Strawberry (Fragaria ×ananassa Duch.) production in California uses plastic mulch–covered beds that provide many benefits such as moisture conservation and weed control. Unfortunately, the mulch can also cause environmental problems by increasing runoff and soil erosion and reducing groundwater recharge. Planting cover crops in bare furrows between the plastic cover beds can help minimize these problems. Furrow cover cropping was evaluated during two growing seasons in organic strawberries in Salinas, CA, using a mustard (Sinapis alba L.) cover crop planted at two seeding rates (1× and 3×). Mustard was planted in November or December after strawberry transplanting and it resulted in average densities per meter of furrow of 54 and 162 mustard plants for the 1× and 3× rates, respectively. The mustard was mowed in February before it shaded the strawberry plants. Increasing the seeding rate increased mustard shoot biomass and height, and reduced the concentration of P in the mustard shoots. Compared with furrows with no cover crop, cover-cropped furrows reduced weed biomass by 29% and 40% in the 1× and 3× seeding rates, respectively, although weeds still accounted for at least 28% of the furrow biomass in the cover-cropped furrows. These results show that growing mustard cover crops in furrows without irrigating the furrows worked well even during years with relatively minimal precipitation. We conclude that 1) mustard densities of ≈150 plants/m furrow will likely provide the most benefits due to greater biomass production, N scavenging, and weed suppression; 2) mowing was an effective way to kill the mustard; and 3) high seeding rates of mustard alone are insufficient to provide adequate weed suppression in strawberry furrows.
Cover crop stands that are sufficiently dense soon after planting are more likely to suppress weeds, scavenge nutrients, and reduce erosion. Small-scale organic vegetable farmers often broadcast cover crop seed to establish cover crops but lack information on the most effective implements to incorporate the seed into the soil. Experiments were conducted with winter- and spring-sown cover crops to compare drilling vs. broadcasting methods for establishing rye (Secale cereale L.) mixed with either purple (Vicia benghalensis L., winter) or common vetch (V. sativa L., spring) on bed tops at a seeding rate of 140 kg·ha−1 in Salinas, CA. Broadcast seed was incorporated with a rototiller, cultivator, or tandem disc. Cover crop stand uniformity was assessed visually, and cover crop emergence over time and seeding depth were measured. Stands were more uniform after drilling or broadcast + rototiller incorporation compared with the other methods. Cover crops emerged sooner and in higher densities after drilling compared with broadcasting. The delayed emergence of broadcast seed was most apparent during the cooler winter experiment, particularly with purple vetch. Most drilled seed emerged from 2-cm depth compared with the broadcast seed that emerged from up to 11-cm depth with the greatest variability after disc or rototiller incorporation. The data indicate that the cultivator and rototiller are preferable implements to incorporate broadcast seed on beds, but that 50% to 100% higher seeding rates for broadcasting than drilling are needed. The practical implications for weed and soil management, and planting costs are discussed.