**4. The corn-soybean rotation**

One of the more widely practiced rotations in the United States involves the corn-soybean rotation scheme used extensively in the North Central and Mid-Atlantic States. Within the 20 year period between 1988 and 2008 nearly 30 publications were known to have been published that compared corn-soybean rotations to continuous corn (Erickson, 2008). Virtually all of this research showed increases in corn grain yields from plots that had been planted to soybean the previous year. A few of these experiments followed soybean with two years of corn and in those studies yields from the second year corn crop were equal to or still greater than those from plots of continuous corn but less than the first year corn crop. One of these studies (Porter et al., 1997) examined the effects of various corn-soybean rotation schemes at three locations in the northern Corn Belt. Data from these studies showed that not only were both corn and soybean yields higher in rotation compared to monocultures of the two crops (Table 5), but that differences between rotations and monocultures were greater in low-yielding environments than in high-yielding conditions.


†Crops were grown under corn or soybean monoculture of the respective crop in the following sequence: 1st-yr, 2nd-yr, 3rd-yr, 4th-yr and 5th-yr corn or soybean after 5 yr of corn or soybean; Cont. (continuous corn or soybean); and S-C (alternating soybean and corn). Values followed by the same letter or letters within each crop species are not significantly different at (P0.05).

Table 5. Corn and soybean yields from 3 locations in Minnesota and Wisconsin representing 29 environments. (Porter, et al., 1997)

stated that producers growing continuous rice will likely experience lower grain yields than

A common rotation with rice in southern and eastern Asia is a rice-wheat rotation system that occupies an estimated 24 to 27 million hectares (Wassmann, et al., 2004). Lattimore (1994) reviewed the literature pertaining to rice-pasture rotations in southeastern Australia. Annual pastures based on subterranean clover (*Trifolium subterraneum* L.) are well adapted to this part of the world and the rice cropping system. It provides considerable fixed N to the rice crop thus reducing the need level of supplemental N fertilizer as well as breaking weed cycles. It helps sustain a complimentary animal agriculture to use crop residues and provides opportunities for improved farm income. With respect to disease control in rice, both false smut (*Ustilaginoidea virens* (Cooke) Takah) and kernel smut (*Neovossia horrid*a (Takah.) Padwick & A. Khan, syn. *Tilletia barclayana* (Bref.) Sacc. & P. Syd.) two serious fungal pests in rice production areas of the United States, appear to be best controlled when rice is grown in three year rotations with soybean and corn between rice crops (Brooks, 2011). Traditional rotations of rice-soybean, with winter wheat grown between the two summer annuals, were observed to

One of the more widely practiced rotations in the United States involves the corn-soybean rotation scheme used extensively in the North Central and Mid-Atlantic States. Within the 20 year period between 1988 and 2008 nearly 30 publications were known to have been published that compared corn-soybean rotations to continuous corn (Erickson, 2008). Virtually all of this research showed increases in corn grain yields from plots that had been planted to soybean the previous year. A few of these experiments followed soybean with two years of corn and in those studies yields from the second year corn crop were equal to or still greater than those from plots of continuous corn but less than the first year corn crop. One of these studies (Porter et al., 1997) examined the effects of various corn-soybean rotation schemes at three locations in the northern Corn Belt. Data from these studies showed that not only were both corn and soybean yields higher in rotation compared to monocultures of the two crops (Table 5), but that differences between rotations and monocultures were greater in low-yielding environments than in high-yielding conditions.

have the highest levels of these diseases especially with high N- fertility levels.

Yield (Mg ha-1)

S-C rotation

Crop† 1st-yr 2nd-yr 3rd-yr 4th-yr 5th-yr Cont.

letter or letters within each crop species are not significantly different at (P0.05).

Corn 9.00a 8.04b 7.90b 7.90b 7.88b 7.81b 8.83a Soybean 3.26a 2.99b 2.84c 2.82cd 2.8cd 2.77d 3.05b †Crops were grown under corn or soybean monoculture of the respective crop in the following sequence: 1st-yr, 2nd-yr, 3rd-yr, 4th-yr and 5th-yr corn or soybean after 5 yr of corn or soybean; Cont. (continuous corn or soybean); and S-C (alternating soybean and corn). Values followed by the same

Table 5. Corn and soybean yields from 3 locations in Minnesota and Wisconsin representing

those using a rice-soybean rotation.

**4. The corn-soybean rotation** 

29 environments. (Porter, et al., 1997)

 Studying the net returns of various crop rotation schemes involving corn, Singer and Cox (1998) calculated a greater net return (\$250 US ha-1) with a corn-soybean rotation than a continuous corn (\$193 US ha-1) or a three year soybean-wheat/red clover rotation (\$133 US ha-1). A recent study reported though, that yield comparisons are not the appropriate basis for decision making on cropping systems but rather economics is most important (Stanger et al., 2008). This report showed that, with the exception of continuous corn grown with 224 kg N ha-1, a corn-soybean rotation was the most stochastically efficient cropping system across a range of N fertility treatments and other rotation schemes.

### **4.1 Other soybean rotations**

Though soybean is one of humankind's oldest crops, it did not really become of significance in the United States until the late 1940's. The species was introduced in Europe from China in the mid 18th century and into the new world in the early 19th century where it was used primarily as a hay crop. The combination of the destruction in China from World War II and the Cultural Revolution removed it as the world's primary supplier of soybeans and opened an opportunity for the United States to develop the crop as a major oil seed (North Carolina Soybean Producers Assn. , 2011). Currently the United States produces about 40% of the world's soybeans followed by Brazil and Argentina combining to produce 50%. Besides corn, soybean is being rotated with rice or cotton in the Mid South and Southeastern States (Anders et al., 2004: Stallcup, 2009). In the eastern Great Plains soybean is often rotated with wheat or grain sorghum (*Sorghum bicolor* L. Moench) as well as corn (Kelley et al., 2003). Kelley et al. (2003), found that in general soybean yields grown in rotations with wheat or grain sorghum produced a 16% greater seed yield than when grown in a monoculture (Table 6). One of these rotations was soybean double-cropped behind winter wheat which is frequently practiced in areas of the United States south of 39o N latitude. This practice does risk failure from drought either causing poor emergence or poor seed set. Above 39o N there is also the risk of early frost terminating growth and above 40o N the practice of double-crop soybean after wheat is not advisable.


†W-S/S=Wheat-double crop soybean/soybean; W-F/S= Wheat-fallow/soybean; GS/S= Grain sorghum/soybean; Cont. S= continuous soybean.

**‡**All means are significantly different by LSD (P0.05).

Table 6. 10 Year average 2nd year soybean yields in a two year rotation scheme at Columbus, KS from1980 to1998. (Kelley et al., 2003)
