Modelling Yields of Non-Irrigated Winter Wheat in a Semi-Arid Mediterranean Environment Based on Drought Variability

Abstract

Regression models for the prediction of grain yields of non-irrigated winter wheat in a semi-arid Mediterranean environment were developed based on drought variability. Twenty-five years (1980-2004) of climate data and yield data from four soils (sandy loam, clay, clay loam and sandy clay loam soil) in northern Greece were used for this purpose. Two variables were selected as explanatory variables of the models: (a) the monthly precipitation versus the monthly reference evapotranspiration ratio (P/ETo ), which describes the monthly drought and consequently the water deficit conditions during the wheat-growing season and (b) the mean observed yield ( y) of each soil, which indirectly describes the intrinsic fertility of the soils. A resampling technique using subsets of the data (bootstrapping) was applied to estimate the coefficients of the models, to assess the uncertainty of the selected explanatory variables and to validate the models. The models showed adequate predictive ability of wheat yields, defining the time and intensity of drought effects. The most crucial period for winter wheat was found to be primarily the vegetative-reproductive stage period between late winter and mid-spring (i.e. February to April). Soil clay content was found to be the most representative parameter in describing most of the physico-chemical parameters and properties of the soils and consequently the mean yield, indicating that yield is non-linearly correlated with most soil properties. With the proposed models, yield gap (YG) predictions between two growing seasons of the selected soils presented 84% accuracy in all years in the identification of the correct signal (+ or -) of yield increase or decrease, respectively, and adequate performance in the prediction of the mean YG

Climate variability and landscape dynamics in the Late Hellenistic and Roman north-eastern Peloponnese

“…The modelling of future scenarios emphasises that areas characterised by drier conditions are more vulnerable to further reductions in precipitation (amplified or modulated by possible shifts in potential evapotranspiration) that will cause a decline in the moisture content of soils available for plants (Nastos et al 2013). Field research and modelling have demonstrated the effects of reduced amounts of precipitation, including water stress and drought on modern yields of rain-fed winter wheat and barley in Greece (Halstead 1989: 72-73;Kosmas et al 1993;Aschonitis et al 2013;Tigkas & Tsakiris 2015). Starting from a lower baseline value for precipitation, the impact of drier conditions would have been stronger in the already drier north-east, where reduced precipitation levels could affect agricultural output directly.…”

“…1993; Aschonitis et al . 2013; Tigkas & Tsakiris 2015). Starting from a lower baseline value for precipitation, the impact of drier conditions would have been stronger in the already drier north-east, where reduced precipitation levels could affect agricultural output directly.…”

Warfare, Weather, and the Politics of Grain Shortage in the Early 2nd c. BC Achaian League

“…125 Foxhall andForbes 1982;Isager and Skydsgaard 1992, 20-6;Braun 1995. 126 Liakatas 1997Dalezios et al 2002;Mavromatis 2007, 915;Reidsma et al 2009, 32;Aschonitis et al 2013;Tigkas and Tsakiris 2015, 98. 127 Tyrt.…”

An Integrated Approach to Assessing the Soil Quality and Nutritional Status of Large and Long-Term Cultivated Rice Agro-Ecosystems

“…According to Aschonitis et al [53], the mean value of long-term yield of winter wheat in different soils of the Thessaloniki region is strongly associated with clay percentage. The yields showed a bell-shaped response versus the increase of clay, where values below <20% and values >50% were responsible for an~25% yield decrease in comparison to the maximum observed mean yields (see Figure 2 in [53]).…”

“…According to Aschonitis et al [53], the mean value of long-term yield of winter wheat in different soils of the Thessaloniki region is strongly associated with clay percentage. The yields showed a bell-shaped response versus the increase of clay, where values below <20% and values >50% were responsible for an~25% yield decrease in comparison to the maximum observed mean yields (see Figure 2 in [53]). The yield decrease for low clay values is probably connected to a lower cation exchange capacity (a low degree of nutrient retention) and a lower water holding capacity and availability, while the respective decrease for the high clay values is probably associated with low soil aeration, problems in water movement, and low water availability due to the higher degree of moisture retention at lower water potentials, which make it difficult for plants to uptake water.…”