20 University oi- Xi:\\ IIampsiiire [Sta. Bull. 324 



Odland (18) reported that over a 40-year period, yields of potatoes 

 have averaged about the same for five different rotations including three, 

 four, five, and six-year rotations with legume and non-legume hays, corn, 

 and rye. In a five-year study of continuous culture versus rotation for 

 potatoes, Brown (5) obtained results favorable to the rotation during the 

 two dry years of the experiment, and an index of 109 for the potatoes in 

 the rotation as compared to 100 for potatoes continuously. Chucka and 

 Lovejoy (9) obtained increases in potato yields when green manures and 

 farmyard manure were utilized in arldition to regular commercial fertili- 

 zers. An increase of 156 bushels resulted from the addition of one green 

 manure crop and 20 tons of manure per acre. Other tests showed very 

 marked yield increases from manure. These increased yields were be- 

 lieved due mainly to the beneficial efTect of the (jrganic matter. 



Metzger (16) concluded that, in general, nianurt' and green manure 

 treatments maintained higher soil nitrogen and carbon levels than control 

 plots. Commercial fertilizers tended to produce similar results, but they 

 were much less marked. 



Studies have been made on the soils of the Jackson and Lane farms to 

 note any differences which may have occurred in organic substance. Each 

 plot on these farms was sampled to plow-depth at the 1)eginning of the ex- 

 periments. The samples were air-dried and sealed in Mason jars. At 

 the end of two rotations on the Lane farm and four rotations on the Jack- 

 son farm, the fields were again completely sampled and organic carbon 

 analyses were made on all samples. All samples were pulverized to pass 

 a 100-mesh screen and analyzed by the dry combustion method. 



Experimental Data 

 Lane farm results : 



TABLE XX. Fertilizer treatments and organic carbon in pounds per acre at 

 the beginning and end of six-year period with odds for significance. 



•L equals SOO lbs. ground limestone, LL equals 1000 lbs. 



