This paper presents the results of 2 experiments: An incubation experiment and a subsequent field experiment. An incubation experiment was set up in order to determine the mineralization potential of different organic materials (OMs) (well-rotted farmyard manure [FTM], guano [G], soybean seed [S], and forage pea seed [P]), the kinetics of mineral nitrogen (N) release and the correlation between OM content and the quantity of mineralized N. | Research Article Turk J Agric For 34 (2010) 163-172 © TÜBİTAK doi: Organic materials: sources of nitrogen in the organic production of lettuce Maja MANOJLOVIĆ1,*, Ranko ČABILOVSKI1, Martina BAVEC2 1Faculty of Agriculture, University of Novi Sad, 21 000 Novi Sad, SERBIA 2Faculty of Agriculture, University of Maribor, 2000 Maribor, SLOVENIA Received: Abstract: This paper presents the results of 2 experiments: an incubation experiment and a subsequent field experiment. An incubation experiment was set up in order to determine the mineralization potential of different organic materials (OMs) (well-rotted farmyard manure [FTM], guano [G], soybean seed [S], and forage pea seed [P]), the kinetics of mineral nitrogen (N) release, and the correlation between OM content and the quantity of mineralized N. The results of the incubation experiment were checked under field conditions in which different OMs were used as N sources for −1 lettuce (Lactuca sativa L.). The highest mineralization rate constant k ( day ) and net mineralization rate (NM) −1 ( of total applied N) were obtained with G, and the lowest k ( day ) and NM ( of total applied N) were obtained with FYM. In the field experiment in 2007 and 2008 we applied different OM sources that contained the same −1 amount of potentially mineralizable N (40 and 35 kg N ha , respectively), calculated on the basis of k and NM. The use of OMs increased the concentration of mineral N in the soil and increased the yield of fresh lettuce. Nitrate content in the fresh lettuce was within acceptable limits both years () and a narrow C/N ratio (<20) (Cordovil et al. 2005; Burgos et al. 2006), and via their mineralization in the soil and significant N content of its mineral, the available form of N can be released, satisfying crop requirements for N (Amlinger et al. 2003; Bavec et al. 2006). On the other hand, materials with a wider C/N ratio cause immobilization of N (Chaves et
