抄録
In this experiment, four plots which were combined non-tillage and tillage in autumm and spring were prepared as follows; non-tillage in autumn and spring (Nt-Nt), non-tillage in autumn and tillage in spring (Nt-T), tillage in autumn and non-tillage in spring (T-Nt), and tillage in autumn and spring (T-T). The experiments were continuously conducted from wheat in 1964 to rice in 1968. Soil of this paddy field was fluvio-marine soil (CL), and wheat variety used was Shirasagikomugi. The wheat yield of non-tillage plot (Nt-Nt) was fairly decreased in first year, and was recovered in and after second year. In plots (Nt-T and T-Nt), where non-tillage and tillage were combined, more yields were produced than those in plots(Nt-Nt and T-T) where non-tillage or tillage was continued. The amounts of wheat growth were smaller atearly growth stage and were larger at late stage in the plots of non-tillage in autumn (Nt-T and Nt-Nt)than those in plots of tillage in autumn (T-Nt and T-T). The macro pore ratio (air ratio at pF-1.5) at plow layer in non-tillage plot (Nt-Nt) was considerably decreased in first year, and was hardly changed in subsequent years. It was presumed that the decreasing of macro pore ratio in first year was due to the condition of field puddled at transplanting culture of rice before initiation of non-tillage continuation. The macro pore ratios at lower part of plow layer and at subsoil layer were higher in plots combined non-tillage and tillage (Nt-T and T-Nt) than in plots continued non-tillage or tillage (Nt-Nt and T-T). And those macro pore ratios were closely correlated with yield. It was considered from results obtained that wheat cultivation, in which non-tillage and tillage were combined in rice-wheat cropping, contributed to formation of the suitable soil conditions for root development and resulted to increase yield. It was also assumed that the continuation of non-tillage for several years did not decrease yield.
