AGRICULTURAL UNIVERSITY OF ATHENS DEPARTMENT OF CROP SCIENCE LABORATORY OF AGRONOMY Effect of deficit irrigation practice on the weed flora in a corn crop V. E. Kotoulas, K. Karfi, I. S. Travlos, D. Voloudakis, G. Economou and A. Karamanos HUESCA 4-8 SEPTEMBER 2011

 At present and more so in the future, irrigated agriculture will take place under water scarcity  Irrigation management will shift from emphasizing production per unit area towards maximizing the production per unit of water consumed, the water productivity.

 To cope with scarce supplies, deficit irrigation, defined as the application of water below full crop- water requirements (evapotranspiration), is an important tool to achieve the goal of reducing irrigation water use.  2 ways: a. During whole growing period b. only during “biological windows”  The level of deficit irrigation is calculated according to plant water demands based on Penman-Monteith equation.

 Many researches were conducted on the effects of deficit irrigation on several crops or trees.  However, it is not still clear the way that deficit irrigation practices affects the growth of the weeds.

 The way that water shortage affects the weed development in relation to corn crop yield. Sub objective  The physiological effects of water shortage on the weed flora.

To investigate if the deficit irrigation can be used as an effective mean for weed management.

 Crop: Zea mays L.  Weeds: Amaranthus retroflexus, Solanum eleagnifolium, Tribulus terrestris  No application of herbicides  Irrigation method: Drip irrigation (except the first 2 irrigations that were applied with sprinklers)  Beginning of DI treatments: When the corn developed 5-6 leaves

 Irrigation dose: Based on Penman – Monteith equation we calculated ET 0 and we used it to calculate Etc (ET c = Kc*ET 0 ).  Data we used in order to calculate Evapotranspiration (ET 0 ): Air Temperature, Relative Humidity, Wind speed and Solar radiation. Treatments:  Full Irrigation (A): 80%*Etc  Deficit Irrigation 1 (B): 65%* Etc  Deficit Irrigation2 (C): 50%* Etc

Measurements and observations:  Weed density (plants/m 2 )  Dry weight  Stomatal resistance  Leaf water potential  Corn yield

Fig. 1. Air temperature during the experimental period Fig. 2. Relative humidity during the experimental period Fig. 3. Solar radiation during the experimental periodFig. 4. Wind speed during the experimental period

ET 0 ET c DAS Precipitation during the experimental period Reference (ET 0 )and Crop (Etc) Evapotranspiration

Weed density of the 3 weed species 110 DAS

Dry weight of the 3 weed species and the corn 110 DAS

Fig.9. Leaf water potential of the 3 weed species and the corn 110 DAS

Fig.10. Stomatal resistance of the 3 weed species and the corn 110 DAS

Fig.11. Corn yield

1. As far as the density of weeds concerns, no significant differences were observed among the water treatments 2. The highest dry weight values were observed for the second level of deficit irrigation for S. eleagnifolium and T. terrestris, but not for A. retroflexus. On the contrary, corn showed the highest value of dry weight when irrigated full

Physiological point of view  Leaf water potential values were higher in full irrigation treatment and lower in the second level of deficit irrigation both for weeds and corn.  Stomatal resistance values were higher in C treatment and lower in A and B.  Especially for Solanum and Tribulus did not differ between A and B treatments.

 Corn as a C4 plant reacts faster and better than the other species (C3 plants), making corn more competitive against the weeds in full irrigation conditions.  On the other hand, when deficit irrigation is applied, weeds (Solanum and Tribulus) are presented more competitive against corn.

 S. eleagnifolium at high risk as an invasive weed to Mediterranean type regions have was affected from water shortage.  A. retroflexus: DI could be an effective method for the control of these weeds, especially in other crops (cotton) that respond better than corn in water shortage.

The expected climate change will cause an expantion of the xerothermic zone and this will favour the occurance of such xerophytic weeds.

Thank you for your attention