Abstract
Runoff losses of nitrogen (N) and phosphorus (P) from paddy fields pose considerable eutrophication risks to surrounding water and raise non-point source pollution. Unknown of long-term patterns of losses and mechanisms driving runoff N and P in double-rice cropping systems limited the development of effective mitigation strategies. In this study, typical subtropical double-cropped paddy ecosystems were selected for observation, and total nitrogen (TN) and total phosphorus (TP) concentrations, TN and TP loss loads, grain yields, and soil fertility under no fertilization (TR1), conventional fertilization (TR2, with chemical fertilizer inputs of 150/180 kg N ha −1 and 90/90 kg P 2 O 5 ha −1 for the early/late rice seasons), optimized fertilization (TR3, 105/135 kg N ha −1 and 67.5/36 kg P 2 O 5 ha −1 ), reduced N and P fertilization (TR4, 52.5/67.5 kg N ha −1 and 33.8/18 kg P 2 O 5 ha −1 ), increased N and P fertilization (TR5, 180/210 kg N ha −1 and 112.5/112.5 kg P 2 O 5 ha −1 ), and straw return (TR6, with chemical fertilizer inputs of 78.9/82.8 kg N ha −1 and 60.6/22.2 kg P 2 O 5 ha −1 , and 2250/4500 kg ha −1 rice straw returning to fields to maintain equivalent N and P inputs as TR3) were continuously monitored for seven years. The results revealed that (1) the 0–20 days after fertilization was a high-risk period, contributing 41.7–56.6 % of annual TN and 20.2–25.8 % of TP loss loads. (2) TN loss predominantly occurred during the early rice season (58.3–61.3 %), while TP loss is evenly distributed across the winter fallow and two rice seasons. (3) Optimized fertilization significantly decreased TN and TP losses by 11.7 % and 13.7 % compared with conventional fertilization ( P < 0.05), with marginal yield reduction (6.03–6.18 %). Straw return further diminished TN and TP losses by 20.1 % and 11.5 %, and enhanced soil organic matter and TN contents by 6.34 % and 4.57 %, respectively. (4) Runoff TN and TP concentrations increased sharply when soil TN and TP exceeded 1.99 and 1.02 g kg −1 , respectively. (5) Fertilizer rate primarily impacted TN loss, while soil TP content strongly correlated with TP loss, with runoff volume affecting both. This study emphasizes that P loss in the winter fallow season should not be overlooked, and that combining optimized fertilization with straw return is an eco-friendly, cost-effective measure that lowers N and P losses without crop yields reduction and soil fertility degradation. Understanding N and P losses patterns in subtropical double-cropping paddy fields with various agricultural management measures aids in assessing runoff water reuse potential, to achieve a virtuous cycle of water and nutrients.
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Claims 17
Claim · model-written summary
The first 20 days after fertilization accounted for 41.7–56.6 % of annual TN loss.
- Taxon
- rice
Oryza sativat0 - Outcome
- TNe0
- Value
- 41.7–56.6 %e0
Not reportedOrgan / stage
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the 0–20 days after fertilization was a high-risk period, contributing 41.7–56.6 % of annual TN and 20.2–25.8 % of TP loss loads”
t0“double-rice cropping systems”
Claim · model-written summary
The first 20 days after fertilization accounted for 20.2–25.8 % of annual TP loss.
- Taxon
- riceOryza sativat0
- Outcome
- TP loss loadse0
- Value
- 20.2–25.8 %e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the 0–20 days after fertilization was a high-risk period, contributing 41.7–56.6 % of annual TN and 20.2–25.8 % of TP loss loads”
t0“double-rice cropping systems”
Claim · model-written summary
The early rice season accounted for 58.3–61.3 % of TN loss.
- Taxon
- riceOryza sativat0
- Outcome
- TN losse0
- Value
- 58.3–61.3 %e0
- Setting
- early rice seasone0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“TN loss predominantly occurred during the early rice season (58.3–61.3 %)”
t0“double-rice cropping systems”
Claim · model-written summary
TP loss was distributed evenly across winter fallow and both rice seasons.
- Taxon
- riceOryza sativat0
- Outcome
- TP losse0
- Setting
- winter fallow and two rice seasonse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“TP loss is evenly distributed across the winter fallow and two rice seasons”
t0“double-rice cropping systems”
Claim · model-written summary
Optimized fertilization decreased TN loss 11.7 % against conventional fertilization.
- Taxon
- riceOryza sativat0
- Treatment
- Optimized fertilizatione0
- Outcome
- TNe0
- Direction
- decreasede0
- Value
- 11.7 %e0
- Comparator
- conventional fertilizatione0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Optimized fertilization significantly decreased TN and TP losses by 11.7 % and 13.7 % compared with conventional fertilization”
t0“double-rice cropping systems”
Claim · model-written summary
Optimized fertilization decreased TP loss 13.7 % against conventional fertilization.
- Taxon
- riceOryza sativat0
- Treatment
- Optimized fertilizatione0
- Outcome
- TP lossese0
- Direction
- decreasede0
- Value
- 13.7 %e0
- Comparator
- conventional fertilizatione0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Optimized fertilization significantly decreased TN and TP losses by 11.7 % and 13.7 % compared with conventional fertilization”
t0“double-rice cropping systems”
Claim · model-written summary
Optimized fertilization reduced grain yield by 6.03–6.18 %.
- Taxon
- riceOryza sativat0
- Outcome
- yielde0
- Direction
- reductione0
- Value
- 6.03–6.18 %e0
Not reportedTreatmentComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“with marginal yield reduction (6.03–6.18 %)”
t0“double-rice cropping systems”
Claim · model-written summary
Straw return reduced TN loss by 20.1 %.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Straw return further diminished TN and TP losses by 20.1 % and 11.5 %”
t0“double-rice cropping systems”
Claim · model-written summary
Straw return reduced TP loss by 11.5 %.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Straw return further diminished TN and TP losses by 20.1 % and 11.5 %”
t0“double-rice cropping systems”
Claim · model-written summary
Straw return increased soil organic matter by 6.34 %.
- Taxon
- riceOryza sativat0
- Outcome
- soil organic mattere0
- Direction
- enhancede0
- Value
- 6.34 %e0
Not reportedTreatmentComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“enhanced soil organic matter and TN contents by 6.34 % and 4.57 %, respectively”
t0“double-rice cropping systems”
Claim · model-written summary
Straw return increased soil TN content by 4.57 %.
- Taxon
- riceOryza sativat0
- Outcome
- TN contentse0
- Direction
- enhancede0
- Value
- 4.57 %e0
Not reportedTreatmentComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“enhanced soil organic matter and TN contents by 6.34 % and 4.57 %, respectively”
t0“double-rice cropping systems”
Claim · model-written summary
Runoff TN concentration rose sharply above soil TN of 1.99 g kg −1.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Runoff TN and TP concentrations increased sharply when soil TN and TP exceeded 1.99 and 1.02 g kg −1 , respectively”
t0“double-rice cropping systems”
Claim · model-written summary
Runoff TP concentration rose sharply above soil TP of 1.02 g kg −1.
- Taxon
- riceOryza sativat0
- Compound
- TPe0
- Outcome
- TP concentrationse0
- Direction
- increased sharplye0
- Value
- 1.02 g kg −1e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Runoff TN and TP concentrations increased sharply when soil TN and TP exceeded 1.99 and 1.02 g kg −1 , respectively”
t0“double-rice cropping systems”
Claim · model-written summary
Fertilizer rate primarily affected TN loss.
- Taxon
- riceOryza sativat0
- Treatment
- Fertilizer ratee0
- Outcome
- TN losse0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Fertilizer rate primarily impacted TN loss”
t0“double-rice cropping systems”
Claim · model-written summary
Soil TP content was strongly correlated with TP loss.
- Taxon
- riceOryza sativat0
- Compound
- soil TP contente0
- Outcome
- TP losse0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“soil TP content strongly correlated with TP loss”
t0“double-rice cropping systems”
Claim · model-written summary
Runoff volume affected both TN and TP loss.
- Taxon
- riceOryza sativat0
- Outcome
- runoff volumee0
Not reportedSettingDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“with runoff volume affecting both”
t0“double-rice cropping systems”
Claim · model-written summary
The authors recommend optimized fertilization with straw return to lower N and P losses.
- Taxon
- riceOryza sativat0
- Treatment
- optimized fertilization with straw returne0
- Outcome
- combining optimized fertilization with straw returne0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“combining optimized fertilization with straw return is an eco-friendly, cost-effective measure that lowers N and P losses without crop yields reduction and soil fertility degradation”
t0“double-rice cropping systems”
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