# Soil compaction at harvest: protecting our Żuławy alluvial soils

Soil compaction at vegetable harvest: how a compacted topsoil differs from a compacted subsoil, why wet alluvial soil is worst hit, and how we limit passes.

Soil compaction at vegetable harvest is the squeezing of the ground by the wheels of harvesters, tractors and trailers that drive across the field in autumn with a full load, often after rain. On the Żuławy alluvial soils the effects last for years: water stands on the surface, roots do not go down deep, and the next crop's yield suffers. We limit it in three ways: we drive on fixed tramlines, we watch axle load and the number of passes, and we harvest in dry weather windows, not by the calendar.

## Two layers, two different problems

Compaction is not one phenomenon. It works differently in the topsoil than in the subsoil, and the ways to deal with each are different too.

| Feature | Topsoil (down to cultivation depth) | Subsoil (below the topsoil) |
| --- | --- | --- |
| What pressure depends on | contact area and tyre pressure | load per axle |
| What helps | wider tyres, tracks, lower pressure | less load per axle, fewer passes, dry soil |
| How long it lasts | until the next cultivation and winter | years, ploughing does not reach it |
| How you see it | clods, crusting, uneven emergence | standing water after rain, shallow roots, weaker yield |

So a wide tyre or a track protects the surface, but a heavy load reaches the subsoil regardless of what it is riding on. That is why changing tyres alone does not solve the problem. What also counts is how many tonnes go onto the field, how many times, and what state the ground is in at the time.

## Why wet alluvial soil is the worst case

The Żuławy alluvial soils are heavy, humus-rich and very fertile, comparable to the polders in the Netherlands. When dry they hold up well under machinery. After rain, water fills the pores and acts like a lubricant: soil particles slide under the wheel, the pores close up, and the same machine compacts the ground deeper than on a dry field. The first pass does the most damage, and later passes over the same track add less. More about this soil in our post on [Żuławy soils, alluvial soil for onions](/blog/gleby-zulawskie-mady-pod-cebule).

In Żuławy there is also the low-lying terrain, where water will not drain off the field on its own. A compacted layer holds it on the surface, so the drainage problem and the compaction problem feed each other.

{% callout tone="info" %}
The 2025 season showed this in practice. In a single July day, 150 to 220 litres of water per square metre fell on us, drainage canals overflowed, and the soil compacted and gave up less of its yield. On a field like that, every pass has to be thought through, because the effects stay for the crops that follow.
{% /callout %}

## How we limit compaction at harvest

Harvest is the hardest moment of the year for the soil. The harvester rolls along, a full tridem trailer alongside it, and autumn weather rarely helps. Here is how we handle it:

- **Fixed tramlines with GPS RTK.** We steer our machines to an accuracy of around 2-3 cm, so most passes run along the same tracks. We compact a smaller part of the field, instead of the whole field in random spots. How this works, we describe in our post on [GPS RTK in precision agriculture](/blog/gps-rtk-rolnictwo-precyzyjne).
- **Tracks for the heaviest work.** After harvest, for ploughing and cultivation, the heaviest work here is done by the John Deere 8RX 410, a 410 hp tractor on four tracks. Tracks spread the weight over a larger area than wheels, so the topsoil gets less pressure.
- **Fewer harvester passes.** The AVR Puma 3 takes four rows of potatoes or two onion windrows at once and unloads on the move into the trailer driving alongside, so a full harvester does not have to cross the field to the edge of the plot. It is a heavy machine, so we count its passes just as carefully as the trailers' passes.
- **Mid-range tractors for haulage.** For the trailers we do not need record power, just manoeuvrability and low ground pressure. Haulage is done, among others, by a John Deere 6930 Premium with a Wielton tridem trailer, which spreads the load across three axles. We describe this split of roles in the fleet in our post on [our Fendt and John Deere tractors](/blog/ciagniki-fendt-i-john-deere-w-gospodarstwie).
- **Dry weather windows.** When a dry day comes along in a wet season, we harvest after dark too. We would rather work at night on a field that has dried out than in daylight straight after a downpour.

{% captionedImage src="/images/video/precyzja-osprzet-pole.webp" alt="Tractor with a sprayer guided along a tramline through young onions on our field" caption="Steering with GPS RTK: the machines come back to the same tracks, and more of the field stays clear of wheels." /%}

## What compaction does to the vegetables and the batch

A compacted field lowers the yield, but it also spoils the batch. Onions have shallow, delicate roots and emerge unevenly on compacted soil, and uneven emergence gives a batch with a scattered size grade. On compacted alluvial soil, potatoes come out of the ground together with clods, which bruise the tubers in the harvester and travel with the produce onto the sorting line. Every clod is a risk of bruising and extra work at sorting.

That is why we think about the soil already when planning the harvest. We put the spots where water stands longest under crops less sensitive than onions. We leave onion fields in a rough furrow over winter, and we vary the ploughing depth from year to year, so as not to create a plough pan under the onions. What this autumn work looks like, we describe in our post [preparing the field for onions in autumn](/blog/przygotowanie-pola-pod-cebule-jesienia).

## How to check whether a field is compacted

The simplest tool is a spade. Dig a hole two spade-depths deep and look at its wall: healthy soil crumbles into small clumps, a compacted layer comes away in sheets with sharp edges, and the roots turn sideways above it instead of going down. The second sign is water that stands in wheel ruts and on the headlands longer than on the rest of the field after rain. Headlands are compacted hardest, because that is where machines turn most often.

Subsoiling only helps when it is done on dry soil and when the same passes do not compact it again afterwards. Without a change in how we drive, the effect disappears after one wet harvest. We show the whole process, with soil as the starting point, in our guide [onions from Żuławy: how we grow them](/blog/cebula-z-zulaw-jak-uprawiamy), and the machines we work with on the [machinery park](/park-maszynowy) page.

If you are looking for a vegetable supplier who watches the soil as closely as the produce, get in touch through the [contact form](/kontakt). We calculate the price based on current market rates, and we fit delivery dates to your schedule.

## Frequently asked questions

### What is soil compaction?

It is the compression of the ground by the wheels and tracks of machines. The pores in the soil close up, water and air penetrate less well, and plant roots grow more shallowly. Wet, heavy soil, such as the alluvial soils in Żuławy, compacts the most.

### Does a tracked tractor not compact the soil?

It does compact it, but differently. Tracks spread the weight over a larger area, so the topsoil gets less pressure than under a wheel. The deeper layers are loaded above all by the weight of the machine and its cargo, so tracks do not excuse us from watching the number of passes and the state of the field.

### Why do fixed tramlines reduce compaction?

Because the first pass does the most damage, and later passes over the same track add less. By driving along the same tramlines with GPS RTK, we compact a smaller part of the field, and more of it keeps its structure.

### How long does subsoil compaction last?

For years. A compacted topsoil is broken up by cultivation and winter frost, but the subsoil lies below the reach of the plough. That is why it is easier not to compact it than to repair it afterwards.

### Does soil compaction affect vegetable quality?

Yes. On a compacted field, onions emerge unevenly, which gives a batch with a scattered size grade, and at potato harvest, clods of soil bruise the tubers. Protecting the soil is therefore also protecting the batch that reaches the buyer.