Argyrolobium uniflorum seedlings respond strongly to small doses of phosphorus: Consequences for rehabilitating degraded arid fallows in Presaharian Tunisia

In North African dryland research, few recognize that phosphorus (P) is the main soil nutrient limiting plant growth for legumes, in particular. P-fertilisation of legume reseedings could boost biological N-fixation and N-yield through enhanced biomass production, which, in turn, can benefit the re-establishment of resource-responsive perennial grasses. This is the hypothesis underlying a short-term fertilization experiment carried out with seedlings of Argyrolobium uniflorum, a native palatable legume. A secondary question was whether plant-available P, as measured by the Olsen method, is the best way to assess P-status in arid, calcareous, and nutrient-depleted soils that are renowned for their resource patchiness. Results show a significant effect of phosphorus addition on dry matter and N-yield. Seedlings responded to 25-kg P ha-1 by almost doubling dry matter production, yet no further improvement was observed for 50-kg P ha-1. The better plant growth corresponded with higher numbers of active nodules on P-fertilized seedlings. Plant P-content showed a positive and significant linear correlation with dry matter yield, whereas soil total and Olsen P-content did not, suggesting that plant P-content might be a more sensitive indicator of plant-available P than Olsen soil P-content. The observation that nodulation was efficient even though the land had not carried any legumes for over twenty years suggests that reseeding is feasible without inoculation. The strong response of Argyrolobium uniflorum seedlings to modest doses of phosphorus confirms the role of both legumes and phosphorus as key factors for restoring degraded drylands. © 2012 Copyright Taylor and Francis Group, LLC.