Varietal Differences in the Responses of Yield Components of Rice Plants to Nitrogen-Free Basal Dressing Accompanied withSparse Planting Density in the Tohoku Region of Japan

Grain yield of rice plants is composed of different yield components that vary with the genotype, environmental condition and cultivation practice. Experiments were conducted in 1999, 2000 and 2001 in the field of Iwate University, Japan to study the responses of yield components to the practice of nitrogen-free basal dressing accompanied with sparse planting density (BNo) in 12 rice cultivars or lines. The results showed that the number of spikelets per panicle (NSp-1), especially in the late-maturing cultivars and in 2001, was often larger in BNo than in the conventional cultivation (CONT). The number of panicle m-2 (NPm-2), however, was significantly smaller in BNo than in CONT, resulting in a small number of spikelets m-2 (NSm-2) in BNo. The difference between BNo and CONT in NSm-2 varied with the cultivar and the year, and it was often smaller in the late-maturing cultivars than in the early- and medium-maturing ones, and was also smaller in 2001 than in 1999 or 2000. The percentage of ripened grains (PRG) was higher in BNo than in CONT in all cultivars, and the average PRG of 12 cultivars in BNo was 14.0%, 9.0% and 4.8% higher than that in CONT in 1999, 2000 and 2001, respectively. Grain weight (1,000-grain weight) was heavier in BNo than in CONT in most cultivars, and the 1,000-grain weight averaged over cultivars and years was 0.8 g (3%) heavier in the former than in the latter. High temperatures during the grain-filling period significantly and adversely affected 1,000-grain weight in CONT, but only slightly in BNo. The stably high PRG and heavy 1,000-grain weight in BNo, especially in the year with unfavorable weather (1999), could compensate for the small NPm-2 in BNo so as to achieve a high and stable yield in the Tohoku region

Analysis of the Dry Matter Production Process Related to Yield and Yield Components of Rice Plants Grown under the Practice of Nitrogen-Free Basal Dressing Accompanied with Sparse Planting Density

Experiments were carried out in 1999, 2000 and 2001 on the field of Iwate University, Japan to examine the effect of nitrogen-free basal dressing accompanied with sparse planting density (BNo) on the dry matter production (DMP) of 12 rice cultivars or lines belonging to the early, medium and late-maturing genotypes. During the period from transplanting to panicle initiation (PI), DMP was lower in BNo than in the conventional cultivation (CONT) in all 3 years. The DMP during the period from PI to full heading (FH) was also lower in BNo than in CONT, particularly in the high solar radiation year of 1999, because of the small leaf area index. During the ripening stage, leaf area index in BNo was smaller, but crop growth rate in BNo was similar to or higher than that in CONT due to the large net assimilation rate, which resulted from the largeflag leaf and 2nd leaf, and the heavy specific leaf weight in BNo. The DMP per panicle during the period from PI to FH positively and significantly correlated with the number of spikelets panicle-1. The percentage of ripened grains (PRG) was also closely related with the amount of carbohydrates from stems (ᴪჭS) and photosynthesis after FH (ǭW) contributed to a spikelet during the early ripening period (during 20 days after FH). The higher DMP per panicle in BNo compared with CONT during the period from PI to FH, therefore, resulted in a larger number of spikelets panicle-1 in the former. On the other hand, the large amount of carbohydrate supply per spikelet during the early ripening period could also secure a high and stable PRG in BNo, especially under unfavorable weather conditions

Varietal Differences in Tillering and Yield Responses of Rice Plants to Nitrogen-Free Basal Dressing Accompanied withSparse Planting Density in the Tohoku Region of Japan

At present, the main challenge in rice production is to achieve a high and stable yield with low input. In this study, the growth of tillers and yield of 12 rice cultivars and lines in the practice of nitrogen-free basal dressing with sparse planting density (BNo) was examined and compared with those in the conventional cultivation (CONT). The results in 1999, 2000 and 2001 showed that the numbers of both primary and secondary tillers m−2 were smaller in BNo than in CONT for all cultivars. However,ǽa large number of tillers in CONT, especially the secondary tillers, were nonproductive, and most of those in BNo were productive. The difference between BNo and CONT in the number of panicles m−2 was larger for the cultivars of the panicle-number type than for those of the panicle-weight type. Grain yield was often lower in BNo than in CONT, and the yield averaged over years and cultivars was 748 g m−2 in BNo and 772 g m−2 in CONT (the ratio of value in BNo to that in CONT was 97 %). The differenceǽbetween BNo and CONT in grain yield varied with the cultivar and the year. Under favorable weather conditions in 2000 and 2001, grain yield was high in both CONT and BNo, and was higher in CONT than in BNo for most cultivars. Nevertheless, under the unfavorable weather condition in 1999, grain yield was low in both CONT and BNo, and was similar or higher in BNo than in CONT. In all 3 years, the grain yield of Akitakomachi and Fukuhibiki was lower, and that of Ouu316 and Hitomebore tended to be higher in BNo than in CONT. The practice of BNo was found to be effective for achieving a stable and high yield of Ouu316 and Hitomebore in the Tohoku region

Analysis of Lodging-Resistant Characteristics of Different Rice Genotypes Grown under the Standard and Nitrogen-Free Basal Dressing Accompanied with Sparse Planting Density Practices

Field experiments were carried out in 2001 and 2002 to examine the lodging-resistance characteristics of various rice cultivars bred for the Tohoku region of Japan including the widely-cultivated cultivars (WCC) and the newly-released cultivars (NRC). The difference in these characteristics between the plants grown under standard (CONT) and nitrogen-free basal dressing accompanied with sparse planting density (BNo) practices was also analyzed. The lengths of the lower internodes and culms were often shorter in NRC than in WCC. Bending moment by whole plant was not different between NRC and WCC, but the breaking strength at the basal internode (IV) with leaf sheaths was often larger in NRC than in WCC. As a result, the lodging index was smaller in the former than in the latter. Breaking strength at the basal internode (IV) without leaf sheaths was also often larger in NRC than in WCC due to a larger cross section modulus or bending stress in NRC. Although the lengths of the upper internodes (I+II+III) were not different between BNo and CONT, the lower internodes (IV+V) were shorter in BNo, resulting in the shortened culms in BNo, especially in the long-culm cultivars. Breaking strength at the basal internode (IV) with leaf sheaths was significantly larger in BNo than in CONT, and thus the lodging index was smaller in BNo. The breaking strength at the basal internode (IV) without leaf sheaths and its two components, cross section modulus and bending stress, were also significantly larger in BNo than in CONT, particularly in the long-culm cultivars. These results suggest that besides creating new cultivars with short and stiff lower internodes, cultivation with sparse planting density accompanied with application of a small amount of nitrogen fertilizer in the early growth stage like BNo may also effectively increase the lodging resistance in rice plants

Effect of Top-dressing and Planting Density on the Number of Spikelets and Yield of Rice Cultivated with Nitrogen-free Basal Dressing

The effects of nitrogen-free basal dressing (BNo) and top-dressing on the growth and yield of two rice varieties, Akitakomachi and Hitomebore, planted at a standard density (22.2 hills m−2) and sparse density (16.7 hills m−2) were examined. The maximum number of stems and the number of panicles per unit area were lower in both BNo plots with a standard planting density (BNo22) and sparse planting density (BNol7) than in the control plot with standard nitrogen dressing and standard planting density (CONT) in both varieties. The number of panicles and spikelets per unit area was lower in both BNo22 and BNo 17 than in CONT, but the number of spikelets per panicle in BNo 17 was significantly higher than that in CONT, although that in BNo22 was not. In BNo22, the percentage of ripened grains and 1,000 grain weight were significantly higher than those in CONT, but in BNo 17, 1,000 grain weight was similar to that in CONT, although the percentage of ripened grains was higher than that in CONT. Grain yield in both BNo22 and BNo 17 was not significantly different from that in CONT, and that in BNo 17 was 660 and 710 g m−2 in Akitakomachi and Hitomebore, respectively. The leaf area index was lower and crop growth rate was higher in both BNo22 and BNol7 than in CONT at the grain-filling stage. The net assimilation rate and specific leaf weight were significantly higher in BNo22 and BNo 17 than in CONT at the panicle formation and grain-filling stages, respectively. Nitrogen top-dressing at the neck node differentiation stage was found to be very useful for the cultivation of these rice varieties under BNo with sparse planting density in the Tohoku district