Red River Valley Research Evaluates Impact Eight Years After Lime Application
By Carol Windels, Jason Brantner, Albert Sims & Carl Bradley*
The spreading of spent lime on sugarbeet fields around Minnesota and eastern North Dakota has increased significantly in recent years — with a primary motivation, in many instances, being to help manage Aphanomyces root rot.
The Aphanomyces pathogen is an economic issue in more than 90% of the township sections planted to sugarbeets in the Red River Valley and, as well, in numerous beet fields in the Southern Minn growing region. After several years of lower activity, the pathogen made a “comeback” in 2011 due to the late planting season along with warm and wet soil conditions.
For those growing planting sugarbeets in Aphanomyces-infested fields, management recommendations typically consist of planting early, using tolerant or partially resistant varieties treated with Tachigaren®, and employing certain cultural practices (e.g., cultivation and improved drainage) to avoid or reduce disease pressure. But when the inoculum densities are high and the soil is warm and wet, these measures may not be enough — with the result being poor-yielding or even abandoned fields.
That’s where spent lime from the region’s beet factories comes into play. The seven factories in the Red River Valley and southern Minnesota generate about 500,000 tons (dry weight) of spent lime annually. Some has been stockpiled for as long as 20 years. Along with increasing soil pH and supplying crop nutrients, spent lime also has been shown to reduce Aphanomyces on sugarbeets.
But how long does it take, following application, for spent lime to have an effect on Aphanomyces? And, for how long does that influence persist?
Those were the core questions addressed in field trials at two Red River Valley locations where several rates of spent lime had been applied eight years previously. Our goals were to (1) determine the lime’s long-term effects on Aphanomyces diseases and (2) measure the lime’s effect on sugarbeet yield and quality.
One of two trials was established in a commercial field near Hillsboro, N.D., in October 2003, and the other in a field near Breckenridge, Minn., in April 2004. At that time, the Hillsboro site had a history of moderate Aphanomyces root rot (a soil index value of 48, with 100 being highest possible level) while the Breckenridge field had severe Aphanomyces (soil index value of 98).
Spent lime treatments (each replicated four times) at Hillsboro were at rates of zero, five, 10, 20 and 30 tons per acre on a wet-weight basis. (That corresponds to dry weights of zero, 3.3, 6.5, 13 and 19.5 tons, respectively.) At Breckenridge, the rates were zero, five, 10, 15 and 20 wet-weight tons/acre (zero, 2.7, 5.3, 8.0 and 10.6 tons dry-weight basis).
To allow the lime treatments to stabilize in 2004, corn was sown across the four experiments at Hillsboro, while spring wheat was planted at Breckenridge. Sugarbeets have since been grown in one experiment each year from 2005 to 2011. Corn, wheat and soybeans (and, at Hillsboro, fallow) were rotated onto the other three experiments in the other years. Each experiment plot was one acre in size.
In 2011, two Roundup Ready® sugarbeet varieties were sown in one experiment at both locations. Those plots were last planted to sugarbeets four years earlier, in 2007. Standard fertility and production practices were followed to obtain maximum sucrose yield and quality. Here are the results from those two 2011 beet experiments:
Table 1 shows the 2011 sugarbeet trial results at Hillsboro, where the Aphanomyces pressure was considered “moderate.” There were no significant differences in sugarbeet plant stand among limed and non-limed treatments at 36 days after planning; nor were there differences in the numbers of harvested roots. Disease ratings were highest in the non-limed control and decreased linearly with increasing rates of lime. Root yield also increased significantly as liming rates increased.
Table 2 shows the 2011 sugarbeet data from Breckenridge. Seedling stands at 35 days after planting were not significantly different among non-limed and any of the limed plots. But by harvest, the numbers of harvested roots were significantly higher for all rates of lime compared to the non-limed control. Low numbers of roots and severe Aphanomyces root rot in all treatments resulted in very poor yields, although yield, recoverable sucrose per acre and revenue per acre did increase along with liming rates. Overall, however, economic returns were very poor.
What can be concluded from the 2011 findings? There are three main points:
Under prolonged environmental conditions that are highly favorable for disease (especially in soils with high populations of Aphanomyces), even the best management practices — plant resistance, Tachigaren seed treatment, good soil drainage, early planting and application of factory lime — fail. Under such conditions, the pathogen predominates, overriding plant resistance and all other management strategies. In a more-typical season, however, the same management practices are effective, economic strategies for managing this disease.
* Carol Windels, Jason Brantner and Albert Sims are professor (plant pathology), research fellow (plant pathology) and associate professor (soil science), respectively, with the University of Minnesota Northwest Research & Outreach Center, Crookston. Carl Bradley, currently extension plant pathologist with the University of Illinois, formerly was with North Dakota State University.
Editor & General Manager of The Sugarbeet Grower