Grain Yield Response to Planting Density in Forage Rice with a Large Number of Spikelets

Abstract

Because forage rice {Oryza sativa L.) must be cost-competitive with other forage crops, high grain yield is essential. The objective of the present study was to determine the effects of planting density (11, 25, or 100 hills m-^) and N application method (the 79-21N method, with 79% of the N applied before the panicle initiation stage and 21% after, or the 36-64N method, 36% before and 64% after) on grain yield and its components in the cultivar Mizuhochikara, which produces an unusually large number of spikelets per square meter. Grain yield was not different between N application methods but increased from 799 g m"^ to 870 g m-ŵ ith increasing planting density. The number of spikelets per square meter was not strongly influenced by the planting densities. The percentage of filled spikelets and the 1000-grain weight was higher at 100 and 25 hills m"^ than at 11 hills m-2. The amount of nonstructural carbohydrate (NSC) in the leaf sheaths plus stems per square meter at the full heading stage was larger at 100 and 25 hills m-^ than at 11 hills m"^. The percentages of both primary and secondary spikelets increased with increasing planting density, whereas that of tertiary spikelets decreased. Grain weight per spikelet was generally higher at primary and secondary spikelets than at tertiary spikelets. At each position in the panicle, grain weight per spikelet was heavier at 100 and 25 hills m-^ than at 11 hills m-^. Thus, dense planting may increase the grain yield, the percentage of filled spikelets, and the 1000-grain weight by increasing NSC at full heading stage and decreasing the number of tertiary spikelets even at a large number of spikelets per square meter in Mizuhochikara.

Yield Response to Cultivar and Sowing Pattern in High‐Yielding Rice

“…Some studies reported that grain yield was closely related to CGR from 14 d before heading to full heading, which closely related to the NSC amounts at full heading and the number of spikelets (Horie et al, 2003; Takai et al, 2006). The grain yield of Mizuhochikara in a recent study (8.70 Mg ha −1 ) (Nakano et al, 2012) was higher than that in the present study (7.02 Mg ha −1 ) (Table 1). Coincidently, it was found that the NSC amount at full heading (295 g m −2 ) was much higher than in the present study (232 g m −2 ) but the values of ∆W were almost the same (Table 2).…”

“…The main plot and subplot were cultivar and sowing pattern, respectively. The average temperature and solar radiation during the cropping season is described in Nakano et al (2012).…”

Effects of plant density on the performance of selected African upland rice varieties

“…All the previous studies mentioned in the previous paragraph are unanimous in showing the positive relation between panicles/m 2 and plant density. The same response was found by Harrell and Blanche (2010) for direct seeded rice in the USA and by Nakano et al (2012) for a Japanese highyielding rice for feed use. Huang et al (2013) reported an exceptional case for Chinese hybrid varieties that while the effect of plant density on panicles/m 2 was positive and significant for crops planted early, no significant relation was found for crops planted late.…”

“…The spikelets/panicle equation revealed that its negative relation with plant density was significant, when variations due to varieties and seasons were controlled (Table 2). The negative effect of plant density on spikelets/panicle, which is expected result from the competition among plants at higher plant density, has also been widely reported for lowland and upland rice varieties alike (Kondo, 1944;Matsushima, 1966;Akita, 1982b;Yamaguchi, 1982;Hossain et al, 2003;Zhang and Yamagishi, 2010;Nakano et al, 2012;Clerget et al, 2016), and it is hardly possible to find plant-density studies that reported otherwise.…”

Effect of low planting density on the spikelet number in ‘Tachisuzuka’, a rice (Oryza sativa L.) cultivar with a short panicle for whole crop silage use

“…; Nakano et al . ). In other words, there is no report that demonstrates a clear negative correlation between spikelet number and planting density.…”