Page 146 - Breeding and regulatory opportunities, Renaud

Chapter 4

One of the reasons for only the small magnitude of the Management system

relative to other environmental factors on head weight could be the fact that

on average over all trials, this trait did not signiicantly difer when cultivars

were grown under organic and conventional conditions even though variances

difered. This is in contrast with much of the literature [e.g. de Ponti et al. (2012)

and Seufert et al. (2012)] who after reviewing comparative studies, concluded

overall that organic yields were on average lower (reduction of 5-34%) compared

to conventional. Their reviews suggested that when farms have been managed

organically over a long period of time with consistent soil building practices,

soil fertility increases due to higher levels of organic matter and improved water

holding capacity and increased particulate organic matter (POM), can produce

higher or comparable yields to conventionally produced crops. When comparing

the soil quality of the Oregon and Maine trial locations, the soils at both of the

conventional trial sites had higher levels of immediately available Nitrogen (N)

compared to the organic sites at the time of trial implementation, but had lower

POM levels indicating that their long term available N was less compared to

the organic sites (Table 4.2). Our results in Oregon and Maine demonstrated

that organic is not lower yielding compared to conventional. Broccoli
per se

grown under organic conditions in the spring, however, may be at more of

a disadvantage due to slower nitrogen mineralization rates under cooler

temperatures resulting in lower yields than conventional. This was shown in

trials in Oregon where there were 100 fewer GDD in Spring 2008 compared to

2007 and where organic yields were lower than under conventional conditions

(Table 4.2).

Despite comparable mean head weights between organic and conventional

growing conditions, the overall range in head weight across cultivars was greater

in organic than conventional across all trials, (Figure 4.1c) which represents a

larger variance in organic compared to conventional. This diference in head

weight variance was even more pronounced in the fall trials compared to the

spring trials (Figure 4.1d). Ceccarelli (1994; 1996) in discussing barley breeding

for marginal, low input and drought-prone environments indicated that such

environments can be heterogeneous, and genetic variance can be greater

compared to more homogeneous high input low stressed environments, and

that by breeding solely under high input conditions, an opportunity to exploit

genetic diferences at lower input levels can be lost. While our organic trial

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