AGRICULTURAL ENERGY REQUIREMENTS

11.3.1 Desalination

Water is a renewable resource with both highly variable and limited availability. Rainfall, temperature, evaporation, and runoff determine its total availability, and human decisions determine who gets what. Nearly every country in the world experiences water shortages during part of the year, and more than 80 of them suffer from serious water shortages. Clean water resources per capita are declining rapidly as human population increases. Population growth reduces water availability per person and stresses the entire environmental system. Pollution, erosion, runoff, and salinization associated with irrigation, plus the overall inefficient use of water, contribute to the decline in water resources. Allocation of increasingly scarce fresh water generates conflicts between and within countries, industries, and individual communities, with the majority of it everywhere consumed by agriculture. Water shortages are also severely reducing biodiversity in both aquatic and terrestrial ecosystems (Pimentel and Burgess 2013).

The world’s 11.2 billion people circa 2100 won’t be able to feed themselves with its remaining arable land unless they become able to irrigate it. Because irrigated land almost always produces higher yields than do rain-fed farms and permits double and sometimes even triple cropping in warmer regions, such lands currently provide around 40 percent of global cereal supply. Pumping water onto approximately 10% of the world’s total currently arable land (around 300 M ha) consumes around 0.225 EJ/yr. Another 0.05 EJ/yr of indirect energy is devoted to the manufacture and delivery of irrigation equipment (Smil 2008). Around two-thirds of the water currently used for irrigation is drawn from underground aquifers. Energy-intensive electricity-powered deep well pumping accounts for about two-thirds of that, and projections suggest that it will become ~90% by 2050 when shallow reserves are almost depleted (by 2100 they will be totally depleted unless radical changes take place). Current aquifer water extraction rates exceed recharge rates - grossly so in many places. Additionally, global warming is simultaneously exacerbating droughts and melting the glaciers feeding the rivers that provide much of the world’s cheap-to-deliver irrigation water. Global warming has caused Mount Kilimanjaro’s “snows” to disappear along w'ith most of those w'ithin the United States’ Glacier National Park. Building more dams won’t solve the problem because dams do not create water. Additionally, a comprehensive review of Nigeria’s outside-funded dam projects (Tomlinson 2018) concluded that while they do make money for local promoters and the outsiders that fund/support them, they decrease net agricultural productivity by turning fertile downstream floodplains into deserts. In addition to killing wetland-dependent wildlife, those dams have served to lower, not raise, the incomes of far more people than have benefited. Most such dams also don’t generate nearly as much electrical power as “promised” due to inadequate maintenance and low (water-limited) capacity factors. Finally, at best, dams represent a temporary fix for the problems that they are built to address because their reservoirs will eventually fill with mud.

Water shortages plus the high cost of desalination - primarily due to high electricity costs - have led some countries rich enough to do so (e.g., China) to reduce their own crop production and rely more heavily upon imported grains.

Because today’s situation is unsustainable, I’ll next assume that most of the water irrigating the future’s farmlands would be generated by desalinating seawater - the earth’s only truly inexhaustible/sustainable water source. Israel’s solution to its water issues (Israel 2018), demonstrates how a properly managed future technological society could address the whole world’s water- related woes. About 20% of Israel’s area - about 4500 km²- is devoted to agriculture. Its 8.5 million people are fed by -1.045E+9 m³ of fresh water applied to its mostly irrigated farmland (Israel 2018). The World Bank reports that about 37.7% of the world’s total land area is considered agricultural land, of which approximately 10.6% or about 14 million km² is deemed to be arable. Extrapolating Israel’s agricultural water demand to that of the whole world suggests that our descendants will need something like 3.2E+12 m³ (1.045E+9 x 14E+6/4500) of irrigation water. Assuming the ~3 kWh/т³ energy requirement of today’s most popular approach to desalination, reverse osmosis (RO), providing it would require an energy input of 3.51 + 19 joules/a, which corresponds to the full-time output of-1113 one-GWe (“full sized”) nuclear reactors.

The contractual cost of the world’s biggest (-1 million m³/day) RO-based desalination plant (located in Saudi Arabia) is $1.89 billion (Desalination 2020). Collectively, these numbers suggest that building enough RO plants to irrigate the future’s farmlands to the same degree that Israel currently does would require a one-time capital expenditure of $16.6 trillion [3.2E+12 x 0.00189/ (365 x 1E+6] - about 75% of the United States’ current annual GDR Similarly addressing California’s Central Valley’s chronic irrigation water problems should cost only about $40 billion.

In principle, at least, Siemen’s electrodialysis-based desalination technology would require only about one-half that number of reactors and is also less apt to become fouled by seawater’s other- than-salt impurities (Hussain and Abolaban 2014).

To continue, the world’s farmlands’ average elevation is about 600 m (2000 feet) above sea level. Assuming that all of the world’s desalinated irrigation water would have to be pumped uphill that far, the energy needed to do so would be 1.88E+19 joules [3.2E+12 m³ x 1000 kg/m³ x 600 m x 9.8 m/s], which would require another 596 full-sized power plants.

It’s useful to note here that the Western world’s recent Middle East military incursions will probably end up costing its citizens -30 times more ($4-$6 trillion) than it would to have built enough nuclear-powered desalination plants to provide sufficient fresh water for everyone living there and thereby address a root cause of that region’s almost perpetual turmoil. For example, a recent paper in the Proceedings of the (US) National Academy of Sciences (Kelley et al. 2015) points out that the chief driver for today’s Syrian conflict is the unrest/poverty generated by relentlessly worsening droughts, not a desire for “regime change.”

Another plus for desalination is that its product does not add additional salts to soil and is also better at remediating already oversalinized soils than is groundwater. A final advantage is that because deionized water doesn’t already contain near-equilibrium levels of calcium, magnesium, carbonate/bicarbonate, silica, etc., it is a better rock solvent (more corrosive) than is groundwater. The next section will reveal why this is important.

• 11.3.2 Fertilizers
• 11.3.2.1 Nitrogen

We’ll start with an assumption that the future will be fed with today’s four most popular food crops (maize or Zea mays, wheat, rice, and soybeans) in the same proportion that they are raised today. We’ll also assume that 100% of the world’s nominally arable land will be devoted to their cultivation and that

TABLE 11.1

Current Basis Crop Characteristics

^a https://apps.fas.usda.gov/psdonline/circulars/production.pdf. ^ь Cao. P. ct al.. Earth Syst. Sci. Data, 10. 969-984. 2017.

^c US Agricultural Research Service National Nutrient Database for Standard Reference Legacy Release, https://ndb.nal.usda.gov/ndb/foods/show/305217.

TABLE 11.2

Scale up to 14 Million Km² (2.01 times larger acreage)

the same yields/ha_? composition, and fertilizer needs will not change. Table 11.1 contains the necessary data. The sum of the acreage devoted to their production is currently 6.95 million ha (sum of column 2).

Table 11.2 summarizes the results of extrapolating acreage up to 14 million ha, calculating the recommended amount of nitrogen, and adding up the amounts of P and К required to replace that removed by harvesting the crops. At the bottom, the table also compares the total “food value” (calories) of that food relative to that required by 11.2 billion people consuming 2500 kcal/day.

Assuming the total nitrogen application rate given in Table 11.2 (1.67E+08 Mg), fertilizing the world’s cropland would require 2.01 E+8 Mg of ammonia each year (one kg N я 1.21 kg of ammonia). An up-to-date estimate (Thyssenkrupps 2019) of ammonia synthesis’s energy requirements concludes that each Mg of ammonia made with electrochemically generated hydrogen, pressure swing-generated atmospheric nitrogen, and conventional Haber Bosch processing equipment (in other words, “conventionally”) would require about 10 MWh’s [10 x 3.6E+9 J] worth of electricity. That, in turn, suggests that satisfying my scenario’s nitrogenous fertilizer requirement would require the full-time output of another ~230 one-GWe power plants.

11.3.3 Everything Else That Plants Require

Because...

• 1. Much of the world’s farmland has already lost a great deal of its topsoil via erosion,
• 2. Much of its remaining topsoil is mineral depleted,
• 3. Basaltic rocks are both intrinsically basic (contain a good deal of magnesium and calcium) and rapidly weathered by natural phenomena and thereby constitute the mechanism

FIGURE 11.2 The earth’s carbon cycle. (From http://www.columbia.edu/~vjdl/carbon.htm.)

limiting the earth’s atmospheric C0₂ concentration (Figure 11.2) via “mineralization” extant in cultivated soils (Moulton et al. 2000),

• 4. Most of the earth’s crust consists of basalt, a good deal of which is either on or close to the surface of its continents,
• 5. Such rock contains relatively high concentrations of potassium and phosphorous along with all of the other biologically important elements, which explains why soils comprised of weathered volcanic ash are exceptionally productive (Hensel 1894; Beerling et al. 2018),

...I’ll next assume that the phosphorous and potassium required to produce the future’s food circa 2100 AD will be provided by amending its farmland with powdered basalt. In order to be effective, any such amendment must weather rapidly enough to release sufficient potassium and phosphorous to support high-yield agriculture, which, in turn, means that the raw silicate rock surfaces must be “fresh” (not already equilibrated with the atmosphere and thereby covered/blocked with secondary phases), ground to a considerably smaller particle size than is the quarry waste-type soil amendment rock powder currently being marketed to hobby farmers, and also mixed with root- zone topsoil, not just dumped upon the surface of the ground (Priyono and Gilkes 2004; Campbell 2009). Based upon the rather limited amount of scientifically planned/supervised experimentation described in the open-access (not paywalled) technical literature, I’m next going to assume that this would require grinding it so that the particles comprising >80% of it possess diameters <10 microns. Since rock grinding is highly energy intensive - much more so than is simply recovering it from a quarry’s rock outcrop or waste dump - the cost estimate for this part of my scenario will be based upon that step’s energy demand plus the resulting powder’s transport and distribution costs.

First, how much powdered rock must be made? The crops assumed above contain phosphorous and potassium that unless recycled back to those fields in some fashion (nightsoils?) must be replaced each year. The compositions of flood basalts vary considerably, but since all originate from the earth’s fairly well-mixed underlying magma, for the following estimate I’m going to assume a composition with which I’m familiar (Leeman 1982; Siemer 2019b, see Table 11.3) - that of the basalt comprising Idaho’s “Craters of the Moon” National Monument and covering much of the rest of Idaho’s Snake River Plain. It contains an average of 0.61 wt% K₂0 and 0.55 wt% P₂0₅ which translates to 0.00506 tons of К and 0.00231 Mg of P per Mg of rock dust. Since for this combination of crops, phosphorus comprises Liebig’s limiting nutrient, the amount of powdered basalt required to replace that removed with the grain comes to 1.26E+10 Mg [2.91 E+7 Mg P/0.00231 Mg P/Mg basalt] - an average of about 9 Mg/ha over 14 million km² of arable land.

TABLE 11.3

Weight % Composition of Major Basalt Types in the Northwest United States

Source: Leeman, W.P., Olivine tholeiitic basalts of the Snake River Plain, Idaho, in B. Bonnichsen and R. M. Breckenridge, Eds., Cenozoic Geology of Idaho, Idaho Bureau of Mines and Geology Bulletin, 26, pp. 181-191, 1982.

A review of rock-grinding technologies (Jankovic 2003) suggests that producing one Mg (ton) of <10 micron basalt powder would require about 100 kWh’s worth of electricity. If so, making 1.26E+10 Mg of it would require 4.16E+18 J, which if spread out uniformly throughout one year would require the full-time output of 131 one-GWe power generators.

If that pow'der were to be transported an average of 1930 km (1200 miles) from mine to farm via an electrified rail system as energy efficient as that currently used to move US coal (185 km/L diesel fuel/short ton), its energy cost would be about 2.43E+17 J (assumes 1.1 Mg/short ton, 33% heat-to-mechanical engine efficiency, and 44.5 MJ/kg diesel fuel with an SpG of 0.85). Trebling that figure to account for fuel consumed by trucks and tractors at the rail heads brings the total to 7.28E+17 joules/a, which corresponds to an annual transportation/distribution energy demand requiring another 23 one-GWe power supplies to satisfy.

Note that the rock pow'der’s transportation cost is much lower than its grinding cost and both are much lower than the cost of the desalinated water and/or nitrogenous fertilizer.

A rock powder application rate of 9 Mg/ha/year is not really very large because it represents only about 0.5% of the mineral matter already within a six-inch deep (typical annual crop root zone) layer of normal density/composition topsoil and is also similar to w'hat current farming practices often lose via wind/water erosion (5-30 Mg/ha/a; see Pimentel and Burgess 2013). Consequently, since my scenario’s rock grinding/distribution costs are a fraction of its irrigation water and nitrogenous fertilizer costs, it might be a good idea to at least start out with considerably larger powder application rates, perhaps 40-50 Mg/ha. Doing so would also reduce the chance of crop “starving” due to slower-than-I’ve assumed weathering rates.

• 11.3.4 Other Reasons for Powdered Rock Fertilization
• 11.3.4.1 Addressing Already Oversalinized Soils

Here’s a statement cut and pasted from one of the best-written soil science papers I’ve seen to this day (Said Hassan and El Toney 2014):

With unique 92+ essential elements, consisting of a broad range of trace minerals along with small amounts of macro elements, the soil nutrients which have been slowly lost through the ages by erosion, leaching and farming are gently regenerated. Rock dust not only improves soil vitality, but also increases plants’ overall health while strengthening immunity and pest resistance. Resulting in a completely natural and disease-free final product, unique in flavor and mineral composition.

The paper goes on to show that powdered basalt would address another of the issues that is becoming more prevalent throughout much of the world, the oversalination of irrigated soils. The reason for that is that freshly powdered basalt exhibits a huge ion exchange capacity that “pulls” excess ions (e.g., Na⁺) out of soil solutions.

11.3.4.2 "Climate Change"

Finally, another virtue of such “natural” fertilization is that the weathering of powdered basalt would retain (sequester) soil-generated CO, that would otherwise “respire” back to the atmosphere. The weathering of 1.26E+10 Mg of “Snake River Plain Basalt” [10.06 wt% CaO and 7.65 wt% MgO=’s 7.35 milliequivalents’ [0.1006 x 2/(40 + 16)+0.0765 x 2/(24.32 + 16)] worth of base per gram] would therefore in effect remove about 4.1 GT of carbon dioxide from the atmosphere - that’s about 11% of today’s anthropogenic CO, emission rate. A good deal of theorizing has been done about how the “enhanced weathering” of mafic rocks could address global warming (see Schuiling and Krijgsman 2006; Hartmann et al. 2013), but very little realistic experimental work has been done to date. Thankfully, that subject is beginning to receive more attention (Taylor et al. 2017), and some hopefully realistic experimental studies have apparently begun (Beerling et al. 2018).

11.3.5 Other Agricultural Energy Requirements

I’ll next assume that the rest of my scenario’s on-farm agricultural energy can be approximated as follows:

• • Assumptions
• • 200 horsepower-to-the-ground tractors drag 5-meter-wide machinery at 8 km/hour over 14 million km² of land three times per year.
• • For simplicity’s sake I’ll next assume that those tractors, possess 72% efficient drive trains powered with 95% efficient electric motors and 50 kWh “TESLA 3” battery pack modules ...
• • .. .and that the overall energy source (nuclear reactor) to battery to motor efficiency is 90%
• • Calculations
• • Kilometers traveled by tractors per year = 3 x 14E+6 km² x 1000 m/km/5 m = 8.3E+9 km.
• • Hours so-traveled per year = 8.3E+8/8 = 1.06E+9.
• • 200 hp = 5.36E+8 J/hour = 149 kWh.
• • At 75% discharge/cycle (greater discharge seriously reduces battery life), each battery module would provide 50 x 0.75 = 37.5 kWh of energy per discharge cycle.
• • Which, if 200 hp is to be delivered to the load, would last 0.72 x 0.9 x 37.5 = 0.172 hours (10.3 minutes).
• • Total from source energy required per year = 1.05E+9 hrs x 5.36E+8 J/hour/0.9/ .72/0.95 = 9.14E+17 J/year.
• • That’s 29 full-sized lGWe power plants required to power the world’s tractors
• • At 3 cents/kWh, that’s $7.6 billion worth of electricity.
• • However, since farm tractors run only, let’s say, 10% of the time and for, let’s say, ~6 hours each time, the number of battery modules required would be ~4.19Е+7 [1.08E+9 h/yr/
• (.1 x 24 x 365) h/yr x 6 hr/. 172 hr/L (that’s 39 battery modules per tractor), which at $7000 each represents a whole world up-front cost of $293 billion).
• • Since Mr. Musk (2019) currently claims that those modules could sell for $7000 apiece (far less/kWh than do his/TESLA’s “Power Walls”) and will last 1500 cycles, their steady state replacement cost would be 28.5 $billion per year.

These figures suggest (to me anyway) that battery-powered tractors are unlikely to replace internal combustion engine powered tractors.