Page 223 - Breeding and regulatory opportunities, Renaud

General Discussion

compared to mineral fertilised soils with water soluble nitrogen. In this study,

the higher total nitrogen and higher potentially mineralizable nitrogen of

the organic locations provided higher nitrogen availability compared to the

conventionally managed trial sites. Soil levels of P and K in both management

systems were adequate for good broccoli production (Greenwood et al., 2005,

2006; Li et al., 2011).

In this study, we found that the broccoli cultivars grown under organic

management produced on average comparative yields (head weight) to

those grown under conventional management. This is in contrast to much of

the literature (de Ponti et al., 2012; Seufert et al., 2012) who after reviewing

comparative studies concluded that overall organic yields were on average

lower (a reduction of 5-34%) compared to conventional. The farms for the

study were chosen intentionally for long-term organic management (>5 years)

because of what earlier studies had revealed (Smukler et al., 2008; Knight et al.,

2010). The comparable yields between organic and conventional trials were

also in contrast to what we anticipated, because such ield comparisons had

not yet been published in the literature for broccoli.

This study did reveal a broader variance in trait performance under organic

compared to conventional conditions, and certain cultivar trait rank changes.

In certain trials (speciically in Oregon) some cultivars showed higher yields

under organic than under conventional, as often experienced under organic

conditions where mineralisation continues under warm fall conditions and

favours nitrogen responsive cultivars. Broccoli grown under spring conditions

may be at more of a disadvantage due to slower nitrogen mineralization rates

under cooler temperatures afecting soil microbial activity resulting in reduced

yields compared to conventional production ields. This was observed in trials

in Oregon where there were 100 fewer growing degree days (GDD) in Spring

in 2008 compared to 2007 and where organic yields were lower than under

conventional conditions. This supports the argument of the organic sector

that yield stability across various growth conditions is even more important for

organic growers than for conventional growers who can support crop growth

more easily with water soluble fertilisers. One of the organic plant breeding

challenges identiied from this study is the need to breed for better nitrogen

use eiciency under cool spring conditions.

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