【Objective】 The aim of this paper was to study the mechanisms of interspecific nitrogen facilitation and transfer in the relay-planting systems of wheat/maize/soybean and wheat/maize/sweet potato. 【Method】 The methods of root barrier and 15N-isotope dilution were used to investigate the nitrogen transfer, nitrogen uptake and utilization in the two relay-planting systems.【Result】 Comparing the no barrier with solid barrier, the results showed that the 15N total uptake and crop recovery rate of wheat were highly remarkable and 15N% abundance and N% content of soil was lower obviously than that of solid barrier. In the wheat/maize/soybean system with no barrier, the 15N total uptake, 15N grain uptake, 15N crop recovery rate, soil 15N% abundance and N% content of maize increased by 17.62%, 24.52%, 17.63%, 13.9% and 10.1%, respectively. But in the wheat/maize/sweetpotato system with no barrier, the value of above index reduced by 50.19%, 42.58%, 33.42%, 29.6% and 5.2%, respectively. For soybean, the 15N total uptake, 15N grain uptake, and 15N crop recovery rate reduced, but the soil N% content increased by 6.06%. For sweetpotato, the 15N total uptake and crop recovery rate increased, but soil 15N% abundance and N% content reduced by 0.9% and 4.95%. 【Conclusion】 There existed nitrogen interspecific competition and facilitation and nitrogen transfer in the two relay-planting systems. In the wheat/maize/soybean system, the nitrogen uptake from fertilizer, soil fertility remaining and sustainable crop production were better than the system of wheat/maize/sweetpotato.

【目的】探讨“小麦/玉米/大豆”(以下简称麦/玉/豆)和“小麦/玉米/甘薯”(以下简称麦/玉/薯)两种三熟套作体系的氮素种间竞争促进作用和高效吸收利用特性。【方法】采用根系分隔盆栽试验和15N土壤稀释标记法,研究两种三熟套作体系的氮素转移及吸收利用情况。【结果】不分隔与分隔相比,两种体系中小麦的15N总吸收量和15N作物回收率提高,土壤残留15N%丰度及总N含量降低。“麦/玉/豆”中玉米的15N总吸收量、籽粒15N吸收量、15N作物回收率、土壤残留15N%丰度及总N含量提高17.62%、24.52%、17.63%、13.9%和10.1%,“麦/玉/薯”则降低50.19%、42.58%、33.42%、29.6%和5.2%;降低了大豆的15N总吸收量、籽粒15N吸收量和15N作物回收率,但土壤总N含量提高6.06%;提高了甘薯的15N总吸收量和15N作物回收率,但土壤残留15N%丰度和总N含量降低0.9%和4.95%。【结论】两种体系均存在氮素种间竞争促进作用和氮素转移,“麦/玉/豆”较“麦/玉/薯”更有利于肥料氮的吸收、土壤肥力的保持和周年作物的可持续生产。

Root exudates play a role in adjusting physical and chemical characteristics of soil, improving soil fertility, and facilitating nutrient uptake. Thus, they are used to explaining the mechanism of high nutrient utilization efficiency for plants. In the relay cropping system of wheat/maize/soybean, nitrogen use efficiency appears higher than that in the cropping system of wheat/maize/sweet potato. For explaining the relationship between the high use efficiency of nitrogen and the effects of rhizosphere microenvironment in the wheat/maize/soybean cropping system, the characteristics of wheat root exudates as well as its effects on wheat roots, wheat rhizosphere soil, and nitrogen uptake in wheat were studied in a two-year continuous experiment from 2006 to 2008 with four cropping systems, including two sole cropping systems (wheat–soybean and wheat–sweet potato) and two rely cropping systems (wheat/maize/soybean and wheat/maize/sweet potato). In the wheat/maize/soybean system, the soil moisture, soil pH and soil quick-acting N (NO₃⁻-N and NH₄⁺-N) content at wheat rhizosphere reduced at both flowering and maturity stages, and the total nitrogen uptake in shoots, root activity, root dry matter weight and soil total nitrogen content of wheat increased. At flowering stage, the total amount of organic acids and the content of soluble sugar of wheat rhizosphere increased in the wheat/maize/soybean system. The total amount of organic acid and the content of soluble sugar of wheat were higher in relay cropping system than in sole cropping system. In the two sole cropping systems, the wheat–soybean mode had higher amount of organic acid and higher content of soluble sugar than wheat–sweet potato. Wheat plants from fringe rows could exude organic acids and higher soluble sugar content than those from central rows, and the amount of root exudates in fringe rows was the highest among all the cropping systems. At jointing stage, the content of acetic acid in the sole cropping systems increased, which accounted for 47.8% to 51.6% of the total of organic acid. The content of citric acid in the relay cropping systems increased from 31.7% to 55.1% of total organic acid. At flowering stage, the content of acetic acid in sole and relay cropping systems was also promoted from 33.3% to 78.3% of the total organic acid. The root exudates were in favor of improving root growth condition, activating soil nutrition, enhancing nitrogen uptake and increasing nitrogen use efficiency in the wheat/maize/soybean relay cropping system.

为探讨小麦/玉米/大豆多熟套作体系下小麦根系分泌物的分泌特性及其对根系生长环境和植株氮素吸收的影响，2006—2008年连续两个生长季采用田间定位试验，研究了小麦-大豆、小麦-甘薯、小麦/玉米/大豆和小麦/玉米/甘薯4种种植模式下小麦根系分泌物的数量与种类、小麦根系生长、土壤水分、土壤氮含量及植株吸氮量的变化特性。结果表明，与小麦-大豆和小麦-甘薯两种净作模式及小麦/玉米/甘薯套作模式相比，小麦/玉米/大豆套作降低了开花期和成熟期小麦生长区的土壤湿度、pH值及NO₃^--N和NH₄⁺-N的含量，提高了小麦植株地上部总吸氮量、根系活力、根干重及土壤总氮含量，并且，开花期小麦根系分泌有机酸总量和可溶性糖含量增加，表现为套作>净作，大豆茬口>甘薯茬口，边行>中行，其中以小麦边行处理的分泌量最高。拔节期根系分泌的有机酸，净作处理以乙酸含量较高，占总量的47.8%~51.6%，套作处理以柠檬酸含量较高，占总量的31.7%~55.1%；开花期根系分泌的有机酸，净作和套作处理均以乙酸含量较高，占总量的33.3%~78.3%。小麦/玉米/大豆套作对小麦根系分泌有机酸和可溶性糖有促进作用，从而改善了根系生长环境，提高了小麦对氮素的吸收。

A root barrier pot experiment was carried out to investigate the nitrogen transfer, uptake and utilization in the relay-planting system of "wheat/maize/soybean" using the method of 15N-isotope dilution. The results showed that it was useful to accelerate the nitrogen uptake of wheat from fertilizer and soil in the relay-planting system of "wheat/maize/soybean". With no barrier, the biomass and 15N total uptakes and recovery rate were significantly higher than that of solid barrier, and 15N% abundance and total N content of soil reduced markedly. For maize, there were advantage among the competition of interspecies in the relay-planting system (Awc<0，NCRwc<0). With no barrier, the grain yield, 15N grain uptake, 15N total recovery rat, soil 15N% abundance and N% content of maize increased by 17.17%, 24.52%, 17.63%, 13.9% and 10.1%, respectively. However, soybean with no barrier, there were disadvantage among the competition of interspecies in the system, and all the values of 15N total uptakes, 15N grain uptake, 15N total recovery rat and soil 15N% abundance reduced. The content of the soil total N increased by 6.06%. From the above results, we could suppose that there existed bi-directional N transfer in the “wheat/maize/ soybean” relay-planting systems, and the main modes of N transfer were from maize to wheat and from soybean to maize.

在根系分隔盆栽条件下，采用¹⁵N土壤稀释标记方法，研究了“小麦/玉米/大豆”三熟套作体系不同作物间的相互作用及氮素的转移、吸收利用特性。结果表明，“小麦/玉米/大豆”套作体系促进小麦对肥料氮和土壤氮的吸收，不分隔处理的生物产量、¹⁵N总吸收量和总回收率得到显著提高，土壤残留¹⁵N丰度及总氮含量明显降低；玉米表现出套作优势（Awc<0，NCRwc<0），不分隔处理的籽粒产量、籽粒15N吸收量、¹⁵N总回收率、土壤残留¹⁵N丰度及总氮含量较分隔处理提高17.17%、24.52%、17.63%、13.9%和10.1%；大豆表现出套作劣势，不分隔处理的¹⁵N总吸收量、籽粒¹⁵N吸收量、¹⁵N总回收率和土壤残留15N丰度降低，土壤总氮含量提高6.06%。“小麦/玉米/大豆”套作体系存在氮素的双向转移，以玉米向小麦、大豆向玉米转移为主。

研究了不同施氮量对套作和单作条件下春、夏玉米氮利用以及产量和品质的影响. 结果表明，随着施氮量的增加，单作和套作条件下，春、夏玉米吸氮量显著增加，籽粒产量、生物产量和籽粒蛋白质产量也显著增加.由于春、夏玉米需求的养分种类与形态一致，低氮条件时竞争较激烈，春玉米处于优势地位，但其吸氮量仍低于单作.增加施氮量可以缓解这种竞争，利于玉米的高产优质.施氮量由187.5 kg·hm^-2增至375 kg·hm^-2时，春、夏玉米单作时生物产量平均增加1.717 kg·kg^-1 N，而套作时平均增加12.179 kg·kg^-1 N；春、夏玉米单作时蛋白质产量平均增加0.305 kg·kg^-1 N，而套作时平均增加1.829 kg·kg^-1 N；春夏玉米套作的土地当量比由1.59增加到1.91.与单作相比，春夏玉米套作可显著提高玉米产量和改善品质，增施氮肥有利于套作条件下玉米高产优质潜力的充分发挥.

Application of nitrogen (N) fertilizer is one of the most important measures to increase grain yield and protein content in winter wheat (Triticum aestivum L.) production. However, misuse of N fertilizer will not only affect grain yield and quality, but also cause the decline of economic effects and related environmental effects. It is essential to study reasonable nitrogen applying regimes for profitable yields, efficient N utilization, and reduction of possible environment pollution. The objectives of this study were to determine the N uptake and translocation in wheat plant by using 15N isotope tracer in PVC cylinders (2.05 m length, Ф0.2 m, without bottom) with seven treatments: without applying N fertilizer (N0); N application rate of 168 kg N&#903;ha^-1 (0.527 g/pot), ratios of base fertilizer to topdressing of 1:1 (N1), 1:2 (N2) and 0:1(N3); N application rate of 240 kg N&#903;ha^-1 (0.753 g/pot), ratios of base fertilizer to topdressing of 1:1(N4), 1:2(N5) and 0:1(N6). Treatment N4 is a regime applied now in local wheat production. At the same time, the field experiment was conducted in the same field, and experimental design is same as that of the 15N isotope tracer experiment with three repetitions. The plot area was 3 m×8 m=24 m². At the three-leaf stages, the seedlings were thinned to a density of 150 plants per m².
¹⁵N tracer experiment showed that main basal nitrogen absorbed by plant from sowing to jointing stage accounted for 78.04%–89.67%; fertilizer-N use efficiency (N fertilizer accumulation in plant/N supplied, FNUE) of topdressing was markedly higher than that of basal nitrogen; reducing basal nitrogen amount and increasing topdressing nitrogen amount could appropriately promote plant to absorb more fertilizer nitrogen, and enhance FNUE, of which treatment N2 was the highest. In high-yield condition this study concerned, when nitrogen (N) fertilizer rate increased from 168 kg·ha^-1 to 240 kg·ha^-1, the amount of N accumulation in plant and in grain had no significant difference between treatments with the same ratio of base fertilizer to topdressing; with reducing basal nitrogen amount and increasing topdressing nitrogen amount appropriately, the translocation efficiency (accumulation amount from vegetative organs to grain/N accumulation in vegetative organs on anthesis, TE) heightened, and the amount of nitrogen assimilation for grain after anthesis and its contribution proportion (the amount of nitrogen assimilation to grain after anthesis/N accumulation in grain) also increased, in other words grain N accumulation amount increased with increasing amount of topdressing nitrogen in the same nitrogen fertilizer rate. There was no significant difference among treatments N2, N3, N5 and N6 in grain nitrogen accumulation. Appropriate N fertilizer rate with reducing basal nitrogen amount and increasing topdressing nitrogen amount such as in N2, N5 and N6 increased grain yield and protein content. In conclusion, under the condition of this experiment, as far as grain yield, protein content and fertilizer-N use efficiency are concerned, the most appropriate nitrogen fertilizer applying regime recommended is treatment N2, its nitrogen fertilizer rate is 168 kg·ha^-1 and ratio of base fertilizer to topdressing is 1:2.

应用¹⁵N示踪技术研究了高产麦田中施氮量和底施与追施氮肥的比例对小麦氮素吸收转运及籽粒产量的影响。共设7个处理，对照为不施氮肥(N0)；在施纯氮量为168和240 kg/hm²条件下，各设底肥氮量与追肥氮量比例（底追比例）为1∶1 (N1和N4)、1∶2 (N2和N5)、0∶1(N3和N6)。结果表明，播种至拔节期植株积累的底施氮占植株全生育期积累底施氮总量的78.04%~89.67%；小麦植株对追肥氮的利用率显著高于对底肥氮的利用率，适当增加追施氮肥的比例可提高氮肥利用率，其中N2处理的最高。在相同底追比例下，不同施氮量处理相比较，植株与籽粒中的氮素积累量均无显著差异；施氮量相同，随追施氮肥比例的增加，开花前贮存氮素的转运量和转运效率呈先增加后降低的趋势，N2和N5的转运量及转运效率最高；开花后氮素的同化量及对籽粒的贡献率则随追施氮比例的增加而提高；籽粒氮素积累量在N2、N3、N5和N6处理间无显著差异，但显著高于N1和N4。适量施氮并增加追施氮肥的比例可显著提高籽粒产量、蛋白质含量，N2、N5和N6均效果较好。在本试验条件下，施氮量为168 kg/hm²及底追比例为1∶2的处理是兼顾产量、品质和效益的最佳氮肥运筹方式。

In recent years, nitrogen over fertilization has become an unassailable fact in summer maize-winter wheat cropping system in north China plain, especially in summer maize growing season, resulting in N use efficiency (NUE) rapidly decrease and causing a series of ecological and environmental problems, such as underground water pollution, acid rain, global warming and stratospheric ozone depletion, and so on. The objective of this experiment was to study the effects of three application rates (0, 90 and 180 kg N/ha) of three types of nitrogen fertilizer (common urea, coated urea and compound fertilizer) on N absorption, accumulation, translocation and nitrogen fertilizer (NF) utilization of summer maize cultivars, Zhengdan 958 and ND 108 under condition of lower NF application rate, and to provide some beneficial references for ameliorating the fertilization techniques and increasing NUE of summer maize in this area. The main results showed that N accumulation amount was increased but nitrogen physiological efficiency, nitrogen fertilizer efficiency and NUE descended with the increment of N application rate from 0 to 180 kg N/hm2. Under condition of the same N application rate, NUEs of coated urea and compound fertilizer treatments were bigger than that of common urea treatments, especially in the treatments of 90 kg N/ha for Zhengdan 958 and 180 kg N/ha for ND 108 (Table 2, 5 and 6). Difference existed in N staggered accumulation trends between two cultivars under zero N application, and their alternation under N application showed genotypic difference likewise (Table 2). In N application treatments, N accumulation amount was increased before silking stage, but descended in middle and late filling stage, and this trend was more evident for Zhengdan 958. N absorption of summer maize, especially of Zhengdan 958 in the middle and late filling stage could be restrained if N accumulation amount was too much in the stage of sowing to 21 d after silking. There was a genotypic difference in nitrogen harvest index (NHI), nearly 6% more in Zhengdan 958 than in ND 108. With NF application, NHI of Zhengdan 958 was descended evidently, but that of ND 108 changed unconspicuously. Compared to NHI under common urea application, NHI under coated urea and compound fertilizer application was lower and the difference was significant at 0.05 probability level when N application rate was 90 kg N/ha for Zhengdan 958 and 180 kg N/ha for ND 108 (Table 2). Translocation amount of leaf N and stem-sheath N and their contribution rates to grain N were increased with the increment of N application. Leaf N was translocated to grain mainly from 21 d after silking to maturing stage, but stem–sheath N did mainly from silking to 21 d after silking stage (Table 4). Fertilizer-N played the role mainly before silking, especially from 12–leaf to silking stage, and the difference of N accumulation amount between N application treatments and zero N treatment reached to the maximum around silking stage.

在较低施氮量下，研究了3种类型氮肥(普通尿素、包膜尿素和复合肥)不同施用量(0、90和180 kg N/hm²)对夏播玉米郑单958与农大108氮素吸收、累积、转运及氮肥利用的影响。结果表明，在本试验范围内，施氮量增大，植株氮素累积量增加，氮生理效率、氮肥效率与氮肥利用率(NUE)下降。同等施氮量下包膜尿素与复合肥较普通尿素NUE高，郑单958施90 kg N/hm²与农大108施180 kg N/hm²时尤为明显；氮素阶段性累积规律，两品种在不施氮和施氮条件下均具有基因型差异。播种至吐丝后21 d氮素累积量太大对夏玉米灌浆中后期氮素累积有一定抑制作用，郑单958表现特别明显；氮收获指数(NHI)具明显基因型差异，郑单958较农大108高近6个百分点。施氮使郑单958 NHI显著降低，农大108变化不明显。与普通尿素相比，包膜尿素与复合肥处理NHI较低，在郑单958施90 kg N/hm²与农大108施180 kg N/hm²时差异达显著水平；叶、茎鞘氮素转运量及其对籽粒氮贡献率随施氮量增大而增大，叶氮素转运主要在吐丝后21 d至成熟期，茎鞘氮素转运主要在吐丝至吐丝后21d；肥料氮主要在吐丝前发挥作用，且最主要是在12叶展至吐丝期，施氮与不施氮处理的氮素累积量差异在吐丝前后达最大。