristics

When look at the effects on soil efficiency of head lettuce cultivation following winter green head lettuce manure was considered, organic substance amount in soil samples taken from lettuce cultivation until cultivation period end, first and second year ranged from 2.17-3.60 %,to 1.03-3.87 % respectively, (Figure 1).

Figure 1. The amount of OM (%) change (1 seed sowing green manure; 2 head lettuce planting, harvest head lettuce 3). (GM:green manuring; HL: head lettuce, S soyabean;CP:cowpea; M mazie; C: control)

According to GM+PM application and control, soil organic substance increased 25.39 % in the first year, and the second year 31.79 % in the first year cultivation. Legumes fixes nitrogen into the soil about 34 kg per hectar a year. This is approximately 20-60 % of the (6.8-20.4 kg da-1), depending on climate and soil conditions used by the next product (11). Leguminous crops increased available nitrogen in the soil by breaking down rapidly (4, 5, 10). Since poultry manure is richer in terms of nitrogen content between farm manures, after the application, available nitrogen in soil increases (38). In addition, root depth of the species cultivated is also significant. Owing to head lettuce is shallow root vegetable and has short cultivation period, Green manure plants which are increased available nitrogen on topsoil should be selected (39).

Figure 2. The amount of N (%)change (1 seed sowing green manure; 2 head lettuce planting, harvest head lettuce 3). (GM:green manuring; HL: head lettuce, S soyabean;CP:cowpea; M mazie; C: control)

Total nitrogen was found as 0.23 % in the soil sample taken from planting green manure seeds. Depending upon applications and date samples takentotal N content ranged from 0,17 to 0.30 % and 0.14-0.22 %., in the first and second year, respectively,1 Total N content. In head lettuce harvest, according to average control in PM application increased 24.05%, and according to PM + GM application and control 6.25 %, respectively in the second year 15% and 8% (fig. 3, 4). Using green manure is different from other organic manures in terms of providing N to the crops produced afterwards. Especially legumes provide desired nutrients in nitrogen by means of confining nodosity nitrogenous (40). Green manure plant needs N sources in the soil during their developments, and green manure plants release after removing N from the soil. Therefore, green manure plants is not only available N in the soil, but also affects distribution throughout the soil profile (41). While legume green manure plants using N on topsoil, N in deeper is consumed, however, subsequent mineralization enriches the topsoil (4, 12, 13, 15, 42).

4. Conclusions

As a result, it is determined that summer green manure improve the amount of total N and organic substance of soil, and provides nutrients to the crops after it was grown.

ACKNOWLEDGEMENTS

This project (105O571) was supported by the Scientific and Technological Research Council of Turkey (TÜBİTAK).