Effects of Irrigation Regimes during Grain Filling on Grain Quality and the Concentration and Distribution of Cadmium in Different Organs of Rice

Abstract

The objective of this study was to investigate whether the grain quality could be improved and the proportion of cad-mium(Cd)be reduced in grains through a proper irrigation regime when rice was planted in Cd-contaminated soil.Two rice cul-tivars of Yangjing 9538(japonica)and Yangdao 6(indica)were pot-grown.150 mg kg-1 Cd was added into pots before seedling transplanting(Cd treatment),and no Cd addition was taken as control(CK).Three irrigation regimes,well-watered(WW),mod-erate dry-wet alternate irrigation(MD,soil was re-watered when soil water potential reached at-20 kPa),and severe dry-wet al-ternate irrigation(SD,soil was re-watered when soil water potential reached at-40 kPa),were imposed from 7 d after heading to maturity.The results showed that under the same Cd concentration in soil and when compared to WW,MD significantly increased,whereas SD significantly reduced,seed-setting rate,1 000-grain weight,grain yield,brown rice rate,milled rice rate,and head rice rate.MD markedly reduced,while SD increased,chalkiness.There were no significant differences in the seed-setting rate,1 000-grain weight,and each index of rice quality between the Cd treatment and the control.Under the Cd treatment and com-pared to WW,MD,and SD significantly increased the concentration and proportion of Cd in roots,while significantly reduced Cd concentration in stems and leaves and reduced Cd proportion in grains.Cd concentrations in grains and milled rice were signifi-cantly higher under SD than under WW,and exhibited no significant difference between MD and WW.SD showed lower propor-tion of Cd in milled rice,when compared to MD or WW.The two cultivars behaved the same.The results indicate that a moderate dry-wet alternate irrigation during grain filling could increase grain yield,improve milling and appearance quality and not in-crease Cd concentration or even reduce Cd proportion in grains.Reasons for variations in grain yield,quality,and the concentra-tion and proportion of Cd under different irrigation regimes were analyzed from the aspects of root activity,photosynthetic cha-racters,and Cd translocation.