Cover Crops As Strategy to Enhance Biodiversity In Perennial Cropping Systems: The Case of Asparagus Production

Benefits of crop rotation are multiple and well understood by most growers.  Unfortunately, short and medium term crop rotation is not possible in perennial crops like asparagus (Asparagus officinalis) that are established for 15 to 20 years of production.  Cover crops could help improve biodiversity and capture some of the benefits of crop rotation in perennial cropping systems.  Currently cereal rye (Secale cereale) is the most utilized cover crop to improve asparagus cropping systems. Studies were conducted from 2008 to 2010 to test the potential for integrating Brassica cover crops in asparagus cropping systems.  Treatments included Brassica cover crops [a mixture of oilseed radish (Raphanus sativus) at 6.0 kg/ha and Oriental mustard (Brassica juncea) at 3.5 kg/ha in 2008 and 2009], and control without a cover crop.  Treatment rows were separated with a guard row to avoid contamination. Plots were managed following commercial production practices. Evaluations consisted of cover crop biomass, total asparagus shoot biomass after the first killing frost (in November), spear yield (in April-June), and soil microbial biomass.  Timing of cover crop seeding and environmental conditions seemed to influence cover crop establishment.  During 2008 season when herbicides were not applied to the trial, cover crop establishment was excellent with about 7.5 t/ha of dry biomass.  In 2009 and 2010; however, cover crop biomass was only 2.5 and 0.7 t/ha, respectively, due to the effect of residual herbicides.  Total soil microbial biomass was reduced under Brassica cover crops.  The cover crops also reduced asparagus fern growth in 2009.  However, yield from the cover crop treatment (3. 3 kg/plot) was similar to that from the control (3.1 kg/plot).  The integration of Brassica cover crops in asparagus production system seemed to be promising.  A cover crop rotation including Brassica species and rye could be used for long-term soil management in asparagus production. It appears that the Brassica cover crops should be planted early in August when the soil has adequate moisture for germination.  Residual herbicide should also be tested for their impact on cover crop establishment.