Available phosphorus below the canopy of warm-season, native and introduced perennial grasses in rangelands of southwestern Buenos Aires

TORRES, Y.A., C.A. BUSSO, O.A. MONTENEGRO, H.D. GIORGETTI, G.D. RODRÍGUEZ, T. MONTANI AND A. MAIDANA

Tafí del Valle, Tucumán

Jornada; Jornadas de la Asociación de Biología de Tucumán; 2007

Asociación de Biología de Tucumán

It has been reported that concentration of soil available phosphorus and other nutrients is greater under the canopy of palatable than unpalatable perennial grasses to domestic livestock. The objective of this study was to determine the soil available phosphorus concentration under the canopy of the native warm-season grass Pappophorum subbulbosum and under that of 2 warm-season perennial grasses recently introduced in Argentina from the U.S.A., Leymus cinereus cultivars ‘Magnar’ and ‘Trailhead’. All 3 genotypes are palatable to domestic livestock and tolerate water stress. Studies were conducted in the Chacra Experimental de Patagones (40º 39´ S, 62º 53´ W; 40 m.a.s.l.), South of Buenos Aires Province within the Phytogeographical region of the Monte. Plants were obtained from seeds and then established in experimental plots (14 plots/genotype x 3 genotypes = 42 plots). Twelve plants of each genotype were transplanted to those plots (12 plants/plot x 42 plots = 504 plants). Plants were 30 cm from each other within the plots in horizonal and vertical lines. Between the end of November and mid-December 2006, half of the plants were defoliated to 5 cm stubble height while the other half remained undefoliated (control). Apical meristems were not removed by the defoliation treatment since they were at 5.8 ± 0.9 mm from the soil surface. Soil samples were taken from under the plant canopies at each sampling date using an auger of 170 cm3 volume. Roots were separated from soil using a 60 mesh screen, and soil available phosphorus was determined.  Data were analyzed using two-way ANOVA and LSD when F tests were significant (p<0.05). Differences were only found in the first sampling date, when L. cinereus cv ‘Trailhead’ showed greater (p<0.05) soil available phosphorus (control = 6.76 ± 0.53; defoliation = 7.53 ± 0.82 ppm) than P. subbulbosum (control = 4.49 ± 0.53; defoliation = 4.33 ± 0.79 ppm). No differences (p>0.05) were found between defoliation treatments. At the second sampling date, differences between defoliation treatments or genotypes were also non-significant (p>0.05). Results suggest that all 3 genotypes present similar palatability characteristics if these are related with soil phosphorus concentrations under their canopies.