Yankai HUANG, Lixia SHEN, Ting LI

College of Water Conservancy and Engineering, Taiyuan University of Technology, Taiyuan 030024, China

Nitrogen is an important nutrient for growth and development of maize. Particularly, it plays a key role in grain development of maize at the grain filling stage. The properties of genes[1-3]and demand for nitrogen are different among maize varieties with different nitrogen efficiencies.Li et al.[4-7]studied the differences in grain filling characteristics among different maize varieties under the same nitrogen application treatment.However, there are rare reports on the differences in grain development among different varieties under different nitrogen application levels. The application time and amount of nitrogen fertilizer have a significant impact on crop yield and nitrogen utilization rate[8-10]. This study aimed to compare the differences in grain filling characteristics among different maize varieties and to discuss the effect of nitrogen fertilizer on grain development of maize varieties with different nitrogen efficiencies, based on the determination of sensitivities of different maize varieties to nitrogen fertilizer.Thus the nitrogen utilization rate will be further improved, and the yield potential of maize will be tapped, thereby providing a scientific basis for reasonable application of nitrogen fertilizer and variety breeding with high nitrogen efficiency.

Materials and Methods

Test time and site

The test was carried out in the Integrated and Efficient Water-saving Agriculture Technology Research and Demonstration Area located in Hecun Village, Lingjingdian Town, Yangqu County, Shanxi Province during April to October,2013.The test site is located in the typical semi-arid region with continental monsoon climate, annual average precipitation of 434.7 mm,average annual evaporation of 328.9 mm and annual average temperature of 6.86 ℃.

Materials

Tested varieties According to years of tests, the varietal characteristics of Tunyu 99 (TY), Luyu 19 (LY) and Xianyu 335 (XY) are high nitrogen and high efficiency(yield is low when nitrogen fertilizer is not applied, but is increased significantly after nitrogen fertilizer is applied),low nitrogen and high efficiency (yield is high when nitrogen fertilizer is not applied, but changed insignificantly after nitrogen fertilizer is applied)and double high (yield is high when nitrogen fertilizer is not applied,and increased after nitrogen fertilizer is applied).

Tested soil The top 0-20 cm soil had organic matter of 7.66 g/kg, total nitrogen of 0.67 g/kg, hydrolyzable nitrogen of 53.33 g/kg, available phosphorus of 4.68 mg/kg and rapidly available potassium of 81.67 mg/kg.

The top 20-40 cm soil had organic matter of 7.81 g/kg, total nitrogen of 0.64 g/kg,hydrolyzable nitrogen of 60.5 g/kg, available phosphorus of 3.98 mg/kg and rapidly available potassium of 85 mg/kg.

Methods

Test design The two-factor (nitrogen application level and maize variety) randomized block design was adopted, and there were three replicates for each treatment. A total of three nitrogen application levels were arranged, including pure nitrogen of 0(N0),140 (N1)and 210 (N2)kg/hm2.Before the sowing, nitrogen fertilizer was not applied, and the phosphorus and potassium fertilization was same with that of general fields. For N1 and N2 treatments, additional 140 kg/hm2of pure nitrogen were applied at the jointing stage; for N2 treatment, additional 70 kg/hm2of pure nitrogen were applied at the big trumpet period. The plot area was 36 m2. The optimum planting density was adopted for each maize cultivar. There were total 10 rows in each plot with row spacing of 60 cm.The planting densities of Tunyu 99, Luyu 19 and Xianyu 335 were 54 000,57 000 and 60 000 plants/hm2,respectively.

Determination of indicators and methods Before the silking in maize,a total of 60-70 representative maize plants with robust and uniform growth were selected and labeled in each plot.During the 5thto 45thd since pollination,total 5 representative labeled maize plants were selected once (5th-25thd,once every 5 days; 25th-45thd, once every 7 days) from each plot, and the grains in the upper and middle-lower parts of the spikes were sampled. The top 3rdto 13thcircles of grains were sampled as upper-part sample, and the 13thto 33rdcircles of grains were sampled as middle-lower-part sample.

The upper- and middle-lower-part grains were mixed respectively and then sampled randomly.The 100-grain fresh weight of each sample was first weighed; and then, the grains were dried at 105 ℃for 15-20 min and subsequently at 80 ℃to constant weight,and till then, the 100-grain dry weight of each sample was weighed.

Statistics and analysis The data processing and statistics and graphing were performed using Microsoft Excel.

Results and Analysis

Variation of fresh weight of upperand middle-lower-part grains in maize under different nitrogen application levels

As shown in Fig.1, the fresh weights of upper- and middle-lowerpart grains of Tunyu 99, Luyu 19 and Xianyu 335 were all trended to be increased with the proceeding of observation. In overall, the fresh weight of middle-lower grains was larger than that of upper grains, and the fresh weight of nitrogen application treatment was larger than that of nitrogen free treatment.Among the three nitrogen application levels, the grain fresh weight of Tunyu ranked as N2 ＞N1 ＞N0; the grain fresh weight of Luyu 19 ranked as N1 ＞N2 ＞N0; the fresh weight of Xianyu 335 ranked as nitrogen application treatments ＞nitrogen free treatment, and there was no significant difference between N1 and N2.

Variation of fresh weight difference of upper-, middle- and lower-part grains in maize between nitrogen application treatment and nitrogenfree treatment

The grain fresh weight differences of Tunyu 99, Luyu 19 and Xianyu 335 between N1,N2 and N0 treatments on the 15th, 20th, 25th, 32ndand 39thd since the pollination were calculated. Then the curves of fresh weight difference of upper- and middle-lower-part grains in maize were obtained (Fig.2, Fig.3).The fresh (dry)weight difference percentage referred to the percentage between grain fresh (dry) weight increment of each nitrogen application treatment and grain fresh weight of nitrogen free treatment(Table1,Table2).

Fresh(dry)weight difference percentage = [(Fresh weight of nitrogen application treatment-Fresh weight of nitrogen free treatment)×100%]/Fresh weight of nitrogen free treatment.

Within 5thto 15thd since the pollination,the grain fresh (dry)weight differed insignificantly among different treatments, so the differences in grain fresh (dry)weight during that duration was not discussed.

As shown in Fig.2, the grain fresh weight difference was all increased first and then decreased as time went by.It was indicated that the grain fresh weight difference was more significant at grain filling and maturity stages, but was insignificant in late period.

Between the N2 and N0 treatments, the grain fresh weight difference of Tunyu 99 was largest on the 32ndd (8.08 g), and the fresh weight difference percentage was largest on the 25thd (47.8%); on the 39thd, the grain fresh weight difference was 6.3 g(27.4%).Between the N1 and N0 treatments, the largest fresh weight difference of Luyu 19 was 7.74 g, and the largest fresh weight difference percentage was 51.9%; on the 39thd, the difference was 3.28 g (13.3%). Between N1 and N0 treatments, the largest fresh weight difference of Xianyu 335 was 4.1 g with largest freshweight percentage of 34.7%, and the difference was 2.02 g (6.9%) on the 39th d; between N2 and N0 treatments, the largest fresh weight difference of Xianyu 335 was 4.48 g with largest fresh weight percentage of 37.9%, and on the 39th d, the difference was 1.34 g (4.7%). The variation of fresh weight difference was not completely in line with the variation of fresh weight difference percentage(Table 1, Fig.2). On the 39thd, the grain fresh weight difference of Tunyu 99 between N2 and N0 treatments was largest(6.3 g,27.4%),followed by that of Luyu 19 between N1 and N0 treatments.The grain fresh weight differences of Xianyu 335 between N1 and N0 (2.02 g, 6.9%), N2 and N0(1.34 g, 4.7%) treatments were most unobvious.

In the comparison between N1 and N2 treatments, the largest fresh weight difference and fresh weight difference percentage of Tunyu 99 were 4.36 g and 31.28%, respectively, and on the 39thd,the difference was 3.16 g with difference percentage of 13.74%;the largest fresh weight difference and fresh weight difference percentage of Luyu 19 were 3.1 g and 27.39%, respectively, and on the 39th d, the difference was 2.0 g with difference percentage of 8.09%; the largest fresh weight difference and fresh weight difference percentage of Xianyu 335 were 0.38 g and 3.74%, respectively,and on the 39th d, the difference was-0.68 g with difference percentage of-2.32%. It suggested that the difference of Tunyu 99 was most significant,followed by that of Luyu 19, and the difference of Xianyu 335 was most insignificant.

Table 1 Percentage values of grain fresh weight differences of maize %

Table 2 Percentage values of grain dry weight differences of maize %

Fig.3 showed the variation of fresh weight difference of middle-lower-part grains in maize. The largest fresh weight difference and fresh weight difference percentage of Tunyu 99 between N2 and N0 treatments were 6.56 g and 38.6%, respectively,and on the 39th d, the fresh weight difference was 4.18 g with difference percentage of 11.3% . The largest fresh weight difference and fresh weight difference percentage of Luyu 19 between N1 and N0 treatments were 6.24 g and 27.2%, respectively,and on the 39thd,the fresh weight difference was 2.0 g with difference percentage of 5.9% . The largest freshweight difference and fresh weight difference percentage of Xianyu 335 between N1 and N0 treatments were 4.2 g and 16%, respectively, and on the 39th d,the fresh weight difference was 0.62 g with difference percentage of 1.4%; the largest fresh weight difference and fresh weight difference percentage of Xianyu 335 between N2 and N0 treatments were 4.68 g and 17.3%, respectively, and on the 39th d,the fresh weight difference was 1.34 g with difference percentage of 2.4%.As shown in Table 2 and Fig.3, on the 39th d, the grain fresh weight difference of Tunyu 99 between N2 and N0 treatments was most significant (4.18 g, 11.3%), followed by that of Luyu 19 between N1 and N0 (2 g, 5.9%); and the grain fresh weight differences of Xianyu 335 between N1 and N0 treatments(0.62 g,1.4%),N2 and N0 treatments (1.34 g, 2.4%) were most insignificant.

In the comparison between N1 and N2, the largest grain fresh weight difference and fresh weight difference percentage of Tunyu 99 were 2.86 g and 16.82% respectively, and on the 39th d, the difference reached 2.18 g with difference percentage of 5.89%;for Luyu 19, the largest grain fresh weight difference and grain fresh weight difference percentage were 2.72 g and 13.7%respectively,and on the 39th d, the difference and difference percentage were 0.5 g and 1.47%; the largest grain fresh weight difference and grain fresh weight difference percentage of Xianyu 335 between N1 and N2 treatments were 0.48 g and 1.28%, and on the 39th d,the difference and difference percentage were 0.42 g and 0.96%. Therefore, the difference advantage of Luyu 19 (5.89%) was most obvious, followed by that of Tunyu 99 (1.47%),and the difference of Xianyu 335 was most insignificant(0.96%).

Based on the above analysis, in the comparison between nitrogen application treatments and nitrogen free treatment,theupper-part (6.3g,27.4%)and middle-lower-part (4.18 g, 11.3%)grain fresh weight differences of Tunyu 99 between N2 and N0 treatments were largest; the upper-part (3.28 g,13.3% ) and middle-lower-part grain fresh weight differences of Luyu 19 between N1 and N0 treatments ranked second; the upper-part and middlelower-part grain fresh weight differences of Xianyu 335 between N1 and N0 treatments (2.02 g, 6.9%; 0.62 g,1.4%)and N2 and N0 treatments(1.34 g, 4.7%; 1.34 g, 2.4%) were smallest.In the comparison between nitrogen application treatments (N1 and N2),the difference advantages of Tunyu 99 in the upper-(3.16 g,13.74%)and middle-lower (2.18 g, 5.89%) parts were most obvious, followed by those of Luyu 19 in the upper-(2 g, 8.09%) and middle-lower(0.5 g,1.47%)parts;and the difference advantages of Xianyu 335 in the upper (-0.68 g, -2.32%)and middle-lower(0.42 g,0.96%)parts were the most unobvious.

Variation of dry weight of upper-,middle- and lower-part grains in maize under different nitrogen application levels

The upper- and middle-lower-part grain dry weights of Tunyu 99,Luyu 19 and Xianyu 335 were all trended to be increased with the proceeding of test 5040 d after the pollination (Fig.4).Considering the grain dry weight, the nitrogen application treatments ＞nitrogen free treatments; for Tunyu 99,N2＞N1＞N0; for Luyu 19, N1＞N2＞N0;for Xianyu 335, nitrogen application treatments ＞nitrogen free treatments,but there was no significant difference between N1 and N2 treatments. The grain dry weight in the middle-lower part was significantly higher than that in the same-period upper part, indicating that the development of middlelower-part grains inhibited the development of upper-part grains.

Variation of dry weight difference of upper-, middle- and lower-part grains in maize between nitrogen application treatment and nitrogenfree treatment

Based on the grain dry weight dif-ferences of Tunyu 99,Luyu 19 and Xianyu 335 between N2 and N0 and N1 and N0 treatments on day 15, 20, 25,32 and 39, the dry weight difference curves of upper-and middle-lower-part grains were drawn(Fig.5,Fig.6).

As shown in Fig.5, the grain dry weight differences of the three maize varieties were all trended to be increased with the proceeding of test,indicating that the grain dry weights at various stages from grain filling to maturity in the nitrogen application treatments were all higher than those in the nitrogen free treatments.

The largest grain dry weight difference and grain dry weight difference percentage of Tunyu 99 between N2 and N0 treatments were 4.33 g and 61.5%;the largest grain dry weight difference and grain dry weight difference percentage of Luyu 19 between N1 and N0 treatments were 4.67 g and 66.7%;the largest grain dry weight difference and grain dry weight difference percentage of Xianyu 335 between N1 and N0 treatments were 2.07 g and 28.9%, and between N2 and N0 treatments were 2.1 g and 38.7%.On day 39,the grain dry weight difference of Luyu 19 between N1 and N0 treatments was largest [4.67 g(42%)], followed by that of Tunyu 99 between N2 and N0 treatments[4.33 g(38%)],and the grain dry weight differences of Xianyu 335 between N1 and N0 treatments[2.07 g(14.6%)]and N2 and N0 treatments [2.1 g (14.8%)]were smallest.

In the comparison between N1 and N2 treatments, the largest grain dry weight difference and grain dry weight difference percentage of Tunyu 99 were 1.48 g and 21.5%;the largest grain dry weight difference and grain dry weight difference percentage of Luyu 19 were 1.59 g and 60.8%, and on day 39, its weight difference and difference percentage were 1.59 g and 14.3% ; for Xianyu 335, the largest grain dry weight difference and grain dry weight difference percentage were 0.36 g and 23.2%, and on day 39, the weight difference and difference percentage were 0.03 g and 0.2%.Therefore, the difference of Luyu 19 was most obvious,followed by that of Tunyu 99, and the difference of Xianyu 335 was most unobvious.

Fig.6 showed the variation of grain dry weight differences of the three maize varieties between nitrogen application treatments and nitrogen free treatment throughout the test period. The largest grain dry weight difference and grain dry weight difference percentage of Tunyu 99 between N2 and N0 treatments were 3.22 g and 24.7%, and on day 39, the grain dry weight difference and difference percentage were 2.28 g and 12%; the largest grain dry weight difference and grain dry weight difference percentage of Luyu 19 between N1 and N0 treatments were 3.06 g and 47.2%,and on day 39,the grain dry weight difference and difference percentage were 2.49 g and 13%; the largest grain dry weight difference and grain dry weight difference percentage of Xianyu 335 between N1 and N0 treatments were 1.9 g and 25%, and between N2 and N0 treatments were 2.28 g and 30.2%.The grain dry weight difference of Luyu 19 between N1 and N0 treatments(2.49 g,13%)was largest,followed by that of Tunyu 99 between N2 and N0 treatments (2.28 g, 12%), and the differences of Xianyu 335 between N1 and N0 treatments (1.9 g, 8.6%) and N2 and N0 treatments(2.28 g,10.4%)were smallest.Compared with the upper-part grain dry weight differences,the middle-lower-part grain dry weight differences between nitrogen application treatments and nitrogen free treatment were smaller, which was due to adequate nutrients, high moisture content and hard abortion in middle-lower-part grains.

In the comparison between N1 and N2 treatments, the largest grain dry weight difference and grain dry weight difference percentage of Tunyu 99 were 1.22 g and 16.9%,and on day 39, the difference and difference percentage were 0.76 g and 4% ; the largest grain dry weight difference and grain dry weight difference percentage of Luyu 19 were 1.96 g and 30.2%,and on day 39, the difference and difference percentage were 1.34 g and 7%;the largest grain dry weight difference and grain dry weight difference percentage of Xianyu 335 were 0.66 g and 6.8%, and on day 39, the difference and difference percentage were 0.38 g and 1.8%. So the difference advantage of Luyu 19 was most obvious(7%),followed by that of Tunyu 99(4%), and the difference advantage of Xianyu 335 was most unobvious(1.8%).

Based on the above analysis, in the comparison between nitrogen application treatments and nitrogen free treatment, the upper-part (4.67 g,42%) and middle-lower-part (2.49 g,13%) grain dry weight differences of Luyu 19 between N1 and N0 treatments were largest; the upper-part(4.33 g, 38%) and middle-lower-part(2.28 g, 12%) grain dry weight differences of Tunyu 99 between N2 and N0 treatments ranked second;the upper-part and middle-lower-part grain dry weight differences of Xianyu 335 between N1 and N0 treatments (2.07 g,14.6%;1.9 g,8.6%)and N2 and N0 treatments (2.1 g, 14.8% ; 2.28 g,10.4%)were smallest.In the comparison between nitrogen application treatments(N1 and N2),the difference advantages of Luyu 19 in the upper(1.59 g, 14.3%) and middle-lower (1.34 g,7%)parts were most obvious,followed by those of Tunyu 99 in the upper(1.48 g, 13%) and middle-lower (0.76 g, 4%) parts; the difference advantages of Xianyu 335 in the upper(0.03 g, 0.2%) and middle-lower (0.38 g,1.8%)parts were the most unobvious.

Discussion

Grain filling is an extremely important stage for growth and development of maize. Maize yield is greatly affected by dry matter accumulation amount at the grain filling stage[11].Grain filling rate is affected combinedly by genotype and environmental conditions[12]. Grain filling duration and grain filling rate determine the dry matter accumulation amount in maize at the grain filling stage[13]. Li et al.[14]found that grain filling rate and dehydrating rate differed significantly among different varieties and filling stages. For the same variety, maize grains were increased significantly in the nitrogen application treatment compared with those in the nitrogen free treatment at all the filling stages[15]. Within a certain range, different nitrogen application amounts all could significantly improve maize yield and nutrient content[16-18].Different moisture contents inharvested maize grains were caused by different moisture contents in maize grains at the physiological maturity stage and different dehydrating rates in maize grains after the physiological maturity stage[19]. At the harvesting stage, too high moisture content in maize grains was detrimental to maize seed quality and commercial quality[20],resulting in reduced germination rate and easy mildewing during the storage and transportation of maize seeds[21].The selection of regional optimum varieties, optimum planting density, optimum fertilization amount and appropriate harvesting period all could reduce moisture content in maize grains[22].The maize grain fresh weight difference is composed of grain dry weight difference and moisture content difference. The grain fresh weight difference and grain dry weight difference of Tunyu 99 between N2 and N0 treatments were 6.3 and 4.33 g in the upper part and 4.18 and 2.28 g in the middle-lower part; the grain fresh weight difference and grain dry weight difference of Luyu 19 between N1 and N0 treatments were 3.28 and 4.67 g in the upper part and 2 and 2.49 g in the middle-lower part; the grain fresh weight difference and grain dry weight difference of Xianyu 335 between N1 and N0 treatments were 2.02 and 2.07 g in the upper part and 0.62 and 1.9 g in the middle-lower part, and between N2 and N0 treatments were 1.34 and 2.1 g in the upper part and 1.34 and 2.28 g in the middle-lower part. For each maize variety, the weight differences of maize grains in the upper part were all greater than those in the middle-lower part,indicating that the maize grains in the upper part had greater filling potential and fertilization could reduce the risk of abortion. The grain fresh weight difference of Tunyu 99 was greater than its grain dry weight difference,indicating that the grain moisture content in the nitrogen application treatment was higher than that in the nitrogen free treatment,which affected the storage the maize grains during the harvesting period. The grain fresh weight difference of Luyu 19 was smaller than its dry weight difference,indicating that the maize grains in the nitrogen application treatment were fuller and contained lower moisture content than those in the nitrogen free treatment and nitrogen application had obvious dehydrating effect on maize grains. The grain fresh weight difference of Xianyu 335 was smaller than its grain dry weight difference, but the dehydrating effect of nitrogen application on Xianyu 335 was weaker than that on Luyu 19.

Conclusions

As a representative of low-nitrogen and high-efficiency maize, Luyu 19 showed most obvious development advantage under low nitrogen level(140 kg/hm2); the grains of Luyu 19 contained higher content of dry matter;the dehydrating effect of nitrogen application was greater in Luyu 19 at the maturity stage.Tunyu 99 is high-nitrogen and high-efficiency maize. Under high nitrogen level (210 kg/hm2), the development advantage of Tunyu 99 ranked second; although the grain fresh weight difference was largest,the moisture content in maize grains of Tunyu 99 was higher. The difference advantage of Xianyu 335, as double high maize, was most unobvious; the nitrogen application promoted the accumulation of dry matter in maize grains of Xianyu 335,but its dehydrating effect on Xianyu 335 was weaker than that on Luyu 19.

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