Nov 18, 2009

Growing Better Carrots

Back in the good old days, carrot growers in Michigan didn’t need to grow perfect carrots. They had a pretty good market for cull carrots, as the state’s half-million deer hunters lapped them up to use as bait for the state’s 2 million deer.

Feeding deer – for bait in bow hunting or just to make them easier to attract and look at – was something of a rural sport.

Then, in the fall of 2008, one deer was found with Chronic Wasting Disease, a first cousin to Mad Cow Disease and part of the fearsome complex of brain-attacking spongiform encephalopathies that affect humans, too.

In one stroke, the state banned feeding and baiting of white-tailed deer, and the market for thousands of acres of Michigan carrots was gone.

It wasn’t long after that Michigan State University horticulturist Dan Brainard’s request to MSU’s Project GREEEN program for $21,000 in grant money to find ways to improve the quality of Michigan carrots was approved. The Michigan Carrot Research Committee has also contributed funding for the work, and a recent successful grant from the USDA’s Specialty Crop Block Grant program will help insure the continuation of his research in this area.

“It is estimated that in 2008, as many as 2,000 acres of carrots in Michigan were planted solely for this baiting market,” Brainard said. “In addition, growers of carrots for fresh market and processing have lost a major market for culled carrots that do not meet the demands of purchasers due to splits, forks, decay and malformation. Overall, 20-30 percent of all carrots produced in the state were sold for bait before the ban went into effect.”

Brainard finished his first year of research this fall and was to present the results during the carrot session at the Great Lakes Fruit, Vegetable and Farm Market EXPO in December. He hopes for continued funding from Michigan’s Project GREEEN.

“This summer, we had two field trials,” he said. “In the first trial, we compared strip-tillage to conventional tillage and compost compared to no-compost for their effects on yield and culls of processing carrots. In the second trial, we tested planting density and variety effects on yield and culls in processing carrots.”

Data is based on only one year of field trials and should be interpreted cautiously, he said.

Strip tillage had no effect on marketable yield or quality compared to conventional tillage, he said.

“The fact that strip tillage had no negative effect on yield or culls is a good thing. Growers view strip tillage as an insurance policy against extreme weather (especially wind),” he said, “and I’m told they sleep better at night with carrots protected by pre-established barley or wheat windbreaks left in place with the strip-tillage system. In the event of high winds like they’ve had in the past, strip-tillage could save their crop or save them the trouble of re-planting.”

Compost at the rate of 3 tons per acre increased yield and reduced culls (mostly forks) in both strip and conventional tillage systems for some varieties but not others, he said.

Reduced tillage benefits in terms of soil quality are likely to take several years to be noticeable. MSU soil scientist Stuart Grandy is collaborating on the project to assess improvements in soil quality that are likely to accumulate over time.

Heavy rain and washout shortly after planting in the density trial lowered densities more than wanted.

“Nonetheless, we found that the percentage of split carrots was reduced at higher densities. Density had little effect on the percentage of forked carrots. Some varieties were less prone to splitting than others. Marketable yield increased for all varieties at higher densities. Based on our data, it is too early to recommend optimal seeding rates, but we do know that optimal seeding rate is likely to vary with variety, and that without a good cull market, optimal density may be higher than what most growers currently use.”

There is a general belief that soil quality and carrot quality are related, and that soils with higher levels of organic matter produce better carrots. In the case of compost, it both adds organic matter and suppresses some diseases and nematodes, and nematodes are a cause of forked carrots, he said.

“The use of compost resulted in a big drop in forked carrots for one of the varieties we tested,” Brainard said.

The use of wheat and rye strips, besides serving as a windbreak, also serves as a cover crop and adds organic matter to the soil, he said.

Split carrots are thought to be caused by fluctuations in soil moisture and the use of too much nitrogen fertilizer, he said. Higher carrot density leads to fewer large carrots, which are more likely to split.

In their joint proposal, Brainard and Grandy wrote, “Soil health is critical for buffering carrots from biological and environmental stresses that contribute to culls and reduced yields. Improvements in soil health for carrot production also bring benefits to crops commonly rotated with carrots, including potatoes, snap beans, corn and squash.

“Soil organic matter (SOM) loss is associated with reduced water availability for crop growth; loss of soil structure with concomitant effects on soil aeration, infiltration rates, porosity and erosivity; lower rates of nutrient retention and increased dependence on chemical fertilizers; and increases in N leaching.

“Further, declines in organic matter, nutrient availability and biological function may contribute to increased severity of soilborne diseases, such as Verticillium wilt and potato common scab.

“Indeed, SOM and soil health are intimately linked to the economic success of vegetable farmers in Michigan. Despite the potential value of strip-tillage for vegetables, relatively little research has been conducted to help growers overcome obstacles and optimize strip-tillage systems. In particular, nutrient and weed management in these systems is more complex than in conventional tillage.

“Successful adoption of strip-tillage requires better understanding of its impacts on weed management. This is particularly critical in carrot production, where weeds are often a major constraint.”