氮肥运筹对秸秆全量还田双季稻氮产量及氮素吸收利用的影响

以南方双季稻系统为研究对象,研究稻草全量还田条件下不同氮肥运筹策略对早稻及晚稻产量和氮素吸收利用的影响。结果表明:稻草全量还田条件下,与当地习惯施氮量相比,氮肥减施(早稻约18%,晚稻约15%)并不显著影响早稻及晚稻的产量;与当地农民习惯施氮量相比,氮肥减施处理可提高晚稻的氮素积累。在施氮量相同的情况下,氮肥适当后移有利于早稻及晚稻对氮素的吸收。早稻及晚稻减氮施肥处理的氮肥利用率均高于习惯施肥处理,氮肥后移有利于早稻及晚稻氮肥利用率的提高。稻草全量还田条件下,适当减氮并加大追肥比例既能稳定双季稻产量,又能促进稻株氮素吸收,提高氮肥利用率。使用秸秆促腐菌剂可进一步提高水稻对氮素的吸收利用。     

水氮组合模式对双季稻氮肥利用效率的影响

为双季稻水肥高效利用调控技术提供支撑,采用水肥耦合方式,设置间歇灌溉和淹水灌溉2种灌溉方式,高氮、中氮、低氮和不施氮4种施肥方式,开展大田试验研究不同水氮组合对双季稻氮积累量和氮肥利用效率的影响。结果表明,淹水灌溉下,以施高氮处理的植株氮积累量最高,早稻分别比施中氮、低氮和不施氮高20.8%、22.7%和59.4%,晚稻分别高出13.9%、27.0%、58.6%;间歇灌溉下,早稻以施中氮处理的植株氮积累量最高,分别比施高氮、低氮和不施氮高5.2%、15.8%和59.5%,晚稻以施高氮处理最高,依次比施中氮、低氮和不施氮高1.9%、15.4%、56.3%。水稻植株氮积累量总体随着施氮量的增加而增加。同一灌溉条件下,氮素农学利用率、氮素干物质生产率、氮素稻谷生产率、氮素偏生产力和氮素生理利用率均随施氮量的增加而减少;相同施氮水平下,间歇灌溉的水稻植株氮积累量、氮素农学利用率、氮素生理利用率均要高于淹水灌溉。间歇灌溉有利于提高氮素利用率,促进双季稻节水节肥生产。     

猪粪化肥配施对稻田土壤氮素含量及氮肥利用效率的影响

化肥有机肥在农田的配施对改良土壤性质、提高养分利用率具有较好的效果,还提升了有机废弃物的循环利用效率。为此,为明确猪粪化肥配施对南方典型双季稻田土壤氮素含量及氮肥利用效率的影响,在双季稻田系统进行田间定位试验。试验共设置了4个处理,即不施氮肥处理(N0)、50%化学氮肥处理(1/2N)、100%化学氮肥处理(N)和猪粪替代50%氮肥处理(1/2N+M)。测定了稻田土壤全氮、有效氮(铵态氮和硝态氮)、微生物生物量氮、水稻氮含量并计算氮吸收量。结果表明:在定位试验开展后第5~6年,猪粪替代50%氮肥处理土壤全氮含量较100%化学氮肥处理显著提高15%;而不施氮肥导致土壤全氮含量显著下降达20%。猪粪化肥配施显著增加晚稻季土壤铵态氮含量。水稻氮肥吸收主要与氮肥用量、土壤全氮含量、铵态氮含量和微生物生物量氮成正相关。2年内猪粪化肥配施较全量氮肥显著提高了晚稻季水稻氮素吸收及氮肥利用率,提升幅度分别为9.2%~18.0%和19.6%~43.0%,且水稻产量略有提升。早稻季猪粪化肥配施较全量氮肥水稻籽粒产量、水稻氮素吸收及氮肥利用率无显著差异或出现显著下降。研究表明,双季稻体系猪粪替代50%氮肥可提高晚稻季稻田土壤氮素有效性,减少化肥施用并提高氮肥利用率。     

秸秆还田与水氮管理对水稻氮素利用及土壤理化性质的影响

在川西平原稻油轮作典型的砂质壤土区,设置不同秸秆还田方式(堆腐还田和直接还田)、灌溉方式(淹灌和有氧灌溉)和施氮水平(0、75、150、225 kg/hm2)的3因素裂区试验,分析秸秆还田与水氮管理对水稻氮素利用特征与土壤理化性质的影响.结果表明:秸秆还田与水氮管理对主要生育时期水稻氮素积累、结实期(抽穗和成熟期)氮素转运与利用、稻谷产量及成熟期稻田耕层(0～20 cm)土壤脲酶活性、铵态氮和硝态氮质量分数均存在显著或极显著的互作效应;秸秆堆腐还田对水稻氮素利用和产量及土壤理化性质的调控作用显著高于秸秆直接还田的,同一水氮管理下,成熟期植株和籽粒氮积累量分别提高了9.7％～32.9％和7.5％～45.3％,增产7.3％～18.5％,各生育期的平均土壤脲酶活性提高4.8％～9.7％;同一秸秆还田和施氮量处理下,相比于淹灌处理,有氧灌溉能不同程度的提高产量和氮肥表观利用率,并能提高多数处理的氮肥农学利用率、土壤铵态氮和硝态氮质量分数及脲酶活性;同一秸秆还田和灌溉方式,随着氮肥用量的增加,水稻氮肥表观利用率、农学利用率、产量、各器官(除2017年成熟期的穗外)和植株的氮素积累量及抽穗至成熟期茎鞘的氮素转运量、转运率、贡献率、土壤脲酶活性和硝态氮质量分数均先增加,施氮量为150 kg/hm2时最高,继续增加施氮量,这些指标反而降低.本研究条件下,油菜秸秆堆腐还田和有氧灌溉与配施150 kg/hm2氮肥的综合管理模式可有效增强结实期土壤耕层脲酶活性,提高植株氮素积累量、结实期茎鞘的氮素转运量和转运率,从而促进水稻产量及氮肥利用率的同步提高.     

生活污水尾水灌溉对秸秆还田稻田氨挥发的影响

通过土柱模拟实验,研究了生活污水尾水灌溉对秸秆还田稻田田面水氮素转化、氨挥发排放以及水稻产量的影响。结果表明:生活污水尾水灌溉显著提高了稻田田面水NO_3~--N浓度和田面水pH,并显著提高了产量、植株吸氮量和土壤脲酶活性。与清水灌溉处理相比,不施氮肥时生活污水尾水灌溉可使秸秆还田稻田氨挥发累积排放量显著降低35%;正常施氮时生活污水尾水灌溉增加了秸秆还田稻田氨挥发排放总量,但由于显著增加了水稻产量,因此单位产量氨挥发排放量有所降低。由此可见,秸秆还田稻田利用生活污水尾水灌溉,不仅可消纳净化生活污水、替代部分氮肥,还可增加水稻产量、降低单位产量稻田氨挥发排放。     

水分管理与秸秆还田对作物吸收土壤中砷的影响

为了解农田水分管理方式与秸秆还田对砷污染农田中生长农作物吸收砷的影响,在某一砷污染农田的水稻-油菜连作系统中设置稻季淹水灌溉与湿润灌溉和稻季秸秆还田与油菜季秸秆还田双因素试验,分析不同水分管理和秸秆还田对水稻和油菜各器官中砷积累的影响。结果表明,油菜籽粒中砷含量明显低于水稻谷物;稻季湿润灌溉水稻籽粒及茎叶中砷含量低于淹水灌溉,前者为后者的47.59%~48.30%和6.43%~13.36%;稻季水分管理方式对后续作物油菜籽粒砷积累影响不明显。水稻秸秆在油菜田还田处理的水稻籽粒中砷含量低于油菜秸秆在水田还田处理的水稻籽粒,但秸秆还田时间对油菜籽粒中砷含量影响不明显。分析表明,湿润灌溉土壤水溶性As(Ⅲ)和As(Ⅴ)总量及As(Ⅲ)/As(Ⅴ)的比例都显著低于淹水灌溉。研究认为,湿润灌溉和水稻秸秆油菜季还田可降低农产品中砷的积累。     

添加生物炭对滨海盐渍型水稻土供氮能力的影响

采用室内淹水培养的方法,研究了添加等碳量的水稻秸秆生物炭、腐熟水稻秸秆和普通水稻秸秆及不同淹水培养时间(淹水培养30 d、60 d、90 d和180 d)对滨海盐渍型水稻土供氮能力的影响,为制定合理的秸秆还田措施提供科学参考。结果表明,各处理均可以提高土壤有机碳含量和碳氮比(C/N),添加生物炭的土壤有机碳和C/N显著高于其他处理(P<0.05)。各处理对土壤氮素矿化有显著影响,其中,添加生物炭处理明显提高了土壤氮素矿化量。各处理土壤供氮能力均随培养时间的延长呈现先增加后降低的趋势,培养90 d时土壤氮素矿化量最高。添加生物炭可以促进滨海盐渍型水稻土氮素的矿化,增强土壤供氮能力。     

江西省双季稻氮肥用量研究

2011²012年在江西11个县的双季稻田进行了氮肥不同施用量的试验研究。结果显示:随氮肥施用量的增加,单位氮素的水稻增产量呈下降趋势,氮素利用率和氮肥农学利用效率不断降低。利用拟合方程计算出最高产量和最佳经济产量条件下的施氮量,结合氮肥农学利用效率,确定江西早稻、晚稻的平均最佳经济施氮量分别为12.6、15.0 kg/667 m2。     

灌水方式对湘南丘岗区水稻生长发育及产量的影响

为探索湘南节水栽培模式,确保双季晚稻稳产高产,设置了4个不同灌水处理试验,研究灌水方式对水稻生长发育及产量的影响。结果表明:不同水分管理对早稻生育期、茎蘖数量无影响;晚稻分蘖差异显著,湿润灌溉有利于水稻分蘖,而零灌溉抑制水稻分蘖;各处理净光合速率、蒸腾速率以及水分利用率之间均表现出显著差异;灌溉水利用效率以零灌溉最高,与其他处理间差异显著;各处理早稻产量间差异不显著,晚稻产量存在显著差异,零灌溉产量显著减少,而雨时深灌旱时浅灌与湿润灌溉增加了产量,且比淹水灌溉节水。双季晚稻依靠早稻生育中后期深蓄雨水,采用免耕移栽,建立起抗旱群体,可确保晚稻稳产。     

江西省双季稻氮肥用量研究

2011~2012年在江西11个县的双季稻田进行了氮肥不同施用量的试验研究。结果显示:随氮肥施用量的增加,单位氮素的水稻增产量呈下降趋势,氮素利用率和氮肥农学利用效率不断降低。利用拟合方程计算出最高产量和最佳经济产量条件下的施氮量,结合氮肥农学利用效率,确定江西早稻、晚稻的平均最佳经济施氮量分别为12.6、15.0 kg/667 m2。     

Substituting nitrogen and phosphorus fertilizer with optimal amount of crop straw improves rice grain yield,nutrient use efficiency and soil carbon sequestration

Crop straw return after harvest is considered an important way to achieve both agronomic and environmental benefits.  However, the appropriate amount of straw to substitute for fertilizer remains unclear.  A field experiment was performed from 2016 to 2018 to explore the effect of different amounts of straw to substitute for fertilizer on soil properties, soil organic carbon (SOC) storage, grain yield, yield components, nitrogen (N) use efficiency, phosphorus (P) use efficiency, N surplus, and P surplus after rice harvesting.  Relative to mineral fertilization alone, straw substitution at 5 t ha^–1 improved the number of spikelets per panicle, effective panicle, seed setting rate, 1 000-grain weight, and grain yield, and also increased the aboveground N and P uptake in rice.  Straw substitution exceeding 2.5 t ha^–1 increased the soil available N, P, and K concentrations as compared with mineral fertilization, and different amounts of straw substitution improved SOC storage compared with mineral fertilization.  Furthermore, straw substitution at 5 t ha^–1 decreased the N surplus and P surplus by up to 68.3 and 28.9%, respectively, compared to mineral fertilization.  Rice aboveground N and P uptake and soil properties together contributed 19.3% to the variation in rice grain yield and yield components.  Straw substitution at 5 t ha^–1, an optimal fertilization regime, improved soil properties, SOC storage, grain yield, yield components, N use efficiency (NUE), and P use efficiency (PUE) while simultaneously decreasing the risk of environmental contamination.     

秸秆还田和氮肥用量对冬小麦产量和氮素利用的影响

【目的】在陕西关中小麦-玉米轮作区通过连续7年田间定位试验,探索秸秆还田配施化学氮肥对冬小麦产量、籽粒蛋白质含量、地上部吸氮量、收获期土壤硝态氮残留量及土壤氮素平衡的影响,为小麦增产及氮素高效利用提供科学依据。【方法】试验采用裂区设计,主处理为玉米秸秆还田和不还田,副处理设置5个施氮水平,分别为0（N0,不施用氮肥）、84 kg·hm^-2（N84,当地推荐氮肥用量的一半）、168 kg·hm^-2（N168,当地推荐氮肥用量）、252 kg·hm^-2（N252,高氮肥用量）、336 kg·hm^-2（N336,超高氮肥用量）。【结果】与秸秆不还田处理相比秸秆还田未提高冬小麦籽粒产量,施用氮肥较不施氮肥小麦增产18%—29%,而超高氮肥用量较推荐氮肥用量有减产风险。秸秆还田和氮肥用量对小麦产量有交互效应。与秸秆不还田处理相比,秸秆还田在氮肥用量为252和336 kg·hm^-2时,公顷小麦穗数增加5%—7%,产量平均增加5%—6%。秸秆还田对小麦籽粒蛋白质含量无显著影响,施用氮肥的籽粒蛋白质含量较不施用氮肥增加16%—33%。秸秆还田对小麦地上部吸氮量无显著影响,施用氮肥的地上部吸氮量较不施用氮肥增加36%—72%。秸秆还田和氮肥用量对小麦地上部吸氮量有交互效应。与秸秆不还田处理相比,秸秆还田在氮肥用量为252和336 kg·hm^-2时地上部吸氮量平均增加5%—8%。与秸秆不还田相比,秸秆还田使土壤硝态氮残留量平均增加18%,增加的硝态氮含量主要分布在70—170 cm土层。N168处理在秸秆不还田条件下土壤氮处于亏损状态,秸秆还田后有效地弥补了氮亏缺,进一步增加氮肥用量,将大幅增加土壤氮盈余量。相对于秸秆还田,氮肥用量对土壤氮盈余量的影响更大。【结论】秸秆还田配施高氮肥用量能增加小麦产量和地上部吸氮量,但同时增加了土壤硝态氮残留量和氮盈余量。综合考虑小麦籽粒产量、土壤硝态氮残留和土壤表观氮平衡等,秸秆还田配施168 kg·hm^-2氮肥更利于维持小麦产量和保护生态环境。     

Apparent variations in nitrogen runoff and its uptake in paddy rice under straw incorporation

Straw incorporation is a widespread practice to promote agricultural sustainability. However, the potential effects of straw incorporation with the prolonged time on nitrogen (N) runoff loss from paddy fields are not well studied. The current study addresses the knowledge gap by assessing the effects of straw incorporation on the processes influencing N runoff patterns and its impacts on crop yield, N uptake, total N (TN), and soil organic matter (SOM). We conducted field experiments with rice (Oryzasativa L.)–wheat (Triticumaestivum L.) rotation, rice–tobacco (Nicotianatabacum L.) rotation, and double-rice cropping in subtropical China from 2008 to 2012. Each rotation had three N treatments: zero N fertilization (CK), chemical N fertilization (CF), and chemical N fertilization combined with straw incorporation (CFS). The treatment effects were assessed on TN runoff loss, crop yield, N uptake, soil TN stock, and SOM. Results showed that TN runoff was reduced by substituting part of the chemical N fertilizer with straw N in the double rice rotation, while crop N uptake was significantly (P<0.05) decreased due to the lower bioavailability of straw N. In contrast, in both rice–wheat and rice–tobacco rotations, TN runoff in CFS was increased by 0.9–20.2% in the short term when straw N was applied in addition to chemical N, compared to CF. However, TN runoff was reduced by 2.3–19.3% after three years of straw incorporation, suggesting the long-term benefits of straw incorporation on TN loss reduction. Meanwhile, crop N uptake was increased by 0.8–37.3% in the CFS of both rotations. This study demonstrates the challenges in reducing N runoff loss while improving soil fertility by straw incorporation over the short term but highlights the potential of long-term straw incorporation to reduce N loss and improve soil productivity.     

猪粪化肥配施对双季稻稻田土壤活性碳氮含量及水稻产量的影响

以湖南省长沙典型红壤性水稻土为对象,采用田间定位试验,设置了不施氮(CK)、常规氮肥减半(50%N)、常规全量氮肥(100%N)、猪粪替代50%氮肥(50%N+PM)四个氮肥处理,研究猪粪部分替代化学氮肥对双季稻田土壤活性碳氮含量和水稻产量的影响。2012年结果表明,在早稻整个生长期和晚稻孕穗期以前,50%N+PM与100%N处理相比,其对土壤NH4+-N含量无明显影响,而在晚稻完熟期,50%N+PM处理土壤NH4+-N含量增加了65%。50%N+PM处理在早稻移栽期、晚稻孕穗期、早稻晚稻乳熟期和完熟期较100%N处理显著提高了土壤可溶性有机氮(DON)含量,增幅在50%-102%之间。在整个水稻季,50%N+PM处理与100%N处理相比,提高了土壤微生物生物量碳(MBC)和微生物生物量氮(MBM)含量,提高幅度为21.5%-22.8%和5.3%-7.1%,而对水稻产量差异不显著,但明显高于50%N和CK处理。与CK处理相比,猪粪化肥配施和100%N处理的年产量分别提高了47.0%和32.9%。表明猪粪化肥合理配施可以维持水稻产量和土壤无机氮水平,同时可提高土壤微生物生物量碳和微生物生物量氮,改善土壤肥力。     

减量化肥配施紫云英对稻田土壤碳、氮的影响

以11 a(2008—2018年)长期定位试验为对象,研究了减施40%化肥下紫云英不同翻压量对双季稻产量及土壤活性有机碳、氮(DOC+MBC、DON+MBN)的影响,以探讨紫云英替代化肥的可行性和适宜翻压量。试验设置CK(不施紫云英和化肥)、GM_(22.5)(单施紫云英22.5 t·hm~(-2))、100%CF(常规施肥)和减施40%化肥(60%CF)条件下将紫云英翻压量设为15、22.5、30、37.5 t·hm~(-2)4个水平,共7个处理。于2018年晚稻收获后采集土壤样品,分析土壤微生物量碳、氮(MBC、MBN)和可溶性有机碳、氮(DOC、DON)。结果表明:与常规施肥相比,减施40%化肥下各紫云英不同翻压量处理早稻及全年两季稻谷产量持平或略有增加,且均随紫云英翻压量增多而提高。紫云英翻压量为15～30 t·hm~(-2)时,晚稻稻谷产量随紫云英翻压量的增多而提高,当紫云英翻压量多于30 t·hm~(-2)时,则呈下降趋势。除翻压紫云英15 t·hm~(-2)外,其他紫云英与化肥配施处理晚稻稻谷产量与常规施肥相比无显著差异;与常规施肥相比,紫云英与化肥配施均不同程度地提高了土壤MBC、MBN、DOC、DON含量。紫云英翻压量为15～22.5 t·hm~(-2)时,土壤MBC、MBN、DOC、DON均随紫云英翻压量增加而增加,当翻压量多于22.5 t·hm~(-2)时呈下降趋势;MBC/SOC和MBN/TN均随紫云英翻压量的增加呈先增加后降低的趋势,MBC/SOC在60%CF+GM_(22.5)处理最高,MBN/TN以60%CF+GM_(30)处理最高。DOC/SOC和DON/TN均在60%CF+GM_(15)处理最高;相关分析结果表明,土壤MBC、MBN、DOC、DON、DOC+MBC、DON+MBN与土壤有机碳(SOC)、全氮(TN)呈极显著正相关(P0.01)。土壤各活性有机碳、氮与早、晚稻及全年两季稻谷产量均呈极显著正相关(P0.01)。综合考虑双季稻的产量效应及土壤培肥效果,在本试验条件下或与该试验区域气候特点和种植制度类似的南方水稻主产区,在减少40%化肥条件下,紫云英翻压22.5～30 t·hm~(-2)较为适宜。     

Increase in yield and nitrogen use efficiency of double rice with long-term application of controlled-release urea

Controlled-release urea (CRU) has better characteristics than conventional urea for synchronizing nitrogen (N) release with plant uptake. Understanding the effects of CRU on crop yield and N use efficiency (NUE) has long been the key to evaluate the performance of CRU. A long-term experiment over five consecutive years was conducted in Changsha, Hunan Province, China, to investigate the effects of polyethylene-coated urea with a 90-d release period on the yield and NUE of double rice (early and late crops are grown in the same year), the amount of residual soil mineral N and the soil–plant N balance, as well as on the economic benefits. Four N fertilizer treatments including CK (no N fertilizer), U (conventional urea), CRU1 (polyethylene-coated urea with equal N application rate to U) and CRU2 (20% reduction in N application rate of CRU1) were established. The results indicated that CRU1 application increased the yield and NUE of double rice by 11.0 and 13.5%, respectively, compared with U. Higher yield and NUE of late rice were found than in early rice in CRU treatments. Compared with conventional U, the yield and NUE of early rice in the CRU1 treatment were increased by 6.0 and 10.2%, respectively, and those of late rice were increased by 15.4 and 13.8%, respectively. There was no significant difference between CRU1 and CRU2 in double rice yield. Furthermore, CRU treatments (including CRU1 and CRU2) had higher apparent residual N_min rate (ARNR) and apparent N recovery rate (ANRR), but lower apparent N loss (N_S) than the conventional U treatment. Concentrations of NH₄⁺-N and NO₃^–-N were greater in the surface soil (0–20 cm) and lower in the deeper soil layer (40–60 cm) with CRU treatments than in the U treatment after harvest. Moreover, CRU application produced a greater economic benefit than conventional U application. In general, CRU outperformed U fertilizer in terms of rice yield, NUE, soil–plant N balance, economic benefit, and CRU2 provided greater comprehensive benefits than CRU1. It is suggested that CRU application is beneficial for solving N management challenges in the production of rice.     

灌溉模式与施氮水平对土壤渗滤液氮浓度动态变化的影响

以Ⅱ优838为水稻供试品种,湖北潮土为供试土壤,通过2年稻麦轮作柱栽试验研究2种灌溉模式(FW:土表淹水3cm;CW:保持土壤湿润但土表不积水)和4个施氮水平(N0:0kg·hm-2,N1:126.0kg·hm-2,N2:157.5kg·hm-2,N3:210.0kg·hm-2)对水稻土渗滤液不同形态氮浓度变化动态的影响。结果表明:土壤渗滤液的总氮浓度随水稻生育期推移呈由高到低的变化趋势,氮素淋失风险主要存在于水稻移栽后的前40d左右;在稻麦轮作制中,前作小麦明显提高后作水稻土壤渗滤液氮浓度;硝态氮(NO3--N)和可溶性有机氮(SON)是土壤渗滤液氮素的主要形态,铵态氮(NH4+-N)所占比例较低;水稻移栽后20～30d左右出现土壤渗滤液NO3--N高峰,在高峰期土壤渗滤液的NO3--N浓度随施氮量增加而提高;减氮25%处理(N2)相对于常规施氮量处理(N3)显著提高氮肥利用率,并降低氮素淋失风险。     

Postponed and reduced basal nitrogen application improves nitrogen use efficiency and plant growth of winter wheat

Excessive nitrogen(N) fertilization with a high basal N ratio in wheat can result in lower N use efficiency(NUE) and has led to environmental problems in the Yangtze River Basin, China. However, wheat requires less N fertilizer at seedling growth stage, and its basal N fertilizer utilization efficiency is relatively low; therefore, reducing the N application rate at the seedling stage and postponing the N fertilization period may be effective for reducing N application and increasing wheat yield and NUE. A 4-year field experiment was conducted with two cultivars under four N rates(240 kg N ha–1(N240), 180 kg N ha–1(N180), 150 kg N ha–1(N150), and 0 kg N ha–1(N0)) and three basal N application stages(seeding(L0), fourleaf stage(L4), and six-leaf stage(L6)) to investigate the effects of reducing the basal N application rate and postponing the basal N fertilization period on grain yield, NUE, and N balance in a soil-wheat system. There was no significant difference in grain yield between the N180 L4 and N240 L0(control) treatments, and the maximum N recovery efficiency and N agronomy efficiency were observed in the N180 L4 treatment. Grain yield and NUE were the highest in the L4 treatment. The leaf area index, flag leaf photosynthesis rate, flag leaf nitrate reductase and glutamine synthase activities, dry matter accumulation, and N uptake post-jointing under N180 L4 did not differ significantly from those under N240 L0. Reduced N application decreased the inorganic N content in the 0–60-cm soil layer, and the inorganic N content of the L6 treatment was higher than those of the L0 and L4 treatments at the same N level. Surplus N was low under the reduced N rates and delayed basal N application treatments. Therefore, postponing and reducing basal N fertilization could maintain a high yield and improve NUE by improving the photosynthetic production capacity, promoting N uptake and assimilation, and reducing surplus N in soil-wheat systems.     

Effect of Nitrogen Applied Before Transplanting on NUE in Rice

Nitrogen （N） application before transplanting, where N fertilizers are applied in seedling-bed and carried to the paddy field with seedlings, is a novel method proposed in this article aiming for improving nitrogen utilization efficiency （NUE） in rice. The effect of this method on mineral N distribution in the rhizosphere soil was investigated in a field experiment with a japonica variety, Ningjing 2, in seasons of 2004 and 2005. There were four levels of N applied 16 h before transplanting： zero N （NO）, 207 kg ha^-1 （NL）, 310.5 kg ha^-1 （NM）, and 414 kg ha^-1 （NH）. The result indicated that N fertilizer before transplantation had positive effect of increasing mineral N content in the rhizosphere soil of rice. Generally, N content in the rhizosphere soil of rice tended to increase with the amount of N fertilizer before transplanting, with the NH treatment having the largest effect. Additionally, N fertilizer before transplanting had significant influence on rice NUE and grain yield. Compared with other treatments, the NM treatment showed the largest influence, with basal-tillering NUE, total NUE, and grain yield being 15%, 12%, and 529.5 kg ha^-1 higher than those of NO treatment. This result indicated that N fertilizer before transplantation had positive effect on mineral N distribution in the rhizosphere soil of rice, thus improving NUE and grain yield.