Winter pulse, spring harvest

August 24, 2016 - Susan V. Fisk

Growers always deal with precipitation amounts. Some get too much water. But for those in drought areas, scientists are working to create imaginative solutions that help the soil, have an economic return, and introduce a different crop – pulses.

“Pulse” refers to a type of legume that is harvested as dry seed. Dry peas, lentils, chickpeas, dry beans – and more – are pulses. They benefit human health when we eat them: think fiber, protein, and essential minerals. And they benefit soil health by adding nitrogen to the soil. Pulses are an important crop around the world, but for many years were ignored by U.S. growers.

Pulses, and in this case dry peas, are a flexible crop with many benefits. They work well for growers when rotated with other crops, delivering long-term benefits to the soil. They are widely adaptable for various rainfall zones. And, this new research shows they can even be planted in fall, a time when growers often have time for field work.

During a webinar for Certified Crop Advisers, Stephen Guy made a case for rotating autumn-sown pulses with winter wheat and summer fallow. “Winter pea is an excellent rotation crop for winter wheat,” says Guy, an agronomist with Washington State University. “Introducing pulses in rotation with winter wheat can increase winter wheat yields.”

How can one crop increase the yield of another? One increased benefit to winter wheat yield is pulses’ ability to fix nitrogen.

Winter peas and other pulses “form symbiotic associations with soil microbes, rhizobia bacteria, to pull nitrogen from the air,” says Guy. This process is called nitrogen fixation. Typically, growers need to apply chemically-made nitrogen fertilizers to crops, because nitrogen is one of the top nutrients plants need. Pulses’ ability to fix nitrogen means they are an environmentally-friendly crop.

“Peas contribute to the residual nitrogen in the soil. The plants are not only growing roots and shoots, but the roots have nodules containing the symbiotic bacteria that fix nitrogen. We found nodules that were active most of the winter this year, because we had a mild winter [in Washington state].”

“All the pea residue, including the roots, stems, leaves, pods that are returned to the soil, contain nitrogen at a much higher level than wheat residue,” says Guy. Thus, growers’ have a reduced need for nitrogen when planting the next crop. “Peas also do not root as deeply as wheat to extract moisture, and when soil moisture determines yields in our dry production areas that is also a benefit of pea over wheat.”

“In the higher rainfall areas, winter pea could replace spring pea because it is more productive and would spread the farmer’s work load,” says Guy. Research shows that many varieties of dry pea planted in autumn push through the soil within weeks to create a winter-hardy crop. “Right now in the lower rainfall areas, winter wheat is predominant and in most places the only crop grown. Winter pea can be part of a rotation with winter wheat to increase diversity and productivity. In some instances, we may be able to introduce winter pea in rotation (winter pea – winter wheat – fallow) and eliminate a year of fallow to make two crops in three years instead of the current (winter wheat – fallow) one crop in two years.”

This means more potential cash for growers. “Depending on the price of peas versus wheat, dry pea can have as good an economic return as winter wheat,” says Guy. Increasing the number of crops planted during a three-year period increases that economic gain. In addition, there are fewer fertilizer costs with pulses.

Dry peas are impressively hearty plants. A 2015 study in Davenport, Washington showed that peas planted 4.5 inches deep in late August were able to germinate and push through the soil crust a few weeks later. The seeds were planted into a no-till, summer fallow system  to a depth of moisture. “Pea has a huge advantage under those circumstances,” says Guy. Winter wheat could not have pushed its way through that soil crust. Two months later, the plants show an extensive root system, which allowed for good interaction with the soil.

In a study in Pullman, Washington, autumn-sown dry peas were able to weather winter snowstorms. “There are winter pea lines and varieties that rival winter wheat in cold tolerance,” says Guy. “There are also management practices that can increase winter survival such as deeper planting, planting timing, residue groundcover, etc. Most places where winter wheat will survive, good varieties of winter pea will survive when managed properly. Cold tolerance/winter survival is also an ongoing selection criterion in the breeding programs.”

Winter peas are generally ready for harvest 2-3 weeks earlier than spring pea. “In most situations, winter pea should be ready before winter wheat,” says Guy. “Another way it fits well in rotation.”

The webinar was funded by a grant from the USDPLC and CSSA and can be accessed online.