Rye Living-Mulch Effects On Soil Moisture and Weeds In Asparagus

Living-mulches growing below the asparagus fern canopy, can provide soil-health benefits and suppress weeds, but may also suppress asparagus through competition for water or nutrients. The central objective of this research was to test whether cereal rye (Secale cereale) living-mulch, in combination with overhead irrigation, could provide comparable weed suppression to standard residual herbicides without reducing asparagus yields.   A field experiment was conducted from 2008-2010 in a mature asparagus planting on sandy soils in Western Michigan, to evaluate the effects of irrigation (none vs overhead), and weed management system (standard herbicides vs rye living-mulch) on weed suppression, soil moisture content, and asparagus yield. Rye living-mulch and herbicide treatments were established immediately following asparagus harvest in late June.  Rye living-mulch reduced available water content in early August by 25-50% compared to non-rye treatments, but had no detectable effect on asparagus yield in either year.  Compared to non-rye treatments, rye living-mulch reduced emergence and growth of fall-germinating weeds including dandelion and horseweed.  However, in 2 of 3 years, rye resulted in greater densities of summer annual weeds during fern growth.  After 3 years, the density of summer annual weeds including Powell amaranth and sandbur was much higher in rye treatments than where standard residual herbicides were used. Our results suggest that (1) soil-improving rye cover crops can partially suppress weeds, but may also compete with asparagus for soil moisture in dry years unless irrigation is used, and (2) successful use of rye living mulches for weed management will depend on identification of complementary weed management practices to avoid build-up of the summer annual weed seedbank.