Effects of different organic amendment on winter wheat yields under long-term continuous cropping

The observations were conducted on chernozem soil in a sugar-beet production region in 1971-2002. Six variants of organic amendment were examined: 1 - straw harvest, 2 - straw harvest + green manuring, 3 - straw incorporation, 4 - straw incorporation + green manuring, 5 - straw burning, 6 - straw burning till 1977 + intercrop, incorporation of farmyard manure at 10 t/ha since 1978. The effect of organic amendment on winter wheat continuous cropping was statistically significant. On average of the whole period (32 years), the highest yields were produced in variants with straw burning (var. 5) - 6.04 t/ha and with green manuring (var. 2) - 6.03 t/ha, and lower yields in variants with straw incorporation into soil (var. 3) - 5.65 t/ha, (var. 4) - 5.67 t/ha. The smallest differences between variants were found in the first decade of the experiment. Over time (in the second and third decades), the differences increased and positive effects of green manuring and straw burning and adverse effects of straw incorporation into soil increased. The yield level of winter wheat continuous cropping was high under the given conditions. The yield for the whole period of the experiment averaged 5.85 t/ha, the yields 5.19, 6.54 and 5.76 t/ha were obtained in the first, second and third decade, respectively.