A greenhouse experiment was conducted to study the effects simulated grazing of Buchloe dactyloides and soil nutrients on the competition between Prosopis glandulosa and B. dactyloides. Prosopis glandulosa (honey mesquite) is a woody plant found in the American southwest which has increased in density over the last 150 years.  Buchloe dactyloides (buffalo grass) is a key element of upland short-grass prairies and can be found growing in the same areas as P. glandulosa. Both species have increased in density on heavily grazed areas. Previous studies have shown that B. dactyloides competes more successfully than P. glandulosa for soil resources. Two levels of simulated grazing were tested -  no clipping and clipping at 10 cm above the soil surface. Two levels of soil nutrients were tested – native soil low in soil nutrients and native soil amended with Hoagland nutrient mixture. Each species was grown alone or in mixture with each other. We hypothesized that when B. dactyloides was not clipped, increased soil nutrients would increase the competitive ability of B. dactyloides which would cause an inhibition of P. glandulosa. We also hypothesized that clipping of B. dactyloides would decrease its competitive ability, regardless of soil nutrient level.

Results/Conclusions

Analysis of variance indicated that all main factors (planting combination, nutrients, and clipping) had a significant effect on B. dactyloides dry mass. In addition, there was a significant interaction between nutrients and clipping. Buchloe dactyloides dry mass was reduced when grown with P. glandulosa, in low soil nutrients, or when clipped. Nutrient additions had a greater effect when B. dactyloides was not clipped. Analysis of variance indicated that nutrients and clipping of B. dactyloides had a significant effect of P. glandulosa dry mass. In addition, there was a significant interaction between planting combination and clipping. Prosopis glandulosa dry mass was reduced in low soil nutrients. Prosopis glandulosa growth was greatest when grown with clipped B. dactyloides, which was not significantly different than growth alone. In addition, growth with clipped B. dactyloides was significantly greater than growth with unclipped B. dactyloides. Soil nutrients had the greatest effect on P. glandulosa when grown alone and a smaller effect when grown with clipped B. dactyloides. Evaluating the competitive abilities of B. dactyloides and P. glandulosa during simulated grazing and altered soil nutrients allowed a better understanding of factors which may contribute to changes in grassland communities in the southwestern United States.