|April 19, 2004:
Intercropping corn and legumes in tropical systems
has been the subject of a number of classic studies, many
done in the 1970’s. These studies were instrumental
in demonstrating the wisdom of many peasant agricultural
systems that had come under criticism at the height of
the green revolution for being “inefficient”
because they didn’t use capital-intensive inputs.
The Land Equivalency Ratio (LER) was developed for
evaluating crop polycultures. The LER basically sums
the value of all of the crops in a polyculture and divides
that sum essentially by the value of the main crop in
Researchers in Thailand, writing in the Japanese journal
Plant Production Science, have recently validated
many of the findings of earlier intercropping research
– that crop polycultures of legumes grown with
corn give about half again the value compared to corn
However, a newer version of the LER was used in this
research, called the Area Time Equivalency Ratio (ATER).
The ATER takes into account not just the land use, but
also the time that the intercrop takes beyond the monoculture.
Legume intercrops generally grow for some time past
the corn harvest, and can take land away from the tightly
scheduled sequential cropping typical of Asian agriculture.
The ATER takes this into account.
In the Thai research, corn, peanut, soybean, and mungbean
were grown in monoculture and as corn-legume combinations.
Corn was planted at 53,000 plants per ha in both monoculture
and polyculture. The legumes were planted at 200,000
plants per ha in monoculture and 133,000 when sown with
corn. Nitogen, phosphorus and potassium fertilizers
were applied at a basal rate of 23, 9, and 18 kg per
Corn yields averaged about 4.1 metric tons per ha and
were not significantly different between any of the
treatments – either in monoculture or any of the
polycultures. Yields of peanut, soybean, and mungbean
were reduced 28%, 39%, and 51%, respectively, by intercropping
each with corn. The number of pods was the yield component
The LER was 1.66, 1.60, and 1.48 for peanut, soybean,
and mungbean, respectively. This means that the value
of the harvest was 66% higher for corn and peanuts together
than for corn or peanuts alone.
The ATER was 1.58, 1.52, and 0.96 for the same crops.
The lower ATER reflects the time taken by the legume
to grow after corn harvest, which prevents immediate
sowing of a follow-up crop. Mungbean can be double cropped
(mono-cropped twice in succession) after corn in Thailand,
plus, it is a shade intolerant crop, thus the ATER below
1. Peanut and soy are more shade tolerant.
Several reports show that corn yields increase by about
20% over monoculture when grown with legumes such as
soybean. These cases may be where soil nitrogen is more
limiting. Corn, with its high nitrogen needs, would
have benefited from the legume nitrogen contribution
in these cases.
It is clear here why intercropping is increasingly
being practiced by organic farmers in the U.S., especially
with vegetable crops. Forms of intercropping that are
compatible with mechanized agriculture are also being
researched – mostly in the form of relay cropping.
Polthanee, A. and Trelo-ges, V. 2003. Growth, yield,
and land use efficiency of corn and legumes grown under
intercropping systems. Plant Production Science.
Don Lotter has a Ph.D. in agroecology and has worked
in sustainable agricultural development in North America,
Latin America, and Africa over the past 25 years. He
can be contacted via his website www.donlotter.com