Optimizing Hill Seeding Density for High-Yielding Hybrid Rice in a Single Rice Cropping System in South China
et al. (2014) Optimizing Hill Seeding Density for High-Yielding Hybrid Rice in a Single Rice Cropping System in
South China. PLoS ONE 9(10): e109417. doi:10.1371/journal.pone.0109417
Optimizing Hill Seeding Density for High-Yielding Hybrid Rice in a Single Rice Cropping System in South China
Danying Wang 0
Song Chen 0
Zaiman Wang 0
Chenglin Ji 0
Chunmei Xu 0
Xiufu Zhang 0
Bhagirath Singh Chauhan 0
Jose Luis Gonzalez-Andujar, Instituto de Agricultura Sostenible (CSIC), Spain
0 1 State Key Laboratory of Rice Biology, China National Rice Research Institute , Hangzhou, Zhejiang , China , 2 Key Laboratory of Key Technology on Agricultural Machine and Equipment, South China Agricultural University , Guangzhou, Guangdong, China, 3 Queensland Alliance for Agriculture and Food Innovation , University of Queensland , Queensland , Australia
Mechanical hill direct seeding of hybrid rice could be the way to solve the problems of high seeding rates and uneven plant establishment now faced in direct seeded rice; however, it is not clear what the optimum hill seeding density should be for high-yielding hybrid rice in the single-season rice production system. Experiments were conducted in 2010 and 2011 to determine the effects of hill seeding density (25 cm615 cm, 25 cm617 cm, 25 cm619 cm, 25 cm621 cm, and 25 cm623 cm; three to five seeds per hill) on plant growth and grain yield of a hybrid variety, Nei2you6, in two fields with different fertility (soil fertility 1 and 2). In addition, in 2012 and 2013, comparisons among mechanical hill seeding, broadcasting, and transplanting were conducted with three hybrid varieties to evaluate the optimum seeding density. With increases in seeding spacing from 25 cm615 cm to 25 cm623 cm, productive tillers per hill increased by 34.2% and 50.0% in soil fertility 1 and 2. Panicles per m2 declined with increases in seeding spacing in soil fertility 1. In soil fertility 2, no difference in panicles per m2 was found at spacing ranging from 25 cm617 cm to 25 cm623 cm, while decreases in the area of the top three leaves and aboveground dry weight per shoot at flowering were observed. Grain yield was the maximum at 25 cm617 cm spacing in both soil fertility fields. Our results suggest that a seeding density of 25 cm617 cm was suitable for high-yielding hybrid rice. These results were verified through on-farm demonstration experiments, in which mechanical hill-seeded rice at this density had equal or higher grain yield than transplanted rice.
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Data Availability: The authors confirm that all data underlying the findings are fully available without restriction. All relevant data are within the paper and its
Supporting Information files.
Competing Interests: The authors have declared that no competing interests exist.
Although transplanting has been a major traditional method of
rice establishment in most Asian countries, the rising labor cost
and developments in rice production technology have improved
the desirability of direct-seeded rice [1]. Direct seeding of rice is a
low-cost establishment technology. It avoids nursery raising,
seedling uprooting, and transplanting, and has the benefits of
saving labor, facilitating timely establishment of rice, and earlier
crop maturity (by 710 days) [24]. Direct seeding helps in solving
the labor scarcity problem, which is now very critical in Chinas
agricultural development. Simultaneously, the chemical weed
control method has made such a switch technically viable. In
2008, for example, 8.3% of the rice-growing area in China was
direct-seeded; in some provinces of south China, it was more than
30% [5].
In the south China irrigated rice ecosystem, broadcasting in wet
conditions (wet seeding) is the principal method of rice
establishment. In this method, pregerminated seeds are sown onto wet
(saturated) puddled soils. But, some difficulties are faced in wet
seeding. First, no specific varieties have been developed in China
for wet seeding. The existing varieties used for transplanting do
not appear to be well-adapted for seedling growth in an initially
oxygen-depleted micro environment. Second, the extent of laser
leveling in China is currently extremely smaller compared with
that in other countries (e.g., 5080% of the rice land in Australia is
laser-leveled) [4]. Due to lack of uniform water distribution
associated with unevenness of the land, the problem of excess- or
no-water-caused yield variability within a field is common, which
leads to poor establishment of direct-seeded rice [3,6]. Third,
surface-sown seeds are damaged by birds and rodents. As a result,
farmers often resort to the costly practice of increasing the seeding
rate for direct-seeded rice, even by two to three times [7]. High
seeding rates can result in large yield losses due to excessive
number of tillers, increased proportion of ineffective tillers, higher
spikelet sterility, and fewer grains per panicle [8]. Moreover, a
dense canopy and less ventilation around the plants at h (...truncated)