Heavy, Man...

The Premise

It's quite simple really, feed your plants heavy water. Heavy water consists of isotopes of hydrogen and oxygen that mass minutely more than normal. If a significant amount of these heavier atoms are absorbed by a plant, the cumulative effect increases the mass of the plant. Of course, this could be taken to the extreme. One could provide a plant with fertilizer that only has heavy isotopes in it, etc. But even the cost of feeding the plant heavy water is rather prohibitive, but nonetheless an interesting exercise. The links throughout the document lead to the math used in this exercise

The Details

Data from CRC Handbook of Chemistry and Physics 67th Edition
	common	mass	half-life
₁H¹	98.985%	1.007825	--
₁H²	0.015%	2.0140	--
₁H³	--	3.01605	12.26 yr.
₈O¹⁶	99.762%	15.944915	--
₈O¹⁷	0.038%	16.999131	--
₈O¹⁸	0.2%	17.999160	--
Other rare isotopes of O exist

A reasonably large squash can easily weigh 386 kg (850 lbs.); the record is 408 kg (900 lbs.). Thusly, to meet the 454 kg (1,000 lb.) goal, an additional 68 kg (150 lbs.) are needed.

To make our heavy water we shall use ₁H²(D) and ₈O¹⁸ because they are the heaviest, stable, reasonably-common isotopes of hydrogen and oxygen respectively. One mole of common H₂O is approximately 18 cm³. A mole of D₂[₈O¹⁸] would fill the same volume, and provide an additonal 4 g/cm³. A squash would then need to contain 304 liters of our heavy water in order to gain the desired 91 kg.

The Problems

Density

304 liters of water masses 304 kg, our initial pumpkin massed 386 kg. This means our plant would be 79% water. Summer squash has a high water content, so this is not entirely improbable. Also, if the plant is fed heavy water throughout its life, the heavy isotopes will; through photosynthesis; be incoprated into the carbohydrates produced adding additonal mass and making the goal more feasible.

How much water would you need?

Making the heavy water

20,368 liters (5,092 gal.) of water would need to be processed to obtain the 304 liters of water necessary. Assuming all the water is incorporated into the squash, see below.

Water Loss

Much of the water provided to the plant would be lost. Either through evaporation from the soil, or respiration. Much more than the 406 liters in the plant would be required.

The Math

Weight Gain 4000

  H₂O			         D₂[₈O¹⁸]
  1.007825                       2.0140
+ 1.007825                     + 2.0140
 15.994915                      17.999160
~~~~~~~~~~                     ~~~~~~~~~~
 18.010565 amu                  22.02716 amu

 22.02176 -18.010565 =4.011195 ~4 amu

How much?

One kilo/liter of water contains 56 moles of H₂O
1000 g / 18 g/mol = 56 mol

Heavy water adds 4 g/mol or 224 g on the kilo/liter.

68,000 g / 224 g = 304 liter

304 liters of water in the plant would need to be replaced
with heavy water to add 68 kg to the plant's mass.

Process

D occurs less than ₈O¹⁸, and is thusly the limiting factor. In other words, if you process enough water (An ideal source for hydrogen and oxygen. "Concentrated", with few "contaminants" Easy to process; electrolosysis.) to obtain enough hydrogen, you will have excess oxygen.


An arbitrary sample of H contains 0.015% D

0.015^-1 = 67

It would take 67 units of H to obtain 1 unit of D.

304 liters * 67 = 20,368 liters

20,368 liters -> 20,368 kg (44,903 lbs.) ~20 tons!

                                           3 elephants!

20,368 liters / 4 liters/gallon =  5,092 gallons