1. Importance of catch crops
There are several main advantages to be gained by growing catch crops:
- protection from soil erosion - wind and water; - moisture retention - so valuable for our climate and soil types; - soil temperature under cover is maintained higher in winter and consequently with higher activity of soil life; - soil structuring through the root system at different depths, improving the pore system and consequently optimizing aeration - highly disturbed in some regions and soils;
- suppression of weedy vegetation; - green manuring - binding of nutrients, their accumulation in readily available compounds, increasing the organic matter content and thus the beneficial soil fauna and generally building humus; - reduction of mineral nitrogen fertiliser rates and thus direct visibility of rapid economic benefit; - some crops have phytosanitary properties and purpose - control of soil pathogens and parasites;
2. Catch crop requirements.
To fulfil their tasks, catch crops must have the following characteristics:
- be fast-growing and form a large volume of organic matter - rapid growth and coverage of the soil surface -thus also suppressing the development of weedy vegetation; - have tender foliage which is quickly mulched to facilitate the sowing of the main crop after it; - the tender foliage is rapidly mineralised and supplies nutrients to the first main crop; - it is advisable to have non-wintering species in the mixtures, which form lush foliage which, after scalding in winter, allows easy mixing with the soil treatments in spring; - to form a root system with a large mass and volume; - it is good to have mixtures with components of different types and depths of root systems, so that a multi-layered soil structure is obtained.
3. Types of catch crops
Basically we can divide the catch crops into the following categories:
a/ according to the period of use - summer and winter catch crops, winter catch crops are often called pre-crops.
b/ according to vegetation - wintering and non-wintering species
c/ by botanical species - legumes, cereals, crucifers, etc.
d/ according to their purpose - for green manuring or biomass production for fodder and other purposes.
The list of species of intercrops eligible under the EOA (Ecologically Oriented Area) in Bulgaria is incomplete, but those who want to bring benefits to their land would be creative in their approach.
Leader Consulting as an importer of seeds from the Austrian brand SAATBAU LINZ offers forage turnips and white mustard as basic catch crops, with an active root system that structures the soil and leave behind a rich organic mass. The below-ground mass of these plants is about 35% of the above-ground vegetative mass formed. They have a good nematicidal effect.
Other catch crops we recommend are spring legumes, also buckwheat, phacelia, which will frost and allow trouble-free pre-sowing preparation for the main crop in spring.
4. Basic technological recommendations for fodder turnips
a/ sowing period: mid-August to mid-September.
Sowing should not be too early to prevent the formation of generative organs, but still not too late, as we aim to obtain a maximum of green mass above ground and root mass in the soil.
b/ sowing density: forage turnips are sown at about 2-2,5 kg/daa at normal row spacing.
At a very low sowing rate or large plant spacing, root crop formation will start, which is not our objective. We are looking for the strong piercing ability of the main root of this plant so that it will structure and loosen our soil in depth. With root formation or tubers, we will have organic mass, but there will not be full structure.
c/ fertilization: What is practiced in West Europe is nitrogen fertilization at the rate of 3-6 kg/daa N to enhance vegetative growth and form more mass. This also makes sense in our conditions, but due to lack of experience it remains to be seen in the coming years whether this fertilisation will pay off economically given the drier autumn conditions. I would recommend approx. 3 kg/daa pre-sowing or, as a second option, foliar feeding of the catch crop with nitrogen after covering the inter-rows.
In any case, the main fertilisation for the following spring crop should be carried out before sowing the catch crop, this refers to phosphorus and potassium fertilisation if it is practised.
d/ plant protection: as a cruciferous crop, fodder turnip is attacked by fleas and whiteflies, the fight is brought out when necessary. I recommend not to underestimate the control of fleas as their density will multiply in the growing regions and other crops in the rotation will suffer. Densities and resources are as for winter oilseed rape.
d/ pre-sowing treatments: pre-sowing treatments should create an optimum soil bed for friendly germination so that no seeds remain in the soil as a weedy background. I would recommend that the main tillage for the next crop should be done before sowing the catch crop - let's save the ploughing and just loosen the topsoil with machines to 20-25 cm, then do shallow tillage for an aligned and settled seedbed.
e/ post-frost treatments of the catch crop: in practice, the main crop can be sown directly on the decomposed plant residues of the pre-crop. A widely practiced treatment is to roll the frosted field, thus breaking up the ice crystals in the cells and leading to easier shattering of the crop residues.
I would still recommend a pre-sowing cultivation to mix the crop residues, refresh the air balance and align the field. It is also necessary to incorporate pre-sowing fertiliser for the main crop.
Note: In case we have used overwintering, non-frost deciduous species such as rape, winter peas/ vetch and the like for catch crops, a more aggressive system of spring tillage is required - disking, mulching etc., which is not always easy with a large mass. I recommend here also a pre-rolling with heavy rollers of the winter-weary plants, so it will be easier to cope with the treatments.
However, in the case of cereals such as wheat, barley, etc., such a rolling would have the opposite effect - positive for their development and if there are any in the mix - better not to roll.
f/ fertilization of the main crop - if the intermediate crop has managed to develop favourably and has formed a luxuriant vegetative mass, I recommend reducing the active substance nitrogen by 3-4 kg/daa in the main crop. For example, if you fertilise maize pre-sowing with 12 kg/daa N, you can certainly reduce to 8-9 kg/daa.
5. Basic technological recommendations for white mustard
These are the same as for fodder turnips, with a difference in the sowing rate - here it can be slightly lower 1 - 2 kg/daa - however, the denser the better the effect.
6. Basic technological recommendations for legumes and other crops
Legumes are a great precursor and I would recommend using them on their own as a staple crop and declaring them as protein crops. But annual legumes with more foliage may also find use as catch crops. For example, Pisum sativum L. (peas of "afila" type) will not leave as much organic matter as the leafy pea, so it is preferable for this purpose.
The main disadvantage of legumes is that they need a lot of moisture to germinate, and this is often lacking in our area in late summer, hence the danger of them not germinating well and appearing as a weed in the main crop.
If you want to put in a cereal as a catch crop, I would not recommend wheat, barley, rye and triticale, which will till heavily and cause problems when sowing the spring crop, and also will not mineralise as quickly to supply readily available nutrients. It is better to use non-wintering cereals from the list to the extent that the conditions for payment under the EOA (Ecologically Oriented Areas) are met.
This of course does not apply to intermediate crops from which the aim is to obtain biomass for fodder, etc. There we are aiming for maximum mass and then triticale and rye are already the main components.
7. Recommendations for mixtures of catch crops
In European countries many ready-made mixtures for catch crops are available. These are not chosen arbitrarily, but contain a minimum of 3 components - plants with different types and depths of root system to loosen and enrich the soil with organic matter at different levels, and the above-ground mass is lush and more complete in composition. Examples of such mixtures I would suggest: forage peas, buckwheat and white mustard; common vetch, phacelia, forage turnips, etc.
engr. Evelina Marinova
Leader Consulting EOOD
01.09.2015