Abstract
Some chemical changes were examined in the mixture of soil, organic materials and calcium cyanamide during composting. Rice straw and leaf mold were used as bulky organic material. Calcium cyanamide was added at the rates of 0.5, 1.0 and 2.0kg as nitrogen per cubic meter of the mixture. The mixtures were piled in the open in mid-August, turned over twice in the fall, and allowed to mature by February.
Immediately after piling, temperature of the mixture rised sharply, then falled gradually and followed to the fluctuation of air temperature. Volume of the mixture was reduced to about 70% as small as that of the original volume. No significant variations were noticed in percentage of loss of ignition. Contents of total nitrogen were decreased, and the ratios of C/N were increased. Exchangeable potassium was significantly reduced, while no apparent reduction in available phosphorus content was noticed.
When the composts matured, tomato seeds were sown in the boxes filled with those varying in their composition. Vigorous growths were obtained in the straw compost with low N and leaf mold composts with low and medium N. On the other hand, straw composts with medium and high N and leaf mold compost with high N showed retardation of seed germination and depression of plant growth. Above all, the seedlings grown in the straw compost with high N showed slight burning of leaf tips four days after emergence, the burning extended soon to the leaf base, and caused death of the plant.
Analyses and incubation tests of the composts revealed that normal mineralization of nitrogen preceeded in those which supported vigorous plant growth, and those which showed plant toxicity had remarkable accumulation of NH4-N, high pH, and low NO3-N content. In the latter, considerable amounts of dicyandiamide and guanidin were detected by paperchromatographic technique using FCNP reagent. Sand culture tests showed that the above mentioned toxicity symptoms were the same as those induced by the cyanamide delivertives rather than by high content of NH4-N.
It was suggested that application of excessive amount of calcium cyanamide should be avoided, because of the possibility of producing cyanamide delivertives harmful to the seedlings under high pH condition, and also accumulation of high NH4-N resulted from depression of nitrification in the compost.
