Organic liquid nitrogen fertiliser: 10% N from plant amino acids and peptides
Liquid nitrogen fertiliser supplies 10% total nitrogen in the form plants evolved to use: plant-derived amino acids and short peptides, rather than nitrate or urea. Plants can and do take up intact amino acids through their roots, and a nitrogen source arriving as peptides feeds soil biology on the way in, which a mineral nitrate salt does not. At 45% organic matter, nearly half of every dose is plant-derived organic matter rather than water and dissolved salt.
Nitrogen is the nutrient that builds a plant. It is in every protein, every enzyme and every chlorophyll molecule, and it is the one gardeners run short of first because it is the one that leaches out fastest. Shortage shows as uniform yellowing that starts on the oldest leaves and works up, with growth slowing to a halt.
It carries no sodium and no chlorine, so it can be used in containers, in drip lines and in recirculating systems without the salt build-up that dogs mineral nitrogen feeding. The solution is brown, which is the organic fraction rather than a fault.
What to use liquid nitrogen for
- Leafy crops through the whole growing period. Lettuce, chard, spinach, kale, cabbage and cutting salads all run on nitrogen from sowing to harvest. This is the most direct application of the product
- Correcting nitrogen deficiency quickly. Uniform pale yellowing on older leaves first, with growth stalling. A foliar application is the fastest available correction, days rather than weeks
- Early vegetative growth on fruiting crops. Tomatoes, peppers, courgettes and cucumbers need nitrogen to build the frame before they set fruit. Feed hard early, then taper as flowering begins
- Brassicas and heavy feeders on the plot. Sprouts, purple sprouting broccoli, leeks and sweetcorn all carry high nitrogen demand over a long season
- After heavy rain on light soil. Nitrate leaches readily through sandy and free-draining ground. A liquid top-up is the practical response to a wet fortnight in early summer
- Feeding soil life alongside the plant. 45% organic matter means each application delivers carbon and amino nitrogen to the microbial community, not only to the crop
- Cold-season growing under cover. Root nitrate uptake slows in cold soil. Amino acid nitrogen and foliar application both help bridge that gap
Amino acid nitrogen compared with mineral nitrogen
Liquid amino acid nitrogen 10% N
- Nitrogen as amino acids and peptides, a form plant roots absorb intact
- 45% organic matter feeds soil biology as well as the crop
- Free of sodium and chlorine, so no salt accumulation in containers
- Works as a root drench or a foliar spray from the same bottle
- Made from plant residue rather than manufactured from natural gas
- Lower risk of the soft, sappy growth that heavy nitrate feeding produces
Ammonium nitrate and mineral nitrogen salts
- Immediately available and cheap per unit of nitrogen
- Manufactured through the Haber-Bosch process, which is energy-intensive
- Leaches readily and contributes to nitrate in groundwater
- No carbon contribution, so it feeds the plant and nothing else
- Easy to overdo, producing soft growth and higher tissue nitrate
Nitrogen late in a fruiting crop pushes leaf at the expense of fruit, delays ripening and softens tissue. Feed nitrogen hard while the plant is building its frame, then taper it off as flowering starts and hand over to potassium. On leafy crops there is no such handover, so keep feeding to harvest.
Made with organic ingredients. Made by Growers. Backed by Science.
The science of amino acid nitrogen
For most of the twentieth century the working assumption was that plants take up nitrogen only as nitrate or ammonium, and that any organic nitrogen has to be mineralised by soil microbes first. That picture turned out to be incomplete. Plants across a wide range of families take up intact amino acids directly through root transporters, and in some systems organic nitrogen accounts for a substantial share of total uptake (Näsholm et al., 2009).
Nitrogen arriving as amino acids has already done part of the plant’s work for it.
Why the form of nitrogen matters
Direct uptake without reduction
Nitrate taken up by a root has to be reduced to ammonium and then assimilated into amino acids before it can be used, a process with a real energy cost. Amino acid nitrogen arrives past that step (Näsholm et al., 2009).
Biostimulant effects beyond nutrition
Plant-derived protein hydrolysates produce responses that cannot be explained by their nutrient content alone: improved root growth, better nutrient uptake and greater tolerance of salinity and drought stress (Colla et al., 2015).
Effects on the root microbiome
Protein hydrolysates alter rhizosphere microbial community composition and activity, with knock-on effects on nutrient availability at the root surface (Colla et al., 2017).
Fertiliser source changes tissue nitrate
In greenhouse lettuce grown on degraded soil, the choice of organic fertiliser source significantly changed leaf nitrate concentration, with the lowest-nitrate treatment sitting 27% below the other organic treatments (Cardarelli et al., 2023). Nitrate accumulation matters most in leafy salads, which accumulate the most.
Carbon alongside nitrogen
At 45% organic matter, each application delivers plant-derived carbon into the root zone. A meta-analysis across tillage systems found organic fertilisation raising soil organic carbon by around 12.9% over mineral-only regimes, rising to 20.6% under no-till (Dal Ferro et al., 2022).
What nitrogen does in the plant
Nitrogen is the backbone of amino acids, and therefore of every protein and every enzyme. It sits at the centre of the chlorophyll molecule, which is why deficiency shows as yellowing. The plant is dismantling chlorophyll in old leaves to move the nitrogen to new growth. That mobility is diagnostic: nitrogen deficiency always appears on the oldest leaves first, where iron or sulphur deficiency appears on the newest (Marschner, 2012).
It is also the nutrient most easily overdone. Excess nitrogen produces large, soft, thin-walled cells that are more attractive to aphids, more susceptible to fungal problems and slower to ripen. The advantage of a peptide-based nitrogen source is that release is somewhat buffered by the need for partial microbial processing, which softens the peaks that a soluble nitrate salt produces.
Sodium, chloride and container growing
The formulation is free of sodium and chlorine. In open ground this matters little. In pots, grow bags and any recirculating system it matters a great deal, because there is no rainfall flushing the root zone. Sodium and chloride accumulate through a season of feeding, raise the osmotic load at the root surface and reduce water uptake. The plant then behaves as though it is short of water while sitting in wet compost.
Plant-derived rather than manufactured
Industrial nitrogen fixation through the Haber-Bosch process consumes roughly 1% to 2% of global energy production. Using nitrogen already fixed in plant material avoids that cost, and the literature on bio-based fertilisers treats plant-derived nitrogen as a credible alternative to manufactured mineral sources (Chojnacka et al., 2020).
Because the feedstock is real plant material, nutrient content varies slightly around the 10% specification between batches.
References
- Näsholm, T., Kielland, K. & Ganeteg, U. (2009). Uptake of organic nitrogen by plants. New Phytologist, 182(1), 31–48.
- Colla, G., Nardi, S., Cardarelli, M., Ertani, A., Lucini, L., Canaguier, R. & Rouphael, Y. (2015). Protein hydrolysates as biostimulants in horticulture. Scientia Horticulturae, 196, 28–38.
- Colla, G., Hoagland, L., Ruzzi, M., Cardarelli, M., Bonini, P., Canaguier, R. & Rouphael, Y. (2017). Biostimulant action of protein hydrolysates: unravelling their effects on plant physiology and microbiome. Frontiers in Plant Science, 8, 2202.
- Marschner, P. (ed.) (2012). Marschner's Mineral Nutrition of Higher Plants, 3rd edition. Academic Press.
- Cardarelli, M., El Chami, A., Iovieno, P., Rouphael, Y., Bonini, P. & Colla, G. (2023). Organic fertilizer sources distinctively modulate productivity, quality, mineral composition, and soil enzyme activity of greenhouse lettuce grown in degraded soil. Agronomy, 13(1), 194.
- Dal Ferro, N. et al. (2022). Influence of organic and mineral fertilizers on soil organic carbon and crop productivity under different tillage systems: a meta-analysis. Agriculture, 12(4), 464.
- Chojnacka, K. et al. (2020). Bio-based fertilizers: a practical approach towards circular economy. Bioresource Technology, 295, 122223.
How to use liquid nitrogen fertiliser
Shake the bottle gently before measuring. Use a syringe or measuring cup, because guessing with nitrogen is how people end up with soft, sappy plants covered in aphids. Always dilute into water. The solution is brown; that is the organic fraction, not sediment. Before any first foliar application, spray two or three leaves and leave them 24 hours to check the plant is happy with the rate.
Application rates
Root drench, regular feeding
The standard rate for container growing, raised beds and greenhouse crops. Use the lower end as a background feed and the upper end for leafy crops in full growth or for plants visibly short of nitrogen.
Heavier root feed, open ground and hungry crops
For brassicas, sweetcorn, leeks and other heavy feeders on the plot, and for recovering ground that has been leached by a wet spell. Water into the root zone rather than over the foliage.
Foliar spray, fast correction
A 1% to 1.5% solution. This is a strong foliar rate, so patch-test on a few leaves first and start at 10 ml per litre. Spray to run-off in early morning or evening, never in strong sun. It is the quickest route to correcting a visible deficiency, and useful when cold or waterlogged soil is holding back root uptake.
Mixing
- Half-fill the watering can or sprayer with water.
- Measure the dose with a syringe and add it to the water.
- Top up to full volume and agitate briefly.
- Apply the same day.
- Rinse the sprayer through with clean water afterwards.
When to apply through the season
| Crop | When to apply |
|---|---|
| Salads and leafy greens | From establishment right through to harvest |
| Brassicas, leeks, sweetcorn | Weekly through the main growing period |
| Tomatoes, peppers, cucumbers | From transplant until flowering begins, then taper |
| Potatoes | Through tuber development, particularly on sandy soil |
| Top fruit and soft fruit | Spring flush and early growth; stop well before harvest |
| Lawns | Growing season only, never into autumn, which softens turf before winter |
| Ornamentals and bedding | Through vegetative growth, easing off as buds form |
Late nitrogen on fruiting crops delays ripening and pushes leaf instead of fruit. Late nitrogen on lawns and woody plants produces soft growth that goes into winter unhardened. And sustained overfeeding produces thin-walled tissue that aphids find far more attractive. More is not better with this one.
Storage
Cap tight, dark and dry, between 10 and 25 °C. Shelf life 18 months to 2 years. Do not let it freeze.
What to pair it with
Pair this with the rest of the Dr Forest liquid range. Liquid Seaweed Biostimulant covers alginates and natural growth promoters that a straight nutrient feed does not. Liquid Gypsum supplies calcium and sulphur, the two things most liquid feeds leave out. Micro 7 chelated micronutrients fills the trace element gap on long cropping runs. For a full-season plan, see the Dr Forest feeding programme.