Trends of wheat yield variability by planning regions of Bulgaria for 1960-2006
2008
Toncheva, R., Institute of Soil Science ” N. Pushkarov”, Sofia (Bulgaria) | Samalieva, A., Institute of Soil Science ” N. Pushkarov”, Sofia (Bulgaria) | Klevtsov, A., Institute of Soil Science ” N. Pushkarov”, Sofia (Bulgaria)
On the basis of long-term statistical data of wheat (46-yiear period) the yield trends have been analyzed for six planning regions of Bulgaria. The yield growth rate of wheat has been estimated by regions as data has been divided into 4 periods. Data assessment has been conducted by simple linear regression of yields against time for each period, using natural log transformation of yield as a dependent value. The slope coefficients of regression explain the growth rate and the mean standard error of estimation - annual percent deviation from the trend. The economic situation in Bulgaria and the unfavorable meteorological conditions have a great influence on the wheat yield trends The mean yield data in table 1 indicate highly significant increase between 1960 and 1974 due to the consolidation and intensification of the agriculture. The input quality of NPK (active matter) varies from 90.7 to 159.2 kg/ha. The wheat yields are most instable during the 1985-1995 period (and at the beginning of the next period) and there is a tendency to decrease due to changes in land property after 1990. The quantity of mineral fertilizers sharply decreases from 151 kg/ha during 1991-1992 to 58 kg/ha during 1996-1997. The growth rate increases for North Bulgaria from 3.6 to 5.3% during the last examined period (1996-2006) while the yield increase is from 0.6 to 2.6% for South Bulgaria. The annual percent deviation from the trend is about 5.5% for North Bulgaria and 0.9-3.9% - for South Bulgaria. The yield instability reflects on the grain balance of the country. Therefore a more thorough risk assessment and analysis of this trend is needed due to differences of wheat production and yields by years and planning regions. Thus a more detailed valuation of regional environmental conditions will be possible.
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