The Efficacy Of Rice As A Leaching

The concluding phase(s) of a rice rotation experiment presented the opportunity to assess the effect of consecutive crops of rice on the chemistry of the soil profile. An experiment which aimed to determine the potential to use high salinity groundwater for the irrigation of the non-rice phases of a wheat - sub.clover - rice rotation, and then use rice, irrigated with low salinity channel water (<0.1 dS/m), as a leaching crop was undertaken. The rotation included a single rice crop between each cycle of the application of saline groundwater. Although soil salinity of most horizons under saline treatments could be reduced by leaching in the rice phase (single crop), this was not true for sodicity. Average rootzone sodicity remained elevated above control values at the end of each cycle and increased following successive cycles. This project was implemented to further assess the effectiveness of rice as a leaching crop. As the blocks completed two cycles within the rice rotation the opportunity to grow successive crops of rice was undertaken. At the time of soil sampling (May, 2000) separate blocks had grown one, two, three or four consecutive rice crops. Soil samples were taken from each plot and processed for electrical conductivity and sodium (Na) content. Additional consecutive crops of rice resulted in more leaching of salt from the profile. After three crops sufficient salts had been leached to reduce ECe to below 0.6 dS/m to at least the depth sampled in this project (90 cm). Similar values were measured after a fourth crop. The levels of SARe measured after a second consecutive crop of rice were still higher than pre-treatment levels. Even after three and four crops of rice the SARe at profile depths below 60 cm, whilst reduced from the pre-treatment level, were still between 6 and 8.