An assessment of the relative effects of adverse physical and chemicalproperties of sodic soil on the growth and yield of wheat (Triticumaestivum L.)

摘要

Two wheat varieties were grown in artificially created sodic soils in pots at a range of sodicity levels (exchangeable sodium percentage (ESP) 15-52), with and without an anionic polyacrylamide soil conditioner (PAM) to stabilise soil aggregates. Increasing sodicity decreased the % water stable aggregates (% WSA) in soil and survival, grain and straw yield of wheat. Plants grown at high sodicity also had higher Na+, lower K+ and Ca2+ concentrations and lower K+/Na+ ratio in flag leaf sap than plants grown in control (non-sodic) soil. Sodicity had no effect on the concentrations of Cu2+, Fe2+, Mn2+ and Zn2+ in grains and straw, but total uptake of these micronutrients was deceased due to lower dry weight of these tissues per plant. At all sodicity levels treatment of sodic soil with PAM increased the % WSA to values greater than in the non-sodic control soil, and slightly lowered ESP. Over the range ESP 15-44 the effects of PAM on wheat grain yield increased as sodicity increased, so that at ESP 44 grain yield in the treatment with PAM was only 25% lower than in the non-sodic control. However at ESP 52 the effects of PAM were smaller, and grain yield was 86% lower than in the control. At this sodicity level the decreases in grain yield due to sodicity and the increases in reponse to treatment of sodic soil with PAM were similar in the two varieties tested. At high sodicity levels (ESP 44 and 52) treatment of sodic soil with PAM decreased the concentration of Na+ and increased K+ and K+/Na+ ratio in flag leaf sap. However, at the highest sodicity level (ESP 52), flag leaf Na+ concentration remained above the level (100 mol m(-)3) at which it has been found to be toxic. Concentrations of Cu2+, Fe2+, Mn2+ and Zn2+ in grain and straw were unaffected by PAM. These results suggest that at ESP up to 40-50 adverse physical characteristics are the major cause of low wheat yield in sodic soils, either due to their direct effects in decreasing growth, or their indirect effects in increasing uptake of Na+ and decreasing uptake of K+. Above ESP 50, roots are less able to exclude Na+, even in the presence of improved soil physical conditions, so that at these sodicity levels, both adverse physical and adverse chemical properties contribute to the decreased yield.