yield response to different planting geometries in maize ... · 25 abstract: 26 planting geometries...

Yield response to different planting geometries in maize-soybean 1

relay strip intercropping systems 2

Feng Yang†, Xiaochun Wang†, Dunping Liao, Fengzhi Lu, Rencai Gao, Weiguo Liu, 3

Taiwen Yong, Xiaoling Wu, Junbo Du, Jiang Liu, Wenyu Yang* 4

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F. Yang, X. Wang, D. Liao, F. Lu, R. Gao, W. Liu, T. Yong, X. Wu, J. Du, J. Liu, and 6

W. Yang, College of Agronomy, Sichuan Agricultural University, Chengdu 611130, 7

P.R. China; F. Yang and W. Yang, Key Laboratory of Crop Ecophysiology and 8

Farming System in Southwest, Ministry of Agriculture, Chengdu 611130, P.R. China. 9

* Corresponding author ([email protected]). † These authors contributed equally to 10

this work. 11

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of 31Agronomy Journal Accepted paper, posted 09/08/2014. doi:10.2134/agronj14.0263

Abstract: 25

Planting geometries directly affect crop yields in intercropping systems. Two 26

different field experiments were conducted in 2012-2013 to analyze how different 27

planting geometries in maize (Zea mays L.) and soybean [Glycine max (L.) Merr.] 28

relay strip intercropping systems at 2:2 maize-to-soybean affect yields. Maize plants 29

were planted in narrow-row planting patterns, whereas soybeans were planted in wide 30

rows. The effects of bandwidth, row spacing, plant spacing, and the distance between 31

maize and soybean rows on crop yields were studied. Total intercrop yields were 32

higher than those of sole crop maize and soybean, and the land equivalent ratios of the 33

intercropping systems were above 1.3. The yield of the intercropped maize increased 34

with bandwidth reduction at the same plant density, and similar results were found 35

with increased maize narrow-row spacing at the same bandwidth. Plant spacing had a 36

dominant function when the bandwidth of the intercropped soybean was greater than 37

200 cm. By contrast, the distance between maize and soybean rows had a dominant 38

function when bandwidth was less than 200 cm. The optimum bandwidth and maize 39

narrow-row spacing in maize-soybean relay intercropping systems were 200 and 40 40

cm, respectively. These results suggest that the appropriate reduction in the spacing of 41

the narrow maize rows and increase in the distance between maize and soybean rows 42

could be used to achieve high yields in maize-soybean intercropping. 43

Abbreviations: LER, Land Equivalent Ratio; SM, Maize sole crop; SS, Soybean sole 44

crop 45

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1. Introduction 47

Relay cropping and intercropping are the collective planting of two or more crop 48

species in the same field (Willey, 1979; Echarte et al., 2011; Lithourgidis et al., 2011). 49

These methods have been widely used in various countries worldwide, such as in 50


China, India, Southeast Asia, Latin America, and Africa to increase crop productivity 51

(Vandermeer, 1989; Rodriguez-Navarro et al., 2011). Intercropping is used in more 52

than 2.8×107 ha of the arable land in China (Qin et al., 2013), and half of the total 53

grain yield in China is produced through multiple cropping (Yang et al., 2014). 54

Maize-soybean relay strip intercropping is a major planting pattern in southwestern 55

China (Yan et al., 2010). 56

Maize-soybean intercropping is an important type of cereal and legume 57

intercropping that often yields more than those of their sole crop because of its more 58

efficient use of resources and the reduced incidence of weeds, insect pests, and 59

diseases (Echarte et al., 2011; Yang et al., 2014). Soybean is a C3 legume that fixes 60

atmospheric nitrogen (N) for its own growth, which minimizes inorganic fertilizer 61

input, and helps reduce the carbon (C) footprint in cropping systems (Gan et al., 2011; 62

Qin et al., 2013). Maize, a cereal and a C4 crop, has higher photosynthetic and C gain 63

activities (Omoto et al., 2012). Thus, maize-soybean intercropping systems use 64

various resources at different times, and acquire nutrients from different parts of the 65

soil or aerial environment or in diverse forms (Echarte et al., 2011). 66

In maize-soybean relay strip intercropping systems, maize is usually sown using 67

narrow-wide row planting pattern at the end of March or the beginning of April, and 68

the crop is harvested at the end of July or the beginning of August. Soybean is sown in 69

wide rows between maize rows at the beginning of June and is harvested at the end of 70

October (Yang et al., 2014). Therefore, both crop species can be grown during one 71

season in production areas in China, where the growing season is too short for double 72

cropping. 73

Maize-soybean intercrops include tall (maize) and short (soybean) crops. 74

Soybean grows as the subordinate late-sown crop of the pair (Echarte et al., 2011). 75


Planting patterns change in the light environment of the soybean canopy through its 76

lower layer (Awal et al., 2006), especially as the distance between the maize and 77

soybean rows is reduced (Yang et al., 2014). Soybean is highly sensitive to low light 78

which results in its low yield (Wolff and Coltman, 1989). Most studies have mainly 79

analyzed the effects of light enrichment and shading on sole soybean yield (Mathew et 80

al., 2000; Liu et al., 2006; Liu et al., 2010a; Liu et al., 2010b; Wang et al., 2013). The 81

intercropped soybean yield in maize-soybean relay strip intercropping systems has 82

been reported to be lower than that of sole crop (Yang et al., 2013). However, the 83

appropriate planting patterns to improve the lighting of the soybean canopy and 84

increase the total yield of maize-soybean relay strip intercropping have not been 85

examined. Relatively little research has done studying the effect of light on soybean 86

seedling growth (Yang et al., 2014). 87

Plant spacing and row spacing also affect the yield in intercropping systems 88

(Echarte et al., 2011; Borghi et al., 2012). The grain yield of intercropped maize is 89

lower than that of sole crop when the plant spacing of the intercropped maize is lower 90

than that of the sole crop at the same plant density (Echarte et al., 2011). The maize 91

grain yield from narrow-row spacing is higher than that from wide-row spacing at the 92

same plant density in maize and palisade grass intercropping (Borghi et al., 2012). 93

Plant spacing and row spacing are decreased in intercropping systems to ensure that 94

the plant density of the intercrop is consistent with that of the sole crop (Echarte et al., 95

2011). Thus, intercrop yield decreases because of intra-specific competition 96

(Maddonni et al., 2006; Zhang et al., 2011). Previous studies have primarily analyzed 97

the effects of planting ratio (e.g., three rows of soybean alternated with one row of 98

maize or three rows of soybean alternated with two rows of maize) and plant density 99

on the yield of a certain crop in intercropping (Gao et al., 2010; Zhang et al., 2011; 100


Echarte et al., 2011; Borghi et al., 2012). However, few studies have addressed the 101

impact of row spacing and bandwidth arrangement on the yield of each crop and the 102

mixed yield in maize-soybean relay strip intercropping. 103

Maize-soybean relay strip intercropping is becoming more common in the hilly 104

southwestern regions of China (Yan et al., 2010). The maize-to-soybean row ratio is 105

generally 2:2 (Yang et al., 2014). The effects of border rows contribute to intercrop 106

overyielding and small mechanical operations in this planting pattern (Knörzer et al., 107

2009). The plant density of the intercrop should match that of sole crop ensure the 108

yield of each crop and mixed yields in maize-soybean intercropping. Therefore, 109

optimum spatial arrangement has a significantly facilitates high yield and efficiency in 110

maize-soybean relay strip intercropping systems. 111

This study was designed to: (i) measure the grain yield and shoot biomass of 112

intercrops and sole crops with different planting pattern arrangements in 113

maize-soybean relay strip intercropping systems and land equivalent ratio (LER); (ii) 114

explore the relationships among the intercrop yield, plant spacing and row spacing; 115

and (iii) determine the optimum planting geometry for maize-soybean relay strip 116

intercropping. 117

2. Materials and methods 118

2.1 Site description and experimental design 119

Two experiments were conducted at the experimental farm in Sichuan Agricultural 120

University in Ya’an from 2012 to 2013. Fields were assigned to different treatments 121

using a randomized block design with three replications. The climate of the 122

experimental site was subtropical and humid. The soil was clay loam. The 123

precipitation rates and air temperature during the intercropping growth seasons from 124

2012 to 2013 are shown in Fig. 1. Plots were treated with basal fertilizers. Prior to 125


sowing, intercropped and sole-cropped maize were fertilized by hand with basal N at 126

135 kg ha-1 as urea, P at 40 kg ha-1 as calcium superphosphate, and K at 10 kg ha-1 as 127

potassium sulfate. Basal N at 75 kg ha-1 as urea, P at 40 kg ha-1 as calcium 128

superphosphate, and K at 4 kg ha-1 as potassium sulfate were applied to all soybean 129

plots. At the sixth leaf stage (V6) of maize and beginning bloom stage (R1) of 130

soybean, N at 135 and 75 kg ha−1 as urea were applied for maize and soybean 131

treatments, respectively. Weeds were eliminated using a manual hoe. Chemical 132

control was implemented to regulate insect populations. 133

2.1.1 Experiment 1 134

The experimental factors were six planting patterns. Treatments other than the sole 135

crops of maize and soybean were the intercrops composed of different bandwidths 136

(160, 180, 200, and 220 cm) of maize-soybean relay strip intercropping (Fig. 2a). The 137

maize-to-soybean row ratio in a single strip was 2:2. Narrow-row planting pattern was 138

adopted, with 40 cm row spacing. Soybeans were planted in the wide rows before the 139

reproductive stage of maize, with 40 cm row spacing. The row spacing of the sole 140

crop maize and soybean was 70 cm. Each plot was 6 m long, with three strips. The 141

maize cultivar was Chuandan418, whereas the soybean cultivar was Gongxuan1. 142

Maize was sown on 28 March 2012 and 4 April 2013, and soybean was sown on 13 143

June of each year. Maize was harvested on 8 August 2012 and 2 August 2013. 144

Soybean was harvested on 29 October 2012 and 28 October 2013. The plant densities 145

of maize and soybean were 6 and 10 plants m-2, respectively, in both sole crops and 146

intercrops. 147

2.1.2 Experiment 2 148

This experiment comprised six maize and soybean cropping systems to estimate 149

the effects of maize narrow-row spacing on maize and soybean yields in the same 150


bandwidth. The maize cultivar used was Chuandan418, whereas the soybean cultivar 151

was Nandou12. The following maize planting patterns were adopted: “180+20” 152

narrow-row planting (180 cm wide row and 20 cm narrow row), “160+40” 153

narrow-row planting, “140+60” narrow-row planting, and “120+80” narrow-row 154

planting (Fig. 2b). Maize-to-soybean row ratio was also 2:2. Soybean was planted in 155

the wide rows before the reproductive stage of maize, with 40 cm row spacing. The 156

row spacing of the sole crop maize and soybean was 70 cm. The plot size was 6 m × 7 157

m. Maize was sown on 1 April 2012 and 30 March 2013, and the crop was harvested 158

on 1 August 2012 and 28 July 2013. Soybean was sown on 15 June 2012 and 16 June 159

2013. Hand sowing was performed at high density, and the seedlings were 160

subsequently thinned to achieve the target density and uniformity of plant spacing. 161

Maize and soybean plant densities were similar to those in experiment 1 for sole crops 162

and intercrops. 163

2.2 Grain yield and shoot biomass 164

Maize was harvested at grain harvest moisture and soybean plants were 165

harvested at physiological maturity to determine shoot dry matter and grain yield. The 166

maize plants of a strip per plot were sampled to calculate grain yield, and 10 167

consecutive plants were used to analyze the relationship between grain yield and 168

shoot biomass per plant. The sampling method for soybeans was similar to that for 169

maize, but 20 consecutive plants were used to analyze the relationship between grain 170

yields and shoot biomass per plant. Plant shoot samples were cut at the soil surface 171

level. Samples were oven-dried at 105 °C for 30 min to destroy the tissues and were 172

then dried at 80 °C until the weight was constant before weighting. 173

2.3 Land Equivalent Ratio (LER) 174

Intercropping advantage was assessed by calculating the LER (Zhang et al., 2011), 175


which is an index of intercropping advantage and indicator of intercropping efficiency 176

for using the environmental resources compared with those of sole crops (Mead and 177

Willey, 1980). LER is calculated as (Li et al., 1999; Fetene, 2003) 178

LER=ss

is

sm

im

Y

Y

Y

Y+ (1) 179

where Ysm and Yim are the sole and intercropped maize yields, respectively. Yss and Yis 180

are the sole and intercropped soybean yields, respectively. Intercropping favors the 181

growth and yield of the species when LER is >1. Intercropping is disadvantageous if 182

LER is <1. A LER of 1.0 indicates no advantage of intercropping over sole cropping 183

(Dabbagh et al., 2011). 184

2.4 Statistical analysis 185

One-way ANOVA was performed to test the effects of spatial planting pattern on 186

maize and soybean grain yields in intercropping. Regression analysis was conducted 187

to determine the relationships between plant spacing, row spacing, and grain yield per 188

plant in maize-soybean relay strip intercropping. SPSS v16.0 and Microsoft Excel 189

2003 were used for statistical analyses. 190

3. Results 191

3.1 Experiment 1: Effects of bandwidth on the intercrop yield in maize-soybean 192

relay strip intercropping 193

3.1.1 Grain yield and LER 194

Maize and soybean grain yields in sole cropping and relay intercropping are 195

shown in Table 1. Mixed yields are the total maize and soybean yields in the 196

intercropping systems. The mixed yields of the maize-soybean intercrop were higher 197

than that of sole maize or sole soybean in all treatments (P < 0.05). The intercropped 198

maize yields decreased with increasing maize-soybean relay strip intercropping 199


bandwidth from 160 cm to 220 cm. The maximum yields were 9131 and 6329 kg ha-1 200

in 2012 and 2013, respectively. Different trends were observed in intercropped 201

soybeans from 160 cm to 200 cm, the soybean yield decreased when the bandwidth 202

was higher than 200 cm. The maximum soybean yield (1291 and 1516 kg ha-1 for 203

2012 and 2013, respectively) and mixed yield (9618 and 7385 kg ha-1 for 2012 and 204

2013, respectively) appeared at the 200 cm bandwidth of maize-soybean relay strip 205

intercropping (P < 0.05). 206

The LERs in both years were above 1.3 for all treatments (Table 1). LERs of 207

both intercrops with different bandwidth treatments improved when the bandwidth 208

increased up to 200 cm, and then decreased from 220 cm bandwidth for 209

maize-soybean intercrop in both years. The LERs followed a “low-high-low” trend in 210

both years. The maximum LERs were 1.64 and 2.07 in 2012 and 2013, respectively. 211

3.1.2 Maize and soybean yield per plant response to shoot biomass per plant 212

The relationship between shoot biomass and the grain yield of the intercrops (Fig. 213

3) was determined to elucidate the effects of shoot biomass at different bandwidth 214

patterns on the maize and soybean yields of maize-soybean relay strip intercropping 215

systems. Grain yield was found to be positively related to the maize shoot biomass per 216

plant (R2 = 0.90, P < 0.001). Statistically significant yield differences observed for 217

soybeans (R2 = 0.97, P < 0.001). The maximum grain yield and shoot biomass of 218

soybean were 19.6 and 40.2 g plant-1, respectively, in 2012, and the corresponding 219

values in 2013 were 13.8 and 31.8 g plant-1 (Fig. 3). The biomass of the intercropped 220

maize in both years decreased with increasing maize-soybean relay strip intercropping 221

system bandwidth from 160 cm to 220 cm. Contrasting trend was observed for 222

intercropped soybeans from 160 cm to 200 cm, and soybean biomass decreased when 223

the bandwidth was greater than 200 cm (Table 2). Crop yields and shoot biomasses 224


had remarkable differences between 2012 and 2013. 225

3.1.3 Relationship between intercrop yields and different planting geometries 226

The relationships among grain yield, plant spacing, and row spacing in 227

maize-soybean relay strip intercropping systems were determined to confirm the 228

sensitivity of grain yields to planting geometries. The results are shown in Figs. 4 and 229

5. Soybean yield per plant slightly increased with plant spacing up to 10 cm (200 cm 230

bandwidth treatment), but decreased with further increase in plant spacing (< 200 cm 231

bandwidth treatments). The yield per plant increased with increasing distance between 232

maize and soybean rows up to 60 cm, but decreased with further increase the distance 233

between maize and soybean row. The maize-soybean relay intercropping of 200 cm 234

bandwidth served as the turning point of yield per soybean plant in both years, 235

regardless of whether soybean plant spacing or distance between maize and soybean 236

rows changed (Fig. 4). The relationship between the spacing of maize and soybean 237

rows and yield per plant (R2 = 0.81 and 0.93 for 2012 and 2013, respectively) showed 238

higher coefficients of determination than soybean plant spacing (R2 = 0.71 and 0.88 239

for 2012 and 2013, respectively). 240

The effect of soybean on maize growth was not remarkable because maize was the 241

high-layer crop in maize-soybean relay strip intercropping systems, and the seedling 242

phase of soybeans and reproductive phase of maize overlapped for 8 weeks between 243

the sowing of soybean and harvest of maize. Maize plant spacing was an important 244

factor in increasing grain yield at the same plant density (Fig. 5). The yield per maize 245

plant increased with the increase in plant spacing in maize-soybean relay strip 246

intercropping in 2012 and 2013 (Fig. 5). 247

3.2 Experiment 2: Effects of rows spacing on intercrop yield in maize-soybean relay 248

strip intercropping 249


3.2.1 Grain yield and LER 250

The mixed yield of the maize-soybean intercrop was higher than sole crop yield in 251

both years, but the maize and soybean yields in intercropping conditions were lower 252

than those in sole crop (Table 3, P < 0.05). The sole maize yields were 6451 and 6311 253

kg ha-1 in 2012 and 2013, respectively, whereas sole soybean yields were 1993 and 254

1854 kg ha-1 in 2012 and 2013, respectively. Intercropped maize yield increased as 255

maize narrow-row spacing increased from 20 cm to 80 cm in the maize-soybean relay 256

strip intercropping systems, whereas the opposite trend was observed in the 257

intercropped soybean except for lowest. This result suggests that soybean suffered 258

from the shading by maize in the relay intercropping systems. Intercropped maize 259

yields accounted for 77% to 89% of the total yield (Table 3), showing that 260

intercropped maize crops were the main contributors to the productivity of 261

intercropping than the intercropped soybean. 262

The LER changes in the maize-soybean relay strip intercropping of different 263

maize narrow-row spacing patterns are shown in Table 3. LER slowly increased in the 264

20 cm to 40 cm narrow-row spacing conditions, regardless of maize narrow-row 265

spacing treatment, and then rapidly decreased when maize narrow-row spacing 266

increased from 40 cm to 80 cm. The maximum LER was observed in the 40 cm 267

narrow-row spacing of maize-soybean relay strip intercropping (1.59 and 1.61 for 268

2012 and 2013, respectively). 269

3.2.2 Maize and soybean yield per plant response to shoot biomass per plant 270

The relationships between crop yield and the shoot biomass of different maize row 271

patterns in maize-soybean relay strip intercropping and sole crop conditions are 272

shown in Fig.6. The relationships of grain yield with shoot biomass in different maize 273

narrow-row spacing treatments were similar to those in different bandwidth 274


treatments under maize-soybean relay strip intercropping conditions (Fig. 3). A 275

significantly positive relationship was observed between grain yield and the shoot 276

biomass of intercrops and sole crops (P < 0.001). The determination coefficient of 277

grain yield and soybean shoot biomass (R2 = 0.79) was lower than that of maize (R2 278

=0.92) in different maize narrow-row spacing conditions of maize-soybean relay strip 279

intercropping and sole crop. The grain yield and shoot biomass of sole crops were 280

higher than those of intercropped maize and soybeans in the relay strip intercropping 281

systems during 2012 and 2013. Intercropped maize shoot biomass increased as maize 282

narrow-row spacing was increased from 20 cm to 80 cm in the maize-soybean relay 283

strip intercropping systems. A contrasting trend was observed in the intercropped 284

soybean (Table 4). 285

3.2.3 Relationship between intercrop grain yields and different planting 286

geometries 287

The relationship between grain yield and maize narrow-row spacing in the 288

maize-soybean relay strip intercropping is shown in Fig. 7. The plant spacings were 289

16.7 and 10 cm for maize and soybean, respectively, in all treatments, because the 290

bandwidth of maize-soybean intercropping was 200 cm (Fig. 2). This result indicates 291

that the intercropped maize and soybean yields were affected by maize narrow-row 292

spacing and by the distance between maize and soybean rows, respectively. Therefore, 293

the yield per maize plant increased with increasing maize narrow-row spacing (Fig. 294

7a). Contrasting results were found in soybean in maize-soybean relay strip 295

intercropping during 2012 and 2013 (Fig. 7b). The soybean yield per plant in the 296

maize-soybean intercropping systems decreased with increasing maize narrow-row 297

spacing from 20 cm to 80 cm (decreased with decreasing distance between maize and 298


soybean row from 70 cm to 40 cm). 299

4. Discussion 300

4.1 Grain yield and LER 301

Intercropping is common in many countries because it results high yields and high 302

resource efficiency (Gao et al., 2009). Maize-soybean relay strip intercropping has 303

been widely practiced in southwestern China over the last decade because the 304

significant reduction in the soybean cultivated area has allowed the expansion of the 305

maize area in the Yellow and Huai River Valleys and Northeastern China (He et al., 306

2013). In addition, the economic efficiency of soybean is lower than that of maize. 307

Therefore, intercropping usually facilitates the production of maize with minimal to 308

no yield loss and subsequently a reasonable soybean yield as well. The mixed yields 309

of the maize-soybean intercrop were higher than that of sole maize or sole soybean in 310

this study. Maize-soybean intercrop yields were similar or less than those of the 311

reference sole crops (Tables 1 and 3). These results were similar to those from 312

published reports in which the total yield of the sunflower-soybean intercrop is higher 313

than that of sole sunflower or sole soybean, but the maize and soybean yield in 314

intercropping is less than those of the reference sole crops (Echarte et al., 2011). 315

Aggarwal and Sidhu (1988) also reported that cereal and legume yields in 316

intercropping are less than that of the reference sole cereal. The maximum total yields 317

of the maize-soybean relay strip intercropping were observed in the 200 cm 318

bandwidth treatment in this study (Table 1). These results explain why the 200 cm 319

bandwidth was chosen in maize-soybean relay intercropping systems. 320

The intercropping advantages were assessed by calculating LER (Mead and 321

Willey, 1980). The LERs of all the planting geometries in the maize-soybean relay 322

strip intercropping systems were above 1.3, suggesting better yield and substantially 323


higher land-use efficiency (Tables 1 and 3). The maximum LER was obtained in the 324

200 cm bandwidth of maize-soybean intercropping with different bandwidth patterns. 325

LER was also higher with 40 cm maize narrow-row spacing in the 200 cm bandwidth 326

of maize-soybean relay strip intercropping. These results are consistent with the report 327

that different planting geometries directly affect LER (Zhang et al., 2011; Mao et al., 328

2012). These results indicate that the optimum bandwidth and maize narrow-row 329

spacing in maize-soybean relay intercropping systems (with maize-to-soybean row 330

ratio of 2:2) are 200 and 40 cm, respectively. 331

4.2 Relationship between grain yield and shoot biomass of intercrops 332

The relationship between grain yield and shoot biomass per plant allows 333

physiological traits (e.g., dry matter production and dry matter allocation to 334

reproductive organs) to affect the yield response to resource availability (Echarte et al., 335

2011; Vega et al., 2000). The different planting geometry treatments used in this study 336

produced wide range of intercrop grain yields and shoot biomass per plant in 337

maize-soybean relay strip intercropping systems. A significantly positive relationship 338

was observed between grain yield and shoot biomass of intercrops and sole crops 339

(Figs. 3 and 6, P <0.001). The grain yield and shoot biomass of the intercrops in 340

maize-soybean relay strip intercropping systems were lower than those of sole crops. 341

These results are similar to those of previous reports on the relationship between 342

intercropped maize grain yield and shoot biomass per plant (Echarte et al., 2011). 343

Therefore, intercropping leads to lower yield per plant at the same plant density as 344

sole crop, resulting in low intra-row spacing and biomass reduction (Tables 2 and 4). 345

4.3 Effects of spatial arrangement on intercropped soybean yield 346

Crop yield was affected by different spatial arrangements (e.g., plant spacing, row 347

spacing and plant density) in intercropping (Echarte et al., 2011; Borghi et al., 2012). 348


The plant spacing of soybean decreased with increasing bandwidth in the 349

maize-soybean relay strip intercropping. However, the soybean yield per plant 350

followed a “low-high-low” trend (Fig. 4a). Similar results were also found with 351

increasing distance between maize and soybean rows, and the turning point was the 352

200 cm bandwidth treatment (Fig. 4b). These results imply that plant spacing 353

significantly affects soybean yield when the bandwidth of maize-soybean 354

intercropping is higher than 200 cm at the same overall plant density. Otherwise, the 355

distance between maize and soybean rows was the dominant factor. Soybean is highly 356

sensitive to shading (Wolff and Coltman, 1989). Significant differences in the 357

morphological parameters of the soybean seedlings were observed in the 358

maize-soybean relay intercropping system compared with those of the sole cropping 359

system (Yang et al., 2014). Morphological traits were directly correlated with crop 360

yield (Yan et al., 2010). The authors have previously shown that the quality and 361

quantity of irradiance decrease with decreasing distance between the maize and 362

soybean rows in intercropping (Yang et al., 2014). The results in this study also 363

confirm the significance of the distance between the maize and soybean rows in 364

increasing soybean yield (Fig. 7b). Therefore, appropriate planting patterns are 365

important in improving the light environment of the soybean canopy and increasing 366

the total yield of maize-soybean relay strip intercropping. 367

4.4 Effects of spatial arrangement on intercropped maize yield 368

The planting pattern is an agronomic management system that optimizes the use 369

of available natural and non-natural resources (Sharratt and McWilliams, 2005). Row 370

spaces are adjusted to improve the planting patterns for crop development and 371

increasing yield (Liu et al., 2012b). Narrow-row maize planting pattern promotes 372

photosynthesis and increases grain yield (Liu et al., 2012a). This pattern also provides 373


space for soybean in maize-soybean relay strip intercropping (Yang et al., 2014). 374

Planting patterns are important in maintaining maize grain yield and increasing the 375

total intercrop yield in maize-soybean intercropping systems. The maize yield per 376

plant decreased in the experiments under different bandwidth treatments (180 to 220 377

cm) (Table 1), but opposite results were found with different maize narrow-row 378

spacing (20 cm to 80 cm) in maize-soybean relay strip intercropping under 200 cm 379

bandwidth (Table 3) (Experiment 2). These results support previous findings (Echarte 380

et al., 2011). Intercropped maize was sown at a bandwidth wider than the spacing of 381

the sole crop rows (200 cm vs. 70 cm), and intra-row spacing was changed to 382

maintain the same plant density between intercrops and sole crops. For example, the 383

plant spacing at the same plant density was 16.7 cm for 200 cm bandwidth of 384

maize-soybean intercropping and 23.8 cm for sole maize (row spacing was 70 cm). 385

The intercropped maize yield was lower than that of sole maize in all treatments 386

(Tables 1 and 3; P < 0.05). Crop plants showed diverse responses to different spatial 387

arrangements, and maize grain yield increased at a relatively narrow-row spacing 388

(Stacciarini et al., 2010; Das and Yaduraju, 2011). Therefore, maintaining maize grain 389

yield level and increasing the total yield of the maize-soybean relay strip 390

intercropping by establishing better planting patterns could reduce competition 391

between plants for resources. 392

5. Conclusions 393

The total yields of the maize-soybean intercropping systems were higher than those 394

of sole maize and sole soybean, and the LERs of all planting geometries in the 395

maize-soybean relay strip intercropping systems were above 1.33. The optimum 396

bandwidth and maize narrow-row spacing in the maize-soybean relay intercropping 397

systems (the ratio of maize to soybean rows was 2:2) were 200 and 40 cm, 398


respectively, and the maximum LER was higher than 1.59. These results suggest 399

enhanced yield and substantially higher land-use efficiency under maize-soybean 400

relay strip intercropping. 401

Intercropped soybean yield was affected by the distance between maize and 402

soybean rows and plant spacing. Plant spacing had a dominant function when the 403

bandwidth of the maize-soybean relay strip intercropping was higher than 200 cm at 404

the same plant density. Otherwise, the distance between maize and soybean rows had 405

a dominant function. This result suggests that plant competition and maize shading 406

affect soybean yield in maize-soybean relay strip intercropping systems under 407

different planting geometries. 408

Intercropped maize yield increased with decreasing maize-soybean relay strip 409

intercropping bandwidth and increasing maize narrow-row spacing in maize-soybean 410

relay strip intercropping of 200 cm bandwidth. These results imply that competition 411

between plants for resources should be considered in planting geometries. 412

A significant positive correlation between grain yield and shoot biomass per plant 413

was found in this study according to the data sets of maize and soybean under sole 414

crop and intercropping conditions. The grain yield of intercrops was lower than that of 415

sole crop at the same plant density, which resulted from the lower inter- or intra-row 416

spacing and biomass reduction. Therefore, the effects of intercrop competition on 417

grain yield should be estimated to identify of suitable planting patterns in 418

intercropping systems in the future. 419

Acknowledgements 420

The research was supported by National Program on Key Basic Research Project 421

(2011CB100402), Public Research Funds Projects of Agriculture, Ministry of 422

Agriculture of the PR China (201203096; 201103001), and Program on Industrial 423


Technology System of National Soybean (CARS-04-PS19). 424

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536


Fig. 1. Mean air temperature and monthly precipitation during the growth stage of the 537

intercrops in 2012 and 2013 538

Fig. 2. Planting geometry arrangements of the maize-soybean intercrop in experiment 539

1 (a) and 2 (b). Intercropped and sole maize were sown at 6 plants m−2. Intercropped 540

and sole soybeans were sown at 10 plants m−2. Maize and soybean had different plant 541

spacings in experiment 1 (i.e., the plant spacings of maize in 160 and 180 cm 542

bandwidth treatments were 20.8 and 18.5 cm, respectively. Plant spacings of soybean 543

were 12.5 and 11.1 cm, respectively). Plant spacings of maize and soybean were 544

similar to those in experiment 2 (i.e., the plant spacings of maize and soybean in all 545

treatments were 16.7 and 10 cm, respectively). Solid and dashed lines represent maize 546

rows and soybean rows, respectively. Each solid circle represents one maize plant, 547

and each solid grey circle represents one soybean plant. 548

Fig. 3. Grain yield per plant (g plant-1) as a function of shoot biomass per plant for 549

maize (a) and soybean (b) during 2012 (empty symbols) and 2013 (solid symbols). 550

Regression lines determination coefficients (R2), and significance values (P) are for 551

data from the two years. The ↑ symbol shows the grain yield and shoot biomass of 552

sole crops. Other symbols represent the grain yield and shoot biomass of intercrops. 553

Fig. 4. Yield per soybean plant as a function of plant spacing (a) and row spacing (b) 554

in maize-soybean relay intercropping at different bandwidths. Plant spacings of 555

soybean in the 160, 180, 200, and 220 cm strip width treatments were 12.5, 11.1, 10, 556

and 9.6 cm, respectively, and the distances between maize and soybean rows were 40, 557

50, 60, and 70 cm, respectively. Dashed lines and empty circles represent values from 558


2012, and solid lines and circles represent values from 2013. 559

Fig. 5. Yield per maize plant as a function of plant spacing in maize-soybean relay 560

intercropping at different bandwidths. Maize plant spacings in 160, 180, 200, and 220 561

cm strip width treatments were 20.8, 18.5, 16.7, and 15.2 cm, respectively. Dashed 562

lines and empty circles represent values from 2012, and solid lines and circles 563

represent values from 2013. 564

565

Fig. 6. Grain yield per plant (g plant-1) as a function of shoot biomass per plant, for 566

maize (a) and soybean (b) during 2012 (empty symbols) and 2013 (solid symbols). 567

Regression lines determination coefficients (R2), and significance (P) are for the data 568

from both years. The ↑ symbol shows the grain yield and shoot biomass of sole crops. 569

Other symbols represent the grain yield and shoot biomass of intercrops. 570

Fig. 7. Yields per plant of maize (a) and soybean (b) as a function of maize 571

narrow-row spacing in maize-soybean relay intercropping with 200 cm bandwidth at 572

different maize narrow-row spacing. Distance between maize and soybean rows in 20, 573

40, 60 and 80 cm maize narrow-row spacing treatments were 70, 60, 50, and 40 cm, 574

respectively. Dashed lines and empty circles represent values from 2012, and solid 575

lines and circles represent values from 2013. 576

577

578

579

580

581


Table 1. Grain yields of the intercrops and LERs in 2012 and 2013. The different 582

bandwidths of maize-soybean relay strip intercropping were 160, 180, 200, and 220 583

cm (2:2 maize-to-soybean rows ratio in a single strip). Maize sole crop (SM) and 584

soybean sole crop (SS) are controls. Different lower case letters indicate significant 585

differences (LSD, P < 0.05). 586

587

Treatment

2012 2013 Component yield Mixed

yield‡ LER Component yield Mixed

yield‡ LER Maize Soybean Maize Soybean kg ha-1 kg ha-1

160 9131 a 479e 9610 a 1.33 6329 a 708 e 7037 b 1.56 180 8413 b 856d 9269 b 1.43 5802 c 1064 c 6866 c 1.73 200 8327 b 1291b 9618 a 1.64 5869 c 1516 a 7385 a 2.07 220 7422 c 1057c 8479 cd 1.42 5217 d 916 d 6133 d 1.53 SS - 1961a 1961 e - - 1380 b 1380 e - SM 8448 b - 8448 d - 6071 b - 6071 d -

‡ Mixed yields are the sum of the yields produced by the two component crops 588

589

590

Table 2. Maize and soybean shoot biomass values in 2012 and 2013. Different 591

bandwidths of maize-soybean relay strip intercropping are 160, 180, 200, and 220 592

cm (2:2 maize-to-soybean rows ratio in a single strip). Maize sole crop (SM) and 593

soybean sole crop (SS) are controls. Different lower case letters indicate significant 594

differences (LSD, P < 0.05). 595

Treatment 2012 2013

Maize Soybean Maize Soybean g plant-1 g plant-1

160 322.0 b 12.3 d 235.7 a 17.9 c 180 310.2 bc 17.6 c 224.0 bc 23.2 b 200 305.8 c 28.4 b 218.2 c 33.0 a 220 299.2 c 25.8 b 214.3 c 24.5 b SS - 40.2 a - 31.8 a SM 344.3 a - 252.7 b -

596

597

598


Table 3. Intercrop grain yields and LERs in 2012 and 2013. Different maize 599

narrow-row spacings of 20, 40, 60, and 80 cm in maize-soybean relay intercropping 600

of 200 cm bandwidth (2:2 maize-to-soybean rows ratio in a single strip). Maize sole 601

crop (SM) and soybean sole crop (SS) are controls. Different lower case letters 602

indicate significant differences (LSD, P < 0.05). 603

Treatment

2012 2013 Component yield Mixed

yield‡ LER Component yield Mixed

yield‡ LER Maize Soybean Maize Soybean kg ha-1 kg ha-1

20 5044 d 1472 b 6516 b 1.52 5099 c 1396 b 6496 b 1.56 40 5718 c 1399 b 7117 a 1.59 5570 ab 1348 b 6919 a 1.61 60 6107 b 1082 c 7190 a 1.49 5855 ab 1136 c 6991 a 1.54 80 6313 ab 819 d 7132 a 1.38 6049 ab 730 d 6780 ab 1.35 SS - 1993 a 1993 c - - 1854 a 1854 c - SM 6451 a - 6451 b - 6311 a - 6311 b -

‡ Mixed yields are the sum of the yields produced by the two component crops 604

605

Table 4. Maize and soybean shoot biomass in 2012 and 2013. Different maize 606

narrow-row spacings of 20, 40, 60, and 80 cm in maize-soybean relay intercropping 607

of 200 cm bandwidth (2:2 maize to soybean rows ratio in a single strip). Maize sole 608

crop (SM) and soybean sole crop (SS) are controls. Different lower case letters 609

indicate significant differences (LSD, P < 0.05). 610

Treatment 2012 2013

Maize Soybean Maize Soybean g plant-1 g plant-1

20 119.6 d 20.9 b 122.4 d 25.3 b 40 147.8 c 19.0 b 150.1 c 25.1 b 60 164.4 b 16.4 c 158.3 c 18.0 c 80 174.7 b 13.8 d 173.4 b 13.6 d SS - 28.3 a - 33.9 a SM 190.9 a - 195.3 a -

611

612


Fig. 1. Mean air temperature and monthly precipitation during the growth stage of the intercrops in 2012 and 2013

61x88mm (300 x 300 DPI)


Fig. 2. Planting geometry arrangements of the maize-soybean intercrop in experiment 1 (a) and 2 (b). Intercropped and sole maize were sown at 6 plants m−2. Intercropped and sole soybeans were sown at 10

plants m−2. Maize and soybean had different plant spacings in experiment 1 (i.e., the plant spacings of

maize in 160 and 180 cm bandwidth treatments were 20.8 and 18.5 cm, respectively. Plant spacings of soybean were 12.5 and 11.1 cm, respectively). Plant spacings of maize and soybean were similar to those in

experiment 2 (i.e., the plant spacings of maize and soybean in all treatments were 16.7 and 10 cm, respectively). Solid and dashed lines represent maize rows and soybean rows, respectively. Each solid circle

represents one maize plant, and each solid grey circle represents one soybean plant. 98x78mm (300 x 300 DPI)


Fig. 3. Grain yield per plant (g plant-1) as a function of shoot biomass per plant for maize (a) and soybean (b) during 2012 (empty symbols) and 2013 (solid symbols). Regression lines determination coefficients (R2), and significance values (P) are for data from the two years. The ↑ symbol shows the grain yield and

shoot biomass of sole crops. Other symbols represent the grain yield and shoot biomass of intercrops. 63x88mm (300 x 300 DPI)


Fig. 4. Yield per soybean plant as a function of plant spacing (a) and row spacing (b) in maize-soybean relay intercropping at different bandwidths. Plant spacings of soybean in the 160, 180, 200, and 220 cm strip width treatments were 12.5, 11.1, 10, and 9.6 cm, respectively, and the distances between maize and soybean rows were 40, 50, 60, and 70 cm, respectively. Dashed lines and empty circles represent values

from 2012, and solid lines and circles represent values from 2013. 60x24mm (300 x 300 DPI)


Fig. 5. Yield per maize plant as a function of plant spacing in maize-soybean relay intercropping at different bandwidths. Maize plant spacings in 160, 180, 200, and 220 cm strip width treatments were 20.8, 18.5,

16.7, and 15.2 cm, respectively. Dashed lines and empty circles represent values from 2012, and solid lines

and circles represent values from 2013. 32x24mm (300 x 300 DPI)


Fig. 6. Grain yield per plant (g plant-1) as a function of shoot biomass per plant, for maize (a) and soybean (b) during 2012 (empty symbols) and 2013 (solid symbols). Regression lines determination coefficients (R2), and significance (P) are for the data from both years. The ↑ symbol shows the grain yield and shoot

biomass of sole crops. Other symbols represent the grain yield and shoot biomass of intercrops. 62x90mm (300 x 300 DPI)


Fig. 7. Yields per plant of maize (a) and soybean (b) as a function of maize narrow-row spacing in maize-soybean relay intercropping with 200 cm bandwidth at different maize narrow-row spacing. Distance

between maize and soybean rows in 20, 40, 60 and 80 cm maize narrow-row spacing treatments were 70,

60, 50, and 40 cm, respectively. Dashed lines and empty circles represent values from 2012, and solid lines and circles represent values from 2013.

62x93mm (300 x 300 DPI)


yield response to different planting geometries in maize ... · 25 abstract: 26 planting geometries...

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