Establishment of a native bunch grass and an invasive perennial on disturbed land using straw-amended soil

Native grasslands around the word face increased threats from non-native species. Fescue prairie in North America, in good rangeland condition, is dominated by the perennial bunch grass, Festuca hallii, whereas disturbances are often colonized by Poa pratensis, an introduced perennial rhizomatous grass which is competitive in nitrogen rich soils. F. hallii thrives in typical low nitrogen grassland soils and recovers poorly once disturbed. Disturbance to soil caused by well site construction may decrease organic carbon and potassium, and increase nitrogen, phosphorus, pH and electrical conductivity, creating conditions conducive to invasion by P. pratensis. This research tested the hypothesis that F. hallii would tolerate nitrogen depleted soil, through addition of carbon as a straw amendment to newly reclaimed well sites, better than P. pratensis. Our second hypothesis was that F. hallii is negatively affected by disturbed soil and P. pratensis is not. We treated three sites with three straw amendment rates, seeded monocultures of F. hallii and P. pratensis, and monitored establishment over three years. F. hallii biomass, root biomass, leaf length and cover increased in response to straw treatments, whereas P. pratensis showed little response. F. hallii was positively affected by prior-year soil water, and current-year ammonium and potassium. P. pratensis was positively affected by current-year soil water, potassium and nitrate. P. pratensis responded positively to higher pH and electrical conductivity found in disturbed soil and F. hallii responded poorly. The positive relationship of P. pratensis to pH above 7 could explain why it can invade reclaimed disturbed grassland; whereas the negative reaction of F. hallii might explain its failure to recover. We concluded the addition of straw as a soil amendment is a possible solution to poor establishment of F. hallii.