Sõnniku mõjust maheviljeluslikult majandatavas külvikorras
Organic agriculture is a production system which relies on ecological processes. In the organic farming systems, it is important to improve soil fertility and to protect soil physical condition for its healthy functioning. The benefit from organically cultivated crops is strongly related to the maintenance of soil fertility based to a great extent on the soil organic matter content. Farmyard manure is one of the more valuable organic fertilizers maintaining soil fertility in the systems of alternative agriculture. To investigate the influence of manure from several aspects, a field experiment was carried out on a sandy loam Luvisol. A five-year crop rotation (potato (Solanum tuberosum L.) → oat (Avena sativa L.) → spring barley (Hordeum vulgare L.) → red clover (Trifolium pretense L.)→ winter rye (Secale cereale L.) was organically managed without manure (Org I) and with manure (Org II) treatments. 8.3 t ha-1 of organic dry matter as straw-based cattle farmyard manure was ploughed into the soil for potato grown the next year. During a seven-year experimental period, no significant (p < 0.05) changes were found in the soil organic carbon content. For the Org I treatment, a significant decrease in potassium, copper and boron contents in the soil occurred. The application of manure counterbalanced the need for potassium, and significantly increased the contents of phosphorus and magnesium in the soil. Manure stimulated microbial life in the soil: the communities of cellulose-decomposing bacteria, nitrifying bacteria and total bacteria increased significantly. Under the influence of manure, the yields of potato, oat and barley increased by 52, 23 and 10%, respectively; this allowed us to gain an extra 30 GJ metabolizable energy during the crop rotation. In organic farming systems, the regular application of solid farmyard manure is recommendable for the maintaining and improving the status of available nutrients and microbial activities in the soil, and for the economic profitability.