Critical phosphorus concentrations for oats, barley, triticale, and narrow-leaf lupin

Diagnostic critical phosphorus (P), which is the P concentration in tissue that was related to 90% of the maximum, P nonlimiting yield measured at the time of sampling, was determined for dried whole shoots and seed (grain) of oats (Avena sativa L.), barley (Hordeum vulgare L.), triticale (xTriticosecale L.), and narrow-leaf lupins (Lupinus angustifolius L.). For all species, diagnostic critical P in dried whole shoots generally decreased with increasing plant age and was larger for grain than dried whole shoots near maturity. For dried whole shoots, diagnostic critical P ranges (%P, dry weight basis) [days from sowing (DAS)] were oats, 0.72 (30 DAS)-0.23 (105 DAS); barley, 1.09 (30 DAS)-0.24 (203 DAS); triticale, 1.2 (30 DAS)-0.11 (120 DAS); and lupin, 0.60 (66 DAS)-0.21 (163 DAS). For grain, mean diagnostic critical P (range) was oats, 0.27 (0.18-0.39); barley, 0.32 (0.23-0.35); triticale, 0.22 (0.19-0.25); and lupin, 0.31 (0.25-0.41). In addition, we related the P concentration in dried whole shoots to grain yield measured at the end of that growing season (prognostic critical P). For dried whole shoots of each of the four plant species, the decrease in both diagnostic and prognostic critical P concentration as the plants matured was very similar, so both procedures predicted similar grain yields at the end of that growing season.