8 TEXAS AGRICULTURAL EXPERIMENT STATION. 



The run-off in dry climates is less than in humid. It is, of course, 

 difficult to estimate accurately the run-off from cultivated lands. The 

 above figures may be an aid in forming an estimate. The run-off also 

 depends on the rate of precipitation. There will be more run-off from 

 a precipitation of one inch during three hours than from the same 

 quantity during forty-eight hours. 



PERCOLATION APPARATUS. 



A percolation apparatus consists of a definite area of soil enclosed 

 in a water-tight receptacle, with an outlet tube at the bottom, and a 

 vessel to receive the water which percolates. All the water which falls 

 in this apparatus must either evaporate or percolate through the soil. 

 There is no run-off. In some experiments, plants have been grown in 

 such vessels. Percolation apparatus are in use at the Rothamsted, Eng- 

 land, Experiment Station, at the New York Cornell Station, and at the 

 Florida Station. Other investigators and experiment stations have also 

 carried out experiments with this form of apparatus. 



Description of Apparatus. The percolation apparatus used in this 

 work consists of 48 galvanized iron cans 12 inches in diameter and 

 24 inches deep, with a block tin tube at the bottom. These cans are 

 buried in the ground. Figures 1 and 2 are drawn to scale, and show 

 the arrangement of the apparatus. The cans are connected with the 

 bottles to receive the water by means of a tight cork. The apparatus 

 was set up and filled with soil in March, 1910. Six pots were filled 

 with each soil. Each pot of the same soil receives a different treat- 

 ment. Each of the pots received first ten pounds of washed gravel, 

 which filled them to a depth of one and one-half inches. The sub- 

 soil and surface soil were then placed in them. The first forty-two 

 pots were filled in the middle of March, 1910. The last six pots 

 were filled about ten days later. As the earth settled considerably, fur- 

 ther additions of soil, to the amounts shown in the table below, were 

 made on May 24, 1910. The soil was in all cases in a moist condition 

 as it was received from the field. 



On account of various difficulties and for the purpose further of 

 allowing the soil to settle and assume more or less its natural condi- 

 tion, the percolation waters were not collected until January 1, 1911. 

 At the end of December, 1910, a heavy rainstorm set in, which saturated 

 the soils thoroughly; they therefore went into the experiment in a satu- 

 rated condition. 



The folloAving table shows the quantities of the soil added to the pots : 



Pots Nos. 1-6 inc. Norfolk sand, surface soil about 117 pounds, 

 No. 2377. 



Pots Nog. 7-12 inc. Orangeburg fine sandy loam, 110 pounds, No. 

 2378. 



Pots Nos. 13-18 inc. Houston loam, 57 pounds surface soil, No. 

 3333: 57 pounds subsoil, No. 3334. 



Pots Nos. 19-24 inc. Houston black clay, 45 pounds surface soil, No. 

 3335 ; 45 pounds subsoil, No. 3336. 



Pots Nos. 25-30 inc. Yazoo clay, 47 pounds surface soil, No. 3341; 

 47 pounds subsoil, No. 3342. 



