Determination of the mean root absorption zone in a system of crops and weeds competing for water

Maize (Zea mays L., cv. DEA) crop ecosystem was compared with a crop ecosystem consisting of pale smartweed (Polygonum lapathifolium L.) planted between maize rows. In presence of pale smartweed plants, the leaf area index of maize was reduced by 15% at flowering. Contrasting O-18 concentration in both soil profiles and plant collars of these different plants suggested that water uptake of pure maize crop was supplied by the upper part of the soil, above the tillage sole. In contrast, the water uptake by maize and pale smartweed in the mixed crop was supplied by deeper soil layer below the tillage sole tinder condition of high transpiration. However, neither maize transpiration nor,maize gas exchange were modified compared to unmixed maize at flowering.