26 MISCELLANEOUS PUBLICATION 9 52, U.S. DEPT. OF AGRICULTURE 



grass: four ages of stand, 2. 4, 6, 

 and S years: and two nitrogen- 

 fertilizer levels. and 40 pounds 

 of nitrogen per acre. Plots in grass 

 for 20 years and a sequence of grain- 

 fallow were used as checks. Maz- 



urak and coworkers (54) used rate 

 of water entry into the soil to 

 determine the effect of grasses, age 

 of stand, and nitrogen fertilizer on 

 the physical properties of soil (table 

 17). 



Table 16. — Changes in total nitrogen and organic-carbon contents of Holdrege 

 silt ham, by soil depths, as influenced by years in perennial grass. North 

 Platte, Xebr.. 1935-44 1 



Years in sod 



Gain or loss of total 



nitrogen at depth 



(inches) of — 



Gain or loss of organic 



carbon at depth 



(inches) of — 



Oto 6 



6 to 12 



Oto 6 



to 12 



9 



8 



6ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZI 



5 



4 



3 



2 



1 



2 



Least significant difference at 5 

 percent level 



i Data from McHenry and coworkers (4.7). 

 2 Continuously cultivated plots. 



Percent 

 -0.003 



-. 001 

 -.006 

 -. 009 

 -. 011 

 -.014 

 -. 019 

 -. 021 

 -. 01S 

 -.016 



o. 013: 



Percent 

 -0. 003 

 -.009 

 -.005 

 -.006 

 -. 016 

 -.009 

 -.008 

 -.008 

 -. 010 

 -.013 



Percent 

 -0.01 

 -.02 

 -.02 

 -. OS 

 -. 11 

 -. 12 

 -.20 

 -.20 

 -. 17 

 -.23 



0. IS 



Percent 

 -0. 00 

 -.05 

 -.04 

 -.06 

 -.07 

 -.OS 

 -. 11 

 -.09 

 -. 11 

 -. 11 



Table 17. — Average rates, at several intervals, of water entry into soil 

 cropped to grain, fallow and to grass for various number of years, 

 North Platte, Nebr. t 1956 l 



Rotation and age of grass stand (years) 



Rate of water entry, per hour, at end of — 



5 10 20 60 120 360 



min. min. min. min. min. min. 



5-year grain, fallow 

 Grass: 



9 



4_. 

 6_. 

 8_. 

 20. 



Cm. 

 8.4 



9.3 



10.0 



8.4 



8.0 



10. 8 



Least significant difference at 

 5-percent level 



Cm. 

 3. 7 



5.9 

 6. 6 

 6.0 

 5.2 

 7.3 



Cm. 

 2.2 



3.9 

 4 8 

 4.0 

 3.9 

 5. 1 



Cm. 

 1. 2 



2.0 

 3.0 

 2.5 

 3.0 

 4. 6 



Cm. 

 1.05 



1. 8 

 2.8 



2. 6 



3. 2 

 4.8 



Cm. 

 0.95 



1.6 

 2.8 

 2. 1 

 3.4 

 4.9 



0. 4 



0. 3 0. 3 



0.3 



'Data from Mazurak and coworkers (04). 



