P .2 System Boundaries first elimination step in this regard, we constructed the scatter-plot diagrams showing yield vs. farmgate price (shown on the previous two pages). This is a crude mechanism for several reasons. For example, production costs are not taken into account, thus the economic values do not represent net profit. Furthermore, a great deal of the production values we have are for field-based production, which does not accurately reflect greenhouse yields. However, we considered this to be suitable as a first measure of elimination, since many of the later analysis steps took these factors into account. • Prioritizing for perennial plants We also chose to prioritize for perennial crops, such as berries, fruit trees, and certain perennial vegetables. Even though these are not always the most profitable crops, they create interesting opportunities for temporal stacking, and establish a more permanent ecosystem foundation. • For all perennials, we eliminated crops that require over five years to reach bearing age. system can still be intercropped with short-lived plants for added value use of the space. • Labor requirements It is difficult to estimate how much labor a polyculture system will require per hectare when compared to a traditional monocultural system, since a number of activities will be shared between crops. However, some crops require additional care, such as pruning and training, which can alter the cost associated with cultivating that crop. We used labor statistics found in pre-assembled crop budgets to make a basic categorization of “high,” “medium,” or “low” labor. However, we ultimately determined that this was perhaps an unreasonable criterion for elimination, since it would get rid of many crops of particular interest. Instead we chose to consider the labor requirements when making the actual spatial arrangements of crops - for example, ensuring that “high labor” crops would be clustered together in areas of easy access. We also relied on these labor estimates in making our final cost calculations. These were organisms that we included in the design regardless of their specific profitability, which in some cases was zero - though in all cases they represented at least some avoided cost. Beyond these support modules, we also wanted to intercrop with companion plants. There are various functions that companion plants can perform, all of which we wanted to include strategically in our final system. These functions include, among others: • • • • • • • • • • • enhanced flavor greater yield trellising or groundcover shading retaining moisture pest suppression pollinator and predator recruitment hosting beneficial insects trapping pests disease resistance pattern disruption (preventing pests from easily jumping from one food plant to the next) We finally settled on a limited number of very versatile “helper plants”: • Comfrey Comfrey is a dynamic accumulator that extracts a wide range of nutrients from the soil, collecting them in its fast-growing leaves. Each plant contains up to 2 kg of leafy material when harvested, and breaks down easily when added into compost. Sterile cultivars exist, which can keep Also for economic reasons, we ensured that all crops within the system would have productive yields within a reasonable amount of time. Some crops take a very long time to reach productivity, which can be fine on cheap land in an outdoor field, but is difficult to justify in a greenhouse. Prior to reaching maturity, all crops in the Polydome 3. Supporting Elements We defined a number of secondary elements that we considered necessary for system functioning. These include a vermiculture compost system, honeybees for pollination, and certain plant types that provide key ecosystem support functions. 62 Pagina 61
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