CONSERVATION RESEARCH REPORT 5, U.S. DEPT. OF AGRICULTURE 



the irrigated area north of the Canadian River. 

 The Canadian River bisects the High Plains in an 

 east-west direction north of the station. 



Soil 



The soil on the experimental site is Pullman silty 

 clay loam (3, 15). Organic matter content in the 

 0- to 6-inch depth after several years of tillage 

 ranges from 1.6 to about 2.1 percent, as compared 

 to a native grass site of 2.6 percent. A caliche 

 layer (CaC0 3 ) occurs at a depth of 3.5 to 4 feet. 

 The proportion of CaC0 3 by weight in the caliche 

 layer is as high as 45 percent (15). The soil of a 

 given layer is extremely uniform in physical 

 properties and moisture-holding characteristics 

 for extensive areas. 



Bulk density determinations to a depth of 5 feet 

 were made at four locations on the experimental 

 site on September 18, 1956, by the use of two 

 1.85- by 4-inch cores per foot of depth. The 

 standard error of the mean of four cores was 0.056, 

 or 3.8 percent of the mean volume weight. These 

 data and soil moisture characteristics are summa- 

 rized in table 1. Field capacity values given are 

 the mean of high values measured 5 to 10 days 

 after a preplanting irrigation. Wilting percent- 

 ages are the mean of low values measured near 

 harvest on the drier plots. These field capacity 

 values would not be the maximum obtainable 1 to 

 2 days after excessive irrigation. However, they 

 indicate available water-holding capacity under 

 normal irrigation practices when evapotranspira- 

 tion rates are low. The rate of internal drainage 

 by gravity on this soil is veryslow. Therefore, when 

 evapotranspiration rates are high, the effective 

 available water-holding capacity is greater than 

 the values given in table 1, because evapotran- 



Table 1. — Soil density and moisture-holding 

 characteristics, Pullman silty clay loam 



Depth increment 



Bulk 



density 



Field 



capac- 

 ity i 



Wilting 

 point l 



Avail- 

 able 

 water 



Inches 

 0-12 



G./cc. 

 1.38 

 1.52 

 1. 52 

 1. 50 

 1.40 



3 1.50 



Percent 

 24. 6 

 22. 7 

 21.0 

 20.4 

 21. 9 

 19.9 



Percent 



12. 6 



13. 5 

 13.0 

 13. 5 



3 13. 5 

 13.4 



Inches 

 1. 99 



12-24 



1. 67 



24-36 



1 46 



36-48 



1. 24 



48-60 2 



1. 41 



60-72 2 _. ... 



1. 17 







Total: 



0-48--. 









6. 36 



0-72-.. 









8. 94 













1 On an oven-dry weight basis. 



2 Contains as much as 45 percent CaC03 by weight. 



3 Estimated. 



spiration demands can be met with water that 

 ordinarily drains from the profile in the 5- to 10- 

 day period after irrigation. 



Low intake rates on these soils limit the amount 

 of irrigation water that can be applied in 12 to 24 

 hours to 4 to 5 inches during the growing season. 

 A summary of intake measurements made in an 

 adjacent experiment that uses level basins and 

 tillage practices similar to those used in this ex- 

 periment is presented in table 2. A 4-inch ir- 

 rigation during the growing season requires about 

 16 to 20 hours to be absorbed. The intake from 

 to 0.33 hour ranges from 1.9 to 2.3 inches, and 

 the intake from 0.33 to 15.33 hours ranges from 

 1.7 to 2 inches. Intake rates are higher during 

 the preplanting irrigations. Intake rates when 

 large furrows are used between sorghum rows on 



Table 2. — Average intake rates for preplanting irrigations and cropping season irrigations on grain sorghum 

 with sweep-chisel tillage used during the fallow period, Bushland, Tex., 1957-59 



Year 



Irrigation 





Intake rates for time interval after applying water 





0.33- 



0.67- 



1.33- 



2.00- 



2.67- 



3.33- 



4.67- 



7.33- 



10.67- 



0.67 



1.33 



2.00 



2.67 



3.33 



4.67 



7.33 



10.67 



15.33 



hour 



hours 



hours 



hours 



hours 



hours 



hours 



hours 



hours 



In./hr. 



In./hr. 



In./hr. 



In./hr. 



In./hr. 



In./hr. 



In./hr. 



In./hr. 



In./hr. 



0. 504 



0.356 



0. 252 



0. 224 



0. 216 



0. 168 



0. 129 



0. 108 



0.080 



.638 



. 279 



. 161 



. 122 



. 140 



. 118 



. 104 



. 083 



. 081 



. 624 



. 240 



. 108 



. 108 



. 072 



. 120 



. 105 



. 084 



. 091 



1. 104 



.480 



.264 



. 120 



. 144 



. 168 



. 162 



. 154 



. 154 



.457 



. 156 



. 108 



. 120 



. 108 



. 120 



. 096 



.082 



.084 



Weighted 

 average 



1957-. 



1958-- 

 1959. . 



Preplant 



Average (1 and 2) 1 

 Average (1 and 2) 1 



Preplant 



Average (1 and 2) 1 



In./hr. 

 0. 145 

 .110 

 . 114 

 .242 

 . 128 



1 Average of the 1st and 2d irrigation during the crop season. 



