Nitrogen is the element plants take up in the largest amount after carbon, hydrogen and oxygen. It is part of every amino acid, protein, chlorophyll molecule and strand of DNA. Plants absorb it mainly as nitrate (NO3-) and ammonium (NH4+), and they move it freely from old leaves to new growth.
In practice
A deficient plant yellows from the bottom up, evenly across the leaf, while new growth stays green. Excess gives very dark, glossy leaves, clawed tips and soft, leafy growth. Hydro and coco feeds typically run about 150-200 mg/L (ppm) N in veg and somewhat less in late flower. Saloner and Bernstein found that lower N supply in flower can raise cannabinoid and terpene percentage while reducing total yield, a trade-off rather than a free win.
Don't confuse with
- Nitrate: one ionic form of nitrogen, not the element itself.
- Iron or sulfur deficiency: those yellow the new growth first; nitrogen yellows the old growth first.
- Natural late-flower fade: some lower-leaf yellowing near harvest is normal remobilisation.
Myth check
The GenetixBay approach is to taper nitrogen in late flower, not to flush. Cut N back towards zero near the finish while keeping P, K, Ca, Mg, S and the micros fed. A plain-water flush starves the plant of everything at its most productive stage. See the flush debate and Mythbusters.
The green pigment in chloroplasts that absorbs mainly blue and red light to drive photosynthesis; chlorophyll a and b are the main forms in plants.Nitrate (NO3-) is the main form of nitrogen in hydroponic and soilless feeds; its uptake tends to push root-zone pH upward.Ammonium (NH4+) is the positively charged form of nitrogen; a small share stabilises root-zone pH, but too much reduces cannabis yield and quality.A cannabinoid is any compound that binds the body's cannabinoid receptors or shares the typical cannabis terpenophenolic structure; the plant-made ones are phytocannabinoids such as THCA and CBDA.Terpenes are volatile hydrocarbon compounds built from five-carbon isoprene units; in cannabis they are made in the trichome heads and are a major part of aroma and flavour.Sulfur (S) is a secondary nutrient taken up as sulfate, used in the amino acids cysteine and methionine; deficiency yellows new growth fairly evenly.Gradually cutting nitrogen in late flower, toward zero near the finish, while still feeding phosphorus, potassium, calcium, magnesium, sulfur and micronutrients; GenetixBay's alternative to flushing.Feeding only plain water for days or weeks before harvest to "clean" the plant; GenetixBay rates it a Myth that harms yield, unlike a root-zone salt flush.A macronutrient is an essential element plants need in large amounts, measured in tens to hundreds of mg/L: nitrogen, phosphorus and potassium, plus calcium, magnesium and sulfur.A mobile nutrient is one the plant can move from older leaves to new growth, so its deficiency shows first on lower, older leaves: N, P, K, Mg, Cl, Mo.Urea is a 46% nitrogen organic compound that soil enzymes convert to ammonium; it is cheap in field fertilisers but a poor choice for hydroponic cannabis.The N-P-K ratio is the three numbers on a fertiliser label giving percent nitrogen, phosphate (P2O5) and potash (K2O) by weight, not elemental P and K.
