time required for a test of this kind is twenty to twenty-five days, at the 

 close of which period both the green weight and transpiration of the 

 plants are ascertained. A fuller description of the method is given in 

 Circular No. 15 of this Bureau. 



The sample of soil used in this instance is a composite. It was taken 

 to a depth of 6 inches. In 1903 the soil was broken about 6 inches 

 deep, and treated with stable manure at the rate of 8 loads per acre, 

 and also with 200 pounds of the fertilizer already described. The yield 

 for that year was about 700 pounds of seed cotton per acre. In 1904 

 the soil was broken a little deeper than in the preceding year, and was 

 given the same amount of stable manure and 300 pounds per acre of 

 the fertilizer above mentioned. The result was a yield of 800 to 850 

 pounds of seed cotton per acre. 



The following table shows the results of the wire-basket experiment, 

 the relative growth of plants being expressed on the basis of 100 for the 

 untreated soil : 



Relative growth of wheat plants on Cecil silt loam with various treatments. 



It is obvious from the above data that cowpeas and nitrate of soda 

 are very beneficial manures for this soil. The quantities of cowpeas 

 and manure, as given in the table, are based on water-free substance, 

 and in case of the former would represent, in the respective items, a 

 little less than 6 tons and 3 tons of cowpea hay per acre. In growing 

 a crop of cowpeas for green manure a yield of 3 tons of hay would be 

 considered good, whereas 6 tons might be beyond what could be 

 expected. It should be noted, in this connection, however, that the 

 roots and stubble of the crop would probably equal 50 per cent of the 

 weight of the tops, and that they not only possess a manurial value, 

 but also materially improve the physical condition of the soil through 

 : their penetration of it. Acid phosphate and sulphate of potash were 

 used at the rate of 200 pounds per acre alone and in combination with 

 nitrate of soda and lime. They are not mentioned in the above table 

 for the reason that they gave no appreciable increase in growth. It 

 would seem, therefore, that 'neither potash nor phosphorus is required 

 in order to increase the productivity of this soil. 



