All I can buy in my country is traditional solid NPK fertilizer as shown in this picture:
How can I prepare a nutrient solution for growing lettuce with this. (I also have Calcium Nitrate and Magnesium Sulphate if needed)
Plants require 14 essential elements, and it sounds like you're only going to provide nitrogen, potassium, phosphorus, calcium, magnesium and sulphur. You also need to dissolve the constituents with distilled water unless you can compensate for the Ca, Mg, and S in tap water.
Plants require 14 essential elements in the root zone,including the macronutrients (needed in relatively large quantities) of nitrogen,phosphorus, potassium,sulfur,calcium and magnesium; and the micronutrients (needed in relatively small quantities) of iron, manganese, zinc, boron, copper, molybdenum, chloride and nickel.All of these nutrients must be supplied by the hydroponic nutrient solution, although chloride and nickel aren’t included in most recipes, as they’re available in sufficient quantities as impurities with the fertiliser.
Since you only want to grow lettuce, you only need a vegetative recipe for the whole growth cycle, and not an additional one for flowering.
Cornell’s Controlled Environment Agriculture group have used this recipe for many years for growing lettuce.
You normally make up two separate solutions as when concentrated together insoluble precipitates can form.
I have heard of people using human urine (instead of fish waste) to grow plants hydroponically and this is known as peeponics. This is possible because animals and plants have evolved closely together so they fulfil our needs as we fulfil theirs. This does need the addition of some wood ash to make up for the inadequate potassium and calcium present in urine, and there may be some health concerns with E. Coli, and medications in the urine.