Thomas G. Chastain

Dry conditions are normal for the Willamette Valley in July and August.  This is an important period for flowering and seed development in red clover seed crops.  While much of the region’s red clover seed crop is not irrigated, would the crop benefit from additional water during this dry period?  That is one of the questions that the seed production research and extension team has addressed.

Field trials investigating the effects of irrigation on red clover seed production have been conducted at Oregon State University’s Hyslop Farm near Corvallis  from 2011 to 2014.  Rainfall for the July through September period in each of the years averaged only 37% of the long-term mean so the test conditions have been quite dry.  Following herbage removal and once regrowth had occurred, approximately four inches of irrigation water was applied to plots over a two-day period by using a custom-designed linear irrigation system equipped with minimum-drift sprinklers.  This single irrigation was strategically-timed to coincide with first flowering (BBCH 60) and was compared to plots receiving no irrigation.

The application of this single strategically-timed irrigation on red clover resulted in increased seed yields and the increases ranged from 10% to 24% depending on year and crop stand age.  Several measures of crop growth and development were not affected by the irrigation.  However, the number of seeds produced and seed weight were both increased by irrigation, and contributed to the improvement in seed yield with irrigation.

A single irrigation to support flowering and seed development in red clover is a beneficial practice in the extended dry weather of the typical Willamette Valley summer.