Increased risk of zinc deficiency in wheat on soils limed to correct soil acidity

Abstract

Addition of lime to ameliorate soil acidity has been observed to induce zinc (Zn) deficiency for wheat in sandy soils of south-western Australia, reducing grain yields. The implications of widespread use of lime to treat acid soils for the residual value of Zn in these soils are not known. In a glasshouse experiment, using a Zn-deficient sand from south-western Australia, 3 levels of finely powdered calcium carbonate were added and incubated in moist soil for 6 weeks at 22°C to produce three different pH values (1 : 5 soil : 0.01 m CaCl2): 4.9 (original soil not treated with calcium carbonate), 5.8, and 7.4. Five amounts of Zn, as solutions of Zn sulfate, were then incubated in moist soil for 0, 30, 60, 120, and 180 days before sowing spring wheat (Triticum aestivum L.). The residual value of the applied Zn was determined using yield of dried shoots, Zn content in dried shoots, and soil test Zn (DTPA extraction). This was done by calculating the effectiveness of the incubated Zn for all 3 soils relative to the effectiveness of Zn applied just before sowing wheat (0 day incubation, freshly applied Zn) for the soil not treated with calcium carbonate. As measured using yield of dried shoots, Zn content of dried shoots, or soil test Zn, the residual value of the incubated Zn decreased with increasing soil pH and with increasing period of incubation of Zn with moist soil before sowing wheat. The critical Zn concentration, associated with 90% of the total yield of dried wheat shoots, was (mg Zn/kg) 13 in the youngest mature growth (apex and youngest emerged leaf), and 20 for rest of dried shoots. These values were similar to current critical values for unlimed soils. The relationship between yield of dried shoots and DTPA soil test Zn was similar for unlimed and limed soils, so similar critical soil test Zn was applicable on the sandy soil regardless of soil pH. Critical DTPA soil test Zn, the soil test Zn that was related to 90% of the maximum yield of dried shoots, was 0.14 mg Zn/mg soil. To combat the increased risk of Zn deficiency on soils limed to ameliorate soil acidity, fertiliser Zn needs to be re-applied to the soil when soil and plant tests indicate a high likelihood of deficiency.