Abstract
The objective of this study was to identify the response of grain yield to plant density and nitrogen rate in spring maize hybrids released from 1970 to 2010 and grown extensively in Northeast China. Twenty-one hybrids were grown for 2 years in Northeast China at densities of 30,000, 52,500, 75,000, and 97,500 plants ha− 1 and N application levels of 0, 150, 300, and 450 kg N ha− 1. Irrespective of density or nitrogen application rate, grain yields both per plant and per unit area were significantly higher for newer than older hybrids. As plant density increased from 30,000 to 97,500 plant ha− 1, yield per plant of 1970s, 1980s, 1990s, and 2000s hybrids decreased by 50%, 45%, 46%, and 52%, respectively. The response of grain yield per unit area to plant density was curvilinear. The estimated optimum plant densities were about 58,000, 49,000, 65,000, and 65,000 plants ha− 1 for hybrids released in the 1970s, 1980s, 1990s, and 2000s, respectively. The theoretical optimum densities for the hybrids released from the 1970s to the 2000s increased by 1750 plants ha− 1 decade− 1. Nitrogen fertilization significantly increased grain yields per plant and per unit area for all hybrids. The theoretical optimum N application rates for high yield for hybrids released in the 1970s and 1980s were about 280 and 360 kg ha− 1, and the hybrids from the 1990s and 2000s showed highest yield at 330 kg ha− 1 N. No significant difference in the grain yields of 2000s hybrids between the N levels of 150 to 450 kg ha− 1 was found. Significant yield gains per plant and per unit area were found, with average increases of 17.9 g plant− 1 decade− 1 and 936 kg ha− 1 decade− 1 over the period 1970–2010, respectively. Yield gains were attributed mainly to increased yield per plant, contributed by increases in kernel number per ear and 1000-kernel weight. The rates of lodging and barren plants of newer hybrids were significantly lower than those of older ones, especially at high plant density.
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Claims 20
Claim · model-written summary
Grain yields per plant and per unit area were significantly higher for newer than older maize hybrids.
Zea maysOrganisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“spring maize hybrids”
e1“Irrespective of density or nitrogen application rate, grain yields both per plant and per unit area were significantly higher for newer than older hybrids”
Claim · model-written summary
As plant density rose from 30,000 to 97,500 plants per hectare, yield per plant of 1970s hybrids decreased by 50%.
- Material
- 1970se2
- Treatment
- plant densitye2
- Outcome
- yield per plante2
- Direction
- decreasede2
- Value
- 50%e2
- Comparator
- 30,000e2
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“spring maize hybrids”
e2“As plant density increased from 30,000 to 97,500 plant ha− 1, yield per plant of 1970s, 1980s, 1990s, and 2000s hybrids decreased by 50%, 45%, 46%, and 52%, respectively”
Claim · model-written summary
As plant density rose from 30,000 to 97,500 plants per hectare, yield per plant of 1980s hybrids decreased by 45%.
- Material
- 1980se2
- Treatment
- plant densitye2
- Outcome
- yield per plante2
- Direction
- decreasede2
- Value
- 45%e2
- Comparator
- 30,000e2
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“spring maize hybrids”
e2“As plant density increased from 30,000 to 97,500 plant ha− 1, yield per plant of 1970s, 1980s, 1990s, and 2000s hybrids decreased by 50%, 45%, 46%, and 52%, respectively”
Claim · model-written summary
As plant density rose from 30,000 to 97,500 plants per hectare, yield per plant of 1990s hybrids decreased by 46%.
- Material
- 1990se2
- Treatment
- plant densitye2
- Outcome
- yield per plante2
- Direction
- decreasede2
- Value
- 46%e2
- Comparator
- 30,000e2
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“spring maize hybrids”
e2“As plant density increased from 30,000 to 97,500 plant ha− 1, yield per plant of 1970s, 1980s, 1990s, and 2000s hybrids decreased by 50%, 45%, 46%, and 52%, respectively”
Claim · model-written summary
As plant density rose from 30,000 to 97,500 plants per hectare, yield per plant of 2000s hybrids decreased by 52%.
- Material
- 2000se2
- Treatment
- plant densitye2
- Outcome
- yield per plante2
- Direction
- decreasede2
- Value
- 52%e2
- Comparator
- 30,000e2
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“spring maize hybrids”
e2“As plant density increased from 30,000 to 97,500 plant ha− 1, yield per plant of 1970s, 1980s, 1990s, and 2000s hybrids decreased by 50%, 45%, 46%, and 52%, respectively”
Claim · model-written summary
The response of grain yield per unit area to plant density was curvilinear.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“spring maize hybrids”
e3“The response of grain yield per unit area to plant density was curvilinear”
Claim · model-written summary
The estimated optimum plant density was about 58,000 plants per hectare for 1970s hybrids.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“spring maize hybrids”
e4“The estimated optimum plant densities were about 58,000, 49,000, 65,000, and 65,000 plants ha− 1 for hybrids released in the 1970s, 1980s, 1990s, and 2000s, respectively”
Claim · model-written summary
The estimated optimum plant density was about 49,000 plants per hectare for 1980s hybrids.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“spring maize hybrids”
e4“The estimated optimum plant densities were about 58,000, 49,000, 65,000, and 65,000 plants ha− 1 for hybrids released in the 1970s, 1980s, 1990s, and 2000s, respectively”
Claim · model-written summary
The estimated optimum plant density was about 65,000 plants per hectare for 1990s hybrids.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“spring maize hybrids”
e4“The estimated optimum plant densities were about 58,000, 49,000, 65,000, and 65,000 plants ha− 1 for hybrids released in the 1970s, 1980s, 1990s, and 2000s, respectively”
Claim · model-written summary
The estimated optimum plant density was about 65,000 plants per hectare for 2000s hybrids.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“spring maize hybrids”
e4“The estimated optimum plant densities were about 58,000, 49,000, 65,000, and 65,000 plants ha− 1 for hybrids released in the 1970s, 1980s, 1990s, and 2000s, respectively”
Claim · model-written summary
The theoretical optimum plant density for hybrids released from the 1970s to the 2000s increased by 1750 plants per hectare per decade.
- Material
- hybrids released from the 1970s to the 2000se5
- Outcome
- theoretical optimum densitiese5
- Direction
- increasede5
- Value
- 1750 plants ha− 1 decade− 1e5
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“spring maize hybrids”
e5“The theoretical optimum densities for the hybrids released from the 1970s to the 2000s increased by 1750 plants ha− 1 decade− 1”
Claim · model-written summary
Nitrogen fertilization significantly increased grain yields per plant and per unit area for all hybrids.
- Material
- all hybridse6
- Treatment
- Nitrogen fertilizatione6
- Outcome
- grain yields per plant and per unit areae6
- Direction
- increasede6
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“spring maize hybrids”
e6“Nitrogen fertilization significantly increased grain yields per plant and per unit area for all hybrids”
Claim · model-written summary
The theoretical optimum N application rate for high yield was about 280 kg N per hectare for 1970s hybrids.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“spring maize hybrids”
e7“The theoretical optimum N application rates for high yield for hybrids released in the 1970s and 1980s were about 280 and 360 kg ha− 1, and the hybrids from the 1990s and 2000s showed highest yield at 330 kg ha− 1 N”
Claim · model-written summary
The theoretical optimum N application rate for high yield was about 360 kg N per hectare for 1980s hybrids.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“spring maize hybrids”
e7“The theoretical optimum N application rates for high yield for hybrids released in the 1970s and 1980s were about 280 and 360 kg ha− 1, and the hybrids from the 1990s and 2000s showed highest yield at 330 kg ha− 1 N”
Claim · model-written summary
Hybrids from the 1990s and 2000s showed highest yield at 330 kg N per hectare.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“spring maize hybrids”
e7“The theoretical optimum N application rates for high yield for hybrids released in the 1970s and 1980s were about 280 and 360 kg ha− 1, and the hybrids from the 1990s and 2000s showed highest yield at 330 kg ha− 1 N”
Claim · model-written summary
No significant difference in grain yields of 2000s hybrids was found between N levels of 150 to 450 kg per hectare.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“spring maize hybrids”
e1“No significant difference in the grain yields of 2000s hybrids between the N levels of 150 to 450 kg ha− 1 was found”
Claim · model-written summary
Yield per plant increased on average by 17.9 g per plant per decade over 1970–2010.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“spring maize hybrids”
e1“Significant yield gains per plant and per unit area were found, with average increases of 17.9 g plant− 1 decade− 1 and 936 kg ha− 1 decade− 1 over the period 1970–2010, respectively”
Claim · model-written summary
Yield per unit area increased on average by 936 kg per hectare per decade over 1970–2010.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“spring maize hybrids”
e1“Significant yield gains per plant and per unit area were found, with average increases of 17.9 g plant− 1 decade− 1 and 936 kg ha− 1 decade− 1 over the period 1970–2010, respectively”
Claim · model-written summary
Yield gains were attributed mainly to increased yield per plant, contributed by more kernels per ear and heavier 1000-kernel weight.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“spring maize hybrids”
e1“Yield gains were attributed mainly to increased yield per plant, contributed by increases in kernel number per ear and 1000-kernel weight”
Claim · model-written summary
Rates of lodging and barren plants were lower for newer hybrids than older ones, especially at high plant density.
- Outcome
- rates of lodging and barren plantse1
- Direction
- lowere1
- Qualifier
- especially at high plant densitye1
- Comparator
- older onese1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“spring maize hybrids”
e1“The rates of lodging and barren plants of newer hybrids were significantly lower than those of older ones, especially at high plant density”
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