A comparison of the potassium requirements during early growth of Lotus pedunculatus, Medicago murex, M. polymorpha, M. truncatula, Ornithopus compressus, Trifolium balansae, T. resupinatum, Pennisetum clandestinum, and Phalaris aquatica

Abstract

A comparison was made of 9 pasture species, some of which are coming into increasing use in Australia, for potassium (K) requirements and early growth. Plants were grown in sand culture in glasshouse experiments and were provided with nutrient solutions containing 7 rates of K (0-5 mmol/L), and nitrogen (12 mmol/L). Plants were sampled twice, the second sampling coinciding with flowering of most species. Symptoms indicating K deficiency were recorded, and diagnostic indices were derived for blades and petioles of the youngest open leaves (YOL), or for youngest expanded blades, and for whole shoots. Medicago murex and M. truncatula had the highest yield at the first sampling. Pennisetum clandestinum, Phalaris aquatica, and M. polymorpha had the highest yield at the second sampling and had a lower internal requirement for K than the remaining species, while Ornithopus compressus had the lowest yield. In all species except M. murex, critical K concentrations in whole shoots declined with plant age. Only in L. pedunculatus did the use of the YOL yield similar K concentrations at the 2 samplings. Ornithopus compressus was shown to have a low requirement for K and a high K efficiency, but it also showed poor scavenging ability. All plant parts sampled could be used to discriminate between K-deficient and K-sufficient plants. Critical K concentrations were higher in petioles than in blades of the YOL and, generally, were higher in whole shoots than in blades. The critical K concentrations derived for some species were similar to critical concentrations previously reported for other members of the same genera.