Residual values of soil-applied zinc fertiliser for early vegetative growth of six crop species

Zinc (Zn) oxide is the most widely used fertiliser for the predominantly acidic to neutral soils of south-western Australia. For these soils, the residual value of Zn oxide has been determined for wheat and lupin, but not for barley, oats, canola and triticale, which are also grown in the region. Just after termination of a long-term (17 year) field experiment that measured the residual value of Zn oxide for wheat, soil samples were collected from selected plots to use in 2 glasshouse experiments. The field experiment was on previously unfertilised, newly cleared duplex soil (sand with much lateritic ironstone gravel over clay) and before the experiment started DTPA extractable Zn for the top 10 cm of soil was <0.2 mg Zn/kg. In the first glasshouse experiment, soil samples from the nil-Zn treatment of the field experiment were used to measure the critical Zn concentration in young mature growth of 6 crop species (wheat, barley, oats, lupin, canola and triticale) when 7 levels of Zn (0, 50, 100, 150, 200, 300 and 600 mg Zn/kg soil) were applied to the soil. In the field experiment, 0.5 and 1.0 kg Zn/ha, as Zn oxide, had been applied once only in each of the following years to previously nil-Zn plots: 1983, 1984, 1986, 1990, 1992, 1996 and 2000. Soil samples were collected from these plots to use in the second glasshouse experiment. This experiment estimated how long the Zn treatments applied in the field remained effective, as estimated using shoot yields and critical Zn concentrations in young mature growth of the same 6 crop species used in experiment 1. Critical Zn concentration in young mature growth was about 14 mg/kg for wheat, barley and lupin, 15 mg/kg for triticale, and 18 mg/kg for oats and canola. The residual value of Zn varied with crop species. As estimated from shoot yields, the 0.5 kg Zn/ha treatment was effective for ≤10 years for wheat, barley and oats, ≤14 years for lupin and canola, and >17 years for triticale. The 1.0 kg Zn/ha treatment remained fully effective for all crop species. As determined from projected estimates of the data, the time taken for Zn concentrations in young mature growth to reach critical values, the residual value of the 0.5 and 1.0 kg Zn/ha treatments were least for wheat, barley and oats, were greater for lupin and canola, and greatest for triticale. There were a total of 7 wheat crops and 10 pasture years during the 17 years of the field experiment. For the 0.5 and 1.0 kg Zn/ha treatment applied in the field in 1983, 30–34% of the applied Zn was removed in grain of the 7 wheat crops grown before soil samples were collected to do the glasshouse experiments. The pasture was grazed by sheep and it was estimated that 16–24% of the Zn applied in 1983 may have been removed in wool and meat. Removal of Zn in grain and animal products therefore decreased the residual value of the Zn oxide fertiliser.

Residual value of zinc fertiliser for production of wheat

Zinc deficiency is common on the sandy acidic soils in south Western Australia for grain production of wheat grown with diammonium phosphate containing low levels of zinc contamination. The effectiveness of zinc fertiliser (zinc oxide or zinc contamination of single superphosphate that were widely used for crops in south Western Australia) was measured in 1996 for grain production of wheat, for zinc applied once only to plots, either in 1996 (current zinc) or in a previous year (previous zinc) (1983, 1984, 1986, 1990, 1992). Relative to current zinc applied as zinc oxide with diammonium phosphate, the effectiveness of previous zinc for dry matter, zinc uptake (zinc concentration × yield) and grain production of wheat decreased relative to the effectiveness of current zinc, the decrease being larger with increasing time since application. Thirteen years after application, the decrease in the effectiveness was about half for dry matter and grain production where wheat was grown with diammonium phosphate. Both currently and previously applied zinc fertiliser increased wheat dry matter, zinc content of the dry matter and grain yields. Zinc applied as a zinc contaminant in single superphosphate in 1983 produced wheat grain yields on the maximum grain yield plateau (about 2.4 t/ha) achieved for the 5 amounts of zinc oxide applied in the current year (1996). The critical concentration of zinc in the youngest emerged leaf and grain for diagnosing zinc deficiency was 12 mg zinc/kg. However, when relating the zinc concentrations in the youngest emerged leaf to the grain yield (prognosis), a zinc concentration of 14 mg zinc/kg was determined.

Grain yield responses of faba bean (Vicia faba L.) to applications of fertiliser phosphorus and zinc.

Seed (grain) yield responses of faba bean (Vicia faba L. cv. Fiord) to applications of fertiliser phosphorus (0, 5, 10, 20 and 40 kg P/ha as triple superphosphate) and zinc (0, 0.5, 1 and 2 kg Zn/ha as zinc oxide) were measured in 3 field experiments conducted in 1997 and 1998 on neutral to alkaline soils in south-western Australia. Additions of fertiliser phosphorus significantly (P<0.001) increased grain yields by about 50 and 100% in 2 experiments, but in the third experiment differences in grain yield due to applications of fertiliser phosphorus were not significant (P>0.05). Increases in grain yields due to zinc fertiliser were small (<10%) and were only significant (P<0.05) in 1 experiment. This suggests the 3 sites chosen had adequate soil zinc for grain production of faba bean. In 1 experiment the increase in grain yield due to addition of phosphorus fertiliser was due to an increase in the number of pods per plant; numbers of seed per pod and mean seed weight were unaffected by additions of phosphorus and zinc fertiliser. Adding phosphorus and zinc fertiliser increased concentrations of both elements in grain, but had no effect on the concentrations of other nutrient elements (N, K, S, Ca, Mg, Na, Cu, Mn, Fe) measured in grain. These findings support results of a previous study in Western Australia indicating that phosphorus is the major nutrient element deficiency for grain production of faba bean in neutral to alkaline soils.