Abstract
We evaluated the performance of maize ( Zea mays L.) cultivars representing 10‐yr eras in 12 treatment combinations of plant densities and N levels. There were four open‐pollinated (OP) varieties and six 10‐yr (1930 to 1980) eras, four cultivars per era, of singlecross hybrids. A primary purpose was to compare the hybrids and eras for interaction with plant densities and N levels. The cultivars were grown for 2 yr near Ames, IA at densities of 34 445, 51 661, and 68 889 plants ha −1 and N levels of 0, 80, 160, and 240 kg N ha −1 . Grain yields among densities averaged over N levels and cultivars were not different; yields among N levels averaged over densities and cultivars were highly significantly different (P < 0.01). The yield increase from 0 to 80 kg N ha −1 was 78.1%; from 80 to 160 kg N ha −1 , 15.8%, but there was no further increase at 240 kg N ha −1 . Cultivars ✕ densities and cultivars ✕ N‐levels interactions were highly significant. Cultivars from OP to 1960 eras had either nonsignificant (positive or negative), or significantly negative linear responses to plant densities. Conversely, all cultivars in the 1970 and 1980 eras had positive linear responses; for five of the eight, the responses were significant. All cultivars had highly significant, positive linear responses to N levels. There was no directional trend over successive eras of hybrids for relative values of linear responses to N levels. The second‐order interaction of densities ✕ N levels ✕ cultivars was significant for yield. Eighteen of 28 cultivars had significant linear ✕ linear components; consequently, densities and N levels were not independent factors, and a cultivar seemed to have a specific density ✕ N‐level combination for maximum grain yield. Ear length was the yield component that had highest correlations with yield, among treatments combinations.
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Claims 13
Claim · model-written summary
Grain yields did not differ across planting densities.
Zea maysNot reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Grain yields among densities averaged over N levels and cultivars were not different”
t0“Maize”
Claim · model-written summary
Grain yields differed across nitrogen levels.
Not reportedComparatorDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“yields among N levels averaged over densities and cultivars were highly significantly different (P < 0.01)”
t0“Maize”
Claim · model-written summary
Yield rose 78.1% from 0 to 80 kg N ha −1.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The yield increase from 0 to 80 kg N ha −1 was 78.1%; from 80 to 160 kg N ha −1 , 15.8%, but there was no further increase at 240 kg N ha −1 .”
t0“Maize”
Claim · model-written summary
Yield rose 15.8% from 80 to 160 kg N ha −1.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The yield increase from 0 to 80 kg N ha −1 was 78.1%; from 80 to 160 kg N ha −1 , 15.8%, but there was no further increase at 240 kg N ha −1 .”
t0“Maize”
Claim · model-written summary
Yield did not rise further at 240 kg N ha −1.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The yield increase from 0 to 80 kg N ha −1 was 78.1%; from 80 to 160 kg N ha −1 , 15.8%, but there was no further increase at 240 kg N ha −1 .”
t0“Maize”
Claim · model-written summary
Cultivar responses to density and nitrogen varied significantly.
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Cultivars ✕ densities and cultivars ✕ N‐levels interactions were highly significant.”
t0“Maize”
Claim · model-written summary
Earlier cultivars had nonsignificant or negative density responses.
- Material
- Cultivars from OP to 1960 erase0
- Outcome
- linear responses to plant densitiese0
- Direction
- negativee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Cultivars from OP to 1960 eras had either nonsignificant (positive or negative), or significantly negative linear responses to plant densities.”
t0“Maize”
Claim · model-written summary
All 1970 and 1980 cultivars responded positively to density; five of eight responses were significant.
- Material
- cultivars in the 1970 and 1980 erase0
- Outcome
- linear responsese0
- Direction
- positivee0
- Value
- five of the eighte0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“all cultivars in the 1970 and 1980 eras had positive linear responses; for five of the eight, the responses were significant.”
t0“Maize”
Claim · model-written summary
All cultivars had significant positive linear nitrogen responses.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“All cultivars had highly significant, positive linear responses to N levels.”
t0“Maize”
Claim · model-written summary
Nitrogen response slopes showed no directional trend across hybrid eras.
- Material
- hybridse0
- Outcome
- relative values of linear responses to N levelse0
- Direction
- no directional trende0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“There was no directional trend over successive eras of hybrids for relative values of linear responses to N levels.”
t0“Maize”
Claim · model-written summary
Density, nitrogen, and cultivar had a significant three way yield interaction.
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The second‐order interaction of densities ✕ N levels ✕ cultivars was significant for yield.”
t0“Maize”
Claim · model-written summary
Eighteen of 28 cultivars had significant linear by linear density and nitrogen components.
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Eighteen of 28 cultivars had significant linear ✕ linear components”
t0“Maize”
Claim · model-written summary
Ear length correlated most strongly with yield among yield components.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Ear length was the yield component that had highest correlations with yield, among treatments combinations.”
t0“Maize”
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