Opportunities for beet leaves in circular agriculture?

One of the principles of circular agriculture is that the animals are fed as much as possible with residual flows that are not suitable for human consumption. This would prevent competition from food production. An example that is often mentioned is the use of beet leaves as animal feed.

The above sounds logical, because previously beet leaves were ensiled together with the beet heads and used as feed for cows (so apparently it is possible). This involves large quantities (approximately 80.000 hectares of sugar beet at approximately 40 tons of beet leaves per hectare) and contains a relatively large amount of protein (approximately 600 kilos per hectare). However, this now remains unused on land.

That's a shame, isn't it? However, when ideas seem very appealing but are not implemented, something is often overlooked. And I think that's the case here too. It is therefore good to mention these things as well.

Suitable as animal feed?
The fact that beet leaves used to be fed to cows is not a strong argument. This is because beet leaves are not an ideal animal feed for cows; certainly not for the current high-yielding dairy cattle. But what are the main disadvantages† A first disadvantage is that beet leaves often contain too much soil. In addition, it often gives the milk an aftertaste and the calcium content is too high for dry cows. Incidentally, unprocessed beet leaves are unsuitable as animal feed for other animals, such as chickens and pigs.

More than 2 hectares of sugar beet are harvested in approximately 3 to 80.000 months. This means that in a short period (in theory) about 2.400.000 tons of beet leaves will become available, but unfortunately that does not store well. The leaf consists for a very large part of water (at least 90%).

In short: the available quantity cannot be used to feed the Dutch cattle fresh. Saving is also not attractive. In the past, beet leaves were ensiled (just like grass and silage maize), thus preserving them. However, this is accompanied by large losses (about 40% leakage juice). As a result, the protein composition changes and the nutritional value decreases sharply.

Processing into animal feed is difficult and expensive
Is it an option to process beet leaves directly into animal feed raw materials (protein)? Apart from the requested capacity to process 2,4 million tons within a few months, that beet leaf proves difficult to process. The biggest challenge is to extract the protein (the most important raw material for animal feed) in a usable form at all.

Simple and cheap techniques do not succeed in this, while the more complex technology is too expensive for low-value application as a raw material for animal feed. It is therefore understandable that the sugar industry (together with Wageningen University and Research and TNO, among others) focuses on extracting high-quality protein products from beet leaves, and not on the production of animal feed raw materials.

Dragging with a watery product is very unattractive anyway. That already starts on the plot: the harvest of 80 to 120 tons of sugar beet (15% to 20% sugar) already has a significant impact on the soil structure, partly due to the heavy machinery. If on top of that 40 tons of beet leaves have to be harvested, the machines will become even heavier or an extra machine will be added. There will also be extra transport on the plot to remove the leaf.

The costs of the further process (transport and processing) are added to this. In short: the logistics surrounding the harvest and processing is an expensive activity, which all have to be earned back with the yield of the beet leaves as animal feed.

Source of organic matter and minerals
The beet leaves that remain on the land are an important source of organic matter and minerals for the next crop. This yields approximately 900 kilos of effective organic matter per hectare. In comparison: onions leave behind 300 kilos of effective organic matter, potatoes 900 kilos and wheat (excluding straw) 1600 kilos.

In addition, the beet leaves contain many minerals: about 100 to 120 kilos of nitrogen, 35 kilos of phosphate and 185 kilos of potassium. Nitrogen is often lost (via gaseous losses), but phosphate and potassium do become available for the next crop. It is therefore understandable that arable farmers like to leave the beet leaves on the land.

My conclusion
In the context of circular agriculture, in my opinion, it is not a good idea to promote beet leaves as animal feed (raw material). There are good reasons why beet leaves are not used as animal feed (fresh or processed). Research has been done on this before, also in the context of the biobased economy, and the conclusion is the same every time. As far as I'm concerned, this idea will quickly disappear from the agenda, because it is not worth spending time and money on it again.

Unless I'm totally wrong. I don't know who got the idea back on the agenda, but I would like to ask him/her to respond to the above points. If I am convinced otherwise, then I promise to write a new blog with my new insights. However, if I turn out to be right, I give the other person the honor of expressing it in a blog…

Peter Wolf

Pieter de Wolf is a senior applied researcher at WUR Open Crops in Lelystad. He is involved in all challenges in the arable farming sector. Sometimes critical, but always involved.

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