Nitrogen Contribution from Winter-Killed Faba Bean Cover Crop to Spring-Sown Sweet Corn in Conventional and No-Till Systems

Abstract

The N release trend of winter-killed faba bean (Vicia faba L.) residues has not been previously investigated. A 2-yr experiment was conducted in 2013–2015 to investigate potential N accumulation in fall-grown faba bean as cover crop and N contribution to subsequent sweet corn under no-till (NT) and conventional tillage (CT) systems. Faba bean biomass prior to winter-kill was reduced linearly with delayed planting. The amount of reduced biomass estimated approximately 180 and 210 kg ha⁻¹ d⁻¹ in 2013 and 2014, respectively. Faba bean sown on 1 August accumulated as much as 192 kg N ha⁻¹ vs. 67 kg N ha⁻¹ when planted on 14 August. Under CT, 50% of N was released from residues by the end of May however NT system delayed 50% N release until end of June, thus providing better synchrony with N uptake by sweet corn. Averaged over two years, sweet corn planted into the residues of the earliest sown faba bean produced 19% more marketable ears, 23% higher fresh ear weight, and 39% less unfilled ear tip compared with sweet corn grown in plots lacking a prior faba bean cover crop. Both number of marketable ears and fresh ear yield of sweet corn were significantly higher in NT compared with CT systems. On average, sweet corn seeded in faba bean residues and amended with an additional 50 kg N ha⁻¹yielded similarly to sweet corn received 100 kg N ha⁻¹ with no prior faba bean cover crop.

Full text

1
Nitrogren Contribution from Winterkilled Faba Bean Cover Crop to Spring-Sown Sweet 1
Corn in Conventional and No-Till Systems 2
Masoud Hashemi,* Fatemeh Etemadi, Omid Zandvakili, Aria Dolatabadian, and Amir 3
Sadeghpour 4
M. Hashemi, F. Etemadi, O. Zandvakili, Univ. of Massachusetts, 201 Natural Resource Way, 5
Bowditch Hall, Amherst, MA 01003; A. Dolatabadian, Univ. of Western Australia, School of 6
Plant Biology, Faculty of Science, Perth, Western Australia, 6009, Australia; A. Sadeghpour, 7
Dep. of Plant, Soil, and Agricultural Systems, Southern Illinois Univ. of Carbondale, College of 8
Science, Carbondale, IL 62901. Received 30 Aug. 2017. Accepted 5 Jan. 2018. *Corresponding 9
author (masoud@umass.edu). 10
ABSTRACT 11
Legumes can potentially replace, or significantly contribute to, the nitrogen (N) fertilizer 12
requirements of N demanding non-legume crops such as sweet corn (Zea mays L.). The N release trend of 13
winterkilled faba bean (Vicia faba L.) cover crop residues has not been previously investigated. A two-14
year experiment was conducted in 2013-2015 to investigate potential N accumulation in fall grown faba 15
bean cover crop and successive N contribution to subsequent sweet corn production under both no-till 16
(NT) and conventional tillage (CT) systems. This experiment utilized a randomized complete block 17
design with a split-plot arrangement. Main plots consisted of NT and CT treatments. Sub-plots were 18
allocated to a factorial combination of three faba bean planting dates (August 1, 8, and 16) and no cover 19
crop (control) with supplemental N rates (0, 25, 50, 75, 100 kg N ha
-1
) applied to sweet corn the following 20
spring. A mesh bag technique was used to investigate the trend of faba bean residue decomposition and N 21
release over time. Faba bean biomass accumulation measured just prior to winterkill was significantly 22
influenced by date of planting. Final faba bean biomass prior to winter-kill was reduced linearly with 23
delayed planting. The effect of planting delay on final biomass was significant. The amount of reduced 24
biomass estimated as much as 180 kg ha
-1
day
-1
and 210 kg ha
-1
day
-1
in 2013 and 2014, respectively. Faba 25
bean sown on August 1 accumulated as much as 192 kg N ha
-1
versus 67 kg N ha
-1
when planted on 26
August 14. Under CT, 50% of N was released from faba bean residues by the end of May. By contrast, 27
under NT conditions, 50% of N was released by the end of June, thus providing better synchrony with N 28
uptake by sweet corn. Averaged over two years, sweet corn planted into the residues of the earliest sown 29
faba bean produced 19% more marketable ears, 23% higher fresh ear weight, and 39% less unfilled ear tip 30
compared with sweet corn grown in plots lacking a prior faba bean cover crop. Both the number of 31
marketable ears and the ear yield of sweet corn were significantly higher in NT compared with CT 32
systems. On average, sweet corn that followed a faba bean cover crop, and that was amended with an 33
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additional 50 kg N ha
-1
, yielded similarly to sweet corn that received 100 kg N ha
-1
but that had no prior 34
faba bean cover crop. 35
Abbreviations: N, nitrogen; NT, no-till; CT, conventional till. 36
Keywords: Faba bean, tillage system, faba bean decomposition trend, fertilizer replacement 37
Core Ideas: 38
• Faba bean cover crops sown on August 1 accumulated up to 192 kg N ha
-1
. 39
• Better synchrony between faba bean residue decomposition and N uptake by sweet corn 40
was achieved under NT management. 41
• Sweet corn yielded higher under NT versus CT system. 42
• On average, faba bean provided approximately 50 kg ha
-1
of subsequent sweet corn N 43
requirements. 44
INTRODUCTION 45
Legumes can potentially replace, or significantly contribute to, the N fertilizer requirements of N 46
demanding crops such as sweet corn (Zandvakili, et al., 2012; Jahanzad, et. al., 2014; Hardarson and 47
Atkins, 2003; N’Dayegamiye et al., 2015). Additionally, grain legumes serve as an excellent protein 48
source in human and livestock diets (Huang et al., 2016; Ito et al., 2016). Faba bean is known as one of 49
the oldest crops in the world, and it is the third most important grain legume after soybean (Glycine max 50
L.) and pea (Pisum sativum L.) (Mihailovicet et al., 2005; Daur et al., 2011; Singh et al., 2013). However, 51
faba bean is not currently grown as a cover crop mainly due to its large seed size and relatively low 52
biomass production that makes it non-competitive compared with other legume cover crops (Etemadi et 53
al, 2017). 54
Diverse ecosystem services are expected from growing faba bean (Ko¨pke and Nemecek, 2010), and in 55
recent years increasing attention has been given to using faba bean as a multi-purpose legume cover crop 56
(L´opez-Bellido et al., 2005; Etemadi et al, 2015; Landry et al., 2015) as well as in intercropping systems 57
(Zhang et al., 2004; Song et al. 2007; Li et al., 2009). Arguably, the most important contribution of faba 58
bean to agricultural ecosystems is the substantial amount of atmospheric N that can be fixed by the crop 59
and its associated rhizobia. Depending on the growing conditions, faba bean is reported to fix up to 160 60
kg N ha
-1
(Cline and Silvernail, 2002; Hoffmann et al., 2007; Horst et al., 2007). For this reason, faba 61
bean can be considered as one of the most efficient nitrogen-fixing cool season legumes (Herridge et al., 62
1994). Interestingly, faba bean maintains its nitrogen-fixing capabilities even in soils that are rich in N 63
(Peoples et al., 2009; Ko¨pke and Nemecek, 2010). Other benefits and potential uses for faba bean include 64
the following: i. break crop in a broader rotational program (Ko¨pke and Nemecek, 2010; Abera et al., 65
2015; Landry, et al., 2015), ii. feed source for pollinators and beneficial insects (Somerville, 2002; 66
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Etemadi et al., 2015), iii. enhanced soil microbial activity (Wang et al., 2007; Van der Putten et al., 2013; 67
Wahbi et al., 2016), iv. control of soil-borne diseases (Jensen et al., 2010), and v. a rich source of L-Dopa 68
for medicinal use (Etemadi et al, 2017). Therefore, integrating faba bean into cropping systems as either a 69
cover crop or a dual purpose cash/cover crop can enhance the sustainability and resiliency of agricultural 70
production systems. 71
In the northeast U.S., unlike many common legumes such as peas, lentils, and beans, faba bean continues 72
its growth and fixation of atmospheric N until winterkill in early to mid-December (Etemadi and 73
Hashemi, 2014). Griffin et al. (2000) stated that in northern climates, legume cover crops seeded after the 74
main crop’s harvest has limited opportunity for accumulating considerable amount of biomass . When 75
grown solely as cover crop, faba bean can be sown as late as early September; however, pod harvest 76
opportunity is unlikely in late planting. Eearlier planting of faba bean results in greater biomass 77
production and root activity thus provides more ecological services – including increased N contributions 78
to the subsequent cash crop (Song et al., 2007; Ko¨pke and Nemecek, 2010). Growing dual-purpose faba 79
bean as a cash and cover crop requires an earlier sowing in July (unpublished data). 80
In New England, sweet corn is cultivated on 5,540 hectares (Nass, 2014), and is one of the most widely 81
grown vegetable crop. Like other types of corn, sweet corn is considered as a high N demanding crop, 82
requiring 130-160 kg N ha
-1
on average (New England Vegetable Guide, 2016). Nitrogen utilization 83
efficiency can be substantially improved by including legume cover crops in cropping systems, and also 84
by improving the synchronization of N inputs and uptake sinks (Essah and Delgado, 2009). A previous 85
report suggested that faba bean as green manure can significantly lower the cost of N fertilizer and the 86
crop may also offer additional soil health benefits (Ko¨pke and Nemecek,2010). 87
In southern New England, active decomposition of winterkilled cover crops, including fall grown faba 88
bean, generally begins as early as mid, March. However, sweet corn is commonly planted in mid, May. 89
In contrast to winterkilled faba bean, spring-grown faba bean residues generally have a significantly 90
lower C:N ratio that causes the N mineralization of the residues to occur much faster (Shi, 2013). This 91
fast rate of decomposition may not be well synchronized with the N uptake pattern of the following crop, 92
which results in a higher risk of N loss to the environment (Jensen et al., 2010), especially in CT systems. 93
Improving the synchrony of N release from faba bean residues can enhance the N uptake/utilization 94
efficiency of the succeeding crop, thus reducing potential environmental hazards (Thompson et al., 2015). 95
The C:N ratio of cover crop residues is an important functional trait that influences the subsequent crop 96
yield (Kuo and Sainju, 1998; Starovoytov et al., 2010).The C:N ratio can be manipulated by mixing 97
legume and non-legume cover crop species (Teasdale and Abdul-Baki, 1998; Finney et al., 2016). For 98
example, a mixed vetch and winter rye cover crop may supply sufficient, timely N to NT field corn 99
(Griffin, et al., 2000; Cline and Silvernail, 2002). Mixing faba bean with a grass companion cover crop 100
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has been suggested in order to balance its C:N ratio (Ranells and Wagger, 1997; Villamil et al., 2006). 101
However, when faba bean is grown as a dual- purpose cash and cover crop, the use of a companion grass 102
with faba bean is not practical. Implementing a NT system in which winter killed faba bean residues 103
remain on the soil surface may be a viable option to slow down the N mineralization rate in the spring, 104
thus providing improved synchrony with N uptake of sweet corn. Moreover an integrated cover crops 105
and NT system is an effective strategy to build soil organic matter (Sainju et al., 2002). 106
There is a need for a better understanding of the trend of N release from winterkilled faba bean residues. 107
We hypothesized that leaving fall sown faba bean cover crop residues on the soil surface would provide a 108
better N release/uptake synchrony with spring sown sweet corn as opposed to incorporating the faba bean 109
residues into the soil. Therefore, the main goals of the current study were to: 110
1) Evaluate the decomposition trend of winterkilled faba bean residues in CT and NT systems. 111
2) Assess the contribution of faba bean residues to the N demand of succeeding sweet corn. 112
113
MATERIALS AND METHODS 114
Experimental site and weather conditions 115
A two-year experiment was conducted in 2013-2015 at the University of Massachusetts Amherst 116
Agricultural Experiment Station Crops and Animal Research and Education Farm in South Deerfield (42° 117
28′ 37″N, 72° 36′ 2″ W). The soil type at the experimental site was a Hadley fine sandy loam (nonacid, 118
mesic Typic Udifluvent). Composite soil sample (0-0.2 m depth) taken prior to planting indicated soil pH 119
(1:1, soil/H
2
O) was 6.6, cation exchange capacity (CEC) was 8.1 meq/100g, and available P, K and Mg 120
were all in the optimum range thus no fertilizer was applied to the experimental plots in either year. Due 121
to the humid northeastern climate, N recommendations are not based on specified soil nitrate test results 122
(Lawrence et al., 2008). Weather conditions including growing degree days (GDD), precipitation 123
throughout the experiment period (2013-2015), and the norm (average of 20 years), for the region are 124
presented in Table 1. 125
126
Experimental setup, treatments and field operations 127
The experiment was laid out as split-plot arrangement within a randomized complete block design with 128
four replications at the same experimental units as the previous year. Main plots consisted of NT and CT 129
treatments. Sub-plots were allocated to a factorial combination of three faba bean planting dates (August 130
1, 8, and 16) and no cover crop (control) with supplemental N rates (0, 25, 50, 75, 100 kg N ha
-1
) applied 131
to sweet corn the following spring. Individual sub-plots consisted of three rows, 4.2 m long and 0.76 m 132
wide. Faba bean (cv. Windsor) was planted with a plot grain drill at a density of 8.8 plant m
-2
. Seeds 133
were inoculated with peat base Rhizobium Leguminosarum (VERDESIAN, N.DURE, , carry, NC) prior to 134
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sowing in both years. No irrigation was used in this experiment as irrigation is not a common practice for 135
agronomic field crops in Massachusetts.. Faba bean biomass was determined prior to winterkill (roughly 136
mid-December in both years) by harvesting one square meter from all plots. 137
In the spring, faba bean residues were disked into the soil in the CT plots. Residues remained on the soil 138
surface in the NT treatment. An early maturity sweet corn (Spring Treat F1 (se) Nat II , 66 days) was 139
planted on faba bean stubble rows on May15
th
in both years at a population density of 65,000 plants ha
-1
. 140
Nitrogen fertilizer in the form of calcium ammonium nitrate (27% N) was side dressed to sweet corn at 141
0, 25, 50, 75, 100 kg N ha
-1
within each faba bean cover crop date of planting. 142
In faba bean plots, weeds were controlled mechanically (by hand and rototiller) three times during its 143
growing period. Weed control in sweet corn was similar in both years and consisted of 2.2 kg ai. ha
-1
dual 144
magnum (2-chloro-2',6'-diethyl-N-(methoxymethy1)-acetanilide, and 1.8 kg ai. ha
-1
treflan (a,a,a-145
Trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) pre-emergence herbicide. 146
Sweet corn ears from center rows were hand harvested on August 6
th
in 2014 and August 10
th
in 2015 at 147
peak marketable stage. The marketable ear number (minimum of 17 cm in length), ear fresh yield, and 148
percentage of unfilled ear tip were determined. 149
150
Faba bean residues decomposition 151
A mesh bag technique was used based on the procedure fully described by Jahanzad et al. (2016). Mesh 152
bags (60 µm) were made of polyamide nylon with a finished size of 20 cm x 10 cm. Prior to winterkill, 10 153
faba bean plants were dug out carefully, washed, and air dried. Total fresh biomass including roots and 154
shoots were determined. The tissue samples were dried in a forced air oven at 80°C for 36 h. Dried 155
samples were weighed, then ground fine to pass through a 0.42 mm screen. A 200 mg subsample was 156
used for N analysis. A Kjeldahl method of digestion (potassium sulfate, cupric sulfate, sulfuric acid) was 157
used, followed by N measurement with a Lachat 8500 FIA spectrophotometer, Lachat Method Number 158
13-107-06-2-D (Zellweger Analytical, Milwaukee, WI, USA). 159
Eighty mesh bags were filled with 200 g of uniformly mixed fresh chopped plant tissues. Forty mesh 160
bags were left on the soil surface (simulating NT system) and forty bags were buried 20 cm deep in the 161
soil (simulating CT system). Three mesh bags, representing three replications, were recovered from both 162
tillage systems on a weekly basis beginning April 1
st
. At each retrieval time, the content of each bag was 163
dried in a forced-air oven set at 70°C, ground, weighed, and analyzed for dry matter and N content. 164
165
166
Statistical analysis 167
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Analysis of variance (ANOVA) was conducted with the mixed model procedures in SAS (SAS 168
Institute, 2003). Data shown in figures are the arithmetic means of four replicates of each treatment. 169
Mesh bag retrieval dates were a continuous array of treatments, so trends in cover crop residue dry 170
matter and N release during decomposition were assessed by regression analysis. Effects were 171
considered significant at P ≤ 0.05 by the F test, and when the F test was significant, Fisher’s Least 172
Significant Difference Test (LSD) was used for mean separation. 173
174
RESULTS AND DISCUSSION 175
Weather 176
Cumulative growing degree days (GDD
4
0C
) at Orange Airport, MA (roughly 27 Km away from 177
the research site) during the growth period of faba bean cover crop (August-December) were 1843 and 178
1889 in 2013 and 2014, respectively which were lower than the norm for this location (Table 1). 179
Cumulative GDD during the months of May through August when sweet corn normally grows in New 180
England were similar to the norm for the location in both years of the study. From August to December, 181
months that spanned the faba bean growth period, precipitation totaled 418 mm in 2013 and 499 mm in 182
2014, which were comparable to the norm for the area. However in spring 2014, the sweet corn crop 183
experienced an unusual drought condition throughout the entire growing season (Table 1). Therefore, 184
when averaged across all faba bean planting dates, the sweet corn yielded roughly 15% less overall in 185
2014 than in 2015. The influence of year and the interaction of year by trait were significant; 186
accordingly, the results of the two years are presented separately. 187
188
Cover crop biomass and decomposition trend 189
Faba bean biomass just prior to winter kill was dramatically influenced by date of planting (Table 190
2). The key benefit of legume cover crops is their role in supplying significant amounts of atmospheric N 191
to a successive crop. However, it is well documented that the magnitude of agronomic services from 192
cover crops in general, and N contribution from legumes in particular, are largely dependent on the 193
amount of biomass they can produce by the termination time (Snapp et al., 2005; Hashemi et al., 2013; 194
Finney et al., 2016; Mirsky et al., 2017). Early planting has been recognized as one major factor that 195
influences cover crops biomass yield (Hashemi et al., 2013; Lounsbury and Weil, 2014; Komainda et al., 196
2016). In the current study, faba bean biomass decreased linearly as planting date was delayed. The 197
amount of biomass loss for each day of delay was significant and estimated around 180 kg ha
-1
and 210 198
kg ha
-1
in 2013 and 2014, respectively. However, the first week of planting delay (August 8
th
vs August 199
1
st
) was responsible for only a 19% and 7% biomass reduction in 2013 and 2014, respectively. 200
Conversely, the second week of planting delay (August 16
th
vs August 1
st
) resulted in a reduction of faba 201
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bean biomass of up to 62% and 55% in 2013 and 2014, respectively. Drier conditions in 2013, especially 202
during the month of October when faba bean is actively growing, could in part explain the difference in 203
total biomass production in the two years of this experiment. We presumed that a higher Rhizobium 204
population in the soil in the second year of the experiment could also have played a role in the 205
production of more faba bean biomass in 2014. The presence of higher N concentrations in faba bean 206
tissues in 2014 support this assumption (Table 2). 207
Nitrogen yield of a cover crop is a product of tissue N concentration and biomass accumulation, which 208
indicates the potential amount of N that can be released into the soil during the decomposition process. 209
Nitrogen accumulation of faba bean in 2013 and 2014 is presented in Table 2. As mentioned above, the 210
N concentration in faba bean plants was significantly higher in 2014 compared with 2013. Although the 211
Rhizobium population was not analyzed in this experiment, it is logical that the Rhizobium population 212
would naturally be higher in the second year of the experiment conducted in the same location compared 213
to the first year of the study. The difference in the N concentration of faba bean in each year of the 214
experiment could be at least partly attributed to the hypothesized higher bacterial population and 215
resultant activity in 2014. The results indicate that faba bean sown on August 1
st
, 2014, accumulated as 216
much as 192 kg ha
-1
(Table 2), which is greater than earlier reports (Bremer, et al., 1988; Unkovich and 217
Pate, 2000; Cline and Silvernail, 2002) who reported that faba bean can fix up to 160 kg N ha
-1
. Also, 218
Duc et. al., (1988) and Schwenke et. al., (1998) reported that faba bean can fix up to 330 kg N ha
-1
. 219
Additionally, in the dryer condition of 2013, faba bean fixed 50% less N than in 2014, averaged 220
over the three planting dates. The results obtained in the current study, as well as in earlier reports 221
(Oplinger et al., 1990; Baddeley et al., 2014 ), revealed that in general, faba bean and its associated 222
Rhizobium are more efficient in fixing atmospheric N than vetch (Spargo et al., 2016; Mirsky et al., 223
2017) and many other grain legumes (Peoples et al., 2009). 224
The trends of N release for each of the two tillage systems are presented in Figure 1. When the first 225
decomposition sample was retrieved on April 1 for analysis, almost 30% of the N content of the faba 226
bean residues in CT, and 20% in NT, had already been mineralized. The difference in the N release rate 227
between the two tillage systems widened as the growing season progressed. Rapid decomposition of 228
cover crop residues is not necessarily desirable because the mineralized N is subject to various avenues 229
of environmental loss if it is not captured by plants (Lupwayi et al., 2004; Tonittoa et al., 2006; Cook et 230
al., 2010). The results confirmed our hypothesis and also the earlier report by Drinkwater et al. (2000) 231
that the use of a NT method would slow down decomposition of faba bean residues, providing a better 232
timing between N mineralization and N uptake by sweet corn plants. In CT system, almost 50% of N 233
was released by the end of May, whereas in NT, release of 50% of N was delayed for approximately one 234
month and occurred at the end of June. In New England, sweet corn traditionally is planted in early-mid 235
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May and commences its rapid growth stage in mid-June (4R Plant Nutrition, 2015). Therefore the delay 236
in 50% N release from faba bean residues can significantly improve the synchrony between N release 237
from faba bean residues and N uptake by sweet corn. 238
239
Sweet corn yield 240
Influence of faba bean residues and tillage systems 241
Sweet corn marketable ear number and fresh ear yield, as well as percentage of unfilled ear tip, were 242
significantly influenced by the amount of faba bean biomass accumulated at each planting date (Table 3). 243
Averaged over two years, sweet corn planted into residues of the earliest sown faba bean produced 244
roughly 19% more marketable ear, 23% higher fresh ear weight, and 39% less unfilled ear tip compared 245
with those grown in no faba bean plots (Table 3). The positive influence of faba bean residues on 246
aforementioned traits dropped to 11, 7, and 6%, respectively when planting of faba bean was delayed for 247
only two weeks. The difference in influence of faba bean residues on yield performance of sweet corn is 248
mainly attributed to the total N contribution of their residues (Table 2). 249
As previously stated, more ecological benefits can generally be expected from higher cover crop biomass 250
production. In addition to the higher accumulated N in early sown faba bean residues, other factors, such 251
as type of tillage system, might have played a role in this study. Marketable ear yield of sweet corn were 252
significantly higher in NT than in CT systems (Figure 2a). Averaged over faba bean residue, sweet corn 253
plants produced roughly 22% higher marketable ear and 31% less unfilled ear tip compared with 254
conventional system (Figure 2 a ,b). This could be primarily due to better synchrony existed between faba 255
bean decomposition with sweet corn growth in no-till system (Figure 1). The interaction between tillage 256
system and presence of faba bean residue was significant. For example the ear yield differce between corn 257
grown into faba bean residues was higher in no-till plots compared with conventional tillage system 258
(Figure 4). Averaged over two years, the maximum marketable ear (12.8 Mg ha
-1
) was obtained from corn 259
planted in no-till plots, covered with faba bean residues (Figure 4). Reports on the influence of tillage 260
systems on sweet corn yield planted following various types of cover crops are contradictory and seem 261
greatly influenced by the amount of residues produced at cover crop termination time (Teasdale et al., 262
2008) and the C:N ratio of the cover crops (Cline and Silvernail, 2002; Kuo and Jellum, 2002). Cline and 263
Silvernail (2002) concluded that NT sweet corn yielded similar to CT when planted after vetch, whereas 264
sweet corn grown after rye or rye and vetch mixture experienced a yield penalty. In addition to C:N, time 265
and method of termination of cover crops may also interact with the influence of tillage system. Winter 266
legumes grown as green manure in spring and/or summer generally have a lower C:N, and they thus 267
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release substantial amounts of N in CT systems. In NT systems the release of N is slower and therefore 268
may not meet the N requirement of a high N demanding crops such as sweet corn. 269
Recently, Lowry and Brainard (2017) reported that the influence of the tillage system on organic sweet 270
corn biomass is pronounced when soil moisture was non-limiting. Also, the lack or negative response of 271
NT systems on integrated organic cover crop/sweet corn production might be related to higher weed 272
population that is usually higher in NT compared with CT systems. 273
Influence of supplement N application 274
In both years, averaged over faba bean planting dates and tillage systems, the response of sweet corn 275
marketable ear number and fresh ear yield to application of supplemental N was quadratic (Table 3) and 276
reached its peak at approximately 80 kg N ha
-1
(Figure 3). Unfilled ear tip decreased linearly as N 277
application rate increased (Table 3). As expected, the response of sweet corn to supplemental N was more 278
pronounced when sweet corn was planted in plots without a prior faba bean cover crop (Figure 3). In plots 279
with no faba bean cover crop, a linear increase in sweet corn marketable ear yield was detected with 280
increased supplement N fertilizer rate (Figure 3). Although the faba bean cover crop was effective in 281
fixing and conserving N, the faba bean residues did not provide sufficient N to the following sweet corn 282
crop. As a result, when corn was planted into faba bean residues an asymptotic response to increased N 283
application rate with a peak at approximately 60 kg ha
-1
was observed (Figure 3). The impact of faba bean 284
residues on sweet corn response to supplemental N was more noticeable in 2014 than 2015 presumably 285
due to differences in the amount of percipiation (Table 1). The results obtained from this study do not 286
confirm some of the earlier reports (Griffin et al., 2000; Cline and Silvernail, 2002) that indicated sweet 287
corn planted after a legume cover crop usually does not respond to supplemental N. Based on results 288
obtained in the current study, we concluded that averaged over two years, the yield of sweet corn grown 289
after faba bean was responsive to the first three increments of N up to 60 kg ha
-1
as opposed to the linear 290
response in no faba bean plots. We found no significant interaction between faba bean date of planting 291
and tillage system or between supplemental N application rate and tillage system. 292
Further investigation on faba bean as the major N source for succeeding vegetables under different sets of 293
environmental conditions and management practices would be valuable for developing strategies to 294
increase economic returns and to limit adverse environmental impacts of commercial fertilizers. 295
CONCLUSION 296
The results of this experiment provide a better understanding of the efficiency of N contribution of faba 297
bean grown as a cover crop in rotation with sweet corn in the northeast USA. Nitrogen yield of faba bean 298
is a function of both its biomass production and its plant tissue N concentration. Therefore, earlier 299
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10
planting of faba bean dramatically influences the potential N that could be fixed and subsequently 300
contributed to the following crop. In the current study, our measurements revealed that potential N was as 301
much as 192 kg N ha
-1
when faba bean was planted as early as August 1
st
and weather conditions were 302
favorable (2014). The tillage system can significantly influence the trend of residue decomposition. No-303
till system delayed 50% N release from faba bean residues by approximately one month, which can 304
significantly improve the synchrony between mineralization of faba bean residues and N uptake by sweet 305
corn. Sweet corn planted into faba bean residues produced greater marketable ear number, higher fresh 306
ear weight, and less unfilled ear tip compared with those grown in no faba bean plots. Since fall grown 307
faba bean is not considered to be a high residue cover crop, spring-sown sweet corn can benefit from NT 308
compared with CT system. Averaged over two years and faba bean planting dates, sweet corn yielded 309
26% higher and unfilled ear tip 30% lower in NT compared with CT, respectively. Although the faba 310
bean cover crop was effective in fixing and conserving N, its residues did not provide sufficient N to the 311
following sweet corn crop. On average, sweet corn responded positively to applications of supplemental 312
N up to 60 kg ha
-1
. Averaged over two years, sweet corn following faba bean, plus approximately 50 kg N 313
ha
-1
, yielded similarly to those that received 100 kg N ha
-1
without a prior faba bean cover crop. 314
315
ACKNOWLEDGEMENTS 316
This material is based upon work supported through grants awarded by Northeast SARE and 317
Massachusetts Department of Agriculture. Authors thank Neal Woodard, Sarah Weis, and Kelly Kraemer 318
for their field work assistance. 319
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505
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Table1. Precipitation and accumulated GDD during growing seasons of faba bean (2013 and 506
2014), sweet corn (2014 and 2015), and faba bean residues decomposition (2014 and 2015) 507
compared with 20 years average of corresponding months for the experimental location. 508
†GDD calculated as GDD = Ʃ (T
max
- T
min
)/2 –T
b
where T
max
and T
min
are daily maximum and minimum 509
temperatures, respectively. Base temperature ( T
b
) was set as 4
o
C and 10
o
C for faba bean and sweet corn, 510
respectively. 511
512
513
514
515
516
517
518
519
520
521
Month GDD † Precipitation (mm)
(Faba bean) 2013 2014 Norm 2013 2014 Norm
Aug 858 835 907 99 92 91
Sep 591 630 643 77 41 109
Oct 316 368 286 67 160 110
Nov 68 45 89 94 90 77
Dec 10 11 16 81 116 79
Total 1843 1889 1941 418 499 466
(No crop) 2014 2015 Norm 2014 2015 Norm
Jan 9 0 3 82 83 67
Feb 0 0 2 59 37 69
Mar 3 2 47 82 43 95
Apr 167 157 204 112 51 80
Total 179 159 256 335 214 311
(Sweet corn) 2014 2015 Norm 2014 2015 Norm
May 516 674 515 29 26 88
Jun 785 715 767 1 192 116
Jul 947 938 942 55 85 98
Total 2248 2327 2224 84 303 302
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Table 2. Faba bean biomass and N concentration in faba bean aerial biomass prior to winter kill as 522
influenced by its date of planting. 523
Faba bean Biomass (Mg ha
-
1
) N in residues (g kg
-
1
) N yield (kg ha
-
1
)
planting date 2013 2014 2013 2014 2013 2014
Aug 01 4.0±0.1
5.3±0.1 25±0.2 36±0.5 101±0.1 192±0.5
Aug 07 3.3±0.1 4.9±0.1 23±0.1 31±0.2 75±0.3 154±0.2
Aug 14 1.5±0.1 2.4±0.2 22±0.1 28±0.2 33±0.3 67±0.2
Trend Q
*
Q
*
Q
*
Q
*
Q
*
Q
*
Q = quadratic 524
significantly at P= 0.05 525
526
Table 3.Sweet corn marketable ear number and fresh ear yield and unfilled tip percentage affected by faba 527
bean (FB) residues planted at three dates of planting (DOP) and supplement N application rate to sweet 528
corn. 529
Treatments
Ear # (ha
-1
)
Ear wt. (Mg ha
-1
)
Unfilled ear tip (%)
2014 2015 2014 2015 2014 2015
FB DOP
Aug01 51793 55380 11.94 13.53 11.1 5.8
Aug07 49800 52591 10.34 12.73 16.4 7.2
Aug14 45760 51630 9.85 11.14 17.4 8.5
No FB 38547 48607 9.15 10.43 18.3 9.2
Trend L* L* Q* L* Q* L*
Supp. N
rate
(kg ha
-1
)
0 37050 45816
6.37 9.95 17.1 10.0
25 49005 54582 11.14 12.73 16.4 8.2
50 52629 57568 11.65 14.32 14.3 6.6
75 52721 57680 11.66 14.33 14.2 6.1
100 53754 58621 11.78 14.43 13.9 5.6
Trend Q* Q* Q* Q* L* L*
*, ** significantly at P= 0.05 and P=0.01, respectively, ns= not significant 530
L and Q = linear and quadratic, respectively. 531
532
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Fig.1. Nitrogen release trend from decomposing faba bean residues in conventional 533
tillage (CT) and no-till (NT) systems and sweet corn growth pattern. Means are 534
averaged over two growing seasons. 535
536
Fig. 2. Effect of tillage system on sweet corn ear yield (a) and unfilled ear tip percentage (b). 537
Means are averaged over three faba bean dates of planting and two growing seasons. 538
539
Fig.3. Sweet corn ear yield influenced by presence or absence of 540
faba bean residues and supplement N fertilizer rates in 2014 and 2015. 541
Values are averaged over two tillage systems. 542
543
Fig .4. Interactive effect of tillage system and faba bean residues 544
on sweet corn ear yield. Values are averaged over 2014 and 2015. 545
546
547
548
549
550
551
552
553
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0
50
100
150
200
250
300
350
0
20
40
60
80
100
120
0246810 12 14 16
Sweet corn biomass (g plant -1)
%N remaining in faba bean residues
Series2
Series3
Series5
Series6
CT
Sweet corn biomass in NT
Sweet corn biomass in CT
NT
Apr 01
Apr 15
Apr 30
May 15
May 30
Jun 15
Jun 30
Jul 15
Jul 30
Aug 15
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0
2
4
6
8
10
12
14
NT CT
Sweet corn ear yield (Mg ha-1)
0
5
10
15
20
25
NT CT
Unfilled ear tip (%)
Tillage system
b
a
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y = -0.001x2 + 0.1686x + 4.4171
R² = 0.9885
y = -0.001x2 + 0.1463x + 6.6257
R² = 0.9717
0
2
4
6
8
10
12
14
16
020 40 60 80 100 120
Without FB
With FB
N Fertilizer (Kg ha-1)
Sweet corn ear yield (Mg ha-1)
2014
y = -0.0008x2 + 0.1511x + 6.8714
R² = 0.9933
y = -0.0008x2 + 0.1224x + 10
R² = 0.9845
0
2
4
6
8
10
12
14
16
020 40 60 80 100 120
without FB
with FB
Sweet corn ear yield (Mg ha
-1
)
N Fertilizer (Kg ha-1)
2015
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0
2
4
6
8
10
12
14
16
0 0.5 1 1.5 2 2.5
with FB
without FB
Sweet coen ear yield (Mg ha -1)
Tillage system
Till No-Till
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