Studies on Utilization of Soil Organic Phosphorus to Crop Plants (Part 3) : On Reduction of Organic Phosphorus Content in Soils Caused by Cropping

Abstract

Changes in the content of organic phosphorus in soils by cropping were examined this time. Two soils, used in this experiment were virgin upland soil at NISHIGAHARA and paddy soil at KONOSU, the latter being manured every year with organic fertilizers (Part 2). The results obtained are summarized as follows : 1. Maize and rice plant were cultured in pots of the above two soils for 110 days for the formers and 133 days for the latter. Of soils, taken from the pots, were analyzed organic phosphorus. It was observed that soil organic phosphorus decreased more in cropped soils than in non-cropped, and the rate of decrease was greater in soil of paddy-field than that of upland field. (Table 2) 2. Maize and rice plant seedlings were planted for 40 days on soils which were added with phytin and nucleic acid, 50 and 25 mg P per 100 g of air-dry soil respectively in order (Table 3 and 4). Decrease of added organic phosphorus was more remarkable in cropped soil than in non-cropped (Table 5 and 6). Nucleic acid, added to paddy soil, was almost dephosphorylated during this experimental period, thus the decreasing rate of nucleic acid was always faster than that of phytin (Table 6) in both soils, cropped and non-cropped. The greater decrease of organic phosphorus in case of cropped soil was thought to be due to the accerelated mineralization of soil organic phosphorus caused by cropping.