Abstract
SUMMARY The effect of different rates (0–140 kg/ha) of nitrogen fertilizers on soil cyanobacteria and rice crop performance were studied in a rice-cropping system on an alkaline Fluvent soil at Valencia, Spain, during three consecutive crop seasons (1990–92). The results showed that the rice fields of Valencia favour the development of N 2 -fixing cyanobacteria. Nitrogen fixation varied during the cultivation cycle, reaching its highest values at the maximum tillering stage, 5–6 weeks after sowing, and showed a positive correlation with the abundance of cyanobacteria and a negative correlation with the amount of N fertilizers used. Grain yield increased with increasing amounts of N fertilizers up to 70 kg N/ha. N rates appeared to affect grain yield by causing variations in the number of panicles/m 2 . Leaf chlorophyll readings at the end of the tillering stage were positively correlated with the number of panicles/m 2 , suggesting that it could be a useful parameter for predicting productivity. There was a significant increase in the N uptake of the rice but a decrease in the apparent N recovery and Nuse efficiency of applied fertilizer N, with the application of increasing rates of N fertilizer. In all instances, except in plots fertilized with 140 kg N/ha, the amount of N removed by plants was significantly higher than that applied as N fertilizer. The differences were positively correlated with the values for N fixation, suggesting a significant contribution by N fixation to rice production. These results show that a rational use of biological N fixation, in combination with inorganic N fertilization, would permit the input of N fertilizers to be reduced by c . 50% without any significant loss of productivity and with an ecological benefit for the whole ecosystem.
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Claims 10
Claim · model-written summary
Nitrogen fixation correlated positively with cyanobacteria abundance in rice fields.
- Taxon
- rice
Oryza sativat0 - Organ / stage
- maximum tillering stagee1
- Interactor
- cyanobacteriaCyanobacteriotae1other
- Outcome
- Nitrogen fixatione1
- Direction
- positivee1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“Nitrogen fixation varied during the cultivation cycle, reaching its highest values at the maximum tillering stage, 5–6 weeks after sowing, and showed a positive correlation with the abundance of cyanobacteria”
t0“rice growth”
Claim · model-written summary
Nitrogen fixation correlated negatively with the amount of N fertilizer applied.
- Taxon
- riceOryza sativat0
- Treatment
- N fertilizerse2
- Outcome
- Nitrogen fixatione1
- Direction
- negativee2
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“Nitrogen fixation varied during the cultivation cycle, reaching its highest values at the maximum tillering stage, 5–6 weeks after sowing, and showed a positive correlation with the abundance of cyanobacteria”
e2“a negative correlation with the amount of N fertilizers used”
t0“rice growth”
Claim · model-written summary
Grain yield increased with increasing N fertilizer amounts up to 70 kg N/ha.
- Taxon
- riceOryza sativat0
- Treatment
- increasing amounts of N fertilizers up to 70 kg N/hae3
- Outcome
- Grain yielde3
- Direction
- increasede3
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e3“Grain yield increased with increasing amounts of N fertilizers up to 70 kg N/ha”
t0“rice growth”
Claim · model-written summary
N rates may affect grain yield by varying the number of panicles per square metre.
- Taxon
- riceOryza sativat0
- Treatment
- N ratese4
- Outcome
- number of panicles/m 2e4
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e4“N rates appeared to affect grain yield by causing variations in the number of panicles/m 2”
t0“rice growth”
Claim · model-written summary
Leaf chlorophyll readings at end of tillering correlated positively with panicle number.
- Taxon
- riceOryza sativat0
- Organ / stage
- end of the tillering stagee5
- Compound
- chlorophylle5
- Outcome
- number of panicles/m 2e5
- Direction
- positively correlatede5
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e5“Leaf chlorophyll readings at the end of the tillering stage were positively correlated with the number of panicles/m 2”
t0“rice growth”
Claim · model-written summary
Increasing N fertilizer rates significantly increased N uptake of rice.
- Taxon
- riceOryza sativae6
- Treatment
- increasing rates of N fertilizere6
- Outcome
- N uptakee6
- Direction
- increasee6
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e6“There was a significant increase in the N uptake of the rice but a decrease in the apparent N recovery and Nuse efficiency of applied fertilizer N, with the application of increasing rates of N fertilizer”
t0“rice growth”
Claim · model-written summary
Increasing N fertilizer rates decreased apparent N recovery and N use efficiency of rice.
- Taxon
- riceOryza sativae6
- Treatment
- increasing rates of N fertilizere6
- Outcome
- apparent N recovery and Nuse efficiencye6
- Direction
- decreasee6
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e6“There was a significant increase in the N uptake of the rice but a decrease in the apparent N recovery and Nuse efficiency of applied fertilizer N, with the application of increasing rates of N fertilizer”
t0“rice growth”
Claim · model-written summary
Rice removed more N than was applied as fertilizer, except at 140 kg N/ha.
- Taxon
- riceOryza sativat0
- Outcome
- amount of N removed by plantse7
- Direction
- highere7
- Qualifier
- except in plots fertilized with 140 kg N/hae7
- Comparator
- that applied as N fertilizere7
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e7“In all instances, except in plots fertilized with 140 kg N/ha, the amount of N removed by plants was significantly higher than that applied as N fertilizer”
t0“rice growth”
Claim · model-written summary
The N balance differences correlated positively with N fixation values, suggesting a contribution of N fixation to rice production.
- Taxon
- riceOryza sativat0
- Outcome
- differencese0
- Direction
- positively correlatede0
- Comparator
- the values for N fixatione0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The differences were positively correlated with the values for N fixation, suggesting a significant contribution by N fixation to rice production”
t0“rice growth”
Claim · model-written summary
Rational use of biological N fixation with inorganic N could reduce N fertilizer input by about 50% without loss of productivity.
- Taxon
- riceOryza sativat0
- Outcome
- input of N fertilizerse0
- Value
- c . 50%e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“a rational use of biological N fixation, in combination with inorganic N fertilization, would permit the input of N fertilizers to be reduced by c . 50% without any significant loss of productivity”
t0“rice growth”
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