485 The influence of organic mulches on soil properties and crop yield A. Sinkevičienė, D. Jodaugienė, R. Pupalienė and M. Urbonienė Lithuanian University of Agriculture, Studentų 11 Akademija, LT-53356 Kaunas distr. Lithuania; e-mail: ausrasinkevicienelzuu@gmail.com Abstract. The application of organic mulches as a soil cover is effective in improving the quality of soil and increasing crop yield, especially in organic farming. The field experiment was carried out in the Pomological Garden of Lithuanian University of Agriculture in 2005– 2008. The soil type – Calc(ar)i- Endohypogleyic Luvisol. Treatments: 1) without mulching; 2) chopped wheat straw; 3) peat; 4) sawdust; 5) grass. The aim of this investigation was to evaluate the effect of different mulches on soil properties and crop yield. All examined organic mulches significantly decreased soil temperature. Mulched plots also had higher soil moisture content throughout the experimental period. The highest soil moisture content was in plots mulched with peat or sawdust. The tendency of a higher amount of available phosphorus in the soil in mulched plots in 2005–2006 was established. The positive effect of grass mulch on available potassium in the soil was estimated. Mulching decreased weed density. During all years of the experiment significantly higher crop yields were obtained in grass-mulched plots. Peat mulch significantly decreased weed number although it has a significant negative effect on crop yield. Key words: organic mulch, soil properties, crop yield, organic farming INTRODUCTION Crops are influenced by a variety of factors when mulching is used. Weeds are an important factor determining crop yields, and mulches are important for weed control (Bilalis et al., 2002; Radics & Bognar, 2004; Jodaugienė et al., 2006 ). Mulch can have positive or negative effects on crops apart from its impacts on weeds. Mulches reduce water evaporation from soil and help maintain stable soil temperature (Lal, 1974; Ji & Unger, 2001; Kar & Kumar, 2007). Sønsteby et al. (2004) established increased amounts of phosphorus and potassium levels in crop leaves in plots mulched with wood chips. In 1963 Tukey & Schoff reported increased amounts of available soil P and K under mulches. They suggested that the release of nutrients from decomposing mulches (rapidly and slowly decomposing) might have a positive effect on the soil. Application of straw mulch (Sønsteby et al., 2004) and grass mulch (Cadavid et al., 1998) significantly increased the available phosphorus and potassium in the soil. The influence of organic mulches on crop yield is unequal. Mulching improves plant growth, yield and yield quality (Sharma & Sharma, 2003; Singh et al., 2007). Gill et al. (1996) state that yield increase with mulching was also greater for the early Agronomy Research 7(Special issue I), 485–491, 2009