Statistical analysis revealed significant effects of intercrop fertilization and interaction between intercrop fertilization and straw fertilization on savoriness of potato tubers (table17). Intercrop fertilization improved the savoriness of potato tubers in comparison with savoriness of potato tubers harvested from control object. The best savoriness had potato tubers fertilized with white clover, the mixture of white clover with Italian ryegrass, and phacelia both plowed down in the autumn, and left till spring in the form of mulch. Savoriness of potato tubers fertilized with Italian ryegrass did not significantly differ from savoriness of potato tubers fertilized with farmyard manure. There has been an interaction which shows that the best savoriness had potato tubers fertilized with white clover in combination without straw and with straw, and the worst potato tubers from control object.

3. Discussion

Shortage of farmyard manure due to the decline in farm animal stocks, low profitability and the rationale for integrated production tend to look for alternative and efficient ways of potato fertilization. The most important here are green fertilizers from undersown crops and stubble crops and straw left on field after cereal harvest. Selection of underplant crops as alternative sources of biomass, dictated the results of Batalina et al. (1968) and Ceglarka (1982). Batalin et al. (1968) initiated studies to evaluate the fertilizer value of underplant crops legumes, and Ceglarek (1982) conducted a thorough research on the determination of yield and chemical composition of crop residues of underplant crops. However Gutmanski et al. (1998) have evaluated the value of fertilizer of oil radish, white mustard and phacelia used in sugar beet cultivation, which became the motivation for taking this type of research in potato cultivation. Under the conditions of this experiment, from the group of underplant crops yielding on the highest level was Italian ryegrass and a mixture of white clover with Italian ryegrass. The high biomass production of grasses also show results of Gromadzinski and Sypniewski (1971), Zajerc and Witkowicz (1996), Ceglarka et al. (1998), Witkowicz (1998) and Kuraszewicza and Palys (2002). In own researches, phacelia grown in stubble intercrop yielded at a similar level as white clover cultivated as an intercrop. This is consistent with the results of Gromadzinski and Sypniewski (1971), Witkowicz (1998), Trawczynski and Grzeskiewicz (1997) and Nowakowski et. al. (1997), Ceglarek and Plaza, 2000). In the experiment the addition of straw to the intercrops caused a significant increase of the amount of dry matter and macronutrients.

Nowak (1982) indicates a predominance of green manure on the farmyard manure. This follows from the fact that the nutrients contained in green manure are generally more easily absorbed than the components of farmyard manure, due to rapid decomposition of organic matter. In this experiment, among intercrops the highest value of fertilizing showed undersown: a mixture of white clover with Italian ryegrass and white clover. Batalin et. al. (1968) the highest yields of potato tubers received after plowing the undersown of red clover and serradella, and Ceglarek et al. (1998) after plowing the mixtures of legume with Italian ryegrass. These differences are due to different rates of mineralization used forms of fertilization and the fact that the introduction into the soil with a mixture of larger amounts of biomass and macronutrients. According to Nowak (1982), during the decomposition of legumes may occur high losses of nitrogen. Depending on the temperature, humidity and time of decomposition, nitrogen losses could amount up to 50%. To prevent it, to the decomposing mass of legumes material rich in carbon should be added, such as grasses, in order to increase the C:N. In this experiment yields of potato tubers fertilized with Italian ryegrass were significantly smaller than in farmyard manure. However, in this case, tuber yields were significantly higher than those obtained on control object, without intercrop fertilization. The increase of tuber yield after plowing down the grass also found Sadowski

(1992) , Spiertz et al. (1996), Duer and Jonczyk (1998) and Reust et al. (1999), but yields were lower than on the farmyard manure. This is because the introduction into the soil a large amount of biomass, with a low content of macronutrients (Sadowski 1992; Duer and Jonczyk 1998). In addition, grasses have a wide ratio C:N. In this case, the less nitrogen mineralization, which is used primarily by soil microorganisms. In own research, the value of stubble crop fertilizer from phacelia plowed down in autumn and left till spring in the form of mulch equal the fertilizer value of farmyard manure. This is understandable because of non-legume stubble crops biomass of this plant was notable for its high content of macronutrients. This is confirmed by results of Dzienia (1989), Trawczynski and Grzeskiewicz (1997) and Nowakowski, et al. (1997) and Rozylo (2002).

In potato fertilization of stubble crops can also be used in the form of mulch. However, thus fertilizing the position, with the exception of phacelia, in terms of fertilizer could not match with farmyard manure. This is confirmed by research of Boliglowa and Dzienia (1996) and Dzieni and Szarka (2000) on potato fertilization by mulch from white mustard. In the system of integrated agriculture can recommend this method of fertilization, especially with phacelia mulch, while significantly reducing of costs. The beneficial effects of intercrops plants left on the field in the form of mulch slows the mineralization of organic matter, does not allow for leaching of nitrogen, stored water from the autumn-winter rainfalls, improves soil structure and enriches it in organic matter (Hoyt et al. 1986; Frye et al., 1988; Dzienia and Boligowa, 1993; Gutmanski et al., 1999).

In that experiment fertilization with spring barley straw gave a lower effect than farmyard manure fertilization. This is consistent with the results of Sadowski (1992), Szymankiewicz

(1993) , Snieg and Piramowicza (1995) and Ceglarek et al. (1998). However, its use combined with intercrop undersown of white clover and stubble crop left till spring in the form of mulch clearly strengthened its fertilising value. Potato tubers yields of after fertilization of these forms were comparable, in the case of white clover yields higher than those recorded on farmyard manure. Also Ceglarek et al. (1998) recommend the combined use of legumes as undersown.

Intercrops fertilization with straw affects not only for the amount of received yieldss, but also on quality, so reciprocal arrangement of the components involved in potato tubers (Roztropowicz, 1989; Grzeskiewicz and Trawczynski, 1997; Boliglowa and Glen 2003). The dry matter content and starch in potato tubers depends on the genetic factor, the distribution of rainfall and temperatures during the growing season and on agronomic factors, mainly from fertilizer (Rostropowicz, 1989; Grzeskiewicz and Trawczynski 1997; Ceglarek et al., 1998; Dzienia and Szarek, 2000; Leszczynski 2002; Plaza and Ceglarek 2009; Makaraviciute 2003). In own studies, intercrop fertilization stimulated the content and dry matter yield of potato tubers and starch content and yield. The highest concentration of dry matter were characterized potatoes fertilized with mixture of white clover with Italian ryegrass and with phacelia plowed down in the autumn and left till spring in the form of mulch, and starch — potatoes fertilized with Italian ryegrass and phacelia plowed down and left till spring in the form of mulch. Research of Ceglarek et al. (1998) showed that potatoes fertilized with legume mixtures with Italian ryegrass include the most dry matter and Italian ryegrass fertilized include the most starch. Boliglowa and Glen (2003) have not indicated significant differences between the starch content in potatoes fertilized with farmyard manure, and white mustard both plowed down in the autumn, as left till spring in the form of mulch. a Different view present Mazur and Julkowski (1982) claiming that potato fertilization with legumes works better on the percentage starch content than with farmyard manure fertilization. In own studies, potato fertilization with stubble intercrop in the form of mulch increased the concentration of dry matter and starch in potato tubers as compared to that of intercrops plowed down in autumn. A similar relationship, but in sugar beet cultivation proved Gutmanski et al. (1998). However Dzienia and Szarek (2000) and Boliglowa and Glen (2003) found no significant differences between the starch content in potato tubers fertilized with farmyard manure, and white mustard both plowed down in the autumn, and left till spring in the form of mulch. Under the conditions of this experiment straw fertilization increased starch content in potato tubers, and in studies Glen et al. (2002) did not decrease significantly the concentration of this component. Consumption potato tubers should contain about 0.3% reducing sugar, and 1% of total sugars. With increased content of total sugars, potatoes taste sweet (Gluska 2000; Leszczynski, 2000, 2002). In own studies, fertilization of potato with intercrop and straw caused a significant decrease in reducing sugars and total sugars in potato tubers as compared to the control object, without intercrop fertilization. Also, according to Leszczynski (2002) and Makaraviciute (2003) organic fertilizers reduce the concentration of sugars in potato tubers. However, the studies of Mondy and Munshi (1990) showed that enrichment of soil in substance abounds in nitrogen reduces the starch content and increases the sugar content in potato tubers. In own studies, potato fertilization with white clover did not result in significant differences in the amount of reducing sugars and total sugars as compared to farmyard manure fertilization.

In light of these studies used forms of organic fertilization stimulated the concentration of vitamin C in potato tubers. The highest concentrations of vitamin C were characterized in potatoes fertilized with white clover and phacelia both plowed down in the autumn, and left till spring in the form of mulch in combination without the straw and with straw. Also, the findings of other authors (Garwood et al. 1991; Weber and Putz 1999; Leszczynski 2002; Sawicka and Kus 2002; Hamouz et al. 2005, 2007; Plaza and Ceglarek 2009) indicate a positive correlation between organic fertilization and vitamin C content in potato tubers.

In own researches, intercrop fertilization preferably affected on protein content in potato tubers. Also in the researches of Mazur and Julkowskiego (1982), Sawicka (1991), Leszczynski (2002) and Sawicka and Kus (2002) saw an increase in concentration of true protein in potato tubers cultivated in organic fertilizers. Most preferably, the discussed feature influenced white clover fertilization, also phacelia both plowed down in the autumn, and left till spring in the form of mulch in combination, without straw and with straw. A similar relationship has proved Wiater (2002). Potatoes cultivation in the position fertilized with legume plants and phacelia plants take larger amounts of nitrogen from soil than potatoes cultivated in position fertilized with green fertilizers. Nitrogen contained in the biomass of white clover and phacelia, is gradually mineralization is evenly shared to the potato crop, leading to total conversion of protein nitrogen. In own stuies, the lowest nitrate content was reported in potato tubers fertilized with white clover and phacelia both plowed down in the autumn and left till spring in the form of mulch. Only after Italian ryegrass applying nitrate content in potato tubers did not differ significantly from that recorded in potatoes fertilized with farmyard manure. The above relationship is explained by the fact that the biomass of white clover, or phacelia outside the higher content of nitrogen contained a few fibers which ensured its rapid degradation. Thanks to this all nutrients, including nitrogen available to potatoes plant are evenly distributed, allowing the total conversion of mineral nitrogen in protein nitrogen. This is consistent with the results of Dzienia et al. (2004) and Boliglowy and Glen (2003), who showed that potato tubers fertilized with white mustard and rye straw contained significantly less nitrates than potatoes fertilized with farmyard manure. According to Leszczynski (2002) use of farmyard manure, whose chemical composition is not controlled, may increase for example nitrogen and other components content in the plant. However Boliglowa and Glen (2003) showed that the nitrate content in potato tubers fertilized with white mustard developed at a similar level as in the potatoes fertilized with farmyard manure. In own studies the highest concentration of nitrates reported in potato tubers from the control object, only with mineral fertilization. This is due to the fact that mineral fertilizers, especially nitrogen increased the content of nitrogen compounds, mainly non-protein, including free amino acids, amines, ammonium nitrogen and nitrate nitrogen and reduces the share of protein in general (Wiater, 2002).

In this experiment the lowest concentration of glycoalkaloids in potatoes fertilized with white clover, a mixture of white clover and Italian ryegrass and phacelia both plowed down in the autumn, and left till spring in the form of mulch. According to Rudella et al. (2005) intercrop cultivation with a favorable ratio of carbon to nitrogen regenerates the soil environment, increases the humus content, the number of microorganisms, enzymes and other biologically active compounds in the soil, which inhibits the accumulation of harmful substances in potato tubers. In the experiment only after the applying of Italian ryegrass the concentration of glycoalkaloids in potato tubers was at the similar level as in the potato fertilized with farmyard manure. However, in this case the content of glycoalkaloids in tubers was significantly lower than that in potatoes cultivated without intercrop fertilization. Leszczynski (2002) shows that organic fertilizers reduce the harmful substances content in potato tubers by enriching the soil with organic substance which inhibits the synthesis process of glycoalkaloids. In own studies, straw fertilization also significantly differentiate the content of glycoalkaloids in potato tubers. On objects with straw the content of glycoalkaloids in potato tubers was significantly lower than on objects without straw. This is consistent with the results of research of Plaza et al. (2010). In this experiment the highest concentration of glycoalkaloids in potato tubers has been harvested from the control object, only with mineral fertilization. Also, the studies of Mondy and Munshi (1990), Hamouz et al. (2007), Kolodziejczyk et al. (2007) and Rytel et al. (2008) mineral fertilization increased the content of glycoalkaloids (solanine and chakoniny) in potato tubers. However, it should be noted that the potato in comparison with other crops have little ability to accumulate harmful substances for human. Moreover, the use of green manure and straw greatly reduces their concentration in comparison to traditional farmyard manure.

[1] In our case bioprocess parameter E was not considered-

[2] Bioprocess parameters and values of their levels are indicated in Table 1.

[3] Means in the same column followed by same letter do not differ by the Tukey test (P <0.05).

Adapted from Costa & Leal (2008)

Table 1. Leaf area (LA), leaf fresh mass (LFM) and leaf dry mass (LDM) for the strawberry cultivar Tudla, during August-October (ASO) and November to March (NDJFM).

Cultivars of chicory (Cichorium endivia L.), AF-254 and Marina, produced under a natural environment and within a low tunnel constructed of white polypropylene in the region of Ponta Grossa-PR/Brazil, presented greater head mass in the low tunnel and a greater number of leaves in the natural environment. The AF-254 cultivar was more productive but more susceptible to tipburn in the protected environment (SA & Reghin, 2008).

Cunha et al. (2005) evaluated the radiation balance and yield of sweet pepper, hybrid Elisa, in a protected environment (a non-acclimatized greenhouse oriented in the NNW-SSE direction, covered with low density polyethylene film) and in a field located in Botucatu — SP/Brazil. The authors observed that plants in the protected environment present not only greater plant height and total dry matter during of total cycle, but also a greater leaf area index. However this environment showed less net energy for growth and development of the crop.

Interactions between greenhouse environments, substrates types and different cucumber hybrids were evaluated by Costa et al. (2010) and verified different behavior of the substrates in the different environments studied, noting that the seedling growth was affected by the environments and the substrates. Response of cucumber hybrids in terms of seedlings dry biomass depended on the substrate and the growing environment. The substrate "soil and coconut fiber" increased biomass accumulation in the greenhouse and nursery with black the monofilament screen. The substrate "soil and organic compost" showed greater aerial biomass in the nursery with the aluminized screen. Hybrid ‘Safira’ accumulated more root biomass in the substrate "soil and coconut fiber" and when using the screens. The hybrid ‘Nikkei’ accumulated higher root biomass in the nursery with the aluminized screen and in the substrate "soil and coconut fiber" and did not differ from the substrate "soil and saw-dust". Hybrids ‘Aladdin F1’ and ‘Nobre F1’ accumulated similar root biomass in the environments, where the ‘Aladdin F1’ had a higher accumulation of biomass in the substrates "soil and organic compound" and "soil and coconut fiber", while the hybrid ‘Noble F1’ showed greater accumulation in "soil and coconut fiber", showing no difference from "soil and saw-dust" (Tables 2 and 3).