ENGINEERING FOR RURAL DEVELOPMENT Jelgava, 29.-30.05.2014. 109 OPTIMIZATION OF TECHNOLOGICAL MEASURES TO PROMOTE CEREAL STRAW DECOMPOSITION IN THE POST HARVEST PERIOD Ausra Arlauskiene, Aleksandras Velykis, Alvyra Slepetiene Lithuanian Research Centre for Agriculture and Forestry arlauskiene.ausra@gmail.com Abstract. Investigations of post harvest technological measures for promotion of initial winter wheat straw decomposition were carried out over the period 2008-2011 in the model field experiments at the Joniškėlis Experimental Station of the Lithuanian Research Centre for Agriculture and Forestry. Measures used for straw decomposition: 1) stubble cultivation at 10 cm depth, straw removed from the field, 2) nitrogen fertilizer use on non-incorporated straw, 3) nitrogen fertilizer use with straw incorporation during stubble cultivation, 4) slurry use with straw incorporation during stubble cultivation. Changes in dry matter, carbon, nitrogen, phosphorus and potassium were observed at 9 months after incorporation the straw. Straw decomposition was slowest when straw was spread on the surface with N fertilizer without incorporation into the soil. DM content in the straw decreased similarly when it was incorporated with N fertilizer or with slurry. C decreased by 15.5 % in straw incorporated only with the stubble cultivator and with N fertilizer – 20.4 % compared with the former quantity. C:N decreased from 100 to 43 in straw, when it was incorporated together with N fertilizer. This affected higher mineral nitrogen N min. of soil by 10.3 % in spring if compared to the plot without straw. Keywords: cereal straw, technological measure, decomposition. Introduction Cereal straw is of renewed interest as a potential source of bioenergy. However, the sustainability of this practice which implies systematic removal of aerial biomass of cereal crops is a controversial issue, particularly in soils having a low soil organic carbon (SOC) content [1]. Straw is natural organic manure that is decomposed by microorganisms of the soil and transformed into other organic compounds. The primary division of straw or N immobilisation is affected by a wide C and N ratio in straw [2]. In order to make the decomposition of straw more rapid and to increase N immobilisation to the biomass of microorganisms and organic compounds of soil, it is necessary to incorporate additional nitrogen fertilizer, to increase the contact with the soil microorganisms, the soil moisture and nutrients [3]. It was defined that upon incorporation straw of crops to the soil and nitrogen fertilizer increases the activeness of microorganisms, carbon and nitrogen content in their biomass while in soil – the content of easily assimilative organic compounds; humus destruction reduces together with leaching of nitrogen. Incorporation of straw into soil can be a strong means for controlling N dynamics in soil and reduces the leaching of N fertilizer, because straw will enhance microbial N immobilization due to the high C:N ratio of the materials [2]. Later, upon decomposition of straw, nitrogen has a low effect on the decomposition of the straw mass. Then organic compounds that are difficult to decompose (lignin) are decomposed and transformed [4]. The degradation of organic macromolecules, including lignin, in plant-derived soil organic matter, is important to the global carbon cycle. When straw is applied for manure, the humus content in the soil is increased as well as the physical and chemical properties [5]. Therefore, practice of appropriate application of straw for manure may complement to the restoration and increase of the soil fertility [6]. The aim of the experiments was to define the effect of different technological measures on the intensity of decomposition of winter wheat straw on the primary stage as well as peculiarities of emission of biological elements. Materials and methods Experimental site and soil. The research was done in the northern part of Central Lithuania lowland (56º12’ N, 24º20’ E). The soil of the experimental site is Endocalcari – Endohypogleyic Cambisol (CMg-n-w-can). The soil texture is clay loam on silty clay with deeper lying sandy loam. The topsoil is close to neutral, medium in phosphorus (P 2 O 5 146-169 mg·kg -1 soil), high in potassium (K 2 O 221-260 mg·kg -1 soil) and moderate in organic carbon 1.50 %. Three analogous field experiments were carried out. The experiments were organised after the winter wheat harvesting in different periods: 2008-2009 (I experiment), 2009-2010 (II experiment) and 2010-2011 (III experiment). Stimulation of decomposition of straw of winter wheat was affected