The effect of additions of nitrogen on the decomposition of sugar cane trash under field conditions

Cane trash that was chopped and turned into the surface soil on March 10 caused a marked lowering of the nitrate nitrogen in the soil. The depressive effect lasted for 3 months. Cane trash that was applied in the same manner on October 2, had decomposed sufficiently by the following April to have ceased to lower the available soil nitrogen, both ammonia and nitrate. By the addition of inorganic nitrogen with the cane trash at the rate of 5 pounds of nitrogen per ton of fresh field trash and the incorporation of the mixture within the surface 5 inches of soil, the rate of decomposition will be increased and the presence of available soil nitrogen insured. Since the nitrate nitrogen disappears from the surface soil during the winter and spring, an early application of the trash alone with the supplemental nitrogen being added in the spring directly ahead of the crop, would prove the more practical method for the use of trash. The application of cane trash to the soil increased the soil nitrogen and organic matter. The gain in the soil nitrogen from the use of trash was, within the limit of experimental error, equivalent to the nitrogen content of the trash. The resultant decomposition following the application of trash increased the availability of phosphorus 15 to 20 pounds per acre during the earlier stages of decomposition. After the organic material had decomposed to the nitrogen-carbon ratio of the untreated soil, 14% of the soil organic matter still remained as carbohydrates. The fact that it is possible to estimate only the microbial carbohydrate material puts somewhat of a limit on the disappearance of carbohydrates as a measure of the rate of decomposition. The lignin fraction of cane trash undergoes slow decomposition and tends to accumulate in the soil when the trash is buried, but when the trash turned into the surface soil there is no excessive accumulation from lignin. True lignin of the plant material gradually changed to lignin-humus material which had a much lower carbon content than the original lignin. Lignin-humus decomposes slowly in winter and spring but very appreciably in summer.