What should you look for in a soil test before planting on degraded land?

Read it in this order

A soil report arrives as a table, and the order it is printed in is not the order it should be read in. Start with what cannot be changed and work toward what can.

1. pH

Read this first, because it governs everything below it.

Soil pH decides which nutrients are chemically available to roots. A soil can hold plenty of a nutrient and still starve a plant of it if the pH puts that nutrient into a form roots cannot take up. Correcting a deficiency without looking at pH treats a symptom.

Strongly alkaline soil is common on degraded land in dry regions and it narrows the species list considerably. Strongly acidic soil narrows it differently. Either is a finding that changes the planting plan, not an input that can be dosed away in a season.

Look for electrical conductivity alongside it, which indicates salinity. Salinity and alkalinity together are among the few findings that should lead to a straightforward answer that a particular parcel is not suitable for a particular planting.

2. Organic carbon

The single best indicator of whether soil is alive.

Soil organic carbon is decayed plant and animal matter. It holds water, holds nutrients against leaching, and feeds the microbial community that makes nutrients available in the first place. Degraded land is usually degraded in this figure above all others.

A low reading is not a reason to walk away. It is the baseline the project exists to move, and it is the number worth measuring carefully at the start precisely because it is the one restoration is supposed to change.

It moves slowly. Cover, root growth, returned residue and additions such as biochar and digestate rebuild it over years.

3. Texture and depth

Texture is the proportion of sand, silt and clay, and it decides how water behaves. Sandy soil drains fast and holds little, so plants on it depend on frequent rain or deep roots. Clay holds water and can hold it too tightly, and it cracks and seals. Loam sits in between and is what most planting is easiest on.

Depth is how far down before rock or a hard pan. This sets the ceiling on what can be planted, because a deep rooting species has nowhere to go in shallow soil.

A hard pan, a compacted layer that roots cannot penetrate, is worth finding before planting rather than after. It can sometimes be broken mechanically, and knowing it is there changes both the species and the preparation.

Neither texture nor depth can be changed across a field. They are the constraints the plan works within.

4. Nutrients

Nitrogen, phosphorus, potassium and the micronutrients come last, and they are the figures most reports lead with.

They come last because they are the most correctable. Deficiencies can be addressed with compost, manure, digestate or targeted inputs, and nitrogen fixing species in the mix add some of it biologically.

They still matter. A phosphorus deficiency on land being planted will slow establishment in the first years, which is the period when losses are highest. But a nutrient figure read without the pH above it can point in the wrong direction entirely.

Sampling beats precision

A laboratory can measure to more decimal places than the sampling justifies.

If a block is sampled in one place and that place happens to sit on a slope where topsoil has washed away, the report describes the eroded patch rather than the block. Precision on the wrong sample is worse than an approximate figure from the right ones, because it invites confidence.

Divide the block by what you can see: slope position, soil colour, existing vegetation, previous use. Take several cores within each zone, combine them into one composite per zone, and label them so the same zones can be sampled again in three years.

Record the date, the depth, the zone boundaries and the laboratory. Those four make the next test comparable. Without them the second test is a new measurement rather than a second reading.

What changes as a result

A soil report should change three things, or it was not worth commissioning.

The species list, because pH, salinity and depth rule options in and out. The preparation, because a hard pan or a crusted surface needs work before planting rather than after. And the measurement plan, because the baseline recorded now is what every later reading is compared against.

That last one is why the sampling method is written down before the first sample is taken, and why it does not change afterwards.

See also topsoil, degraded land and choosing species for arid degraded land.

Related questions

How many samples does a block need?

Enough to represent the variation, not enough to average it away. Divide the block by what you can see: slope position, colour change, existing vegetation, previous use. Sample each zone separately, taking several cores within it and combining them into one composite per zone. One composite sample for a varied block describes a piece of land that does not exist anywhere on it.

What depth should samples be taken from?

At least two depths. The surface layer, where most organic matter and biological activity sit, and a deeper one that shows what roots will meet as they go down. A single surface sample misses a hard pan or a salinity problem that will stop the planting in its second year.

Can poor soil be fixed?

Some of it. Organic matter can be rebuilt over years through cover, root growth and additions such as biochar and compost. Nutrient deficiencies can be corrected directly. Texture and depth cannot be changed at field scale, and severe salinity or alkalinity is slow and expensive to shift, so those are the findings that change the plan rather than the inputs.

How often should soil be retested?

On a fixed schedule set before planting, using the same zones, the same depths and the same laboratory. Soil organic carbon moves slowly, so annual claims about it deserve care. Consistency across years is what makes the comparison meaningful, which is why the schedule is written down at the start.