Effect of different cover crops and nitrogen split on ...

Technical Journal of Engineering and Applied Sciences Available online at www.tjeas.com ©2013 TJEAS Journal-2013-3-13/1324-1330 ISSN 2051-0853 ©2013 TJEAS

Effect of different cover crops and nitrogen split on control of biomass and density of annual and perennial weeds of forage corn Rasoul Fakhari1*, Ahmad Tobeh2, Abdolghayoum Gholipouri2, Hassan Khanzadeh3, Mohamadtaghi Alebrahim2 1. M.Sc. Student of Weed Science University of Mohaghegh Ardabili, Ardabil, Iran 2. Department Of Agronomy and Crop breeding, University of Mohaghegh Ardabili, Ardabil, Iran 3. M.Sc graduate of Research Center of Moghan Corresponding author email: [email protected] ABSTRACT: In order to evaluate the use of cover crops to control weeds in forage corn an experiment with three factor factorial in a randomized complete block design with three replications was done in 2012 at the Agricultural Research Station (Samian) Ardabil. The first factor of treatments consists of rye, hairy vetch, clover as a cover crop and no cover crop with maize cultivation practices and without weed control. The second factor consists of nitrogen split of 225 kg urea per hectare with 2 levels, the first level (1/2 at sowing + 1/2 in the 8 to 10 leaf stage of corn), second level (1/3 at planting + 1/3 in the 8 to 10 leaf +1/3 a week before tasseling of corn) to the desired split in two and three corn growth stages were used. The third factor consisted of two levels of weed sampling frequency of 60 days and 90 days after planting corn. Combined analysis of variance showed a rye cover crop, hairy vetch and clover annual weed biomass compared to the control treatment (no cover crop and no weeding), which is equivalent to 190.33 grams per square meter was respectively 90, 84 and 66 percent of annual weed density compared to control (without plant cover and without weeding), respectively 70, 54 and 32% decreased. Also mentioned coating plants, decreased perennial grass biomass than the control treatment, respectively 62, 50 and 22% and density of perennial weeds compared to control decreased 80, 76 and 59% respectively. Cover crops and nitrogen split interactions have significant effects on plant height, diameter and length of corn ear, so that the maximum height, diameter and length of corn ear of weeds and weeding treatments were fertilizer levels split second. The highest fresh forage yield of corn (51.3073 ton per hectare) of weeding treatments were full of weeds. After weeding treatments, forage yield compared to hairy vetch cover crop treatment, with the most significant difference. Overall, taking into account the interests of more effective control of weeds and forage production, treatment of hairy vetch cover crop and the second split of nitrogen fertilizer level was appropriate. Key words: Plant height, Rye, fresh forage yield of corn, weeding INTRODUCTION Increase agricultural production during the 20th century has resulted in increased use of inputs, and intensification of agricultural activities in order to control weeds, soil erosion, pollution by chemicals and herbicide-resistant weeds have emerged (Santiago, 2005). Species of Amaranthus L., Chenopodium L., Convolvulus arvensis and Cynodon L. are known as the most important weeds in corn fields (Mousavi, 2001). One of the ways that can potentially replace conventional methods in combating weeds in sustainable agriculture, is the use of cover plants with allelopathic properties (Duke, 1987). Among the various plants, rye (Secale cereale L.) due to condense biomass production and having allelopathic compounds, is one of the best plants for planting a cover crop is (Mighati, 2003). Cover crops can also be useful by reducing inputs for crop production inputs such as industrial nitrogen fertilizer (Jensen, 2012). Experimental results showed that the effects of rye on soybean grown in the spring, could decrease weed biomass by 60 to 90 percent compared to the control without cover crop of rye (Ateh and Doll, 1996). In another experiment to determine the effect of cover crops of rye, hairy vetch, red clover, white clover, subterranean clover, yellow clover, persian clover and berseem on weeds of maize, was found that cover crops could reduce the weeds biomass up to 78 percent.

Tech J Engin & App Sci., 3 (13): 1324-1330, 2013 And also to avoid compromising the performance of the original plant, it is better to cultivate cover crops with the main crop (Abdin et al, 2000). Plants compete for light access is granted. A negative relationship is reported between weed biomass and land cover by crop and cover crop. Fertilization by changing the percentage of land cover, made by plants, can be effective on weed biomass. The report stated that the deterrent effect of weeds, is influenced by cover percentage of the soil surface by major crop or cover crop (Rasmussen et al., 2007; Uchino et al., 2009 and 2011). When the corn grown under no-till or plant residues, may be due to reduced plant canopy, the rate and right time of fertilizer application is very important (Mock and Erbach, 1977). In an experiment (Reeves et al., 1993) the effect of nitrogen application rate and planting cover crops of clover and rye on dry matter accumulation and grain yield were examined, it was found that the dry matter accumulation in maize was not affected by time of nitrogen application. It also was determined that the use of nitrogen fertilizer after 6 weeks after corn planting not only hasn't any effect on the yield, but also decrease it. Cover crops may not increase crop yield (Olson et al., 2010). In an experiment, treatment of 19% clover reduces corn yield with respect to the control of without cover crop, due to competition of clover with corn (Abdin et al, 2000). The report stated that in some cases, planting cover crops will not only reduces weed growth but also reduces main crop growth due to competition for light (Hooks and Johnson, 2001). The purpose of this experiment is to examins the controlling potential of different cover crops and nitrogen split on biomass control, density and variety of annual and perennial weeds in forage corn field. MATERIALS AND METHODS The experiment with three factor factorial in a randomized complete block design with three replications was done in spring of 2012 at the Agricultural Research Station (Samian) Ardabil. The first factor of treatments consists of rye, hairy vetch, clover as a cover crop and no cover crop with maize cultivation practices and without weed control. The second factor consists of nitrogen split of 225 kg urea per hectare with 2 levels, the first level (1/2 at sowing + 1/2 in the 8 to 10 leaf stage of corn), second level (1/3 at planting + 1/3 in the 8 to 10 leaf +1/3 a week before tasseling of corn) to the desired split in two and three corn growth stages were used. The third factor consisted of two levels of weed sampling frequency of 60 days and 90 days after planting corn. after selection of the project site and preparation operations, soil sampling was randomly performed from multiple place of farm for soil analysis (to determine the amount of N.P.K. fertilizers). In the spring of 2012, medium corn seed KSC400 were planted in early May in rows 75 cm wide and 15 cm between plants as cover 2 crops. Each plot was 12 m , the distance between the two plots was 1.5 m and the distance between the two blocks, including water and sanitation streams, was 3.5 m. Due to the high solubility of urea, in order to prevent entering the drainage water from one plot to other plots, a major stream for water and a stream for water exit of each block were prepared The cover crop seeding rate for rye, hairy vetch and clover, were 45, 160 and 30 kg ha, respeectively; that planted by hand between rows of corn. The first irrigation was done after planting and subsequent irrigation based on weather conditions generally ranges between 5 to 8 days and was leaking. Sampling of cover crops and weed biomass was performed using 0.5×0.5 m quadrats. Major weeds in the experimental area were redroot pigweed (Amaranthus retroflexus L.), lamb's squarters (Chenopodium album L.), bindweed (Convolvulus arvensis L.) and Bermuda grass (cynodon dactylon L.). After counting the weeds, species were placed in separate envelopes and transported to the laboratory. For measuring dry biomass, the plant materials were dried in an oven with 75°C for 48 hours and then weighed with a 0.01 g scale. Fresh forage yield of corn was performed at milky stage of seeds, from the two central rows of each plot and after deletion of the marginal effect as about 0.5 m from top and bottom. The studied traits were plant height, ear length, ear diameter and the wet forage yield. The data of the tests were analyzed by SAS software, after normality test of data and change of requiring data, based on statistical design; and Duncan test at 5% level was used for mean comparison. Charts were plotted by Excel software Table1. Mean comparison of the main effects of cover crops biomass Treatments cover crops

Mean- square rye hairy vetch clover

Biomass (gr/m2) 431.08 a 374.64 b 192.72 c

Means with common letters are not significantly different with each other

RESULTS AND DISCUSSION Analysis of variance (data not shown) showed that different treatments of cover crops in terms of biomass production, showed significant differences. The mean comparison of cover crops biomass showed that cover crop rye significantly produced greater amount of biomass relative to hairy vetch and clover (Table 1).

1325

Tech J Engin & App Sci., 3 (13): 1324-1330, 2013 Cover crops with high biomass production caused more rapid canopy closure and overcome the weeds (Tokasi et al., 2008; Linars et al., 2008). Annual weeds Common annual weeds such as lamb's squarters and pigweed were included in this trial. Analysis of variance of annual weed density and biomass revealed the main effects of each of the three factor, cover crops and nitrogen split and sampling frequency, were significant at the 1% level. The interaction between cover crops and sampling frequency on the yield of dry biomass of weeds has also been significant at the 1% level (Table 2). According to the table of mean comparisons (Table 3), the highest and lowest density of weeds in cover crops treatment was observed, in the control (without cover crops and without weeding) 21.50 plants per square meter, and rye with 8.24 plants per square meter, respectively. In other words, the density of weeds in the cover crops treatments of rye, vetch and clover, were 62, 50, and 22% lower than the control, respectively. In nitrogen split treatment the highest and lowest density were observed in two times and three times nitrogen split, respectively. According to the sampling frequency, the first sample had highest density and the second had the lowest density. Dry biomass of weeds showed that, the highest and lowest biomass of weeds in cover crops treatment was observed, in the control (without plant cover and without weeding) 190.33 grams per square meter, and rye with 18.58 grams per square meter, respectively. In other words, the dry biomass of weeds in the cover crop treatments of rye, vetch and clover, were 90, 84, and 66% lower than the control, respectively. Further reduction in the density and biomass of weeds in rye treatment can be due to high production of the plant biomass. It is known that in cases where the cover crops adequately developed and produced a lot of biomass, weed density and biomass will decrease (Chikoye et al., 2002). In nitrogen split treatment the most biomass was observed in split of twice fertilizer, and the lowest biomass was observed in split of three times fertilizer. Reduced weed biomass by the use of fertilizers has been reported in various literature. In an experiment (Olasantan et al., 1994) with fertilizer application, a significant reduction in weed biomass is reported. According to the sampling frequency, the first sample had largest biomass and the second had the lowest biomass. Table 2. Analysis of variance based on the mean squares (MS) on the biomass and density of annuals and perennial weeds Source of variation Replication Cover crops Nitrogen split Sampling frequency Cover crops × Nitrogen split Cover crops × Sampling frequency Nitrogen split × Sampling frequency Cover crops × Nitrogen split × Sampling frequency Error cv

df 2 3 1 1 3

Mean- square Annual weeds Density 9.33ns 426.17** 44.08** 176.33** 0.81 ns

Biomass 117.97ns 74107.08** 1857.54** 8270.85** 142.56ns

Perennial weeds Density 8.39ns 1313.08** 256.69** 252.31** 9.08ns

Biomass 35.78ns 7216.46** 188.02** 194.33** 6.35ns

3

1.50 ns

1530.28**

2.19ns

116.3 **

1

2.08 ns

0.04ns

2.52ns

3.83ns

3

1.47 ns

16.19ns

1.58ns

5.61ns

30

1.89 10.12

43.63 8.97

3.62 9.05

9.89 10.19

Ns, * and ** represent non-significant and significant at P≤5 and P≤1, respectively. Table 3. Mean Comparison of effects of density and dry biomass of annual and perennial weeds Treamtent

Cover crops

Nitrogen split Sampling frequency

rye hairy vetch clover without cover crops and without weeding twice three time first second

Mean- square Annual weeds Density (no/m2) 8.24 d 10.83 c 16.75b

Biomass (gr/m2) 18.58 d 30.89c 64.83b

Perennial weeds Density (no/m2) 10.42d 15.83c 23.25b

Biomass (gr/m2) 13.53d 16.18 c 27.08b

21.50 a

190.33a

34.58a

66.55a

15.67a 12.96 b 15.75a 12.92b

82.34a 69.94b 89.28a 63.03b

23.33a 18.71b 22.17a 18.71b

32.81a 28.85b 32.84a 28.82b

Means with common letters are not significantly different with each other.

Perennial weeds Perennial weeds in the field are bindweed and bermuda grass.It was observed that the main effect of each of the three factor of cover crops, nitrogen split and sampling frequency on the characteristics of the

1326

Tech J Engin & App Sci., 3 (13): 1324-1330, 2013 density and biomass of perennial weeds is significant at 1% (Table 2). In addition, weed biomass has affected by cover crops interactions and sampling frequency (p ≤ 1%). As observed in Table 3, in cover crops treatment the most and the least weeds density were observed in the control (without cover crops and without weeding) 34.58 plants per square meter, and rye with 10.42 plants per square meter, respectively. In other words, the weeds density in the cover crops treatments of rye, vetch and clover, were 70, 54, and 32% lower than the control, respectively. In nitrogen split treatment the most weeds density was observed in split of twice fertilizer, and the lowest weeds density was observed in split of three times fertilizer. According to the sampling frequency, the first sample had highest density and the second had the lowest density of perennial weeds. Dry biomass of weeds showed that, the highest and lowest biomass of weeds in cover crops treatment was observed, in the control (without plant cover and without weeding) 66.55 grams per square meter, and rye with 13.53 grams per square meter, respectively. In other words, perennial weed biomass in the treatment of cover crops of rye, vetch and clover, were 80, 76, and 59% lower than the control, respectively. In nitrogen split treatment the most biomass was observed in split of twice fertilizer, and the lowest biomass was observed in split of three times fertilizer. According to the sampling frequency, the first sample had highest biomass and the second had the lowest biomass. In general, the perennial weeds due to reproduction by vegetative organs such as tubers and rhizomes, rarely affected by the inhibitory effects of cover crops and fertilization management (Uchino et al., 2012). Related traits of corn The results in Table 4 show that the effects of two treatments of nitrogen split and cover crops were significant at P≤1, and their interactions on corn height were significant at P≤5. The maximum plant height (185.72 cm) and the lowest plant height (146.04 cm) were gained from control (no cover crop with complete weeds weeding) and no weeding control treatments, respectively (Table 5). Plant height of corn planted hairy vetch cover crop of clover and rye was significantly greater. Comparison of plant height in nitrogen split showed, plant height in three times nitrogen split was significantly higher than the other treatments (Table 5). The effect of interaction of control treatment (weeding) with treatment of three times nitrogen split showed, the greatest plant height (189.24 cm) and the lowest plant height (10/144 cm) were related to the control (no weeding) and twice nitrogen split treatments, respectively (Figure 1). In an experiment Muthukumar et al., (2005) reached the highest corn height with a three-step nitrogen split. The greatest plant height in three times nitrogen split treatment was due to nitrogen application during vegetative rapid growth before flowering (Kernele et al., 1987). The results in Table 4 show that the effect of two treatments of cover crops and nitrogen split were significant at P≤1, and their interactions on the corn ear diameter were significant at P≤5. The maximum corn ear diameter (52.33 mm) and the lowest corn ear diameter (40.33 mm were gained from control (no cover crop with complete weeds weeding) and no weeding control treatments, respectively (Table 5). The results in Table 4 show that the effect of two treatments of cover crops and nitrogen split were significant at P≤1, and their interactions on the corn ear diameter were significant at P≤5. Comparing the amounts of corn ear length at different levels of cover crops showed that corn ear length in control (weeding) was the most (42/34 cm) and the lowest (32/29 cm) for this trait was in control (no weeding) were observed (table 5). The three traits of hairy vetch cover crop in the treated ear length and diameter were significantly more clover and rye (Table 5). The values of these two traits in three times nitrogen split had more significant differences compared to twice nitrogen split (Table 5). It seems that in three times nitrogen split treatments, nitrogen use efficiency towards vegetative growth, relative to other treatments have advantages. Changes in the characteristics of corn between cover crops, probably due to the extraspecies competition that reduces the amount of corn traits in these situations. Tuna and Orak, (2007) in cultivation of oats with vetch have reported that plant height increases or decreases depends on the intensity of competition between the two plants. Reduction in corn height grown with cover crops, probably due to limited photosynthetic production because of water and nutrients limitations (Moll and Kamparth, 1977). In experiments of corn cultivated with cover crops was observed that, with increasing plant density per unit area, the competition between plants for light absorption, more photosynthesis active radiations and nutrients, increases; and so the length and diameter of corn ear has been reduced (Turgat , 2000; Has, 2002). Table 4 . Analysis of variance based on the mean square (MS) on plant height, diameter and length corn ear Source of variation Replication Cover crops Nitrogen split Cover crops Nitrogen split× Error cv

df 2 4 1 4 18

Mean- square Plant height 12.50** 1479.78** 279.49**

Ear diameter 0.83ns 162.75** 112.13**

Ear length 0.36ns 20.84** 11.82**

4.26 *

7.05*

2.04*

1.32 0.70

1.20 2.37

0.39 1.98

Ns, * and ** represent non-significant and significant at P≤5 and P≤1, respectively.

1327

Tech J Engin & App Sci., 3 (13): 1324-1330, 2013

Table 5. Mean comparison of plant height, length and diameter of ear influenced by the effect of different levels of cover crops and nitrogen split. Treatments Cover crops

rye hairy vetch clover control (weeding) control (without weeding) twice three time

Nitrogen split

Mean- square Plant height (cm 153.14 d 172.47 b 162.46 c 185.72 a

Ear diameter (mm) 41.83 d 50.33 b 46.83 c 52.33 a

Ear length (cm) 31.27 d 33.77 b 32.82 c 34.42 a

146.04 e

40.33 e

29.32 e

160.82 b 167.11 a

44.40 b 48.27 a

31.49 b 33.15 a


a

height plant (cm)

200 180 160

c f

d

g

d

e

b g

h

140 120 100

three time

80 60 40

twice

20 0

cover crops Figure 1. Interaction of cover crops and nitrogen split on corn height

Table 6 . Analysis of variance based on the mean square (MS) on the final fresh forage yield of corn Source of variation Replication Cover crops Nitrogen split Nitrogen split× Cover crops Error cv

Mean- square The final fresh forage yield of corn 5687887** 378555162** 34955167** 2712117ns 326150 1.12

df 2 4 1 4 18

Ns, * and ** represent non-significant and significant at P≤5 and P≤1, respectively. Table 7 – The main effect of cover crops and nitrogen split on the final fresh forage yield of corn Treatments

Cover crops

Nitrogen split

rye hairy vetch clover control (weeding) control (without weeding) twice three time

Mean- square The final fresh forage yield of corn (ton/ha) 44.127d 48.771b 45.593c 51.307a 30.819e 43.053b 45.194a


1328

Tech J Engin & App Sci., 3 (13): 1324-1330, 2013

60 a b

50

c

fresh forage yield (ton/ha)

d 40

e 30

20

10

0

cover crops Figure 4. Effect of cover crops on the fresh forage yield of corn

Fresh forage yield (ton/ha)

50 45 40 35 30 25 20 15 10 5 0

a

b

Twice

Three times Nitrogen split

Figure 5. Effect of nitrogen split on the fresh forage yield of corn

Fresh forage yield of corn Analysis of variance showed that the effects of two treatments of nitrogen split and cover crops were significant at P≤1, but their interactions on fresh forage yield of corn were not significant. Table of Means comparison of the effect of two factors on the trait (table 7) showed that the maximum fresh forage yield

1329

Tech J Engin & App Sci., 3 (13): 1324-1330, 2013 (51.307 tons per hectare) and the lowest fresh forage yield (30.819 tons per hectare) were gained from control (no cover crop with complete weeds weeding) and no weeding control treatments, respectively (Table 7). Between cover crops, the fresh forage yield of corn in hairy vetch was higher than clover and rye (Figure 4). In nitrogen split treatment, the fresh forage yield of corn in three times nitrogen split was more than twice nitrogen split (Figure 5). In general, the reason of decreasing fresh forage yield of corn treated with cover crops, is due to the inter-species competitions with corn (Osei-Bonsu and Buckles, 1993). Intercropping of Hairy vetch with corn also decreased corn yield (Reddy and Koger, 2004). We concluded that vetch treatment was successfully effective on weed control, and had less inhibitory effect on the main crop and fresh forage yield. Overall, taking into account the benefits of effective weeds control and produce more forage, treatments of hairy vetch cover crop and three times nitrogen split is recommended. REFERENCES Abdin OA, Zhou XM, Cloutier D, Coulman DC, Faris MA, Smith DL. 2000. Cover crops and interrow tillage for weed control in short season maize (Zea mays). Europ J of Agron. 12: 93–102. Ateh CM, Doll JD.1996. Apring-planted winter rye (Secale cereale) as a living mulch to control weed in soybean (Glycine max). Weed Tech. 10: 347- 353. Chikoye D, Ekeleme F, Udensi UE. 2001. Imperata cylindrical suppression by intercropping cover crops in maize/cassava cropping systems. Weed Sci. 49 (in press). Duke SO, Vaughn KC, Croom EM, Elsholy HN.1987. Artemisinin, a constituent of annual wormwood (Artemisia annua) is a selective phytotoxin. Weed Sci. 35: 499-505. Has V. 2002. Fresh market sweet corn production. Biotechnol Sci. 5(6): 213-218. Hooks CRR, Johnson MW. 2001. Broccoli growth parameters and level of head infestations in simple and mixed plantings: impact of increased flora diversification. Ann Appl Biol. 138: 269–280. Jensen ES, Peoples MB, Boddey RM, Gresshoff PM, Hauggaard-Nielsen H, Alves BJR, Morrison MJ.2012. Legumes for mitigation of climate change and the provision of feedstock for bio fuels and bio refineries A review. Agron for Sustain Develop. DOI 10.1007/s13593-011-0056-7. Kernele DL, Sadler EL, Comp CR. 1987. Corn yield and residual soil nitrate as affected by time and rate of nitrogen application. Agron J. 81: 720- 726. Linares J,Scholberg JMS, Chase C, Mcsorely R, Ferguson J. 2008. Evaluation of annual warm-season cover crops for weed management in organic citrus. In: Proceedings of 16th IFOAM Organic Congress, 16-20, 2008. Modena, Italy. Mighati F. 2003. Allelopathy: from concept to application. Partov Vaghea Publications. Mock JJ, Erbach DC. 1977. Influence of conservation tillage environments on growth and productivity of corn. Agron J. 69: 337- 340. Moll RH, Kamparth EJ.1977. Effect of population density up on agronomic traits associated with genetic increases in yield of Zea mays L. Agron J. 69: 81-84. Mousavi M.2001. Weed control (Principles and Methods). Marze Danesh Publications. Muthukumar VB, Velaudham K, Thavaprakaash N. 2005. Growth and yield of bady corn (Zea mays L.) as Influenced by plant growth regulators and different time of nitrogen application. J Agric Biol Sci. 1: 303-307. Olasantan F, Lucas E, Ezumah H.1994. Effects of intercropping and fertilizer application on weed control and performance of cassava and maize. Field Crops Res. 39: 63–69. Olson KR, Ebelhar SA, Lang JM.2010. Cover crop effects on crop yields and soil organic carbon content. Soil Sci. 175:89-98. Osei-Bonsu P, Buckles D. 1993. Controlling weeds and improving soil fertility through the use of cover crops: experiences with Mucuna spp. in Benin and Ghana. West African Farm. Syst. Res Network Bull. 14: 2–7. Rasmussen J, Norremark M, Bibby BM. 2007. Assessment of leaf cover and crop soil cover in weed harrowing research using digital images. Weed Res. 47: 299–310. Reddy KN, Koger CH.2004. Live and killed hairy vetch cover crop effects on weeds and yield in glyphosate-resistant corn. Weed Tech. 18: 835-840 Reeves DW, Wood CW, Touchton JT.1993. Timing Nitrogen Applications for Corn in a Winter LegumeConservation-Tillage System. Agron J. 85: 98-106. Santiago LP. 2005. Structure of weed communities of occurring in mono culture and intercropping of field pea and barley. J of Agric. 109: 48–58. Tokasi S, Rashed Mohassel MH, Rezvani Moghaddam P, Nassiri Mahallati M, Aghajanzadeh S, Kazerooni Monfared E. 2008. Orange orchard weeds management using cover crops and rice mulch. J. of Iran. Field Crop Res. 6 : 49-57(In Persian with English summary). Tuna C, Orak A. 2007. The role of intercropping on yield potential of common vetch (Vicia sativa L.) / oat (Avena sativa L.) cultivated in pure stand and mixtures. J Agric Biol Sci. 2: 14-19. Turgat I. 2000. The effect of plant population and nitrogen doses on fresh ear yield and yield components of sweet corn (Zea mays saccharata sturt), grown under Bursa condition. Turk J Agric Sci. 24: 341-247. Uchino H, Iwama K, Jitsuyama Y, Ichiyama K, Sugiura E, Yudate T, Nakamura S, Gopal J. 2012. Effect of interseeding cover crops and fertilization on weed suppression under an organic and rotational cropping system 1.Stability of weed suppression over years and main crops of potato, maize and soybean. Field Crops Res. 127: 9–16. Uchino H, Iwama K, Jitsuyama Y, Ichiyama K, Sugiura E, Yudate T. 2011. Stable characteristics of cover crops for weed suppression in organic farming systems. Plant Prod Sci. 14: 75–85. Uchino H, Iwama K, Jitsuyama Y, Yudate Y. Nakamura S. 2009. Yield losses of soybean and maize by competition with interseeded cover crops and weeds in organic-based cropping systems. Field Crops Res. 113: 342–351.

1330