Introduction Methods Conclusions ...

Exploring the functional role of diversity in a broccoli and living mulch agroecosystem Nicholas D. Warren1, John E. Carroll1, Richard G. Smith1, Rebecca G. Sideman2 1Department

of Natural Resources and the Environment

2

Department of Biological Sciences, University of New Hampshire

Results

Introduction

Diversifying agroecosystems is a method for intensifying food production systems on existing agricultural land. The intercropping of cash crops with cover crops (a living mulch), offers the opportunity for increased ecosystem services over conventional methods, however, competition for resources may limit crop yields. Our objectives were to describe competitive relationships between broccoli and living mulch so that interspecific diversification can be used effectively.

Methods

We conducted an experiment evaluating the first-year effects of inter-row 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. Treatments were inter-row management (Figure 1) and fertility (Table 1). Soil moisture, crop leaf chlorophyll content, marketable crop yield, and nitrogen use efficiency were calculated to gain a better understanding of the functional outcomes of diversity.

Figure 2. Living mulch reduced mean broccoli head weight in 2012 (B) but not 2011 (A). Fertility increased mean head weight (C & D).

Figure 4. In 2011, the total harvestable yield of bare soil and living mulch was equal at the recommended fertility rate (106) and higher, while total yields were reduced in 2012. BS = bare soil, LM = living mulch.

Living Mulch Ryegrass (Lolium multiflorum) & White Clover (Trifolium repens)

Figure 3. Fertility reduced competitive effects in living mulch treatments.

Bare Soil Maintained weed free

Additional Results

Figure 1. Inter-row Management Table 1. Fertility Treatments 2011 2012 Fertilitya(n=4) Fertility (n=5) 22 62 49 106 106 164 164 212 263 a kg N ha-1 equivalent

Figure 2. (Below) Overhead fish eye photo taken in August 2012. Pictured are four replications of inter-row management treatments with five fertility levels within each treatment. Top and bottom rows act as buffers.

• No evidence for soil moisture competition. • Living mulch reduced the prevalence of hollow stem in 2011. • Living mulch suppressed weed growth.

Conclusions  In a broccoli-living mulch system, we observed broccoli yield loss and physiological changes in leaf chlorophyll content that we attribute to competition for soil nutrients. The results of this study suggest that the severity of the competition is dependent both on available fertility and environmental conditions.

Figure 2

Acknowledgements:

Figure 5. Competition resulted in physiological changes of leaf tissue chlorophyll concentrations near harvest in 2012. BS = bare soil, LM = living mulch.

 The appropriate application of in-field diversity must weigh the opportunity for enhanced ecosystem services against anticipated cash crop yield reduction.  A significant challenge remains in understanding yield variation and competitive relationships in intercropping systems. Describing those relationships in terms of benefits and trade offs (e.g. both economic and ecological) that extend beyond a strict evaluation of cash crop yield is essential for growers to make informed decisions about their management practices.

We would like to thank John McLean, Evan Ford, the Woodman farm crew, and Kaitlyn Orde for all of their help. Thank you also to the Smith lab members and summer technicians: Joshua Cain, Daniel Tauriello, Lucie Lynn Worthen, and Kelsey Juntwait, along with Rebecca Day. David Goudreault and Jonathan Ebba at the MacFarlane greenhouses were accommodating and helpful in germinating the broccoli.