Exploring the functional role of diversity in a broccoli - living mulch agroecosystem

Background/Question/Methods

Diversifying agroecosystems is a possible avenue for intensifying food production systems on existing agricultural land. The intercropping of cash crops with cover crops (utilized as a living mulch), offers the opportunity for agricultural systems to provide enhanced ecosystem services; however, competition for resources may limit crop yields. By understanding the effects of living mulch on crop yields, we can employ interspecific diversification successfully. We conducted an experiment evaluating the effects of interrow management and fertility on marketable yield of broccoli in plastic covered raised beds at the University of New Hampshire’s Woodman Horticultural Research Farm in Durham, NH. Interrow management treatments were either a mixture of ryegrass (Lolium multiflorum) and white clover (Trifolium repens c.v. ‘New Zealand’) (living mulch), or weeded bare soil, established and maintained between bed rows.  Fertilizer was the subplot treatment and was applied at four (2011) and five (2012) levels, directly to broccoli bed rows. Soil moisture, crop leaf chlorophyll content, marketable crop yield, and nitrogen use efficiency were calculated to gain a better understanding of the ecosystem service trade-offs associated with crop diversification. 

Results/Conclusions

Living mulch did not affect mean broccoli head weight in 2011 (p = 0.1217), but reduced yields in 2012 (p = 0.0135). For the total marketable yield (kg ha^-1) in 2011, there was a significant interaction for between interrow management and fertility (p = 0.016). Total marketable yield in 2012 was reduced by living mulch (p = 0.0002) and increased with fertility (p<0.0001). Competition between living mulch and broccoli, as measured by the relative neighbor effect, was reduced with increasing fertility in 2011, but results were variable in 2012. At several sampling dates during both growing seasons, soil moisture was either unaffected by interrow management, or increased with living mulch. Establishing living mulch appears to have a neutral to a moderately negative effect on broccoli yield.  Fertility accounted for much of the yield variability observed over the two seasons. These results suggest that using living mulches to diversify agroecosystems may be a viable option for small-scale farmers typical of the Northeast, with the understanding that the effects of living mulches on crop yields may be variable.