Long-term yield patterns for continuous winter wheat cropping in northern Greece

Continuous winter wheat (Triticum aestivum L.) cropping is a common practice for many growers in Greece, particularly in soils with low fertility or non-irrigated fields where other crops cannot grow profitably. The effect of continuous cropping on grain yields of wheat grown under the same conventional tillage practices for 25 years was studied in four soils of northern Greece. Grain yields varied considerably from year to year, regardless of soil type, showing a high temporal variability. Grain yields from the sandy loam and the clay soil were the most unstable across years compared with those from the clay loam and the sandy clay loam soil, which showed lower variability in time. Grain yields from the sandy loam soil showed a high correlation with rainfall during March to May (r = 0.71), whereas grain yields from the clay soil showed a high correlation with total rainfall during growing season (r = 0.89). Grain yields of the clay loam and the sandy clay loam soil appeared to depend on rainfall less than yields of the other two soils. On the average, grain yield was much lower in the sandy loam and the clay soil (1.94 and 2.46 Mg ha(-1), respectively) than in the clay loam and the sandy clay loam soil (3.48 and 3.72 Mg ha(-1), respectively) showing a dependence of wheat yield on soil type. Despite the high temporal variability of grain yields, no significant trends towards yield decline were observed for any of the soils studied. In addition, no significant differences were detected in soil pH values and organic matter content at the middle or at the end of the experiment. Given that annual fertilization is maintained and weeds are controlled effectively, it could be concluded that continuous wheat cropping may be practiced for many years without significant yield decline or significant change in soil pH and organic matter content. (c) 2006 Elsevier B.V. All rights reserved.