ST. LOUIS, Mo. — A new Rabobank report suggests increases in corn yields will continue to go down over the next several years. The Netherlands-based agricultural lender is also projecting corn yields of 156 bushels an acre for 2012. The USDA’s estimate, released in February, is 164.

The latest Rabobank Industry Note is called Can Corn Keep Up? It’s written by Sterling Liddell, Al Griffin and Nicholas Higgins and published by the Food and Agribusiness Research and Advisory, an arm of Rabobank International.

The report says while consumption of coarse grains has surged over the past seven years, increases in yield rates have declined. One of the culprits, authors say, is limited arable land that can produce the most corn.

From a slightly different angle it points to increased corn planting as the culprit behind lower yields per acre, since the additional acres often have to be planted on marginal land, which ends up being less productive. It also points to a shift in where corn is being planted, from the traditional Corn Belt to Plains states, where the weather has been more “volatile.”

That’s been the case recently in Kansas, where the weather has been hot and dry. In the Dakotas, wet weather has been a problem. The increase in corn planting in these states is lowering the corn yield overall. “Based on recent systemic changes in the geographic area of production, Rabobank believes yield is likely to grow at a much slower rate than historical and common trendline analysis suggests,” the report stated.

Also, because farmers are planting more corn, they are planting fewer soybeans, which means they are rotating their crops less. According to the report, less crop rotation leads to more pests and a reduction in soil productivity. It quotes Iowa State University experts who say corn-after-corn acres results in an average reduction in yield of 15 bushels. Although this practice is nothing new in the Corn Belt, the authors say it’s something happening significantly more often today.

Another factor affecting corn yields is overall pest activity and the inability of today’s pesticides to effectively deal with it. The emergence of Bt-resistant western corn rootworm, for example, “threatens” yields as well as farmers’ profits, since they will end up having to spend more money on pesticides. Farmers might also be forced to put more of their crop onto marginal land, which will also reduce their yield, the authors said.

Further, technological advancements aren’t keeping up with this development. Since scientists are telling farmers the best way to manage pests is to rotate their crops, this could result in farmers planting more soybeans in the Corn Belt, which would in turn result in the planting of even more corn in the Plains states, which tend to produce less corn per acre.

Another reason behind the authors’ view of near-term future corn yields is that plantings per acre are already at “optimal” levels. The report stated technological advancements have made it so farmers can plant their seeds closer together and thereby increase their yields; however, further improvements in this area are likely to be limited and gradual, and will likely diminish over time, the authors believe.