Abstract
Excessive N fertilization in intensive agricultural areas of China has resulted in serious environmental problems because of atmospheric, soil, and water enrichment with reactive N of agricultural origin. This study examines grain yields and N loss pathways using a synthetic approach in 2 of the most intensive double-cropping systems in China: waterlogged rice/upland wheat in the Taihu region of east China versus irrigated wheat/rainfed maize on the North China Plain. When compared with knowledge-based optimum N fertilization with 30-60% N savings, we found that current agricultural N practices with 550-600 kg of N per hectare fertilizer annually do not significantly increase crop yields but do lead to about 2 times larger N losses to the environment. The higher N loss rates and lower N retention rates indicate little utilization of residual N by the succeeding crop in rice/wheat systems in comparison with wheat/maize systems. Periodic waterlogging of upland systems caused large N losses by denitrification in the Taihu region. Calcareous soils and concentrated summer rainfall resulted in ammonia volatilization (19% for wheat and 24% for maize) and nitrate leaching being the main N loss pathways in wheat/maize systems. More than 2-fold increases in atmospheric deposition and irrigation water N reflect heavy air and water pollution and these have become important N sources to agricultural ecosystems. A better N balance can be achieved without sacrificing crop yields but significantly reducing environmental risk by adopting optimum N fertilization techniques, controlling the primary N loss pathways, and improving the performance of the agricultural Extension Service.
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Claims 9
Claim · model-written summary
Current high nitrogen practices do not significantly raise crop yields relative to optimum fertilization.
Verbatim
e0“When compared with knowledge-based optimum N fertilization with 30-60% N savings, we found that current agricultural N practices with 550-600 kg of N per hectare fertilizer annually do not significantly increase crop yields”
e1“waterlogged rice/upland wheat in the Taihu region of east China versus irrigated wheat/rainfed maize on the North China Plain”
Claim · model-written summary
Current high nitrogen practices cause about twice the environmental nitrogen losses of optimum fertilization.
Verbatim
e0“When compared with knowledge-based optimum N fertilization with 30-60% N savings, we found that current agricultural N practices with 550-600 kg of N per hectare fertilizer annually do not significantly increase crop yields but do lead to about 2 times larger N losses to the environment”
e1“waterlogged rice/upland wheat in the Taihu region of east China versus irrigated wheat/rainfed maize on the North China Plain”
Claim · model-written summary
Residual nitrogen was little used by succeeding crops in rice/wheat systems compared with wheat/maize systems.
- Taxon
- rice/wheat
Oryza sativa
Triticum aestivume0 - Outcome
- utilization of residual N by the succeeding crope0
- Direction
- littlee0
- Comparator
- wheat/maize systemse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The higher N loss rates and lower N retention rates indicate little utilization of residual N by the succeeding crop in rice/wheat systems in comparison with wheat/maize systems”
Claim · model-written summary
Periodic waterlogging caused large nitrogen losses through denitrification in the Taihu region.
- Taxon
- rice/upland wheate1
- Treatment
- Periodic waterlogging of upland systemse0
- Outcome
- N losses by denitrificatione0
- Direction
- largee0
- Setting
- Taihu regione0
Not reportedComparator
Verbatim
e0“Periodic waterlogging of upland systems caused large N losses by denitrification in the Taihu region”
e1“waterlogged rice/upland wheat in the Taihu region of east China”
Claim · model-written summary
Ammonia volatilization was a main nitrogen loss pathway for wheat at 19%.
- Taxon
- wheatTriticum aestivume0
- Outcome
- ammonia volatilizatione0
- Value
- 19%e0
- Setting
- wheat/maize systemse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“ammonia volatilization (19% for wheat and 24% for maize) and nitrate leaching being the main N loss pathways in wheat/maize systems”
Claim · model-written summary
Ammonia volatilization was a main nitrogen loss pathway for maize at 24%.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“ammonia volatilization (19% for wheat and 24% for maize) and nitrate leaching being the main N loss pathways in wheat/maize systems”
Claim · model-written summary
Nitrate leaching was a main nitrogen loss pathway in the wheat/maize system.
- Taxon
- wheat/maizeTriticum aestivum
Zea mayse0 - Outcome
- nitrate leachinge0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“ammonia volatilization (19% for wheat and 24% for maize) and nitrate leaching being the main N loss pathways in wheat/maize systems”
Claim · model-written summary
Atmospheric deposition and irrigation water nitrogen increased more than twofold and became important nitrogen sources to agricultural ecosystems.
- Taxon
- wheat/rainfed maizeTriticum aestivumZea mayse1
- Outcome
- atmospheric deposition and irrigation water Ne0
- Direction
- increasese0
- Value
- More than 2-folde0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“More than 2-fold increases in atmospheric deposition and irrigation water N reflect heavy air and water pollution and these have become important N sources to agricultural ecosystems”
e1“irrigated wheat/rainfed maize on the North China Plain”
Claim · model-written summary
The authors recommend optimum nitrogen fertilization, control of loss pathways, and extension-service improvements to improve nitrogen balance without sacrificing yields.
Verbatim
e0“A better N balance can be achieved without sacrificing crop yields but significantly reducing environmental risk by adopting optimum N fertilization techniques, controlling the primary N loss pathways, and improving the performance of the agricultural Extension Service”
e1“waterlogged rice/upland wheat in the Taihu region of east China versus irrigated wheat/rainfed maize on the North China Plain”
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