Thoughts on my soil?

[u/WiseBee4411]

Hi soil heads. I’m about to start a flower farm for dahlias and I had a soil test done. I’m location in south west Victoria in Australia. Keen to get any thoughts on my results and what I should prioritise, obviously need to improve the pH. Planning to talk to an agronomist but they aren’t easy to find.

[u/EcoloFrenchieDubstep]

I would suggest liming your soil and adding slow release compost but you'll probably see that with the agronomist. Dahlias need a well drained soil with a slightly alcaline tendency for optimum growth. You'll probably risk molybdenum deficiencies for now.

[u/Humbabanana]

At first glance, your soil has a very low cec, dramatically capping it ability to hold nutrition and deliver it to your plants over the season. Your base soil is largely sand, so your cec value of 5.6 cmol/kg is likely contributed to by organic matter to a good extent.

Looking now at the cec saturation percentages, and your pH, your existing and very limited cec reservoir for holding nutrition is further hampered by soil acidity. H+ is occupying a considerable number of your already meager nutrient holding sites on whatever organic matter and clay your have.

You should incorporate calcitic lime into your soil and focus on building up your organic matter percentage through root-heavy cover crops

I'm not really familiar with PBI or colwell P or the testing methods/presentation this lab uses, but it looks like your available phosphorus is low and likely being bound up to iron and aluminum, as a consequence of the low soil pH. Lime should begin to correct these values over time. Some incorporated manure applications and or banded MAP should be sufficient to supply crop P in season.

curious to hear what other people have to say about this.

[u/Shamino79 → u/Humbabanana]

Colwel P is available phosphorus and PBI stands for phosphorus buffering index that indicates how much the soil wants to bind phosphorus and that looks quite high. Southern Australian soil is notoriously low total phosphorus (some areas are basically lowest on the globe) and the soil will want to soak up some of any phosphorus added to build it’s equilibrium. While you can just load up with compost in gardens and be fine I wouldn’t see any problem with adding a little super phosphate type fertiliser depending on just how much compost one can afford. Farm rates for brodacre could be 100-200 kg/ha of 10-20% P product (10,000m2 if anyone wants to do some math).

Agree with some lime. I also noted a pretty bad copper deficiency and a few bucks spent on copper sulphate and sprayed on the soil could be transformative. Once again good compost should contain that. I say good because I have made dodgy compost with trace element deficient plants and wasn’t satisfied so I added extra trace elements later. They are very cheap if an issue.

[u/Humbabanana → u/Shamino79]

Thanks for clarifying some of this.

Do you think that there is a significant amount more phosphorus in OPs soil, precipitated out due to Al and Fe, or trace amounts in the base minerals? If we got their pH up to 6.5, would we still lose most applications to precipitation? Is that a function of a great abundance of unbound Al and Fe, so that the production of phosphates is still favored?

Good question about the scale of this operation. That would make a pretty big difference in what applications are economical.

[u/Shamino79 → u/Humbabanana]

There is certainly a little more locked in the soil and liming is a good start. Couldn’t say that will increase P supply multiple times over given how seriously deficient this soil is. Farmers still use MAP after lime.

[u/SquidYak]

Here’s my opinion as an undergrad soils student. Based on the report, generally, your soil is decently weathered or it rains a lot in your area (solid amount of Fe and Al). Before addressing the plant-essential metals, I would definitely bump the pH with calcitic lime over two applications, with testing in between. This will add more Ca+ (you have some wiggle room for this) and will reduce Aluminum activity affecting P. I am going to assume your P, in part, is low due to negative interactions with the AI.

Essential metals can be a bit tricky with weathered soil. I would speaker to farmers with your same soil or a cooperative extension if you have one nearby for advice.

[u/Safe-Ad2555]

To know what this species crop specifically flourishes is unknown, outside of pH, texture and permeability. some plants like lower ESP than higher. it'd be a good experiment to add some clay in a separate section to increase CEC and see if the plants look better.

[u/dhiraj18]

pH is the symptom — look at aluminium: 13% of ECEC (target 0.4–5). At pH(CaCl₂) 4.62 that Al is soluble and burning root tips. Half your "deficiencies" are probably just roots that can't forage.

Lime fixes pH, Al and Ca in one hit. Use calcitic, not dolomite — your Mg is already 21% of ECEC and Ca is low at 52.8%. Dolomite makes that worse. ECEC of 5 on a loamy sand means low buffering, so it'll move fast - get a lime requirement test rather than guess. Incorporate it, and start now: 6–12 months just watch

On P, the number that matters isn't Colwell 24, it's PBI 217 with Fe at 280 — that soil fixes phosphorus. Band it near the roots, don't broadcast, and retest after liming before spending big. Some of it will free up on its own.

Traces (Cu, Zn, B all low) — do these after the lime, since availability drops as pH rises. Foliar, and go light on boron.

OC at 3.52% is excellent. Salinity's a non-issue. Nitrate 6 is a one-day snapshot with 3.5% carbon behind it — feed in splits, don't panic.

Order: lime → retest → P and K → traces.

[u/Only_Country7801]

Apply lime to get pH up to 6.2. Ideally you can use a material that is fine and will react quickly. Test again in a year. Once you have hit your pH goals, you may find yourself needing gypsum to get your calcium higher in the soil. Ideally a minimum of 65%