96 Elementary Principles of Agriculture 



sorghum on some soils is much greater than could result 

 from the loss of fertilizing substance removed by the 

 crop. The effect is probably due to the formation of 

 some harmful substance by the roots. These injurious 

 substances are dissolved in the soil moisture. Deep 

 plowing and the application of composts tend to over- 

 come the bad effects of the poisonous substances. 



135. Soil Conditions That Affect Production. The in- 

 telligent farmer watches his crop closely from day to 

 day, and studies all the conditions that affect the vigor 

 or fruitfulness of his crop, of which there are many. 

 The general health of the plant may be affected as 

 much by conditions above the ground as by conditions 

 below the ground. If the plants are not growing properly, 

 close observation will often lead one to discover the 

 unfavorable condition, and a remedy for it. 



136. Excessive Droughty Conditions are noticed by 

 wilting, twisting, or drooping conditions of the leaves. 

 The plants endure but do not make profitable growth 

 when this condition exists, even for a part of the day. 

 Where irrigation is not possible, prevention is the only 

 remedy. (See 1 95, 105.) 



137. Wet Soil Conditions often cause the leaves and 

 stems to grow slowly and assume a yellowish cast, with 

 splashes of purple. This condition is not the result of 

 too much water in the plant, but of some injurious 

 effect of water-logged soils -on the roots. Many plants 

 can be grown to full maturity with their roots in water, 

 but not in a water-logged soil. Soils that frequently 

 retain injurious amounts of water should be drained. 

 (See K 107.) 



138. Soils Deficient in Essential Elements. Some soils 

 do not have enough of some one or more of the essential 



