氮肥运筹对不同玉米品种氮素吸收、利用及田间氮平衡的影响

李强, 孔凡磊, 袁继超

华北农学报. 2022, 37(4): 169-181

华北农学报 ›› 2022, Vol. 37 ›› Issue (4) : 169-181. DOI: 10.7668/hbnxb.20192665
资源环境·植物保护

氮肥运筹对不同玉米品种氮素吸收、利用及田间氮平衡的影响

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Cultivar Differences in Nitrogen Uptake,Utilization and Field Nitrogen Balance of Maize Hybrids in Response to Nitrogen Management

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摘要

为了提高玉米产量、减少氮肥施用及提高氮肥利用效率,对氮高效玉米品种进行筛选和推广,研究氮肥管理对不同氮效率玉米品种氮吸收、利用和田间氮平衡的影响,探明氮肥运筹对不同氮效率玉米品种氮素吸收、利用及田间氮平衡的影响对于玉米的高效育种和栽培至关重要,因此,于2015-2016年在川中丘陵区开展了为期2 a的田间试验。结果表明:正红311(ZH311)在吐丝期和成熟期茎鞘和叶片氮分配比例均显著高于先玉508(XY508)。此外,ZH311花后籽粒氮积累量和花后氮籽粒贡献率显著高于XY508,而花前氮转运及花前氮转运贡献率显著低于XY508。氮高效品种ZH311营养器官中较高的氮分配比例使得其各阶段氮积累量均显著高于氮低效品种XY508,吐丝后氮素积累优势较吐丝前更明显。ZH311吐丝后氮的高效积累抑制了其吐丝前氮的转运,使得其吐丝前氮积累的转运率和对籽粒的贡献率均显著低于XY508,且ZH311的氮素吸收效率、氮素回收效率和氮素偏生产力均显著高于XY508。与XY508相比,ZH311根系能更有效地吸收和利用40~80 cm土层中的无机氮,减少氮沉降,显著减少表观氮损失,且2个品种氮素表观损失差异主要来自追肥后。综上所述,氮高效玉米品种ZH311较氮低效品种XY508不仅能提高单位面积产量,而且能减少氮损失,从而降低环境风险。

Abstract

To increase crop yields,reduce the application of chemical fertilizers,and improve nutrient utilization efficiency,N-efficient maize cultivars were screened and popularized. An understanding of nitrogen uptake,utilization,and field balance in maize cultivars with contrasting nitrogen efficiency response to N management is essential for efficient breeding and cultivation of maize to produce fodder and bio-energy. To determine the effects of N management on these factors during maize cultivation,a two-year field experiment was conducted in 2015 and 2016 in a subtropical semi-humid climate zone. The results showed that the proportion of N in the stem plus sheath and leaves in ZH311 during VT and R6 was significantly higher than that of XY508. In addition,the N accumulation into grain post-silking(NAG)and contribution of NAG to grain(CNAG)of ZH311 were significantly higher than those of XY508,while the N redistribution rate(NRR)and contribution of NRA to grain yield(CNRA)of ZH311 were significantly lower than those of XY508. The higher proportion of N in the vegetative organs of a N-efficient cultivar,ZH311,led to a significantly higher N accumulation in each stage than that observed for the N-inefficient cultivar XY508. The N accumulation advantage of ZH311 was higher after silking than before silking. The high post-silking N accumulation of ZH311 inhibited the pre-silking N transport that determines the N transport rate and contribution rate to grain of pre-silking N accumulation,which were significantly lower than those of XY508. Meanwhile,the N uptake efficiency,N recovery efficiency,and N partial productivity of ZH311 were significantly higher than those of XY508. Compared with that of XY508,the root system of ZH311 could more effectively absorb and utilize inorganic N in the 40-80 cm soil layer,reduce N deposition,and significantly decrease apparent N losses. The differences in apparent N losses between the two cultivars were mainly elicited post-topdressing. In summary,ZH311 has not only a higher yield per unit area than XY508,but also lower N losses,consequently reducing environmental risks.

关键词

玉米 / 氮管理 / 无机氮 / 氮平衡

Key words

Maize / Nitrogen management / Inorganic N / Nitrogen balance

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李强 , 孔凡磊 , 袁继超. 氮肥运筹对不同玉米品种氮素吸收、利用及田间氮平衡的影响. 华北农学报. 2022, 37(4): 169-181 https://doi.org/10.7668/hbnxb.20192665
Qiang LI , Fanlei KONG , Jichao YUAN. Cultivar Differences in Nitrogen Uptake,Utilization and Field Nitrogen Balance of Maize Hybrids in Response to Nitrogen Management. Acta Agriculturae Boreali-Sinica. 2022, 37(4): 169-181 https://doi.org/10.7668/hbnxb.20192665
Maize(Zea mays L.)crops over 177 million ha worldwide and their total yield exceeds that of all other grains[1].Maize production by 2050 should be double that in 2005 to meet the growing demand for food and bio-fuels[2]. However,with the expansion of infrastructure,industrialization,and urban encroachment,arable land area has shrunk rapidly in recent years[3]. Meanwhile,the current scenario of environmental disasters and the concurrent need for adequate food productivity makes it essential to consider approaches that simultaneously sustain both the environment and food economy[4].
N is typically considered to be the most influential factor for crop productivity and grain quality,and N fertilizer is widely used to increase yield and profit[5]. In China,several farmers apply more chemical N fertilizer than needed to ensure high grain yields;however,owing to the high N-fertilization rates,yield is no longer limited by nutrient availability,and additional input has a limited,or even negative,effect on crop yield[6-7]. In some regions,over-application of N fertilizer has resulted in decreased N use efficiency(NUE)and increased N losses to water bodies,through nitrate leaching and surface runoff,and atmosphere,through ammonia(NH3)volatilization and nitrous oxide(N2O)emissions[3,8-9]. NUE depends on the optimization of nitrogen management techniques and the N absorption and utilization ability of the crop plant[10-11]. N-efficient cultivars have strong roots with well-developed lateral roots and are sensitive to nitrate stimulation[12-13]. With sufficient N supply,root length and surface area increase,reducing N accumulation and unnecessary losses in deep soil[14-15]. Under N-deficient conditions,maize root elongation is beneficial as it expands the space occupied by the root system,thereby improving the spatial availability of soil N[4,16]. Therefore,the biomass yield[17],N accumulation[18],and grain yield of N-efficient maize cultivars are markedly higher than those of N-inefficient maize cultivars under both N-sufficient and deficient conditions[19-20].
In addition to N application rate,the difference in N uptake,utilization,and losses are also related to the N application period,rainfall and irrigation,soil mineralization,crop species,and cropping system[21-22]. Over irrigation or long-term excess N application can lead to nitrate accumulation in the soil below the root zone,decreasing its bioavailability. Thus,nitrate leaching is a major mechanism of N loss in farmlands[23]. No obvious accumulation of N-N O3-was noted in the 100-200 cm soil layer with an N fertilizer rate of 168 kg/ha and base to topdressing ratio of 1∶2,and the apparent loss of nitrogen was the least[24]. Gu et al[9]reported that using manure instead of urea application could reduce ammonia volatilization by 66.6% and could also reduce fertilizer and irrigation supply during the pre-winter stage,this being an effective way to reduce N loss.
Previous studies have focused on the differences among maize cultivars with differing N efficiencies with regard to biomass production,N uptake and utilization,and yield response to N fertilizer levels[20,25-26]. However,few studies have examined differences in their responses to N management. Therefore,the effects of N management of maize cultivars with different N efficiency on soil inorganic N distribution and field N balance remain unclear. In this study,a two-year field experiment was conducted in the hilly area of central Sichuan,a main maize producing area of Southwest China. The N-efficient maize cultivar Zhenghong 311(ZH311)and N-inefficient maize cultivar Xianyu 508(XY508)were used to assess differences in N uptake,utilization,and field N balance response to N management[12]. These results can provide useful information for clarifying the mechanisms by which N-efficient maize cultivars reduce N losses in paddy fields,and can also help guide local farmers to optimize fertilization according to the fertilizer requirements of maize cultivars with different N efficiency levels.

1 Materials and Methods

1.1 Experimental site

The experiments were conducted in Sichuan,China,in 2015-2016. The daily air temperature,precipitation,and sunlight hours recorded during the maize growth period are shown in Fig.1.The experimental soil was purple clay. The basic soil physicochemical property in 2015 and 2016 were shown in Tab.1.
Fig.1 Daily average temperature,sunshine hours, and precipitation during the growing season of maize in 2015 and 2016

Full size|PPT slide

Tab.1 Basic physicochemical properties of the tested soil
Year Soil layer/
cm		 Organic
matter/ (g/kg)		 Total N/
(g/kg)		 Available nutrient /(mg/kg) pH Bulk
density/
(g /cm3)
Alkali
hydrolysable N		 Olsen-P Exchangeable K
2015 0-20 13.83±0.12 1.87±0.05 55.65±0.12 4.75±0.05 160.33±1.03 8.11±0.03 1.30±0.02
20-40 11.44±0.08 1.83±0.03 30.74±0.17 1.56±0.03 123.83±0.85 8.14±0.02 1.40±0.03
40-60 9.18±0.11 1.62±0.02 15.23±0.05 0.71±0.02 104.17±0.47 8.19±0.01 1.42±0.01
60-80 7.25±0.05 1.37±0.02 10.59±0.04 0.49±0.02 89.72±0.79 8.19±0.02 1.43±0.03
2016 0-20 12.05±0.07 1.21±0.05 61.83±0.05 4.35±0.05 146.13±0.56 7.81±0.02 1.28±0.03
20-40 10.31±0.05 1.27±0.03 53.67±0.09 2.36±0.03 111.76±0.92 7.84±0.01 1.41±0.02
40-60 8.45±0.04 1.16±0.02 34.83±0.05 0.84±0.01 100.43±0.34 7.91±0.01 1.42±0.02
60-80 6.05±0.07 1.02±0.01 29.75±0.07 0.53±0.02 78.52±0.59 7.90±0.02 1.44±0.01

1.2 Plant materials

We used two maize hybrids with different N efficiency levels,i.e.,ZH311 and XY508[12]. ZH311 was developed in 2006 by the Sichuan Nongda Zhenghong Seed Co.,Ltd,Sichuan Province,China,while XY508 was developed in 2005 by the Pioneer Technology Co.,Tieling,Jilin Province,China.

1.3 Experimental design

We used a randomized block experimental design with three replicates. The plots were 7.5 m long,with six rows spaced by 1.4 m+0.6 m. Two hybrids(ZH311 and XY508)and five N treatments were randomly assigned to each replicate. The five N treatments were:①No N application(B1);②N 225 kg/ha(100% basic fertilizer,B2);③N 225 kg/ha(75% basic fertilizer+25% topdressing,B3);④N 225 kg/ha(50% basic fertilizer+50% topdressing,B4);⑤N 225 kg/ha(25% basic fertilizer + 75% topdressing,B5). The basic N fertilizer was applied before sowing,and the topdressing N fertilizer was applied at the V8 stage. Plots were fertilized with 75 kg/ha P2O5 and 90 kg/ha K2Obefore sowing. No irrigation was used during the whole growing season,except during seeding. Disease,pest,and weed controls in each treatment were well controlled by routine management.

1.4 Sampling and measurements

At the V12 stage,VT stage,and R6 stage,samples were randomly collected from four plants with an average height from the middle of each plot,and samples were divided into stem plus sheath,leaf lamina,and panicle. Fresh samples were oven-dried at 105 ℃ for 60 min and then at 75 ℃ until a constant weight to determine the dry matter weight. The dry samples were milled and sifted through a 0.5 mm screen to determine the N concentration using a Kjeldahl apparatus(Kjeltec-8400;Foss Analytical,Höganäs,Sweden).
For soil inorganic N accumulation analysis,five 80 cm-deep soil cores were obtained from each plot and separated into 0-20 cm,20-40 cm,40-60 cm,and 60-80 cm soil layers before sowing,pre-topdressing,and post-harvest. According to the method of Deng et al[8],fresh soil samples were immediately dissolved after mixed by 2 mol/L potassium chloride solution(soil solution ratio,1∶5). The content of NH4-N and NO3-N was analyzed by an automated continuous flow analyzer(Alliance/FUTURA+/E,France).Meanwhile,the soil bulk density and moisture content were determined by the cutting ring method and oven-drying at 105 ℃.

1.5 Calculation methods

The N redistribution pre-silking and N accumulation post-silking were calculated as follows:
N redistribution amount(NRA,t/ha)= N accumulation of vegetative organs at VT-N accumulation of vegetative organs at R6;
N redistribution rate(NRR,%)= NRA/N accumulation of vegetative organs at VT;
Contribution of NRA to grain yield(CNRA,%)=NRA/N accumulation of grain×100;
N accumulation into grain post-silking(NAG,t/ha)=N accumulation of grain-NRA;
Contribution of NAG to grain(CNAG,%)=NAG/N accumulation of grain × 100.
The method described by Gu et al[9] was used to calculate the N dry matter production efficiency(NDMPE),N physiological efficiency (NPE),N uptake efficiency (NUE),N recovery efficiency (NRE),N agronomic efficiency (NAE),N partial factor productivity (NPFP),and N harvest index(NHI)as follows:
NDMPE(kg/kg)=Dry matter accumulation of plant/N accumulation of plant;
NPE(kg/kg)=(Yield of N application-Yield without N fertilizer)/(N accumulation of N application-N accumulation without N fertilizer);
NUE(%)=Total N accumulation/Total N supply(N application + Soil inorganic N before sowing) ×100;
NRE(%)=(N accumulation of N application-N accumulation without N fertilizer)/ Total N application amount×100;
NAE(kg/kg)=(Yield of N application-Yield without N fertilizer)/Total N application amount;
NPFP(kg/kg)=Yield of N application / Total N application amount;
NHI=Grain N accumulation/Plant N accumulation.
According to previous studies[8-9] the apparent N mineralization(ANM)during the maize growing season was calculated as the difference between N output,i.e.,plant N uptake + residual soil Nmin in 0-80 cm soil layers,and N input,i.e.,initial soil Nmin in the 0-80 cm soil layers,in the plots with no N treatment. The apparent N losses(Nloss)were calculated as follows:
Nloss(kg/ha)=(Initial soil Nmin in the 0-80 cm soil layers+N fertilizer rate +ANM)-(Residual soil Nmin in the 0-80 cm soil layers+Plant N uptake).

1.6 Data analysis

Data were analyzed with three-way analysis of variance(ANOVA)using the SPSS software package(Version 20.0)to test whether significant differences existed between the N treatments and cultivars. The statistical significance of differences between means was determined by least significant difference(LSD)test at the 0.05 probability level. Graphs were prepared using Graph Pad Prism 5.0.

2 Results and Analysis

2.1 Nitrogen accumulation and distribution

N management and cultivar type affected N accumulation in various stages and throughout the growth period. N accumulation of ZH311 was 16.51%,41.29%,26.73%,and 20.65% higher during the sowing stage-V12,V12-VT,VT-R6,and over the whole growth period than that of XY508 in 2015 and 30.00%,7.56%,12.18%,and 18.93% higher in 2016,respectively(Tab.2). Except for those during V12-VT in 2016,N accumulation differences between the two cultivars were highly significant(P<0.01). N accumulation differences between the two cultivars in 2015 were evidently higher than those in 2016 owing the fertility of the tested soils in 2016 being higher than that in 2015,indicating that N accumulation differences between maize cultivars were also closely related to soil fertility status. N management and its interaction with cultivar type had significant(P<0.05)effects on N accumulation in various stages(except for V12-VT in 2015)and for the whole growth period. A high base fertilizer ratio(B2)improved N accumulation during the sowing stage-V12 and VT-R6 of ZH311,and significantly increased N accumulation in the whole growth period compared to that of other treatments for both years. For XY508,high B2 increased N accumulation in sowing stage-V12,while high topdressing ratio(B5)increased N accumulation in V12-R6,which led to the N accumulation with B5 being higher than others in both years.
Tab.2 Nitrogen accumulation in maize in different growth periods kg/ha
Cultivar Nitrogen
management		 Nitrogen accumulation
Sowing stage-V12 V12-VT VT-R6 Nitrogen accumulation
2015 2016 2015 2016 2015 2016 2015 2016
ZH311 B1 52.61±0.82e 53.40±1.86f 12.12±1.33c 13.86±2.56fg 53.78±4.89de 64.38±0.50cd 118.50±2.71f 131.64±1.89g
B2 71.60±1.35a 106.48±2.08a 25.47±1.87b 19.77±4.08de 72.83±4.59a 89.85±3.67a 169.91±5.01a 216.10±4.76a
B3 67.89±1.80b 96.60±4.34b 15.84±1.26c 24.58±5.23bcd 64.57±4.44bc 62.07±4.69cd 148.30±3.14c 183.25±3.07d
B4 61.57±0.45c 89.23±2.40c 28.20±3.28ab 41.11±1.02a 70.67±3.32ab 75.11±4.21b 160.44±3.18b 205.45±3.21b
B5 57.08±0.38d 81.09±2.96d 35.22±5.69a 30.05±2.91b 70.26±7.34ab 87.12±0.86a 162.57±3.30b 198.26±1.88c
Average 65.15±0.41A 85.36±0.67A 23.37±2.13A 25.88±1.09A 66.42±3.25A 75.70±1.52A 151.94±2.01A 186.94±1.43A
XY508 B1 44.69±2.73f 38.36±2.34h 12.98±0.48c 11.24±3.49g 38.74±5.66f 61.72±2.23cd 96.40±3.26g 111.33±3.39h
B2 65.67±0.58b 87.58±2.54c 17.33±3.51c 22.42±4.18cde 46.46±2.12ef 65.05±3.62c 129.46±2.89e 175.06±2.32e
B3 62.58±2.42c 87.95±1.72c 12.19±3.26c 17.88±0.34ef 59.10±1.39cd 59.25±2.58d 133.86±2.46de 165.08±1.25f
B4 60.11±3.00c 66.56±4.34e 14.81±1.80c 27.98±1.52bc 54.76±3.99d 66.52±2.23c 129.69±2.97e 161.07±1.43f
B5 46.57±1.00f 47.85±2.42g 25.40±2.78b 40.76±3.05a 63.10±3.33bc 84.83±2.39a 135.06±0.86d 173.44±0.70e
Average 55.92±1.10B 65.66±0.43B 16.54±1.63B 24.06±0.55A 52.43±1.37B 67.48±1.39B 124.90±1.91B 157.19±1.27B
F value Years(Y) 722.17** 23.24** 126.48** 2 183.88**
Cultivar(C) 447.38** 17.31** 105.49** 1 555.40**
Nitrogen(N) 458.84** 48.56** 45.11** 847.35**
Y×C 120.80** 5.81* 7.11* 3.51ns
Y×N 85.06** 5.68** 12.76** 54.73**
C×N 15.78** 5.44** 13.04** 42.41**
Y×C×N 9.60** 5.02** 0.79ns 4.20**
Note:Values with different lowercase letters are significantly different at P<0.05;within cultivars,values with different uppercase letters are significantly different at P<0.05 according to the least significant difference test. **.P<0.01;*.P<0.05;ns.Not significant.The same as Tab.3-7.
N distribution ratio in maize stem plus sheath was highest in V12,and the proportion of N in leaves was highest in VT,while that in the panicle was highest in R6(Tab.3). In ZH311,the proportion of N in the stem plus sheath and leaves during VT and R6 was significantly(P<0.01)higher than that for XY508. In 2015, N proportion in stem plus sheath and that in leaves was higher by 15.07 percentage points and 4.14 percentage points at VT, and 12.55 percentage points and 25.94 percentage points at R6, respectively. Meanwhile, these factors were higher by 2.25 percentage points, 6.50 percentage points, 5.69 percentage points, and 16.61 percentage points, respectively, in 2016. The higher N partitioning ratio of stem plus sheath during VT of ZH311 could promote the absorption and transport of nutrients,which was beneficial to the nutrient absorption capacity of roots. Meanwhile,the higher N distribution ratio of leaves of ZH311 in R6 could delay leaf senescence in the late growth stage to maintain high biomass production capacity. Considering the whole growth period,N application increased N distribution in the stem plus sheath and decreased the N proportion in leaves of maize. B2 increased the N proportion in the stem plus sheath and decreased the N distribution ratio in leaves,which resulted in the highest N proportion in the stem plus sheath and the lowest N proportion in the leaves. High N proportion in the stem plus sheath and low N distribution in the leaves may be important to achieve high biomass and N accumulation under high B2.
Tab.3 Nitrogen distribution ratios of maize organs subjected to various treatments %
Cultivar Nitrogen
management		 Ratio of stem plus sheath Ratio of leaf lamina Ratio of panicle
V12 VT R6 V12 VT R6 VT R6
2015
ZH311 B1 38.11±0.76e 23.03±0.93cd 11.39±0.13f 61.89±0.76a 62.96±2.86a 12.38±0.79b 14.01±3.74c 76.23±0.75a
B2 47.93±0.95a 31.27±1.89a 18.28±0.59a 52.07±0.95e 53.15±0.74c 13.12±0.57ab 16.91±1.38bc 68.60±1.07de
B3 42.38±0.80d 28.42±3.33ab 16.58±0.35b 57.62±0.80b 54.21±1.74c 13.61±0.45a 17.37±3.10bc 69.81±0.15cd
B4 44.63±1.41bcd 25.62±2.69bc 15.98±0.37bc 55.37±1.41bcd 57.98±1.38b 13.58±0.16a 16.74±2.55bc 70.44±0.35c
B5 46.33±0.95ab 21.06±1.45d 19.34±0.75a 53.67±0.95de 64.83±1.36a 12.86±0.27ab 14.11±0.38c 67.80±0.52e
Average 43.88±0.37A 25.88±1.41A 16.32±0.26A 56.12±0.37A 58.62±0.66A 13.11±0.21A 15.83±0.54B 70.58±0.32B
XY508 B1 44.38±1.32bcd 20.37±1.82d 13.73±1.59e 55.62±1.32bcd 63.81±3.47a 9.97±0.73d 15.81±1.91bc 76.30±1.36a
B2 44.83±1.53bc 22.80±1.84cd 14.95±0.57cd 55.17±1.53cd 55.02±3.30bc 9.99±0.29d 22.18±1.64a 75.06±0.79a
B3 45.17±0.70bc 27.34±1.81b 14.84±0.51d 54.83±0.70cd 53.32±1.65c 10.02±0.32d 19.34±1.70ab 75.14±0.70a
B4 43.20±1.42cd 21.40±1.05d 15.33±0.40cd 56.80±1.42bc 55.72±1.34bc 11.32±0.58c 22.87±2.17a 73.36±0.85b
B5 44.61±2.31bcd 20.54±3.21d 13.63±0.60e 55.39±2.31bcd 56.93±2.02bc 10.75±0.17cd 22.53±2.50a 75.62±0.77a
Average 44.44±0.56A 22.49±1.54B 14.50±0.48B 55.56±0.56A 56.29±1.87B 10.41±0.07B 20.55±1.86A 75.10±0.52A
2016
ZH311 B1 41.61±2.16cd 25.24±1.12de 10.07±0.41e 58.39±2.16ab 59.86±0.36a 16.77±0.56a 14.91±1.45de 73.16±0.19b
B2 47.58±1.93a 32.12±0.50a 18.80±1.42a 52.42±1.93d 55.30±0.18bcd 15.86±0.68a 12.58±0.67e 65.34±1.54f
B3 45.70±1.03ab 29.04±1.66b 17.62±0.52b 54.30±1.14cd 55.68±2.14bc 14.18±0.53b 15.29±2.47de 68.20±0.12e
B4 42.99±2.66bcd 29.52±0.49b 17.31±0.86b 57.01±2.66abc 57.71±0.72ab 13.35±0.75bc 12.77±0.52e 69.33±1.32e
B5 39.54±2.19d 29.33±1.26b 17.99±0.77ab 60.46±2.19a 55.44±2.04bc 13.21±0.57bc 15.22±2.58de 68.81±0.25e
Average 43.49±1.21A 29.05±0.38A 16.36±0.33A 56.52±1.21A 56.80±0.35A 14.67±0.24A 14.15±0.66B 68.97±0.56B
XY508 B1 45.67±2.77ab 22.65±0.77d 12.97±0.56d 54.33±2.77cd 50.71±2.54e 11.76±0.63de 26.64±2.09a 75.28±0.29a
B2 41.27±0.81cd 29.70±0.18b 17.31±0.86b 58.73±0.81ab 54.33±0.93cd 11.15±0.38e 15.97±1.09de 71.54±0.72cd
B3 44.27±1.54abc 26.85±0.82c 15.07±0.43c 55.73±1.54bcd 54.86±0.79cd 13.95±0.76b 18.28±0.37cd 70.98±0.53d
B4 41.01±1.52cd 21.75±0.64e 18.25±0.26ab 58.99±1.52ab 54.07±1.08cd 12.65±0.67cd 21.18±1.18bc 69.10±0.86e
B5 40.61±2.12cd 25.43±2.14cd 13.80±0.39d 59.39±2.12ab 52.80±2.03de 13.40±0.85bc 21.77±2.18b 72.80±1.10bc
Average 42.57±0.84A 25.88±0.29B 15.48±0.28B 57.44±0.84A 53.35±0.74B 12.58±0.14B 20.77±0.64A 71.94±0.15A
F value Years(Y) 5.39* 60.63** 7.83** 5.39* 25.29** 155.13** 1.60ns 127.86**
Cultivar(C) 0.13ns 60.71** 54.27** 0.13ns 37.10** 254.89** 97.74** 315.81**
Nitrogen(N) 5.29** 29.95** 103.85** 5.29** 14.20** 0.96ns 0.95ns 76.25**
Y×C 2.31ns 0.07ns 6.55* 2.31ns 1.38ns 4.09ns 2.76ns 13.47**
Y×N 7.85** 6.45** 10.64** 7.85** 14.91** 7.82** 10.66** 4.12**
C×N 10.94** 2.96* 48.66** 10.94** 7.41** 15.99** 2.90* 27.32**
Y×C×N 1.59ns 3.48* 1.78ns 1.59ns 9.89** 14.67** 3.57* 6.54**

2.2 Nitrogen redistribution and transformation

N management and cultivar type both had significant effects on pre-silking N transport and post-silking N transformation. Results showed that the NAG and CNAG of ZH311 were significantly(P<0.01)higher than those of XY508 in both years(Tab.4),with NAG being higher by 40.39% and 30.30%,and CNAG being higher by 9.31 and 2.84 percentage points in 2015 and 2016,respectively. Meanwhile,the NRR and CNRA of XY508 were significantly(P<0.01)higher than those of ZH311 in both years,and with NRR being higher by 9.56 and 4.02 percentage points,and CNRA being higher by 9.31 and 3.13 percentage points in 2015 and 2016,respectively. These results indicated that the differences in grain N accumulation between different N-efficient maize cultivars were mainly derived from post-silking N transformation. The higher N accumulation of the N-efficient cultivar inhibited the transport of N accumulated pre-silking,leading to NRR and CNRA being significantly lower than those of the N-inefficient cultivar. N management had a significant effect on pre-silking N transport and post-silking N transformation in maize(P<0.01). In the two-year trial,the NRA of ZH311 was highest under the B4 treatment,while that of XY508 was highest under the B2 treatment. Meanwhile,the post-silking N accumulation was highest under B5 treatment in both cultivars. This indicated that balanced N management during the growth period(B4)was beneficial for the promotion of pre-silking N transport and increase of post-silking N accumulation of the N-efficient cultivar ZH311,leading to high N accumulation. High base fertilizer ratio(B2)could promote the pre-silking N transport of N-inefficient cultivar,while high topdressing ratio(B5)could improve the post-silking N accumulation,which led to N accumulation of XY508 under B2 and B5 being higher those under other N management scenarios.
Tab.4 Effects of nitrogen management on redistribution of pre-silking nitrogen and transformation of post-silking nitrogen
Cultivar Nitrogen
management		 NRA/ (t/ha) NRR/% CNRA/% NAG/(t/ha) CNAG/%
2015 2016 2015 2016 2015 2016 2015 2016 2015 2016
ZH311 B1 38.40±7.00bc 44.53±0.84d 56.18±4.54abc 62.34±0.25a 47.40±5.48cd 48.02±0.38b 42.88±4.99de 47.65±0.79de 52.60±4.48ab 51.98±0.38c
B2 45.94±1.07ab 53.87±3.04c 45.07±0.80d 40.67±2.87e 42.77±1.45cd 42.07±2.56cd 61.57±4.23a 74.23±3.92ab 57.23±1.45ab 57.93±2.56ab
B3 40.91±6.01bc 66.40±2.51a 46.36±3.36d 52.18±1.51b 43.51±6.21cd 56.45±2.52a 53.08±4.64abc 51.27±3.57d 56.49±4.21ab 43.55±2.52d
B4 44.45±4.94bc 66.28±2.79a 47.07±2.13d 48.47±2.96c 42.48±4.01cd 48.92±3.55b 60.07±3.24ab 69.40±4.13bc 57.52±4.01ab 51.08±3.55c
B5 41.97±5.00bc 51.76±1.20c 42.88±5.89d 44.36±0.65d 40.73±4.93d 40.51±0.80d 60.80±5.07a 76.04±1.96a 59.27±4.93a 59.49±0.80a
Average 42.33±3.40A 56.47±0.81A 47.51±1.81B 49.61±0.51B 43.38±3.38B 47.19±0.65B 55.68±3.24A 63.72±0.85A 56.62±3.38A 52.81±0.65A
XY508 B1 36.59±2.18c 33.69±1.22e 60.40±0.83ab 64.68±0.84a 57.83±4.97ab 45.34±1.33bc 26.98±5.93f 40.63±1.71f 42.17±3.97cd 54.66±1.33bc
B2 53.26±3.62a 63.17±3.56ab 61.07±2.07a 54.67±2.28b 62.23±2.48a 57.77±3.75a 32.28±1.83f 46.22±4.48def 37.77±2.48d 42.23±3.75d
B3 43.57±2.68bc 60.82±2.15b 55.47±1.94bc 54.73±1.27b 48.47±1.54cd 58.45±2.36a 46.27±0.33cde 43.26±2.83ef 51.53±1.54ab 41.55±2.36d
B4 42.41±4.87bc 47.01±3.52d 53.78±3.10c 47.32±2.03cd 50.62±4.97bc 48.24±2.73b 41.30±3.85e 50.37±1.88d 49.38±4.97bc 51.76±2.73c
B5 40.99±4.84bc 43.50±3.30d 54.12±3.48c 46.73±2.55cd 44.28±4.46cd 40.36±2.66d 51.48±3.19bcd 64.24±2.42c 55.72±4.46ab 59.64±2.66a
Average 43.37±2.20A 49.64±0.60B 56.97±1.21A 53.63±0.55A 52.69±2.05A 50.32±0.94A 39.66±1.53B 48.94±1.36B 47.31±2.05B 49.97±0.94B
F value Years(Y) 95.62** 0.89ns 0.27ns 57.40** 0.27ns
Cultivar(C) 7.72** 102.48** 29.13** 181.40** 29.13**
Nitrogen(N) 31.86** 51.77** 10.93** 46.70** 10.93**
Y×C 14.19** 16.68** 8.27** 0.30ns 8.27**
Y×N 10.55** 8.58** 7.11** 6.62** 7.11**
C×N 9.22** 10.91** 6.66** 11.12** 6.66**
Y×C×N 2.13ns 1.22ns 0.76ns 0.77ns 0.76ns

2.3 Nitrogen absorption and utilization

There was a significant difference in N uptake and utilization efficiency between maize cultivars(Tab.5). NUE,NRE,and NPFP of ZH311 were significantly higher(P<0.01)than those of XY508 in both years,with NUE being higher by 8.23 and 9.00 percentage points,NRE being higher by 2.75 and 5.25 percentage points,and NPFP being higher by 11.94% and 11.00% in 2015 and 2016,respectively. These results indicated that the advantages in N uptake and utilization of ZH311 compared with XY508 were mainly reflected in NUE,NRE,and NPFP,while the differences between the two cultivars in NDMPE,NPE,NAE,and NHI were affected by the tested soil and climatic conditions. The interaction between N management and cultivar type had significant(P<0.01)effects on the N uptake and utilization efficiency of maize. For ZH311,NUE and NRE were the highest under the B2 treatment in both years,and NAE and NPFP were the highest under the B4 treatment for both years,while those of XY508 were the highest under the B5 and B2 treatment in 2015 and 2016,respectively. Taken together,the results from both years indicated that the advantage of ZH311 over XY508 regarding N uptake and utilization was more pronounced under the B4 treatment than that under the B2 and B5 treatments,showing that balanced N management during the growth period(B4)could promote the N uptake and utilization of N-efficient maize cultivars,while relatively higher base fertilizer and topdressing ratios could also improve the N uptake and utilization of N-inefficient maize cultivars.
Tab.5 Effects of nitrogen management on nitrogen absorption and utilization of maize
Cultivar Nitrogen
management		 NDMPE/
(kg/kg)		 NPE/
(kg/kg)		 NUE/
%		 NRE/
%		 NAE/
(kg/kg)		 NPFP/
(kg/kg)		 NHI
2015
ZH311 B1 111.68±0.30a - - - - - 0.65±0.01a
B2 98.46±1.07d 20.82±3.60cde 49.46±1.33a 22.85±2.01a 4.74±0.83b 36.83±0.97b 0.60±0.01e
B3 101.11±0.65c 41.69±4.88a 43.18±1.11c 13.24±2.20d 5.35±0.92ab 37.44±0.97b 0.60±0.01e
B4 97.94±1.21d 36.30±3.45ab 46.71±1.28b 18.64±2.57b 6.65±0.40a 38.74±1.20a 0.62±0.00cd
B5 98.16±0.69d 29.01±4.36bcd 47.33±1.32b 19.58±2.62b 5.60±0.46ab 37.69±1.44ab 0.60±0.00e
Average 101.47±0.49A 31.95±3.97A 46.67±1.03A 18.58±2.08A 5.59±0.42A 37.68±1.02A 0.62±0.00B
XY508 B1 110.04±2.16b - - - - - 0.63±0.02cd
B2 102.55±0.48c 31.33±3.13abc 37.69±1.14e 14.69±1.63cd 4.57±0.08b 34.48±0.85c 0.63±0.01c
B3 98.28±0.19d 17.17±0.90e 38.98±0.97de 16.65±2.07bc 2.87±0.47c 32.78±0.76d 0.64±0.01bc
B4 95.34±0.64e 17.47±3.40de 37.76±1.11e 14.79±0.68cd 2.59±0.57c 32.50±0.44d 0.61±0.01de
B5 101.02±0.04c 29.13±7.70bcd 39.32±0.50d 17.18±1.09bc 4.98±1.51b 34.89±2.13c 0.65±0.01ab
Average 101.45±0.55A 23.78±1.76B 38.44±0.85B 15.83±1.30B 3.75±0.48B 33.66±1.02B 0.63±0.01A
2016
ZH311 B1 120.53±1.61a - - - - - 0.66±0.00a
B2 90.71±1.36h 15.26±1.49d 60.59±1.19a 37.54±1.78a 5.71±0.28cd 40.78±0.59c 0.56±0.01g
B3 106.15±1.74b 32.73±2.07a 51.38±0.59d 22.94±0.52d 7.50±0.39b 42.57±0.26b 0.61±0.00cd
B4 94.61±0.58g 28.77±2.38ab 57.61±1.03b 32.80±1.86b 9.44±0.90a 44.50±0.57a 0.63±0.02b
B5 97.80±0.29ef 15.75±2.62d 55.59±0.55c 29.61±1.06c 4.64±0.63d 39.71±0.82d 0.61±0.01c
Average 101.96±0.84A 23.13±1.01A 56.29±0.10A 30.73±0.67A 6.83±0.23A 41.89±0.22A 0.62±0.01A
XY508 B1 103.82±0.84c - - - - - 0.64±0.00b
B2 99.29±0.70def 27.25±2.46b 49.09±0.70e 28.32±0.57c 7.72±0.76b 39.12±0.38d 0.60±0.00de
B3 97.62±1.03f 20.88±2.59c 46.29±0.59f 23.89±1.38d 5.01±0.87d 36.41±0.52f 0.60±0.01cde
B4 99.68±0.33d 26.42±4.52b 45.16±0.62f 22.11±1.75d 5.89±1.45cd 37.29±0.39ef 0.58±0.01fg
B5 99.35±0.46de 24.32±3.97bc 48.63±0.19e 27.61±1.36c 6.74±1.35bc 38.14±0.30e 0.59±0.01ef
Average 99.88±0.62B 24.72±3.20A 47.29±0.43B 25.48±1.20B 6.34±1.08A 37.74±0.10B 0.60±0.00B
F value Years(Y) 4.42* 7.20* 1 243.64** 496.54** 61.16** 383.23** 37.79**
Cultivar(C) 16.99** 5.02* 1 081.09** 66.71** 22.53** 372.07** 0.07ns
Nitrogen(N) 429.36** 2.10ns 46.11** 32.49** 2.71ns 3.60* 38.38**
Y×C 16.24** 11.03** 2.15ns 6.50* 7.60** 0.10ns 31.50**
Y×N 27.77** 1.93ns 7.88** 5.94** 5.04** 6.72** 9.75**
C×N 123.64** 21.02** 37.03** 25.81** 23.24** 31.04** 20.88**
Y×C×N 63.60** 1.20ns 3.30* 2.56ns 1.78ns 2.37ns 7.83**

2.4 Nitrogen balance

N management,cultivar types,and their interaction had significant effects on inorganic N accumulation in different soil layers(Tab.6). Soil inorganic N accumulation in the 0-20 cm soil layer pre-topdressing and post-harvest of ZH311 were higher than those of XY508,while those in 20-80 cm soil layers of XY508 was higher than those of ZH311. In 2016,the soil inorganic N accumulation in the 0-40 cm soil layers pre-topdressing and post-harvest were higher than those of XY508,and those in 40-80 cm soil layers were lower than those of XY508. Soil inorganic N accumulation pre-topdressing and post-harvest in the topsoil(0-40 cm)and lower soil(40-80 cm)of ZH311 were higher and lower,respectively,than those in XY508.
Tab.6 Effects of N management on inorganic N accumulation in different soil layers kg/ha
Cultivar Nitrogen
management		 Pre-topdressing Post-harvest
0-20 cm 20-40 cm 40-60 cm 60-80 cm Total 0-20 cm 20-40 cm 40-60 cm 60-80 cm Total
2015
ZH311 B1 53.94±2.75g 42.41±1.21f 20.81±1.45h 16.42±2.57f 133.59±4.64f 43.30±0.46h 40.16±0.62e 23.59±0.66d 14.51±0.61f 121.55±1.46d
B2 132.98±1.64a 82.88±3.67b 46.16±1.77ab 39.89±1.73a 301.91±2.64a 91.94±1.51b 47.18±0.78d 35.35±1.06bc 31.18±1.02e 205.64±4.36c
B3 120.40±0.94b 63.62±2.03d 44.61±0.27b 35.83±0.75b 264.46±1.32c 82.90±0.37d 59.81±0.80b 45.51±3.56a 37.14±0.69d 225.36±2.33ab
B4 94.28±1.04d 65.54±2.41d 37.67±1.43d 25.73±1.23d 223.22±2.19d 94.85±2.30a 47.21±2.01d 38.10±0.09b 41.54±0.13bc 221.70±0.95b
B5 68.62±0.52f 56.44±2.61e 31.22±1.13f 19.96±1.31e 176.24±3.47e 78.42±0.24e 47.84±1.39cd 32.55±1.80c 52.39±1.74a 211.21±4.13c
Average 94.05±0.70A 62.18±0.55B 36.10±1.20B 27.57±0.27B 219.88±2.11A 78.28±0.75A 48.44±0.14B 35.02±0.75A 35.35±0.63B 199.09±1.43A
XY508 B1 49.14±1.54h 41.92±1.15f 24.82±2.01g 12.64±0.85g 128.52±3.05f 42.06±1.43h 41.39±0.57e 19.24±0.83e 11.76±1.98g 114.45±3.50d
B2 119.02±0.55b 87.16±3.47a 46.83±1.64a 41.04±1.07a 294.05±4.07b 81.57±1.51d 52.29±1.44c 42.83±1.16a 50.72±0.44a 227.41±2.39ab
B3 113.36±0.67c 77.93±0.83c 39.39±0.50d 33.92±0.90b 264.60±1.68c 85.21±1.11c 57.22±1.05b 36.63±0.33bc 42.39±0.59b 221.45±1.51b
B4 89.78±1.37e 61.90±1.30d 41.86±2.26c 29.68±2.90c 223.22±2.90d 67.97±0.60g 64.92±4.54a 37.07±1.47b 40.03±1.80c 210.00±4.56c
B5 55.50±0.16g 57.72±0.60e 34.89±0.82e 27.62±1.39cd 175.73±1.69e 75.16±0.30f 61.20±0.91ab 42.78±2.06a 50.91±0.32a 230.04±4.65a
Average 85.36±0.73B 65.32±0.65A 37.56±0.93A 28.98±0.31A 217.22±1.14B 70.39±0.18B 55.40±1.20A 35.71±0.86A 39.16±0.30A 200.67±0.44A
2016
ZH311 B1 64.26±1.94f 37.81±1.97fg 28.82±1.35e 21.28±1.51f 152.17±2.86g 50.28±0.74e 20.32±3.62d 19.55±1.66f 16.24±0.45e 106.38±2.44d
B2 122.80±2.92a 75.70±4.91a 46.48±2.12b 43.86±1.66bc 288.84±4.60a 67.25±1.88b 49.39±2.72b 25.52±1.66e 21.03±1.53d 163.19±3.77c
B3 105.33±4.24c 65.38±2.67b 41.45±3.13bc 36.85±3.38d 249.02±4.43c 77.51±1.86a 51.38±2.73ab 31.86±2.31c 27.64±2.44b 188.39±4.32a
B4 88.71±3.53d 51.25±1.54c 35.54±3.21d 27.43±0.99e 202.93±6.87de 68.16±2.47b 52.94±0.82ab 28.22±0.29d 32.32±2.23a 181.64±3.07ab
B5 64.51±1.94f 46.08±2.11d 37.42±1.48cd 22.56±0.80ef 170.56±3.18f 48.91±2.38e 53.02±1.95ab 32.99±1.92c 32.68±1.72a 167.60±4.06c
Average 89.12±1.59A 55.24±2.14A 37.95±0.61B 30.40±0.89B 212.70±2.27A 62.42±0.66A 45.41±1.02A 27.63±0.75B 25.98±0.76A 161.45±0.72A
XY508 B1 63.14±0.94f 35.82±1.18g 23.20±0.94e 27.83±2.26e 149.99±4.00g 47.98±1.22e 20.57±3.41d 15.73±1.12g 14.63±1.06e 98.91±4.32d
B2 112.00±1.06b 55.58±0.44c 53.72±3.32a 53.10±3.28a 274.40±4.56b 68.39±1.09b 45.39±1.36c 38.80±2.02b 23.69±0.82c 176.28±4.06b
B3 103.53±3.26c 42.87±2.39de 52.62±2.21a 45.72±1.18b 244.73±2.89c 62.41±0.53c 51.32±0.67ab 39.03±1.99b 23.50±0.62cd 176.26±3.51b
B4 89.93±0.97d 40.06±1.64efg 43.24±1.88b 38.85±3.99cd 212.08±4.39d 60.42±1.22c 45.59±1.29c 36.67±1.93b 33.87±1.88a 176.55±3.32b
B5 69.98±1.46e 42.78±5.09def 42.82±4.42bc 39.16±3.16cd 194.74±4.36e 56.20±0.44d 54.52±0.44a 44.86±0.45a 32.88±1.30a 188.46±0.96a
Average 87.72±0.25A 43.42±1.31B 43.12±1.48A 40.93±1.90A 215.19±1.65A 59.08±0.70B 43.48±0.77B 35.02±1.20A 25.71±0.64A 163.29±2.31A
F value Years(Y) 6.14* 479.21** 31.88** 130.58** 16.65** 1478.74** 136.68** 58.21** 1 105.68** 1 124.10**
Cultivar(C) 95.02** 43.40** 25.59** 85.33** 0.01ns 252.42** 15.45** 58.19** 26.62** 6.21*
Nitrogen(N) 2 328.73** 329.77** 155.79** 177.80** 2 192.35** 1 104.41** 200.55** 176.40** 751.07** 1 049.90**
Y×C 49.51** 129.05** 8.00** 49.71** 5.19* 41.41** 48.33** 40.03** 35.34** 0.63ns
Y×N 75.24** 14.78** 3.48* 1.46ns 45.69** 222.84** 29.02** 7.17** 134.48** 25.76**
C×N 13.36** 4.96** 3.01* 8.22** 11.86** 84.70** 6.48** 31.96** 48.05** 35.78**
Y×C×N 7.67** 26.23** 10.19** 0.24ns 6.19** 81.17** 14.16** 7.12** 32.26** 1.85ns
These results indicated that compared with XY508,ZH311 could better absorb and utilize nutrients in the soil low layers,maintain nutrients in the topsoil,reduce inorganic N deposition,and decrease the risk of N loss. The soil inorganic N accumulation pre-topdressing of both cultivars decreased significantly with increasing topdressing ratio in both years and was the highest under the B2 treatment in all soil layers. The soil inorganic N accumulation post-harvest of ZH311 under the B3 and B4 treatments was significantly higher than that in other treatments for both years,while that in XY508 was the highest under the B5 treatment in both years. These results showed that the differences between different maize cultivars regarding N uptake were mainly found in the post-topdressing period. These results suggested that balanced use of fertilizers during the growth period was beneficial for maintaining efficient N uptake levels in the N-efficient cultivar during the whole growth period,while a high topdressing ratio could improve N supply in the later growth period for N-inefficient cultivars.
Temperature and rainfall were important factors leading to N loss. High rainfall and temperatures in the late growth period of maize in Southwest Hilly Regions caused high N loss levels(Tab.7). Excluding the treatment with no N,the apparent N loss from the maize production system was 75.93-125.40 kg/ha,and the apparent N loss rate reached 16.40%-27.08%. Considering the cultivars,the total N output of ZH311 was significantly(P<0.01)higher than that of XY508 in both years,by 7.21% and 8.70% in 2015 and 2016,respectively. The low total N output led to the apparent N loss and loss rate of XY508 being significantly(P<0.01)higher than that of ZH311,by 32.10% and 5.95 percentage points in 2015 and 40.05% and 7.16 percentage points in 2016,respectively. Compared with that of N-inefficient cultivar,the total N output increased in the N-efficient cultivar by efficient N absorption,thereby effectively decreasing the apparent N losses and loss rate of the maize production system and reducing the risk of environmental pollution caused by N application.
Tab.7 Nitrogen balance in soil-maize systems subjected to different treatments
Cultivar Nitrogen
management		 Nitrogen input/ (kg/ha) Nitrogen output /(kg/ha) Apparent N loss
/ (kg/ha)		 Apparent N loss
efficiency /%
Nmin before
sowing		 Nitrogen
fertilizer		 Apparent
Nmin		 Total
input		 Crop N
uptake		 Residual Nmin
after harvest		 Total
output
2015
ZH311 B1 160.12 0 79.93 240.05 118.50±2.71f 121.55±1.46d 240.05±2.89f 0.00±2.89g 0.00±1.20f
B2 160.12 225 79.93 465.05 169.91±5.01a 205.64±4.36c 375.55±5.26ab 89.50±5.26de 19.25±1.13d
B3 160.12 225 79.93 465.05 148.30±3.14c 225.36±2.33ab 373.66±2.75b 91.39±2.75d 19.65±0.59d
B4 160.12 225 79.93 465.05 160.44±3.18b 221.70±0.95b 382.14±4.08a 82.91±4.08e 17.83±0.88d
B5 160.12 225 79.93 465.05 162.57±3.30b 211.21±5.13c 373.78±5.79b 91.28±5.79d 19.63±1.24d
Average 160.12 180 79.93 420.05 151.94±2.01A 199.09±1.43A 349.03±1.57A 71.02±1.57B 15.27±0.22B
XY508 B1 160.12 0 79.93 240.05 96.40±3.26g 114.45±3.50d 210.86±5.16g 25.86±1.80f 10.77±0.75e
B2 160.12 225 79.93 465.05 129.46±2.89e 227.41±2.39ab 356.87±4.44d 108.18±4.44b 23.26±0.96bc
B3 160.12 225 79.93 465.05 133.86±2.46de 221.45±1.51b 355.31±3.59d 109.74±3.59b 23.60±0.77b
B4 160.12 225 79.93 465.05 129.69±2.97e 210.00±6.56c 339.68±4.61e 125.37±4.61a 26.96±0.99a
B5 160.12 225 79.93 465.05 135.06±0.86d 230.04±6.65a 365.10±6.96c 99.95±6.96c 21.49±1.50c
Average 160.12 180 79.93 420.05 124.90±1.91B 200.67±0.44A 325.57±1.51B 93.82±1.42A 21.22±0.26A
2016
ZH311 B1 214.61 0 23.40 238.01 131.64±1.89g 106.38±2.44d 238.01±4.32f 0.00±4.32g 0.00±1.82h
B2 214.61 225 23.40 463.01 216.10±4.76a 163.19±4.77c 379.30±11.46ab 83.72±11.46de 18.08±2.47ef
B3 214.61 225 23.40 463.01 183.25±3.07d 188.39±4.32a 371.64±3.19bc 91.38±3.19cd 19.74±0.69de
B4 214.61 225 23.40 463.01 205.45±3.21b 181.64±3.07ab 387.09±3.76a 75.93±3.76e 16.40±0.81f
B5 214.61 225 23.40 463.01 198.26±1.88c 167.60±4.06c 365.86±8.46c 97.16±8.46c 20.98±1.83d
Average 214.61 180 23.40 418.01 186.94±1.43A 161.45±0.72A 348.38±1.68A 69.64±1.68A 15.04±0.53B
XY508 B1 214.61 0 23.40 238.01 111.33±3.39h 98.91±5.32d 210.24±6.69g 27.78±6.69f 11.67±2.81g
B2 214.61 225 23.40 463.01 175.06±2.32e 176.28±4.06b 351.34±6.22d 111.68±6.22b 24.12±1.34bc
B3 214.61 225 23.40 463.01 165.08±1.25f 176.26±3.51b 341.34±4.10de 121.68±4.10ab 26.28±0.89ab
B4 214.61 225 23.40 463.01 161.07±1.43f 176.55±3.32b 337.61±3.86e 125.40±3.86a 27.08±0.83a
B5 214.61 225 23.40 463.01 173.44±0.70e 188.46±0.96a 361.90±0.27c 101.11±0.27c 21.84±0.06cd
Average 214.61 180 23.40 418.01 157.19±1.27B 163.29±2.31A 320.49±3.34B 97.53±3.34B 22.20±0.96A
F value Years(Y) - - - - 2 183.88** 1 124.10** 4.34* 0.76ns 1.23ns
Cultivar(C) - - - - 1 555.40** 6.21* 348.21** 358.88** 377.07**
Nitrogen(N) - - - - 847.35** 1 049.90** 1 631.36** 679.24** 363.18**
Y×C - - - - 3.51ns 0.63ns 2.58ns 3.62ns 3.23ns
Y×N - - - - 54.73** 25.76** 1.54ns 1.55ns 1.13ns
C×N - - - - 42.41** 35.78** 21.17** 22.20** 28.15**
Y×C×N - - - - 4.20** 1.85ns 1.35ns 1.22ns 0.85ns
N management had a significant(P<0.01)effect on N total input,total output,apparent N losses,and loss rate in the maize production system(Tab.7). ZH311 exhibited the highest total N output under the B4 treatment in both years,which resulted in the lowest apparent N losses and loss rate under the B4 treatment for both years. Meanwhile,XY508 had the highest total N output,and the lowest apparent N losses and loss rate under the B5 treatment for both years. The differences in apparent N losses between the two cultivars initially increased and then decreased with increasing N topdressing ratio and were the largest under the B4 treatment in both years,with those of XY508 being 42.46,49.47 kg/ha higher than those of ZH311 in 2015 and 2016,respectively. Balanced application of N fertilizer during the growth period could promote N uptake and maintain higher post-harvest soil N nutrition of N-efficient cultivars. This led to a significant decrease in apparent N losses compared to that in the other treatment,while a high topdressing ratio could increase soil inorganic N accumulation and improve N uptake in the N-inefficient cultivar,leading to the lowest apparent N losses in all treatments.
The apparent N losses post-topdressing were higher than those pre-topdressing by 190.57% and 92.13% in 2015 and 2016,respectively(Fig.2),indicating that maize apparent N losses mainly occurred in the middle and late growth periods. Pre-topdressing and post-topdressing apparent N losses of XY508 were higher than those of ZH311 by 8.89,22.80 kg/ha in 2015,and 17.21,27.89 kg/ha in 2016,respectively. Pre-topdressing apparent N losses of the two cultivars exhibited the same trend,decreasing with increasing topdressing ratio,and those of the B2 treatment were the highest in both years.
There was a significant interaction between the effect of N management and cultivar on post-topdressing N losses. The post-topdressing apparent N losses of ZH311 were lower than those of XY508,and increased with increasing of topdressing ratio,being the highest under the B5 treatment. Contrastingly,those of XY508 first increased and then decreased with increasing topdressing ratio,being the highest under the B4 treatment. This showed that the higher N uptake ability of ZH311 compared to that of XY508 could effectively control the post-topdressing apparent N losses,while higher topdressing ratios promoted the N uptake of XY508 in the late growth stage,alleviating the post-topdressing apparent N losses.
Fig.2 Effects of N management on apparent N loss pre-topdressing and post-topdressing
Data are mean ±s of three replicate pots. Values with different lowercase letters are significantly different at P<0.05.

Full size|PPT slide

3 Discussion and Conclusions

N accumulation of maize is closely related to soil basic fertility,meteorological factors,and cultivation management. Higher soil basic fertility and suitable rainfall made the N accumulation in 2016 significantly higher than that in 2015. Results showed that the N accumulation in the different stages of ZH311 was higher than that of XY508,and that the advantages of ZH311 were particularly evident in post-silking. Similar to the results of Li et al[17] using Xianyu 335 and Nongda 108,obtaining N-efficient cultivars could maintain the proportion of N in vegetative organs during the late growth stage to delay leaf senescence and improve N accumulation. Under high base fertilizer ratio(100% base fertilizer),the N accumulation and dry matter accumulation were higher than with other management types. Meanwhile,taking together the results of both years,the highest yield of ZH311 was under the B4 treatment(50% base fertilizer + 50% topdressing ratio)and that of XY508 was under the B5 treatment(75% base fertilizer + 25% topdressing ratio). This showed that although high base fertilizer ratio could significantly improve N accumulation and dry matter production of maize,this could not be translated into yield advantage,which may be caused by excessive vegetative growth in the early stage,affecting the transformation to reproductive growth,and ultimately grain yield. The effect on the N-efficient cultivar was more evident than that on the N-inefficient cultivar. Therefore,the amount of N fertilizer should be controlled in the early growth stage for N-efficient maize cultivars.
In addition to increasing grain yield and ammonia volatilization loss,the soil residual inorganic N content can directly reflect whether the application of N fertilizer is reasonable. Previous studies have shown that N application could significantly increase the inorganic N content in the topsoil of agricultural land post-harvest,while higher residual inorganic N increases soil N supply capacity and the underground migration of N to groundwater pollution[27-28]. These results indicated that high base fertilizer significantly increased the soil inorganic N accumulation of maize pre-topdressing,while the soil inorganic N accumulation post-harvest was greatly affected by cultivar type. The soil inorganic N accumulation post-harvest of ZH311 was the highest under the B3 and B4 treatments,while that of XY508 was the highest under the B5 treatment for both years. Regarding soil layer,the soil inorganic N accumulation in the 0-40 cm soil layer pre-topdressing and post-harvest of ZH311 was significantly higher than that of XY508,while that in the 40-80 cm soil layer of XY508 was obviously higher than that of ZH311. This indicated that the root system of ZH311 could absorb and utilize 40-80 cm soil inorganic N more efficiently,and could not only maintain higher soil nutrients in the topsoil layer,but also decrease the N deposition and reduce the risk of environmental pollution compared to that of XY508.
Increasing grain yield while improving the absorption and utilization efficiency of N fertilizer is an important goal for reducing environmental pollution and improving the sustainability of agricultural development[23]. Li et al[29] showed that the N-efficient maize cultivar fully absorbed and utilized N,and had NRE,NAE,and NPFP higher than those of the N-inefficient cultivar. Our results showed that the NAG and CNAG of ZH311 were evidently higher than those of XY508,which led to the NUE,NRE,NAE,and NPFP of ZH311 being significantly higher than those of XY508,while XY508 had higher NRR and CNRA that led to the NHI of XY508 being higher than that of ZH311 in both years. The difference of NUE(1 081.09**)between the two cultivars was significantly higher than the other indicators in both years,indicating that the N efficiency of ZH311 compared to that of the N-inefficient cultivar XY508 was mainly reflected in nitrogen uptake.
Reasonable N application is one of the important ways to improve N absorption and utilization efficiency of crops[8-9]. The higher N accumulation of ZH311 under the B2 treatment made the NUE and NRE of B2 higher than those of other treatments. Moreover,ZH311 grain yield under the B4 treatment led NAE and NPFP under this treatment to be the highest in both years. XY508 had higher N accumulation and grain yield both B2 and B5,which led to N absorption and utilization of B2 and B5 being higher in both years. These results indicated that balanced fertilization during the growth period(50% base fertilizer + 50% topdressing ratio)of N-efficient cultivar ZH311 could not only maintain high N absorption and utilization efficiency,but also obtained the highest grain yield. Moreover,both high base fertilizer ratio(100% base fertilizer)and high topdressing ratio(75% base fertilizer + 25% topdressing ratio)could improve grain yield and N absorption and utilization efficiency of N-inefficient cultivar XY508.
N balance requires the quantification of total N input(soil inorganic N,mineralized N,N fertilizer and other N)and total N output(plant N accumulation,N loss,and soil inorganic N)throughout the growth period. This is widely used to evaluate the sustainability and efficiency of N management,and the ability to maintain soil fertility in agricultural production systems. Compared with that of the N-inefficient cultivar XY508,the total N output of the N-efficient cultivar ZH311 significantly increased through high crop N uptake,thereby significantly reducing the apparent N losses,which decreased by 24.30% and 28.60% in 2015 and 2016,respectively. On average,the apparent N loss of ZH311 increased by 70.62,56.69 kg in 2015 and 2016,respectively,for each additional ton of maize grain,while that of XY508 increased by 100.64,61.12 kg,respectively. These results showed that the N-efficient maize cultivar could more effectively reduce apparent N losses compared to the N-inefficient cultivar,and that the N lost to the environment during the production of equivalent grain yield was significantly lower for the N-efficient than for the N-inefficient cultivar. Therefore,the popularization and planting of N-efficient cultivars could be of great significance for the environmental sustainability of maize production.
A large amount of N fertilizer input increased the chance of N loss in the early stage of fertilization. Results showed that the apparent N loss post-topdressing was significantly higher than that pre-topdressing,and that the differences between the two cultivars in apparent N loss post-topdressing were significantly higher than those pre-topdressing. This was caused by the topdressing of maize in the hilly area of Sichuan meeting the high-temperature and high-rainfall period causing N loss,while the efficient N absorption by N-efficient cultivars could effectively reduce apparent N loss,especially during the early period of topdressing. This result was consistent with those of Chen et al[3],i.e.,compared to N-inefficient cultivars,N-efficient cultivar can significantly reduce apparent N losses by reducing ammonia volatilization,N2O emissions,N leaching and runoff,and the differences between two types cultivar in apparent N losses mainly appear post-topdressing.
High N proportion in the vegetative organs of N-efficient cultivar ZH311 led to a significantly higher level of N accumulation in each stage than that of the N-inefficient cultivar XY508. Moreover,the N accumulation advantage of ZH311 was higher after silking. The high post-silking N accumulation of ZH311 reduced the pre-silking N transport that determines N transport and contribution rates to grain of pre-silking N accumulation,which were significantly lower than those of XY508,while the ZH311 NUE,NRE,and NPFP were significantly higher than those of XY508. The root system of N-efficient cultivar ZH311 can more effectively absorb and utilize inorganic N in the 40-80 cm soil layer,reduce N deposition,and significantly decrease apparent N losses compared to the N-inefficient cultivar XY508. The differences between the apparent N losses of the two cultivars mainly occurred post-topdressing. In summary,compared to the N-inefficient cultivar XY508,the N-efficient cultivar ZH311 could not only increase the yield per unit area,but also reduce N losses,consequently reducing environmental risks. A substrate of 50% base fertilizer+50% topdressing was optimal for realizing the potential of this cultivar. Meanwhile,using 25% base fertilizer+75% topdressing treatment,N-inefficient cultivar XY508 could have similar effects on yield and N loss to those of ZH311.

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