The effects of cover crops, cultivation system and location on soil mineral nitrogen, growth and yield organically produced oil pumpkins (Cucurbita pepo L. convar. citrullina (L.) Greb. var. styriaca Greb.)

Posamezni agrotehnični ukrepi so ključnega pomena za ekološko pridelavo. V letih 2004 in 2005 smo na Pohorskem dvoru pri Mariboru in Ptuju izvedli ekološki poljski poskus z oljnimi bučami. Namen raziskave je bil proučiti vplive leta, lokacije, zasnove posevka (seme, sadika), gnojenja s hlevskim gnojem in prekrivnih rastlin (Trifolium incarnatum L. in Trifolium alexandrinum L.), na količino mineralnega dušika v tleh, razvoj in pridelek oljnih buč. Z vključenimi obravnavanji smo želeli zagotoviti dovolj mineralnega dušika v tleh v tistih razvojnih fazah oljnih buč, ki so pomembne za oblikovanje in kakovost pridelka bučnic. Setvene pasove, smo na parcelah s prekrivnimi rastlinami, preorali tri tedne pred sajenjem buč. Razvojne faze buč smo spremljali 20, 40, 90 in 115 dni po zasnovi posevka. Mineralni dušik smo vzorčili do 0,6 m, v fazah BBCH 001, 500 in 909. Ugotovili smo, da so leto, lokacija, prekrivne rastline in gnojenje statistično značilno vplivali na morfološke lastnosti oljnih buč v razvojni fazi BBCH 700 ter pridelek v fazi BBCH 909. Zasnova posevka s sadiko je značilno vplivala na višji pridelek bučnic. Na količino Nmin v tleh so v maju vplivala vsa vključena obravnavanja, v juniju pa samo leto in lokacija. Rezultati raziskave so pokazali, da lahko prekrivni posevki in hlevski gnoj ob primerni razporeditvi padavin v rastni dobi, zagotavljajo primerno oskrbo oljnih buč z mineralnim dušikom.Each part of cultivation system is the key factor for organic production. In 2004 and 2005, an investigation was carried out to determine effects of cover crop (Trifolium incarnatum L., Trifolium alexandrinum L.), sowing/planting system and fertilisation with stable manure on growth, yield of oil pumpkins and soil mineral nitrogen content in organic farming under field condions at the Pivola near Maribor and Ptuj. With the set treatments, we intended to provide sufficient mineral nitrogen amount in the soil at those growth stages, which are important for the yield of oil pumpkins. In spring time, only the sowing strips for oil pumpkins were ploughed in plots with cover crops (two strips 1,2 m wide per plot). The ratio between ploughed and unploughed production land area was 0.78:1. Control plots were ploughed in autumn and then cultivated short time before the sowing of oil pumpkins in May. Growth stages of oil pumpkins were determined 20, 40, 90 and 115 days after sowing. Soil mineral nitrogen was analysed up to 0,6 m at BBCH stages 001, 500 and 909. The morphological characteristics of oil pumpkins in BBCH 700 growth stage and crop yield were significantly affected by the year, location, cover crop and fertilization. Plantings have significantlly higher yield of oil pumpkins than the seeds. The amount of soil Nmin in May was affected by all investigated treatments, and only by the year of production and location in June. The results showed that the cover crops and stable manure, along with a proportionale precipitation during growing season, provide an adequate supply of mineral nitrogen for oil pumpkins