Nutrient solution for rice hydroponics culture

Abstract

This represents a heavily modified Yoshida's solution. Compared to Yoshida's formulation, this solution has almost the same concentration of macro and micronutrients, but the formulation has been simplified. Key advantages:

The solution is now formulated as three solutions at 1000× concentration, greatly simplifying dilution.
The solution is less acidic than Yoshida's formulation, reducing the amount of hydroxide required to adjust pH.
The solution eliminates Na+ and almost all Cl- from the medium, allowing independent investigation of toxicities of these ions. In addition much of the K+ is supplied as KOH, potentially allowing control of the Na/K ratio independently of absolute concentrations and of Cl- levels.

Before start

Steps

Solution A, 1000× (Main macro and micronutrients)

Make this solution up as a SINGLE stock solution. For 1L of stock solution,

Start with ~600mL de-ionised water.
Weigh out and dissolve each component (except ferric chloride and citric acid) directly in the 600mL solution. Allow each to dissolve completely before adding the next.
For the KOH, add pellets slowly, a few at a time, with constant mixing.
Dissolve the citric acid separately in 100mL de-ionised water. Dissolve the ferric chloride 6-hydrate directly in the citric acid solution. Stir the ferric chloride-citrate solution for 15 minutes, then add slowly to the main stock solution while stirring.
Make up to 1L.

Solution B, 1000× (Ca, NO3)

For 1L of stock solution, dissolve the calcium nitrate 4-hydrate directly in 700mL de-ionised water. Make up to 1L.

Solution C, 1000× (Mg, S)

For 1L of stock solution, dissolve the magnesium sulfate 7-hydrate in 700mL de-ionised water. Make up to 1L.

Solution D, 1000× (silicon)

(Optional): For 1L of stock solution, dissolve 4.50g sodium metasilicate 9-hydrate in 700mL de-ionised water. Make up to 1L.

The sodium metasilicate can also be weighed out and dissolved directly in the growth medium at the time of preparation.

Preparation of hydroponics medium

For 100L of 1× hydroponics solution:

Prepare ~90L of water.
Mix in 100mL of each stock solution, mixing well before adding next stock solution.
Add sodium metasilicate 9-hydrate (0.00450g/L) and dissolve with stirring, if not done as solution D.
Adjust pH to 5.5
Dispense to growth trays.

Monitor and adjust pH of stock solution daily at pH 5.5 with KOH/HCl as required.

Refresh stock solution twice per week.