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Weed control by cover crops under organic farming of maize, soybean and potato

Hiroshi Uchino, Kazuto Iwama, Takayoshi Terauchi and Yutaka Jitsuyama

Crop Science Laboratory, Department of Botany and Agronomy, Graduate School of Agriculture, Hokkaido University Email


Weeds are one of the major issues in organic farming where herbicides are prohibited. This study was conducted to clarify the effect of cover crops on weed control under uncompetitive condition with main crops (potato, soybean and maize) in organic farming. The experiment was done over two years at Hokkaido University (Sapporo, Japan, 43N, 141E). Ten species of cover crops including hairy vetch (Vicia villosa) as an allelopathic plant were grown without the main crop to compare the weed control ability. Weed dry weight correlated negatively with the covering rate of cover crops, but not with cover crop height. Winter rye (Secale cereale) and hairy vetch that had a higher rate of soil surface covering and lower plant height were the best cover crops to prevent weed growth. These two species were grown in the inter-row space as cover crops. Cover crops were sown a few weeks after the main crops were planted to reduce the competition of growth among crops. Weeds were significantly reduced by cover crops in mixed cropping with maize and soybean, but suppressed without cover crops in potato. Intercepted radiation ratio (IRR) was higher in maize and soybean plots with cover crops. Our results indicate that weeds can be controlled by using late sowing cover crops through increasing IRR.

Media Summary

Weeds can be controlled by using a late sowing cover crop through increasing intercepted radiation ratio (IRR).

Key Words

Weed suppression, environmental conservation agriculture, sustainable agriculture


Weed control is one of the most difficult problems in organic farming. The use of cover crops for weed control is an alternative that is less harmful to the environment than pesticides or other chemical practices. Cover crops can suppress weed density by competing for light (Teasdale 1993) and through the production of allelopathic compounds (Kamo et al. 2003). But there are practical limitations to using cover crops for weed control, due to the strong risk of a decrease in growth and yield of main crops (Garibay et al. 1997). It is necessary to clarify the differences of weed control ability among cover crop species and to find a new use of cover crops for preventing the decrease of the main crop yield. This experiment was conducted to study the effect of weed control by the use of cover crops under uncompetitive conditions with main crops.


Screening test of cover crops

Ten cover crops were used for screening for their weed suppression ability. Dry weight of the weed, coverage of cover crops and plant height of cover crops were measured at 28 days after planting (DAP) and 69 DAP. After omitting weeds from plant community, coverage of cover crops was evaluated by observation and the average of 32 grid (5 cm x 5 cm) of coverage was calculated within 40 cm x 20 cm range.

Mixed cropping test

Potato and soybean were planted at May 4th and May 22nd in 2003, respectively and potato and silage maize were planted at May 6th and May 20th in 2004, respectively as main crops. Four treatments were applied (Table 1). Winter rye and hairy vetch were sown at 38 DAP (potato plot in 2003), 33 DAP (soybean plot), 35 DAP (potato plot in 2004) and 29 DAP (maize plot). Seeding densities of cover crops were 213 grain/m2, 333 grain/m2 and 320 grain/m2 in furrow of potato, soybean and maize, respectively. IRR of the canopy was measured every week by line quantum sensor (LI-191, LI-COR Inc.) and dry weight of main crop, cover crop and weed were recorded at the end of vegetative growth. The experiment was conducted until harvest time.


Screening test (Table 2)

Weeds were suppressed in WR-W, HV(H) and WR-F(H) (abbreviations are shown in Table 2). Higher coverage of cover crops was observed in WR-W and WR-F(H) among gramineae and higher in HV(H) among leguminosae. There are strong correlations between weed dry weight at 69DAP and coverage of cover crops at 28DAP (r=-0.81, P<0.01). Importance of the early coverage is suggested for weed control. Because weeds were not suppressed in HV(L), it is thought that weed control effect of hairy vetch was mainly due to coverage.

Mixed cropping experiment (Table 3)

Potato: Weed dry weight was significantly lower in NC, WR-F and HV that had higher IRR at 64 DAP. A similar result was observed in 2004 (data not shown).

Soybean: Weed dry weight tended to be lower in WR-F and HV that had higher IRR at 61 DAP.

Maize: Weed dry weight tended to be lower in WR-F and HV that had comparatively higher IRR at 61DAP.

These results indicate that cover crops contribute to weed control through increasing IRR.


Our results show that weed can be controlled by using late sowing cover crops, though further experiments are necessary to investigate effects of sowing date of cover crops on ability control weeds and competition between main crops, cover crops and weeds.


Garibay SV, Stamp P, Ammon HU and Feil B (1997) Yield and quality components of silage maize in killed and live cover crops. European Journal of Agronomy 6, 179-190

Kamo T, Hiradate S and Fujii Y (2003) First isolation of natural cyanamide as a possible allelochemical from hairy vetch Vicia villosa. Journal of Chemical Ecology 29(2), 273-282

Teasdale JR (1993) Reduced-herbicide weed management systems for no-tillage corn (Zea mays) in hairy vetch (Vicia villosa) cover crop. Weed Technology 7, 879-883

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