Abstract
Like everything for the past 2 centuries, agriculture has depended increasingly on fossil fuel energy. Pressures to shift to renewable energy and changes in the fossil fuel industry are set to massively alter the energy landscape over the next 30 years. Two near-certainties are increased overall prices and/or decreased stability of energy supplies. The impacts of these upheavals on specialty crop production and consumption are unknowable in detail but the grand lines of what will likely change can be foreseen. This foresight can guide the research, extension, and teaching needed to successfully navigate a future very unlike the recent past. Major variables that will influence outcomes include energy use in fertilizer manufacture, in farm operations, and in haulage to centers of consumption. Taking six increasingly popular fruit and vegetable crops and the top two horticultural production states as examples, here we use simple proxies for the energy requirements (in gigajoules per ton of produce) of fertilizer, farm operations, and truck transport from Florida or California to New York to compare the relative sizes of these requirements. Trucking from California is the largest energy requirement in all cases, and three times larger than from Florida. As these energy requirements themselves are all fairly fixed, but in future will likely rise in price and/or be subject to interruptions and shortages, this pilot study points to two commonsense inferences: First, that fruit and vegetable production and consumption are set to reposition to more local/regional and seasonal patterns due to increasing expenses associated with fuel, and second, that coast-to-coast produce shipment by truck will become increasingly expensive and difficult.
In common with all other industries, horticulture is at present overwhelmingly fossil-fueled—in everything from the manufacture of fertilizer and other chemical inputs, through farm operations, to produce distribution (Paris et al. 2022; Pelletier et al. 2011). This high fossil fuel dependency makes horticulture at least as subject as any other sector to the uncertainties and disturbances that transitioning away from fossil fuels on the “Net Zero by 2050” timeline—or anything close to it—will bring (Bouckaert et al. 2021; Hagens 2020; Michaux 2023; Smil 2016, 2022; Smith et al. 2023). Specific forecasts of how production and consumption of specialty crops will respond to the coming changes are clearly impossible. However, some general trends are fairly foreseeable, given three reasonable assumptions about how the projected shift to renewable energy and changes in the fossil fuel industry will impact energy prices and availability. These assumptions are as follows:
- i) Rising carbon taxes and falling energy return on energy invested (ERoEI) for oil and natural gas derived from hydraulic fracturing of shale will drive up fossil fuel energy prices (Ahmad and Zhang 2020; Hagens 2020; Hall et al. 2014; McKinsey Global Institute 2022; US Energy Information Administration 2021).
- ii) Limited metal mining capacity and reserves, infrastructure build rates, and availability of financial capital will delay—and likely disrupt—the transition from fossil fuels to electricity, creating system-wide instability (Allwood et al. 2021; Michaux 2021, 2023; Smil 2016, 2022).
- iii) Even if average electricity prices fall as the transition proceeds, absent new technology to store power or balance variable supplies, wind and solar grids will lead to large diurnal and seasonal price variation and volatility and make shortages more likely (Michaux 2021; Seel et al. 2018).
This short, perspective-type article is a pilot effort to view foreseeable trends through an energy lens, taking as illustrations six popular specialty crops and two states that grow them. It follows in a long tradition of energy-centric analysis of agriculture and the food system (Madison 1997; Pimentel et al. 1973). It does not aim to be comprehensive or authoritative, but to spark actionable conversations—and follow-up studies—about how transitioning away from fossil fuels will change horticulture and how research, teaching, and extension should adapt. We first give a broad-brush picture of energy use in horticulture and explain the choice of crops and states. We then estimate the energy needed to grow these crops and transport the produce to New York, as a representative consuming area. Last, we discuss what our estimates imply for a future in which assumptions i to iii above hold.
Energy Use in Horticulture and Future Uncertainties
Figure 1 splits energy use items into three categories: energy embedded in inputs coming through the farm gate; on-farm operations; and energy to transport and maintain cold-chain after produce leaves the farm. The major sources of energy for each item are shown in italics below it, for the current situation (upper frames) and for the projected “Net Zero by 2050” scenario (Bouckaert et al. 2021; Michaux 2021) (lower frames). The current situation runs mainly on diesel, natural gas, and fossil fuel electricity. The 2050 scenario is very different; most items are powered primarily by renewable electricity from wind and solar, either directly or indirectly via hydrogen or ammonia made using renewable electricity. The planned penetration of renewable energy from wind and solar into horticultural energy use over less than 30 years is thus massive, as symbolized by the thicket of green arrows at the bottom of Fig. 1.
Major uses of energy in specialty crop agriculture and their sources at present (above) and broadly as projected for 2050 in the Net Zero by 2050 Roadmap and related policies (below). “Before farm” uses are energy-intensive inputs delivered to the farm. “On-farm” uses are for conventional (nonorganic), open-field agriculture (as opposed to greenhouses or other controlled environments). “After farm” uses get produce at least most of the way to consumers. The three highlighted uses are typically the largest in each category (see text). The types of energy used are shown in italics. The sources of electrical energy shown are the now-dominant ones or those projected to become dominant by 2050. Note the uncertainty in what (if anything) will replace diesel in farm operations and long-distance haulage. Note also that fossil fuel use in phosphate and potash mining seems unlikely to disappear by 2050 (Michaux 2021), and that it is highly uncertain if production of biomass for biodiesel and use as a chemical feedstock can be scaled up enough to fully replace their fossil fuel counterparts (Yang et al. 2021).
Citation: HortScience 59, 5; 10.21273/HORTSCI17724-24
The likelihood that the transition from fossil fuels will not go as fast and as far as currently envisioned creates uncertainty (assumption ii), and the lack of mature, scalable technologies to store electricity (assumption iii) and to power heavy trucks and tractors (see question marks in Fig. 1) adds further uncertainty. Yet more uncertainty comes from the dependence of renewable (green) technologies on incentivization by government policies, which can and do change (Sarfo 2022), and from the potential for climate change to cause disruptive spikes in peak electricity demand (Auffhammer et al. 2017).
Choice of Illustrative Specialty Crops and States
We chose crops whose consumption per capita has risen over the past 30 years and that are grown in both Florida and California. The rationale for the rising consumption criterion is that it signals robust demand that will likely be sustained in the future, particularly given the emphasis now being placed on the health benefits of fruits and vegetables (The White House 2022). Florida and California were chosen because they are the top two states in horticultural production, sustain year-round production, to some extent compete with each other, and are on opposite sides of the country and so illustrate the importance of distance from major centers of consumption (which is a key part of their competition). Both states also have comprehensive research and extension programs that encourage producers to minimize nutrient and water losses to the environment.
Comparing the most recent data from the US Department of Agriculture (USDA) Economic Research Service on fruit and vegetable availability per capita with data from 30 years ago showed ∼90% to >600% increases in consumption of blueberries, avocados, and strawberries, and ∼40% to >300% increases for broccoli, bell peppers, and romaine and leaf lettuce (Supplemental Fig. 1). These six specialty crops all have documented nutritional and health benefits and are produced in Florida and California, and so became our test set.
Energy Use Estimates
Case study parameters.
We focused our analysis on typical open-field horticulture and took the energy embedded in nitrogen fertilizer plus on-farm diesel use as a proxy for total energy used in production. Nitrogen fertilizer and diesel-driven farm operations are generally the two largest items in crop energy budgets and together typically make up about two-thirds of the total (Paris et al. 2022; Pelletier et al. 2011). We excluded energy embedded in phosphate and potash fertilizers, which is far less than in nitrogen fertilizer, and energy embedded in pesticides and other chemical inputs, which is likewise comparatively minor (Paris et al. 2022) and varies between sites and years, making it complicated to budget with accuracy. We also excluded irrigation, which is often not more than a quarter of the total and varies greatly (Paris et al. 2022) according to soil, water quality, crop, and climatic factors, and in whether it is diesel or electrically powered. In addition, we excluded the energy embodied in farm equipment or trucks, and human labor, as is usual for this type of study (Paris et al. 2022). Energy use per acre per season was converted to per ton of harvested produce using average yields from the USDA National Agricultural Statistics Service or other authoritative source (Supplemental Table 1). We assumed that yields and energy use in production are comparable in California and Florida. Although this is a drastic oversimplification, we considered it warranted here because differences would have to be at least 2-fold to change our main conclusions, as is seen later in the Take-homes section. For energy use in post-farmgate transport between representative centers of production and consumption, we compared a refrigerated 18-wheeler hauling a full (20-ton) load from Modesto in California’s Central Valley or Orlando in Central Florida to New York (2892 or 1073 miles, respectively).
Nitrogen fertilizer.
The energy embedded in nitrogen fertilizer depends somewhat on the efficiency of the manufacturing process and on the nitrogen’s final form (ammonia, urea, ammonium nitrate, etc.); the energy is used mostly in the N2 → NH3 reduction step in the Haber-Bosch process (Michaux 2021). We used an average energy content of 40 GJ per ton of nitrogen, based on four sources (Supplemental Table 2). The nitrogen used to produce each crop was based on the recommended application rates in recent extension publications (Supplemental Table 3).
On-farm diesel.
We took the energy content of diesel fuel as 0.145 GJ per gallon (Bureau of Transport Statistics 2021). On-farm diesel use was estimated from expert assessments of the type and number per year of operations (e.g., plowing, laying plastic mulch, spraying) for each crop, and standard values for fuel consumption per acre in each operation (Supplemental Table 4). For avocado and blueberry, we used data for the diesel needed to manage an established orchard.
Long-distance refrigerated haulage.
The energy used per ton-mile in long-distance truck transport varies with cargo weight, route, truck model, and—for round trips—whether the truck runs empty on the backhaul (Transportation Research Board 1977). Literature values reflect this, ranging from 2.6 to 4.4 MJ/ton-mile (Supplemental Table 5). We used an average of 3.6 MJ/ton-mile, based on five sources; this number was then raised by 0.3 MJ/ton-mile to account for energy use in trailer refrigeration, giving a final value of 3.9 MJ/ton-mile (Supplemental Table 5).
Comparisons among Crops and between Production and Transport Costs
The left frame of Fig. 2 shows the energy in the nitrogen fertilizer and diesel fuel needed to grow 1 ton of each crop. The right frame shows the energy needed for refrigerated transport of 1 ton of fresh produce from California or Florida to New York, which is the same for all the crops. Comparing the individual crops shows a 9-fold range in energy inputs, with lettuce and bell peppers the lowest and blueberries and avocados the highest. In broad terms, the prices paid to producers (Fig. 2, inset) track the energy inputs, as might be expected. The most striking result, however, is that the various crops’ production energy requirements are all less than half the energy used for transport from California, and the requirements for all except blueberries and avocados are smaller than for transport from Florida. For lettuce and bell peppers, production energy requirements are more than 10-fold smaller than transport from California. Although it is self-evident that transportation costs can substantially impact the costs of marketing produce (Volpe et al. 2013), Fig. 2 makes starkly clear just how much coast-to-coast transport could do this in an energy economy in which energy prices are higher and less predictable and shortages are possible.
Estimated energy (nitrogen fertilizer and diesel fuel) used in production of six specialty crops and in refrigerated transport to New York from California or Florida. Inset plots the National 2022 Marketing Year Average fresh market price received by producers against the energy used for nitrogen fertilizer and diesel for each crop. Data points are color coded by crop as in the main figure. Price data are from the USDA National Agricultural Statistics Service Quick Stats database https://quickstats.nass.usda.gov/.
Citation: HortScience 59, 5; 10.21273/HORTSCI17724-24
Take-Homes
As said at the outset, this is a pilot study. It basically uses “Fermi calculations” (Janzen et al. 2022), also called “back-of-envelope” calculations, to reach rough but reliable—and hence actionable—conclusions. We reached two such take-home conclusions.
First, the next 30 years are likely to be a rough ride from the energy standpoint. Rising fossil fuel prices and the uncertainties surrounding how wholesale electrification cannot be delivered fast enough, how well variable electricity supplies will match expanding demands, and what forms of energy will power tractors and trucks (Fig. 1) add up to change and instability on a scale seen previously only in wartime. This puts a premium on resilience for growers even if this means sacrificing some cost efficiency. A flat equipment battery can be a disaster in an electricity outage; charging a battery is a time-thief in a production and transportation environment in which timeliness is critical. Well into the future, diesel power is therefore likely to remain a surer option than renewable electricity or fuels produced from renewable electricity such as green ammonia.
Second, the relative amounts of energy needed to produce specialty crops vs. truck them over long distances (Fig. 2) point to a strongly increasing competitive cost advantage for nearby rather than far-off producers as fuel costs rise (i.e., Florida is favored over California for East Coast markets in our example). More generally, these relative energy demands imply a return toward the more local/regional and seasonal production and consumption patterns of 40 years ago (Campbell and McAvoy 2020; Volpe et al. 2013; Weidner et al. 2022)—hence in part the use of the word “repositioning” (in space and time) in this article’s title. In this connection, note that international air freight uses at least three times more energy per ton-mile than heavy truck transport (Volpe et al. 2013) so that what applies to trucked produce does so in spades for produce shipped by air. Note also that irrigation, purposely left out of our main analysis, can have a high diesel or electricity demand (Supplemental Table 6) that varies by location and season. The energy demand for irrigation, and water availability—particularly in California (California Natural Resources Agency 2022)—will therefore likely play into decisions about what is grown where, and when, in much the same way as the energy demand of long-distance haulage. Also playing into decisions will be the energy demands of distant open-field or tunnel production vs. local controlled environment production, which can require substantially more energy than field systems but may use less transportation energy (De Villiers et al. 2009; Nicholson et al. 2023). Increases in farmland prices (US Department of Agriculture 2022) will be another factor in the de-risking strategies intrinsic to the re-distribution of production over a wider geographic area and nearer to consumption centers than at present (Malcolm et al. 2012).
In conclusion, the transition away from fossil fuel energy is happening now and will accelerate over the next decades (Bouckaert et al. 2021). If the transition is to go anything like the “Net Zero by 2050” plan, displacing the current energy system by a reimagined electrical one that has yet to be built means that horticultural research, teaching, and extension will also need to be reimagined. Hence again the use of “repositioning” in our title—in this case in an intellectual and ethical sense. It signals the opportunity for horticulturists to develop technical innovations and to encourage the individual and societal changes necessary to reposition our systems in the context of optimizing the overall food system.
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