One hundred and six Australian cereal genotypes, including wheat, triticale, and rye, were screened for their ability to take up and utilise soluble phosphorus at different rates of P supply. Plants were screened in outdoor tanks irrigated at regular intervals with nutrient solution amended with 3 rates of P. Genotypes were ranked according to the following 3 criteria: shoot growth at deficient P supply, the relative shoot growth rate (dry weight at deficient P/dry weight at sufficient P), and phosphorus utilisation efficiency (amount of dry matter produced per unit of P accumulated in shoots corrected for seed P content). Considerable genotypic variation in growth and P utilisation efficiency was found in the cereal germplasm. Rye and triticale were generally more efficient in taking up and utilising P than wheat at low rates of P supply. Wheat genotypes Egret and Durati showed relatively high, and genotype Cadoux relatively low, P efficiency.
Two glasshouse experiments were conducted to evaluate the genotypic variation amongst cereal genotypes in phosphorus uptake from relatively insoluble iron phosphate. Optimum rates of iron phosphate were established by growing 3 wheat and 1 triticale genotype on an infertile sand amended with iron phosphate. Shoot dry weight of all genotypes showed a classic Mitcherlich response with 95% maximum growth achieved with 174�mg P/kg soil. Two rates of FePO4 were selected representing a deficient and sufficient supply (26 and 339 mg P/kg soil, respectively). These rates were used to screen 99 wheat, 8 triticale, and 4 cereal rye genotypes for phosphorus-use efficiency. Phosphorus efficiency was rated by 4 criteria: shoot dry weight at deficient P supply, shoot weight at deficient supply relative to shoot weight at sufficient P supply, P uptake efficiency (amount of P taken up per unit of P supplied), and P utilisation efficiency (shoot weight per unit P in plant). No genotypes were rated as efficient under all 4 criteria. Only 2 genotypes were rated efficient (rye Bevy, rye PC00361) and one inefficient (Machete) under 3 criteria. Seven genotypes were rated as efficient on 2 indices (wheat Chinese 80-55, Westonia, and Wawht 2147; triticale Treat, AT48-94, and TX93-78-1; rye Bulgarian Pento), whereas 7 genotypes were rated as inefficient on 2 indices (Boricuta, Cadoux, Cunderdin, Insignia, Kalingri, Perenjori, and triticale Abacus). Significant genotypic variation was identified in cereals in the ability to take up and utilise P from poorly soluble Fe-P, although all genotypes were able to utilise this source of phosphorus to some degree.
The effect of sulfur (S) supply on growth and S distribution within lupin and wheat plants was studied in a glasshouse experiment using pots containing 11 lupin or 15 wheat plants in 6 kg soil. Shoot growth and grain yield increased with increasing S supply, and both species produced maximum grain yield at 60 mg S/pot. Wheat yielded a lower percentage of maximum grain yield than lupin where no S was applied. Sulfur concentrations in all shoot parts increased with increasing S supply in both wheat and lupins. In wheat, S concentrations decreased with increasing plant age. At all rates of S, concentrations in old leaves were higher than in the youngest leaves. In lupins, S accumulated in stems when supply was adequate but decreased markedly with S deficiency and plant age. Concentrations in other parts of lupins generally did not change with plant age. Sulfur concentrations in the youngest open leaf blades were higher than those in old leaves at all rates of S. For lupins, critical S concentrations in the young leaves (0.28%), stems (0.07%), and whole shoots (0.15%), and the critical nitrogen (N) to S ratio in young leaves (22), are likely to be valid as diagnostic indices for S deficiency as they do not appear to be affected by plant maturity. In contrast, critical S concentrations (0.14-0.31% S) and N to S ratio (9-19) in young leaves of wheat plants changed sharply with plant age; neither is useful as a diagnostic aid unless the maturity of the plant in known. Field surveys were conducted in the agricultural regions of Geraldton and Dowerin in Western Australia to investigate the incidence of S deficiency in lupin and wheat crops. Sulfur concentrations in lupins and wheat from Dowerin were higher than those sampled at Geraldton. Lupin crops from both regions and wheat from Dowerin had an adequate S supply. Of the wheat sampled at Geraldton, 36% was deficient or marginal in S.
In many soils, organic P is the major component of the total P pool. Genotypic differences in wheat for P acquisition from organic P in the form of phytate, a common organic phosphorus component in soil, were investigated in a glasshouse experiment. Twenty genotypes differing in the ability to utilise poorly soluble phosphate sources were grown in P-deficient brown sand amended with phytate or inorganic phosphate. The P efficiency of wheat genotypes was evaluated by 3 criteria: growth at low phytate-P supply; growth at low phytate-P supply relative to growth at the same rate supplied as soluble inorganic P; and phosphorus acquision efficiency (PAE), calculated as the amount of P in the plant divided by the amount of P supplied in the soil. All wheat genotypes tested were able to utilise phytate as a source of P, albeit at a lower efficiency than soluble inorganic phosphate. Across the genotypes tested, plants supplied with 20 mg P as phytate produced only 23% of the shoot biomass of plants supplied with 20 mg P as inorganic P. When P supply was increased to 100 mg P as phytate, this increased to 88%. There was a significant variation in wheat genotypes in the ability to acquire P from phytate. Genotypes more efficient in acquiring P from sparingly water-soluble Fe phosphates were also more efficient in taking up P from phytate-amended soil. The genotypes Cadoux, Blade, ES8, Chinese 80-55, Wawht 2066, and Wawht 2128 were rated as efficient, whereas Janz, Machete, Kalingri, and Spear were rated inefficient on all 3 criteria.
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