Effect of long-term organic matter application on physico-chemical properties in paddy soil. 1. Changes of the soil-chemical properties of paddy field by long-term application of organic matter

This experiment was carried out to investigate the effects of long-term application of organic matters on the chemical properties and on the application levels of nitrogen in fluvio-alluvial plain of Chonbuk series. The amounts of application of rice straw and compost, the sources of organic matters, were 500 and 1,000kg/10a in combination with the different nitrogen levels of 0.15 and 20kg/10a, respectively. In long-term application of organic matter the soil pH showed the lowest value in the 3rd-4th year at rice straw and 5th-6th year at compost but it varied less in control plot for 9 years. Organic matter content in the soils increased gradually by yearly application of organic matter, while it was higher in rice straw than in compost since the 5th year. The contents of available silicate and available phosphate in soil increased rapidly by long-term application of organic matter and it was especially higher in rice straw than in compost, but it decreased gradually in the control plot. The contents of exchangeable cations (Ca, Mg and K) and the total nitrogen increased by long-term application of organic matter. But they showed decreasing tendency in the control plot. The soil Eh was lower in the order of rice straw, compost and control plot, however, application of organic matter resulted in increasing soil Eh due to the rapid reduction of soil from panicle formation to heading stage in rice cultivation. The number of panicles per m** (2) and the number of grains per panicle increased by increment of nitrogen levels in all treatments and especially most in rice straw application. But 1,000 grain weight increased in low nitrogen level with long-term application of organic matter were 21, 24 and 20 kg/10a for lst-3rd, 4th-6th and 7th-9th year in rice straw application, and 16 and 19 kg/10a for lst-3rd and 4th-9th year in compost application, respectively