Assumptions Can Be Wrong

Assumptions Can Be Wrong

Assumptions Can Be Wrong

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“Research is formalized curiosity. It is poking and prying with a purpose –“  Zora Neale Hurston

Successful research projects often validate assumptions.  But proving assumptions wrong with research can be just as beneficial to the grower, as a group of wine grape growers in California learned.

The planting of winter cover crops is a widely used management practice in California’s Paso Robles Groundwater Basin’s vineyards due to the many benefits, such as reduced erosion and nonpoint source pollution, increased soil organic matter, and improved infiltration of rainwater. However, declines in the groundwater basin and many years with little rain have growers looking closer at water conservation practices. These growers became concerned that the common cover cropping practices were depleting soil moisture that had been replaced by any winter rains. They questioned if the benefits realized from their cover cropping practices were worth the potential cost in terms of water that would have to be replaced by irrigation during the growing season.

To determine if this was indeed the case, the grower group Vineyard Team led a study investigating whether and to what degree the depletion of soil moisture over the winter by certain cover cropping practices might affect the quantity of groundwater pumped for irrigation to replace these losses. The researchers and growers started with the assumption that different species of cover crops would deplete soil moisture at different rates during the winter and early spring and that the timing and manner of terminating a grass cover crop would impact how much water was lost from the soil.

Instead, the project team found that neither the timing and method of terminating a grass cover crop nor the selection of cover crop species differed consistently in terms of soil moisture depletion compared to clean cultivation or fallow/no-till control, according to Craig Macmillan, Vineyard Team’s Technical Program Manager.

“These outcomes suggest that growers have the freedom to choose cover cropping management practices based on factors other than potential soil moisture depletion in this area during low-rainfall years,” states Macmillan. And in exit interviews of cooperating growers, there was agreement with this assertion.

Over 40 growers attended two tail gate meetings to view the experiments and learn of the results. In addition, the Vineyard Team’s educational module attracted 28 visitors.

Where to Learn More

Fact Sheets

Educational Module

Want more information? See the related SARE grant(s) OW14-032, Selecting and Managing Vineyard Cover Crops to Reduce Consumption of Net Basin Water .

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2016 Annual Report

For the first time, we are sharing a yearly snapshot of our work. The stories provided here typify the creative, participatory and integrated research Western SARE annually funds – led by land grant institution researchers and graduate students, Extension and other ag professionals, and nonprofit leaders in full partnership with producers.