The Influence of a Three- Year Rotation and Fertilizer 

 Treatments on the Organic Carbon of Soils 



by W. H. Coates 



THE organic carbon level of soils and its turnover are important in tbe 

 growtli of crops. Its level is also one of the controlling factors of 

 accelerated erosion and soil tilth. The effects of various fertilizer 

 treatments and a 3-year rotation are presented with general observations 

 concerning erosion. 



Thorne (26j has reviewed the research w(jrk dealing with manure and 

 chemicals of the long-time experiments at Rothamsted, Pennsylvania, and 

 at Ohio, Missouri, and Indiana experiment stations. The literature re- 

 viewed and the data presented by Dr. Thorne show that yields may be as 

 successfully maintained by chemical fertilizers as by manure for ordinarv 

 farm crops. No attempt is made to disprove the value of manure. Blair 

 (1) presents similar data showing that gains in soil nitrogen and organic 

 carbon can be made only by losing a large amount of that which is applied. 



Turk and Millar {27 ) concluded that nitrogen content depends on 

 climate and cropj^ng systems, with emphasis on biological activity and or- 

 ganic matter turnover. Certain crops may demand a uniform water stip- 

 })ly which a high organic matter level helps to maintain. Lime increased 

 organic matter decomposition, but increased the crop residues enough to 

 balance this loss. A high correlation coefficient was found when differ- 

 ences in organic matter were correlated with differences in water-holding 

 capacity. Stauff'er (24) found 1.70 per cent organic carbon in plots crop- 

 ped to corn ; 2.20 per cent in plots cropped to corn when fertilized, and 

 2.90 per cent in a fertilized rotation of corn, oats, and red clover. Water- 

 holding capacity varied from 56 per cent by weight for the soil cropped 

 continuously to corn, to 75 per cent for the fertilized rotation. 



Bushnell (8) showed that corn as green manure gave larger amounts 

 of organic matter to plow under than either sweet clover or soybeans. 

 Potato yields have been highest after corn. Additional nitrogen was sup- 

 ])lied to compensate for adding large amounts of organic matter which 

 was low in this element. Smith (22) has outlined an extensive experi- 

 ment using green manure crops to increase potato yields, and has given 

 preliminary data showing highest organic matter vields from corn and 

 sunflowers. 



Salter and Green (19) compared the effects of continuous corn, wheat, 

 and oats, and 3-year and 5-year rotations on the nitrogen and organic 

 carbon level in the soil. In the 3-year rotation of corn, wheat, and clover, 

 the accumulative effect of the clover crop on the limed but otherwise un- 

 treated soil, approximately balanced the destructive effect of the corn crop. 

 Residues of the corn crop were of little value in conserving soil nitrogen 

 nr organic carbon; those from oats were notably effective; and those from 

 wheat intermediate in value. 



