Straw return and appropriate tillage method improve grain yield and nitrogen efficiency of winter wheat

Journal of Integrative Agriculture 2017, 16(8): 1708–1719 Available online at www.sciencedirect.com

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RESEARCH ARTICLE

Straw return and appropriate tillage method improve grain yield and nitrogen efficiency of winter wheat CHEN Jin*, ZHENG Meng-jing*, PANG Dang-wei, YIN Yan-ping, HAN Ming-ming, LI Yan-xia, LUO Yongli, XU Xu, LI Yong, WANG Zhen-lin Agronomy College, Shandong Agricultural University/State Key Laboratory of Crop Biology, Ministry of Science and Technology, Tai’an 271018, P.R.China

Abstract Straw return is an important management tool for tackling and promoting soil nutrient conservation and improving crop yield in Huang-Huai-Hai Plain, China. Although the incorporation of maize straw with deep plowing and rotary tillage practices are widespread in the region, only few studies have focused on rotation tillage. To determine the effects of maize straw return on the nitrogen (N) efficiency and grain yield of winter wheat (Triticum aestivum L.), we conducted experiments in this region for 3 years. Five treatments were tested: (i) rotary tillage without straw return (RT); (ii) deep plowing tillage without straw return (DT); (iii) rotary tillage with total straw return (RS); (iv) deep plowing tillage with total straw return (DS); (v) rotary tillage of 2 years and deep plowing tillage in the 3rd year with total straw return (TS). Treatments with straw return increased kernels no. ear–1, thousand-kernel weight (TKW), grain yields, ratio of dry matter accumulation post-anthesis, and nitrogen (N) efficiency whereas reduced the ears no. ha–1 in the 2011–2012 and 2012–2013 growing seasons. Compared with the rotary tillage, deep plowing tillage significantly increased the grain yield, yield components, total dry matter accumulation, and N efficiency in 2013–2014. RS had significantly higher straw N distribution, soil inorganic nitrogen content, and soil enzymes activities in the 0–10 cm soil layer compared with the DS and TS. However, significantly lower values were observed in the 10–20 and 20–30 cm soil layers. TS obtained approximately equal grain yield as DS, and it also reduced the resource costs. Therefore, we conclude that TS is the most economical method for increasing grain yield and N efficiency of winter wheat in Huang-Huai-Hai Plain. Keywords: grain yield, N efficiency, straw return, tillage method, winter wheat

1. Introduction The Huang-Huai-Hai Plain is one of the most important Received 22 August, 2016 Accepted 22 February, 2017 Correspondence LI Yong, E-mail: [email protected]; WANG Zhen-lin, E-mail: [email protected] * These authors contributed equally to this study. © 2017, CAAS. Publishing services by Elsevier B.V. All rights reserved. doi: 10.1016/S2095-3119(16)61589-7

agricultural regions in China. It produces more than 60% of China’s winter wheat (Man et al. 2015). The average yield of winter wheat is approximately 5 540 kg ha–1, and yields in excess of 9 000 kg ha–1 have also been reported in the region (NBSC 2013). However, the output of grain production in this region was based on the higher rate of fertilizer appli-

CHEN Jin et al. Journal of Integrative Agriculture 2017, 16(8): 1708–1719

cation (Jin et al. 2012; Chen et al. 2014). Although the use of fertilizer has temporarily increased the yield, its excessive application has brought a series of environmental problems, such as water pollution, field greenhouse gas emission, and soil quality degradation, etc. (Snyder et al. 2007; Dai et al. 2013; Zhang et al. 2013). Therefore, in addition to ensuring a higher production, it is equally important to improve the nitrogen (N) use efficiency and reduce N loss (Zhang et al. 2008; Chen et al. 2011). Many studies have shown that crop residue is rich in organic materials and soil nutrients, and therefore, it is considered to be an important natural organic fertilizer, that could replace chemical fertilizers (Zhao and Chen 2008; Chen et al. 2015). Conservation agriculture, which consists of straw return, is an important strategy for combating soil degradation (Tian et al. 2010; He et al. 2015). Compared to conventional agricultural practice, such strategy is useful for improving soil physical characteristics, increasing soil fertility indicators (Powlson et al. 2011; Tian et al. 2012; Zhu et al. 2014; Nie et al. 2015), as well as enhancing the crop productivity and nutrient utilization efficiency (Zhao and Chen 2008; Chen et al. 2015). However, inappropriate methods of straw incorporation could deteriorate soil structure and unbalance nutrients distribution (Kong 2014; Pang et al. 2016). These could limit the action of roots (Guan et al. 2014), which is not beneficial for growing winter wheat. Thus, optimizing straw return method is essential for winter wheat production. Traditional tillage practices in agriculture, including deep plowing tillage and rotary tillage, are common in HuangHuai-Hai Plain, China (Shi et al. 2016). Deep plowing tillage has a higher cost than rotary tillage due to the requirement of expensive farming machinery. In contrast, rotary tillage is increasingly considered by farmers on account of greatly simplified operation, as well as its low cost in field preparation, fuel, equipment, and labor (Wang et al. 2006). However, rotary tillage often increases soil bulk density in the top 10–30 cm soil layer in the absence of plowing. This leads to a reduction in air-filled pore space, which is not beneficial for growing winter wheat (Václav et al. 2013). Furthermore, the rotary tillage shallows the plough layer, enriches surface nutrient, and emaciates deeper soil, thus resulting soil infertility and impeding the uptake of soil nutrient by crops (Tian et al. 2012; Nie et al. 2015). As a consequence, agricultural practices that improve soil quality are essential to promote agricultural sustainability and reduce resource consumption (Zhang et al. 2016). Many studies have indicated that straw return show remarkable effects on nitrogen utilization and grain yield (Duan et al. 2014). For example, both no-tillage and conventional tillage with residue applied had higher total N uptake and crop yield than methods with no residue applied

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in middle-lower Yangtze area of China (Xu et al. 2010). In Central China, deep-tillage with crop residue application at 30 cm soil depth had distinctly higher crops yield than those without straw application (Zhao et al. 2014; Chen et al. 2015). However, in Northwest China, there was no significant difference in N uptake between straw return treatments and the treatments without straw return under no-tillage condition (Zhang et al. 2009). Apparently, the effects of tillage on crop yield and nitrogen utilization vary with the regional climate, soil condition, residue management practice, and crop rotation (Ponnamperuma 1984). Therefore, the investigation on tillage reform and straw return manner for specific soil, climate, and cropping system is necessary to improve nitrogen utilization and grain yield. The studies mentioned above focused mainly on the effects of one soil tillage practice, i.e., reduced or no-till tillage, and plowing tillage, on soil structure, grain yield, and N utilization. However, studies on the effects of soil tillage practices, especially rotational tillage with deep plowing tillage (at 2 years interval) on the distribution of straw N, N utilization, and grain yield are limited. Therefore, we undertook this study with the objective of assessing tillage methods to evaluate their impact on (1) the distribution of N released from the applied crop residue, (2) characteristic of dry matter accumulation, and (3) grain yield and N efficiency over 3 years.

2. Materials and methods 2.1. Experimental site Field experiments were carried out in 2011–2012, 2012– 2013, and 2013–2014 at Yangzhuang Village (116°48´E, 35°29´N), Yanzhou County, Shandong Province, China. This experimental field has meadow-cinnamon soil and the cropping pattern is wheat-maize rotation. The information of summer maize of the 3 years is shown in Table 1. Properties of the upper 20 cm soil were 12.3 g kg–1 organic C, 1.11 g kg–1 total N, 87.2 mg kg–1 available N, 8.6 mg kg–1 available Olsen-P, and 0.58 mmol kg–1 exchangeable K. The precipitation and monthly average temperature in the growing period of winter wheat from 2011 to 2014 are shown in Fig. 1.

2.2. Experimental design Treatments were a combination of tillage and total aboveground residue returned from the previous crop. Five treatments were applied during the wheat growing season for 3 years, including rotary tillage without straw return (referred to as RT), deep plowing tillage without straw return (DT), rotary tillage with total straw return (RS), deep plowing tillage

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Table 1 Crop information for summer maize of the experimental plot from 2011 to 2013 Sowing date 15 Jun. 13 Jun. 13 Jun.

Variety

2011 2012 2013

3 Oct. 5 Oct. 4 Oct.

40

200

Precipitation (mm)

Harvest date

2011–2012 2012–2013 2013–2014 2011–2012 2012–2013 2013–2014

150

100

30 20 10

50

0

n.

Ju

r.

ay

ar .

M

Month

Ap

b.

M

n.

Fe

ec

Ja

D

N

O

.

–10

ct . ov .

0

Monthly average temperature (°C)

Planting density (plant ha–1) Zhengdan 958 60 000 Zhengdan 958 60 000 Zhengdan 958 60 000

Year

Fig. 1 Monthly average precipitation and temperature during the study period of winter wheat.

with total straw return (DS), and rotary tillage of 2 years and deep plowing tillage in the 3rd year with total straw return (TS). The experimental design was a random complete block design with three replications. The plot size was 4 m× 30 m with plots separated by 1 m. Winter wheat cultivar Jimai 22 was sown (2.25×106 plants ha–1) with 0.25 m row spacing. In every wheat growing season, phosphorus (105 kg P2O5 ha–1 as calcium superphosphate), and potassium (75 kg K2O ha–1 as KCl) were applied together with basal N (half of 225 kg N ha–1). The other half of the nitrogen fertilizer was applied by furrow at jointing stage. The treatments were assigned in the same experimental

N rate (kg N ha–1) 300 300 300

P rate (kg P2O5 ha–1) 120 120 120

K Grain yield (kg K2O ha–1) (Mg ha–1) 240 10.23 240 10.92 240 11.12

plot in every wheat seasons. The operation procedures of land preparation and the equipment used for different tillage practices are shown in Table 2. Seedling of winter wheat was done 1 day after land preparation, i.e., 5 Oct. 2011, 7 Oct. 2012, and 6 Oct. 2013. Micro-area frames were made by galvanized steel sheet (60 cm in length, and 40 cm in width and 55 in cm height), and they were placed in soil with 5 cm of the frame above the ground in order to prevent the fertilizer and crop residue from mixing each other in vivo and in vitro. In order to obtain the residue labeled as 15N, urea (abundance of 15 N was 20.05) was used to feed maize at another field. Maize was harvested on the same day with field experiment and the dry weight of maize straw was determined by measuring the moisture content of subsamples in an oven. After land preparation, micro-area frames were placed in the corresponding field plot, residue of 15N was returned to the micro-area according to tillage depth, and the soil structure was not destroyed. Residue of 15N was chopped in accordance with the field experiment. The amount of returned residue in each micro-area was calculated based on its area. The information of applied crop residue is summarized in Table 3. Seeding age and density were in accordance with the field experiment. Crop management followed standard cultural practice. Disease and insects were intensively controlled by chemicals to avoid yield losses. Herbicide was used to control weeds. Final harvest was done on 10 June 2012, 8 June 2013, and 6 June 2014.

Table 2 Operation procedures and the equipment used of different tillage practices Tillage1) RT DT

RS DS

TS 1)

Operation procedure2) Total maize straw removed from the field→Base fertilizer spreading→Rotary cultivating 2 times with IGQN-200K-QY rotary cultivator (working depth was about 10–12 cm)→Forming the border-check→Seeding with common seeder Total maize straw removed from the field→Base fertilizer spreading→Mouldboard plowing once with ILFQ330 turnover plough (working depth was about 25–30 cm)→Rotary cultivating 2 times with IGQN-200K-QY rotary cultivator→Forming the border-check→Seeding with common seeder Total maize straw returned to the field→Base fertilizer spreading→Rotary cultivating 2 times with IGQN-200K-QY rotary cultivator (working depth was about 10–12 cm)→Forming the border-check→Seeding with common seeder Total maize straw returned to the field→Base fertilizer spreading→Mouldboard plowing once with ILFQ330 turnover plough (working depth was about 25–30 cm)→Rotary cultivating 2 times with IGQN-200K-QY rotary cultivator→Forming the bordercheck→Seeding with common seeder The same to RS in the first two seasons and the same to DS in the 3rd season

RT, rotary tillage without straw return; DT, deep plowing tillage without straw return; RS, rotary tillage with total straw return; DS, deep plowing tillage with total straw return; TS, rotary tillage of 2 years and deep plowing tillage in the 3rd year with total strwa return. 2) The manufacturers of IGQN-200K-QY rotary cultivator is YTO Group Corporation, China. The manufacturers of ILFQ330 turnover plough is Runlian Scientific and Technological Development Co., Ltd., China.

CHEN Jin et al. Journal of Integrative Agriculture 2017, 16(8): 1708–1719

2.3. Methods Plant and soil samples Fifteen uniform and accordant plant samples were obtained from the center of each plot at jointing stage (JS), anthesis stage (AS) and maturity stage (MS). Samples were then oven-dried at 70°C to measure the dry matter weight. Soil samples of each field experimental plot were collected from the 0–10, 10–20, and 20–30 cm soil layers using a soil corer at MS. These samples were used for the determination of soil enzyme activities, NO3–-N, and NH4+-N. Soil samples of each micro-area were collected from 0–10, 10–20, and 20–30 cm soil layers, air-dried, screened through 100-mesh sieve (Cao et al. 2015), and used for the measurement of 15N abundance and soil total nitrogen content. Fifteen uniform and accordant plant samples in every micro-area were harvested at maturity, separated by grains, leaves, glumes, and stems, oven-dried, screening through 100-mesh sieve (Chen et al. 2016), and used for the measurement of 15N abundance. Sample analysis 15N abundance of both soil and aboveground samples was measured by Stable Isotope Ratio Mass Spectrometer (Iso prime 100; Iso Prime Co., UK). Contents of soil NO3–-N and NH4+-N were measured by continuous flow analyzer (AA3; Bran+Luebbe Co., Germany) and soil samples were extracted using 1 mol L–1 KCl. Activities of soil enzymes were conducted by Enzyme-Linked Immunosorbent Assay (ELISA, Labsystems Multiskan MS-352; Thermo Co., Finland). At MS, soil bulk density of micro-area was measured by cutting-ring method. The 3 m2 plants obtained from 4 rows at the center of each experimental plot were used to measure yield (moisture content was approximately 14%). Tissue N concentration was determined by micro Kjeldahl digestion, distillation, and titration to calculate the aboveground total N uptake. N efficiency and N distribution of applied residue NitroTable 3 Information of applied crop residue of the experimental plot from 2011 to 2013 Amount of N content Year straw returned (kg ha–1) –1 (Mg ha ) 2011 10.29 80.23 2012 11.37 95.74 2013 10.68 84.19

Abundance of 15N C:N ratio (%) – 3.78 3.80

71.56:1 68.23:1 70.53:1

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gen utilization efficiency (NUE), N partial factor productivity (PFPN) and N harvest index (NHI) were defined as follows: NUE=Y/TN PFPN=Y/N NHI=GN/TN Where, Y is the grain yield and TN is the total N uptake of wheat and GN is N accumulated in grain at maturity stage. N of applied residue intercepted by soil=(SBD×N content×Soil bulk)/15N abundance of residue N of applied residue uptake by plant=(DM×N content×15N abundance of plant)/15N abundance of residue N distribution of applied residue=N intercepted by plant (or soil)/N of applied residue Where, SBD is the soil bulk density (g cm–3), DM is the dry matter at maturity stage (Mg ha–1).

2.4. Statistical analysis The mean values were calculated for each measurement and one-way ANOVA was used to compare the effects of different treatments on the measured variables. If the Fvalue was significant (P<0.05), multiple comparisons of annual mean values were performed based on the least significant difference (LSD). SPSS 19.0 (SPSS Inc, Chicago, IL) was used for all statistical analyses. All graphs were drawn using Sigmaplot 10.0.

3. Results 3.1. Analysis of variance The combined analysis of variance using data from 3 years indicated that the year and tillage methods and their interaction significantly affected the grain yield, total dry matter accumulation (TDM), PFPN, NUE, and NHI (Table 4). Similarly, the combined analysis of variance using data from 2 years indicated that the effects of tillage method and the interaction between tillage method and year were extremely significantly for N distribution of applied residue both in plants and 0–30 cm soil layer (Table 4).

3.2. Grain yield The grain yield and its components are shown in Table 5. The

–, no data.

Table 4 Analysis of variance of grain yield, total dry matter accumulation (TDM), N partial factor productivity (PEPN), nitrogen utilization efficiency (NUE), N harvest index (NHI), and straw N distribution Source of variation Year (Y) Treatment (T) Y×T NS, not significant.

Yield 8.81** 42.35** 18.69** *

TDM 51.63** 297.99** 116.70**

PFPN 8.57** 41.74** 18.18**

NUE 8.95** 37.63** 23.09**

, significant at P≤0.05; **, significant at P≤0.01.

NHI 49.67** 24.15** 2.74*

Straw N in plants NS 56.19** 48.41**

Straw N in 0–30 cm soil NS 13.81** 12.61**

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result indicated that the highest yield on average was 8.6 Mg ha–1 for DS and 8.4 Mg ha–1 for TS for 3 years. In the first 2 years, grain yields under straw return were higher than that under the straw removal. The grain yields of RS, DS and TS during the growing seasons of 2011–2012 and 2012–2013 were on average 13.2, 11.2, and 6.0% higher than that of RT, and 9.8, 7.8, and 2.6% higher than that of DT, respectively. The grain yield of RS in 2013–2014 showed a reduction of about 17.4% from the first 2 years. On the contrary, grain yield of TS in 2013–2014 showed an increase of about 11.8% from the first 2 years. The production of DS was found to increase continuously in 3 years (Table 5). High yields were obtained in straw return treatments, particularly due to high kernel weight and kernel number per ear in the growing seasons of 2011–2012 and 2012–2013. Similarly, the decline of ears per hectare in 2013–2014 was the main reason for the reductions of yields for RT and RS (Table 5).

3.3. Dry matter The dry matter (DM) weight was significantly affected by tillage method and straw return over the three growing seasons (Fig. 2). At JS, a significantly higher DM was observed in DT and DS in 2011–2012 and 2013–2014, respectively, whereas there were significant differences among the five treatments in 2012–2013. At AS, a significantly higher DM was observed in treatments with straw removed in the first two growing seasons, but a significantly higher DM accumulation was observed in treatments with deep plowing tillage in the 3rd year (Fig. 2). The DM accumulation in MS showed obvious differences among the three growing seasons. In 2011–2012, treatments with straw return had relatively higher DM than the straw removal treatments, whereas there were no significant differences among the five treatments in 2012–2013. Contrary to the first 2 years, the DM in deep plowing tillage was significantly higher in the rotary tillage in the 3rd year, and an obvious reduction in the DM of RT and RS was observed in the 3rd year, respectively. The DM of RT and

RS in the 3rd year was on average 10.9 and 9.5% lower than the first 2 years, respectively (Fig. 2). The DM accumulation of pre-AS and post-AS under different treatments showed consistent trends during the study period, i.e., treatments with straw return had relatively higher ratio of DM accumulations in post-AS than the straw removal treatments (Fig. 2). In the first 2 years, the highest ratio of DM accumulation was observed in RS, whereas relatively higher values were observed in DS and TS in the 3rd year (Fig. 2).

3.4. Nitrogen efficiency The tillage practice and straw return had significant impacts on N efficiency of winter wheat (Table 6). In 2011–2012 and 2012–2013 growing seasons, straw return significantly increased PFPN and NHI, and a higher NUE was obtained compared with the RT and DT. However, the trends of PFPN and NUE for different treatments in 2013–2014 were not consistent with those in the first 2 years. RT and RS showed lower PFPN and NUE than the other treatments. PFPN and NUE of RT and RS were significantly decreased compared with the last 2 years. The PFPN and NUE of RT and RS were on average 14.4, 12.1, 17.1, and 17.8%, respectively lower than the first 2 years.

3.5. N distribution of applied crop residue Fig. 3 shows the straw N distribution in the treatments with straw return during 2012–2013 and 2013–2014 growing seasons. The highest straw N distribution in the 0–30 cm soil layer was observed in DS (Fig. 3-A and B), which was mainly due to higher straw N intercepted in 10–20 and 20–30 cm soil layers in the 2 years (Fig. 3-E and F). However, significantly higher values of straw N distribution in the 0–10 cm were observed in RS during the study period. Compared with RS, DS had higher N distribution in plants (Fig. 3-A and B), and it was mainly due to higher distribution in grain (Fig. 3-C and D). Compared to RS, TS had

Table 5 Yield (Mg ha–1) and yield components in response to cultivation method and straw return Tillage RT DT RS DS TS 1)

1)

Kernels no. ear–1 30.4 b 31.3 ab 33.9 a 32.2 ab 32.0 ab

2011–20122) 　 TKW Ears no. GY (g) ha–1 (Mg ha–1) 39.7 b 7.1 b 7.52 b 39.2 b 7.6 a 7.66 b 44.5 a 6.4 c 8.48 a 43.5 a 6.9 bc 8.19 a 43.2 a 6.8 bc 8.03 ab

Kernels no. ear–1 31.3 b 34.3 a 34.7 a 36.4 a 33.7 ab

2012–20132) TKW Ears no. (g) ha–1 39.6 b 7.1 a 40.1 b 6.8 a 44.0 a 6.4 a 41.7 ab 6.7 a 41.4 ab 6.9 a

2013–20142) 　 Kernels TKW Ears no. GY GY (Mg ha–1) no. ear–1 (g) ha–1 (Mg ha–1) 7.66 b 33.5 b 45.0 b 5.4 b 6.51 d 8.00 b 33.9 b 41.4 c 6.8 a 7.92 b 8.65 a 37.5 a 48.2 a 5.3 b 7.11 c 8.65 a 36.5 a 47.9 a 6.4 a 8.88 a 8.14 ab 36.4 a 46.5 ab 6.7 a 8.98 a

RT, rotary tillage without straw return; DT, deep plowing tillage without straw return; RS, rotary tillage with total straw return; DS, deep plowing tillage with total straw return; TS, rotary tillage of two years and deep plowing tillage in the 3rd year with total straw return. 2) TKW and GY represent thousand-kernel weight and grain weight, respectively. Within a column, means follow by the different letters are significantly different according to LSD (P<0.05).

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significantly higher straw N distribution values in plants and

growing season. The tillage practices and straw return

the 0–30 cm soil layers (Fig. 3-B), which were mainly due

significantly affected the contents of soil NO3–-N and NH4+-N

to significantly higher N in grain and in the 10–30 cm soil

in the 0–30 cm soil layer, where treatments with straw return

layers (Fig. 3-D and F).

(RS, DS, TS) had significantly higher contents of NO3–-N and NH4+-N at the three soil depths (Fig. 4). The soil NO3–-N and

3.6. Soil NO3–-N and NH4+-N

NH4+-N in the straw return treatments were about 9.0–35.7% and 7.4–73.8%, respectively, higher than the straw removal

The contents of soil NO3 -N and NH4 -N in the 0–30 cm soil

treatments. Except DS, the soil NO3–-N and NH4+-N gen-

layer were assessed at the maturity stage in 2013–2014

erally decreased with an increase in soil depth under all

DT

RT

Propotion of dry matter accumulation (%)

Dry matter accumulation (Mg ha–1)

25

RS

2011–2012

DS

TS 2013–2014

2012–2013

25

20

20

15

15

10

10

5

5

0

JS

AS

MS

JS

AS

Pre-AS

JS

AS

Post-AS 2012–2013

2011–2012

100

MS

0

MS 2013–2014

100

80

80

60

60

40

40

20

20

0

RT

DT

RS

DS

TS

RT

DT

RS

DS

TS

RT

DT

RS

DS

Dry matter accumulation (Mg ha–1)

+

TS

0

Propotion of dry matter accumulation (%)

–

Fig. 2 Accumulation of dry matter (DM) at different grow periods from 2011 to 2014. JS, AS, and MS represent jointing stage, anthesis stage, and maturity stage, respectively. RT, rotary tillage without straw return; DT, deep plowing tillage without straw return; RS, rotary tillage with total straw return; DS, deep plowing tillage with total straw return; TS, rotary tillage of 2 years and deep plowing tillage in the 3rd year with total straw return. Error bars represent ±standard error of means.

Table 6 The N partial factor productivity (PFPN), nitrogen utilization efficiency (NUE), and N harvest index (NHI, kg kg–1) in different treatments from 2011 to 2014 Treatment1) RT DT RS DS TS 1)

PFPN 33.4 b 34.1 b 37.7 a 36.4 a 35.4 ab

2011–2012 NUE 35.7 b 30.1 c 38.6 a 34.5 b 36.1 ab

NHI 0.75 c 0.79 bc 0.82 ab 0.81 bc 0.88 a

　 　

PFPN 34.1 b 35.6 b 38.5 a 38.5 a 36.1 ab

2012–2013 NUE 35.1 b 27.8 d 38.3 a 31.3 c 35.5 b

NHI 0.74 b 0.76 b 0.82 a 0.82 a 0.84 a

　 　

PFPN 28.9 d 35.1 b 31.6 c 39.5 a 39.9 a

2013–2014 NUE 31.1 b 33.3 ab 32.8 ab 34.4 a 34.7 a

NHI 0.73 ab 0.72 b 0.73 ab 0.74 ab 0.77 a

RT, rotary tillage without straw return; DT, deep plowing tillage without straw return; RS, rotary tillage with total straw return; DS, deep plowing tillage with total straw return; TS, rotary tillage of 2 years and deep plowing tillage in the 3rd year with total straw return. Within a column, means follow by the different letters are significantly different according to LSD (P<0.05).

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RS

40

20

10

N distribution (kg ha–1)

0–30 cm soil layer

20

15 5

0 E

Plants

Grain

Blade Glume

Stem

25 20 15 10 5

0–10 10–20 20–30 Different soil layers (cm)

TS

D

2013–2014

50

40

20

10

N distribution (kg ha–1)

N distribution (kg ha–1)

C

B N distribution (%)

50

DS

Plants

0–30 cm soil layer

20 15 10 5

0 F

25

N distribution (kg ha–1)

N distribution (%)

A

2012–2013

20

Grain

Blade Glume

Stem

15 10 5 0

0–10 10–20 20–30 Different soil layers (cm)

Fig. 3 The N distribution in plants and 0–30 cm soil layer (A and B), different organs of winter wheat (C and D), and different soil layers (E and F) in 2012–2013 and 2013–2014 growing seasons. RS, rotary tillage with total straw return; DS, deep plowing tillage with total straw return; TS, rotary tillage of 2 years and deep plowing tillage in the 3rd year with total straw return. Error bars represent ±standard error of means.

treatments. In the 0–10 cm soil layer, higher contents of NO3–-N and NH4+-N were observed in RS. Compared with the DS, the NO3–-N and NH4+-N contents were respectively 7.9 and 29.1% higher in the RS. Similarly, compared with the TS, the NO3–-N and NH4+-N contents were respectively 7.5 and 13.5% higher in the RS. On the contrary, higher contents of NO3–-N and NH4+-N were observed in DS and TS at 10–30 soil layers.

3.7. Activities of soil enzymes Activities of soil enzymes in the 0–30 cm soil layer were assessed at maturity stage in the growing seasons of 2013 to 2014. As shown in Fig. 5, the different treatments significantly affected the activities of sucrose, protease, and

urease in the 0–30 cm soil layer. The treatments with straw return had significantly higher values and the increases were in the range of 3.1–25.1%, 8.4–65.1%, and 14.0–71.1%, compared with the treatments with straw removal. Tillage methods and straw return affected the vertical distribution of soil enzymes activities. In the 0–10 cm soil layer, significantly higher activities were observed in RS compared with DS and TS. However, remarkably higher soil enzymes activities were obtained with DS and TS in the 10–20 and 20–30 soil layers.

4. Discussion Many studies have reported that there is an insignificant increase or even a decrease in the grain yield associated with

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RT

25

DT

DS

RS

TS

Soil NH4+-N content (mg kg–1)

Soil NO3–-N content (mg kg–1)

14 20

15

10

12

10

8

6 5

0–10

10–20

20–30

0–10

10–20

20–30

Different soil layers (cm)

Fig. 4 Contents of soil NO3–-N and NH4+-N in the 0–30 cm soil layer under different treatments in 2013–2014. RT, rotary tillage without straw return; DT, deep plowing tillage without straw return; RS, rotary tillage with total straw return; DS, deep plowing tillage with total straw return; TS, rotary tillage of 2 years and deep plowing tillage in the 3rd year with total straw return. Error bars represent ±standard error of means.

RT

DS

600 500

0–10

10–20 20–30

C 25

40 30 20 10

TS

Activities of urease (IU L–1)

700

400

RS

B 50 Activities of protease (IU L–1)

Activities of sucrose (IU L–1)

A 800

DT

0–10 10–20 20–30 Different soil layers (cm)

20 15 10 5

0–10

10–20 20–30

Fig. 5 Activities of soil enzymes (A, sucrose; B, protease; C, urease) in the 0–30 cm soil layer under different treatments in 2013–2014. RT, rotary tillage without straw return; DT, deep plowing tillage without straw return; RS, rotary tillage with total straw return; DS, deep plowing tillage with total straw return; TS, rotary tillage of 2 years and deep plowing tillage in the 3rd year with total straw return. Error bars represent ±standard error of means.

straw return, especially without the application of N fertilizer

with straw return regardless of rotary or deep tillage in the

(Liu et al. 2001; Zhao and Chen 2008). A multi-location

first 2 years. The results are consistent with the findings

research project on the management of crop residue for

of Wang et al. (2012) and Zhang et al. (2014). Treatments

sustainable production concluded that residue incorporation

with straw return had higher dry matter accumulation post-

does not lead to higher grain yields (IAEA 2003). In some

AS, and this characteristic of dry matter accumulation is

cases, where N fertilizer is not applied, straw return often

beneficial to the formation of grain weight (Yu 2003; Jin

reduces both yield and N uptake significantly. So, the effect

et al. 2012). In the 3rd year, the grain yields under rotary

of straw return on grain yield depends on soil condition, till-

tillage were obviously lower than the first 2 years, which

age method, and the quantity of N-fertilizer application (Xu

indicated that the continuous rotary tillage was adverse to

et al. 2010). In our study, higher grain yield was observed

stabilization and increase in spike number. The straw return

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CHEN Jin et al. Journal of Integrative Agriculture 2017, 16(8): 1708–1719

and long-term inappropriate tillage method could also lead to poor seeding quality and cause the reduction in germination rate and ultimately affect the wheat population (Liu et al. 2001; Li et al. 2006). It may cause an unreasonable soil structure and imbalance the distribution of soil nutrient in plough layer (Kong et al. 2010; Liu et al. 2015; Nie et al. 2015). Furthermore, in 2013–2014 growing season, the total dry matter accumulation in RT and RS was significantly lower than the others, respectively, indicating that continuous rotary tillage reduced the biomass of winter wheat and it was not beneficial for producing grain yield. In the 3rd year, TS had 26.8% higher grain yield than RS, the possible reason might be that deep plough tillage can significantly improve the soil structure, break the plough pan, and promote the root grow and nutrient absorption (Izumi et al. 2009; Hou et al. 2012; Jiang et al. 2012). The result clearly indicated that the rotation tillage or deep plough tillage every few years is an effective way to eliminate the adverse effect of monoculture (Tang et al. 2013; Pang et al. 2016). Duan et al. (2014) concluded from 15 years’ data from northern and central China that there is a consistent increase in NUE associated with the applied residue for wheat-maize rotation. In our study, we found that there was a consistent effect of straw return on NUE. Particularly, the straw return increased NUE among the three crop seasons. The high PFPN from all treatments with the residue application were due to high grain yield and it is consistent with the finding of Zhao and Chen (2008). Straw return increased the activities of soil microorganism and enzyme, which significantly promoted the availability of soil N (Xu et al. 2009). The low PFPN from rotary tillage treatments were due to low grain yield in 2013–2014 growing season. It suggested that the long-term inappropriate tillage method causes the physical, biological, or chemical degradation of soil, referred to as “poor, less-responsive soils” by Vanlauwe et al. (2011). However, contrary to our finding, many studies on straw return showed that the PFPN of wheat did not change after applying residue in addition to chemical fertilizers while it increased after the ratio of chemical N fertilizer was decreased in the combined fertilization (Aulakh et al. 2000). The different results might vary with the nutrient condition of soil and the rate of residue applied (Kaewpradit et al. 2009; Pan et al. 2009). In our study, straw return obviously increased NHI, and it might be because the straw return facilitated N transfer from nutritive organs to the grain. Soil nutrient contents are considered to be good indicator of soil quality and productivity, which is derived from the mineralization of organic material and fertilizer (especially soil NO3–-N and NH4+-N) (Zhang et al. 2015). Suitable soil tillage practice can increase the soil nutrient content, and improve nutrient density of the plough layer (Duan et al. 2012). The effect of tillage methods on nutrient dynamics

depends on the tillage intensity (Yang et al. 2003). In our study, at 0–10 cm soil depth, the N distribution of applied residue and the soil NO3–-N, and NH4+-N under rotary tillage were higher than deep plough tillage, but significantly lower at 10–20 and 20–30 cm soil depths, indicating that the tillage affected the vertical distribution and accumulation of soil nitrogen (Liu 2009). Soil nutrient content under deep plough tillage at deeper soil both were higher than that of the rotary tillage. It might be due to the fact that deep plowing tillage mixes the basal fertilizer to deeper soil layer (Pang et al. 2016). On the other hand, our results suggested that the deep plowing tillage could intercept significantly more straw N, indicating that the deep plowing tillage could mix straw into the deeper soil layer, making soil nutrient well distributed at different depths (Gao et al. 2000). Therefore, the residue decomposition rate was increased and the equilibrium of the nitrogen content at each soil layer was improved (Li et al. 2012). Moreover, residue application in the soil increased the activity levels of soil enzymes in our study. Compared with RT and DT, treatments with straw return had higher activities of soil enzymes. It indicated that the carbon input via straw return enhanced soil carbon and nitrogen pools (Karami et al. 2012), improved soil biological fertility (Zhao et al. 2016), and promoted mineralization of organic material and availability of soil nutrient (Wei et al. 2015), which is beneficial to the nutrient absorption of crop (Liang et al. 2009). In the present study, on average of the 3 years, DS and TS had approximately equal grain yield and N efficiency. However, TS reduced the input of equipments and energy consumption during the study period of 3 years, as reported by Shi et al. (2016) and our operation procedures summarized in Table 2, which suggested that TS is a more beneficial practice for promoting agricultural profit. Based on our study, it can be inferred that the total straw return significantly regulates N utilization not only by increasing the intercepted quantity of N but also increasing N distribution in plants, especially, improving the availability of soil N and its related enzymes. These findings are valuable for promoting grain yield, N efficiency, and agricultural profit.

5. Conclusion Straw return significantly increased the grain yield and N efficiency in the first 2 years irrespective of different tillage practice. In the 3rd year, significantly higher values were observed particularly in DS and TS. Greater straw N distribution in plants and 0–30 cm soil layer, soil enzymes activities and inorganic N contents in 10–30 cm were also found in DS and TS. Compared to DS, TS reduced the costs of agriculture production during the study period of 3 years. Therefore, this study demonstrated that TS was a

CHEN Jin et al. Journal of Integrative Agriculture 2017, 16(8): 1708–1719

high-efficiency and economical approach to obtain a high yield of winter wheat.

Acknowledgements The research was supported by the National Key Research and Development Program of China (2016YFD0300400), the National Basic Research Program of China (973 Program, 2015CB150404), the Special Fund for Agroscientific Research in Public Interest of China (201203100), the National Key Technologies R&D Program of China during the 12th Five-year Plan period (2012BAD04B05), the Project of Shandong Province Higher Educational Science and Technology, China (J14LF12), the Shandong Province Mount Tai Industrial Talents Program, China, and the Shandong Province Key Agricultural Project for Application Technology Innovation, China.

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