Root dry weight was determined at heading time and root oxi-dation activity (ROA) was measured at the same dates as leafphotosynthesis measurement (D1, D2, W1 and W2). To maintaincanopy conditions, the vacant spaces left after sampling for mea-surements of root and shoot biomasses were immediately replacedwith hills taken from the borders and these replanted hills were notsubjected to sampling any more.