**3. Factors to influence continuous cropping soybean**

#### **3.1 Soybean cyst nematode (SCN)**

SCN forms the cyst containing a large number of eggs (Ichinohe, 1955a). Two or three generations of SCN can grow up in the soybean growing period of Hokkaido (Ichinohe, 1955a). SCN inhibits rhizobial adherence, too (Ichinohe 1955a). The damage of SCN is most remarkable if SCN invaded to soybean at 2-3 weeks after sowing (Okada, 1968). The damage of SCN is reduced by fertilization (Okada, 1966). SCN reduces the growth of soybean, but

Farming System and Management 257

release isothiocyanates, and suppress a nematode (Oka, 2010). Probably Marigold

Host crops of SCN is soybean, adzuki bean and kidney bean (Ichinohe, 1953). SCN is not parasitic on a non-leguminous crop. SCN is parasitic on other leguminous crops, but cannot become the adult (Ichinohe, 1953). After five years cultivation of corn (*Zea mays*) which is non-host crop, SCN increases by soybean cultivation (Porter et al., 2001). By the planting of the single resistant variety, the races adapted to the resistant variety increased (Shimizu & Mitsui, 1985). In contrast, the leguminous crop red clover (*Trifolium pratense*) may be used as trap crop (Kushida et al., 2002). Red clover hatch the egg of SCN, but the hatched larva cannot become the adult (Kushida et al., 2002). Therefore, after red clover cultivation, the

In Memuro continuous cropping experiment, SCN density decreased by 5 years continuous cropping of soybean. In other experiments, the density of SCN decreased by continuous cropping, too (Hashimoto et al., 1988). This phenomenon is called "SCN decline". SCN decreases in wheat-soybean double cropping (Bernard et al., 1996). It is suggested that these phenomena are caused because fungus or bacteria are parasitic on SCN. *Hirsutella* is parasitic on the second larva of SCN (Liu & Chen, 2000). *Fusarium* and *Verticillium* are parasitic on a female, cyst and egg of SCN (Bernerd et al., 1996; Sayre, 1986, Siddiqui & Mahmood, 1996). The nematode control using these microorganisms is possible. However, in Memuro continuous cropping experiment, soybean might be cropped continuously before the experiment station establishment. Long term continuous cropping may be needed

In American Corn Belt, the potential yield of soybean is estimated at 6 - 8t/ha (Salvagiotti et al., 2008). Because soybean is crop which is high grain protein content, soybean need a large quantity of nitrogen. Nitrogen of 106 – 310 kg N / ha is necessary to get a yield of 2 t / ha (Salvagiotti et al., 2008). In the Tokachi district, the fixed nitrogen of soybean is 4 – 127 kg N /ha (Nishimune et al., 1983). There is negative correlation between amount of applied fertilizer and N2 fixation (Salvagiotti et al., 2008). Fertilizer nitrogen for soybean is less than 40kgN/ha. Therefore, soybean needs to absorb nitrogen from soil. Soybean yield will

0 2 4 6

HWEN (mg / 100g dry soil)

Fig. 6. The relationship of the hot water extractable nitrogen (HWEN) of postharvest soil and

suppresses a nematode by α- terthienyl (Oka, 2010).

density of SCN decreased (Kushida et al., 2002).

**3.2 Nitrogen supply and soybean yield** 

increase with soil nitrogen absorption.

0

○ : C0, M15, M30, M50, □ : B15, B30, B50, ▲ : F0, F15, F30, ● : R.

1

2

Yield (t/ha)

3

4

to "SCN decline".

soybean yield (1994).

```
○ : C0, M15, M30, M50, □ : B15, B30, B50, ▲ : F0, F15, F30, ● : R. 
Graph A : ANOVA for 1981 – 1995 (All period of continuous cropping), 
Graph B : ANOVA for 1990 – 1991 (D-D for "Kitami-shiro"), 
Graph C : ANOVA for 1992 – 1995 (D-D for "Toyo-musume"). 
Solid line : the value of R, 
Dotted lines : solid line ± l.s.d. from Studentized range.
```
\*\* is significantly in 1%, \* is 5%.

Fig. 5. The treatment effects to soybean yield.

SCN cannot increase with poor growth soybean (Ichinohe, 1955b). Therefore, if the soybean growth is less, the density of SCN may be less. In Memuro continuous cropping experiment, the egg density of SCN was low in the cool summer damage year (1983).

Soil fumigation, organic matter application and cultivation of non-host crops or the resistant variety is effective for control of SCN. D-D etc are used for soil fumigation. Organic acid or ammonia released from organic matter suppresses a nematode (Oka, 2010). By organic matter including the chitinous substance, chitinase activity in the soil rises, and a nematode is suppressed (Akttar & Malik, 2000; Oka, 2010). Brassicaceae crops including glucosinolates

0 10 20 30 40 50

The amount of oraganic matter (t/ha)

0 10 20 30 40 50

The amount of organic matter (t/ha)

0 10 20 30 40 50

The amount of organic matter (t/ha)

SCN cannot increase with poor growth soybean (Ichinohe, 1955b). Therefore, if the soybean growth is less, the density of SCN may be less. In Memuro continuous cropping experiment,

Soil fumigation, organic matter application and cultivation of non-host crops or the resistant variety is effective for control of SCN. D-D etc are used for soil fumigation. Organic acid or ammonia released from organic matter suppresses a nematode (Oka, 2010). By organic matter including the chitinous substance, chitinase activity in the soil rises, and a nematode is suppressed (Akttar & Malik, 2000; Oka, 2010). Brassicaceae crops including glucosinolates

the egg density of SCN was low in the cool summer damage year (1983).

1

B\*\*

C\*

A \*\*

○ : C0, M15, M30, M50, □ : B15, B30, B50, ▲ : F0, F15, F30, ● : R. Graph A : ANOVA for 1981 – 1995 (All period of continuous cropping),

Graph B : ANOVA for 1990 – 1991 (D-D for "Kitami-shiro"), Graph C : ANOVA for 1992 – 1995 (D-D for "Toyo-musume").

Dotted lines : solid line ± l.s.d. from Studentized range.

Fig. 5. The treatment effects to soybean yield.

Solid line : the value of R,

\*\* is significantly in 1%, \* is 5%.

Yield (t/ha)

Yield (t/ha)

2

Yield (t/ha)

3

release isothiocyanates, and suppress a nematode (Oka, 2010). Probably Marigold suppresses a nematode by α- terthienyl (Oka, 2010).

Host crops of SCN is soybean, adzuki bean and kidney bean (Ichinohe, 1953). SCN is not parasitic on a non-leguminous crop. SCN is parasitic on other leguminous crops, but cannot become the adult (Ichinohe, 1953). After five years cultivation of corn (*Zea mays*) which is non-host crop, SCN increases by soybean cultivation (Porter et al., 2001). By the planting of the single resistant variety, the races adapted to the resistant variety increased (Shimizu & Mitsui, 1985). In contrast, the leguminous crop red clover (*Trifolium pratense*) may be used as trap crop (Kushida et al., 2002). Red clover hatch the egg of SCN, but the hatched larva cannot become the adult (Kushida et al., 2002). Therefore, after red clover cultivation, the density of SCN decreased (Kushida et al., 2002).

In Memuro continuous cropping experiment, SCN density decreased by 5 years continuous cropping of soybean. In other experiments, the density of SCN decreased by continuous cropping, too (Hashimoto et al., 1988). This phenomenon is called "SCN decline". SCN decreases in wheat-soybean double cropping (Bernard et al., 1996). It is suggested that these phenomena are caused because fungus or bacteria are parasitic on SCN. *Hirsutella* is parasitic on the second larva of SCN (Liu & Chen, 2000). *Fusarium* and *Verticillium* are parasitic on a female, cyst and egg of SCN (Bernerd et al., 1996; Sayre, 1986, Siddiqui & Mahmood, 1996). The nematode control using these microorganisms is possible. However, in Memuro continuous cropping experiment, soybean might be cropped continuously before the experiment station establishment. Long term continuous cropping may be needed to "SCN decline".

#### **3.2 Nitrogen supply and soybean yield**

In American Corn Belt, the potential yield of soybean is estimated at 6 - 8t/ha (Salvagiotti et al., 2008). Because soybean is crop which is high grain protein content, soybean need a large quantity of nitrogen. Nitrogen of 106 – 310 kg N / ha is necessary to get a yield of 2 t / ha (Salvagiotti et al., 2008). In the Tokachi district, the fixed nitrogen of soybean is 4 – 127 kg N /ha (Nishimune et al., 1983). There is negative correlation between amount of applied fertilizer and N2 fixation (Salvagiotti et al., 2008). Fertilizer nitrogen for soybean is less than 40kgN/ha. Therefore, soybean needs to absorb nitrogen from soil. Soybean yield will increase with soil nitrogen absorption.

○ : C0, M15, M30, M50, □ : B15, B30, B50, ▲ : F0, F15, F30, ● : R.

Fig. 6. The relationship of the hot water extractable nitrogen (HWEN) of postharvest soil and soybean yield (1994).

Farming System and Management 259

with that soybean N2 fixation decrease at low temperature (F. Zhang et al., 1995). In other words, the nitrogen supply from soil probably become important so as to be a cold area.

The soil organic matter (SOM) is broken down by the soybean planting (Cheng et al., 2003). This effect is called "priming effect". Soil carbon and nitrogen decrease in soybean continuous cropping in comparison with Gramineae - soybean rotation (Kelley et al., 2003; Wright & Hons, 2004). However, soybean-corn rotation can reduce the fertilizer nitrogen of 60kgN/ha/year in comparison with corn continuous cropping (Varvel & Wilhelm, 2003). The soil nitrogen mineralization quantity increases in soybean- corn rotation in comparison with soybean continuous cropping (Carpenter-Boggs et al., 2000). It is suggested that soybean breaks down SOM and will increase inorganic nitrogen, but soybean continuous

In soybean rotation which incorporated alfalfa (*Medicago sativa*), the quantity of soil nitrogen mineralization increases greatly (Carpenter-Boggs et al., 2000). In soybean introducing to the permanent grass pasture, soybean yielded 3 t / ha at no chemical fertilizer (Diaz et al., 2009). One of the causes of these phenomena will be that pasture plant leaves much organic matter

SOM increases by organic matter application. SOM is maintained by no-tillage (Wright & Hons, 2004). Because mineralization of soil nitrogen decreases by no-tillage, N2 fixation probably increases (van Kessel, 2000). These treatments are suggested to increase soybean

SCN inhibits the production of soybean. SCN does not increase by the cropping of non-host crop, but SCN increases by soybean cropping again (Asai & Ozaki, 1965). Gramineous crops such as corn and wheat are non-host crop of SCN. Soybean- corn rotation carried out in the northern part of U.S.A. (Varvel & Wilhelm, 2003; Xing & Westphal, 2009), but SDS by SCN and *Fusarium solani* occurs in this rotation (Rupe et al., 2003; Xing & Westphal, 2009). SDS can lead to defoliation of the leaflets, leaving the petioles attached to the plant after flowering (Rupe et al., 2003; Xing & Westphal, 2009). Pythium have a pathogenicity in

In the Southern U.S.A., soybean is cultivated by no-tillage in soybean - wheat double cropping (Bernard et al., 1996). No-tillage is used to corn, soybean, wheat and etc in U.S.A., and the cultivated area occupies 23% in U.S.A. (Triplett. Jr. & Dick, 2008). No-tillage reduces nematode density in soybean - wheat double cropping (Bernard et al., 1996). However, takeall (G*aeumannomyces graminis*) of wheat cannot be reduced in soybean- wheat double

Some plants are able to control nematodes. Probably Marigold controls nematodes with chemical substances such as α -terthienyl (Oka, 2010). The Brassicaceae plants control nematodes with isothiocyanates which is broken down from glucosinolates (Oka, 2010). The leguminous crops such as red clovers are probably available as trap crop reducing the egg

soybean and corn and cause damping-off (B.Q. Zhang et al., 1998).

**4.1.1 Farming system** 

in soil.

yield.

**4.1.2 Management** 

**4.2.1 Farming system** 

cropping (Cook, 2003).

density of SCN (Kushida et al., 2003).

cropping will cause a decrease of SOM.

**4.2 Soybean cyst nematode (SCN)** 

Soil Nitrogen can be divided into inorganic, humus and biomass nitrogen (Jenkinson & Parry, 1989). Crops absorb inorganic nitrogen. The available nitrogen is organic nitrogen at sowing, but it is mineralized during a growing period. It is suggested that most of available nitrogen come from biomass nitrogen (Sakamoto & Oba, 1993). Organic matter application increases biomass nitrogen (Sakamoto & Oba, 1993). Available nitrogen and the heated water extraction nitrogen (HWEN) have corelation (Akatsuka & Sakayanagi, 1964). In Memuro continuous cropping experiment, the relationship of the HWEN of postharvest soil and soybean yield was investigated in 1994 (Fig. 6). With increase of the HEWN, soybean yield tended to increase. It is suggested that organic matter application increases biomass nitrogen, and contributes to yield increase.

D-D promotes mineralization from biomass nitrogen (Neve et al., 2004). D-D suppresses nitrification from ammonia nitrogen (Neve et al., 2004). Therefore, much ammonia nitrogen in soil will be kept by D-D. In the Memuro continuous cropping experiment, D-D was applied before one month of sowing. Therefore, it is thought that these effects influenced a soybean.

Fig. 7. The nitrogen flow and the factors influence to it.
