The Role of Roots in Different Depth on Water Absorption of Potato

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Two potato varieties with different root mass were examined in the irrigated and unirrigated fields with rain shelters to investigate the changes in water absorption at different depth during the growth, the effect of soil water condition on root development, and the relationship of varietal difference in root mass with transpiration rate, leaf growth and total dry matter production. Additionally four combinations of grafting plants produced with the two varieties were also compared in the present study.At the unirrigated plot the soil water was absorbed stepwise from the shallow depth downward and finally from the depth of 150 cm. The root length in the depth deeper than 20 cm was greater at the unirrigated plot than at the irrigated plot in both varieties. Although the varietal order in root length was consistent at both plots, the varietal difference was larger in the depth of 0-20 cm at the irrigated plot, while in the depth of 20-70 cm at the unirrigated plot. The leaf growth, transpiration rate and photosynthetic rate were severely depressed at the unirrigated plot in both varieties. The extent of the depressions, however, was greater in Konafubuki of smaller root length than in Norin 1 of larger root length. The depression of dry tuber yield by soil dryness was also greater in Konafubuki than in Norin 1. In the grafting plants, the stock genotypes mainly influenced the root growth at both plots and the extent of depressions in shoot and tuber growth at the unirrigated plot.We concluded that the difference in root growth between the two varieties was mainly due to the inherent characteristic in the dry matter partition between root and tuber, and corresponded to the drought tolerance.