Source: The Times-News
As cover crops continue to gain ground across southern Idaho's Magic Valley, growers are finding that species are not interchangeable. Matching the specie or blend of species to particular goals is critical for getting your money’s worth.
“Diverse blends are excellent for building soil health,” Luke Adams told fellow sugarbeet growers during a field day. “But as you blend, you dilute the benefits of each component. If you have a nematode problem and you use a blend, you will reduce the kill.”
Adams has been experimenting with cover crops to control nematodes on his Rupert area farm for about five years. He has tried cover crop blends that include nitrogen fixers and species to trap nematodes as well as trap crops alone.
He has found that when he includes a trap crop in a blend, the nematode population in a field does not increase but the kill is not as high as when the trap crop is planted alone. That may not be a problem if the nematodes are present but not at economically damaging levels.
“Diversity is great,” he reiterated. “There are lots of reasons to do it (plant a diverse mix), but you will get a little of the benefits of all of them.”
One of the benefits of planting a diverse mix is that the cost may be lower than planting just one specie. Growers with severe nematode problems may need to plant specific varieties of trap crops that have been registered. Royalties for those varieties can be expensive, Adams said.
He estimates that it costs $35 to $50 per acre to trap and kill nematodes. In contrast, planting a diverse blend for soil health benefits runs $25 to $35 per acre. “As you build diversity and go more with blends, costs are reduced on average,” Adams said.
Growers who want to control nematodes but also build soil health need to be careful about what species are included in the mix. Tillage radishes are great for breaking through hard pans in the soil and creating pore space but they actually host nematodes and will increase the population. Oilseed radish, on the other hand, stimulates nematodes to feed and begin the life cycle, but do not provide the nutrition the pest needs to mature and lay eggs. That’s the difference between a host crop and a trap crop.
Vetch is another specie that is often included in a cover crop mix that may exacerbate a nematode problem. Hairy vetch is a host crop for nematodes but common vetch is not.
“Unfortunately, it’s very complicated when you start working with blends,” Adams said. “You cannot forget your cash crop when using blends. You need to check that every element is at least neutral.”
He would like to see more university research to determine whether a specie is a trap or host crop and to what extent. Some crops, like bursine clover and red clover, seem to be neutral when it comes to nematodes.
Another concern many sugarbeet growers have about planting cover crops is irrigation. Much of Idaho’s sugarbeet acreage lies over the Eastern Snake Plain Aquifer, where groundwater pumpers are reducing irrigation use as part of an agreement with surface water users to restore aquifer levels.
One strategy for reducing water usage is to include more grains in the crop rotation because grain is harvested early. But growers, like Adams, who plant a cover crop immediately following barley harvest will continue to use irrigation water into the fall.
“How do we weigh the tradeoffs of water use versus the soil health benefits of cover crops?” Adams said. “It takes a lot of water to raise a cover crop.”