Anna Plaza, Feliks Ceglarek, Danuta Buraczynska and Milena Anna Krolikowska

University of Natural Sciences and Humanities in Siedlce

Poland

1. Introduction

Potatoes destined for direct consumption should be distinguished by a high trade yield with the best qualities. (Leszynski, 2002; Boliglowa and Glen, 2003; Plaza and Ceglarek, 2009). In most European countries schemes for the verifiability of the potato product are introduced. The aim is to obtain good quality of potatoes, ensuring the reduction of harmful substances to human health and the natural environment (Spiertz et al., 1996). The beneficial effects of organic fertilization is noted here (Leszczynski, 2002; Boliglowa and Glen, 2003; Makaraviciute, 2003; Plaza et. al., 2009).

Farmyard manure is a basic manure applied in potato cultivation (Batalin et. al., 1968; Kalembasa and Symanowicz, 1985; Rozrtopowicz, 1989). For many years its amount covered the demand, but now the situation has negatively affected due to the decline in livestock, especially cattle. Decreasing amount of farmyard manure, low profitability and the rationale for a system of integrated agriculture, tend to seek alternative, energy-efficient sources of biomass. As a result, a significant role is being attributed to green manures (Grzeskiewicz i Trawczynski, 1997; Zaj^c, 1997; Ceglarek et. al., 1998; Karlsson-Strese et. al., 1998; Plaza i in.,

2009) .

Green fertilizers were mentioned many times in literature. Batalin et. al. (1968), Roztropowicz (1989), Gruczek (1994), Dzienia and Szarek (2000) emphasize that the advantage of using this type of fertilization is high labor and energy saving in relation to its amount spent on works related to the application of farmyard manure. Estler (1991), Stopes et. al. (1995), Spiertz et. al. (1996), Karlsson-Strese et. al. (1998) and Songin (1998) show that the intercrops introduction into the cultivation is not only the production of biomass. They are also a kind of absorbent material to prevent leaching of nutrients into the deeper layers of soil and groundwater, which is important in protecting the agricultural environment. From manuscripts connected with green fertilizers it is clear that among catch crops, undersown crops seem to be the cheapest source of organic matter because it does not require any additional costs associated with the cultivation and preparation of the soil before sowing, which is particularly troublesome in the cultivation of stubble crops (Ceglarek et. al., 1998). Seed cost is also low. As undersown the legumes are recommended to cultivate. The Renaissance intercrops from legumes is linked to the multilateral noticing

them, valuable, but not fully used advantages of agronomic and biological properties. The rediscovery of these plants is associated with current global trends in agricultural techniques, aiming towards the promotion of proecological and ecological agriculture (Stopes et. al., 1995; Spiertz et. al., 1996; Karlsson-Strese et. al., 1998; Duer, 1999). White clover is distinguished by a high capacity of fixing atmospheric nitrogen, and a wide range of crops to allow its existence in a very different soil conditions have long been interested for researchers across Europe (Frye et. al., 1988). In Poland, there is little experimental data determining the suitability of this species to cultivation as undersown, designed for plowing, as a green manure in integrated potato cultivation. Researches of many authors (Batalin et. al., 1968; Gromadzinski and Sypniewski, 1971; Zaj^c, 1997; Ceglarek et. al., 1998) show that undersown legumes are quite unreliable in yielding. More similar are legume mixtures with grasses (Gromadzinski and Sypniewski, 1971; Bowley et. al., 1984; Ceglarek et al,. 1998; Witkowicz, 1998; Plaza et. al., 2009). Reliable in yielding also are grasses grown in pure sowing. As a fast-growing plants and easily shading the soil interact with the position by weed reduction (Szymona et. al., 1983/1984; Sadowski, 1992; Karlsson-Strese et. al., 1998; Majda and Pawlowski, 1998; Kuraszkiewicz and Palys, 2002).

An alternative source of biomass can also be stubble crops, which were mentioned in literature many times (Sadowski, 1992; Roztropowicz, 1989; Boliglowa and Dzienia, 1996; Grzeskiewicz and Trawczynski, 1997; Dzienia and Szarek, 2000). Recently, there has been an interest of the possibility of entering non-legume plants with a short growing season. It is recommended to sow fast-growing species, with good ability of shading, and not able to produce too large, aboveground woody mass. The most common are: white mustard, oil radish and phacelia (Allson and Amstrong, 1991; Boliglowa and Dzienia, 1997; Grzeskiewicz and Trawczynski, 1997; Gutmanski et. al., 1998). Among non-legume plants cultivated in stubble crop phacelia is distinguished by rapid growth, it produces a soft aboveground mass, easily frozen in winter. Is a phytosanitary plant. In Poland, previously carried out researches on fertilizing position of phacelia only in sugar beet cultivation (Nowakowski et. al., 1997; Gutmanski et. al., 1999), still there is no experimental data evaluating its usefulness in the fertilization of potatoes.

Intercrops can be plowed down in autumn or left till spring in the form of mulch. The beneficial effects of intercrops plants left till spring in the form of mulch is to: protect the soil against wind and water erosion, gathering water from rainfall, slowing the process of mineralization of organic matter and prevent from nutrients leaching into the soil, reducing the cost of cultivation by eliminating plowing (Hoyt et. al., 1986; Gutmanski et. al., 1999). It should be noted that the green fertilizers left till spring in the form of mulch causes a slight decrease in yield, but the improvement of the quality characteristics of the fertilized plants compared to fertilization applied in the traditional form.

Another substitute source of biomass can also be the straw left on the field after harvest of cereals (Szymankiewicz, 1993; Gruczek, 1994; Snieg and Piramowicz, 1995; Dzienia and Szarek, 2000), especially used in combination with green fertilizers. Its addition to the legume biomass, not only does not reduce nitrogen losses, but also extends the period of green fertilizers acting (Nowak, 1982). In the case of non-legume plants effect of combined application of these forms of fertilization is not always positive (Dzienia, 1989; Sadowski,

1992) . In Poland, there is little on this experimental data. Thus emerges the need for research aimed at comparing the impact of intercrops biomass, stubble crops both plowed down in autumn and left till spring in the form of mulch in combinations with straw or without

straw, farmyard manure fertilization on yielding and chemical composition of edible potato tubers.