# Preparing the onion field in autumn: winter ploughing on alluvial soil

Preparing the onion field starts right after harvest: field from rotation, soil testing, nutrient maps, perennial weeds and winter ploughing on alluvial soil.

For us, preparing the field for onions starts right after the preceding crop's harvest and ends with winter ploughing, because onions have fine seeds, we sow them shallow and early, and the Żuławy alluvial soils are too heavy to turn into a good seedbed in spring, in the few days between the thaw and the drill. After harvest we confirm the field from the rotation plan, test the soil and work out phosphorus and potassium doses for spring from the maps, control perennial weeds, and finally plough into a rough furrow and hand the field over to the frost. Below is the whole sequence of work across around 250 hectares of onions.

## Why work for onions happens in autumn

Onions from a spring sowing emerge slowly and compete poorly with weeds, and their roots are shallow and delicate. They need soil that in spring is fine on the surface but not compacted underneath, free of perennial weeds and levelled so that the drill places the seed at an even depth, and so that the harvester can lift evenly in autumn. On sandy soil you could do this in spring. On alluvial soil, you cannot.

The Żuławy alluvial soils are heavy, humus-rich and very fertile, comparable to the polders in the Netherlands, but wet in spring and prone to forming clods when worked at the wrong moment. Why they still give onions so much, we describe in our post on [Żuławy soils, alluvial soil for onions](/blog/gleby-zulawskie-mady-pod-cebule). There is one consequence: we build the structure for onions in autumn and winter, and in spring we only finish it off.

## The autumn sequence of work

| Step | When | What for |
| --- | --- | --- |
| Confirming the field from the rotation plan | right after harvest | a gap of several years since the previous onion crop, a cereal as the preceding crop, a field with no history of perennial weed problems |
| Soil testing: pH and nutrient status | August-September | phosphorus and potassium doses worked out from maps, not habit; a control check of the reaction, because we decide on liming a year or two earlier |
| Controlling perennial weeds | after harvest, on regrowing weeds | we remove couch grass and other perennials in autumn, because in onions there is no good moment for it in spring |
| Phosphorus and potassium fertilising plan | autumn and winter, from nutrient maps | doses worked out for every part of the field, applied before sowing in spring, at variable rate |
| Winter ploughing into a rough furrow | late autumn | frost and water break up the clods, so a shallow pass in spring is enough |
| Checking ditches and drains | before winter | the field should drain first in spring, not last |

## Choosing the field: rotation comes first

Onions return to the same field only after several years. A shorter gap means more soil-borne diseases and more weeds that have already learned this crop. The best preceding crop for us is a cereal: it comes off the field early, leaves time for autumn work, and the chopped straw works on the structure of the heavy alluvial soil; the residue is uniform and easy to mix in, unlike after root crops. What this cycle looks like on our fields, we describe in our post on [onion rotation with wheat and triticale](/blog/plodozmian-cebuli-pszenica-pszenzyto).

For the same reason, in autumn after onions we sow winter wheat rather than planning another vegetable straight away. The field "rests" under a cereal, and we have time to prepare a different one for onions. Across more than 800 hectares of the farm, of which around 400 hectares are vegetables, this rhythm forms a multi-year plan, not a decision made season to season.

## Soil testing and reaction

Before the spreader goes in, the soil probe does. From every field destined for onions we take soil samples and test pH and the levels of phosphorus, potassium and magnesium. The results are not uniform even within a single plot, which is why we work out doses on maps, not as an average per hectare.

Onions cope badly with acid soil, and, contrary to popular opinion, alluvial soils are not uniformly alkaline. If a test at the preceding crop shows acidification, we lime for the preceding cereal, a year or two before onions, never right before sowing them, because onions do not like fresh lime. So the autumn soil test before onions is a check: it confirms the reaction we already decided to improve earlier, at the preceding crop. What pH we aim for and when we lime, we describe in detail in our post on [soil pH for onions and liming](/blog/ph-gleby-pod-cebule-wapnowanie).

## Phosphorus and potassium: worked out in autumn, applied before sowing

We apply phosphorus and potassium before sowing, in spring, but we work out the doses already in autumn, from nutrient maps made after soil testing. We spread them at variable rate: a spreader with GPS RTK guidance applies to every part of the field exactly what the test showed, not an average per hectare. How this works in practice, we show in our post on [variable rate fertiliser dosing](/blog/zmienne-dawkowanie-variable-rate).

We do not apply nitrogen for onions in autumn: the onion will only go into the field in spring, and nitrogen spread in autumn would largely wash away with the water, of which Żuławy has no shortage in winter.

{% captionedImage src="/images/galleryPage/1.webp" alt="An onion field on our farm with even rows of plants" caption="Even rows in spring and summer are the result of a field levelled and worked down in autumn, not spring haste." /%}

## Winter ploughing into a rough furrow

The last treatment of autumn is winter ploughing. On alluvial soil we leave it in a rough furrow, without levelling: over winter frost and water break up the clods from the inside, and in spring a shallow pass is enough to get a fine, settled layer for sowing. If we ploughed the same field only in spring, we would drive onto wet soil, compact it with the wheels, and end up with clods that no implement would break up before sowing.

We choose the ploughing date by moisture, not by the calendar: the field has to be dry enough for the furrow to lay over cleanly, not smear. We vary the ploughing depth from year to year and keep to fixed traffic lines steered by GPS RTK, so as not to create a plough pan under the onions, which alluvial soil will not shed in a single season. In a wet autumn that means waiting and working in short weather windows, even on the fields that the drainage system clears fastest.

{% callout tone="info" %}
A rough furrow for winter is not neglect, it is a method. The field looks "unfinished", but it is exactly that uneven surface that gives the frost the most to work on. Alluvial soil levelled and compacted in autumn would crust over on top come spring anyway, while staying compacted underneath.
{% /callout %}

## Water: checking ditches and drains

A large part of Żuławy lies in a depression, and water does not drain off a field on its own. Before winter we check the ditches and the drain outlets, because the field for onions has to drain first in spring: every day sowing is delayed means a shorter season and a smaller size grade in autumn. How our fields' drainage works, we describe in our post on [land drainage in Żuławy](/blog/melioracja-i-odwodnienie-pol-na-zulawach).

## Winter: planning sowing and varieties

While the field lies under snow, we plan the rest: which varieties for which field, what plant density for what size grade, and in what order the drill will start as soon as the alluvial soil dries out. How we work out the sowing rate and why plant density decides the size grade, we write about in our post on [sowing onions: timing and density](/blog/siew-cebuli-termin-i-obsada). We describe the whole cycle from autumn to harvest in our guide [onions from Żuławy: how we grow them](/blog/cebula-z-zulaw-jak-uprawiamy).

For a buyer this autumn plan comes down to one thing: an even field gives even onions, and that produce reaches packing houses and processing plants in the size grade we agreed on. Details in our [onion offer](/oferta/cebula), and we take enquiries about deliveries for the new season through the [contact form](/kontakt).

## Frequently asked questions

### When does field preparation for onions start?

Right after the harvest of the preceding cereal, that is in summer and early autumn. That is when we confirm the field from the rotation plan, test the soil, work out phosphorus and potassium doses for spring from the maps, and control perennial weeds. Winter ploughing closes the season in late autumn.

### Why is winter ploughing for onions left in a rough furrow?

Because over winter, frost and water break up the clods of heavy soil from the inside. In spring a shallow pass is enough to get a fine layer for the onion's shallow sowing. Ploughing in spring on wet alluvial soil would give compacted soil and clods.

### What is the best preceding crop for onions?

A cereal: it comes off the field early, leaves time for autumn work, and the chopped straw improves the structure of the heavy alluvial soil. Onions return to the same field only after several years, to limit soil-borne diseases and weed pressure.

### Is the field for onions fertilised in autumn?

In autumn we test the soil and work out the doses, and we apply phosphorus and potassium before sowing in spring, at variable rate according to the maps. We do not apply nitrogen in autumn: for a crop that will only go into the field in spring, it would largely wash away. If a test calls for liming, we do it for the preceding cereal, a year or two earlier.

### How does field preparation affect onion size?

A level, finely worked field lets us sow at an even depth and get even emergence, and an even plant density decides an even size grade. A compacted or cloddy field gives uneven emergence and a batch that spreads across many sizes after sorting.