Studis on Sub-Soiling in Paddy Field

[摘要] Sub-soiling method, breaking sub-soil and not mixing to surface soil, was tested with regard to the growth and yield of rice plant as a method of deep plowing. By sub-soiling the Eh value of tilled zone of soil was maintained higher (Fig. 1) and the distribution of NH3-N in the soil was wider (Fig. 2) than ordinary plowing plot and consequently the root of rice plant was kept healthy and the growth was vigorous accompanied with increased number of ears and number of grains per ear (Table. 1 and 2). But the yield was unstable due to decreased percentage of ripened grains which causes higher yield in some cases or lower yield in other cases than the yield of ordinary plowing plot according to the extent of decrease of percentage of ripened grains (Table. 1 and 2). Effect of sub-soiling differed with varieties; the varieties with relatively less spikelets per ear were inclined to gain higher yield owing to less decrease in percentage of ripened grains while the varieties with relatively much spikelets per ear showed opposite tendency (Table. 2). Rice plants of sub-soiling plot had higher nitrogen and lower carbohydrate content than ordinary plot (Fig. 4 and 5). After the heading stage the ferrous iron concentration in the tilled zone of the sub-soiling plot increased markedly (Fig. 3) and the contents of FeO in rice plants also increased, resulting in the decreased P2O5/FeO ratio in rice plants (Fig. 5). The ratio of ear to straw in the P2O5 content decreased by sub-soiling, expressing an impeded phosphorus translocation to ear (Fig. 6). These ratio showed varietal differences; varieties which showed greater extent of yield decrease by sub-soiling were accompanied with greater decrease in the ratio (Fig. 4 and 5). Based on these facts, the authors propose a new hypothesis that the nutritional state of plant with regard to iron could be a cause of poor ripening of grain; the poor percentage of ripened grains of sub-soiling plot may possibly be caused by high nitrogen and high FeO content of plant resulting from marked increase of ferrous iron in soil after heading stage, and retarded phosphorus translocation to ear due to high FeO content in the plant.

[学科分类] 农业科学（综合）