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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
5
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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Page 1 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
46
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
Page 2 of 31Agronomy Journal Accepted paper, posted 09/08/2014. doi:10.2134/agronj14.0263
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
Page 3 of 31Agronomy Journal Accepted paper, posted 09/08/2014. doi:10.2134/agronj14.0263
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
Page 4 of 31Agronomy Journal Accepted paper, posted 09/08/2014. doi:10.2134/agronj14.0263
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
Page 5 of 31Agronomy Journal Accepted paper, posted 09/08/2014. doi:10.2134/agronj14.0263
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
Page 6 of 31Agronomy Journal Accepted paper, posted 09/08/2014. doi:10.2134/agronj14.0263
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
Page 7 of 31Agronomy Journal Accepted paper, posted 09/08/2014. doi:10.2134/agronj14.0263
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
Page 8 of 31Agronomy Journal Accepted paper, posted 09/08/2014. doi:10.2134/agronj14.0263
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
Page 9 of 31Agronomy Journal Accepted paper, posted 09/08/2014. doi:10.2134/agronj14.0263
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
Page 10 of 31Agronomy Journal Accepted paper, posted 09/08/2014. doi:10.2134/agronj14.0263
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
Page 11 of 31Agronomy Journal Accepted paper, posted 09/08/2014. doi:10.2134/agronj14.0263
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
Page 12 of 31Agronomy Journal Accepted paper, posted 09/08/2014. doi:10.2134/agronj14.0263
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
Page 13 of 31Agronomy Journal Accepted paper, posted 09/08/2014. doi:10.2134/agronj14.0263
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
Page 14 of 31Agronomy Journal Accepted paper, posted 09/08/2014. doi:10.2134/agronj14.0263
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
Page 15 of 31Agronomy Journal Accepted paper, posted 09/08/2014. doi:10.2134/agronj14.0263
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
Page 16 of 31Agronomy Journal Accepted paper, posted 09/08/2014. doi:10.2134/agronj14.0263
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
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Technology System of National Soybean (CARS-04-PS19). 424
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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
Page 21 of 31Agronomy Journal Accepted paper, posted 09/08/2014. doi:10.2134/agronj14.0263
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
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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
Page 23 of 31Agronomy Journal Accepted paper, posted 09/08/2014. doi:10.2134/agronj14.0263
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
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Fig. 1. Mean air temperature and monthly precipitation during the growth stage of the intercrops in 2012 and 2013
61x88mm (300 x 300 DPI)
Page 25 of 31Agronomy Journal Accepted paper, posted 09/08/2014. doi:10.2134/agronj14.0263
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)
Page 26 of 31Agronomy Journal Accepted paper, posted 09/08/2014. doi:10.2134/agronj14.0263
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)
Page 27 of 31Agronomy Journal Accepted paper, posted 09/08/2014. doi:10.2134/agronj14.0263
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)
Page 28 of 31Agronomy Journal Accepted paper, posted 09/08/2014. doi:10.2134/agronj14.0263
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)
Page 29 of 31Agronomy Journal Accepted paper, posted 09/08/2014. doi:10.2134/agronj14.0263
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)
Page 30 of 31Agronomy Journal Accepted paper, posted 09/08/2014. doi:10.2134/agronj14.0263
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)
Page 31 of 31Agronomy Journal Accepted paper, posted 09/08/2014. doi:10.2134/agronj14.0263