128 



The yields of cowpeas obtained are so variable that 

 conclusions of any kind would be out of place, and 

 unwarranted. However, the writer believes that of 

 the compounds tested, coumarin was the only one that 

 had a detrimental effect on the crop of peas, basing 

 this judgment upon the general appearance of the 

 crops produced by the several pots in the experiment. 

 The rather erratic results obtained are believed to be 

 due to the very high temperatures which existed in 

 the greenhouse during the hot weather of May and 

 early June. 



General Discussion. 



The data presented on the preceding pages of this 

 publication arc the results of experiments continuing 

 over a period of two years. From the beginning of this 

 work, the aim has been to parallel with soil cultures, 

 the solution culture experiments reported by the Bu- 

 reaus of Soils, as far as means and time would permit. 

 A large proportion of the soils of Alabama are natur- 

 ally poor, and require fertilization for high yields. 

 In the light of the experiments of the Bureau, this 

 infertility might be due to the presence in the soil of 

 compounds which are toxic to plants; and the liberal 

 use of fertilizers is necessary in order to overcome or 

 to antidote these toxic substances. If this be true, then 

 the fertility of a soil should be increased in propor- 

 tion to the removal of the inhibiting materials, since 

 all normal soils are supposed to contain at all times 

 a sufficient supply of available plant nutrients. 



It has been shown to be possible to remove the toxic 

 properties of a poor soil extract by the use of absorb- 

 ents like ferric hydrate, finely divided quartz, or car- 

 bon black. Pyrogallol has also been shown to be very 

 c'Ifectivc in certain cases in reducing the toxicicity of 

 such extracts. Logicall5% then, increased yields should 

 be expected from poor soils which have been treated 

 with carbon black, or pyrogallol, since the addition of 

 these would remove the only cause of infertility, i. e., 

 toxic compounds. In no case has this been found to 

 be true, under the conditions of the tests herein report- 

 ed. The addition of calcium carbonate proved to be 

 of little benefit, showing that acidity was not the cause 

 of the low yielding power of the soils used in this work. 



On the other hand, the addition to soils of such toxic 

 compounds as vanillin, coumarin, dihydroxystearic 



