Abstract
Many researchers have demonstrated the effects of deep placement of top dressing in paddy field. However, few reports were published about the mechanism which gives these effects. This experiment was conducted to clarify the mechanism involving the effects of top dressing to deeper layer for rice plant. Experimental plots were consisted of two plots differing in placement of top dressing; soil surface layer (S plot) and deep layer (D plot), and the growth pattern of tops and yield in D plot was investigated in contrast with those in S plot. The results obtained are summarized as follows; 1. The number of spikelets per square meter and yield in D plot were 35% and 6% greater than those in S plot, respectively. And the former in D plot was secured by increase of number of spikelets per panicle (Table 2). 2. The dry matter growth of leaves and stems in D plot continued to increase until heading time, but until 10 days before heading time in S plot (Fig. 2), and the maximum LAI was 6.0 in D plot and 5.8 in S plot (Fig. 1). 3. In D plot, the tops size was larger and the productive structure was better than those in S plot (Fig. 5), respectively. In addition, the higher nitrogen content of leaves was maintained throughout the ripening period, and the duration of bottom leaves was longer (Fig. 3) and the percentage of fruitful stems was higher than those in S plot. 4. Therefore, the effects of the deeper layer application of additional nitrogen fertilizer seem to be brought by the autumn-vigor of growth resulted by less root-rotting, and which leads into increasing yields.
