July 16, 2004



US Soybean Yield Can Be Raised As Corn Yield Has Been


Over the last 75 years the average corn yield per acre has increased sevenfold while soybean yield has not tripled. But two Purdue University agronomists say more progress can be made to increase soybean yields.


Today, soybeans yield 33.4 bushels per acre, according to a Purdue University press release issued Thursday. While in 1930, soybeans produced 13 bushels per acre. Corn yield increased from 20.5 bushels per acre to 142.2 in the same time period, the release said.


This comes out to increase of 1.5 bushels per acre per year for corn, while soybeans yield increased by 0.4 bushels an acre per year. Purdue's Jeff Volenec and Scott Jackson, while admitting that soy advancement will never equal corn, said the 0.4-bushel-per-year figure could be increased.


Volenec and Jackson claim in the release that collaborative research by crop geneticists, physiologists, agronomists and breeders could boost soybean yield potential. However, a boost of more than a few tenths of a bushel in the next 10 years is unlikely, they said.


The challenge, the two agronomists say, is trying to crack the unique genetic makeup of a soybean plant. Because soybeans have half the DNA of corn, the genetic variations in the germplasm are limited, which makes introducing disease and pest-resistant genes into new soybean cultivars difficult, they said in the release. Soybeans are also more difficult to genetically cross, Jackson said.


To genetically cross a soybean plant, "you have to, by hand, take off the male parts of the plant - what we call emasculate," Jackson said. "In a corn plant all you have to do is put pollen on the silks of the plant and bag it up so that no other pollen gets in."


The products of cross genetics offer yet another challenge, Jackson said. If a soybean is crossed, there is a result of one flower and maybe three or four seeds. Meanwhile, corn will produce an entire ear with hundreds of seeds, he explained.


"Genetically it's easier to look for what you want in 200 seeds than it is in three seeds," Jackson said.


The release did point out one particular area in which the Purdue agronomists have hope that the soy yield could be increased.


Volenec said if environmental stress hits early in the growing season, soybean plants are able to make up reproductive losses such as aborted flower and pods because it is an indeterminate plant, which means it continuously produces more pods and more flowers.


Corn, on the other hand, is determinate because it grows, sets an ear and develops a tassel but only once, Volenec said. If a corn plant gets hit early it cannot set another ear or tassel. Volenec sees the aborted flowers and pods in soybeans as opportunity for yield growth.


"If you look at the number of small pods that actually abort from an individual soybean plant, it is about two-thirds of its reproductive potential (that is lost)," he said. "There is a tremendous opportunity to increase yield capacity if we could understand pod and flower abortion."


There also is a great disparity between corn research and soybean research, according to the release. There are about 600 private and public breeders concentrating on corn and only 150 on soybeans, Jackson said. Also, between 1998 and 2003, $106 million went to corn research, while $15 million went to soy, he said.


One other area that holds potential for increasing soybean yield is in photosynthesis. The light availability for corn was maximized 40 years ago when research was able to develop a corn plant that grows its leaves upright instead of down and out. This maximized photosynthesis, and if increased light availability could somehow be given to soybeans also, similar yield-increasing results could follow, the release said.