EFFECTS OF DIFFERENT SYSTEMS OF GRAZING. 



33 



Table 10. — Periods of time when the most important plant species start their 

 spring growth and mature their seed. 



Species. 



Start of spring growth. 



Period of seed maturity. 



Bouteloua gracilis 



Stipa eomata 



Koeleria cristata. 



Carex filifolia 



Carex heliophila. . 

 Artemisia frigida. 



Apr. 15 to May 15 August to Sept. 15. 



Apr. 1 to May 1 June 25 to July 10. 



Apr. 1 to Apr. 25 June 20 to June 30. 



Apr. 1 to Apr. 20 j May 20 to June 1. 



do ! May 25 to June 10. 



Mar. 25 to May 1 Sept. 10 to Oct. 1. 



OTHER STUDIES BEARING UPON THE EXPERIMENT. 



MOWING EXPERIMENT. 



This phase of the studies bearing upon the grazing experiment 

 was started for two reasons: (1) To determine the quantity of hay 

 annually produced 



in 



and ('2) to determine 

 the effects upon total 

 production of annual 

 and biennial mow- 

 ing. The mowing 

 experiment was not 

 begun until 1919, al- 

 though plans had 

 been completed for 

 it previous to that 

 time. Figure 11 

 shows the plan and 

 arrangement of the 

 units for mowing. 

 The units in the cen- 

 ter are mowed an- 

 nually and those on 

 either side in alter- 

 nate years. They 

 are 1 acre in size, 

 and the hay from 

 each is weighed sepa- 

 rately. In 1919 the 9 acres were mowed and weighed. Some of the 

 units had not been cut since 1915, while those on the east side were 

 mowed in 1918. The yields from the different units are presented in 

 Table 11. While there has been only one year, 1921, that the biennial 

 units have been mowed as such, the yield is striking. The same rela- 

 tive difference is also true for the clipped quadrats which are cut 

 annually and biennially and yielded at the rate of 799 and 1,664 

 pounds per acre, respectively. The old growth of 1920 made up 

 about 35 per cent of the total weight. The increased yield, there- 

 fore, is not entirely the accumulated growth of the previous year, but 

 is partly caused by the increased vigor and consequent greater growth 

 of the vegetation of the current season. 



The hay from the units mowed in alternate years was of poorer 

 quality than that from those cut annually. This was because the 



Fig. 11. — Diagram showing the plan of the mowing ex- 

 periment (area, 9 acres) : I, Mowed in odd years ; II, 

 mowed every year ; III, mowed in even years. 



