1966 Volume 35 Issue 2 Pages 134-141
This study was conducted to obtain some informations about chemical properties of the composts. Three soils-volcanic ash soil, clay soil and fine sand-and leaf-mold, as an organic material, were mixed together, varying in their proportions.
1. Base exchange capacities of mixtures were determined by leaching with N-ammonium acetate solution (pH 7.0). The capacities increased with increasing proportions of leaf-mold in the mixture, especially in the cases of clay soil and fine sand.
2. Buffering capacities of mixtures were determined by plotting pH changes against increments of 0 to 20ml of 0.05N Ca(OH)2 and 0.05N H2SO4. Ranges of pH changes were 3.5 to 8.5 in clay soil, and 2.8 to 10.0 in sand. On the other hand, in volcanic ash soil, which contains much allophane, the range was 4.3 to 7. 4, indicating high buffering capacity. Buffering capacity of the leaf-mold was higher in. the alkaline side, but was somewhat lower in the acid side than that of volcanic ash soil. Addition of leaf-mold enhanced buffering capacities of soils, having low buffering capacities.
3. To investigate the effect of various kinds of cations on the buffering capacities, three soils and leaf-mold were treated with 0.05N hydroxides of Na, K, NH4, Ba and Ca. After equilibration, pH was determined. The relative order of selectivity of the cations was as follows : Na<K<NH4<Ba-Ca, with the exception of the NH4 ion for fine sand. Addition of divalent cations showed higher buffering capacities than those obtained with monovalent rations in the leaf-mold.
4. To determine the adsorptive capacities for phosphorus, the mixtures were leached with 2.5% ammonium phosphate solution, and adsorbed quantities of P2O5 were measured. The adsorptive rate were 2270 (mg P2O5/100g soil) for volcanic ash soil, 207 for clay soil and 0 for fine sand and leaf-mold, respectively. By the addition of leaf-mold to the two former soils, the adsorptive capacities decreased considerably.
5. The nitrification rates in the mixtures were determined by the incubation experiments at 27°C, for 4 or 5 weeks. When ammonium sulphate or phosphate was added, formation of nitrates took place normally in volcanic ash soil and clay loam, but failed in sandy soil and fine sand. It was considered that the failure of nitrification in fine sand was caused by low numbers of initial population of nitrifiers, and that failure in the sandy soil was due to both the above fact and to low pH (4. 7) of the soil.
In the volcanic ash soil: leaf-mold (1: 1) mixture, one or two weeks retardation of the nitrification was observed in all inorganic- and organicnitrogenous fertilizer treatments. It was suggested that the retardation of nitrification in this mixture depends on air-drying of the leaf-mold before the incubation.
6. It appears from the above mentioned results that the application of organic matter to soil altered remarkably chenical characters of the composts. And also, it was believed that the improvement of chemical properties, as well as physical ones, may have the important effects upon the growth and development of vegetable seedlings.
