Fertilization of Extremely Grazed and Moderately Grazed Mixed-Grass Prairie with Slow Release Phosphorus and Urea





Methods


This study was conducted at the CGREC located in Kidder and Stutsman counties, North Dakota. Two sites of 148 ft by 197 ft were blocked, one on the extremely grazed pasture and the second on the moderately grazed pasture of the grazing intensity trial established in 1988. Each exclosure was placed in an area with similar topography, plant communities, and soil types in the moderately and extremely grazed pastures.


The extremely grazed pasture was characterized by having 20% of the current year’s crop production remaining at the end of the grazing season, or stocked at a historic average of 2.75 AUMs/ac since 1988. The moderately grazed pasture had 50% of the standing crop produced remaining at the end of the grazing season, or stocked at a historic average of 0.96 AUMs/ac since 1988.


The experiment was a complete randomized block design. Within each grazing intensity site, four replications (69 ft by 49 ft) for each of six fertilizer treatments and one control randomly allocated to each replication.

Individual plot size was 9.8 ft by 49.2 ft. The study area was fenced to exclude grazing. Annual applications of 24 lb P/ac and 48 lb P/ac on 1 May and 20 June with slow release P fertilizer, and 33 lb N/ac and 66 lb N/ac on 20 June with slow release N fertilizer were made using an All Terrain Vehicle (ATV) pulling a Gandy fertilizer spreader.


Over the course of the summer, four clipping sets were taken of five plant species to measure the uptake of phosphorous. Clipping dates occurred approximately between the fifth and seventh of June, July, August and September. The five species clipped were western wheatgrass (Agropyron smithii), green needle grass (Stipa viridula), Kentucky bluegrass (Poa pratensis), smooth brome (Bromus inermis), and western snowberry or buckbrush (Symphoricarpos occidentalis). Also a separate clipping was performed to establish above-ground production on each of the treatments.
 



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