| Long-term(18～27 years) wheat-maize and rice-rice crop rotations experiments were conducted to investigate nitrogen use efficiency (NUE) at eight sites across different soil types (aqui-cinnamon soil, fluvo-aquic soil,cumuli cinnamon soil, red soil, red paddy soil in hilly soil, red paddy soil,red paddy soil in gley region and paddy in Mud-yellow soil) and climate zones in China. This study utilized data from two national long-term fertilization network, i.e.,the National Fertilizer Network and the National Long-term Monitoring Network of Soil Fertility and Fertilizer Effects. The objective was focus on NUE temporal and spatial variation and the effect of soil properties on them under long-term fertilization, to provide scientific references for establishing long-term fertilization mode, improving NUE and realizing sustainable development. The main results were as follows:1.The NUE varied significantly over time under wheat-maize crop rotation. The treatments of mineral nitrogen, phosphorus and potassium combination (NPK) with/without manure (or straw) could improve NUE significantly, and the average NUE of which in wheat and maize is 51.2% and 38.3%,respectively. However, the lowest NUE of wheat and maize (9.5% and 11.7%) was found in the N treatment, with the annual change rates of -1.82%·a-1 and -1.12%·a-1,respectively.2.The response of the NUE to manure varied with soil types.a) For the Aqui-cinnamon soil, the NUE increase rates (per year) of wheat and maize were 1.89%·a-1,2.48%·a-1 in NPK+M treatment. It showed that manure applied in wheat season affected in the maize season.b) For the Fluvo-aquic soil, the NUE increase rates of wheat and maize were 1.44%·a-1 and 2.31%·a-1 in NPK treatment, respectively. The NUE in wheat season showed little change over time but increased in maize season with a rate of 1.87%·a-1 under NPKM treatment.c)For the Cumuli cinnamon soil, the NUE increase rate of wheat was higher in the NPKM treatment (2.91%·a-1) than that in the NPK treatment(2.04%·a-1).However, the NUE of maize was stable during the experiment period. It indicated that the influence of manure on NUE was mainly in the wheat season.d) For the red soil, the NUE in both wheat and maize were decreased annually under the chemical fertilizer treatments, with declined rates of 2.90%·a-1 and 1.96%·a-1,respectively. Apparently, manure could keep the NUE stable over time.3.There was significant difference in NUE in different treatments under the rice-rice cropping rotation. The average NUE of partial fertilization treatment (N, NP and NK) was 29.5% and balance fertilization achieved 36.9%.The NUE in NPK, NPKM and NPKS were 38.9%,35.4% and 38.1%,respectively. And the average NUE in the treatments of different ratio between mineral and organical fertilizer was 34.3%.4.The NUE and its annual change rate showed various in rice-rice rotation under paddy soil types.The NUE of partial fertilization under red paddy soil in hilly soil, red paddy soil and red paddy soil in gley region were 34.0%,21.2% and 29.3%, respectively. For the red paddy soil in hilly soil, the decline rates of early-rice and late-rice in the NK treatment were 1.48%·a-1 and 0.72%·a-1,respectively.For the red paddy soil, the decline rates of early-rice and late-rice in the N treatment were 1.35%·a-1 and 0.86%·a-1,respectively.For the red paddy soil in gley region, the decline rates of early-rice in the NK treatment and late-rice in the NP treatment were 1.31%·a-1 and 0.46%·a-1,respectively.The NUE of balance fertilization under red paddy soil in hilly soil, red paddy soil, red paddy soil in gley region and paddy in Mud-yellow soil were 35.9%,27.4%,33.1% and 47.0%,respectively.The NUE of early-rice in NPK treatment kept stable.The decline rates of late-rice NUE in NPK treatment under red paddy soil in hilly soil, red paddy soil and red paddy soil in gley region were 0.88%·a-1,0.80%·a-1 and 0.44%·a-1,respectively.The NUE of each treatment showed no significant trends over time under paddy in Mud-yellow soil. |
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