The nitrogen, organic carbon, and pH of some southeastern coastal plain soils as influenced by green-manure crops

The total nitrogen, organic carbon, and pH of Greenville, Norfolk, and Tifton sandy loam soils under various systems of green-manuring are reported. These systems include the growing of summer and winter green-manure crops in different cropping systems and with varying crop management for soil improvement. The soils used in the experiments are typical of the soils of the same types in the southeastern coastal plain. The total nitrogen is increased and the organic carbon either increased or maintained under all systems in the experiments. In no case were these constituents raised to levels that correspond to the levels reported for fertile soils in latitudes farther north. In the Greenville soils nitrogen was conserved at the expense of organic carbon with a resulting narrow carbon-nitrogen ratio of about 6.0, under all systems of management. In the Norfolk soil more accumulation of carbon than of nitrogen was obtained under most of the systems with the result that the carbon-nitrogen ratio was broadened to around 10.0. The Tifton soil is intermediate in this respect showing a carbon-nitrogen ratio of about 8.0. The pH is generally lowered by the use of green manures on all the soils. Satisfactory yields of cotton and corn were produced with the following approximate levels of organic carbon and total nitrogen where green manures and commercial fertilizer were applied: 0.44% carbon and .044% nitrogen for the Norfolk soil; 0.34% carbon and 0.058% nitrogen for the Greenville soil; and 0.40% carbon and 0.050% nitrogen for the Tifton soil. More than one green-manure crop in succession results in higher nitrogen and carbon than one crop per year, but the added gain is not sufficient to justify the loss incurred by tying up the land for the time required. The most economical system for using green manure seems to be one in which the most important cash crop follows the green-manure crop.