Organic carbon, pH, and aggregation of the soil of the morrow plats as affected by type of cropping and manurial addition

An investigation of the mechanical analysis, volume weight, pH, total carbon, and aggregate analysis of the soil of the Morrow plats was carried out. These plats, established in 1876 and cut down to 1/20 acre in 1904, have been subjected since 1904 to three different cropping systems, namely, continuous corn, a corn-oats rotation, and a corn-oats-clover rotation, with and without manure, lime, and rock phosphate. Samples were taken from each of six locations on each plat and from four depths at each location to 18 inches, and were analyzed individually. The plats were remarkably uniform in mechanical composition to a depth of 18 inches, with the exception of one location as noted, and fairly uniform in volume weight to a depth of 9 inches. The limed plats were considerably higher in pH than unlimed plats from 0 to 9 inches but not so much below 9 inches. The unfertilized continuous corn plat was lowest in total carbon to a depth of 13 inches, whereas the fertilized corn-oats-clover plat was highest to 9 inches. The fertilizer treatment was more effective in lessening the decrease of the carbon content of the soil with continuous corn and corn-oats-clover than with corn-oats. The fertilized corn-oats rotation was not materially better in maintaining organic matter than fertilized continuous corn. The sod border, in bluegrass continuously for 34 years, was no higher in total carbon than the fertilized corn-oats-clover plat. Grass in the border adjoining the plats exerted the most marked effect on aggregation in the upper 6 inches, with the fertilized corn-oats-clover rotation second. The soil treatment and the rotations practiced, including continuous grass, even when continued for many years, had little effect on the pH, organic matter content, or aggregation of this soil below a depth of 9 inches. Examination and analysis of the samples and borings in the field showed considerable erosion had occurred on the plats of lower elevation and on which corn was grown continuously. Considerable variations in pH and total carbon were observed in the fertilized plats.